109. Keever, CC; Gultekin, L; Bourchier, RS; Myers, JH; Cory, JS. (2021) Post-release genetic assessment of two congeneric weed biological control agents.Biol. Control 152 Post-release genetic assessment of two congeneric weed biological control agents
Population genetics; Invasive species; Larinus; Curculionidae; Hybridization; Classical biological control; Weed biocontrol; Host range
Introductions of biological control agents are unique field experiments to examine the response of novel organisms to new environments. Post-release monitoring is particularly challenging where closely related and morphologically similar biological control agents have been released. Two closely-related phytophagous weevils, Larinus minutus and L. obtusus, were introduced as biological control agents for two major rangeland weeds, diffuse knapweed, Centaurea diffusa and spotted knapweed, C. stoebe subsp. micranthos in North America. The release of the Larinus species coincided with a decline in C. diffusa abundance in many areas. However, it was not clear whether both species of Larinus had become established as they are morphologically very similar. We asked: (1) Could genetic markers be used to identify both the weevil species? (2) Do both weevil species attack both knapweed species in Canada? (3) Are the levels of genetic diversity of the introduced populations of the weevils similar to those of a European source population? (4) Is genetic mixing between the weevil species occurring? Both microsatellite and CO1 mtDNA markers distinguish between the two weevil species. Larinus obtusus was only found on spotted knapweed, while L. minutus was more widely distributed and attacked both weed species. The relatively large initial introductions of weevils to British Columbia (4,300 L. minutus and 5,500 L. obtusus) together with rapid population growth and frequent redistribution among sites has been sufficient to maintain levels of genetic diversity. Results from small samples showed that haplotype, nucleotide diversity and allelic richness of the introduced populations were comparable to those of a European population. We found no evidence for hybridization in the introduced populations. DOI
108. Leung, JPS; Janmaat, AF; Kabaluk, JT; Cory, JS. (2021) The effect of synthetic female sex pheromone on the transmission of the fungus Metarhizium brunneum by male Agriotes obscurus click beetles.J. Invertebr. Pathol. 179 The effect of synthetic female sex pheromone on the transmission of the fungus Metarhizium brunneum by male Agriotes obscurus click beetles
Pathogen transmission; Autodissemination; Wireworms; Microbial control; Metarhizium; Sex pheromone
Autodissemination techniques can potentially be used to distribute insecticides, including microbial insecticides, to cryptic pests. This approach is reliant on the target insect either passing the pathogen passively to other insects or the pathogen cycling within the population after the initial host dies. Here we examine, in small scale experiments, whether male Agriotes obscurus click beetles passively transmit the spores of the fungus Metarhizium brunneum directly, or indirectly via the environment, and whether this is influenced by exposure to synthetic female pheromone. We found that the beetles did not avoid M. brunneum spores and that this behaviour was not affected by pheromone. Exposure to pheromone increased beetle movement and uptake of spores, but this did not result in an increase in infected beetles under our conditions. Beetles were able to transfer spores at high levels via environmental contamination. However, contamination of the environment declined rapidly after exposure to the spores. The results are discussed in the context of developing an autodissemination strategy for click beetles. DOI PubMed
107. Wilson, K; Grzywacz, D; Cory, JS; Donkersley, P; Graham, RI. (2021) Trans-generational viral transmission and immune priming are dose-dependent.J. Anim. Ecol. 90: 1560-1569 Trans-generational viral transmission and immune priming are dose-dependent
baculovirus; immune priming; outbreak pest; vertical transmission; virus triggering
It is becoming increasingly apparent that trans-generational immune priming (i.e. the transfer of the parental immunological experience to its progeny resulting in offspring protection from pathogens that persist across generations) is a common phenomenon not only in vertebrates, but also invertebrates. Likewise, it is known that covert pathogenic infections may become 'triggered' into an overt infection by various stimuli, including exposure to heterologous infections. Yet, rarely have both phenomena been explored in parallel. Using as a model system the African armyworm Spodoptera exempta, an eruptive agricultural pest and its endemic dsDNA virus (Spodoptera exempta nucleopolyhedrovirus, SpexNPV), the aim of this study was to explore the impact of parental inoculating-dose on trans-generational pathogen transmission and immune priming (in its broadest sense). Larvae were orally challenged with one of five doses of SpexNPV and survivors from these treatments were mated and their offspring monitored for viral mortality. Offspring from parents challenged with low viral doses showed evidence of 'immune priming' (i.e. enhanced survival following SpexNPV challenge); in contrast, offspring from parents challenged with higher viral doses exhibited greater susceptibility to viral challenge. Most offspring larvae died of the virus they were orally challenged with; in contrast, most offspring from parents that had been challenged with the highest doses were killed by the vertically transmitted virus (90%) and not the challenge virus. These results demonstrate that the outcome of a potentially lethal virus challenge is critically dependent on the level of exposure to virus in the parental generation-either increasing resistance at very low parental viral doses (consistent with trans-generational immune priming) or increasing susceptibility at higher parental doses (consistent with virus triggering). We discuss the implications of these findings for understanding both natural epizootics of baculoviruses and for using them as biological control agents. DOI PubMed
106. Leung, JPS; Cory, JS; Kabaluk, JT; Janmaat, AF. (2020) Effect of Collection Month, Visible Light, and Air Movement on the Attraction of Male Agriotes obscurus L. (Coleoptera: Elateridae) Click Beetles to Female Sex Pheromone.Insects 11 Effect of Collection Month, Visible Light, and Air Movement on the Attraction of Male Agriotes obscurus L. (Coleoptera: Elateridae) Click Beetles to Female Sex Pheromone
chemical ecology; attraction distance; environmental factors; behavior; pest management
Simple Summary Wireworms are larvae of adult click beetles and can be major pests of many crops. The larvae live for several years in the soil and are difficult to manage, so additional control methods are being investigated, including the targeting of their adult stage, click beetles. For example, sex pheromones of female beetles can be used to attract males to a substrate treated with an insecticide. We examined whether the response of male click beetles to female sex pheromone is affected by environmental and seasonal factors i.e., beetles collected from the field in different months. Using small-scale lab experiments, we found that the beetles' response to pheromone was not affected by light, but that air movement made them move faster. Exposure to pheromone made the beetles move more, but this did not vary with collection month, although beetles collected in May moved more slowly than those collected in March and April. In the field, male beetles were attracted up to 14 m from a pheromone source, the furthest distance tested. Understanding how beetle response to pheromone varies with these factors is important for the refinement of programs aimed at their management. Elaterid female sex pheromone, while currently used for monitoring the adult life stage (click beetle), has only recently been explored as a potential management tool. Consequently, there is little understanding of how abiotic and biotic conditions influence the response of click beetles to the pheromone. We examined whether the response of male Agriotes obscurus L. (Coleoptera: Elateridae) beetles to a cellulose-based formulation of female sex pheromone ('pheromone granules') is influenced by air movement, presence of visible light, and month of beetle collection. In addition, we investigated the distance from which beetles were attracted to the pheromone granules. Click beetle response was determined by measuring movement parameters in free-walking arena experiments. The response to pheromone was not affected by the presence or absence of visible light. We found that beetles collected earlier in the season had increased activity and interaction with pheromone under moving air conditions, compared to beetles collected later. When controlling for storage time, we confirmed that individuals collected in May were less active than beetles collected in March and April. In the field, beetles were recaptured from up to 14 m away from a pheromone granule source, with over 50% being recovered within 4.4 h from a distance of 7 m or less. Understanding how abiotic and biotic factors affect pest response to pheromone can lead to more effective and novel uses of pheromone-based management strategies. DOI PubMed
105. Zurowski, K; Janmaat, AF; Kabaluk, T; Cory, JS. (2020) Modification of reproductive schedule in response to pathogen exposure in a wild insect: Support for the terminal investment hypothesis.J. Evol. Biol.Modification of reproductive schedule in response to pathogen exposure in a wild insect: Support for the terminal investment hypothesis
Agriotes obscurus; fecundity compensation; host-pathogen interactions; Metarhizium brunneum; reproductive trade-offs; sub-lethal effects; Terminal investment hypothesis
Trade-offs in the time and energy allocated to different functions, such as reproductive activities, can be driven by alterations in condition which reduce resources, often in response to extrinsic factors such as pathogens or parasites. When individuals are challenged by a pathogen, they may either reduce reproduction as a cost of increasing defence mechanisms or, alternatively, modify reproductive activities so as to increase fecundity thereby minimizing the fitness costs of earlier death, a behaviour consistent with the terminal investment hypothesis (TIH). The TIH predicts that individuals with decreased likelihood of future reproduction will maximize current reproductive effort, which may include shifts in reproductive timing. We examined how wild, adult female click beetles(Agriotes obscurus)responded after exposure to the fungal pathogenMetarhizium brunneum. Field-collected beetles exposed to a high concentration ofM. brunneumdied earlier and in greater numbers than those exposed to a low concentration. Using a multivariate approach, we examined the impact of pathogen challenge on lifespan and a suite of reproductive traits. Stepdown regression analysis showed that only female lifespan differed among the fungal treatments. Fungal-induced reductions in lifespan drove changes in the reproductive schedule, characterized by a decrease in preoviposition period. Moving the start of egg laying forward allowed the females to offset the costs of a shortened lifespan. These changes suggest that there is a threshold for terminal investment, which is dependent on strength of the survival threat. From an applied perspective, our findings imply that exposing adult click beetles toM. brunneumto reduce their population density might not succeed and is an approach that needs further investigation. DOI PubMed
104. Escasa, SR; Harrison, RL; Mowery, JD; Bauchan, GR; Cory, JS. (2019) The complete genome sequence of an alphabaculovirus from Spodoptera exempta, an agricultural pest of major economic significance in Africa.PLoS One 14 The complete genome sequence of an alphabaculovirus from Spodoptera exempta, an agricultural pest of major economic significance in Africa
Spodoptera exempta nucleopolyhedrovirus (SpexNPV) is a viral pathogen of the African armyworm, Spodoptera exempta (Lepidoptera: Noctuidae), a significant agricultural pest of cereal crops in Africa. SpexNPV has been evaluated as a potential insecticide for control of this pest and has served as the subject of research on baculovirus pathology and transmission. Occlusion bodies (OBs) of SpexNPV isolate 244.1 were examined, and the nucleotide sequence of the genome was determined and characterized. SpexNPV-244.1 OBs consisted of irregular polyhedra with a size and appearance typical for alphabaculoviruses. Virions within the polyhedra contained 1-8 nucleocapsids per unit envelope. The SpexNPV-244.1 genome was comprised of a 129,528 bp circular sequence, in which 139 ORFs were annotated. Five homologous regions (hrs) consisting of a variable number of 28-bp imperfect palindromes were identified in the genome. The genome sequence contained the 38 core genes of family Baculoviridae, as well as three ORFs unique to the SpexNPV sequence and one ORF that was apparently acquired by horizontal gene transfer with a betabaculovirus ancestor. Phylogenetic inference with core gene amino acid sequence alignments placed SpexNPV-244.1 in a lineage containing alphabaculoviruses of Spodoptera frugiperda and Spodopotera exigua which in turn is part of a larger group of alphabaculoviruses from the subfamily Noctuinae in the lepidopteran family Noctuidae. Kimura-2-parameter pairwise nucleotide distances indicated that SpexNPV-244.1 represented a different and previously unlisted species in the genus Alphabaculovirus. Gene parity plots indicated that the gene order of SpexNPV-244. I was extensively collinear with that of Spodoptera exigua NPV (SeMNPV). These plots also revealed a group of 17 core genes whose order was conserved in other alpha-and betabaculoviruses. DOI PubMed
103. Scholefield, JA; Shikano, I; Lowenberger, CA; Cory, JS. (2019) The impact of baculovirus challenge on immunity: The effect of dose and time after infection.J. Invertebr. Pathol. 167 The impact of baculovirus challenge on immunity: The effect of dose and time after infection
Nucleopolyhedrovirus; Cabbage looper; Immunity; Haemocytes; Phenoloxidase; Glucose dehydrogenase; Dose-response
Understanding how hosts respond to pathogen attack is crucial to disease management. The response of a host can be particularly important if hosts have to defend against multiple pathogens which could either benefit from or be suppressed by prior pathogen exposure. Insect defence against viruses is less well understood than responses to other entomopathogens and much of the information available relates to in vitro studies and model systems. Baculoviruses are natural pathogens of insects, particularly Lepidoptera, and have been well-studied in terms of their ecology, pest control potential and molecular biology. In order to examine how an insect reacts to baculovirus challenge, we measured components of the cellular and humoral immune response of the cabbage looper Trichoplusia ni to Trichoplusia ni SNPV, a narrow-host range nucleopolyhedrovirus (NPV), over four doses and three times after pathogen challenge (18, 42 and 90 h). We found that total haemocyte numbers peaked at 42 h post-exposure at all doses, and declined linearly with increasing dose after the 18 h time point. Two immune-related enzymes, phenoloxidase (PO) and FAD-glucose dehydrogenase (GLD), showed very different responses. PO levels were lowest at the 42 h time point and were not influenced by virus dose when each time point was examined separately. GLD levels declined over time but they interacted with virus dose in a non-linear manner, such that there was an increase in levels at intermediate virus doses after 18 h, no effect at 42 h, and then declined as infection progressed at 90 h post-infection. These data suggest that baculoviruses can rapidly infect haemocytes (or cause a reduction in their numbers) in a dose-dependent manner once the infection is systemic, likely reducing the ability of the host to counter subsequent infections. However, the data do not support a direct role for PO in defence against baculoviruses. Whether GLD plays a role in virus defence is still unclear. DOI PubMed
102. Theze, J; Lopez-Vaamonde, C; Cory, JS; Herniou, EA. (2018) Biodiversity, Evolution and Ecological Specialization of Baculoviruses: A Treasure Trove for Future Applied Research.Viruses-Basel 10 Biodiversity, Evolution and Ecological Specialization of Baculoviruses: A Treasure Trove for Future Applied Research
nucleopolyhedrovirus; granulovirus; lepidoptera; phylogenetics; species delimitation; niche conservatism; host shifts; cophylogeny; resource tracking; multitrophic interactions
The Baculoviridae, a family of insect-specific large DNA viruses, is widely used in both biotechnology and biological control. Its applied value stems from millions of years of evolution influenced by interactions with their hosts and the environment. To understand how ecological interactions have shaped baculovirus diversification, we reconstructed a robust molecular phylogeny using 217 complete genomes and similar to 580 isolates for which at least one of four lepidopteran core genes was available. We then used a phylogenetic-concept-based approach (mPTP) to delimit 165 baculovirus species, including 38 species derived from new genetic data. Phylogenetic optimization of ecological characters revealed a general pattern of host conservatism punctuated by occasional shifts between closely related hosts and major shifts between lepidopteran superfamilies. Moreover, we found significant phylogenetic conservatism between baculoviruses and the type of plant growth (woody or herbaceous) associated with their insect hosts. In addition, we found that colonization of new ecological niches sometimes led to viral radiation. These macroevolutionary patterns show that besides selection during the infection process, baculovirus diversification was influenced by tritrophic interactions, explained by their persistence on plants and interactions in the midgut during horizontal transmission. This complete eco-evolutionary framework highlights the potential innovations that could still be harnessed from the diversity of baculoviruses. DOI PubMed
101.Cory, JS. (2017) Evolution of host resistance to insect pathogens.Curr. Opin. Insect Sci. 21: 54-59 Evolution of host resistance to insect pathogens
Insect pathogens are widely used as a tool for sustainable pest management. Their complex mode of action was thought to make them immune to the evolution of resistance; however, several examples of field-based resistance to the bacterium Bacillus thuringiensis and a granulovirus have been recorded. Here I review the scenarios where resistance has evolved and discuss the likelihood of it occurring in other entomopathogens. I highlight recent research on the factors which might influence the evolution of resistance to insect pathogens, including the role of pathogen diversity, host nutrition and transgenerational effects. DOI
100. Olson, GL; Myers, JH; Hemerik, L; Cory, JS. (2017) Phylloplane bacteria increase the negative impact of food limitation on insect fitness.Ecol. Entomol. 42: 411-421 Phylloplane bacteria increase the negative impact of food limitation on insect fitness
Egg quality; emergent effects; fecundity; induced defences; Pseudomonas; starvation
1. When populations of herbivorous insects increase in density, they can alter the quantity or quality of their food. The impacts of diet-related stressors on insect fitness have been investigated singly, but not simultaneously. 2. Foliage quantity and quality of red alder, Alnus rubra, were manipulated together with the presence of non-entomopathogenic phylloplane bacteria to investigate their impacts, singly and in combination, on survival, pupal mass, growth rate, fecundity and egg quality of a cyclic forest insect, the western tent caterpillar, Malacosoma californicum pluviale. 3. Food limitation (half food) had strong negative impacts on all life-history traits. When the larvae were fed continuously, however, neither ingesting phylloplane bacteria nor eating leaves from damaged branches (induced foliage) affected survival. In the half-food treatment, ingesting bacteria further increased mortality, while feeding on induced foliage improved survival. 4. Growth rate and pupal mass of both sexes were reduced for larvae with food limitation compared with continuously fed insects and this was exacerbated when the larvae also ate bacteria-treated leaves. A combination of bacteria and induced foliage also reduced larval growth rate by 5% in the full-food treatment. 5. Fecundity (eggs per egg mass) was 2.7 times greater in full-food than in food-limited treatments but neither phylloplane bacteria nor plant induction had an effect. Insects fed induced foliage produced smaller eggs. Overall, there was no evidence of a three-way interaction between the three stressors, although there were negative synergistic effects, primarily between food limitation and the ingestion of phylloplane bacteria. DOI
99. Swain, JA; Judd, GJR; Cory, JS. (2017) Cold tolerance of the spring-feeding larvae of the eyespotted bud moth, Spilonota ocellana (Lepidoptera: Tortricidae).Canadian Entomologist 149: 291-299 Cold tolerance of the spring-feeding larvae of the eyespotted bud moth, Spilonota ocellana (Lepidoptera: Tortricidae)
In this study, we explore the low-temperature thresholds of a pest of apple (Malus pumila Miller; Rosaceae), the eyespotted bud moth, Spilonota ocellana Denis and Schiffermuller (Lepidoptera: Tortricidae), in the context of spring frost. Spilonota ocellana overwinters as a larva, resuming activity and feeding early in the growing season when it could be vulnerable to unexpected freezing temperatures. We determined that the mean supercooling point of spring instars did not differ for larvae within or outside leaf shelters and ranged from -9.1 +/- 0.2 degrees C for fourth instars, to -7.9 +/- 0.2 degrees C for sixth instars. Larval weight increased with instar and was positively related to the supercooling point. As some insects are freeze tolerant and able to recover from freezing, we also exposed larvae to brief freeze events between -4.5 degrees C and -9.5 degrees C and found that the median lower lethal temperature, was -7.3 +/- 0.4 degrees C across all instars; indicating that S. ocellana spring instars are susceptible to freezing temperatures above their supercooling point. These low-temperature thresholds suggest that in the spring, S. ocellana larvae are chill susceptible, and a hard frost (<-7 degrees C) would be necessary to cause significant larval mortality. DOI
98. Myers, JH; Cory, JS. (2016) Ecology and evolution of pathogens in natural populations of Lepidoptera.Evolutionary Applications 9: 231-247 Ecology and evolution of pathogens in natural populations of Lepidoptera
disease ecology; disease transmission; forest Lepidoptera; insect pathogens; migration; population regulation; tritrophic interactions; virulence
Pathogens are ubiquitous in insect populations and yet few studies examine their dynamics and impacts on host populations. We discuss four lepidopteran systems and explore their contributions to disease ecology and evolution. More specifically, we elucidate the role of pathogens in insect population dynamics. For three species, western tent caterpillars, African armyworm and introduced populations of gypsy moth, infection by nucleopolyhedrovirus (NPV) clearly regulates host populations or reduces their outbreaks. Transmission of NPV is largely horizontal although low levels of vertical transmission occur, and high levels of covert infection in some cases suggest that the virus can persist in a nonsymptomatic form. The prevalence of a mostly vertically transmitted protozoan parasite, Ophryocystis elektroscirrha, in monarch butterflies is intimately related to their migratory behaviour that culls highly infected individuals. Virulence and transmission are positively related among genotypes of this parasite. These systems clearly demonstrate that the interactions between insects and pathogens are highly context dependent. Not only is the outcome a consequence of changes in density and genetic diversity: environmental factors, particularly diet, can have strong impacts on virulence, transmission and host resistance or tolerance. What maintains the high level of host and pathogen diversity in these systems, however, remains a question. DOI
97. Redman, EM; Wilson, K; Cory, JS. (2016) Trade-offs and mixed infections in an obligate-killing insect pathogen.Journal of Animal Ecology 85: 1200-1209 Trade-offs and mixed infections in an obligate-killing insect pathogen
dose-response; entomopathogen; infection diversity; mortality rate; polymorphism; transmission potential; virulence
1. Natural populations of pathogens are frequently composed of numerous interacting strains. Understanding what maintains this diversity remains a key focus of research in disease ecology. In addition, within-host pathogen dynamics can have a strong impact on both infection outcome and the evolution of pathogen virulence, and thus, understanding the impact of pathogen diversity is important for disease management. 2. We compared eight genetically distinguishable variants from Spodoptera exempta nucleopolyhedrovirus (SpexNPV) isolated from the African armyworm, Spodoptera exempta. NPVs are obligate killers, and the vast majority of transmission stages are not released until after the host has died. 3. The NPV variants differed significantly in their virulence and could be clustered into two groups based on their dose-response curves. They also differed in their speed of kill and productivity (transmission potential) for S. exempta. The mixed-genotype wild-type (WT) SpexNPV, from which each variant was isolated, was significantly more virulent than any individual variant and its mean mortality rate was within the fastest group of individual variants. However, the WT virus produced fewer new infectious stages than any single variant, which might reflect competition among the variants. 4. A survival analysis, combining the mortality and speed of kill data, confirmed the superiority of the genetically mixed WT virus over any single variant. Spodoptera exempta larvae infected with WT SpexNPV were predicted to die 2.7 and 1.9 times faster than insects infected with isolates from either of the two clusters of genotypes. 5. Theory suggests that there are likely to be trade-offs between pathogen fitness traits. Across all larvae, there was a negative linear relationship between virus yield and speed of kill, such that more rapid host death carried the cost of producing fewer transmission stages. We also found a near-significant relationship for the same trend at the intervariant level. However, there was no evidence for a significant relationship between the induced level of mortality and transmission potential (virus yield) or speed of kill. DOI
96. Shikano, I; Cory, JS. (2016) Altered nutrient intake by baculovirus-challenged insects: Self-medication or compensatory feeding?Journal of Invertebrate Pathology 139: 25-33 Altered nutrient intake by baculovirus-challenged insects: Self-medication or compensatory feeding?
Costs of infection; Food quality; Foraging; Nutritional ecology; Specialist-generalist; Temperature
Infection by parasites can alter the feeding behaviour of hosts. Some animals seek out substances that can therapeutically clear infections (self-medication), some may seek out resources to recoup resources lost while fighting off infection (compensatory feeding) and others may be manipulated to ingest substances that benefit parasite fitness (parasite manipulation of host). Recent studies have indicated that pathogen challenged insects can self-medicate by increasing their protein intake relative to carbohydrate, which is thought to act by boosting the insect's immune response. However, increased protein intake could also be due to compensatory feeding or pathogen manipulation of the host, and a rigorous examination of all four of the testable predictions, which is necessary for verifying self-medication behaviour, has not been conducted. The therapeutic behaviour must (1) only be employed by infected individuals and (2) alleviate the potential fitness loss of the infected individual. (3) If an uninfected individual engages in the behaviour, they suffer a decrease in fitness, and lastly, (4) the parasite cannot benefit from the behaviour. In response to baculovirus-challenge (AcMNPV) at 24 degrees C, the cabbage looper, Trichoplusia ni, increased proportional protein intake, by increasing protein intake rather than decreasing carbohydrate intake. Increased protein intake did not benefit virus fitness, but it also did not increase the probability of host survival. Increased proportional protein intake did not occur in response to TnSNPV-challenge at 24 degrees C or in response to AcMNPV-challenge at a higher temperature (32 degrees C), indicating that the virus-induced change in nutrient intake depends on virus identity and temperature. Since virus-challenged T. ni did not show the typical costs associated with infection, the altered nutrient intake is likely to be a compensatory response. Understanding the motivation behind pathogen-induced changes in feeding behaviour could have significant implications for determining its importance for species interactions at multiple trophic levels. (C) 2016 Elsevier Inc. All rights reserved. DOI
95. Shikano, I; Hua, KN; Cory, JS. (2016) Baculovirus-challenge and poor nutrition inflict within-generation fitness costs without triggering transgenerational immune priming.Journal of Invertebrate Pathology 136: 35-42 Baculovirus-challenge and poor nutrition inflict within-generation fitness costs without triggering transgenerational immune priming
Ecological immunology; Fecundity; Food quality; Host-parasite interaction; Invertebrate immunity; Maternal effect
Invertebrate hosts that survive pathogen challenge can produce offspring that are more resistant to the same pathogen via immune priming, thereby improving the fitness of their offspring in the same pathogen environment. Most evidence for immune priming comes from exposure to bacteria and there are limited data on other groups of pathogens. Poor parental nutrition has also been shown to result in the transgenerational transfer of pathogen resistance and increased immunocompetence. Here, we combine exposure to an insect DNA virus with a change in the parental diet to examine both parental costs and transgenerational immune priming. We challenged the cabbage looper, Trichoplusia ni, with a low dose of the baculovirus, Autographa californica multiple nucleopolyhedrovirus (AcMNPV) and altered dietary protein to carbohydrate ratio (p:c ratio) after virus exposure. Insects fed a low protein diet had lower haemolymph protein concentrations, and exhibited costs of smaller pupae and slower development, while survivors of virus challenge developed more slowly, irrespective of p:c ratio, and those that were virus-challenged and fed on a low protein diet showed a reduction in haemocyte density. In addition, AcMNPV-challenged parents laid fewer eggs earlier in egg laying although egg size was the same as for unchallenged parents. There was no evidence for increased resistance to AcMNPV (immune priming) or changes in haemocyte number (as proxy for constitutive cellular immunity) in the offspring either as a result of parental AcMNPV-challenge or low dietary p:c ratio. Therefore, although pathogen-challenge and nutritional changes can affect host development and reproduction, this does not necessarily translate into transgenerational immune priming. Our findings contrast with an earlier study on another type of baculovirus, a granulovirus, where immune priming was suggested. This indicates that transgenerational immune priming is not universal in invertebrates and is likely to depend on the host-pathogen system, or the level of pathogen exposure and the type of dietary manipulation. Identifying whether immune priming or transgenerational effects are relevant in field populations, remains a challenge. (C) 2016 Elsevier Inc. All rights reserved. DOI
94.Cory, JS. (2015) Insect virus transmission: different routes to persistence.Current Opinion in Insect Science 8: 130-135 Insect virus transmission: different routes to persistence
Transmission is a fundamental process in disease ecology; however, the factors that modulate transmission and the dynamical and evolutionary consequences of these factors in host populations are difficult to study in natural settings. Much of our current knowledge comes from a limited number of virus groups and few ecological studies. Alternatively, progress has been made in the detection of new viruses and in probing the molecular basis of behavioural manipulation of hosts that might influence virus transmission. An expanding theoretical framework provides guidelines on the conditions under which particular transmission strategies might evolve, and their dynamical consequences, but empirical tests are lacking. DOI
92. Shikano, I; Cory, JS. (2015) Impact Of Environmental Variation On Host Performance Differs With Pathogen Identity: Implications For Host-Pathogen Interactions In A Changing Climate.Scientific Reports 5 Impact Of Environmental Variation On Host Performance Differs With Pathogen Identity: Implications For Host-Pathogen Interactions In A Changing Climate
Specialist and generalist pathogens may exert different costs on their hosts; thereby altering the way hosts cope with environmental variation. We examined how pathogen-challenge alters the environmental conditions that maximize host performance by simultaneously varying temperature and nutrition (protein to carbohydrate ratio; P:C) after exposure to two baculoviruses; one that is specific to the cabbage looper, Trichoplusia ni (TnSNPV) and another that has a broad host range (AcMNPV). Virus-challenged larvae performed better on more protein-biased diets, primarily due to higher survival, whereas unchallenged larvae performed best on a balanced diet. The environmental conditions that maximized host performance differed with virus identity because TnSNPV-challenge inflicted fitness costs (reduced pupal weight and prolonged development) whereas AcMNPV-challenge did not. The performance of TnSNPV-challenged larvae rose with increasing P:C across all temperatures, whereas temperature modulated the optimal P:C in AcMNPV-challenged larvae (slightly protein-biased at 16 degrees C to increasingly higher P:C as temperature increased). Increasing temperature reduced pupal size, but only at more balanced P:C ratios, indicating that nutrition moderates the temperature-size rule. Our findings highlight the complex environmental interactions that can alter host performance after exposure to pathogens, which could impact the role of entomopathogens as regulators of insect populations in a changing climate. DOI
91. Shikano, I; Oak, MC; Halpert-Scanderbeg, O; Cory, JS. (2015) Trade-offs between transgenerational transfer of nutritional stress tolerance and immune priming.Functional Ecology 29: 1156-1164 Trade-offs between transgenerational transfer of nutritional stress tolerance and immune priming
Bacillus thuringiensis; baculovirus; environmental context; fitness costs; food quality; host-parasite interaction; invertebrate immunity; maternal effect; pathogen resistance
Transgenerational effects are often assumed to have adaptive value as a driver of variation in offspring and parental fitness. Studies of transgenerational effects often focus on single environmental variables. However, in nature, it is unlikely for one factor to vary independently from others and there are likely to be trade-offs between different stressors. We altered the nutritional environment of both parents and offspring to examine how nutritional stress influences transgenerational immune priming (TGIP) with a sublethal challenge by the bacterial pathogen Bacillus thuringiensis, in the cabbage looper, Trichoplusia ni. Transgenerational immune priming was adaptive when offspring encountered the same pathogen experienced by their parents, such that offspring resistance to B.thuringiensis increased 15-fold and antibacterial activity in the haemolymph increased by as much as 4-fold. However, this was not a general increase in pathogen resistance as susceptibility to a second pathogen, the baculovirus, TnSNPV remained the same. Interestingly, nutritional stress in the parents both enhanced nutritional stress tolerance of offspring and heightened resistance to both B.thuringiensis and TnSNPV. Elevated pathogen resistance was linked to increased egg size. There was a significant trade-off between TGIP and the transfer of nutritional stress tolerance when parents encountered both stressors simultaneously, such that parents transferred resistance to pathogens but not nutritional stress tolerance. These results highlight the trade-offs that can modulate the occurrence and magnitude of transgenerational effects and illustrate the importance of assessing interactions between multiple environmental variables. At high population densities, disease risk increases and resour-ces become depleted. Thus, our findings could have significant implications for population dynamics. DOI
90. Shikano, I; Olson, GL; Cory, JS. (2015) Impact of non-pathogenic bacteria on insect disease resistance: importance of ecological context.Ecological Entomology 40: 620-628 Impact of non-pathogenic bacteria on insect disease resistance: importance of ecological context
Bacillus thuringiensis; baculovirus; ecological immunology; host plant quality; host-parasite interaction; immune priming; innate immunity; microbial ecology; multi-trophic interaction; phenoloxidase
1. The aerial surface of plants is a habitat for large and diverse microbial communities; termed the phyllosphere. These microbes are unavoidably consumed by herbivores, and while the entomopathogens are well studied, the impact of non-pathogenic bacteria on herbivore life history is less clear. 2. Previous work has suggested that consumption of non-entomopathogenic bacteria induces a costly immune response that might decrease the risk of infection. However, we hypothesised that insect herbivores should be selective in how they respond to commonly encountered non-pathogenic bacteria on their host plants to avoid unnecessary and costly immune responses. 3. An ecologically realistic scenario was used in which we fed cabbage looper, Trichoplusia ni Hubner, larvae on cabbage or cucumber leaves treated with the common non-entomopathogenic phyllosphere bacteria, Pseudomonas fluorescens and P. syringae. Their constitutive immunity and resistance to a pathogenic bacterium (Bacillus thuringiensis; Bt) and a baculovirus (T. ni single nucleopolyhedrovirus) were then examined. 4. While feeding on bacteria-treated leaves reduced the growth rate and condition of T. ni, there was no effect on immunity (haemolymph antibacterial and phenoloxidase activities and haemocyte numbers). Phyllosphere bacteria weakly affected the resistance of T. ni to Bt but the direction of this effect was concentration dependent; resistance to the virus was unaffected. Host plant had an impact, with cucumber-fed larvae being more susceptible to Bt. 5. The lack of evidence for a costly immune response to non-entomopathogenic bacteria suggests that T. ni are probably adapted to consuming common phyllosphere bacteria, and highlights the importance of the evolutionary history of participants in multi-trophic interactions. DOI
89. Franklin, MT; Myers, JH; Cory, JS. (2014) Genetic Similarity of Island Populations of Tent Caterpillars during Successive Outbreaks.PLOS One 9 Genetic Similarity of Island Populations of Tent Caterpillars during Successive Outbreaks
Cyclic or fluctuating populations experience regular periods of low population density. Genetic bottlenecks during these periods could give rise to temporal or spatial genetic differentiation of populations. High levels of movement among increasing populations, however, could ameliorate any differences and could also synchronize the dynamics of geographically separated populations. We use microsatellite markers to investigate the genetic differentiation of four island and one mainland population of western tent caterpillars, Malacosoma californicum pluviale, in two periods of peak or pre-peak density separated by 8 years. Populations showed high levels of genetic variation and little genetic differentiation either temporally between peaks or spatially among sites. Mitochondrial haplotypes were also shared between one island population and one mainland population in the two years studied. An isolation-by-distance analysis showed the F-ST values of the two geographically closest populations to have the highest level of differentiation in both years. We conclude that high levels of dispersal among populations maintain both synchrony of population dynamics and override potential genetic differentiation that might occur during population troughs. As far we are aware, this is the first time that genetic similarity between temporally separated population outbreaks in insects has been investigated. A review of genetic data for both vertebrate and invertebrate species of cyclic animals shows that a lack of spatial genetic differentiation is typical, and may result from high levels of dispersal associated with fluctuating dynamics. DOI
88. Shikano, I; Cory, JS. (2014) Genetic Resistance to Bacillus thuringiensis Alters Feeding Behaviour in the Cabbage Looper, Trichoplusia ni.PLOS One 9 Genetic Resistance to Bacillus thuringiensis Alters Feeding Behaviour in the Cabbage Looper, Trichoplusia ni
Evolved resistance to xenobiotics and parasites is often associated with fitness costs when the selection pressure is absent. Resistance to the widely used microbial insecticide Bacillus thuringiensis (Bt) has evolved in several insect species through the modification of insect midgut binding sites for Bt toxins, and reports of costs associated with Bt resistance are common. Studies on the costs of Bt-resistance restrict the insect to a single artificial diet or host-plant. However, it is well documented that insects can self-select appropriate proportions of multiple nutritionally unbalanced foods to optimize life-history traits. Therefore, we examined whether Bt-resistant and susceptible cabbage loopers Trichoplusia ni differed in their nutrient intake and fitness costs when they were allowed to compose their own protein: carbohydrate diet. We found that Bt-resistant T. ni composed a higher ratio of protein to carbohydrate than susceptible T. ni. Bt-resistant males exhibited no fitness cost, while the fitness cost (reduced pupal weight) was present in resistant females. The absence of the fitness cost in resistant males was associated with increased carbohydrate consumption compared to females. We demonstrate a sex difference in a fitness cost and a new behavioural outcome associated with Bt resistance. DOI
87. Shikano, I; Cory, JS. (2014) Dietary Mechanism behind the Costs Associated with Resistance to Bacillus thuringiensis in the Cabbage Looper, Trichoplusia ni.PLOS One 9 Dietary Mechanism behind the Costs Associated with Resistance to Bacillus thuringiensis in the Cabbage Looper, Trichoplusia ni
Beneficial alleles that spread rapidly as an adaptation to a new environment are often associated with costs that reduce the fitness of the population in the original environment. Several species of insect pests have evolved resistance to Bacillus thuringiensis (Bt) toxins in the field, jeopardizing its future use. This has most commonly occurred through the alteration of insect midgut binding sites specific for Bt toxins. While fitness costs related to Bt resistance alleles have often been recorded, the mechanisms behind them have remained obscure. We asked whether evolved resistance to Bt alters dietary nutrient intake, and if reduced efficiency of converting ingested nutrients to body growth are associated with fitness costs and variation in susceptibility to Bt. We fed the cabbage looper Trichoplusia ni artificial diets differing in levels of dietary imbalance in two major macronutrients, protein and digestible carbohydrate. By comparing a Bt-resistant T. ni strain with a susceptible strain we found that the mechanism behind reduced pupal weights and growth rates associated with Bt-resistance in T. ni was reduced consumption rather than impaired conversion of ingested nutrients to growth. In fact, Bt-resistant T. ni showed more efficient conversion of nutrients than the susceptible strain under certain dietary conditions. Although increasing levels of dietary protein prior to Bt challenge had a positive effect on larval survival, the LC50 of the resistant strain decreased when fed high levels of excess protein, whereas the LC50 of the susceptible strain continued to rise. Our study demonstrates that examining the nutritional basis of fitness costs may help elucidate the mechanisms underpinning them. DOI PubMed
86. Keever, CC; Nieman, C; Ramsay, L; Ritland, CE; Bauer, LS; Lyons, DB; Cory, JS. (2013) Microsatellite population genetics of the emerald ash borer (Agrilus planipennis Fairmaire): comparisons between Asian and North American populations.Biological Invasions 15: 1537-1559 Microsatellite population genetics of the emerald ash borer (Agrilus planipennis Fairmaire): comparisons between Asian and North American populations
COLEOPTERA BUPRESTIDAE; NATURAL ENEMIES; BIOLOGY; DIFFERENTIATION; DIVERSITY; EVOLUTION; VARIANCE; SOFTWARE; CHINA; PHYLOGEOGRAPHY
The emerald ash borer (EAB) (Agrilus planipennis Fairmaire) (Coleoptera; Buprestidae), is an invasive wood-boring beetle native to northeast Asia. This species was first detected in Michigan USA in 2002, and is a significant threat to native and ornamental ash tree species (Fraxinus spp.) throughout North America. We characterized seven polymorphic microsatellite markers for EAB and used these to investigate EAB population structure in the early invasive populations within North America and in comparison with Asia. We found 2-9 alleles per microsatellite locus, no evidence of linkage disequilibrium, and no association with known coding sequences, suggesting that these markers are suitable for population genetic analysis. Microsatellite population genetic structure was examined in 48 EAB populations sampled between 2003 and 2008 from five regions, three in the introduced range, Michigan (US) and Ontario and Quebec (Canada) and two Asian regions, China and South Korea, where EAB is native. We found significant genetic variation geographically but not temporally in EAB populations. Bayesian clustering analyses of individual microsatellite genotypes showed strong clustering among multiple North American populations and populations in both China and South Korea. Finally, allelic richness and expected heterozygosity were higher in the native range of EAB, but there was no difference in observed heterozygosity, suggesting a significant loss of alleles upon introduction but no significant change in the distribution of alleles within and among individuals. DOI
85. Sarfraz, RM; Cory, JS; Myers, JH. (2013) Life-history consequences and disease resistance of western tent caterpillars in response to localised, herbivore-induced changes in alder leaf quality.Ecological Entomology 38: 61-67 Life-history consequences and disease resistance of western tent caterpillars in response to localised, herbivore-induced changes in alder leaf quality
NUCLEAR POLYHEDROSIS-VIRUS; INDUCED PLANT-RESPONSES; BACILLUS-THURINGIENSIS; PAECILOMYCES-FUMOSOROSEUS; VASCULAR ARCHITECTURE; HELIOTHIS-VIRESCENS; INSECT HERBIVORES; NATURAL-SELECTION; DELTA-ENDOTOXIN; IMMUNE DEFENSE
1. Plants can respond to herbivore damage with phenotypically plastic changes in quality that negatively affect herbivores and prevent subsequent attack induced defences. 2. The present study tested whether trees respond to herbivory with localised induction, and whether life-history traits and disease resistance of an insect herbivore are altered on induced branches of the trees. 3. The influences of localised, within-branch, herbivore-induced changes in red alder trees (Alnus rubra Bong.) on fitness characteristics of western tent caterpillars (Malacosoma californicum pluviale Dyar) were evaluated. In the field, randomly selected branches of trees were infested with tent caterpillar larvae and the adjacent branches were maintained as non-infested controls. In the laboratory, larvae were fed leaves from either induced or non-induced branches through to adult emergence. A second cohort of larvae was challenged with a viral pathogen to compare their disease susceptibility on induced versus non-induced foliage. 4. Herbivore-induced, localised responses of damaged branches reduced leaf quality for growth and the fecundity of female western tent caterpillars, but not that of males. Larvae fed induced leaves had a higher survival overall and a reduced mortality due to unidentified non-viral pathogens than did their counterparts on non-induced leaves. However, there was no influence of leaf quality on baculovirus-induced mortality. 5. These findings suggest that localised induced changes in leaf quality could potentially influence populations of tent caterpillars in contradictory ways by reducing their growth rate and fecundity to a modest degree, while improving their survival and resistance to unidentified non-viral pathogens to a larger extent. DOI
84. Vafaie, EK; Fitzpatrick, SM; Cory, JS. (2013) Does rearing an aphid parasitoid on one host affect its ability to parasitize another species?Agricultural and Forest Entomology 15: 366-374 Does rearing an aphid parasitoid on one host affect its ability to parasitize another species?
DIAERETIELLA-RAPAE HYMENOPTERA; FITNESS TRADE-OFFS; BIOLOGICAL-CONTROL; FEMALE PARASITOIDS; CHEMICAL CUES; BODY-SIZE; COLEMANI; BRACONIDAE; PREFERENCE; DISPERSAL
Generalist parasitoids are commonly used for the biological control of insect pests; however, they are often reared on a single host species because this is more practical for commercial production. Few studies have investigated the consequences of rearing a generalist parasitoid on a single host species in terms of performance on other target pests. We investigated the impact of rearing the generalist parasitoid Praon unicumSmith (Hymenoptera: Braconidae, Aphidiinae) on an alternative aphid host Myzus persicaeSulzer (Hemiptera: Aphididae) with respect to its ability to perform on Ericaphis fimbriataRichards (Hemiptera: Aphididae), a pest of highbush blueberries. Parasitoids reared on the two aphid hosts did not differ in physical size measurements.Praon unicum reared on M. persicae had a lower oviposition success over 6days compared with insects reared on E. fimbriata, mainly as a result of differences early in life. There was no difference in parasitoid egg size, lifetime fertility, age-specific fertility, female offspring ratio, development time or calculated intrinsic rate of increase from the two aphid hosts. We conclude that there were no negative consequences of rearing P. unicum on M. persicae on its ability to parasitize E. fimbriata, although further field studies would need to be performed to investigate whether natal host influences parasitoid preference. DOI
83.Cory, JS; Franklin, MT. (2012) Evolution and the microbial control of insects.Evolutionary Applications 5: 455-469 Evolution and the microbial control of insects
Bacillus thuringiensis; baculovirus; diversity; entomopathogen; genotype environment interaction; local adaptation; mixed infection; resistance; virulence
Insect pathogens can be utilized in a variety of pest management approaches, from inundative release to augmentation and classical biological control, and microevolution and the consideration of evolutionary principles can potentially influence the success of all these strategies. Considerable diversity exists in natural entomopathogen populations and this diversity can be either beneficial or detrimental for pest suppression, depending on the pathogen and its mode of competition, and this should be considered in the selection of isolates for biological control. Target hosts can exhibit considerable variation in their susceptibility to entomopathogens, and cases of field-evolved resistance have been documented for Bacillus thuringiensis and baculoviruses. Strong selection, limited pathogen diversity, reduced gene flow, and host plant chemistry are linked to cases of resistance and should be considered when developing resistance management strategies. Pre- and post-release monitoring of microbial control programs have received little attention; however, to date there have been no reports of host-range evolution or long-term negative effects on nontarget hosts. Comparative analyses of pathogen population structure, virulence, and host resistance over time are required to elucidate the evolutionary dynamics of microbial control systems. DOI
82. Franklin, MT; Ritland, CE; Myers, JH; Cory, JS. (2012) Multiple Mating and Family Structure of the Western Tent Caterpillar, Malacosoma californicum pluviale: Impact on Disease Resistance.PLOS One 7 Multiple Mating and Family Structure of the Western Tent Caterpillar, Malacosoma californicum pluviale: Impact on Disease Resistance
Background: Levels of genetic diversity can strongly influence the dynamics and evolutionary changes of natural populations. Survival and disease resistance have been linked to levels of genetic diversity in eusocial insects, yet these relationships remain untested in gregarious insects where disease transmission can be high and selection for resistance is likely to be strong. Methodology/Principal Findings: Here we use 8 microsatellite loci to examine genetic variation in 12 families of western tent caterpillars, Malacosoma californicum pluviale from four different island populations to determine the relationship of genetic variability to survival and disease resistance. In addition these genetic markers were used to elucidate the population structure of western tent caterpillars. Multiple paternity was revealed by microsatellite markers, with the number of sires estimated to range from one to three per family (mean +/- SE = 1.92 +/- 0.23). Observed heterozygosity (H-O) of families was not associated to the resistance of families to a nucleopolyhedrovirus (NPV) (r = 0.161, F-1,F-12 = 0.271, P = 0.614), a major cause of mortality in high-density populations, but was positively associated with larval survival (r = 0.635, F-1,F-10 = 5.412, P = 0.048). Genetic differentiation among the families was high (F-ST = 0.269, P<0.0001), and families from the same island were as differentiated as were families from other islands. Conclusion/Significance: We have been able to describe and characterize 8 microsatellite loci, which demonstrate patterns of variation within and between families of western tent caterpillars. We have discovered an association between larval survival and family-level heterozygosity that may be relevant to the population dynamics of this cyclic forest lepidopteran, and this will be the topic of future work. DOI
81. Kemp, EM; Woodward, DT; Cory, JS. (2011) Detection of single and mixed covert baculovirus infections in eastern spruce budworm, Choristoneura fumiferana populations.Journal of Invertebrate Pathology 107: 202-205 Detection of single and mixed covert baculovirus infections in eastern spruce budworm, Choristoneura fumiferana populations
Sublethal infection; Multiplex PCR; Mixed infections; Pathogen ecology; Vertical transmission
We surveyed for covert baculovirus infections in the eastern spruce budworm, Choristoneura fumiferana (Clemens) and compared the prevalence of virus detected in a laboratory and a field population. DNA was extracted from budworm adults and then PCR with degenerate primers was used to identify individuals carrying baculovirus DNA. Multiplex PCR was then applied to the positive samples to distinguish between the multiple baculovirus types that could potentially be found in C. fumiferana populations. Covert infections were found in both the laboratory and the field population of C. fumiferana, although the frequency of infection and the composition of viruses found were very different. Overall 28% of insects from the laboratory population were positive for baculovirus DNA. Individual adults supported both single and mixed covert infections with CfMNPV plus CfDEFNPV, CfDEFNPV plus a CV and mixtures of all three viruses together. However, the majority of insects supported single virus infections, and surprisingly this virus was CfDEFNPV, a virus that is reported not to have per os activity in C. fumiferana larvae. Insects from field populations showed a very different pattern: 70.5% of individuals were baculovirus positive and all of these were positive for CfDEFNPV only. (C) 2011 Elsevier Inc. All rights reserved. DOI
80. Myers, JH; Cory, JS; Ericsson, JD; Tseng, ML. (2011) The effect of food limitation on immunity factors and disease resistance in the western tent caterpillar.Oecologia 167: 647-655 The effect of food limitation on immunity factors and disease resistance in the western tent caterpillar
Viral epizootic; Population cycles; Forest Lepidoptera; Covert infection; Sublethal affects
Epizootics of nucleopolyhedrovirus characterize declines of cyclic populations of western tent caterpillars, Malacosoma pluviale californicum. In field populations, infection can be apparently lacking in one generation and high in the next. This may suggest an increase in the susceptibility to infection of larvae at peak density or the triggering of a vertically transmitted virus. Here, we test the hypothesis that reduced food availability, as may occur during population outbreaks of tent caterpillars, influences the immunocompetence of larvae and increases their susceptibility to viral infection. We compared immunity factors, hemolymph phenoloxidase and hemocyte numbers, and the susceptibility to nucleopolyhedroviral infection of fifth instar larvae that were fully or partially fed as fourth instars. To determine if maternal or transgenerational influences occurred, we also determined the susceptibility of the offspring of the treated parents to viral infection. Food limitation significantly reduced larval survival, development rate, larval and pupal mass, moth fecundity and levels of hemolymph phenoloxidase, but not the numbers of hemocytes. Neither the food-reduced larvae nor their offspring were more susceptible to viral infection and were possibly even less susceptible at intermediate viral doses. Food reduction did not activate latent or covert viral infection of larvae as might be expected as a response to stress. We conclude that reducing the food intake of fourth instar larvae to an extent that had measurable and realistic impacts on their life history characteristics was not translated into increased susceptibility to viral infection. DOI
79.Cory JS, Ericsson JD. (2010) Fungal entomopathogens in a tritrophic context.Biocontrol 55: 75-88 Fungal entomopathogens in a tritrophic context.
Ecology; Trophic cascade; Bodyguard; Direct effects; Allelochemicals
INDUCED PLANT VOLATILES; PAECILOMYCES-FUMOSOROSEUS DEUTEROMYCOTINA; METARHIZIUM-ANISOPLIAE; BEAUVERIA-BASSIANA; HOST-PLANT; PANDORA-NEOAPHIDIS; INSECT-PATHOGEN; PEA APHIDS; REPRODUCTIVE ISOLATION; NEOZYGITES-TANAJOAE
Variation in plant quality has an important impact on insect growth and development and there is considerable evidence that plants can also influence an insect's natural enemies. Here we discuss the potential for plant-mediated effects on fungal entomopathogens. Fungi differ from other insect pathogens in that they infect an insect directly through its cuticle. This means that they are particularly vulnerable to changes in microclimate and properties of the insect cuticle. Potential direct and indirect mechanisms for plant-mediated effects on fungal entomopathogens are discussed. It is clear from these studies that fungal entomopathogens could be affected by plant volatiles and plant surface chemistry. Plant secondary chemicals can also inhibit fungal growth, potentially protecting the insect herbivore. However, the site of action and the mechanism behind these effects in plant-based studies is not always clear. The implications for biocontrol using fungal entomopathogens are discussed. DOI
78. Georgievska, L; De Vries, RSM; Gao, PJ; Sun, XL; Cory, JS; Vlak, JM; Van Der Werf, W. (2010) Transmission of Wild-Type and Recombinant HaSNPV Among Larvae of Helicoverpa armigera (Lepidoptera: Noctuidae) on Cotton.Environmental Entomology 39: 459-467 Transmission of Wild-Type and Recombinant HaSNPV Among Larvae of Helicoverpa armigera (Lepidoptera: Noctuidae) on Cotton
genetically modified viruses; mixed infection; transmission; Helicoverpa armigera; cotton
Horizontal transmission of insect viruses is a key factor in their cycling in agro-ecosystems. Here we study the transmission of the baculovirus HaSNPV among larvae of Helicoverpa armigera (Hubner) in cotton. Transmission of three HaSNPV genotypes was studied from larvae infected with a single virus genotype and from larvae infected with two different genotypes. Genotypes included a wild-type virus, an ecdysteroid UDP-glucosyltransferase (egt) deletion mutant (HaSNPV-LM2) with slightly enhanced speed of kill, and an egt-negative genotype that expresses a neurotoxin gene derived from the scorpion Androctonus australis Hector (HaSNPV-4A). The latter genotype has a substantially increased speed of kill. In three field experiments, the wild-type and egt deletion virus variants and a mixture of the two had similar rates of transmission. Transmission increased with density of infector insects and decreased with time lapsed since the inoculation of the infector larvae. Transmission of the neurotoxin expressing virus was lower than that of the other two genotypes in a glasshouse experiment. The studied genotypes of HaSNPV have significant differences in time to kill and virus yield, but we found no significant differences in rates of virus transmission at the crop level in the case of the egt deletion variant HaSNPV-LM2. Transmission of the transgenic virus genotype HaSNPV-4A was significantly reduced. Overall, differences in transmission between virus genotypes were subtler, and more difficult to detect with statistical significance, than effects of other factors, such as density of infectors and time delay between release of infectors and recipient caterpillars on the plant. DOI
77. Georgievska, L; Hoover, K; van der Werf, W; Munoz, D; Caballero, P; Cory, JS; Vlak, JM. (2010) Dose dependency of time to death in single and mixed infections with a wildtype and egt deletion strain of Helicoverpa armigera nucleopolyhedrovirus.Journal of Invertebrate Pathology 104: 44-50 Dose dependency of time to death in single and mixed infections with a wildtype and egt deletion strain of Helicoverpa armigera nucleopolyhedrovirus
Helicoverpa armigera; HaSNPV; Genetically modified baculovirus; Mixed infection; Dose range
Recombinant insect nucleopolyhedroviruses lacking the egt gene generally kill their hosts faster than wild-type strains, but the response of insects to mixtures of virus genotypes is less well known. Here, we compared the survival time, lethal dose and occlusion body yield in third instar larvae of Helicoverpa armigera (Hubner) after challenge with wild-type H. armigera SNPV (HaSNPV-wt), a strain with a deletion of the egt gene, HaSNPV-LM2, and a 1:1 mixture of these two virus strains. A range of doses was used to determine whether the total number of OBs influenced the response to challenge with a mixture of virus strains versus single strains. At high virus doses, HaSNPV-LM2 killed H. armigera larvae significantly faster (ca. 20 h) than HaSNPV-wt, but at low doses, there was no significant difference in survival time between the viruses. The survival time after challenge with mixed virus inoculum was significantly different from and intermediate between that of the single viruses at high doses, and not different from that of the single viruses at low doses. No differences in lethal dose were found between single and mixed infections or between virus genotypes. The number of occlusion bodies produced per larva increased with time to death and decreased with virus dose, but no significant differences among virus types were found. (C) 2010 Elsevier Inc. All rights reserved. DOI
76. Georgievska, L; Joosten, N; Hoover, K; Cory, JS; Vlak, JM; van der Werf, W. (2010) Effects of single and mixed infections with wild type and genetically modified Helicoverpa armigera nucleopolyhedrovirus on movement behaviour of cotton bollworm larvae.Entomologia Experimentalis et Applicata 135: 56-67 Effects of single and mixed infections with wild type and genetically modified Helicoverpa armigera nucleopolyhedrovirus on movement behaviour of cotton bollworm larvae
HaSNPV; genetically modified baculovirus; Lepidoptera; Noctuidae; transmission
Naturally occurring insect viruses can modify the behaviour of infected insects and thereby modulate virus transmission. Modifications of the virus genome could alter these behavioural effects. We studied the distance moved and the position of virus-killed cadavers of fourth instars of Helicoverpa armigera (Hubner) (Lepidoptera: Noctuidae) infected with a wild-type genotype of H. armigera nucleopolyhedrovirus (HaSNPV) or with one of two recombinant genotypes of this virus on cotton plants. The behavioural effects of virus infection were examined both in larvae infected with a single virus genotype, and in larvae challenged with mixtures of the wild-type and one of the recombinant viruses. An egt-negative virus variant caused more rapid death and lower virus yield in fourth instars, but egt-deletion did not produce consistent behavioural effects over three experiments, two under controlled glasshouse conditions and one in field cages. A recombinant virus containing the AaIT-(Androctonus australis Hector) insect-selective toxin gene, which expresses a neurotoxin derived from a scorpion, caused faster death and cadavers were found lower down the plant than insects infected with unmodified virus. Larvae that died from mixed infections of the AaIT-expressing recombinant and the wild-type virus died at positions significantly lower, compared to infection with the pure wild-type viral strain. The results indicate that transmission of egt-negative variants of HaSNPV are likely to be affected by lower virus yield, but not by behavioural effects of egt gene deletion. By contrast, the AaIT recombinant will produce lower virus yields as well as modified behaviour, which together can contribute to reduced virus transmission under field conditions. In addition, larvae infected with both the wild-type virus and the toxin recombinant behaved as larvae infected with the toxin recombinant only, which might be a positive factor for the risk assessment of such toxin recombinants in the environment. DOI
75. Redman, EM; Wilson, K; Grzywacz, D; Cory, JS. (2010) High levels of genetic diversity in Spodoptera exempta NPV from Tanzania.Journal of Invertebrate Pathology 105: 190-193 High levels of genetic diversity in Spodoptera exempta NPV from Tanzania
Armyworm; Lepidoptera; Baculovirus; Nucleopolyhedrovirus; Genetic diversity; Phylogeny
The African armyworm, Spodoptera exempta, is a major pest in sub-Saharan Africa. A nucleopolyhedrovirus (NPV) is often recorded in later population outbreaks and can cause very high levels of mortality. Research has been addressing whether this NPV can be developed into a strategic biological control agent. As part of this study, the variation in natural populations of NPV is being studied. An isolate of S. exempta NPV was cloned in vivo and found to contain at least 17 genetically-distinct genotypes. These genotypes varied in size from approximately 115 to 153 kb. (C) 2010 Elsevier Inc. All rights reserved. DOI
72. Zwart, MP; van der Werf, W; Georgievska, L; van Oers, MM; Vlak, JM; Cory, JS. (2010) Mixed-genotype infections of Trichoplusia ni larvae with Autographa californica multicapsid nucleopolyhedrovirus: Speed of action and persistence of a recombinant in serial passage.Biological Control 52: 77-83 Mixed-genotype infections of Trichoplusia ni larvae with Autographa californica multicapsid nucleopolyhedrovirus: Speed of action and persistence of a recombinant in serial passage
Autographa californica multicapsid nucleopolyhedrovirus; Trichoplusia ni; egt gene; Genetically modified organism; Bioassay; Time to death; Fitness; Competition; Real-time PCR
Fast-acting recombinant baculoviruses have potential for improved insect pest suppression. However, the ecological impact of using such viruses must be given careful consideration. One strategy for mitigating risks might be simultaneous release of a wild-type baculovirus, so as to facilitate rapid displacement of the recombinant baculovirus by a wild-type. However, at what ratio must the two baculoviruses be released? An optimum release ratio must ensure both fast action, and the eventual competitive displacement of the recombinant virus and fixation of the wild-type baculovirus in the insect population. Here we challenged Trichoplusia ni larvae with different ratios of wild-type Autographa californica multicapsid nucleopolyhedrovirus (AcMNPV) and a derived recombinant, vEGTDEL, which has the endogenous egt gene (coding for ecdysteroid UDP-glucosyltransferase) deleted. Time to death increased with the proportion wild-type virus in the inoculum mixture, although a 1:10 ratio (wild-type: recombinant) resulted in equally rapid insecticidal action as vEGTDEL alone. Five serial passages of three different occlusion body (OB) mixtures of the two viruses were also performed. OBs from 10 larval cadavers were pooled and used to initiate the following passage. Although the wild-type baculovirus was maintained over five passages, it did not go to fixation in most replicates of the serial passage experiment (SPE), and there was no good evidence for selection against the recombinant. Long-term maintenance of a recombinant in serial passage suggests an ecosystem safety risk. We conclude that for assessing ecological impact of recombinant viruses, SPEs in single and multiple larvae are relevant because of potential modulating effects at the between-host level. (C) 2009 Elsevier Inc. All rights reserved. DOI
71.Cory, JS; Myers, JH. (2009) Within and between population variation in disease resistance in cyclic populations of western tent caterpillars: a test of the disease defence hypothesis.Journal of Animal Ecology 78: 646-655 Within and between population variation in disease resistance in cyclic populations of western tent caterpillars: a test of the disease defence hypothesis
NUCLEAR POLYHEDROSIS-VIRUS; OPERCULELLA ZELLER LEPIDOPTERA; ANTICARSIA GEMMATALIS; VERTICAL TRANSMISSION; GRANULOSIS-VIRUS; TUSSOCK MOTH; CODLING MOTH; POTATO MOTH; NUCLEOPOLYHEDROVIRUS; SELECTION
Epizootics of nucleopolyhedrovirus (NPV) are an obvious component of the population fluctuations of several species of temperate forest Lepidoptera, including the western tent caterpillar, Malacosoma californicum pluviale (Dyer). An observed relationship between epizootics and the subsequent reduction in fecundity of populations led to the formulation of the disease defence hypothesis. This hypothesis predicts that viral epizootics in peak populations select for more resistant moths and that their reduced fecundity in declining populations reflects a cost of disease resistance. To test the disease defence hypothesis, we carried out bioassays to measure the variation in larval resistance to NPV infection for families of western tent caterpillars from four spatially distinct populations over 3 years of peak and declining host densities. Each female moth lays a single egg mass and larvae are gregarious and remain together through development. We found that the resistance to disease of larvae within families was not related to the number of eggs in the mass from which they hatched (the fecundity of their mother). Disease resistance of larvae varied among populations and over time in a manner consistent with selection for resistance. One population that had not experienced a strong viral epizootic during the last population decline was more susceptible to infection in the first year of the study. Larvae from a second population that experienced an early epizootic became significantly more resistant. The resistance of two other populations increased slightly before the viral epizootic occurred in the field however, and thus could not be explained by selection. As population densities declined from peak density, the background mortality of larvae increased and the fecundity of moths decreased. This indicates a general deterioration in the quality of field populations of tent caterpillars associated with the declining populations. Although some evidence suggests that viral epizootics can select for increased resistance of field populations of tent caterpillars, the general deterioration in quality, elevated background mortality, and the reduced fecundity after the epizootic are stronger influences on the population decline. These are possibly related to sublethal viral infection. DOI
70. Myers, JH; Jackson, C; Quinn, H; White, SR; Cory, JS. (2009) Successful biological control of diffuse knapweed, Centaurea diffusa, in British Columbia, Canada.Biological Control 50: 66-72 Successful biological control of diffuse knapweed, Centaurea diffusa, in British Columbia, Canada
CYPHOCLEONUS-ACHATES FAHRAEUS; SPOTTED KNAPWEED; CONTROL AGENTS; COLEOPTERA; INSECTS; CURCULIONIDAE; COLORADO; WEEVIL; WEEDS
The biological control program for diffuse knapweed, Centaurea diffusa Lamarck, a Eurasian plant that has invaded large areas of grasslands in western North America, has gone on for over 35 years. This program involved the release of 12 biological control agents of which four are numerous and widely distributed; two species of Tephritid flies, Urophora affinis and Urophora quadrifasciata, the root boring beetle, Sphenoptera jugoslavica, and the most recently established weevil Larinus minutus. Field observations show that diffuse knapweed densities declined at sites in British Columbia Canada where the weevil L. minutus became established. Decline in diffuse knapweed density did not occur where densities oft. minutus were low. Field cage experiments showed that feeding by L. minutus damaged rosette leaves and bolting stems, seedling density and the density of rosette and flowering diffuse knapweed and reduced seed production, plants. (C) 2009 Elsevier Inc. All rights reserved. DOI
69. Zwart, MP; Hemerik, L; Cory, JS; de Visser, JAGM; Bianchi, FJJA; Van Oers, MM; Vlak, JM; Hoekstra, RF; Van der Werf, W. (2009) An experimental test of the independent action hypothesis in virus-insect pathosystems.Proceedings of the Royal Society B-Biological Sciences 276: 2233-2242 An experimental test of the independent action hypothesis in virus-insect pathosystems
DEVELOPMENTAL RESISTANCE; MAMESTRA-BRASSICAE; SPODOPTERA-EXIGUA; TRICHOPLUSIA-NI; RNA VIRUS; BACULOVIRUS; INFECTION; TRANSMISSION; VIRULENCE; GENOTYPES
The 'independent action hypothesis' (IAH) states that each pathogen individual has a non-zero probability of causing host death and that pathogen individuals act independently. IAH has not been rigorously tested. In this paper, we (i) develop a probabilistic framework for testing IAH and (ii) demonstrate that, in two out of the six virus-insect pathosystems tested, IAH is supported by the data. We first show that IAH inextricably links host survivorship to the number of infecting pathogen individuals, and develop a model to predict the frequency of single- and dual-genotype infections when a host is challenged with a mixture of two genotypes. Model predictions were tested using genetically marked, near-identical baculovirus genotypes, and insect larvae from three host species differing in susceptibility. Observations in early-instar larvae of two susceptible host species support IAH, but observations in late-instar larvae of susceptible host species and larvae of a less susceptible host species were not in agreement with IAH. Hence the model is experimentally supported only in pathosystems in which the host is highly susceptible. We provide, to our knowledge, the first qualitative experimental evidence that, in such pathosystems, the action of a single virion is sufficient to cause disease. DOI
68. Zwart, MP; van der Werf, W; van Oers, MM; Hemerik, L; van Lent, JMV; de Visser, JAGM; Vlak, JM; Cory, JS. (2009) Mixed infections and the competitive fitness of faster-acting genetically modified viruses.Evolutionary Applications 2: 209-221 Mixed infections and the competitive fitness of faster-acting genetically modified viruses
NUCLEAR POLYHEDROSIS-VIRUS; BACULOVIRUS INSECTICIDE; TRICHOPLUSIA-NI; RECOMBINANT; PERSISTENCE; EVOLUTION; FIELD; NUCLEOPOLYHEDROVIRUS; POPULATION; HOST
Faster-acting recombinant baculoviruses have shown potential for improved suppression of insect pests, but their ecological impact on target and nontarget hosts and naturally occurring pathogens needs to be assessed. Previous studies have focused on the fitness of recombinants at the between-hosts level. However, the population structure of the transmission stages will also be decided by within-host selection. Here we have experimentally quantified the within-host competitive fitness of a fast-acting recombinant Autographa californica multicapsid nucleopolyhedrovirus missing the endogenous egt gene (vEGTDEL), by means of direct competition in single-and serial-passage experiments with its parental virus. Quantitative real-time PCR was employed to determine the ratio of these two viruses in passaged mixtures. We found that vEGTDEL had reduced within-host fitness: per passage the ratio of wild type to vEGTDEL was on average enhanced by a factor of 1.53 (single passage) and 1.68 (serial passage). There is also frequency-dependence: the higher the frequency of vEGTDEL, the stronger the selection against it is. Additionally, the virus ratio is a predictor of time to host death and virus yield. Our results show that egt is important to within-host fitness and allow for a more complete assessment of the ecological impact of recombinant baculovirus release. DOI
67. Vilaplana, L; Redman, EM; Wilson, K; Cory, JS. (2008) Density-related variation in vertical transmission of a virus in the African armyworm.Oecologia 155: 237-246 Density-related variation in vertical transmission of a virus in the African armyworm
costs of resistance; gregariousness; phase polyphenism; sublethal effects; transovarial transmission
Larvae of the African armyworm, Spodoptera exempta, are darker and more resistant to baculovirus infection when reared in groups (gregarious form) compared to being reared singly (solitary form). Lepidoptera that survive virus challenge as larvae could potentially retain a sublethal virus infection which is then transmitted vertically to the next generation. Here we examine whether gregarious and solitary forms of the armyworm differ in the costs of surviving virus infection and in their capacity to transmit an active baculovirus infection to their offspring. Pupae of larvae reared gregariously that survived virus challenge weighed significantly less than uninfected individuals, but this was not so for those reared solitarily. This did not, however, translate into differences in fecundity, at least under laboratory conditions. As found in previous studies, pre-oviposition period was shorter for solitary than gregarious insects, and it was also shorter for females that had been challenged with virus as larvae. Both the prevalence of egg batches containing larvae that died from nucleopolyhedrovirus (NPV) infection and the proportion of infected larvae within each egg batch were significantly increased (approximately doubled) when parental moths were previously challenged with the virus during their larval state. This demonstrates that horizontal transmission in one generation can elevate vertical transmission to the next generation. Moreover, prevalence of overt infection in the offspring generation was two to three times greater when parental moths were reared solitarily as larvae than when reared gregariously. Disease prevalence and proportional infection were both independent of the sex of the infected parent and whether or not the egg batch was surface-sterilized to remove potential contaminants. This suggests that the eggs are infected internally (transovarial) rather than externally (transovum). These results help to shed light on the observed temporal pattern of virus epizootics in eastern Africa. DOI
66. Zwart, MP; van Oers, MA; Cory, JS; van Lent, JWM; van der Werf, W; Vlak, JM. (2008) Development of a quantitative real-time PCR for determination of genotype frequencies for studies in baculovirus population biology.Journal of Virological Methods 148: 146-154 Development of a quantitative real-time PCR for determination of genotype frequencies for studies in baculovirus population biology
Autographa californica nucleopolyhedrovirus; quantitative real-time PCR; genotype frequencies; bacmids
Two bacmid-derived Autographa californica Multiple-capsid Nucleopolyhedrovirus genotypes - that differ only in a short tag sequence for differential PCR recognition - were generated. By electron microscopy, these genotypes were found to have identical polyhedra morphology. Mixtures of quantified polyhedra were made and used to validate a SYBR Green I-based quantitative real-time PCR (qPCR) to deter-mine genotype frequencies in mixed genotype populations. The PCR could accurately quantify genotype ratios over a range of 8 orders of magnitude. Only a small correction of the genotype ratio was necessary to obtain a valid result. Low levels of aspecific background (a fluorescent signal when the template corresponding with the primer set used is not present) were measured in these validation experiments and in a typical laboratory setup. A small fitness difference between the genotypes generated was observed in a median lethal dose bioassay. The bacmid-derived virus genotypes generated and the qPCR assays are valuable tools for studying the population biology of baculoviruses. (C) 2007 Elsevier B.V. All rights reserved. DOI
65. Hitchman, RB; Hodgson, DJ; King, LA; Hails, RS; Cory, JS; Possee, RD. (2007) Host mediated selection of pathogen genotypes as a mechanism for the maintenance of baculovirus diversity in the field.Journal of Invertebrate Pathology 94: 153-162 Host mediated selection of pathogen genotypes as a mechanism for the maintenance of baculovirus diversity in the field
Panolis flammea nucleopolyhedrovirus; baculovirus; genotypic variation; host range; REN fragments
The genetic diversity of many DNA Virus Populations in nature is unknown, but for those that have been studied it has been found to be relatively high. This is particularly true for baculoviruses, a family of large double-stranded DNA viruses that infect the larval stages of insects. Why there should be Such heterogeneity within these Virus Populations is puzzling and what Sustains it is still unknown. It has long been recognized that some baculoviruses have a relatively wide host range, but the effect of different host species on the genotypic structure of a baculovirus population has received little attention. We provide evidence that infection of different insect species can influence the genetic diversity of a Panolis flammea nucleopolyhedrovirus (PaflNPV) Population, isolated from the pine beauty moth. Variable regions of the PaflNPV genome were sequenced and novel ORF's were identified on each of the enlarged fragments. The roles of these orfs and the implications of their presence or absence within different genotypes are discussed. The variable fragments were also labelled with P-32 and used as polymorphic genetic markers of genotype abundance. The proportion of polymorphic loci changed after passage in different insect species and this varied among species, suggesting a role for host selection of pathogen genotypes in the field as a mechanism for maintaining genetic diversity. These results have wide-ranging implications for understanding the ecology of insect-virus interactions in the natural environment and the evolution of baculovirus life history strategies. (c) 2006 Elsevier Inc. All rights reserved. DOI
64.Cory, JS; Hoover, K. (2006) Plant-mediated effects in insect-pathogen interactions.Trends in Ecology & Evolution 21: 278-286 Plant-mediated effects in insect-pathogen interactions
Interactions between insect herbivores and their pathogens can be modulated by host plants. Inter- and intraspecific differences in plant chemistry and structure can after the susceptibility of insects to infection and the production and environmental persistence of pathogens. Whether plants can manipulate insect pathogens to act as 'bodyguards' and increase their own fitness remains to be shown. Reduced insect performance owing to poor plant quality can enhance the susceptibility of an insect to disease while these same phytochemicals can also reduce the effectiveness of entomopathogens in killing the host. As we discuss here, plants have an important role in the evolution of insect-pathogen relationships and a tritrophic perspective should thus be incorporated into the study of insects and their pathogens. DOI
63. Jehle, JA; Blissard, GW; Bonning, BC; Cory, JS; Herniou, EA; Rohrmann, GF; Theilmann, DA; Thiem, SM; Vlak, JM. (2006) On the classification and nomenclature of baculoviruses: A proposal for revision.Archives of Virology 151: 1257-1266 On the classification and nomenclature of baculoviruses: A proposal for revision
Recent evidence from genome sequence analyses demands a substantial revision of the taxonomy and classification of the family Baculoviridae. Comparisons of 29 baculovirus genomes indicated that baculovirus phylogeny followed the classification of the hosts more closely than morphological traits that have previously been used for classification of this virus family. On this basis, dipteran- and hymenopteran-specific nucleopolyhedroviruses (NPV) should be separated from lepidopteran-specific NPVs and accommodated into different genera. We propose a new classification and nomenclature for the genera within the baculovirus family. According to this proposal the updated classification should include four genera: Alphabaculovirus (lepidopteran-specific NPV), Betabaculovirus (lepidopteran-specific Granuloviruses), Gammabaculovirus (hymenopteran-specific NPV) and Deltabaculovirus (dipteran-specific NPV). DOI
62. Lee, KP; Cory, JS; Wilson, K; Raubenheimer, D; Simpson, SJ. (2006) Flexible diet choice offsets protein costs of pathogen resistance in a caterpillar.Proceedings of the Royal Society B-Biological Sciences 273: 823-829 Flexible diet choice offsets protein costs of pathogen resistance in a caterpillar
costs of resistance; feeding behaviour; immunity; nutrition; pathogen infection
Mounting effective resistance against pathogens is costly in terms of energy and nutrients. However, it remains unexplored whether hosts can offset such costs by adjusting their dietary intake so as to recoup the specific resources involved. We test this possibility by experimentally challenging caterpillars (Spodoptera littoralis) with a highly virulent entomopathogen (nucleopolyhedrovirus), under dietary regimes varying in the content of protein and digestible carbohydrate. We found that dietary protein influenced both resistance to pathogen attack and constitutive immune function to a greater extent than did dietary carbohydrate, indicating higher protein costs of resistance than energy costs. Moreover, when allowed to self-compose their diet, insects surviving viral challenge increased their relative intake of protein compared with controls and those larvae dying of infection, thus demonstrating compensation for protein costs associated with resistance. These results suggest that the change in the host's nutritional demands to fight infection induces a compensatory shift in feeding behaviour. DOI
61. Bonsall, MB; O'Reilly, DR; Cory, JS; Hails, RS. (2005) Persistence and coexistence of engineered baculoviruses.Theoretical Population Biology 67: 217-230 Persistence and coexistence of engineered baculoviruses
age-structure; baculoviruses; competition; coexistence; egt; mathematical models; non-linear transmission
Baculoviruses, and in particular, the nucleopolyhedroviruses infect a wide range of arthropod hosts and have the potential to be used as biopesticides. However, one of the major drawbacks with these pathogens as biocontrol agents is that they have a slow response time. Alterations to the speed of kill and pathogen life history characteristics can influence the competitive outcome and persistence between wildtype and modified strains. Here, we explore, theoretically, how life-history modifications of pathogens can affect the epidemiology and ecology of strain coexistence. In particular, we show how under simple mass action disease transmission, life-history difference between strains are insufficient to allow coexistence. Additional heterogeneities in transmission are shown to be necessary to facilitate coexistence of wildtype and modified pathogen strains. We also illustrate how the patterns of infectivity of wildtype and modified strains can also affect long-term coexistence, and argue that appropriate assessment of genetic modifications must be presented in terms of relevant ecological theory. © 2005 Elsevier Inc. All rights reserved. DOI
60.Cory, JS; Green, BM; Paul, RK; Hunter-Fujita, F. (2005) Genotypic and phenotypic diversity of a baculovirus population within an individual insect host.Journal of Invertebrate Pathology 89: 101-111 Genotypic and phenotypic diversity of a baculovirus population within an individual insect host
baculovirus; diversity; genotype; hypervariable regions; pathogenicity; polymorphism; population structure; quasispecies; speed of kill; variation; virulence
It is becoming increasingly apparent that many pathogen populations, including those of insects, show high levels of genotypic variation. Baculoviruses are known to be highly variable, with isolates collected from the same species in different geographical locations frequently showing genetic variation and differences in their biology. More recent Studies at smaller scales have also shown that virus DNA profiles from individual larvae can show polymorphisms within and between populations of the same species. Here, we investigate the genotypic and phenotypic variation of an insect baculovirus infection within a single insect host. Twenty four genotypically distinct nucleopolyhedrovirus (NPV) variants were isolated from an individual pine beauty moth, Panolis flammea, caterpillar by in vivo cloning techniques. No variant appeared to be dominant in the population. The Pafl NPV variants have been mapped using three restriction endonucleases and shown to contain three hypervariable regions containing insertions of 70-750 bp. Comparison of seven of these variants in an alternative host, Mamestra brassicae, demonstrated that the variants differed significantly in both pathogenicity and speed of kill. The generation and maintenance of pathogen heterogeneity are discussed. (c) 2005 Elsevier Inc. All rights reserved. DOI
59. Jakubowska, A; van Oers, MM; Cory, JS; Ziemnicka, J; Vlak, JM. (2005) European Leucoma salicis NPV is closely related to North American Orgyia pseudotsugata MNPV.Journal of Invertebrate Pathology 88: 100-107 European Leucoma salicis NPV is closely related to North American Orgyia pseudotsugata MNPV
Leucoma salicis; Orgyia pseudotsugata; Lymantriidae; nucleopolyhedrovirus; LesaNPV; OpMNPV; taxonomy
The satin moth Leucoma salicis L. (Lepidoptera, Lymantriidae) is a frequent defoliator of poplar trees (Populus spp..) in Europe and Asia (China, Japan). Around 1920 the insect was introduced into the USA and Canada. In this paper, a multicapsid nucleopolyhedrovirus isolated from L. salicis larvae in Poland (LesaNPV) was characterized and appeared to be a variant of Orgyia pseudotsugata (Op) MNPV. O. pseudotsugata, the Douglas fir tussock moth (Lepidoptera, Lymantriidae), occurs exclusively in North America. Sequences of three conserved baculovirus genes, polyhedrin, lef-8, and pif-2, were amplified in polymerase chain reactions using degenerate primer sets, and revealed a high degree of homology to OpMNPV. Restriction enzyme analysis confirmed the close relationship between LesaNPV and OpMNPV, although a number of restriction fragment length polymorphisms were observed. The lef-7 gene, encoding late expression factor 7, and the ctl-2 gene, encoding a conotoxin-like protein, were chosen as putative molecular determinants of the respective viruses. The ctl-2 region appeared suitable for unequivocal identification of either virus as LesaNPV lacked a dUTPase gene in this region. Our observations may suggest that LesaNPV, along with L. salicis, was introduced into O. pseudotsugata after introduction of the former insect into North America in the 1920s. (c) 2005 Elsevier Inc. All rights reserved. DOI
58. Raymond, B; Hartley, SE; Cory, JS; Hails, RS. (2005) The role of food plant and pathogen-induced behaviour in the persistence of a nucleopolyhedrovirus.Journal of Invertebrate Pathology 88: 49-57 The role of food plant and pathogen-induced behaviour in the persistence of a nucleopolyhedrovirus
host behaviour; Operophtera brumata; nucleopolyhedrovirus; persistence; transmission
Insect baculoviruses can survive between epidemics as infectious particles external to the host. Many pathogens persist in reservoirs, i.e., microhabitats where survival is enhanced, for example due to protection from the degrading effects of UV irradiation. However, the probability of infecting new susceptible hosts is usually reduced. Persistence of pathogens and their movement in and out of reservoirs is an important, albeit little understood, aspect of insect pathogen ecology. This study investigated interactions between the behaviour of infected insect hosts, virus distribution and plant species on the persistence of the winter moth (Operophtera brumata) nucleopolyhedrovirus. Habitat influenced the persistence of infectious baculovirus in the field: virus on Sitka spruce (Picea sitchensis) and oak (Quercus robur) in forested areas retained more infectivity than virus on heather (Calluna vulgaris) in an unshaded habitat. Plant species per se did not directly affect the persistence of virus on the foliage of potted seedlings. Virally infected insects had altered behaviour and moved down plants relative to control insects, whereas in other systems larvae show height-seeking behaviour. Consequently, the majority of virus particles were distributed on plant stems. In two experiments (one using winter moth NPV and one Mamestra brassicae NPV) virus persisted better oil plant stems relative to foliage. Neonate larvae were shown to be able to acquire infections from tree stems contaminated with a low level of virus. These data suggest that plant steins may be important reservoirs for between-year persistence of this pathogen. The observed virus-induced changes in host behaviour in winter moth could enhance the viral persistence by increasing the deposition of occlusion bodies in these reservoirs. (C) 2004 Elsevier Inc. All rights reserved. DOI
57. Vasconcelos, SD; Hails, RS; Speight, MR; Cory, JS. (2005) Differential crop damage by healthy and nucleopolyhedrovirus-infected Mamestra brassicae L. (Lepidoptera : Noctuidae) larvae: A field examination.Journal of Invertebrate Pathology 88: 177-179 Differential crop damage by healthy and nucleopolyhedrovirus-infected Mamestra brassicae L. (Lepidoptera : Noctuidae) larvae: A field examination
cabbage moth; baculovirus; leaf consumption; feeding rates; biopesticide
Baculovirus infection in Lepidoptera can alter both larval mobility and feeding rates, which can in turn affect pathogen transmission and dispersal in the field. We compared the damage to cabbage plants in the field caused by healthy and nucleopolyhedrovirus-infected Mamestra brassicae L. (Lepidoptera: Noctuidae) larvae released as second and fourth instars. There was no significant difference in plant consumption by healthy and infected larvae for the first 4 days after release. From day 5 onwards, infected larvae caused significantly less defoliation. This pattern was similar for larvae at both larval instars. Defoliation was greater for fourth instars throughout the experiment. (c) 2005 Elsevier Inc. All rights reserved. DOI
56. Bourner, TC; Cory, JS. (2004) Host range of an NPV and a GV isolated from the common cutworm, Agrotis segetum: pathogenicity within the cutworm complex.Biological Control 31: 372-379 Host range of an NPV and a GV isolated from the common cutworm, Agrotis segetum: pathogenicity within the cutworm complex
host range; cross-infection; cutworm; baculovirus; Agrotis segetum; Noctua; Peridroma; Xestia; Ochroplura; vertical transmission; persistent infection
The term cutworm covers a range of species with a similar life history that can be very damaging pests on a wide range of crops. Attacks by cutworms are often made up of more than one species; thus, the most cost effective microbial control agent needs to be pathogenic for multiple species within this complex. In this study we investigate the host range of Agrotis segetum NPV and A. segetum GV for other cutworm species and closely related Noctuinae. Eight species, A. segetum, Agrotis ipsilon, Agrotis exclamationis, Agrotis puta, Noctua comes, Peridroma saucia, Xestia sexstrigata, and Xestia xanthographa, were clearly susceptible to AgseNPV, which was confirmed by DNA analysis. Aglais urticae, Diarsia rubi, Noctua pronuba, and Xestia c-nigrum were not susceptible to AgseNPV at the doses used. Noctua fimbriata, Noctua janthina, and Ochroplura plecta gave ambivalent results: larvae died of NPV infection when they were challenged with AgseNPV, but these individuals only produced weak positives in a squash blot analysis and there was insufficient DNA for confirmation by restriction endonuclease profiling. These ambivalent results could suggest either a weak infection by AgseNPV or partial homology between their own virus and AgseNPV. The untreated control insects of several species died of NPV infection, which indicates that these field-collected insects were probably carrying a vertically transmitted NPV. Fewer species were tested with AgseGV and only N. pronuba and N. comes were susceptible. N. fimbriata and Helicoverpa armigera were not susceptible to AgseGV. Crown Copyright (C) 2004 Published by Elsevier Inc. All rights reserved. DOI
55.Cory, JS; Clarke, EE; Brown, ML; Hails, RS; O'Reilly, DR. (2004) Microparasite manipulation of an insect: the influence of the egt gene on the interaction between a baculovirus and its lepidopteran host.Functional Ecology 18: 443-450 Microparasite manipulation of an insect: the influence of the egt gene on the interaction between a baculovirus and its lepidopteran host
NPV; pathogen fitness; speed of kill; trade-offs; yield
1. Parasites and pathogens manipulate their hosts in a variety of ways that are thought to enhance their fitness. However, it is rare to be able to link such phenotypic changes to specific genes. 2. Here the effect of a single pathogen gene is examined. The ecdysteroid UDP-glucosyltransferase (egt) gene of insect baculoviruses produces an enzyme that interferes with host moulting. 3. The effect of the egt gene was examined by comparing two baculoviruses that differed only in the expression of this gene. All three fitness traits examined - pathogenicity, infection duration and pathogen productivity - were affected by deletion of the gene. 4. Trichoplusia ni larvae in all five instars died earlier when infected with the egt-minus virus compared with those infected by the wild-type Autographa californica nucleopolyhedrovirus. 5. Unexpectedly, the egt-minus virus was more pathogenic to final instar larvae than the wild-type virus. Virus genotype and dose both influenced insect development. 6. Wild-type infected insects had a significantly higher yield of virus at death, cadaver weight and yield of virus per unit weight than those infected with the egt-minus virus. 7. The size of the virus challenge had a major influence on the outcome of the interaction. The consequences of these data for pathogen fitness are discussed.
54.Cory, JS; Myers, JH. (2004) Adaptation in an insect host-plant pathogen interaction.Ecology Letters 7: 632-639 Adaptation in an insect host-plant pathogen interaction
baculovirus; fitness; genotype X environment; local adaptation; microparasite; nucleopolyhedroviruses; tent caterpillars; trade-offs; tritrophic interaction; virulence
Selection on parasites to adapt to local host populations may be direct or through other components of the system such as vectors or the food plant on which the parasite is ingested. To test for local adaptation of nucleopolyhedrovirus among island populations of western tent caterpillars, Malacosoma californicum pluviale, we compared virus isolates from three geographically distinct sites with different dominant host plants. Pathogenicity, speed of kill and virus production of each isolate were examined on the three food plants. Virus isolates from the two permanent host populations had the fastest speed of kill on the host plant from which they were isolated. This was not the case for a caterpillar population that goes extinct when populations are regionally low. Virus isolates on some plant species combined rapid speed of kill with high virus yield. Infection of hosts by mixed microparasite populations could facilitate local adaptation in response to differing food plant chemistry. DOI
53. Cotter, SC; Hails, RS; Cory, JS; Wilson, K. (2004) Density-dependent prophylaxis and condition-dependent immune function in Lepidopteran larvae: a multivariate approach.Journal of Animal Ecology 73: 283-293 Density-dependent prophylaxis and condition-dependent immune function in Lepidopteran larvae: a multivariate approach
condition-dependence; density-dependent prophylaxis; melanism; parasite resistance; trade-offs
1. The risk of parasitism and infectious disease is expected to increase with population density as a consequence of positive density-dependent transmission rates. Therefore, species that encounter large fluctuations in population density are predicted to exhibit plasticity in their immune system, such that investment in costly immune defences is adjusted to match the probability of exposure to parasites and pathogens (i.e. density-dependent prophylaxis). 2. Despite growing evidence that insects in high-density populations show the predicted increase in resistance to certain pathogens, few studies have examined the underlying alteration in immune function. As many of these species show increased cuticular melanism at high densities, the aim of this study was to use a multivariate approach to quantify relative variation in the allocation of resources to immunity associated with both rearing density (solitary vs. crowded) and cuticular colour (pale vs. dark) in a phase-polyphenic Lepidopteran species (Spodoptera littoralis Boisduval). 3. Relative to pale individuals, dark larvae (the high-density phenotype) exhibited higher haemolymph and cuticular phenoloxidase (PO) activity and a stronger melanotic encapsulation response to an artificial parasite inserted into the haemocoel. However, they also exhibited lower antibacterial (lysozyme-like) activity than pale larvae. Larval density per se had little effect on most of the immune parameters measured, though capsule melanization and antibacterial activity were significantly higher in solitary-reared than crowded larvae. 4. Correcting for variation in larval body condition, as estimated by weight and haemolymph protein levels, had little effect on these results, suggesting that variation in immune function across treatment groups cannot be explained by condition-dependence. These results are examined in relation to pathogen resistance, and the possibility of a trade-off within the immune system is discussed.
52. Herniou, EA; Olszewski, JA; O'Reilly, DR; Cory, JS. (2004) Ancient coevolution of baculoviruses and their insect hosts.Journal of Virology 78: 3244-3251 Ancient coevolution of baculoviruses and their insect hosts
If the relationships between baculoviruses and their insect hosts are subject to coevolution, this should lead to long-term evolutionary effects such as the specialization of these pathogens for their hosts. To test this hypothesis, a phylogeny of the Baculoviridae, including 39 viruses from hosts of the orders Lepidoptera, Diptera, and Hymenoptera, was reconstructed based on sequences from the genes lef-8 and ac22. The tree showed a clear division of the baculoviruses according to the order of their hosts. This division highlighted the need to reconsider the classification of the baruloviruses to include one or possibly two new genera. Furthermore, the specialization of distinct virus lineages to particular insect orders suggests ancient coevolutionary interactions between baculoviruses and their hosts. DOI
51. Hodgson, DJ; Hitchman, RB; Vanbergen, AJ; Hails, RS; Possee, RD; Cory, JS. (2004) Host ecology determines the relative fitness of virus genotypes in mixed-genotype nucleopolyhedrovirus infections.Journal of Evolutionary Biology 17: 1018-1025 Host ecology determines the relative fitness of virus genotypes in mixed-genotype nucleopolyhedrovirus infections
competition; differential selection; fitness; host ecology; mixed infection; nucleopolyhedrovirus; Panolis flammea; pathogen; resource partitioning; virulence
Mixed-genotype infections are common in many natural host-parasite interactions. Classical kin-selection models predict that single-genotype infections can exploit host resources prudently to maximize fitness, but that selection favours rapid exploitation when co-infecting genotypes share limited host resources. However, theory has outpaced evidence: we require empirical studies of pathogen genotypes that naturally co-infect hosts. Do genotypes actually compete within hosts? Can host ecology affect the outcome of co-infection? We posed both questions by comparing traits of infections in which two baculovirus genotypes were fed to hosts alongside inocula of the same or a different genotype. The host, Panolis flammea, is a herbivore of Pinus sylvestris and Pi. contorta. The pathogen, PfNPV (a nucleopolyhedrovirus), occurs naturally as mixtures of genotypes that differ, when isolated, in pathogenicity, speed of kill and yield. Single-genotype infection traits failed to predict the 'winning' genotypes in co-infections. Co-infections infected and caused lethal disease in more hosts, and produced high yields, relative to single-genotype infections. The need to share with nonkin did not cause fitness costs to either genotype. In fact, in hosts feeding on Pi. sylvestris, one genotype gained increased yields in mixed-genotype infections. These results are discussed in relation to theory surrounding adaptive responses to competition with nonkin for limited resources. DOI
50. Cooper, D; Cory, JS; Myers, JH. (2003) Hierarchical spatial structure of genetically variable nucleopolyhedroviruses infecting cyclic populations of western tent caterpillars.Molecular Ecology 12: 881-890 Hierarchical spatial structure of genetically variable nucleopolyhedroviruses infecting cyclic populations of western tent caterpillars
local adaptation; pathogen variation; restriction fragment length polymorphism; source and sink populations; spatial structure; vertical transmission
The cyclic population dynamics of western tent caterpillars, Malacosoma californicum pluviale , are associated with epizootics of a nucleopolyhedrovirus, McplNPV. Given the dynamic fluctuations in host abundance and levels of viral infection, host resistance and virus virulence might be expected to change during different phases of the cycle. As a first step in determining if McplNPV virulence and population structure change with host density, we used restriction fragment length polymorphism (RFLP) analysis to examine the genetic diversity of McplNPV infecting western tent caterpillar populations at different spatial scales. Thirteen dominant genetic variants were identified in 39 virus isolates (individual larvae) collected from field populations during one year of low host density, and another distinct variant was discovered among nine additional isolates in two subsequent years of declining host density. The distribution of these genetic variants was not random and indicated that the McplNPV population was structured at several spatial levels. A high proportion of the variation could be explained by family grouping, which suggested that isolates collected within a family were more likely to be the same than isolates compared among populations. Additionally, virus variants from within populations (sites) were more likely to be the same than isolates collected from tent caterpillar populations on different islands. This may indicate that there is limited mixing of virus among tent caterpillar families and populations when host population density is low. Thus there is potential for the virus to become locally adapted to western tent caterpillar populations in different sites. However, no dominant genotype was observed at any site. Whether and how selection acts on the genetically diverse nucleopolyhedrovirus populations as host density changes will be investigated over the next cycle of tent caterpillar populations.
49. Cooper, D; Cory, JS; Theilmann, DA; Myers, JH. (2003) Nucleopolyhedroviruses of forest and western tent caterpillars: cross-infectivity and evidence for activation of latent virus in high-density field populations.Ecological Entomology 28: 41-50 Nucleopolyhedroviruses of forest and western tent caterpillars: cross-infectivity and evidence for activation of latent virus in high-density field populations
baculovirus; cross-infectivity; environmental stressors; latency; persistence; population fluctuation; sublethal infection; tent caterpillar; vertical transmission
1. Cyclic population dynamics of forest caterpillars are often associated with epizootics of nucleopolyhedrovirus, but it is not known how these viruses persist between generations or through the fluctuations in host population density. 2. To explore the question of virus persistence at different phases of the population cycle, the nucleopolyhedroviruses of two species of tent caterpillar that co-occur in British Columbia, Canada, Malacosoma californicum pluviale (western tent caterpillar) and Malacosoma disstria (forest tent caterpillar), were characterised. The cross-infectivity of the viruses in these two host species was investigated to determine whether there might be a route for virus persistence via the alternative host species. Any virus produced in the cross-infections was characterised to confirm true cross-infection or to ascertain whether cross-inoculation triggered latent virus persisting within the population. 3. The virus associated with forest tent caterpillars (MadiNPV) did not infect western tent caterpillars from low-density populations, nor did it trigger a latent virus infection; however, inoculation of forest tent caterpillars from high-density populations with virus from western tent caterpillars (McplNPV) resulted in viral infection, but without a dose-response relationship. 4. Analysis of DNA profiles of virus resulting from cross-infection of the forest tent caterpillar with McplNPV, revealed that 88% of these infections were caused by MadiNPV rather than McplNPV; however the virus from all 44 infected individuals was identical and differed in DNA profile from the stock MadiNPV used for cross-infection. This suggests strongly that forest tent caterpillars from high-density field populations harbour a latent, persistent, or sublethal form of MadiNPV that was triggered by exposure to nucleopolyhedrovirus from the western tent caterpillar. 5. Virus was not activated in western tent caterpillars collected over 2 years of late population decline and the first year of population increase.
47.Cory, JS; Myers, JH. (2003) The ecology and evolution of insect baculoviruses.Annual Review of Ecology Evolution and Systematics 34: 239-272 The ecology and evolution of insect baculoviruses
virulence; resistance; pathogen; variation; transmission
Baculoviruses occur widely among Lepidoptera, and in some species of forest and agricultural insects, they cause epizootics in outbreak populations. Here we review recent developments in baculovirus ecology and evolution, in particular focusing on emerging areas of interest and studies relating to field populations. The expanding application of molecular techniques has started to reveal the structure of baculovirus populations and has highlighted how variable these pathogens are both genotypically and phenotypically at all levels from within individual hosts to among host populations. In addition, the detailed molecular knowledge available for baculoviruses has allowed the interpretation of gene functions across physiological and population levels in a way rarely possible in parasite-host systems and showed the diverse mechanisms that these viruses use to exploit their hosts. Analysis of the dynamic interactions between insects and baculoviruses, and their compatibility for laboratory and field experiments, has formed a basis for studies that have made a significant contribution to unraveling disease interactions in insect populations. In particular, manipulative studies on baculoviruses have been instrumental in developing an understanding of disease transmission dynamics. The results so far indicate that baculoviruses have the potential to be an excellent model for investigations of changes in virulence and resistance in fluctuating and stable host populations. DOI
46. Herniou, EA; Olszewski, JA; Cory, JS; O'Reilly, DR. (2003) The genome sequence and evolution of baculoviruses.Annual Review of Entomology 48: 211-234 The genome sequence and evolution of baculoviruses
Baculoviridae; phylogeny; gene order; gene composition; gene function
Comparative analysis of the complete genome sequences of 13 baculoviruses revealed a core set of 30 genes, 20 of which have known functions. Phylogenetic analyses of these 30 genes yielded a tree with 4 major groups: the genus Granulovirus (GVs), the group I and II lepidopteran nucleopolyhedroviruses (NPVs), and the dipteran NPV, CuniNPV. These major divisions within the family Baculoviridae were also supported by phylogenies based on gene content and gene order. Gene content mapping has revealed the patterns of gene acquisitions and losses that have taken place during baculovirus evolution, and it has highlighted the fluid nature of baculovirus genomes. The identification of shared protein phylogenetic profiles provided evidence for two putative DNA repair systems and for viral proteins specific for infection of lymantrid hosts. Examination of gene order conservation revealed a core gene cluster of four genes, helicase, lef-5, ac96, and 38K(ac98), whose relative positions are conserved in all baculovirus genomes. DOI
45. Burden, JP; Griffiths, CM; Cory, JS; Smith, P; Sait, SM. (2002) Vertical transmission of sublethal granulovirus infection in the Indian meal moth, Plodia interpunctella.Molecular Ecology 11: 547-555 Vertical transmission of sublethal granulovirus infection in the Indian meal moth, Plodia interpunctella
granulin; granulovirus; latency; RT-PCR; sublethal; vertical transmission
Knowledge of the mechanisms of pathogen persistence in relation to fluctuations in host density is crucial to our understanding of disease dynamics. In the case of insect baculoviruses, which are typically transmitted horizontally via a lifestage that can persist outside the host, a key issue that remains to be elucidated is whether the virus can also be transmitted vertically as a sublethal infection. We show that RNA transcripts for the Plodia interpunctella GV granulin gene are present in a high proportion of P. interpunctella insects that survive virus challenge. Granulin is a late-expressed gene that is only transcribed after viral genome replication, its presence thus strongly indicates that viral genome replication has occurred. Almost all insects surviving the virus challenge tested positive for viral RNA in the larval and pupal stage. However, this proportion declined in the emerging adults. Granulin mRNA was also detected in both the ovaries and testes, which may represent a putative mechanism by which reduced fecundity in sublethally affected hosts might be manifested. RNA transcripts were also detected in 60-80% of second-generation larvae that were derived from mating surviving adults, but there was no difference between the sexes, with both males and females capable of transmitting a sublethal infection to their offspring. The data indicate that low-level persistent infection, with at least limited gene expression, can occur in P. interpunctella following survival of a,granulovirus challenge. We believe that this is the first demonstration of a persistent, sublethal infection by a baculovirus to be initiated by a sublethal virus dose. We hypothesize that the 'latent' baculovirus infections frequently referred to in the literature may also be low level persistent, sublethal infections resulting from survival from initial baculovirus exposure.
43. Hails, RS; Hernandez-Crespo, P; Sait, SM; Donnelly, CA; Green, BM; Cory, JS. (2002) Transmission patterns of natural and recombinant baculoviruses.Ecology 83: 906-916 Transmission patterns of natural and recombinant baculoviruses
baculovirus; genetic modification; Lepidoptera; Mamestra brassicae; pathogen; population dynamics; recombinant; refuge; risk assessment; transmission; Trichoplusia ni
The advent of genetically modified organisms such as pathogens has raised ecological questions that need to be addressed in order to assess any risks involved in their use, The baculovirus Autographa californica nucleopolyhedrovirus (AcNPV), which infects a number of lepidopteran species, has been modified to express an insect-selective toxin, This genetic modification increases the speed with which it kills its host. However, in addition to this intended feature of the modified virus, there may be other consequences for the host-pathogen interaction. We report a field experiment in which transmission patterns of the wild-type and the genetically modified baculovirus are measured within and between a model target (susceptible) and nontarget (less susceptible) lepidopteran species. Two foliar feeders were chosen: Trichoplusia ni, the cabbage looper, is highly susceptible to this pathogen, while Mamestra brassicae, the cabbage moth, is semipermissive. These two species are used as both the source and the recipients of infection for both virus types. A series of models are fitted to determine the probabilities of infection (given survival from other sources of mortality) over a 7-d period within contained field cages. Fitting these models to data illustrates teat a substantial fraction of the population escapes infection, and it is the size of the pathogen-free refuge that varies between treatments. When infected individuals from the less susceptible species die, the yield of virus is greater than from susceptible hosts, yet this does not significantly alter the risk of transmission to other hosts. In contrast, the genetically modified baculovirus always results in a lower risk of infection in the field compared to the wild type. This is because the recombinant virus causes paralysis, and as a result, the cadaver may fall from the plant before death and virus release. Hence the number of cadavers remaining on the foliage has a greater influence on transmission than the yield of virus from those cadavers.
42. Hodgson, DJ; Vanbergen, AJ; Hartley, SE; Hails, RS; Cory, JS. (2002) Differential selection of baculovirus genotypes mediated by different species of host food plant.Ecology Letters 5: 512-518 Differential selection of baculovirus genotypes mediated by different species of host food plant
differential selection; genotypic variation; lodgepole pine; microparasite; nucleopolyhedrovirus; Panolis flammea; Scots pine; tritrophic interaction
Recent studies have demonstrated high levels of genotypic and phenotypic variation in populations of parasites, even within individual hosts. Several genetic, immunological and epidemiological mechanisms have been postulated as promoters of such variation, but little empirical work has addressed the role of host ecology. A nucleopolyhedrovirus that attacks larvae of the pine beauty moth, Panolis flammea , exists as a complex mixture of genotypes within individual host larvae. We demonstrate that the food plant species eaten by the host (Scots pine vs. lodgepole pine) differentially affects the pathogenicity and productivity of two virus genotypes originally purified from a single host individual. We hypothesize that such food plant-mediated differential selection will promote genotypic variation between baculovirus populations, and that subsequent remixing of virus genotypes could maintain genotypic variation within individual hosts. Our results provide a tritrophic explanation for the genotypic and phenotypic complexity of host-parasite interactions with complex ecologies.
41. Hyink, O; Dellow, RA; Olsen, MJ; Caradoc-Davies, KMB; Drake, K; Herniou, EA; Cory, JS; O'Reilly, DR; Ward, VK. (2002) Whole genome analysis of the Epiphyas postvittana nucleopolyhedrovirus.Journal of General Virology 83: 957-971 Whole genome analysis of the Epiphyas postvittana nucleopolyhedrovirus
The nucleotide sequence of the Epiphyas postvittana nucleopolyhedrovirus (EppoMNPV) genome has been determined and analysed. The circular dsDNA genome contains 118 584 bp, making it the smallest group I NPV sequenced to date. The genome has a G+C content of 40.7% and encodes 136 predicted open reading frames (ORFs), five homologous repeat regions and one unique repeat region. Of the genome, 92.9% encodes predicted ORFs and 2.2% is in repeat regions; the remaining 4.9% of the genome comprises nonrepeat intergenic regions. EppoMNPV encodes homologues of 126 Orgyia pseudotsugata MNPV (OpMNPV) ORFs and 120 Autographa californica MNPV ORFs, with average identities of 64.7 and 53.5%, respectively. Between the four sequenced group I NPVs, 117 ORFs are conserved, whereas 86 ORFs are conserved between all fully sequenced NPVs. A total of 62 ORFs is present in all baculoviruses sequenced to date, with EppoMNPV lacking a homologue of the superoxide dismutase (sod) gene, which has been found in all other fully sequenced baculoviruses. Whole genome phylogenetic analyses of the ten fully sequenced baculoviruses using the sequences of the 62 shared genes, gene content and gene order data sets confirmed that EppoMNPV clusters tightly with OpMNPV in the group I NPVs. The main variation between EppoMNPV and OpMNPV occurs where extra clusters of genes are present in OpMNPV, with sod occurring in one such cluster. EppoMNPV encodes one truncated baculovirus repeated ORF (bro) gene. The only repeated ORFs are the four iap genes. Eight, randomly distributed, unique ORFs were identified on EppoMNPV, none of which show any significant homology to genes in GenBank.
40. Raymond, B; Vanbergen, A; Pearce, I; Hartley, SE; Cory, JS; Hails, RS. (2002) Host plant species can influence the fitness of herbivore pathogens: the winter moth and its nucleopolyhedrovirus.Oecologia 131: 533-541 Host plant species can influence the fitness of herbivore pathogens: the winter moth and its nucleopolyhedrovirus
baculovirus; insect pathology; population dynamics; tritrophic interactions
Plants can have a significant impact on the fitness and efficacy of natural enemies. These interactions are widespread and suggest that the influences on the population dynamics of insect herbivores cannot be simply divided into "bottom up" and "top down". Several questions remain little studied in this field. Firstly, to what extent can plants affect the interactions between insects and their pathogens? Secondly, what are the effects of variation within natural enemy species on host/enemy/ plant interactions? Finally, if plant/pathogen interactions can occur, do pathogens have increased fitness on the locally abundant food plant of their host? This study explored the influence of three host plant species of the polyphagous winter moth, Operophtera brumata, on infections caused by two geographic isolates of the winter moth nucleopolyhedrovirus (NPV) collected from distinct winter moth habitats. Insects were infected on excised leaf tissue of common oak, Quercus robur, Sitka spruce, Picea sitchenis, and heather, Calluna vulgaris. Parameters fundamental to the basic reproductive rate of the pathogen were estimated: these being infectivity, speed of kill and the yield of virus per insect. Leaf nitrogen and phenolic content were measured as indicators of host plant quality for the three plant species: oak had the highest levels of nitrogen and also the highest levels of phenolic compounds. Heather had higher levels of phenolic compounds than Sitka spruce. Host plant did not affect the infectivity of either isolate but insects that ingested virus on oak foliage died sooner and yielded more virus than insects that ingested virus on Sitka spruce or heather. The effect of host plant species on pathogen yield varied between the two isolates of the NPV but not as predicted by our adaptive hypothesis. The interactions between virus and food plant are discussed in relation to host and pathogen population dynamics. DOI
39. Raymond, B; Vanbergen, A; Watt, A; Hartley, SE; Cory, JS; Hails, RS. (2002) Escape from pupal predation as a potential cause of outbreaks of the winter moth, Operophtera brumata.Oikos 98: 219-228 Escape from pupal predation as a potential cause of outbreaks of the winter moth, Operophtera brumata
The winter moth, Operophtera brumata, shows varying population dynamics in different host plant habitats. Populations in Sitka spruce, Picea sitchensis, plantations and in Scottish moorlands have a tendency to outbreak that is not shown by winter moth in lowland oak woods. Since pupal predators have previously been identified as being important for the regulation of winter moth in a lowland oak wood it was hypothesized that invertebrate pupal predators were failing to control winter moth in outbreak populations. This hypothesis was tested by comparing the abundance of invertebrate predators and patterns of spatially density dependent pupal predation across habitats. Several results supported this hypothesis. Carabid predators of winter moth were one or two orders of magnitude more abundant in oak woods than in moorland or spruce habitats. Staphylinid predators were also more abundant in high winter moth density oak woods than in any other habitat. Beetle predation of tagged cocoons in the field was inversely density dependent in Highland moors in experiments in 1999 and 2000, and in Sitka spruce in 1999. However, in opposition to our hypothesis, pupal predation was also inversely density dependent in oak woods in 2000, although this result may be explained by the low range of winter moth densities in the field that year. These results are discussed in relation to the role of natural enemies in regulating winter moth populations and the differences in life-history of the beetle predators in different habitats.
38. Hernandez-Crespo, P; Sait, SM; Hails, RS; Cory, JS. (2001) Behavior of a recombinant baculovirus in lepidopteran hosts with different susceptibilities.Applied and Environmental Microbiology 67: 1140-1146 Behavior of a recombinant baculovirus in lepidopteran hosts with different susceptibilities
Insect pathogens, such as baculoviruses, that are used as microbial insecticides have been genetically modified to increase their speed of action. Nontarget species will often be exposed to these pathogens, and it is important to know the consequences of infection in hosts across the whole spectrum of susceptibility. Two key parameters, speed of kill and pathogen yield, are compared here for two baculoviruses, a wild-type Autographa californica nucleopolyhedrovirus (AcNPV), AcNPV clone C6, and a genetically modified AcNPV which expresses an insect-selective toxin, AcNPV-ST3, for two lepidopteran hosts which differ in susceptibility, The pathogenicity of the two viruses was equal in the less-susceptible host, Mamestra brassicae, but the recombinant was more pathogenic than the wild-type virus in the susceptible species, Trichoplusia ni. Both viruses took longer to kill the larvae of M. brassicae than to kill those of T. ni. However, whereas the larvae of T. ni mere killed more quickly by the recombinant virus, the reverse mas found to be true for the larvae of M. brassicae. Both viruses produced a greater yield in M. brassicae, and the yield of the recombinant was significantly lower than that of the wild type in both species. The virus yield increased linearly with the time taken for the insects to die. However despite the more rapid speed of kill of the wild-type AcNPV in M. brassicae, the yield was significantly lower for the recombinant virus at any given time to death. A lower yield for the recombinant virus could be the result of a reduction in replication rate. This was investigated by comparing determinations of the virus yield per unit of weight of insect cadaver. The response of the two species (to both viruses) was very different: the yield per unit of weight decreased over time for M. brassicae but increased for T. ni, The implications of these data for risk assessment of wild-type and genetically modified baculoviruses are discussed.
37. Herniou, EA; Luque, T; Chen, X; Vlak, JM; Winstanley, D; Cory, JS; O'Reilly, D. (2001) Use of whole genome sequence data to infer Baculovirus phylogeny.Journal of Virology 75: 8117-8126 Use of whole genome sequence data to infer Baculovirus phylogeny
Several phylogenetic methods based on whole genome sequence data were evaluated using data from nine complete baculovirus genomes. The utility of three independent character sets was assessed. The first data set comprised the sequences of the 63 genes common to these viruses. The second set of characters was based on gene order, and phylogenies were inferred using both breakpoint distance analysis and a novel method developed here, termed neighbor pair analysis. The third set recorded gene content by scoring gene presence or absence in each genome. All three data sets yielded phylogenies supporting the separation of the Nucleo-polyhedrovirus (NPV) and Granulovirus (GV) genera, the division of the NPVs into groups I and II, and species relationships within group I NPVs. Generation of phylogenies based on the combined sequences of all 63 shared genes proved to be the most effective approach to resolving the relationships among the group II NPVs and the GVs. The history of gene acquisitions and losses that have accompanied baculovirus diversification was visualized by mapping the gene content data onto the phylogenetic tree. This analysis highlighted the fluid nature of baculovirus genomes, with evidence of frequent genome rearrangements and multiple gene content changes during their evolution. Of more than 416 genes identified in the genomes analyzed, only 63 are present in all nine genomes, and 200 genes are found only in a single genome. Despite this fluidity, the whole genome-based methods we describe are sufficiently powerful to recover the underlying phylogeny of the viruses.
36. Hodgson, DJ; Vanbergen, AJ; Watt, AD; Hails, RS; Cory, JS. (2001) Phenotypic variation between naturally co-existing genotypes of a Lepidopteran baculovirus.Evolutionary Ecology Research 3: 687-701 Phenotypic variation between naturally co-existing genotypes of a Lepidopteran baculovirus
genotype; mixed infection; nucleopolyhedrovirus; Panolis flammea; phenotype; trade-off
There is increasing evidence that populations of microparasites vary genotypically at a variety of spatial scales, including within host individuals. Understanding this fine-scale structuring of microparasite populations requires descriptions of the relative fitness of individual genotypes isolated from natural mixed infections. Here we examine whether differences between virus genotypes isolated from a single host individual translate into phenotypic differences, and discuss the processes by which such variation might be maintained. Twenty-five genotypic variants of a nucleopolyhedrovirus (Baculoviridae) have been identified and purified from a single pine beauty moth (Panolis flammea) larva. The phenotypes of four genotypes were compared. Genotypes differed in three phenotypic traits, each predicted to be an important component of fitness: pathogenicity, speed of kill and yield. Variation in pathogenicity was described by seven-fold differences in LD50 and by differences in the slopes of the fitted dose-response curves. Mean speed of kill of the genotypes differed by up to 36 h, Two genotypes produced 65% higher yields, over and above any differences predicted by a significant intra-genotypic relationship between yield and speed of kill. Inter-genotypic trade-offs between virus phenotypic traits, which could promote the co-existence of genotypes, were not found. Mechanisms that may promote the co-existence of competing virus genotypes are discussed.
35. Burden, JP; Hails, RS; Windass, JD; Suner, MM; Cory, JS. (2000) Infectivity, speed of kill, and productivity of a baculovirus expressing the itch mite toxin txp-1 in second and fourth instar larvae of Trichoplusia ni.Journal of Invertebrate Pathology 75: 226-236 Infectivity, speed of kill, and productivity of a baculovirus expressing the itch mite toxin txp-1 in second and fourth instar larvae of Trichoplusia ni
Autographa californica; Pyemotes tritici; Trichoplusia ni; tox34; AcMNPV; recombinant baculovirus; genetically modified organism; biopesticide
A cDNA clone of the gene coding for the paralytic neurotoxin (tox34) from the female straw itch mite, Pyemotes tritici, was created by RT-PCR and inserted into the genome of the Autographa californica nucleopolyhedrovirus (AcMNPV) under the control of the AcMNPV p10 promoter. This recombinant virus, AcTOX34.4, caused a rigid paralysis in infected larvae. The infectivity of AcTOX34.4 was compared to the wild-type parent strain, AcMNPV-C6, in second and fourth instar larvae of the cabbage looper, Trichoplusia ni. There were no significant differences in LD,, values between the recombinant virus and its wild-type parent strain but, as expected, the LD,, was lower for second instar larvae. The mean time to death and yield of occlusion bodies were measured in second and fourth instar T. ni larvae at a high (100% mortality) and low (<50% mortality) doses of the virus. The mean time to death of recombinant infected larvae was reduced by 50-60% compared to larvae infected with the wild-type strain, depending on virus dose and instar, with these larvae becoming paralysed after approximately 60 h and dying 10-20 h later. This is among the fastest speeds of kill recorded for recombinant baculoviruses. Fourth instar larvae were found to succumb to the recombinant virus more quickly than the second instar larvae. The increase in the speed of kill of the recombinant virus was accompanied by a large reduction of approximately 95% in the yield of progeny virus. The yield of virus showed a highly significant relationship with time to death, but this relationship was complex and varied between the different viruses, concentrations, and instars. The yield per unit weight of the larvae was found to be constant at a low virus dose and increased over time at a high virus dose, irrespective of instar and virus. It is predicted that these changes in the performance of the recombinant virus would act toward reducing its fitness, leading to it being outcompeted by the wild type in field situations. (C) 2000 Academic Press.
34.Cory, JS. (2000) Assessing the risks of releasing genetically modified virus insecticides: progress to date.Crop Protection 19: 779-785 Assessing the risks of releasing genetically modified virus insecticides: progress to date
risk assessment; baculovirus; host range; recombinant; fitness; transmission; yield
Insect baculoviruses have been genetically modified to improve their speed of kill. Whilst these viruses show considerable promise for improving crop protection, any risks that might be attached to their wide-scale release need to be assessed. The potential hazards of releasing genetically modified baculoviruses are (i) negative effects on susceptible non-target species, and (ii) movement of the introduced gene. One approach to risk assessment is to estimate the relative fitness of the genetically modified virus as compared to the wild type. Initial laboratory and field experiments have shown that both productivity and transmission are significantly reduced in baculoviruses which express insect-selective toxins. This indicates that these viruses are likely to be less fit than the parent wild type. However, further information is needed on whether genetic modification alters baculovirus persistence and how baculoviruses behave in less susceptible species and species with different life history strategies. (C) 2000 Elsevier Science Ltd. All rights reserved.
33.Cory, JS; Hirst, ML; Sterling, PA; Speight, MR. (2000) Narrow host range nucleopolyhedrovirus for control of the browntail moth (Lepidoptera : Lymantriidae).Environmental Entomology 29: 661-667 Narrow host range nucleopolyhedrovirus for control of the browntail moth (Lepidoptera : Lymantriidae)
Euproctis chrysorrhoea; nontarget organism; bioinsecticide; Lymantriidae; host range; baculovirus
The browntail moth, Euproctis chrysorrhoea (L.), is periodically a major urban pest in the southern United Kingdom. High populations cause severe defoliation of a range of host plants, often in urban areas; and urticating hairs of larvae are highly irritating to humans. Control of outbreak populations is therefore desired. As an alternative to chemical insecticide sprays and labor intensive nest removal, nucleopolyhedrovirus (NPV) has been considered as a biological control. To evaluate if use of this spray would affect other lepidopterans we carried out detailed host range testing using a number of wild-caught lepidopteran species. Seventy-three species of Lepidoptera from 14 families, including four species of Lymantriidae and two species of hymenopteran sawfly, were found to be nonpermissive to E. chrysorrhoea NPV at a dose of 10(6) occlusion bodies per second instar. Some individuals from 11 species of Lepidoptera and one hymenopteran sawfly died of baculovirus infection, but none of these were shown, by dot blot analysis of DNA, to be infected with E. chrysorrhoea NPV. In two of these species, uninfected control larvae also died of infection, indicating that they carried an overt infection in the field. However, in eight species of Lepidoptera and one sawfly, there were no control deaths, providing possible evidence that an inapparent or latent infection had been stressed out of the wild-caught insects by inoculation with a high dose of E. chrysorrhoea NPV. Our results suggest this NPV may be monospecific, and that it is unlikely to present a risk to ally nontarget species. These characteristics make it highly suitable for use as a bioinsecticide, particularly in urban areas and nature reserves.
31. Myers, JH; Malakar, R; Cory, JS. (2000) Sublethal nucleopolyhedrovirus infection effects on female pupal weight, egg mass size, and vertical transmission in gypsy moth (Lepidoptera : Lymantriidae).Environmental Entomology 29: 1268-1272 Sublethal nucleopolyhedrovirus infection effects on female pupal weight, egg mass size, and vertical transmission in gypsy moth (Lepidoptera : Lymantriidae)
Lymantria dispar; nucleopolyhedrovirus; vertical transmission; fecundity; population cycles; egt-
Gypsy moth females that survived inoculation with Lymantria dispar (L.) nucleopolyhedrovirus (LdNPV) as fifth instars were smaller as pupae and laid fewer eggs as adults. Treatment with both wild type virus containing the egt gene and a genetically manipulated, egt- virus, lacking this gene, reduced pupal mass to a similar degree. Sublethal infection with wild type virus reduced the masses of surviving pupae at 20, 25, and 28 degreesC. A relationship between virus dose (5,000, 50,000 and 500,000 occlusion bodies per larva), mass of pupae, and egg mass size only occurred in one experiment in which larvae were reared at 25 degreesC and inoculated 5 d after molt to the fifth instar. Vertical transmission of overt infection occurred in two of 13 egg masses (15%) produced by females inoculated with virus as larvae. The five larvae infected with virus were approximate to0.5% of the larvae tested. Whether sublethal effects of LdNPV infection occur in field populations of gypsy moth remains to be tested.
30. Reeson, AF; Wilson, K; Cory, JS; Hankard, P; Weeks, JM; Goulson, D; Hails, RS. (2000) Effects of phenotypic plasticity on pathogen transmission in the field in a Lepidoptera-NPV system.Oecologia 124: 373-380 Effects of phenotypic plasticity on pathogen transmission in the field in a Lepidoptera-NPV system
transmission; mass action assumption; phase polyphenism; Spodoptera exempta; baculoviruses
In models of insect-pathogen interactions, the transmission parameter (v) is the term that describes the efficiency with which pathogens are transmitted between hosts. There are two components to the transmission parameter, namely the rate at which the host encounters pathogens (contact rate) and the rate at which contact between host and pathogen results in infection (host susceptibility). Hen it is shown that in larvae of Spodoptera exempta (Lepidoptera: Noctuidae), in which rearing density triggers the expression of one of two alternative phenotypes, the high-density morph is associated with an increase in larval activity. This response is likely to result in an increase in the contact rate between hosts and pathogens. Rearing density is also known to affect susceptibility of S. exempta to pathogens, with the high-density morph showing increased resistance to a baculo-virus. In order to determine whether density-dependent differences observed in the laboratory might affect transmission in the wild, a field trial was carried out to estimate the transmission parameter for S. exempta and its nuclear polyhedrosis virus (NPV). The transmission parameter was found to be significantly higher among larvae reared in isolation than among those reared in crowds. Models of insect-pathogen interactions, in which the transmission parameter is assumed to be constant, will therefore not fully describe the S. exempta-NPV system. The finding that crowding can influence transmission in this way has major implications for both the long-term population dynamics and the invasion dynamics of insect-pathogen systems.
29. Wilson, KR; O'Reilly, DR; Hails, RS; Cory, JS. (2000) Age-related effects of the Autographa californica multiple nucleopolyhedrovirus egt gene in the cabbage looper (Trichoplusia ni).Biological Control 19: 57-63 Age-related effects of the Autographa californica multiple nucleopolyhedrovirus egt gene in the cabbage looper (Trichoplusia ni)
baculovirus; nuclear polyhedrosis virus; deletion mutant; recombinant virus; microbial control; productivity; speed of kill
The effects of deleting the Autographa californica multiple nucleopolyhedrovirus (AcMNPV) egt gene on speed of kill and virus productivity were compared in second and fourth instar Trichoplusia ni (Hubner) larvae. Time to death was significantly reduced in larvae infected with an egt deletion mutant compared to insects infected with the wild-type virus. Moreover, time to death was reduced by the same proportion (11%) in second and fourth instar larvae. Virus yield was also significantly lower in fourth instar larvae infected with the deletion mutant but no difference was apparent in second instar larvae. A comparison of cadaver weights showed that insects infected with the deletion mutant were lighter than those infected with the wildtype virus, suggesting that the decrease in virus yield resulted from a reduction in larval growth. An analysis of yield per unit body weight showed no evidence for differences in replication rate in the two viruses. To determine whether differences in larval growth rate were related to differences in feeding activity, frass production was monitored in fourth instar larvae. Larvae infected with the deletion mutant produced less frass than larvae infected with the wildtype virus. Whereas the average rate of feeding for fourth instars did not differ between virus treatments, the rate peaked and declined earlier for larvae infected with the deletion mutant than for those infected with wild-type virus, suggesting enhanced early feeding in the absence of egt expression. (C) 2000 Academic Press.
27. Hernandez-Crespo, P; Hails, RS; Sait, SM; Green, BM; Carty, TM; Cory, JS. (1999) Response of hosts of varying susceptibility to a recombinant baculovirus insecticide in the field.Biological Control 16: 119-127 Response of hosts of varying susceptibility to a recombinant baculovirus insecticide in the field
nucleopolyhedrovirus; bioinsecticide; Trichoplusia ni; Mamestra brassicae; Autographa californica; risk assessment; genetically modified virus; neurotoxin
In an attempt to improve the effectiveness of nucleopolyhedroviruses (NPV) as bioinsecticides of lepidopteran pests, the NPV of Autographa californica (AcMNPV) has been genetically modified to include a gene that expresses an insect-selective scorpion toxin, AaHIT. In a field trial, we compared the response of a highly susceptible 'target' host (Trichoplusia ni) and a representative less susceptible species (Mamestra brassicae), following spraying with wild-type AcMNPV and the genetically modified virus. Mortality and therefore risk of infection were significantly lower in the less susceptible species but did not differ between the wild-type and the recombinant viruses. Speed of kill was consistently faster in T. ni infected with the recombinant virus for samples collected 1, 3, and 5 days following spray application. The results for M. brassicae were more variable; time to death induced by both viruses was longer in M. brassicae than in T. ni but the genetically modified virus acted faster only in larvae taken 3 and 5 days following spraying. This contrasts with laboratory assays in which the recombinant virus took longer than the wild-type virus to kill M. brassicae. The results demonstrate that there are differences in virus productivity, distribution, and timing of virus release when two hosts with different susceptibilities are treated with wild-type and recombinant baculoviruses, which will impact on further rounds of virus replication. Thus, the effects of recombinant baculoviruses on less susceptible, potentially nontarget, hosts are not likely to be easy to predict, and they highlight the need for both more information on the behavior of baculoviruses in hosts of varying susceptibility and further studies on the impact of these factors on secondary transmission, (C) 1999 Academic Press.
24.Cory, JS; Bishop, DHL. (1997) Use of baculoviruses as biological insecticides.Molecular Biotechnology 7: 303-313 Use of baculoviruses as biological insecticides
biopesticides; pest control; insect viruses; bioassay; production; application
Naturally occurring baculoviruses can be used to control a wide range of insect pests. Most baculoviruses are Used as biopesticides, that is, they are sprayed onto high-density pest populations in a manner akin to the use of synthetic chemical pesticides. However, other strategies that use the biological features of the viruses are also possible and should increase as we expand our knowledge of baculovirus ecology. In order to develop a baculovirus control program, several areas need to be studied before progressing to large Scale field studies and commercialization. These range from laboratory efficacy testing and the development of production systems to detailed study of pest behavior and the development of appropriate,application strategies.
23.Cory, JS; Hails, RS. (1997) The ecology and biosafety of baculoviruses.Current Opinion in Biotechnology 8: 323-327 The ecology and biosafety of baculoviruses
Advances in the use of molecular techniques - particularly for virus identification, the investigation of latency and the infection process, plus the development of a theoretical framework containing a higher degree of biological realism - have pushed baculovirus ecology forward in the past few years. This has created a scenario in which many hitherto intractable questions about the behaviour of natural and genetically modified baculoviruses can now be addressed. (C) Current Biology Ltd.
22. Lilley, AK; Hails, RS; Cory, JS; Bailey, MJ. (1997) The dispersal and establishment of pseudomonad populations in the phyllosphere of sugar beet by phytophagous caterpillars.FEMS Microbiology Ecology 24: 151-157 The dispersal and establishment of pseudomonad populations in the phyllosphere of sugar beet by phytophagous caterpillars
Mamestra brassicae; Pseudomonas fluorescens; dispersal; colonisation; establishment; leaf surface; genetically modified microorganism
The role of phytophagous insects in the dispersal of phyllosphere bacterial populations has been investigated. Following seed inoculation, a leaf colonising population of Pseudomonas fluorescens SBW25EeZY6KX (lacZY and aph-xylE) was established in field grown sugar beet (Beta vulgaris var. amethyst). Third instar, Mamestra brassicae (Lepidoptera: Noctuidae) larvae were placed onto the emerging leaves of mature plants and the dispersal of the marked strain (ca. 5 X 10(5) cfu/g leaf) to untreated plants monitored. Forty-two days after caterpillar introduction, approximately twenty days after pupation of the larvae, an established population of transferred bacteria was detected at densities similar to those determined for seed inoculated plants of the same age. Under appropriate conditions phylloplane colonising pseudomonads can be dispersed by invertebrates and establish viable populations on the leaves of recipient plants.
21. Clarke, EE; Tristem, M; Cory, JS; OReilly, DR. (1996) Characterization of the ecdysteroid UDP-glucosyltransferase gene from Mamestra brassicae nucleopolyhedrovirus.Journal of General Virology 77: 2865-2871 Characterization of the ecdysteroid UDP-glucosyltransferase gene from Mamestra brassicae nucleopolyhedrovirus
The ecdysteroid UDP-glucosyltransferase (egt) gene of Mamestra brassicae multinucleocapsid nucleopolyhedrovirus (MbMNPV) has been cloned and characterized. MbMNPV egt potentially encodes a protein of 528 amino acids. Analysis of the substrate specificity of the MbMNPV EGT protein showed that it mirrors that of Autographa californica MNPV (AcMNPV) EGT. MbMNPV EGT also appears to be secreted from infected cells. Confirmation that the cloned gene encodes an active EGT was obtained by transient expression assays. Phylogenetic trees of NPVs were generated based on the alignment of baculovirus EGT sequences. These phylogenies support the classification of MbMNPV as a group II NPV that is most closely related to Spodoptera exigua MNPV. Comparison of the EGT-based phylogenies with polyhedrin/granulin-based phylogenies shows that the position of AcMNPV is different in the two trees, possibly indicating that AcMNPV acquired its polyhedrin gene by recombination with another virus.
20. Vasconcelos, SD; Cory, JS; Wilson, KR; Sait, SM; Hails, RS. (1996) Modified behavior in Baculovirus-infected lepidopteran larvae and its impact on the spatial distribution of inoculum.Biological Control 7: 299-306 Modified behavior in Baculovirus-infected lepidopteran larvae and its impact on the spatial distribution of inoculum
Mamestra brassicae; nucleopolyhedrovirus; insect behavior; virus dispersal; cabbage moth; NPV transmission
Quantifying the rate of dispersal of target insects when infected with a disease agent will aid the development of biorational pest control programs. The effect of nucleopolyhedrovirus (NPV) infection on the mobility of second and fourth instar Mamestra brassicae larvae was investigated in the laboratory and field. NPV infection altered larval mobility, with the changes in behavior varying with the timecourse of infection. Diseased larvae moved three to five times further than healthy ones during the middle stages of infection. By the 7th day postinfection diseased larvae were less mobile than healthy counterparts. The same pattern of modified behavior was observed in both instars. Fourth instar larvae moved further than second instars under laboratory and field conditions. In the field, infected larvae tended to die on the apex of the cabbage leaves. Bioassay of the leaves showed a linear decrease in inoculum from central to peripheral plants within the plots, which occurred to the same extent for second and fourth instars. Leaves from plots where infected fourth instar larvae had been introduced had higher inoculum density than those from plots with second instars. (C) 1996 Academic Press, Inc.
19. Vasconcelos, SD; Williams, T; Hails, RS; Cory, JS. (1996) Prey selection and baculovirus dissemination by carabid predators of Lepidoptera.Ecological Entomology 21: 98-104 Prey selection and baculovirus dissemination by carabid predators of Lepidoptera
baculovirus; prey selection; carabids; virus dispersal; nucleopolyhedrovirus; Mamestra brassicae
1. The interaction between coleopteran predators and baculovirus-infected larvae was studied in the laboratory and the field in order to assess the potential role of predators in the dissemination of a nucleopolyhedrovirus (NPV). 2. Preference tests using three carabid species, Harpalus rufipes De Geer, Pterostichus melanarius Illiger and Agonum dorsale Pont. showed no evidenee of discrimination between healthy and diseased larvae of the cabbage moth Mamestra brassicae L. (Lepidoptera: Noctuidae) as prey items. 3. Virus infectivity was maintained after passage through the predator's gut. NPV mortality ranged from 97% to 20% when test larvae were exposed to faeces collected immediately after and 15 days post-infected meal respectively. 4. The potential for transfer of inoculum in the environment was estimated in the laboratory by soil bioassay. Carabids continuously passed infective virus to the soil for at least 15 days after feeding on infected larvae. 5. Field experiments showed that carabids which had previously fed on diseased larvae transferred sufficient virus to the soil to cause low levels of mortality in larval populations of the cabbage moth at different instars.
18. GOULSON, D; CORY, JS. (1995) RESPONSES OF MAMESTRA-BRASSICAE (LEPIDOPTERA, NOCTUIDAE) TO CROWDING - INTERACTIONS WITH DISEASE RESISTANCE, COLOR PHASE AND GROWTH.Oecologia 104: 416-423 RESPONSES OF MAMESTRA-BRASSICAE (LEPIDOPTERA, NOCTUIDAE) TO CROWDING - INTERACTIONS WITH DISEASE RESISTANCE, COLOR PHASE AND GROWTH
PHASE POLYMORPHISM; DENSITY; MAMESTRA BRASSICAE; BACULOVIRUS; GROWTH RATE
This study examines phenotypic plasticity in relation to rearing density in larvae of the moth, Mamestra brassicae. Larval phase, growth rate, weight at moulting and susceptibility to disease were quantified when reared at five densities. Larvae develop more quickly, but attain a smaller size and are more susceptible to disease, when reared at high than at intermediate densities. They also exhibit a higher degree of melanisation than larvae reared at intermediate densities, or singly. A review of the literature suggests that a switch to a rapidly developing dark phase at high densities is a widespread phenomenon within the Lepidoptera. Rapid development at the expense of attaining a large size, and increased melanisation, are interpreted as adaptive responses to reach pupation before food supplies are depleted, as is likely when larval density is high. High susceptibility to viral infection at high density may be a result of physiological stress associated with rapid development, or due to a shift in allocation of resources from resistance to development: larvae that developed quickly were more susceptible to infection. Larvae reared singly appeared to be less fit than larvae reared at intermediate densities: they exhibited many of the characteristics of larvae reared at high density, particularly low weight, a right-hand skew in their weight frequency distribution, and high susceptibility to disease. I hypothesise that expression of resistance may be phenotypically plastic with regard to environment. Contact with other larvae may, up to a point, stimulate both growth and resistance to infection, for the risk of infection will increase with the density of conspecifics.
17. GOULSON, D; CORY, JS. (1995) SUBLETHAL EFFECTS OF BACULOVIRUS IN THE CABBAGE MOTH, MAMESTRA-BRASSICAE.Biological Control 5: 361-367 SUBLETHAL EFFECTS OF BACULOVIRUS IN THE CABBAGE MOTH, MAMESTRA-BRASSICAE
DEVELOPMENTAL TIME; SEX RATIO; FECUNDITY; VERTICAL TRANSMISSION; TRANSSTADIAL TRANSMISSION; NUCLEAR POLYHEDROSIS VIRUS; SUBLETHAL INFECTION; MAMESTRA BRASSICAE
Sublethal effects of pathogens such as baculoviruses, in particular vertical transmission to subsequent host generations, may play an important role in their ecology and population dynamics and could also be of relevance in their use as pest control agents. The effects of a range of sublethal concentrations of a nuclear polyhedrosis virus (NPV) were investigated in fourth and fifth instar larvae of the cabbage moth, Mamestra brassicae. Survivors of the NPV inoculation exhibited an extended developmental time in both the larval and the pupal phase compared with control larvae. There was a general trend toward increasing developmental time with increasing viral concentration. Pupal weight, sex ratio, fecundity, and egg viability were not significantly different between insects subjected to viral challenge and control groups. A low level of NPV mortality (0.55%) was recorded in the progeny of adults which had developed from larvae subject to viral challenge. Viral death in progeny larvae occurred predominantly during the second instar. Vertical transmission, although occurring at low levels, may be vital for the long-term persistence of the virus, particularly in a mobile pest species such as M. brassicae, which occupies ephemeral habitats. (C) 1995 Academic Press, Inc.
16. GOULSON, D; HAILS, RS; WILLIAMS, T; HIRST, ML; VASCONCELOS, SD; GREEN, BM; CARTY, TH; CORY, JS. (1995) TRANSMISSION DYNAMICS OF A VIRUS IN A STAGE-STRUCTURED INSECT POPULATION.Ecology 76: 392-401 TRANSMISSION DYNAMICS OF A VIRUS IN A STAGE-STRUCTURED INSECT POPULATION
BACULOVIRUS; INSTAR; LEPIDOPTERA; MAMESTRA BRASSICAE; MORTALITY RATE; NUCLEAR POLYHEDROSIS VIRUS; PATHOGEN; STAGE; SUSCEPTIBILITY; TRANSMISSION
Despite the blossoming interest in host-microparasite epidemiology, and in use of viruses in the biological control of insect pests, few empirical studies have attempted to quantify transmission and mortality rates under field conditions. We report a laboratory and field study in which the transmission parameter (nu) and mortality rate (alpha) due to nuclear polyhedrosis virus (NPV) are measured in different larval instars of the cabbage moth, Mamestra brassicae (Lepidoptera: Noctuidae), Laboratory studies of food consumption and virus susceptibility were used to produce crude estimates of relative transmission rates in successive instars. Increases in the rate of feeding outstrip increases in virus resistance with instar, so we predict that transmission rates should increase in older larvae (assuming rate of intake of virus to be proportional to rate of feeding). This prediction was tested in a field experiment in which a constant initial density of susceptible and infected (moribund) larvae were reared together on cabbage plants for 2-8 d. Estimates of the linear transmission parameter (nu) did not differ between instars and gave a mean value of 2.16 x 10(-12) for all instars and time points. Causes for the discrepancy between predictions based on laboratory data and field measurements are discussed. Differences were found between instars in the time from infection to death (tau) (equivalent to 1/alpha, where alpha is the rate of mortality due to viral infection). Second-instar larvae died more rapidly once infected than third instars, which, in turn, died more rapidly than fourth instars. The effect of host population stage structure on patterns of viral infection can be pronounced and if recognized, may significantly increase the accuracy and predictive value of models of host pathogen systems.
15. CORY, JS; HIRST, ML; WILLIAMS, T; HAILS, RS; GOULSON, D; GREEN, BM; CARTY, TM; POSSEE, RD; CAYLEY, PJ; BISHOP, DHL. (1994) FIELD TRIAL OF A GENETICALLY IMPROVED BACULOVIRUS INSECTICIDE.Nature 370: 138-140 FIELD TRIAL OF A GENETICALLY IMPROVED BACULOVIRUS INSECTICIDE
IMPROVEMENT of biological pesticides through genetic modification has enormous potential and the insect baculoviruses are particularly amenable to this approach(1,2). A key aim of genetic engineering is to increase their speed of kill, primarily by the incorporation of genes which encode arthropod or bacterially derived insect-selective toxins(3-11), insect hormones(12,13) or enzymes(14,15). We report here the first, to our knowledge, field trial of a genetically improved nuclear polyhedrosis virus of the alfalfa looper, Autographa californica (AcNPV) that expresses an insect-selective toxin gene (AaHIT) derived from the venom of the scorpion Androctonus australis(16-18). Previous laboratory assays with the cabbage looper, Trichoplusia ni, demonstrated a 25% reduction in time to death compared to the wild-type virus, but unaltered pathogenicity(6) and host range(19). In the field, the modified baculovirus killed faster, resulting in reduced crop damage and it appeared to reduce the secondary cycle of infection compared to the wild-type virus.
14. WILLIAMS, T; CORY, JS. (1994) PROPOSALS FOR A NEW CLASSIFICATION OF IRIDESCENT VIRUSES.Journal of General Virology 75: 1291-1301 PROPOSALS FOR A NEW CLASSIFICATION OF IRIDESCENT VIRUSES
The need for comparative studies of iridoviruses to elucidate the relationships between them has been well appreciated. Sixteen iridoviruses, including type species from each of the four recognized genera of the Iridoviridae, were compared by restriction endonuclease characterization, hybridization to the major structural protein (MSP) gene of an invertebrate iridescent virus (IV) isolate at various stringencies, PCR amplification of the MSP gene region and by dot-blot hybridization studies. The results broadly supported previous serological studies. The vertebrate iridoviruses, frog virus 3 (genus Ranavirus) and flounder lymphocystivirus (genus Lymphocystivirus), appeared distinct from one another and from the invertebrate isolates. Naming and numbering invertebrate IV isolates according to history and host is no longer useful since IVs infect a number of species. A revised system, involving names based on the geographical origin of the isolate is proposed, in line with other virus families. The large IVs of invertebrates represented by Vero Beach IV (previously IV3 or mosquito IV; genus Chloriridovirus) showed little similarity to any other IVs. Members of the genus Iridovirus, the small invertebrate IVs, fell into three distinct groups of interrelated isolates. The largest group, containing the Plowden (IV1), Tia (IV2), Nelson (IV9, IV10 and IV18), Aberystwyth (IV22), Srinagar (IV24), Fort Collins (IV29) and Stoneville (IV30) iridoviruses, is named the Polyiridovirus complex. The Plowden iridovirus (IV1) is suggested as type species for this complex given the data available on its molecular biology. Based on previously published data, Timaru (IV16 and IV19) and Uitenhage (IV23) iridoviruses are also assigned to this complex. The second but smaller group is named the Oligoirido-virus complex, which includes Dazaifu (IV6) as the type species and contains Ntondwe (IV21 and IV28) on a tentative basis. Riverside IV (IV31) was distinct from both of the other groups, and is proposed as a third complex, Crustaceoiridovirus.
12. GOULSON, D; CORY, JS. (1993) FLOWER CONSTANCY AND LEARNING IN FORAGING PREFERENCES OF THE GREEN-VEINED WHITE BUTTERFLY PIERIS-NAPI.Ecological Entomology 18: 315-320 FLOWER CONSTANCY AND LEARNING IN FORAGING PREFERENCES OF THE GREEN-VEINED WHITE BUTTERFLY PIERIS-NAPI
PIERIS; BUTTERFLY; FORAGING; FLOWER COLOR; NECTAR; LEARNING
1. Evolutionary pressure should select for efficient foraging strategies, within the constraints of other selective forces. We assess the mechanisms underlying flower choice in the butterfly, Pieris napi (L.), which as an adult forages for nectar. Experiments were carried out on a laboratory colony, using artificial flowers of two colours, and replicated on two successive generations. 2. When nectar was freely available from all flowers, equal numbers of butterflies visited each colour, but individual butterflies exhibited flower constancy, showing a strong preference for one colour or the other. 3. Following 3 day conditioning periods in which nectar was available from flowers of one colour only, butterflies responded by developing a preference for this colour, which persisted when both flower colours were refilled. This preference could subsequently be switched to the other flower colour following a further 3 days of conditioning. These are interpreted as adaptive (learned) responses, which would have obvious selective benefits in the field, enabling butterflies to avoid flower species which experience has shown are poor sources of nectar, and to adapt to temporal and spatial changes in nectar availability.
11. POSSEE, RD; CAYLEY, PJ; CORY, JS; BISHOP, DHL. (1993) GENETICALLY-ENGINEERED VIRAL INSECTICIDES - NEW INSECTICIDES WITH IMPROVED PHENOTYPES.Pesticide Science 39: 109-115 GENETICALLY-ENGINEERED VIRAL INSECTICIDES - NEW INSECTICIDES WITH IMPROVED PHENOTYPES
Baculoviruses are natural pathogens of insects which have been used as biopesticides. In contrast to many chemical agents, baculoviruses affect only a limited number of insects and so can be used to target particular insect species. Unfortunately, unless the host receives a very high virus dose, the insect continues to feed and causes damage to crops, because the virus takes several days to kill it. This lag is unacceptable in the protection of many crops, especially where cosmetic damage seriously reduces the value of a crop (e.g. fruit). Strategies have been devised recently to circumvent this problem. The baculovirus genome has been modified, using genetic engineering techniques, to incorporate foreign genes encoding insect-specific toxins, or hormones or enzymes. Expression of some of these genes in the virus-infected host insect has been shown to reduce both the feeding damage to crop plants and the time taken to kill the insect pest. The current status of this developing field is described, together with an assessment of the possible risks involved in using such genetically modified agents in the environment. DOI
9. BOURNER, TC; VARGASOSUNA, E; WILLIAMS, T; SANTIAGOALVAREZ, C; CORY, JS. (1992) A COMPARISON OF THE EFFICACY OF NUCLEAR POLYHEDROSIS AND GRANULOSIS VIRUSES IN SPRAY AND BAIT FORMULATIONS FOR THE CONTROL OF AGROTIS-SEGETUM (LEPIDOPTERA, NOCTUIDAE) IN MAIZE.Biocontrol Science and Technology 2: 315-326 A COMPARISON OF THE EFFICACY OF NUCLEAR POLYHEDROSIS AND GRANULOSIS VIRUSES IN SPRAY AND BAIT FORMULATIONS FOR THE CONTROL OF AGROTIS-SEGETUM (LEPIDOPTERA, NOCTUIDAE) IN MAIZE
AGROTIS-SEGETUM; BACULOVIRIDAE; BIOCONTROL-FORMULATIONS; BIOLOGICAL-CONTROL; CUTWORM; GRANULOSIS VIRUS; NUCLEAR POLYHEDROSIS VIRUS
Agrotis segetum nuclear polyhedrosis virus (AsNPV) and granulosis virus (AsGV), propagated in laboratory cultures of A. segetum in England and A. ipsilon in Spain, respectively, were applied to plots of maize plants at the one- to four-leaf stage of growth. Plots were arranged in a 6 x 6 Latin square design and infested with second-instar A. segetum larvae (the common cutworm). Each virus was applied in separate treatments by two application methods; as an aqueous spray containing 0.1% Agral as a wetting agent, and as a bran bait. The NPV was applied at a rate of 4 x 10(12) polyhedra/ha, and the GV at 4 x 10(13) granules/ha. Soil and plants were sampled for larvae on three occasions following virus treatment: 24 h, 4 days and 11 days. The larvae were reared on diet in the laboratory, until death or pupation, to examine the rate and level of viral infection. Infection data showed 87.5% and 91% NPV infection and 12.5% and 55% GV infection in spray and bait treatments, respectively, in larvae sampled 24 h after treatment. In larvae sampled 4 days after treatment, the results were 78% and 100% NPV infection, and 13% and 6% GV infection. A total of only six larvae were retrieved on day 11. In both treatments larvae infected with AsNPV died significantly more rapidly and at an earlier instar than those infected with AsGV, indicating that AsNPV appears to have better potential as a control agent for A. segetum.
3. Jones LD, Davies CR, Williams T, Cory J & Nuttall PA. (1990) Non-viraemic transmission of Thogoto virus: vector efficiency of Rhipicephalus appendiculatus and Amblyomma variegatum.Transactions of the Royal Society of Tropical Medicine and Hygiene 84: 846-848. Non-viraemic transmission of Thogoto virus: vector efficiency of Rhipicephalus appendiculatus and Amblyomma variegatum.
Previous studies have demonstrated that Thogoto virus is transmitted from infected to uninfected ticks when co-feeding on uninfected guinea-pigs, even though the guinea-pigs do not develop a detectable viraemia. Furthermore, tick to tick transmission is potentiated by factors associated with the salivary glands of ticks (saliva activated transmission). The vector efficiency of 2 ixodid tick species, Rhipicephalus appendiculatus and Amblyomma variegatum, for Thogoto virus was assessed using this model. The number of uninfected recipient ticks that acquired Thogoto virus when co-feeding with virus-infected ticks (donors) on uninfected guinea-pigs was determined. When nymphs of either tick species were employed as donors, there was no significant difference in the number of infected recipient nymphs. In contrast, a significant difference in the vector efficiency of adults ticks was observed: 77·0% of recipient ticks which co-fed with R. appendiculatus donor adults acquired Thogoto virus compared to 44·7% of recipient ticks which co-fed with A. variegatum donors. No significant difference in susceptibility to Thogoto virus infection was observed between recipient ticks of the 2 species. Thus, adults of R. appendiculatus are more efficient than A. variegatum in mediating non-viraemic transmission. DOI
1. Kelly, P.M. and J.S. Cory. (1987) Operculum closing as a defence against predatory leeches in four British freshwater prosobranch snails.Hydrobiologia 144: 121-124 Operculum closing as a defence against predatory leeches in four British freshwater prosobranch snails
The defence reaction of operculum closing in response to the presence of the molluscivorous leech Glossiphonia complanata (L.) and the non-molluscivorous Erpobdella octoculata (L.) was studied in four species of freshwater prosobranch gastropod. Bithynia tentaculata (L.) and Valvata piscinalis (Müller) can distinguish between the leeches, reacting only to G. complanata. V. piscinalis is capable of a greater degree of distance chemoreception of the leech ‘scent’. Valvata cristata Müller and Potamopyrgus jenkinsi (Smith) did not react to either leech. V. cristata may not be a potential prey item for G. complanata, while P. jenkinsi is fed on by the leech, but is a relative newcomer to the freshwater fauna. DOI