Escape from pupal predation as a potential cause of outbreaks of the winter moth, Operophtera brumata
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| Authors: | Raymond, B; Vanbergen, A; Watt, A; Hartley, SE; Cory, JS; Hails, RS |
| Year: | 2002 |
| Journal: | Oikos 98: 219-228 |
| Title: | Escape from pupal predation as a potential cause of outbreaks of the winter moth, Operophtera brumata |
| Abstract: | 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. |
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