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Biological Improvement of Chestnut Through Technologies That Address Management of the Species, Its Pathogens and Pests
Department of Entomology
The overall impact of this project will be to further the progress being made toward the restoration of chestnut as a tree in North American forests and as a nut in the American marketplace.
2010 Project Description
We are evaluating new ecological interactions associated with an exotic invasive gallmaker, the Asian chestnut gall wasp, as it expands its geographic range in North America. Expanding populations of the exotic gall wasp are recruiting native and introduced natural enemies in North America. Consequences of this recruitment are being investigated in the context of potential biological control of the gall wasp, which could affect commercial chestnut production and American chestnut restoration efforts.
The first objective is to evaluate the suitability of gall wasp infested chestnut foliage for generalist foliage feeders, to assess the extent to which expanding gall wasp populations might affect native and non-native herbivores. I am also characterizing the expanding natural enemy complex of the gall wasp. Parasitization is a primary cause of mortality, and parasitoid recruitment is being evaluated, with six parasitoid species documented as gall wasp associates. Interactions between the most prevalent native parasitoid, Ormyrus labotus, and the introduced parasitoid, Torymus sinensis, which was introduced for Asian chestnut gall wasp control, are being evaluated.
I have also developed a means of rearing gall wasp populations under controlled conditions. Gall-inducing insects are obligate plant parasites, making them difficult to manipulate under laboratory conditions. I have grafted dormant gall wasp infested buds onto chestnut root stock and successfully reared gall wasps through to adulthood. This opens possibilities for manipulative studies evaluating gall wasp development, and provides a mechanism to evaluate host plant and environmental effects.
We are also evaluating spatial distribution patterns of the gall wasp. Beginning on a broad spatial scale we are mapping range expansion along the leading edge of the infestation, and also evaluating these populations for natural enemies.
Additionally we are evaluating patterns of within-tree and within-orchard gall distribution. I am also assessing the effects of orchard floor manipulations on gall wasp populations, to investigate means of sustainably suppressing the gall wasp and other pests of chestnut through habitat manipulation, while enhancing essential ecosystem services. My hypothesis is that habitat manipulation can provide refugia that lead to increased natural enemy activity and reduced pest populations, ultimately leading to increased nut production. Specific objectives are to evaluate habitat manipulation with respect to galling and gall wasp parasitization, ecosystem services such as pollinators, predators, and parasitoids, and chestnut yield. My ultimate goal is to gain an understanding of the ecological interactions, dispersal patterns, and mechanisms regulating gall wasp populations in eastern North America.
On gall wasp infested chestnut, relative growth rate of gypsy moth larvae was greater on gall leaves compared with normal leaves, indicating that, despite their importance, gall leaves may be more suitable to generalist insect herbivores, suggesting limitations to the extended phenotype of the gall wasp and altered host susceptibility to generalist herbivores. These results improve our knowledge of host - Cynipid interactions, gall Source - sink relations, and Asian chestnut gall wasp community interactions.
Evidence suggests that native parasitoids are actively being recruited to the gall wasp as it expands its range, but antagonistic interactions are evolving between the native and introduced species. It appears that native parasitoids are exploiting not only the gall wasp, but also its introduced biological control agent as their hosts, potentially limiting the effectiveness of the introduced species.
Preliminary results suggest that orchard floor manipulations may influence abundance of indigenous beneficial arthropods, but no data are available yet on the effects on gall wasp populations. Ultimately these results will provide a greater understanding of the ecological interactions, dispersal patterns, and mechanisms regulating gall wasp populations in eastern North America.
Cooper, W.R. and L.K. Rieske. 2011. Chestnut species and jasmonic acid treatment influence development and community interactions of galls produced by Dryocosmus kuriphilus. Journal of Insect Science, In review.
Cooper, W.R. and L.K. Rieske. 2011. A native and introduced parasitoid utilize an exotic gall-maker host. Biological Control, In review.
Cooper , W.R. and L.K. Rieske. 2010. Gall structure affects ecological associations of Dryocosmus kuriphilus (Hymenoptera: Cynipidae). Environmental Entomology 39, 787-797.