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Title: Woody stem galls interact with foliage to affect community associations

Author
item Cooper, William - Rodney
item RIESKE, LYNNE - UNIVERSITY OF KENTUCKY

Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/2/2009
Publication Date: 4/1/2009
Citation: Cooper, W.R., Rieske, L.K. 2009. Woody stem galls interact with foliage to affect community associations. Environmental Entomology. 38(2):417-424.

Interpretive Summary: Gall wasps (Hymenoptera: Cynipidae) hijack their of their host plants to produce galls which house wasps throughout their immature stages. We evaluated two way interactions between stem galls produced by the Asian chestnut gall wasp on Chestnut and foliage directly attached to galls (gall leaves) using gall leaf excision experiments and gypsy moth bioassays. Early season gall leaf excision decreased the dry weight per chamber (nutritive index) and thickness of the protective layer surrounding the gall wasp chambers, and increased the number of empty chambers and the occurrence and size of exterior fungal lesions. Leaf excision also caused a modest (alpha=0.1) increase in the incidence of chamber fungi and herbivory by the lesser chestnut weevil, and a modest decrease in parasitoids. This study shows that gall leaves are important for stem gall development, quality, and defenses, adding support for the Nutrient and Enemy hypotheses. We also evaluated the effects of stem galls on the suitability of gall leaves to gypsy moth herbivory to assess the extent of gall defenses in important source leaves. Relative growth rate of gypsy moth larvae was greater on gall leaves compared to 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. Our results improve our knowledge of host-gall wasp interactions, gall source – sink relations, Asian chestnut gall wasp community interactions.

Technical Abstract: Gall wasps (Hymenoptera: Cynipidae) hijack the physiology of their host plant to produce galls which house wasps throughout their immature stages. The gall-maker – host plant interaction is highly evolved, and galls represent an extended phenotype of the gall wasp. We evaluated two-way interactions between stem galls produced by Dryocosmus kuriphilus Yasumatsu on Castanea spp. (Fagales: Fagaceae) and foliage directly attached to galls (gall leaves) using gall leaf excision experiments and herbivore bioassays. Early season gall leaf excision decreased the dry weight per chamber (nutritive index) and thickness of the protective schlerenchyma layer, and increased the number of empty chambers and the occurrence and size of exterior fungal lesions. Leaf excision also caused a modest (alpha=0.1) increase in the incidence of feeding chamber fungi and herbivory by Curculio sayi Gyllenhal (Coleoptera: Curculionidae), and a modest decrease in parasitoids. This study shows that gall leaves are important for stem gall development, quality, and defenses, adding support for the Nutrient and Enemy hypotheses. We also evaluated the effects of stem galls on the suitability of gall leaves to Lymantria dispar L. (Lepidoptera: Lymantriidae) herbivory to assess the extent of gall defenses in important source leaves. Relative growth rate of L. dispar larvae was greater on gall leaves compared to 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. Our results improve our knowledge of host-cynipid interactions, gall source – sink relations, and D. kuriphilus community interactions.