This research will explore for the first time coevolutionary interactions in a three trophic level system consisting of willow, Salix lasiolepis, a stem-galling sawfly, Euura lasiolepis, and a parasitoid, Lathrostizus euurae. The evolutionary forces on each member of the interaction will be studied as they create a "window of vulnerability" for the stem- galler when it can be attacked by the parasitoid. Lathrostizus can only attack larvae in each Euura gall for a limited time period defined by the developmental rates of both the gall and the sawfly. Preliminary evidence suggests that different willow genotypes and phenotypes have galls with different "windows," resulting in widely different parasitism rates. Experiments will answer the following questions: 1) Are gall characters determining vulnerability to Lathrostizus attack heritable characters of Euura, the willow, or interaction between the two? 2) Does the window of vulnerability of Euura to Lathrostizus attack depend on plant genotype? 3) Can the window of vulnerability be altered by changing plant phenotype? 4) Does the window of vulnerability increase resource complexity decreasing the searching efficiency of the parasitoid? 5) Is Lathrostizus better adapted to attacking other gallers in the system? Results will contribute to the basic ecology of tritrophic interactions.
