EFFECTS OF PLANT HYBRIDIZATION ON HERBIVORE-PARASITOID INTERACTIONS

We studied the effects of host plant hybridization on the survival and mortality of the leaf-mining moth Phyllonorycter salicifoliella on hy brid and parental willow plants in the field and in a common garden ex periment. P. salicifoliella survival differed significantly among thre e willow taxa in the field in 1994 but not in the field in 1995 or in the common garden. Parasitism by eulophid wasps differed significantly among taxa in 1994 and appeared to account for the variation in their survival. In the field in 1995, host feeding predation varied signifi cant among taxa. The theory of tritrophic interactions predicts that p lant genotype can affect natural enemy impact, and this study supports this prediction. Significant variation in survival and eulophid paras itism was also found among genotypes within taxa in the field in both years and in the common garden experiment. The common garden results s how that genetic differences in plants affect the herbivore-parasitoid interaction. Variation among years in the patterns of survival and ca uses of mortality among field plants suggest that genotype by environm ent interactions may be important.