INTERSPECIFIC AND TEMPORAL VARIATION IN HERBIVORE RESPONSES TO HYBRIDWILLOWS

We studied herbivory of two species of willows (Salix sericea and S. e riocephala) and their interspecific hybrids to test alternative hypoth eses concerning the effects of hybridization on plant resistance. Indi vidually marked plants were identified using morphological traits in t he field and random amplified polymorphic DNA (RAPD) band analysis was used to verify the genetic status of many parental and hybrid plants. The densities of 12 herbivore species on plants in the field were com pared between two parents and their F-2-type hybrids. We found about e qual support for the additive, dominance, and hybrid susceptibility hy potheses over 4 years. In one year, one species supported the hybrid r esistance hypothesis. Guild membership was not a good predictor of sim ilar responses of species to hybrid versus parental plants. There were marked differences in support for particular hypotheses among years f or four herbivore species. This study demonstrates the diversity of re sponses of phytophages in response to interspecific hybridization, and indicates that year-to-year variation in relative resistance of hybri d plants can be important.