Testing for prerequisites of local adaptation in an insect herbivore, Epirrita autumnata

There are three necessary requirements for local adaptation of insect herbi vores to individual plants, namely the existence ii) plant phenotypic varia tion for traits affecting herbivore performance, ii) genotypic variation in the responses of herbivores to these traits, and iii) a genotypic trade-of f to deal with different plant individuals (i.e., G x E interaction). In th is paper we checked prerequisites 2 and 3 for Epirrita autumnata (Borkhause n) and its main host plant in northeastern Europe, birch trees (Betula spp. ). Phenotypic variation in plant features affecting performance of this her bivore species (point 1) had been thoroughly verified earlier on. We studie d additive genetic variation and maternal effects on larval feeding paramet ers (consumption, digestibility, growth) and pupal masses of the insect wit h a paternal half-sib design. The experiment was replicated on four trees w ith different chemical profiles to check for the existence of G x E interac tion. Additive genetic variance was not significant for pupal mass nor for the feeding parameters studied at 3rd and 5th instar. However, we detected a significant maternal effect on both pupal masses, and rates of consumptio n and growth of the 5th instar larvae. Absence of G x E interactions for al l the study traits suggests that local adaptation of E. autumnata to indivi dual trees within populations is not likely.