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

Abstract

There are three necessary requirements for local adaptation of insect herbivores to individual plants, namely the existence of i) plant phenotypic variation for traits affecting herbivore performance, ii) genotypic variation in the responses of herbivores to these traits, and iii) a genotypic trade-off to deal with different plant individuals (i.e., G ¥ E interaction). In this paper we checked prerequisites 2 and 3 for Epirrita autumnata (Borkhausen) and its main host plant in northeastern Europe, birch trees (Betula spp.). Phenotypic variation in plant features affecting performance of this herbivore species (point 1) had been thoroughly verified earlier on. We studied additive genetic variation and maternal effects on larval feeding parameters (consumption, digestibility, growth) and pupal masses of the insect with a paternal half-sib design. The experiment was replicated on four trees with different chemical profiles to check for the existence of G ¥ E interaction. 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 consumption and growth of 5th instar larvae. Absence of G ¥ E interactions for all the study traits suggests that local adaptation of E. autumnata to individual trees within populations is not likely.