Selective factors affecting clonal variation in the fall cankerworm Alsophila pometaria (Lepidoptera: geometridae)

Abstract

Differences in the frequency of certain clonal genotypes of Alsophila pometaria exist between neighbouring stands of maple and oak, but cannot be detected between individual maple and oak trees within a mixed-species stand. Several genotypes differ in their capacity for survival on maple foliage, but no evidence of differential survival or growth was found on oak foliage. Melanisation of larvae in the later instars, which is associated with the attainment of lower body weight, is a response to interaction among larvae; the tendency to display this response differs among genotypes. The selective factors acting on the clonal polymorphism thus may include environmental heterogeneity and density-dependent selection. Because of larval dispersal, the mosaic of trees in a mixed-species forest is “fine-grained” environmental variation that is unlikely by itself to maintain clonal variation.