The Role of Parthenogenesis and Female Aptery in Microgeographic, Ecological Adaptation in the Fall Cankerworm, Alsophila Pometaria Harris (Lepidoptera: Geometridae)

The larval stage of the fall cankerworm, Alsophila pometaria Harris, feeds on several species of deciduous trees in North America. The ecology of the fall cankerworm parallels the ecology of the winter moth, Operophtera brumata: (1) hatching too long before host tree foliation results in hatchling dispersal and mortality and (2) late hatch results in low fecundity due to deteriorated nutritional quality of the leaves. Certain adaptations by a few moth species have increased synchrony between hatch and foliation in the face of spatial variation in the latter. First, female flightlessness has reduced the effect of intrastand variation in time of foliation. Second, at least in the fall cankerworm, parthenogenetic clones in a gynogenetic system specialize on different tree species as hosts. Since the clones differ in hatching time in the appropriate way, they match interstand differences in time of foliation. Clones specializing on an early foliating tree species eclosed earlier to lay eggs than did clones on a later foliating species. It is hypothesized that increases in the population density of the fall cankerworm should tend to occur during series of years with similar spring phenologies. Under these conditions the frequency of asexuals should increase relative to the sexuals.