Influence of Scelionids, Tachinids, and General Predation on the Survivorship of Fall Cankerworm (Alsophila pometaria) Throughout Its Life History

Outbreaks of fall cankerworm, Alsophila pometaria (Harris) (Lepidoptera: Geometridae), can be destructive and have lasting negative effects on forest health. A multi-year outbreak of fall cankerworm populations on Nantucket Island, Massachusetts, provided an ideal opportunity to study mortality factors across several life stages and their overall contributions to fall cankerworm densities. To achieve these goals, we conducted assessments of mortality from the egg stage through adult eclosion. We found that on average, 33.50% ± 0.04% of eggs failed to produce live caterpillars, and that on average 6.51% ± 2.21% of eggs were parasitized by Telenomus alsophilae Viereck (Hymenoptera: Scelionidae). Larval survivorship in lab conditions was high, with only 6.35% ± 0.48% of larvae failing to reach the pupal stage, while on average 5.02% ± 1.55% of larvae in the field were parasitized by Blondelia eufitchiae (Townsend) (Diptera: Tachinidae). Failure to eclose from the pupal stage was another large source of mortality in this system, with 25.94% ± 5.77% of pupae failing to produce adults. Of the pupae placed in the field for a predation study, 92.8% ± 2.7% of pupae experienced predation. In total, the rate of survivorship of the fall cankerworm population on Nantucket was calculated to be just under 3%, not including predation on the larval or adult stages, which were not included in this study. This low survivorship may explain why outbreaking populations of fall cankerworm quickly return to non-pest status in only a few years after onset.