Large larvae of a flush-feeding moth (Epirrita autumnata, Lepidoptera : Geometridae) are not at a higher risk of parasitism: implications for the moth's life-history

The effect of larval body size of Epirrita autumnata (Lepidoptera, Geometri dae) on the risk of parasitism was studied in a field experiment. The exper iment involved three pair-wise exposures of different larval instars to par asitoids. Three hymenopteran species were responsible for most of the paras itism. Parasitism risk was found to be host-instar independent. This result was consistent across parasitoid species and experiments. The results sugg est that host use by larval parasitoids cannot constrain selection for larg er body size in E. autumnata. However, high mortality due to parasitism may select for a short developmental period (the slow-growth/high-mortality hy pothesis), and smaller body sizes as a by-product. A strong selective effec t of parasitism on the timing of larval development in E autumnata is also unlikely. The larger was the host, the larger was the adult size of the par asitoid and the shorter its development time (for one species). We suggest that the lack of a preference-performance linkage in the system studied may be related to the time stress associated with the short phenological windo w of host vulnerability.