Determinants of parasitoid-host associations: Insights from a natural tachinid-lepidopteran community

A major goal of insect community ecology is to understand how and why herbivorous insect species vary in the diversity of their parasitoid assemblages and the rates of parasitism that they experience. Most studies investigating these issues with Lepidoptera as hosts have relied on literature records of parasitoid-host associations that are. often of limited quality and that do not necessarily reflect local interactions between hosts and parasitoids. We sampled externally feeding Lepidoptera in mesquite-oak savanna habitats of southeastern Arizona (USA) to assess the ecological and evolutionary determinants of parasitoid community structure. We focused on parasitoids in the family Tachinidae (Diptera) due to their dominance as larval parasitoids of macrolepidoptera at our site. Host abundance, morphology, coloration, gregariousness, and diet breadth of the host were all significantly correlated with tachinid species richness among hosts. Tachinid species richness also varied according to host taxonomy (family), but most of this variation appeared to be better explained by morphology and ecology than by phylogenetic position. Characteristics of host habitat and body size had no significant effect on tachinid species richness. Tachinid parasitism rates were higher for abundant, hairy, non-aposematic, and gregarious hosts. Hymenopteran parasitism rates were low and Variable with, only host family explaining a significant amount of variation. In general, we found that a substantial amount of the variation in tachinid species richness and parasitism rates among hosts can be,explained by ecological attributes, and that interactions of host species with their host plants and predators may determine their suitability as hosts for parasitoids.