title: Can caterpillar density or host-plant quality explain host-plant-related parasitism of a generalist forest caterpillar assemblage?
abstract: Herbivore-carnivore interactions are influenced by the plants on which herbivores feed. Accordingly, dietary generalist herbivores have been shown to experience differential risk of mortality from carnivores on different host-plant species. Here, we investigate whether caterpillar density and host-plant quality play a role in driving variation in generalist forest caterpillar mortality from insect parasitoids using a large-scale, multi-year observational study. A total of 4,500 polyphagous caterpillars were collected from eight host-tree species in Connecticut deciduous forests over 5 years, and frequencies of mortality from insect parasitoids (flies and wasps) were compared across the eight host-plant species for the entire generalist caterpillar assemblage (76 species). Separate comparisons were made using seven numerically dominant generalist species, allowing us to account for variation in caterpillar species-specific parasitism risk. We find significant variation in parasitism frequencies of generalist caterpillars across the eight host-plant species when accounting for variation in caterpillar density. We find no support for an influence of caterpillar density on parasitism and no clear evidence for an effect of host-plant quality on parasitism. Therefore, the results of this study discount the hypotheses that variation in caterpillar density and host-plant quality are responsible for variation in parasitism frequencies across host-plant species. Instead, our findings point to other plant-related characteristics, such as plant-derived parasitoid attractants, which may have robust, community-wide effects.
authors.affiliation: Department of Biology, Wesleyan University, Middletown, CT, 06459, USA.
authors.forename: Timothy E
authors.initials: TE
authors.lastname: Farkas
authors.forename: Michael S
authors.initials: MS
authors.lastname: Singer
mesh_terms: D000220:Adaptation, Biological / Q000502:physiology*; D000818:Animals; D058448:Biota; D003237:Connecticut; D006790:Host-Parasite Interactions; D007814:Larva / Q000502:physiology; D007915:Lepidoptera / Q000502:physiology*; D016014:Linear Models; D011156:Population Density; D013045:Species Specificity; D014197:Trees / Q000469:parasitology*