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Examples of Connecticut forest caterpillars that have been attacked by parasitoids: Orthosia rubescens (Noctuidae) with parasitic wasp larvae and tachinid fly eggs. (left); Himella intractata (Noctuidae) with the cocoon of a parasitic wasp (middle); Phigalia titea (Geometridae) with tachind fly eggs. On average, about 25% of these forest caterpillars die from parasitoids, but this mortality risk often depends on the host plant species. Photos by Michael S. Singer.
Tri-trophic interactions can cause trade-offs for insect herbivores in the fitness costs and benefits of using different host-plant species. Ecological trade-offs are theorized to play a central role in structuring ecological communities generally, particularly for species that share resources such as host plants. We hypothesize that patterns of herbivore-plant associations and possibly herbivore-herbivore associations arise from trade-offs between factors known to be consequential to herbivore fitness, such as food quality of host plants and refuge or defense from carnivores conferred by host plants. My lab is investigating this and related trade-off hypotheses in central Connecticut forests, focusing on polyphagous caterpillars, their host trees, and parasitoids. The data gathered for this project (begun in 2004) have proven useful for addressing a variety of ecological issues, including collaborative studies of geographic patterns in caterpillar parasitism (Stireman et al. 2005) and host specificity (Dyer et al., in review) in temperate and tropical forests.