Ecological as well as physiological factors may determine host-plant selection by phytophagous insects. Experimentally separating these factors can be difficult with specialist herbivores that gain ecological and physiological benefits from a single host. In this study, we use the individually polyphagous caterpillar Grammia geneura (Lepidoptera: Arctiidae) to separate performance and defensive benefits from different host-plant species. Previous work shows that certain single host-plant diets (e.g. Malva parviflora) enhanced performance and that other single host-plant diets (e.g. Ambrosia confertiflora) enhanced resistance against parasitoids. Here, we specifically hypothesized that this caterpillar's natural habit of feeding on a mixture of toxic plant species provides resistance against parasitoids. We collected late instar caterpillars from the field, and assuming some proportion was already parasitized, randomly assigned them among two diet treatments for the duration of development in the laboratory. Caterpillars reared on Malva suffered 46% mortality from parasitoids, while those reared on a mixture of Malva, Ambrosia, and Senecio longilobus suffered only 26% mortality from parasitoids. More importantly, the probability of mortality from parasitoids was negatively associated with the proportion of toxic plants (Ambrosia and Senecio) in the diet of individual caterpillars.
Species 1: Lepidoptera Arctiidae Grammia geneura
Keywords: tritrophic interactions
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