Meeting Abstract

S9.3-3  Tuesday, Jan. 7 14:30  Ecological Immunology of Woolly Bear Caterpillars SINGER, M.S.*; MASON, P.A.; SMILANICH, A.M.; Wesleyan University; U. Colorado, Boulder; U. Nevada, Reno msinger@wesleyan.edu

The emerging field of ecological immunology recognizes the role of an organism’s environment in its ability to defend itself against parasites. One important mechanism of ecological immunology is medication behavior, the acquisition of substances that resist or improve tolerance to disease. In the broad sense, medicinal substances can include nutrients as well as pharmacological agents. In this paper, we use adaptive plasticity theory to frame nutritional and non-nutritional aspects of medication behavior of the woolly bear caterpillar, Grammia incorrupta (Lepidoptera; Erebidae; Arctiinae). As grazing herbivores, individual caterpillars can consume many chemically diverse plant species. The most phagostimulatory plants contain pyrrolizidine alkaloids (PAs) and diets including such plants confer resistance against tachinid parasitoids at the cost of reduced nutritive value. As theory predicts, parasitism by tachinids causes caterpillars to exhibit therapeutic self-medication by increasing their ingestion PAs. PA-medication manifests approximately 48 hours after caterpillars become infected with tachinid parasitoids, whereas the caterpillars reduce total food intake during the first 48 hours following infection. Because protein intake is reduced more sharply than carbohydrate intake, we suggest this feeding change is adaptive with respect to immune function. Manipulation of dietary PAs and nutrients exerted no detectable effect on the caterpillar’s immunological melanization response. We conclude that PA-medication is a secondary line of defense contingent on habitat quality and the failure of immunological defenses; and immunological melanization may be robust to variation in dietary nutrients, thus enhancing immune function when reduced protein intake limits parasitoid growth.