How Changes in Diet Can Enable Caterpillars to Overcome Parasite Infection

Wesleyan University, Middletown CT

Investigators

Abstract

Michael S. Singer, Proposal IOS-0744676 How changes in diet can enable caterpillars to overcome parasite infection Changes in feeding behavior can enable individual animals to cure themselves of parasite infections or other physiological distress. All animals have immunological defenses that can potentially change in strength based on an individual's diet. In addition, herbivores such as caterpillars may kill their parasites by ingesting and accumulating toxic chemicals found in the plants they eat. This research project will investigate these two means of anti-parasite behavior by the woolly bear caterpillar Grammia geneura. This species is suspected from previous study to ward off natural parasites through its feeding choices. First, behavioral experiments will characterize the dietary choices of experimentally parasitized caterpillars in relation to unparasitized caterpillars. Second, to evaluate the role of specific diets in resistance against parasites, the survival of parasitized and unparasitized caterpillars on different diets will be tested. Third, physiological experiments will evaluate the effects of these diets on the caterpillar's immune response to parasites. Finally, to analyze direct effects of caterpillar diet without the immune system, the parasites will be raised on artificial diets that reflect different caterpillar diets. Caterpillars newly infected by the potentially lethal, parasitic fly Exorista mella, are expected to choose a nutritious diet to enhance their immunological resistance. This mechanism is expected to carry minimal physiological costs for the caterpillar. However, caterpillars threatened by late-stage parasitic infections are expected to choose a diet rich in natural plant toxins called pyrrolizidine alkaloids. Ingesting unusually large quantities of alkaloids is expected to be physiologically costly for the caterpillar, and thus used as a last resort. The broader impacts of this research include training diverse students and a post-doctoral fellow in linking behavior, physiology, and ecology to animal health. Through public presentations, this project will also educate the public about the scientific link between animal health, behavior, and the environment.