D3342: Behavioral changes in caterpillars of the hawkmoth Manduca sexta induced by the parasitoid wasp Cotesia congregata

Manduca sexta (Sphingidae) is parasitized by the braconid wasp Cotesia congregata. The wasp kills its host but needs the caterpillar to feed and grow while its larvae are feeding in it. Overparasitism of the caterpillar is fatal to both parasites and host. This study examined whether the wasp manipulates the behavior of its caterpillar host to act as a bodyguard. We hypothesized that caterpillars’ defensive strike responses would be amplified in parasitized caterpillars to prevent overparasitism. Using calibrated von Frey filaments, we found that parasitized caterpillars had significantly lower strike and touch response thresholds than unparasitized caterpillars. We then asked whether parasitized caterpillars were better at warding off parasitic wasp attacks than unparasitized caterpillars. We found that when parasitized caterpillars were exposed to additional wasps one, two, and three days after the initial parasitism, the time to parasitism and the number of defensive strikes were significantly greater, making them more effective at repelling wasp attacks than naïve caterpillars. We then examined whether an unparasitized caterpillar with a lower strike threshold would be better at warding off parasitism than a less sensitive individual. This was assessed by testing the strike threshold of a caterpillar, then placing it with a female wasp and recording time to parasitism and number of defensive strikes by the caterpillar. We found that there was a significant impact on the number of strikes but not time to parasitism. Taken together, our evidence indicates that the wasp does indeed turn its host into a bodyguard.