Meeting Abstract
Both mean and fluctuating temperatures can affect the growth, development and survival of ectotherms. These effects have been documented in many insects, including the tobacco hornworm (Manduca sexta), but how fluctuating temperatures alter host-parasitoid interactions is largely unexplored. Larvae of M. sexta are commonly used as hosts by the endoparasitoid wasp, Cotesia congregata; parasitized caterpillars inevitably die after wasp emergence. To investigate the thermal biology of this host/parasitoid system, we reared unparasitized (control) and parasitized M. sexta caterpillars at 3 average temperatures (25, 28 and 30°C) with 2 diurnally fluctuating temperature treatments (±0°C (constant) or ±10°C). Parasitoid survival was high at the lowest average temperature, and the effect of fluctuations was minimal. Wasp survival declined significantly as temperature increased, and mortality was exacerbated by diurnal fluctuations. The combination of the highest mean temperature and large fluctuations greatly reduced wasp survival, with no wasp emergence for most caterpillars. Despite complete wasp mortality, all parasitized caterpillars failed to successfully wander or pupate, and many grew to abnormally large sizes. Our results indicate that C. congregata are unable to successfully complete development at high average temperatures with large diurnal fluctuations. Since parasitism, successful or not, disrupts the normal development of M. sexta, parasitoid failure does not rescue the caterpillar from its inevitable death.
