Seasonal Phenology of Diapause in the Flesh Fly Sarcophaga bullata

Sarcophaga bullata Parker (Diptera: Sarcophagidae) emerges during mid-May in central Illinois. The incidence of pupal diapause is &2% in June and July, 20% in August, and 99% in September. The transition between nondiapause and diapause is in phase with the seasonal change in daylength; the transition occurs at 13–14 hours of daylight. Males comprise 79% of the pupae which enter diapause in August, 45% of those in September. September pupae are capable of terminating diapause immediately upon transfer to 25°C on January 1. Outside, the cold winter months suppress development; the 1st morphological signs of development appear in early April. Field and laboratory results are compared.