What makes a fly enter diapause?

Diapause is a dormant state that insects may undergo as a response to changing environmental conditions. In flies, like many insects inhabiting temperate zones, diapause occurs generally during the winter months when ambient temperatures are cool and food sources scarce. Whilst the environmental factors involved in determining diapause have been known for a long time, the genes and molecular events controling its initiation are poorly understood. Here I outline the factors that initiate diapause and highlight recent studies that implicate insulin signaling in its control.