C. turionellae was studied with light radiation of about 100,000 Lx. Without bright light the ichneumonids start for flights at temperatures between 18 degree C and 30 degree C. Specimens younger than 7 days need higher temperatures than older ones. The radiation induces the warming of the thorax to more than 35 degree C. Higher temperatures are prevented by ventilation. With light C. turionellae starts at lower temperatures from 18 degree C to about 21 degree C in a small temperature range. So the flight activity of females and males is better synchronized. Those specimens which need high air temperatures for flight can use the radiation to warm up their body, and fly at lower temperatures. Others are able to fly at low air temperatures without radiation. There is a continuous change from one type of activity to the other. none