Die Auslösung der Umfärbung durch das Häutungshormon bei Cerura vinula L. (Lepidoptera, Notodontidae)

Abstract

The green larvae of Cerura vinula L. turn dark red when they are going to spin their cocoon. A red ommochrome pigment is formed in the epidermal cells and one day later in the fat body. The epidermal processes of the pupal moult begin only five days later. The colour change can be inhibited by a ligature. Only the part of the body anterior to the ligature will redden. Double ligaturing experiments show that the colour change is caused by a thoracic centre, which has to be activated by a cephalic centre, probably the brain. Extracts of the moulting hormone α-ecdyson were injected into green abdomens of ligatured animals. Small doses (66 Calliphora units) caused reddening of the epidermis. 330 Calliphora units caused reddening of the fat body only, and large doses (3300–6600 units) caused a pupal moult without colour change. It is concluded that both the colour change and the pupal moult are caused by the same hormone, ecdyson, but by different concentrations of it. The normal course of events is probably brought about by a slow increase of hormone concentration. In young larvae premature colour change could be evoked by decapitation. Probably it is normally prevented by the juvenile hormone of the corpora allata.