Physiology of Insect Ecdysis

Abstract

1. In pharate Manduca sexta moths eclosion hormone activity was present in the brain and corpora cardiaca. Bursicon activity was confined to the abdominal nervous system, and was most concentrated in the abdominal perivisceral organs (PVOs). 2. When newly emerged moths were given access to suitable wing-spreading sites, bursicon activity was depleted from the PVOs and appeared in the blood within 15 min after eclosion. This hormone was responsible for the tanning and hardening of the wings. 3. Bursicon release could be delayed for at least 24 h by forcing the newly emerged moth to dig. Secretion then occurred swiftly upon giving the moth a suitable wing-spreading site. 4. The pupal cuticle was removed from pharate Manduca approximately 7 h before their normal eclosion gate, and the peeled moths were provided with a wing-spreading site. These moths did not then secrete bursicon until after their normal time of eclosion. 5. Injection of the eclosion hormone into pharate moths caused early eclosion followed by precocious bursicon secretion. 6. It was concluded that bursicon release is regulated by both neural and hormonal factors. The eclosion hormone triggers a program of neural output which includes the secretion of bursicon. This release, however, can be delayed by neural input which is associated with the digging behaviour of the moth.