HORMONES AND THE TERMINATION AND REINDUCTION OF DIAPAUSE IN CEPHUS CINCTUS NORT. (HYMENOPTERA: CEPHIDAE)

Abstract

Ligation and parabiosis experiments and cytological studies showed postdiapause morphogenesis in Cephus cinctus larvae to be initiated by a growth and differentiation hormone from the prothoracic glands. The prothoracic glands in turn are probably stimulated by a hormone from the protocerebral neurosecretory cells. The brain continues to influence the prothoracic glands even after they have begun to secrete and the influence is more than that of a simple stimulation by the neurohormone. Furthermore, experiments with larvae reared apart from their cocoons suggested that the brain is to some extent influenced by environmental stimuli. If an effective amount of growth and differentiation hormone has not yet been secreted, exposure of a week or less at 35 °C. causes postdiapause C. cinctus larvae to revert to diapause. Forty degrees has a much weaker effect. Cytological examination suggested that 35 °C. halts prothoracic gland activity and, meanwhile, permits the neurohormone to be dissipated. At the end of the heat treatment there is insufficient neurohormone left to reactivate the prothoracic glands, which revert to dormancy.