STUDIES OF THE PROTHORACICOTROPIC HORMONE IN THE TOBACCO HORNWORM,MANDUCA SEXTA

Abstract

Brain removal at appropriate times in the [M. sexta] life cycle uniformly delayed or prevented the onset of all known ecdysone-mediated transitions. This effect was pronounced at larval-larval molts and at the pupal-adult transformation. Loose brains reduced but did not eliminate the delay induced by brain removal. Isolated larval abdomens never developed nor were they induced to do so by implantation of an active brain. Loose pupal brains retained their original commitment to diapause or not to diapause. This was true even when the loose brain was implanted into a brainless host pupa with an opposite diapause commitment. Larval brains effectively elicited the development of pupae, and conversely, pupal brains elicited the development of larvae. Prothoracicotropic activity occurred in the brain but in no other ganglia. Extracts of Bombyx mori PTTH were inactive in Manduca in the concentrations tested. Several mechanisms which might mediate the development of brainless hornworms are considered.