Vertebrate insulin induces diapause termination in Pieris brassicae pupae.

Due to its close structural homology with the 4K prothoracicotropic hormone isolated from Bombyx mori, we tested the ability of vertebrate insulin to break pupal diapause in a Lepidopteran, Pieris brassicae. Injection of 5μg of bovine insulin in diapausing pupae led to diapause termination and synchronous adult eclosion; the effect of insulin was dose-dependent. Bovine insulin-A chain and B chain injected separately failed to show any biological activity suggesting that the intact structure of the molecule is required. Bovine insulin also promoted adult development of decapitated diapausing animals. We show that insulin triggers a reactivation of the neuroendocrine system leading to a neosynthesis of ecdysone beginning 6 days after treatment. This neosynthesis also occurred in beheaded animals suggesting that insulin stimulates the prothoracic glands without acting via the brain.