Endocrine control of diapause termination in the adult female Colorado potato beetle, Leptinotarsa decemlineata

Abstract

To examine the possible involvement of endocrines in the termination of diapause in Leptinotarsa decemlineata, single doses of juvenile hormone III and 20-hydroxyecdysone were injected either alone or in combination, after various periods spent in diapause. 20-hydroxyecdysone alone failed to terminate diapause, whereas juvenile hormone III alone resulted in a temporary break of diapause. Only the combined injections of both hormones caused permanent temination of diapause. Hormonal administration seems most effective during the first month of diapause. Hormonal injections in this period failed, however, to induce reproduction. Exogenous juvenile hormone III inhibited the rate of juvenile hormone synthesis and induced high juvenile hormone esterase activity in haemolymph. In contrast, the endogenous juvenile hormone metabolism in diapause is not affected by 20-hydroxyecdysone when this hormone is injected alone or following an injection of juvenile hormone III. These effects were retained through diapause. The effects of juvenile hormone III on juvenile hormone metabolism were suppressed by an early injection of 20-hydroxyecdysone. The present results suggest that 20-hydroxyecdysone plays a key role in modifying the regulation of juvenile hormone metabolism in diapause. It is suggested that 20-hydroxyecdysone switches off the ‘diapause’ programming of the brain at the end of diapause.