Studies on the Eclosion Behaviour of the Silkworm, Bombyx mori (Lepidoptera: Bombycidae)

V. Sensitivity to Eclosion Hormone in the Pharate-Adults of the Silkworm

Abstract

Development of sensitivity to the eclosion hormone in the pharate-adults of the silkworm, Bombyx mori, was investigated. Changes in the sensitivity to the exogenous eclosion hormone were observed during the last day of the pharate-adult development: early adult eclosion induced by the injection of the exogenous eclosion hormone was observed in the pharate-adults which had developed about 14 to 12hr before the expected eclosion time. However, the administration of the eclosion hormone to the pharate-adults 22 to 17hr before the eclosion time failed to induce early adult eclosion. The relationship between the time of injection of 20-hydroxyecdysone (Ecd) and the sensitivity to the eclosion hormone was also examined. When Ecd was injected into the pharate-adults 23 to 18hr before the expected eclosion time, adult ecdysis was delayed by 1 to 2 days in a dose-dependent manner. However, the ability of the Ecd treatment to delay adult ecdysis was no longer observed at about 16 to 14hr before the eclosion time. The sensitivity to the exogenous eclosion hormone in the pharate-adults subjected to the treatment of Ecd was apparently decreased, when Ecd was injected to the pharate-adults 20hr before the presumed eclosion time. It is suggested that ecdysteroids regulate the rate of development of the pharate-adults of the silkworm, Bombyx mori.