Induction of dauer larvae by a juvenile hormone analogue and their response to ecdysteroids in the silkworm, Bombyx mori

Abstract

A juvenile hormone analogue (JHA), methoprene, applied to the penultimate instar larvae of the silkworm, Bombyx mori did not affect significantly larval ecdysis to the last instar but caused the last larvae to become dauer larvae which lived for more than 3 weeks. The incidence of dauer larvae was strongly affected by the rearing conditions after JHA treatments. Although no sensitive period was detected throughout the penultimate instar, a dose of more than 10μg JHA per larva was required for the full activity. The natural juvenile hormones, JH-I and JH-III, similarly prolonged the last instar periods but did not prevent larval-pupal transformation. The larvae treated with JHA continued to eat food and gained mass weights of 10g or more, their size being twice as large as that of the non-treated control larvae. The allatectomized larvae also became dauer larvae by JHA application, indicating that the JHA action is not mediated through the modification of the corpus allatum activity. Dauer larvae were characterized by decreased levels of ecdysteroids in the hemolymph. Oral administration of exogenous 20-hydroxyecdysone into dauer larvae resulted in the dorsal vessel exposure and cocoon spinning but the larvae could not complete their metamorphosis to pupae in this experiment.