Stimulation of juvenile hormone biosynthesis by different ecdysteroids in Bombyx mori

Precisely controlled juvenile hormone (JH) biosynthesis by the corpora allata (CA) is critical for insect postembryonic development. In the present study, the effects of different ecdysteroids (20-hydroxyecdysone, ecdysone, 2-deoxy-20-hydroxy-ecdysone and 20-hydroxyecdysone-22-acetate) on both the induction of supernumerary larvae and CA activity in vitro were further clarified. We found that 20-hydroxyecdysone as well as ecdysone and 2-deoxy-20-hydroxy-ecdysone stimulated CA activity both in vivo and in vitro. However, 20-hydroxyecdysone-22-acetate had no effect on CA activity. The direct activation of in vitro JH biosynthesis by 20-hydroxyecdysone, ecdysone, and 2-deoxy-20-hydroxyecdysone indicates that different ecdysteroids may exert similar in situ effects in a coordinated manner for eliciting specific events during development. We propose that the activation of JH biosynthesis by elevated hemolymph ecdysteroid levels in larvae treated with different ecdysteroids may be directly responsible for the induction of supernumerary larval molting.