The different effects of ecdysone and 20-hydroxyecdysone on the induction of larval ecdysis in the silkworm, Bombyx mori (Lepidoptera: Bombycidae)

The silkworm, Bombyx mori was reared on artificial diets supplemented with 20-hydroxyecdysone (20E) during the 4th instar and on diets supplemented with various concentrations of either 20E or ecdysone (E) in the 5th (last) instar. The larvae transferred to diet containing E molted to the 6th instar earlier than the control larvae and their mortality was within norm. On the other hand, most of the larvae that were transferred to the diet supplemented with 300 ppm 20E continued to feed until they died without apolysis. The amount of 20E in their hemolymph was higher than in the larvae fed 200 ppm E. Larvae transferred to a diet containing both E and 20E did enter apolysis and their ecdysteroid level was similar as in the non-molting larvae receiving 300 ppm 20E. These results suggest that ingested ecdysone might change the sensitivity of epidermis to 20E.