Penetration of phytoecdysones through the pupal cuticle of the silkworm, Bombyx mori

Abstract

The penetrability of some phytoecdysones, ecdysterone, inokosterone, ponasterone A, and cyasterone, through silkworm pupal cuticle was tested and their effect on pupal-adult development is described. The first three chemicals applied topically to fresh pupae accelerated the pupal-adult development and induced abnormal adults with aberrant legs and antennae, indicating penetration of phytoecdysones through fresh pupal cuticle. Females were more sensitive to the chemicals than males as they showed many more abnormalities. When pupae 1 day after ecdysis were treated topically with phytoecdysones, they transformed into normal adults, suggesting no penetration of ecdysones through old pupal cuticle. By using isolated pupal abdomens in dipping experiments, phytoecdysone dissolved in 50% ethanol penetrated pupal abdomens up to 36 hr old, by dipping for 30 sec the isolated abdomens transformed into adult form. When the dipping duration was prolonged, it was effective on much older pupal abdomens. Ecdysterone dissolved in water, however, was almost ineffective even when applied to fresh pupal abdomens, though it was effective when it contained less than 5% makisterone A.