INDUCTION OF AN INACTIVATION PATHWAY FOR ECDYSTEROIDS IN LARVAE OF THE COTTON LEAFWORM, SPODOPTERA-LITTORALIS

Treatment of the last-instar larvae of the cotton leafworm (Spodoptera littoralis) with ecdysteroids (moulting hormones) results in the indu ction of an ecdysteroid-inactivation pathway. Administration of ecdyso ne, 20-hydroxyecdysone or an ecdysteroid agonist, RH 5849, leads to in duction of an ecdysteroid 26-hydroxylase activity. This induction occu rred in both early sixth-instar larvae and in older larvae which had b een head-ligated to prevent the normal developmental increase in ecdys one 20-mono-oxygenase activity. The induction of 26-hydroxylase activi ty requires both RNA and protein synthesis, as demonstrated by experim ents involving actinomycin D and cycloheximide. The 26-aldehyde deriva tive of ecdysone and ecdyson-26-oic acid were also formed from ecdyson e in the RH 5849-induced systems. Formation of the aldehyde and the co rresponding 26-oic acid (ecdysonoic acid) from 26-hydroxyecdysone was directly demonstrated in a cell-free system, thus establishing the fol lowing inactivation pathway: Ecdysteroid --> 26-hydroxyecdysteroid --> ecdysteroid 26-aldehyde --> ecdysteroid 26-oic acid