Ecdysone 20-monooxygenase activity during larval-pupal-adult development of the tobacco hornworm,Manduca sexta

Abstract

Ecdysone 20-monooxygenase is the insect cytochrome P-450 dependent steroid hydroxylase system responsible for the conversion of ecdysone to 20-hydroxyecdysone. Using an in vitro radioassay, the levels of ecdysone 20-monooxygenase activity were quantified during embryogenesis in the egg, and in the fat body and midgut tissues during the fourth larval, fifth larval, and pupal-pharate adult stadia of the tobacco hornworm Manduca sexta. Although basal, ecdysone 20-monooxygenase activity was detected during the latter stages of larval embryogenesis. Postembryologically, a single major peak or increase was detected in both fat body and midgut tissues during each stadium. In the fourth larval instar, both fat body and midgut ecdysone 20-monooxygenase activities were found to peak in the latter half of the stadium at the time of spiracle apolysis; both activities dropped to basal levels by the time of ecdysis. During the fifth larval stadium, fat body steroid hydroxylase activity was found to rise during the feeding stage (days 1–4), then dropped back to basal levels by the onset of pharate pupal development on day 7 of the stadium. Midgut monoooxygenase activity during the fifth larval stadium, however, remained basal during the feeding stage, then rose dramatically to peak on day 5 with the onset of wandering, then dropped back to basal levels by the onset of pharate pupal development. Both fat body and midgut hydroxylase activities were basal during the pupal stage and only rose late in pharate-adult development, just prior to adult eclosion. Arch. Insect Biochem. Physiol. 41:24–32, 1999. © 1999 Wiley-Liss, Inc.