Feedback inhibition of ecdysone production by 20‐hydroxyecdysone during pupal—adult metamorphosis of Mamestra configurata wlk

Abstract

AbstractLarge peaks of ecdysone (E, 2,875 ng/g live wt) and 20‐hydroxyecdysone (20‐HE, 2,150 ng/g live wt) occur on days 8 and 12, respectively, of postdiapause pupal‐adult metamorphosis at 20°C in the bertha armyworm, Mamestra configurata, and then decline to low levels (< 100 ng/g live wt) prior to eclosion of the moth (50% eclosion at day 31.8). These peaks of E and 20‐HE can be suppressed by treating the developing pupae with a physiological dose (2,500 ng/g live wt) of 20‐HE. Suppression of E and 20‐HE by 20‐HE treatment was dose dependent, rapid (within 24 h of treatment) and permanent. The peaks of E and 20‐HE were suppressed by 20‐HE treatment on days 1, 3, 5, and 7 but the 20‐HE peak was not suppressed by treatment on days 9 or 11.It is proposed that the mechanism by which 20‐HE suppresses the production of E and thereby its own production forms a negative feedback loop that operates during the first 0.4 units of pupal‐adult development in M. configurata. The function of the transitory peaks of E and 20‐HE that form this feedback loop is currently unknown. Since most adults from pupae that had their ecdysteroid levels experimentally suppressed by 20‐HE treatment were morphologically normal, it seems that the peaks of E and 20‐HE have little or no function in controlling morphological development in pupae of M. configurata.