Sexual dimorphism in developmental rate and ecdysteroid titre in Orgyia postica

Abstract

Rates of metamorphosis in the hevea tussock moth, Orgyia postica during postembryonic development appear to be sexually dimorphic. Females, which undergo four moults during their larval periods, have one instar more than males; female development is therefore comparatively retarded. In contrast, female pupal development is accelerated when compared with that of males. Therefore, although male and female larvae pupate at different times, they complete their development in a coordinated fashion. Temporal and quantitative changes in haemolymph ecdysteroid levels between female and male animals during post-embryonic development were determined by radioimmunoassay; results revealed sex-specific ecdysteroid titre patterns. A qualitative analysis of the ecdysteroids for each major peak prior to ecdysis revealed sexual differences in ecdysteroid type. Therefore, it is suggested that quantitative and qualitative changes in haemolymph ecdysteroid titres during postembryonic development of O. postica may be responsible for the sexual dimorphism in developmental rates, as well as for their coordination. The biological significance of sex-specific ecdysteroid titre patterns during development is discussed.