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Summary
The ecdysteroid composition of embryos of M. rosenbergii at various stages of embryogenesis has been studied by means of radioimmunoassay (RIA), high-performance liquid chromatography—RIA (HPLC-RIA) and gas chromatography/mass spectrometry (selected ion monitoring; GC/MS(SIM). In newly-laid eggs, only free ecdysteroids (ecdysone and 20-hydroxyecdysone) were detected, whereas eggs at an early stage of embryogenesis contained ecdysone and also low levels of apolar ecdysteroid conjugates. Mid stage embryonating eggs contained comparatively high levels of both free ecdysteroid (ecdysone, 18.3 ng/g) and apolar conjugates (29.9ng/g). Late embryos contained by far the highest overall level of ecdysteroid, indicating the ability of the developing embryo to synthesize ecdysteroid. In contrast to the other stages, late embryos contained 26-hydroxyecdysone, ecdysonoic acid and 20-hydroxyecdysonoic acid at relatively low levels and 2, 3-diacetylecdysone 22-phosphate at a comparatively high level (324.0 ng/g). These results suggest that the developing embryo of M. rosenbergii is capable of both ecdysteroid biosynthesis (presumably for utilization during specific stages of embryogenesis), conversion into apolar conjugates and inactivation by conversion into 26-oic acids and polar conjugates.