Juvenile hormone counteracts the action of ecdysterone on silk glands of Galleria mellonella L. (Lepidoptera : Pyralidae)

Abstract Morphological and physiological evidence is presented to show that ecdysterone (20E) and juvenile hormone (JH) directly affect the silk glands of Galleria mellonella (Lepidoptera : Pyralidae). Within 1 hr in a culture medium, 20E at 5 or 50 ng/ml stimulates, and at 5 μg/ml inhibits, RNA synthesis. Both these effects are obliterated with physiological (1 ng/ml) and higher doses of JH II or a juvenoid. Dipping of isolated larval abdomens in 0.32% 20E suppresses the rate of RNA synthesis in freshly dissected silk glands incubated in a hormone-free medium. The ultrastructure of silk glands shows functional regression, followed by histolysis within 72 hr after dipping. Both the reduction of RNA synthesis and the cytological changes are prevented when the abdomens receive JH II or a juvenoid simultaneously with 20E. Presence of JH II in the culture medium also enhances RNA synthesis in silk glands dissected from abdomens that had been treated with 20E. The results reveal that the effect of 20E is dose-dependent and may be prevented, and up to a certain point reversed, with JH.