DISTRIBUTION AND SIGNIFICANCE OF ECDYSTEROIDS IN THE FEMALE AND MALE MILKWEED BUG, ONCOPELTUS-FASCIATUS

The ecdysteroid content of whole body extracts of newly hatched females is relatively high but drops sharply to low levels on day 2 and 3 after ecdysis. Then it rises again and stays more or less constant. The rise is correlated with the onset of egg maturation, and the majority of the ecdysteroids are located in the ovary. Ecdysteroid titres of the haemolymph do not reflect the fluctuations of whole body extracts and are always relatively low. Ovariectomized females exhibit a permanently low content in whole body extracts after day 4. There is experimental evidence that this low content is sustained by an ecdysteroid source outside the ovary (and the prothoracic glands which degenerate during the adult moult). The synthesis of vitellogenins is not impaired by ovariectomy and therefore not regulated by ovarian ecdysteroids. Virgin females retain mature eggs in the genital ducts; the ecdysteroid content of such females is correspondingly higher. The present and previous findings indicate that the ovarian ecdysteroids are mostly, if not exclusively, produced in the ovary and that little ecdysteroids, if any, leak from the ovary into the haemolymph. Whereas the ovarian ecdysteroids are incorporated into the egg where they might serve a function, the significance of the low levels of extraovarian ecdysteroids remains unknown. Repeated injection of makisterone A causes a decrease in female fertility, correlated with a dose-dependent suppression of the vitellogenins in the haemolymph. RP-HPLC/RIA analysis and metabolism of labelled exogenous ecdysone suggest that the ovarian ecdysteroids consist of a variety of metabolites especially of high polarity, including conjugates as well as makisterone A. Different female body compartments reveal different metabolite patterns. The ecdysteroid content of whole body extracts of males is comparable to that of females until day 3. Thereafter, it remains almost constantly low in males. The haemolymph titre is also low. Repeated treatment of males with makisterone A and the ecdysone agonist RH 5849 does not induce vitellogenin synthesis as previously reported. The role of ecdysteroids in male and female reproduction is discussed.