The molting hormone activity in Sarcophaga buttata in relation to metamorphosis and reproduction

Ecdysteroid levels were determined by radioimmunoassay, using an antiserum with higher affinity for ecdysterone than for ecdysone. In both sexes, the ecdysteroid level remains low until day 3 after eclosion. When fed liver on day 3, the ecdysteroid titre declines within 4 h in both sexes, stays low in males, but increases again after 12 h in females. The content in non-liver-fed animals, specially females, was significantly higher than if given liver. The level in liver-fed whole animals increased during oogenesis from the onset of follicular growth until the 4B—4C stage, and decreased thereafter.

During embryogenesis, a new high level was found in females, due to the developing embryos which contained a high titre. In isolated ovaries, the ecdysteroid content increased during follicular growth, with a steep increase during the last phase (4C—M and from M to uterine eggs). The ecdysteroid content in hemolymph of 7-day-old females, fed liver or not, was around 10 ng/ml, but in hemolymph of males of the same age no activity was found.

Ovariectomized females contained 12.4 ng/g ecdysteroid. The level during metamorphosis was also determined, mainly to be able to compare our radioimmunoassay results with known bioassay data. Our results support the statement that the ovary cannot be the only site of synthesis of molting hormone in adult S. buttata.