Ecdysone during ovarian development in Locusta migratoria

Considerable amounts of ecdysteroids are produced during each ovarian cycle in adult females of Locusta when vitellogenesis is almost completed. The hormonal molecules are synthesized at the end of the maturation of the terminal oöcytes during each cycle, at the time when vitellogenesis is almost completed. No synthesis takes place in the absence of ovarian development (allatectomy, ovariectomy), whereas extirpation of the prothoracic glands at the beginning of adult life does not affect ecdysteroid production. More than 95% of the total ecdysteroid content of female adults can be recovered from the ovaries. In vitro studies show that the ovaries produce ecdysteroids and convert labelled cholesterol into ecdysone. Microsurgical experiments indicate that this synthesis takes place in the follicle cells surrounding the oöcyte. The newly synthesized ecdysteroids do not enter massively into the blood, but pass into the oöplasm where they are progressively converted to polar compounds; as a result, at the end of each ovarian cycle, egg-laying corresponds to the disappearance of ecdysteroids from the female insects, the hormonal molecules can easily be recovered from the eggs. A gas chromatographic analysis coupled to mass spectrometry shows that the principal ecdysteroid synthesized by the adult females of Locusta is by far ecdysone. Ecdysterone, the paramount ecdysteroid of the larvae of Locusta, is not present in noticeable amounts in the female adult of this species.