INACTIVE PROTHORACIC GLANDS IN LARVAE AND PUPAE OF AEDES-AEGYPTI - ECDYSTEROID RELEASE BY TISSUES IN THE THORAX AND ABDOMEN

We report that the tissue identified as the prothoracic gland in fourth instar Aedes aegypti does not release ecdysteroids. The thorax, without the prothoracic gland, released the same amount of ecdysteroids in vitro as the intact thorax. Ecdysteroids were also released in vitro from the abdomen. Thoracic and abdominal ecdysteroid release was observed in the pupa and in all larval instars. During the fourth instar, a single increase and decrease in the rate of ecdysteroid release was observed from both the thorax and the abdomen. The thoracic and abdominal tissues of both sexes release ecdysteroids synchronously and in equal amounts. Hemolymph ecdysteroid titers are correlated with thoracic and abdominal release of ecdysteroids in vitro. Ecdysteroids are released from all abdominal segments, and the same amounts of ecdysteroids are released from the dorsal and ventral halves of the abdomen. More free ecdysteroids are released in vitro from thoracic and abdominal tissues than are present in the tissues themselves. Additionally, incubation of tissue homogenates with enzymes that hydrolyze ecdysteroid conjugates fails to increase ecdysteroid recovery, suggesting that as yet unidentified cells in both the thorax and abdomen synthesize ecdysteroids de novo.