Influence of development and prothoracicotropic hormone on the ecdysteroids produced in vitro by the prothoracic glands of female gypsy moth (Lymantria dispar) pupae and pharate adults

Fluctuations in hemolymph ecdysteroid titer are part of a complex mechanism that regulates pupal-adult development. The amount of ecdysteroid produced in vitro by prothoracic glands from female Lymantria dispar (L.) (Lepidoptera: Lymantriidae) pupae and pharate adults, as well as the competency of these glands to respond to a prothoracicotropic hormone (PTTH) stimulus in vitro, each correspond temporally with hemolymph ecdysteroid titers. Based on studies of gland kinetics and dose-responses to brain extract using prothoracic glands from different female pupal and pharate adult ages, an in vitro bioassay for the quantification of PTTH activity was developed using glands from day 2 females incubated without stimulus for 1 h followed by a 3 h incubation with stimulus. Only extracts of brains and corpora allata from pupae and pharate adults possess a PTTH factor. This factor is heat stable and can be separated on high performance size exclusion chromatography into two molecular sizes of 13.75 and 3.2 kDa. Ecdysone and 3-dehydroecdysone are produced in vitro by prothoracic glands from all ages of female L. dispar pupae and pharate adults tested. The amount of ecdysone produced by these glands exceeds that of 3-dehydroecdysone production after 4 h of incubation.