INSECT HORMONES IN DEVELOPMENT

Advances in studies of prothoracicotropic hormone (ecdysiotropin), ecdysteroids and juvenile hormones in the past decade are considered:
1. Until recently there has been little progress with prothoracicotropic hormone. The development of a sensitive bioassay for the hormone promises to produce rapid advances.
2. Current methods of hormone analysis are described, with detection limits. The application of these methods in studies of hormones at different stages and in different tissues of insects have revealed a far greater complexity in hormone titres than was predicted from classical studies.
3. Very few studies employ chemical characterization of hormones and some assays do not distinguish biologically inactive metabolites of the hormones from the active hormones. Many studies have thus failed to reveal the numerous rapid fluctuations in hormone titre necessary for insect development.
4. While ecdysteroids act, via a receptor, on specific chromosome sites, the cellular mode of action of juvenile hormone in larval development is still unknown. Recent evidence suggests that juvenile hormone acts prior to the time at which its effects are realized by ecdysteroids.
5. Insect hormones produce dramatic changes in gene activity and their co-ordinate control of specific protein synthesis has been the basis for a number of 'model systems' of gene control in higher eukaryotes.