Question

Regulation of endocrine regulation of moulting and metamorphosis

Answer 1

The endocrine regulation of insect postembryonic development is generally thought to involve three hormones: the prothoracicotropic hormone (PTTH), a cerebral neuropeptide; the steroid hormone 20-hydroxyecdysone; and juvenile hormone, an aliphatic sequiterpene [1]. PTTH is produced by one neurosecretory cell in each hemisphere of the insect brain [2], while 20-hydroxyecdysone is derived from the ecdysone produced by the prothoracic glands (PG) in response to PTTH [3,4]. Juvenile hormone exists in four homologous forms (JH 0, I, II, and III) and is produced by corpora allata (CA) [5]. Although the integration of release of the hormones is critica for their roles in the regulation of insect molting and metamorphosis, the pivot of this regulatory mechanism is the periodic release of PTTH in response to environmental cues. Ecdysone is synthesized and released by the PG in response to PTTH and is then hydroxylated by peripheral tissues to 20-hydroxyecdysone, the hormone that elicits molting. JH acts in conjunction with 20-hydroxyecdysone, presumably at the level of the target tissues to determine the character of the molt