Hormonal Control
Insect growth and metamorphosis are controlled by hormones synthesized by endocrine glands near the front of the body.
Neurosecretory cells in an insect's brain secrete a hormone, the prothoracicotropic hormone (PTTH) that activates prothoracic glands, which secrete a second hormone, usually Ecdysone (a ecdysteroid), that induces ecdysis.
PTTH also stimulates the corpora allata, a retrocerebral organ, to produce juvenile hormone (JH), which prevents the development of adult characteristics during ecdysis. In holometabolous insects, molts between larval instars have a high level of JH, the moult to the pupal stage has a low level of JH, and the final, or imaginal, molt has no JH present at all.
Read more about this topic: Metamorphosing, Insect Metamorphosis
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