Abstract
This chapter discusses the hormones of insect. The development of insects is accomplished through several larval stages, which are separated from one another by ecdyses. In holometabolic insects a special pupa stage is introduced between the larva and the imago. Three different hormones take part in the control of the ecdyses: (1) the brain hormone, produced by the neurosecretory cells of the pars intercerebralis, which acts on the prothoracic glands; (2) the hormone of the prothoracic glands, ecdysone, which starts the ecdysis; and (3) the juvenile hormone of the corpora allata. The normal larval ecdysis is started by the brain hormone that stimulates the prothoracic glands. These produce the molting hormone, ecdysone; simultaneously the juvenile hormone is secreted by the corpora allata and this determines the larval character of the ecdysis. Ecdysone was the first insect hormone to be obtained in pure crystalline form. It has the action of the molting and metamorphosis hormone and has also been called growth and differentiation hormone. The implantation of a small quantity of this extract into pupae causes the development of the pupa into an imago.
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