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21 Neuroendocrinology of Eclosion

John Ewer


The rigid exoskeleton of an insect poses special problems for growth which are solved by a stepwise process in which multiple, progressively larger stages are separated by molting and replacement of the old exoskeleton by a new and larger one. During eclosion, or adult emergence, the insect sheds the remains of the old exoskeleton from the previous immature stage and starts its adult life. The most flamboyant example of this occurs in holometabolous insects, where it marks the end of metamorphosis and leads to emergence of the newly formed adult from the pupal case or chrysalis, followed by the expansion of the wings and the hardening and pigmentation of the body. Eclosion is the culmination of the final molt and is caused by the reactivation, with a few stage-specific modifications, of the behaviors and physiological events collectively known as ecdysis that are used at the end of every one of the insect’s molts to shed the remains of the exoskeleton from the previous stage.

Ecdysis has been investigated in a number of insect species, but our understanding of its neural and endocrine bases stems mostly from work carried out in two holometabolous species: the moth, Manduca sexta, and the fruit fly, Drosophila melanogaster. In this chapter, I review our current understanding of the neuroendocrine control of ecdysis in general, adding, wherever possible, details that are specific to adult ecdysis (eclosion). This includes a discussion of how the time of ecdysis is restricted to the end of the molt, and how...

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