Juvenile hormone and the physiological basis of insect polymorphisms.

Juvenile hormone is involved in the control of gene switching and exerts this control only during certain critical periods. As a rule one or more critical periods exist during each pre-reproductive instar. The presence or absence of JH during any given critical period somehow causes the insect to 'choose' between alternative developmental pathways. Using this model for the action of JH, the authors discuss the endocrine control of metamorphosis, phase determination in locusts and aphids, caste determination in social insects, and certain color polymorphisms. -from Authors