Endocrine Control of Insect Polyphenism

This chapter discusses the endocrine control of insect polyphenism. Polyphenism in insects is associated with some of the most striking and successful life histories. The terms polymorphism and polyphenism have the same meaning, namely intraspecific variation in sets of characters. This phenomenon is seen as an adaptive response that allows genotypes to track short-term cycles of environmental variation and, at the same time, maintains cohesiveness of adapted gene complexes. With recent advances in population genetics, enzymology, genomics, and proteomics, the term polymorphism has now gained a much wider meaning. Polyphenic mechanisms can be described at two levels: cues that serve as proximate triggers of developmental alternatives and endogenous response cascades that drive the developmental responses. Triggering stimuli may consist of external environmental factors, internal genetic factors, or a mixture of the two. Endogenous response cascades involve a series of systems that relay, synchronize, and coordinate differentiated processes in target systems.