Hormonal Control of the Phase Polyphenism of the Desert Locust: A Review of Current Understanding

Locusts show density-dependent continuous phase polyphenism; they appear in two forms or phases, gregari- ous and solitary, and there is a continuous range of intermediates between the extreme phases. The endocrine control of phase polyphenism has been the most intensively studied in desert locusts, Schistocerca gregaria, Indeed, results of inves- tigations over the past 15 years, provide some of the most detailed information on the endocrine mechanisms that poten- tially regulate desert locust phase polyphenism. In addition, recent studies on the juvenile hormone titres, ecdysteroid ti- tres, the discovery of (His 7 )-corazonin as dark-colour-inducing neuropeptide (DCIN) and the involvement of serotonin pulse in the metathoracic ganglion that triggers behavioural gregarization in the desert locust have yielded not only a good progress in our understanding the endocrine control of phase polyphenism but also unexpected results which indicate that the endocrine control of desert locust phase polyphenism is more complex than envisioned by the classical model. This review gives an overview of the progress made to date in elucidating the hormonal control of the desert locust phase polyphenism. Moreover, this review will summarize these findings and present some questions that still need to be an- swered.