Evidence for the Involvement of a Neuropeptide in the Control of Body Color in the Desert Locust, Schistocerca gregaria

The endocrine control of body color polymorphism in the African desert locust, Schistocerca gregaria FORSKAL, was studied by organ implantations and injections of organ extracts, with special reference to the induction of dark color. Implantation of corpora cardiaca taken from crowded nymphs induced darkening in the integument and the compound eyes of isolated green nymphs, and more black patterns appeared as the number of implanted corpora cardiaca increased. Likewise, the corpora cardiaca of the migratory locust, Locusta migratoria L. and the two-spotted cricket, Gryllus bimaculatus DEGEER, were found to contain some factor(s) inducing dark color in isolated green nymphs of S. gregaria. Such factors were all extractable with methanol and they induced black patterns in isolated green nymphs of S. gregaria when dried, mixed with olive oil and injected. Methanol extracts of brains and corpora cardiaca of S. gregaria were both effective in inducing dark color in albino nymphs of L. migratoria, though the higher dark-color inducing activity was obtained from the corpus cardiacum. These results indicate that the two locusts may share a common mechanism controlling the induction of dark color, although whether the factors involved in the two species are the same or not remains unknown. In S. gregaria, methanol extracts of corpora cardiaca dried, dissolved in water and boiled for 10 min retained the dark-color inducing activity after being dried, mixed with olive oil and injected into isolated green nymphs. On the other hand, those incubated with a proteinase at 37℃ for 40 min lost the activity completely. Therefore, this dark-color inducing factor of S. gregaria is probably a heat-stable neuropeptide.