A NEUROPEPTIDE CONTROLLING THE DARK PIGMENTATION IN COLOR POLYMORPHISM OF THE MIGRATORY LOCUST, LOCUSTA-MIGRATORIA

The neuroendocrine control of the dark body color in hoppers of Locust a migratoria was studied using an albino strain as a bioassay system, Methanol or saline extracts of corpora cardiaca originating from 5th i nstar hoppers of a normal (non-albino) strain were dried, dissolved in 10% aqueous ethanol or mixed with peanut oil, and injected into albin o hoppers. No dark color was induced by samples of the methanol extrac ts dissolved in 10% aqueous ethanol. However, samples of the extracts mixed with peanut oil induced dose-dependent darkening in the albino h oppers within a few days after injection; the higher the dose, the dar ker the color induced. Methanol extracts dissolved in saline and heate d at 95 degrees C for 10 min retained the dark-color inducing effect a fter being redried, mixed with peanut oil and injected, but those incu bated with a proteinase for 2 h lost it completely. Therefore, this da rk-color inducing factor seems to be a heat-stable neuropeptide. Organ implantation into albino hoppers revealed that the corpora cardiaca a nd brain of normal solitary hoppers contained this neurohormone as did those of normal gregarious hoppers. Injection of a high dose (2 pairs of corpora cardiaca equivalent) of extract mixed with peanut oil, or daily repeated injections on the first 4 days of the 4th instar, induc ed very dark color after the following ecdysis, but black patterns cha racteristic of gregarious hoppers were not induced, However, some albi no hoppers developed such patterns after receiving 3 daily repeated in jections of 1 pair of corpora cardiaca equivalent during the second ha lf of the 4th instar. The role of this neurohormone in locust polychro matism and in locust phase polymorphism is discussed.