Daily changes in neuroendocrine control of moulting hormone secretion in the prothoracic gland of the cockroach Periplaneta americana (L.)

Time of day related changes in ecdysteroid secretion by the prothoracic gland of last instar nymphs were studied using in vitro coincubations of prothoracic glands and brains under a 12-h light:12-h dark cycle. The experiments reveal that the cells of the prothoracic gland of the cockroach nymphs do not have an endogeneous circadian oscillator determining rhythmicity of ecdysteroid secretion. PTTH release in the scotophase is responsible for the peak of ecdysteroid production during the photophase.