The ‘Brain’ Hormone in the Silkworm, Bombyx mori L.

Abstract

THE imaginal differentiation of lepidopterous insects in which diapause occurs in the pupal stage is not accomplished in one step, but the hormone secreted from the ‘brain’ acts upon the prothoracic gland, and the latter organ in turn secretes a hormone which induces imaginal differentiation1,2. On the contrary, such a system of hormonal action is not yet known in the lepidopterous insects in which diapause does not occur in the pupal stage. One of us3,4 carried out experiments to elucidate this latter problem with the result that an imaginal differentiation in Bombyx silkworm in which diapause occurs in the egg-stage is induced by two hormones, the brain hormone and the prothoracic gland hormone. The former causes the latter to be secreted to induce imaginal differentiation. Further, it was made clear that the brain hormone is secreted from the neurosecretory cells in the brain4.