Studies on the Mode of Action of the Diapause Hormone in the Silkworm, Bombyx Mori L. I. the Action of Diapause Hormone Injected into Pupae of Different Ages

The effect of temperature on the voltinism of the silkworm, Bombyx rnori, was discovered by Watanabe (1918) over 45 years ago. This followed the rinding of the important role of photoperiod during the incubation period of silkworm eggs (Kogure, 1933). In brief, whether diapause or non-diapause eggs are laid depends on temperature and light experienced by the mother during her embryonic life. In 1950, the present author found that the suboesophageal ganglion is the centre responsible for the induction of diapause eggs (Hasegawa, 1950). This finding was the starting-point or the endocrinological investigation of silkworm diapause by surgical manipulations such as transplantation and extirpation of suboesophageal ganglion, brain, corpus allatum, and so forth (Fukuda, 1951-53; Hasegawa, 1950-52; Morohoshi, 1957, 1959). These extensive works on silkworm diapause have made a great contribution to the understanding of insect diapause. Up to 1950 the phenomenon of insect diapause was believed to be due solely to lack of insect growth hormone. This conception, however, is not applicable to the silkworm where the suboesophageal ganglion lying just behind the brain yields an active principle inducing diapause of silkworm eggs, indicating therefore that the induction of insect diapause comprises two features; one of which is the result of shortage of growth hormone, and the other is the result of positive action of a substance released from the suboesophageal ganglion (diapause hormone). As to the nature of silkworm diapause, different investigators have different conceptions, though it is universally admitted that the suboesophageal ganglion is the actual source of the principle responsible for induction of diapause in silkworm eggs. Surgical procedures such as extirpation and transplantation of organs and ligation experiments, however, will leave some uncertainty about the function of the organs concerned, for such operations cause injuries to the organs to be tested, and, furthermore, the transplants may not show uniform development in the host. The development in hosts with the suboesophageal ganglion alone transplanted seems to be slightly delayed when compared with those in which the suboesophageal ganglion with brain attached is transplanted. If that is so, it suggests that the brain may activate the suboesophageal ganglion by way of the oesophageal connectives. From