Studies on the Mode of Action of the Diapause Hormone in the Silkworm, Bombyx Mori L

Abstract

The susceptibility of ‘non-diapause’ pupae to diapause hormone, the sexual difference in production of diapause hormone in the suboesophageal ganglion (SG), the changes in diapause hormone content of the SG during larval-pupal-adult development, and the hormone production in polyvoltine race, were studied by injecting diapause hormone extracts into pupae expected to produce non-diapause eggs. The susceptibility of ‘non-diapause’ pupae of a bivoltine race (Daizo) was very low, or the hormone injected was almost inactivated. The susceptibility of ‘nondiapause’ race to diapause hormone is different in different races. As for sexual differences in content of diapause hormone in moth heads, males are superior to females, which was further substantiated by injecting extracts from the SG of both sexes. From the activity of diapause hormone extracts derived from larval, pupal and adult SG, the hormone production in SG is raised during the late pupal stage, especially in males. It is also observed that larval SG produces the hormone, and the hormone production in the SG of male moths after mating becomes weak. Male moth heads of ‘non-diapause’ worms (polyvoltine race), as well as of ‘diapause ‘worms, contain diapause hormone ; though activity is less than in ‘diapause ‘worms, which reflects the occurrence of diapause eggs caused by SG-transplantation. It is highly probable that the bioassay by injecting diapause hormone extracts reveals the activity of the SG in the silkworm. The activity of the SG in the polyvoltine race has been discussed from the standpoint of diapause determination in the silkworm.