Diapause development in Bombyx eggs in relation to ‘esterase A’ activity

Abstract

Diapause is broken by hydrochloric acid treatment and also terminated by long chilling of eggs in the silkworm, Bombyx mori. One of esterases in silkworm eggs named ‘esterase A’ is closely related to diapause of this insect. Hydrochloric acid treatment of diapause eggs induced a prompt elevation of esterase A activity. The elevation was observed within 30 min after treatment. This HCl treatment effectively stimulated the eggs to hatch. This indicates that the increase of esterase A activity is correlated with an active resumption of morphogenesis. The question was examined of whether chilling also increases esterase A activity or not. It was found that chilling also caused an increase of esterase A activity. This increase occurred before the re-appearance of glycogen in eggs, which indicates the termination of diapause in this insect. In fact, the establishment of hatchability in chilled eggs was observed after esterase A activity has reached the maximum level. Thus the increase of esterase A activity could be regarded as associated with the termination of diapause per se but not with the subsequent process of post-diapause development. This change in esterase A activity was observed only in chilled diapause eggs and was not observed in diapause eggs without chilling and non-diapause eggs. These results suggest that the increase of esterase A activity during chilling may be a kind of activity that occurs during the diapause stage in preparation for resumption of morphogenesis or diapause development.