Induction of non-diapause egg by dark and low temperature incubation in local variety of the silkworm, Bombyx mori

Abstract

Silkworm races are experientially classified into three types of voltinism, such as univoltine, bivoltine and multivoltine, though the voltinism tends to be influenced by emviron-mental condition at various stages. We investigated the induction of non-diapause eggs by dark and low temperature incubation (constant darkness, 15°C) in the local varieties preserved in the National Institute of Sericultural and Entomological Science as genetic resources. Fourty two of 87 univoltine races tested produced only diapause eggs, while five races produced non-diapause egg batches only. Bivoltine races produced non-diapause eggs except one (Seihaku-Ymagata). The character producing non-diapause eggs seemed to be maintained appropriately. While incidence of non-diapause eggs was remarkably high in European races, there was no big difference between Japanese and Chinese races. Two races of the Koishimaru (Sanshi and Watari) were distinguishable from each other by the incidence of non-diapause eggs, even though it was difficult to distinguish them by the external appearance. These data on voltinism of the local silkworm varieties will be recorded into the data base of our Institute and opened to the public in the near future.