A study on the voltinism of some silkworm races which had been reared at Institute of Sericulture

Voltinism of 34 silkworm races was studied in the spring of 2003, 2004 and 2005 at Institute of Sericulture (Ibaraki, Japan). In 2003, fourteen races were tested and in 2004 and 2005 ten races were tested in each year. These races were maintained at natural temperature and photoperiod during their development from the egg stage to the egg laying stage. The eggs of the tested races were transferred to a room with glass windows but without temperature control and artificial lighting on 1sup(st) of April and allowed to remain there till the silkworm hatched, developed, copulated and laid eggs. In the beginning of May the eggs hatched and about 500 larvae were brushed in each race. At this time the mulberry leaf of Institute of Sericulture had developed enough as the feed for the silkworm. The larvae were reared on the leaf. At the beginning of the 4sup(th) instar, 200 larvae were picked up and reared to the cocooning. The length of larval stage, pupation ratio, cocoon weight and shell percentage, the period of moth emergence and survival rate of pupae were recorded. Observed the diapause character of the eggs laid by the female moths of each race and classified into 4 categories, i.e. all diapause eggs, the mix of more diapause eggs and less non-diapause eggs, the mix of less diapause eggs and more non-diapause eggs, and all non-diapause eggs. Results showed that, five Japanese and three Chinese races produced all diapause eggs, four Chinese races produced only non-diapause eggs while the other 22 races produced both kind of eggs. However, the ratio of diapause and non-diapause was varied widely depending on the races. In general, the Japanese races produced more diapause eggs while the Chinese races produced more non-diapause eggs. This study clearly revealed the voltinism character of the races.