The Relationships between Pupal Development and Ecdysteroid Levels in Summer Diapausing Silkworm, Bombyx mandarina.

Abstract

In the silkworm, Bombyx mandarins, duration of pupal-adult development was mainly divided into three different types among the Japanese population: the first one was 2 weeks duration, the second was about 3 weeks and in the third type more than 30 to 40 days were necessary for the adult development, although these were dependent on the rearing seasons. However, the average number of days required for adult development was 14 in the majority of the Chinese population. In the third type of pupal-adult development of Japanese population, the development of pupal stage was arrested. Oxygen consumption of the animals of which adult eclosion occurred at 34 days after pupation was very low during the pupal development. Ovarian development of these animals was also suppressed considerably. The fluctuation patterns of ecdysteroid titer in haemolymph of Japanese population were quite different from that of the Chinese population. Ecdysteroid titer was undetectable at 4 to 13 days after pupation in the Japanese population, but the titer increased by day-15 and reached a maximum level of 4.5 µg at day-20. The reinitiation of ovarian development was coincident to the increase of ecdysteroids in haemolymph of these animals. It was suggested that the delay of pupal-adult development may be due to the low levels of ecdysteroids in the Japanese population of Bombyx mandarina.