Effects of a juvenile hormone analog, fenoxycarb, on 5th stadium larvae of the silkworm, Bombyx mori (Lepidoptera: Bombycidae)

A juvenile hormone analog, fenoxycarb, was topically applied to 5th stadium larvae of the silkworm, Bombyx mori, and the subsequent growth of the larvae was investigated. When fenoxycarb was applied on days 0 to 5 of the 5th stadium, the length of the stage increased and the rate of pupation decreased in a dose-dependent manner. During this period, the later the larvae were treated, the greater were the effects. The treatments also delayed the growth of the silk glands and the rise of the hemolymph ecdysteroid titer in a dose-dependent manner. In addition to the prolongation of the 5th stadium, treatment on days 3 to 5 induced a supernumerary molt to the 6th stadium with pupal characteristics. In these animals, the ecdysteroid titer increased from the day after the treatment and peaked at time of head capsule slippage. Treatment on day 6 or 7 had only slight effects on the subsequent growth. These results indicate that the feeding period of the 5th stadium can be divided into three stages according to the animal's responses to fenoxycarb.