Abstract
Histological observations were carried out on the integument of silkworm larvae infected with nuclear polyhedrosis virus at various stages of the 3rd instar, to determine the effect of virus infection on the formation of new cuticicle during the moulting.
In healthy larvae, the epidermal cell layer became thick by elongation of cells, and glycogen was stored in the cytoplasm near the basement membrane before the 3rd moulting (60 hours after the 2nd moulting). The larvae have exuviated at 84 hours after the 2nd moulting.
In larvae infected with the virus immediately after the 2nd moulting, cytopathological changes caused by the virus were seen in epidermal cells at 36 hours after the infection, and cell layer did not become thick. Glycogen was not stored in the cytoplasm. The larvae died without forming the new cuticle.
In larvae infected with the virus at 24 hours after the 2nd moulting, cytopathological changes caused by the virus were observed in epidermal cells at 48 hours after the infection, and the cell layer became thick at 72 hours after the 2nd moulting. But when most epidermal cells were infected, the storage of glycogen in the epidermal cells was not observed, and no cuticle formation was observed. In the other hand, when the infected cells were very few, the storage of glycogen in the epidermal cells was observed, and new cuticle was normaly formed at 84 hours after the 2nd moulting.
In larvae infected with the virus at 36 hours after the 2nd moulting, infected epidermal cells were not observed during the 3rd moulting, the epidermal cell layer became thick and glycogen was stored in the cytoplasm. The larvae could exuviate to next instar. The pathological changes of infected epidermal cells was observed 60 hours after the innoculation.
