Abstract: The pathological changes of Heliothis assulta were examined after infection with nuclear polyhedrosis virus (NPV). The concentration of hemolymph protein in infected larvae was found to be higher than that in the control at 24 hr and decreased sharply 72 hr after infection. For healthy larvae, the concentration of hemolymph protein peaked at 72 hr and 120 hr. The PAGE pattern revealed that there were 22, 3, and 3 bands of general protein, lipoprotein and glycoprotein respectively isolated from hemolymph samples from both infected larvae and the control. There was close relationship among the three types of protein. The concentrations of some of the main proteins from the controlbecame higher at 48 hr and 120 hr while these of corresponding bands from infected larvae remained unchanged, suggesteng that the syntheses of these proteins were inhibited by NPV infection. Various cytological changes of mid-gut ceils and tracheal matrix were detected by electron microscopy. No virus was found entered columnar cell from microvilli.The mid-gut cells were infected slightly and at later stage. No polyhedron was formed The trachael matrix was sensitive to the infection of NPV and subsequently played an important role in repeated infection.

Key words: Heliothis assulta——NPV——replication——Mid-gut——tracheal matrix——hemolymph