Nucleopolyhedrovirus pathology in spruce budworm larvae

Choristoneura fumiferana (Clemens) (Lepidoptera: Tortricidae) multiple nucleopolyhedrovirus (CfMNPV) expressing green fluorescent protein was used to study aspects of nucleopolyhedrovirus infection in the spruce budworm. The temporal and spatial distribution of fluorescence indicated that the virus infected the midgut, entered the tracheal system, and traveled to the epidermis, fat body, and muscles. In contrast to Autographa californica (Speyer) (Lepidoptera: Noctuidae) multiple nucleopolyhedrovirus (AcMNPV) infection, hemocytes from infected C. fumiferana did not exhibit fluorescence until after CfMNPV had passed from the midgut into the tracheae. Therefore the role of hemocytes may be limited during CfMNPV infection. Also the fluorescence pattern spread from the tracheolar cells to tracheal epithelial cells throughout the tracheal system. Our results indicate that the temporal and spatial events involved in CfMNPV infection of C. fumiferana larvae are consistent with those observed in other lepidopteran hosts infected with AcMNPV. Minor deviations between these two systems may be attributed to differences in virulence, infection rate, and possibly host range of the virus.