Effects of the Epap granulovirus on its host, Epinotia aporema (Lepidoptera: Tortricidae).

The bean shoot borer, Epinotia aporema, is a major pest of soybeans in Argentina. Larvae of this pest are attacked by a granulovirus (EpapGV) that is the most important cause of sporadic epizootics in E. aporema populations. We studied the pathology of this virus in last-instar larvae using light and electron microscopy, and evaluated the effect of the disease on larval growth and development. EpapGV caused a polyorganotropic infection. No nucleocapsids were observed in the nuclei of infected cells prior to nuclear membrane disruption. Nevertheless, granulin was detected in the nucleus by immuno-gold staining, indicating that late gene expression occurred prior to nuclear membrane disruption. Establishment of the virogenic stroma led to complexes of continuous parallel convoluted membranous sheets. Nucleocapsids were enveloped in these areas to form virions, which were then occluded. Apparently as part of the cell-to-cell spread of infection, nucleocapsids were observed enclosed in large numbers within membrane-bound vesicles located between the cells and basal lamina. Larvae infected by EpapGV suffered a retardation of development and typically failed to pupate, but exhibited a weight increase greater than that of healthy E. aporema.