Histopathology of a granulosis in the larva of the fall webworm, Hyphantria cunea

Abstract

Light-autoradiography, light microscope, and electron microscope observations of the larval fat body of the fall webworm, Hyphantria cunea, infected with a granulosis virus revealed that a mitotic cell proliferation and nuclear hypertrophy of the fat-body cells occurred at an early stage of infection, and subsequently, a stained network developed in the entire area of the enormously hypertrophied nuclei. A number of virus rods appeared to protrude from the strands of very dense material of the network into the spaces between the strands, where the virus rods were enveloped with the capsule protein. Light-autoradiography preparations revealed that areas of active synthesis of DNA, RNA, and protein were restricted to the nucleus at an early stage of infection, and at a later stage, the active synthesis was restricted around the strands of network. These results suggested that, although the development of granulosis virus begins in the cell nucleus and continues after early rupture of the nuclear membrane in both the nuclear and cytoplasmic areas, the material used in the formation of the granulosis virus is probably of nuclear origin. In the fat body infected simultaneously with granulosis and nucleopolyhedrosis viruses, no cell with both virus types of infection was detected with the light and electron microscopes.