Development of an intranuclear nonoccluded rod-shaped virus in some midgut cells of an adult insect, Gyrinus natator L. (Coleoptera)

Electron microscopic investigations on the midgut of the adult coleopteron Gyrinus natator L. reveal in most of the insects, collected in numerous stations, the presence of free intranuclear rod-shaped viruslike particles in some epithelial cells. In the cytoplasm of the infected cells, a characteristic network is found. This DNA-virus is different from the nuclear-polyhedrosis and granulosis viruses not only in that it is not occluded in polyhedra or capsules, but also in that naked virus rods cannot be observed. Its mode of replication resembles that of another nonoccluded rod-shaped insect virus ( Rhabdionvirus oryctes). Branched fibrils of viral DNA and cup-shaped membranes, precursors of virus envelopes, are present in the infected nuclei. Sometimes these membranes show a peculiar cylindrical form. The cylinders are covered on the outer surface with a spiny coat; a similar coat is found on the virus envelope. In an autoradiographic study, after tritiated thymidine injection, an interval is noted between the viral DNA synthesis and the appearance of the first virion. Since the state of the insect's infection appears to vary little, it seems that a certain virus—host equilibrium is established.