Electron-microscopic observations on the maturation of a cytoplasmic-polyhedrosis virus

A new cytoplasmic-polyhedrosis virus has been found in larvae of Chironomus plumosus (Diptera: Chironomidae). Larvae die of a massive virus infection in the midgut epithelium. With phase-contrast microscopy, two different types of inclusion bodies can be distinguished in the cytoplasm of infected cells. These correspond in the electron microscope to areas of viral multiplication (largely free virus) and accumulations of polyhedra (occluded virus). In the course of virus maturation, free viruses are individually invested with a thick layer of polyhedral protein. Subsequent to this, the protein coats of adjacent viruses apparently fuse to form polyhedra.