On the multiplication of an insect virus

Abstract

Polyhedral bodies, ultimately averaging 1.0 μ in diameter, are formed in the nuclei of the digestive cells of the mid-gut epithelium of virus-infected European spruce sawfly larvae (Order Hymenoptera). Infected nuclei increase in size and the chromatin coagulates to form several masses. The polyhedra appear, under the light microscope, as minute granules within the chromatic masses. Later they appear throughout the nucleus, gradually increase in size, and become resistant to staining. Rod-shaped virus particles with dimensions of about 250 × 50 mμ and spherical particles varying in size from less than 80 to more than 160 mμ in diameter were isolated from purified polyhedra. Particles similar to these were observed in thin sections of infected nuclei before polyhedral formation indicating that multiplication of the virus takes place in the free state. An electron microscope study of thin sections of infected nuclei and material extracted from infected cells shows that polyhedra arise as ultramicroscopic bodies about 160 mμ in diameter and contain spherical particles about 20 mμ in diameter which increase in number and size as the polyhedra grow. Apparently multiplication and development of the virus particles take place within growing polyhedra as well as in the free state within an infected nucleus.