A strain of nuclear-polyhedrosis virus causing extensive cellular hypertrophy

Abstract

A newly discovered strain of a nuclear-polyhedrosis virus causes extensive hypertrophy to the tracheal cells of the armyworm, Pseudaletia unipuncta. This extreme hypertrophy, the absence of infection in the fat cells, and the long period of lethal infection clearly differentiate it from the typical strain of a nuclear-polyhedrosis virus which has been described previously. It also differs from the typical strain in causing the following cytopathological changes: an increase in the number and an alteration in the appearance of the mitochondria in the infected cell, the development of innumerable folds in the cell and nuclear membranes, and the formation of electron-transparent areas in the cytoplasm. At an early stage of infection when the cellular hypertrophy is marked, there is at first no virus rods. The rods appear later, and the polyhedra still later. The polyhedra and virus rods of the new strain resemble those of the typical strain. Its infectivity is also enhanced by a granulosis virus in a synergistic association as in the case of the typical strain. When armyworm larvae are fed equal concentrations of the new and the typical strains, very few of them, if any, develop the signs and symptoms of the new strain. The larval specimens, from which the new strain was obtained, had been collected in a field in Hawaii during 1958 and 1960, and showed the typical signs and symptoms of nuclear polyhedrosis at the time of collection. Accordingly, the larval specimens may have been infected originally by two strains of a nuclear-polyhedrosis virus. Three larvae collected in alfalfa fields at Davis, California, also exhibited signs and symptoms of the new strain.