Abstract
Symptomatological and histopathological features of a newly discovered nuclear polyhedrosis of the small blackish cochlid, Scopelodes contracta, were described. The virus was pathogenic to the fat body, hypodermis, trachea, and the muscle, but it was not pathogenic to the midgut, silkgland, and Malpighian tubes. The progression of the disease was similar to that of other nuclear polyhedrosis type. Electron micrographs revealed that each hypertrophied nucleus of infected cell contained a central chromatin mass having a micronet structure and a number of “naked” virus rods protruded from the strands of dense material of network into the spaces between the strands. Some of the mature virions were seen outside of the chromatin mass or in the minute polyhedra developing interior to the nuclear membrane. Simultaneously, development of fibril structure was seen both in the nucleus and in the cytoplasm, suggesting that the production of fibrillar masses was certainly related to the synthesis of polyhedral protein. The size of ovoid or irregular-shaped polyhedra varied from <1μ up to 5μ in diameter with the mean of 1.7±0.43μ. Virions occluded in the polyhedra were composed of single rod or 2-5 rods enclosed by a common outer membrane, and most of the virions seen were of double rod type. The size of a single rod was approximately 380nm in length and 35nm in width, while the virion of single rod with outer membrane had a size of 430nm in length and 80nm in width. A cross-infection study showed that a nuclearpolyhedrosis virus of S. contracta did not infect young-instar larvae of Bombyx mori and Arcte coerulea. However, larvae of S. contracta was susceptible to nuclear-polyhedrosis viruses of B. mori and Mamestra brassicae.
