Pathological and Ultrastructural Studies of Nuclear Polyhedrosis Viruses of larvae of the Family Noctuidae

Abstract

Pathological and Utrastructural studies of six nuclear polyhedrosis virus isolated Trichoplusis ni, Autographa californica, Mamestra brassicae and Rachiplusiaou were undertaken. Primary sites of infection for all isolates were the nuclei of fat bodies, tracheal matrix, hypodermis and hemocytes. Mid gut epithelial cells were also infected by some isolates. Utrastructural studies of all isolates were obtained from purified preparations and ultrathin sections. Optimum purification of polyhedra of all isolates was accomplished by putrefaction, filtration and 2 steps of linear sucrose density gradient centrifugation. Virion were liberated from polyhedra by treating the polyhedra with 0.016 M Na2CO3-0.1 M NaCl for 5-10 min. Nucleocapsids were liberated from virions by treatin the latter with Nonidet P-40 for 30 min. Ultrastructural features of polyhedra among the virus isolates were significantly different. Variations in viron size and shape were insignificant for each isolate because the value obtained depended on the number of nucleocapsids present in each envelope. The nucleocapsids of all isolates were morphologically similar in shape but the size varied significantly between virus isolates. Data obtained from this study clearly indicate that pathological and ultrastructural studies can be used to definitively separate and identify several related insect viruses.