A nuclear polyhedrosis virus was isolated from disease larvae of Hyphantria cunea. An established cell line derived from the ovary of adults of the cabbage looper, Trichoplusia ni, surpported growth of the H. cunea nuclear polyhedrosis virus (NPV). It was confirmed that the virus is specifically related to the host, Hyphantria cunea. Typiclal NPV symptoms were obtained when infected cells were fed to neonatal fall webworm, and the cell line produced free virions and inclusion bodies containing virions. Purification of NPV was accomplished by differential centrifugation, treatment with sodium dodecyl sulfate, and velocity sedimentation in sucrose gradients. The inclusion body of H. cunea NPV was studied electron microscopically. The polyhedron was tetrahedron or hexahedron of 0.6-2.5 m in size and the rod-shaped virus particles consisting of 2-22 rods in a bundle were observed. Polyhedral protein preparations from H. cunea NPV and A. californica NPV were characterized by sodium dedecyl sulfate-polyacrylamide gel electrophoresis. In SDS-PAGE, the major protein component ranged from 28,000 to 29,000 dalton among the isolates. Differences were confined to minor protein bands or the band intensity. The $H_c$ NPV revealed a complex but unique composition of 11 bands with molecular weights ranged from 8,900 to 77,000. This study was carried out with a comparision of Autographa californica NPV which was well established in biophysical, biochemical properties.
