ISOLATION AND CHARACTERIZATION OF NUCLEAR POLYHEDROSIS VIRUSES FROM THE BEET ARMYWORM SPODOPTERA-EXIGUA (LEPIDOPTERA, NOCTUIDAE) FOUND IN SHIGA, JAPAN

Eleven larvae of the beet armyworm, Spodoptera exigua, showing symptoms of nuclear polyhedrosis virus (NPV) infection were collected in Shiga Prefecture, Japan. NPVs isolated from each larva were divided into two groups. Group 1 isolates produced cuboidal polyhedra, while group 2 isolates produced icosahedral polyhedra. The restriction endonuclease patterns of viral DNA within the same group were identical. The restriction endonuclease patterns of group 1 were similar to those of Autographa californica NPV (AcNPV), whereas the patterns of group 2 were similar to S. exigua NPV isolated in California. SDS-polyacrylamide gel electrophoresis analysis of polyhedra also indicated that SeNPVs differed between the two groups. Group 1 SeNPVs could infect the cell lines SF-21 and TN-368 and group 2 SeNPVs could not. Furthermore, group 1 SeNPVs were able to infect Spodoptera litura, Plutella xylostella, and S. exigua larvae but not Bombyx mori larvae. Group 2 SeNPVs could infect S. exigua larvae, but not S. litura, P. xylostella, or B. mori larvae. The LD50 of SeNPV #5 (group 1) and SeNPV #1 (group 2) were 58 and 4.8 polyhedra per larva, respectively. These results indicated that the SeNPVs isolated in Shiga Prefecture were composed of two genetically and phenotypically distinct groups.