Genetic and biological comparisons of ten geographic isolates of a nucleopolyhedrovirus that infects Spodoptera litura (Lepidoptera: Noctuidae)

Nine nucleopolyhedrovirus (NPV) isolates from Japan, Vietnam, Malaysia, and India collected from diseased Spodoptera litura larvae and an Egyptian isolate of Spodoptera littoralis NPV were subjected to genetic and biological comparisons to select a candidate isolate for controlling S. litura. In restriction endonuclease (REN) analysis, submolar bands were detected in 6 of the 10 isolates, showing that these viral populations consisted of a mixture of several genotypes. Based on equimolar bands, the isolates could be broadly divided into two groups: S. litura NPV-type and S. littoralis NPV-type. Four isolates from Southern and Southeast Asia and one from the Ogasawara Islands in Japan had S. litura NPV-type REN profiles. Four isolates from the main island of Japan had REN profiles closely related to the Egyptian isolate, S. littoralis NPV-B, suggesting that S. littoralis NPV-B type is widely distributed in Japan. Droplet feeding bioassays with second and fourth instar larvae showed no evidence of differences in biological activity among the 10 isolates based on the infectivity and survival time of infected larvae.