Characteristically distinct isolates of the nuclear polyhedrosis virus from Spodoptera litura

More than 100 isolates were plaque-purified to examine the genetic variations in four wild stocks of Spodoptera litura nuclear polyhedrosis virus (NPV) collected in Japan. These isolates were characterized by their in vitro host range in three established insect cell lines, growth characteristics, polyhedral protein, DNA restriction endonuclease pattern and DNA hybridization. The isolates were separated into four distinct groups: (I) isolates corresponding to Autographa californica NPV, (II and IV) two different groups of isolates of S. littoralis NPV which had been previously characterized and (III) isolates with no correspondence to any reported virus group. Of the S. litura NPV wild stocks, two were mixtures of more than two different groups of NPVs. We have discussed the advantage of having a mixture of different NPV groups in the same wild virus stocks.