Isolation of genotypic variants of Autographa californica nuclear polyhedrosis virus

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Abstract
A nuclear polyhedrosis virus (MNPV) isolated from a lepidopteran (Noctuidae) insect, A. californica, was cloned by successive plaque purification using virions containing only 1 nucleocapsid/envelope as inoculum. The ability to clone the virus by this method was demonstrated by the isolation of nondefective, genotypic variants of the virus with similar but not identical restriction endonuclease fragment patterns. Five distinct variants were identified by genotypic analysis with HindIII, EcoRI, SalI and BamHI restriction endonucleases. The characteristic genotype of each variant was maintained upon passage in insect larvae. The isolation of these virus variants demonstrates the heterogeneity of the uncloned virus preparation and the ability to clone MNPV by plaque purification of media-derived nonoccluded virions. The A. californica MNPV is being considered for commercial use as a pesticide in the USA, and the cloning of the virus, in view of the heterogeneity detected, may be advisable. The cloning and genotypic analyses are also significant with regard to understanding the genetic nature of multiply embedded NPV (those NPV containing more than 1 nucleocapsid/envelope in the occluded form of the virus) and indicate that further genetic analysis of these viruses is possible.