Characterization of a Variant ofAutographa californicaNuclear Polyhedrosis Virus with a Nonfunctional ORF 603

A new genotypic variant ofAutographa californicanuclear polyhedrosis virus (AcMNPV), the V8 variant, was originally identified by an additionalHindIII site in theHindIII–F fragment. Insect bioassays of this variant displayed a decreased time of mortality compared with the L1 variant of AcMNPV inSpodoptera frugiperdalarvae but not inTrichoplusia nilarvae. A 1.8-kb region containing the 3′ end of ORF 5,lef-2,ORF 603, and the 5′ end of the polyhedrin gene (polh) of both L1 and V8 was sequenced. V8 exhibited extensive sequence variation in the region between the 3′ end oflef-2and the 5′ end ofpolh; V8 had six amino acid substitutions in thelef-2gene product and a nonfunctional ORF 603. A site-specific frameshift mutation in ORF 603 of the L1 variant was constructed to determine the effect of ORF 603 inS. frugiperdalarvae. Truncation of ORF 603 was found to decrease the time of mortality inS. frugiperdalarvae. The insect-selective toxin gene,tox34, was inserted into the V8 variant by direct cloning. The efficacy of this recombinant as a biopesticide was equivalent to similar L1 recombinants.