IN-VIVO RECOMBINATION BETWEEN 2 STRAINS OF THE GENUS NUCLEOPOLYHEDROVIRUS IN ITS NATURAL HOST, SPODOPTERA-EXIGUA

The DNA restriction map for the enzymes BamHI, BglII, PstI, and XbaI o f SeMNPV-US (Se-US), the best-studied Nucleopolyhedrovirus strain isol ated from Spodoptera exigua in California, was used as a reference to construct that of SeMNPV-SP2 (Se-SP2), a closely related Spanish strai n of the same virus. After coinfection of S. exigua with both the Se-U S and Se-SP2 strains per os, a recombinant virus (SeMNPV-SUR1 [Se-SUR1 ]) was detected after one passage which quickly replaced the parental viruses. A physical map of Se-SUR1 DNA was constructed for BamHI, BglI I, PstI, and XbaI and compared to that of the parental viruses, Se-US and Se-SP2. Se-SUR1 is the result of at least four crossover events be tween Se-US and Se-SP2 and not of selection of a minor variant in one of the parental viruses. Bioassays of the recombinant and parental str ains against L2 beet armyworm larvae demonstrated that their 50% letha l dose values were not significantly different. The differences in med ian lethal time values are too small to explain the replacement of the parental viruses by the recombinant virus upon successive passage in vivo, although it cannot be ruled out as an explanation for the select ive advantage of the recombinant strain, Se-SUR1. The consequences of the release of nonindigenous or recombinant baculovirus strains in agr o-ecosystems are discussed.