Field studies of a genetically modified baculovirus, Autographa californica nuclear polyhedrosis virus

A genetically modified strain of Autographa californica nuclear polyhedrosis virus (Ac229) lacking the p10 gene and containing a gene marker (beta-galactosidase) or the parental wild-type virus (AcHR-3) was applied to cabbage plants and soil at the center of replicated field plots in 1994. Foliage and soil in treated and nontreated areas were sampled for two seasons (60 weeks) following treatment. Activity of virus on cabbage leaves and soil was determined by bioassay to assess persistence and dispersal of the recombinant. Similar rates of decline in activity occurred on foliage for each strain of virus in the first season. Ac229 was not detected on cabbage leaves in the second season. Activity of Ac229 in soil decreased more rapidly than that of AcHR-3 in the second season. Low concentrations of AcHR-3 and Ac229 were detected on foliage and soil from nontreated areas throughout 1994 and 1995. In 1995, plots of a similar size were treated in a nearby study site. Trichoplusia ni larvae were introduced into the plots prior 60 the application and at biweekly intervals following the application. Inactivation of the primary inocula on foliage was similar for both strains; however, activity of Ac229 declined compared with AcHR-3 during the secondary infection cycles. The majority of infected larvae and contaminated leaf samples collected from outside of the treated areas contained AcHR-3. Factors are suggested to explain differences in long-term persistence and dissemination between the recombinant and the wild-type viruses. (C) 1997 Academic Press.