Competition between wild-type and recombinant nucleopolyhedroviruses in a greenhouse microcosm

Wild-type Autographa californica nucleopolyhedrovirus (AcNPV or AcNPV.WT), AcNPV expressing a scorpion toxin (AcNPV.AaIT), and AcNPV expressing a muta ted juvenile hormone esterase (AcJHE.SG) were compared in their capability to produce epizootics in larvae of Trichoplusia ni infesting collards in a greenhouse microcosm. Larvae treated in four different ways were released i nto 1.8-m(2) microplots in week. 1. The four treatments included (1) uninfe cted larvae (control), (2) 100% AcNPV.WT-infected larvae (WT), (3) 100% AcN PV.AaIT-infected larvae (AaIT), and (4) 1:1 ratio of AcNPV.WT-infected and AcNPV.AaIT-infected larvae (WT+AaIT). On a weekly basis, larvae were sample d and new, uninfected larvae were added to all plots, Sampled larvae mere r eared until death and then subjected individually to DNA-DNA dot-blot hybri dization assay to determine the proportion of insects infected with each vi rus in each plot. The entire experiment was repeated with AcJHE.SG in the p lace of AcNPV.AaIT. Epizootics of AcNPV.WT lasted 8 weeks after a single vi ral release in the replicated greenhouse microplots. AcJHE.SG epizootics al so lasted 8 weeks after viral release, but this virus and AcNPV.AaIT were b oth out-competed by AcNPV.WT. AcNPV.AaIT was no longer detected in the T. n i population by the fourth week after release. AcNPV.WT also increased to g reater numbers in soil than AcNPV.AaIT or AcJHE.SG after 8 weeks. Thus, it was possible to induce 8-week epizootics of AcNPV.WT in replicated microplo ts under artificial greenhouse conditions, and the wild-type virus out-comp eted the recombinant virus for a niche in this greenhouse microcosm, which reduces the probability that the recombinant virus will persist in an agroe cosystem. (C) 2000 Academic Press.