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Recombinant baculoviruses have been genetically engineered to reduce the time to kill infected pests, thus reducing crop damage. In this study, wild-type viruses and recombinant viruses expressing a scorpion toxin were applied to cotton in response to larval infestations of Helicoverpa zea and Heliothis virescens in 1997 and 1998. A chemical standard and an untreated control acted as comparison treatments. The goals of this field study were to (1) assess the efficacy of recombinant baculoviruses in protecting cotton from larval feeding damage; (2) assess the impact of recombinant virus introductions on predator densities and diversity; and (3) determine if cotton predators acquire baculovirus by consuming infected heliothines. When applications were timed at larval emergence, certain recombinant virus treatments protected cotton from damage better than wild-type virus treatments and as well as the chemical standard. Differences in efficacy between recombinant and wild-type baculoviruses were not apparent if treatments were applied 3 to 4 days after peak larval emergence. Predator densities and diversity were similar among recombinant and wild-type baculovirus treatments, whereas plots treated with the chemical standard had consistently smaller predator populations. From polymerase chain reaction analyses of predators in 1997 and 1998, 1.7 and 0.2%, respectively, of predators had consumed a virus-infected heliothine. Nine of the 26 predators carrying viral DNA were positive for recombinant virus. Additionally, 13 of the 26 predators were found to disperse 13.5 to 105 m 2 to 5 days after initial virus applications. Five of these dispersing predators (0.2% of all predators evaluated) carried recombinant viral DNA. These results suggest that the potential for the inadvertent spread of recombinant viral DNA via dispersing predators is low.

Adjacent plots of cotton, Gossypium hirsutum L., and grain sorghum, Sorghum bicolor (L.) Moench, were established in 1997 and 1998 to study the movement of generalist predators in this system. Previous authors have suggested that sorghum acts as a source of generalist insect predators for cotton pests but several questions about the dynamics of insect movement remain unanswered. Mark–recapture methods were used to determine the timing of predator movement and to measure the net gains, if any, for cotton in terms of predators. Destructive sampling of cotton and grain sorghum plants was used to determine which environmental factors might cause predator movement in this system. Results showed that several generalist predators move between cotton and sorghum, most frequently Orius spp. and Hippodamia convergens Guerin-Meneville. Movement of predators into cotton peaked during the hard-dough and soft-dough stages of sorghum phenology in 1997 and 1998, respectively. Although cotton received a net gain in total predators, the number of insects leaving cotton once exceeded the number entering from sorghum, indicating that predator movement is not unidirectional in this system. Further, data on predator dispersal rates suggest that predators possess the necessary mobility for their use in field-scale conservation (as opposed to strip cropping). Results of destructive sampling show that predator movement was positively correlated with ambient temperatures and negatively correlated with local aphid levels. These results support the use of sorghum as a predator conservation tool in cotton and are particularly relevant as the boll weevil eradication programs increase the feasibility of pesticide reductions and conservation in cotton.