Predator Conservation in Cotton: Using Grain Sorghum as a Source for Insect Predators

Adjacent plots of cotton, Gossypium hirsutum L., and grain sorghum, Sorghum bicolor (L.) Moench, were established in 1997 and 1998 to study the movement ofgeneralist 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. Markrecapture 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. andHippodamia convergens GuerinMeneviUe. 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.