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 moveme nt of generalist predators in this system. Previous authors have suggested that sorghum acts as a source of generalist insect predators for cotton pes ts but several questions about the dynamics of insect movement remain unans wered. 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 pred ators. 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 cott on 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 insec ts leaving cotton once exceeded the number entering from sorghum, indicatin g that predator movement is not unidirectional in this system. Further, dat a on predator dispersal rates suggest that predators possess the necessary mobility for their use in field-scale conservation (as opposed to strip cro pping). Results of destructive sampling show that predator movement was pos itively 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 bob weevi l eradication programs increase the feasibility of pesticide reductions and conservation in cotton. (C) 1999 Academic Press.