No abstract

BACKGROUND: Widespread reports of reduced efficacy of imidacloprid for managing cotton aphids (Aphis gossypii Glover) in cotton (Gossypium hirsutum L.) prompted an investigation to characterize the susceptibility of 43 populations over a 2-year period. The susceptibility of A. gossypii populations to imidacloprid was examined by calculating LC50 values. Further analyses related resistance assay results to a gradient of cotton production intensity.RESULTS: Concentration-mortality bioassays documencted populations that were 4.26-607.16 times more resistant than the susceptible laboratory population. There was a significant positive relationship between LC 50 values and percentage of cotton within 2.5-and 5-km buffers surrounding collection sites. No significant relationship was detected between LC 50 values and the percentage of alternative crop and noncrop hosts.CONCLUSION: Variable and high levels of resistance were detected in A. gossypii populations, and this variation was positively associated with cotton production intensity. Cotton is a host that may receive multiple applications of neonicotinoids (via seed treatment and foliar sprays) annually for seedling and mid-season pests. Rotating modes of action and limiting insecticide use should be implemented to delay the evolution of insecticide resistance in A. gossypii populations.