Submitted to: Environmental Entomology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/13/2007
Publication Date: 10/1/2007
Citation: Pietrantonio, P.V., Junek, T.A., Parker, R., Mott, D., Siders, K., Troxclair, N., Vargas-Camplis, J., Westbrook, J.K., Vassiliou, V.A. 2007. Detection and evolution of resistance to the pyrethroid cypermethrin in bollworm, Helicoverpa zea (Lepidoptera, Noctuidae) in Texas. Environmental Entomology. 36:1174-1188. Interpretive Summary: The bollworm is a key insect pest of cotton in Texas that is widely controlled with pyrethroid (cypermethrin-based) insecticides. However, concerns exist regarding decreasing susceptibility to this class of insecticides. Cypermethrin resistance in male bollworm moths from the major cotton production regions of Texas was compared to that of a susceptible field population. Populations from several counties had statistically significant resistance ratios, indicating that resistant bollworm populations are widespread in Texas. Resistance ratios for bollworms varied between counties and years, exemplifying the local and dynamic nature of insecticide resistance in general, and of cypermethrin resistance in particular. Circumstantial evidence suggests that moth migration may contribute to local levels of resistance. Results indicate a rapid evolution of resistance to cypermethrin in bollworm populations that explains the observed pyrethroid control failures in various counties. Further, these results will help in developing pest management strategies for preserving the effectiveness of pyrethroid insecticides.
Technical Abstract: The bollworm Helicoverpa zea (Boddie) is a key pest of cotton in Texas. Bollworm populations are widely controlled with pyrethroid insecticides in cotton and exposed to pyrethroids in other major crops such as grain sorghum, corn and soybeans. A statewide program that evaluated cypermethrin resistance in male bollworm using the adult vial test was conducted from 2003 to 2006 in the major cotton production regions of Texas. Estimated parameters from the most susceptible field population currently available (Burleson County, September 2005) were utilized to calculate resistance ratios and their statistical significance. Populations from several counties had statistically significant (p< 0.05) resistance ratios for the LC50, indicating that bollworm resistant populations are widespread in Texas. The LC50 resistance ratios varied in different counties and years, exemplifying the local and dynamic nature of insecticide resistance in general, and of bollworm cypermethrin resistance in particular. The highest resistance ratios for the LC50 were obtained from Burleson County in 2000 and 2003, Nueces County in 2004, and Williamson and Uvalde counties in 2005. Estimation of the frequencies for the putative resistant allele (q) using 3 micrograms and 10 micrograms as discriminatory dosages for susceptible and heterozygote resistant insects, respectively, suggests that one major allele is responsible for resistance. The influence of migration on local levels of resistance was estimated by analysis of wind trajectories. The results indicate a rapid evolution of resistance to cypermethrin in bollworm populations that explains the observed pyrethroid control failures in various counties.