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Monitoring for Pyrethroid Resistance in Bollworm (Helicoverpa zea) in Texas – 2003

Patricia Pietrantonio, Terry Junek, R. Baker, G. Cronholm, D. Fromme, G. Moore, D. Mott, R.R. Minzenmayer, E. Nino, J. Norman, Jr., R. Parker, R.P. Porter, K. Siders, N. Troxclair, and C.G. Sansone


A statewide monitoring program for males of bollworm (Helicoverpa zea) was conducted from May to October of 2003, surveying fifteen Texas Counties. Moths were trapped near cotton fields using pheromone, Hercon Luretape® with Zealure. Moths were collected early in the morning and assays were performed the same day. Vials were prepared in the Toxicology Laboratory, Department of Entomology at Texas A&M University, College Station, Texas and shipped as needed to Extension personnel. Vials were prepared using acetone only for controls, and cypermethrin (technical grade, 95.2% purity) at 0.3, 1, 3, 5, 10 and 30 μg/vial. One moth was placed in each vial and bioassays were evaluated after 24 h. Moths were classified as alive, dead, or "knocked-down". From Burleson County 1,814 moths were tested. Other counties in Texas participating in the monitoring program were: Castro, Hockley, Hale, Swisher and Martin Counties in the High Plains production region; Tom Green and Runnels Counties in the Southern Rolling Plains region; Ellis and Williamson Counties in the Blacklands region; Uvalde County in the Wintergarden region; Nueces and Wharton Counties in Coastal Bend region; and Hidalgo County in the Lower Rio Grande Valley. A total of 4,134 moths were tested for all areas outside Burleson County. Data from all areas in Texas was sent to Texas A&M University Toxicology laboratory and analyzed using Probit-PC, Probit and Logit Analysis and graphed using SigmaPlot. Only data from valid bioassays were analyzed. A baseline for susceptibility to cypermethrin was established from two areas in Texas with low LC50 values, Hockley County and Wharton County, these values were pooled to obtain a baseline LC50 of 0.283 μg/vial that was used to calculate relative resistance ratios for the rest of the counties. High levels of resistance were detected for Nueces, Burleson and Castro Counties; the LC50 resistance ratio as previously defined was 9 for the first two counties in July and between 4 and 10 for Castro Co., depending on the date. Bollworm populations were most susceptible to pyrethroids in 2003 in Parmer, Hale, Hockley, and Wharton Counties.

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Document last modified 04/27/04