Bollworm Bt Resistance and Management
By David Kerns, Ph.D.
Texas IPM Program Coordinator
Department of Entomology
Texas A&M University
College Station, Texas
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Over the past few years, cotton and corn growers and consultants have been reporting increasing incidences of Helicoverpa zea, bollworms/earworms, successfully feeding and causing injury to Bt cotton and corn. Since 2015, we have been conducting surveys across the southern U.S. of H. zea for resistance to key Bt toxins, Cry1Ac, Cry1F, Cry2Ab2 and Vip3A. Resistance to Cry1Ac and Cry1F appears to be near ubiquitous, and resistance to Cry2Ab2 is common and widespread. Resistance to Cry2Ab2 appears to be controlled by an incomplete dominant gene. Thus far, resistance to Vip3A is very low but there have been incidences of H. zea feeding on and injuring corn and cotton expressing Vip3A. Because of Bt resistance issues, cotton growers have had to commonly utilize insecticides in dual-gene cotton. Among insecticides, those containing chlorantraniliprole (Prevathon and Besiege) offer the longest lasting control.