Efficacy of Bt toxins and foliar insecticides against bollworm, Helicoverpa zea (Boddie), in dried flower corollas of cotton

Authors: Godbold, Russell; WHITNEY, CROW - Mississippi State University; GORE, JEFFREY - Mississippi State University; MUSSER, FRED - Mississippi State University; CATCHOT, ANGUS - Mississippi State University; DODDS, DARRIN - Mississippi State University; COOK, DON - Mississippi State University; Little, Nathan

Submitted to: Journal of Cotton Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/13/2022
Publication Date: 2/2/2023
Citation: Godbold, R.E., Whitney, C.D., Gore, J., Musser, F., Catchot, A.L., Dodds, .M., Cook, D.R., Little, N. 2023. Efficacy of Bt toxins and foliar insecticides against bollworm, Helicoverpa zea (Boddie), in dried flower corollas of cotton. Journal of Cotton Science. 27(1):28-36. https://doi.org/10.56454/ZNAX3626.
DOI: https://doi.org/10.56454/ZNAX3626

Interpretive Summary: Bollworm, Helicoverpa zea (Boddie), is a major pest of cotton in the United States. Bollworm larvae feed on flower buds (squares), fresh flowers, wilting flower corollas (bloom tags), and bolls in cotton. This study evaluated bollworm survival in flowers of different transgenic cotton cultivars treated with various synthetic insecticides. This study found that bollworm exposure to sub-lethal doses of insecticidal Bt proteins in certain transgenic cottons and foliar insecticides, which are commonly-used for supplemental control, likely expedites the development of insect resistance to these toxicants. Findings from this study will assist with improving integrated pest management strategies for bollworm management in cotton across the southern U.S.

Technical Abstract: Foliar insecticides and insecticidal proteins from Bacillus thuringiensis (Bt) in transgenic cotton are common tools used for bollworm management in cotton. Efficacy can be dependent upon larval location in the plant canopy and time of year. Floral structures are known to be a common food source for bollworm. Floral components can complicate bollworm control with foliar insecticides and transgenic cotton by protecting larvae from contact with formulated insecticides and lower concentrations of Bt proteins. Mortality was measured to evaluate the effects of Bt expression and foliar insecticides in flowers of non-Bt, 2-gene Bt, and 3-gene Bt cotton varieties. Bt technologies in flowers provided some efficacy after three days. Bollworm mortality at 3 days after infestation was less than 50% for all varieties. Larval mortality on Bollgard 3 flowers was higher than that on Bollgard II flowers. Surviving larvae on Bollgard 3 flowers weighed less than larvae that fed on Bollgard II flowers, and larvae that fed on Bollgard II flowers weighed less than those that fed on non-Bt flowers. The use of chlorantraniliprole and methoxyfenozide + spinetoram provided some control of bollworms 3 days after being applied to wilting flower corollas (bloom tags). Mortality ranged from 41.9% for the high rate of chlorantraniliprole to 61.0% for methoxyfenozide + spinetoram. Results from this study will be important for improving integrated pest management programs for bollworm management in cotton across the southern U.S.