Efficacy of Bt Toxins and Foliar Insecticides Against Bollworm, Helicoverpa zea (Boddie), in Dried Flower Corollas of Cotton

Foliar insecticides and insecticidal protein from Bacillus thuringiensis (Bt) in transgenic cotton are common tools used for bollworm management in cotton. Efficacy of Bt proteins and foliar insecticides 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, two-gene Bt, and three-gene Bt cotton varieties. Expression of Bt protein in white flowers provided some efficacy after three days. Bollworm mortality at three days after infestation was less than 50% for all varieties in an unsprayed environment. Larval mortality on Bollgard 3 flowers was higher than that on Bollgard II flowers. Surviving larvae feeding 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 or methoxyfenozide + spinetoram provided some control of bollworms three days after application to wilting flower corollas (bloom tags). Mortality ranged from 41.9% following application of chlorantraniliprole to 61.0% following application of methoxyfenozide + spinetoram. Results from this study will be used to improve integrated pest management programs for bollworm management in cotton.