Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/11/2008
Publication Date: 10/1/2008
Citation: Gore, J., Adamczyk Jr, J.J., Catchot, A., Jackson, R.E. 2008. Yield Response of Dual-toxin Bt Cotton to Helicoverpa zea Infestations. Journal of Economic Entomology. 101:1594-1599 Interpretive Summary: Field experiments were conducted to determine the impact of bollworms on yields of Bollgard II and Widestrike cotton. Results from these experiments showed that bollworms rarely cause significant yield reductions in Bollgard II and Widestrike cotton. However, significant yield reductions were observed in one of the three years of the experiment for Bollgard II cotton. During that year, the relationship between cumulative numbers of white flowers infested and yield was weak. The weak relationship during one of the three years indicates that although insecticide applications will likely not result in increased yields, there may be some situations when those applications are economically beneficial. More research will be needed to refine these results.
Technical Abstract: Field cage experiments were conducted to determine the impact of bollworms, Helicoverpa zea (Boddie), on maturity and yield of Bollgard II and WideStrike cotton, Gossypium hirsutum L. One d old bollworm larvae were infested in white flowers of Bollgard II cotton and in white flowers and terminals of Widestrike cotton. The infestation levels included 0, 50, and 100 percent of white flowers for each type of cotton. Terminal infestations included one or two larvae per terminal on Widestrike cotton. Larvae were placed in flowers of Bollgard II cotton each day for 1 to 4 wk during the first 4 wk of flowering during 2003, 2004, and 2005 seasons and in the flowers or terminals of Widestrike cotton each day for 1 to 3 wk. Averaged across years and durations of infestation, yields of Bollgard II cotton were significantly reduced compared with noninfested Bollgard II cotton when 100% of white flowers were infested. For Widestrike cotton, there was a reduction in yield when 100% of white flowers were infested in 2005, but not in 2006. There was a significant relationship for cumulative numbers of white flowers infested on seedcotton yield of Bollgard II during one of the 3 yr of the experiment. The regression equation during that yr had a slope of -0.77. No significant relationships were observed for cumulative numbers of white flowers infested on yields of Widestrike cotton. Results of the current experiment suggest bollworms will rarely cause yield losses of Bollgard II and Widestrike cotton. Future research will need to focus on developing specific thresholds for bollworms on Bollgard II and WideStrike cotton.