Journal of Economic Entomology (2021) 114, 2493-2504

Wilfrid Calvin, Fei Yang, Sebe A. Brown, Angus L. Catchot, Whitney D. Crow, Donald R. Cook, Jeffrey Gore, Ryan Kurtz, Gustav M. Lorenz, Nicholas J. Seiter, Scott D. Stewart, Tyler Towles and David L. Kerns (2021)
Development of economic thresholds toward bollworm (Lepidoptera: Noctuidae), management in Bt cotton, and assessment of the benefits from treating Bt cotton with insecticide
Journal of Economic Entomology 114 (6), 2493-2504
Abstract: Widespread field-evolved resistance of bollworm [Helicoverpa zea (Boddie)] to Cry1 and Cry2 Bt proteins has threatened the utility of Bt cotton for managing bollworm. Consequently, foliar insecticide applications have been widely adopted to provide necessary additional control. Field experiments were conducted across the Mid-South and in Texas to devise economic thresholds for foliar insecticide applications targeting bollworm in cotton. Bt cotton technologies including TwinLink (TL; Cry1Ab+Cry2Ae), TwinLink Plus (TLP; Cry1Ab+Cry2Ae+Vip3Aa), Bollgard II (BG2; Cry1Ac+Cry2Ab), Bollgard 3 (BG3; Cry1Ac+Cry2Ab+Vip3Aa), WideStrike (WS; Cry1Ac+Cry1F), WideStrike 3 (WS3; Cry1Ac+Cry1F+Vip3Aa), and a non-Bt (NBT) variety were evaluated. Gain threshold, economic injury level, and economic thresholds were determined. A 6% fruiting form injury threshold was selected and compared with preventive treatments utilizing chlorantraniliprole. Additionally, the differences in yield from spraying bollworms was compared among Bt cotton technologies. The 6% fruiting form injury threshold resulted in a 25 and 75% reduction in insecticide applications relative to preventive sprays for WS and BG2, respectively. All Bt technologies tested in the current study exhibited a positive increase in yield from insecticide application. The frequency of yield increase from spraying WS was comparable to that of NBT. Significant yield increases due to insecticide application occurred less frequently in triple-gene Bt cotton. However, their frequencies were close to the dual-gene Bt cotton, except for WS. The results of our study suggest that 6% fruiting form injury is a viable threshold, and incorporating a vetted economic threshold into an Integrated Pest Management program targeting bollworm should improve the sustainability of cotton production.
(The abstract is excluded from the Creative Commons licence and has been copied with permission by the publisher.)
(original language: English)
Full text of article
Database assignments for author(s): Ryan W. Kurtz, Nicholas J. Seiter, David L. Kerns

Research topic(s) for pests/diseases/weeds:
control - general
biocontrol - natural enemies
Research topic(s) for beneficials or antagonists:
general biology - morphology - evolution

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Pest and/or beneficial records:

Beneficial	Pest/Disease/Weed	Crop/Product	Country	Quarant.
	Helicoverpa zea	Cotton (Gossypium)	U.S.A. (mid S)
Bacillus thuringiensis genes in crops (entomopathogen)	Helicoverpa zea	Cotton (Gossypium)	U.S.A. (mid S)