Efficacy and Field Performance of Bt Cotton in Louisiana

The bollworm (BW), Helicoverpa zea (Boddie), is one of the most economically important insect pests of Midsouth cotton. In 1996, the first Bt cotton containing the Cry1Ac protein was commercialized for control of fruit and foliage feeding worms. Currently, Bt proteins used in transgenic cotton are categorized into three groups: Cry1, which contains Cry1Ab, Cry1Ac, and Cry1F; Cry2, which includes Cry2Ab and Cry2Ae; and Vip3a. The corresponding cotton varieties include: Bollgard 1 (Cry1Ac), Bollgard 2 (Cry1Ac + Cry2Ab), Widestrike (Cry1Ac + Cry1F), Twinlink (Cry1Ab + Cry2Ae), Widestrike 3 (Cry1Ac + Cry1F + Vip3a), Bollgard 3 (Cry1Ac + Cry2Ab + Vip3a) and Twinlink Plus (Cry1Ab + Cry2Ae + Vip3a). However, extensive and constant exposure of BW to these Bt proteins not only in transgenic cotton, but also in corn, appears to have resulted in a shift towards a reduction in susceptibility in cotton. In 2017-18, all commercially available cotton technologies experienced field control failures in various cotton growing regions in Louisiana. Failure of the Bt technologies, to control BW, resulted in costly applications of diamide insecticides to control larvae and broad-spectrum insecticides to control ovipositing adult moths.