Effectiveness of Transgenic Bt Cottons Against Noctuids in the Lower Rio Grande Valley of Texas

Abstract. The comparative efficacy of Bacillus thuringiensis (Berliner) Bollgard, Bollgard II, WideStrike, and non-Bt expressing cotton, Gossypium hirsutum L., for control of the noctuid complex of bollworm, Helicoverpa zea (Boddie); fall armyworm, Spodoptera frugiperda (J. E. Smith); beet armyworm, Spodoptera exigua (Hübner); and cabbage looper, Trichoplusia ni (Hübner); was evaluated in the Lower Rio Grande Valley of Texas during 2004–2008. When noctuids were abundant, leaves or fruit were significantly less damaged and fewer live larvae were found on Bollgard II cotton compared with non-Bt cotton throughout the growing season. With few to moderate Lepidoptera, cotton with either of the two Bt traits had similar damage. One insecticide application to cotton with Bollgard, Bollgard II, WideStrike, or non-Bt traits resulted in significantly fewer bollworm and beet armyworm larvae and less damage on fruiting structures compared to nontreated cotton. Beet armyworm larval survival and damage to leaves on non-Bt cotton were 3.6-fold greater than on Bollgard II or WideStrike cotton and 1.5-fold greater than on cotton varieties with the Bollgard trait.