Transgenic cotton cultivars engineered to express the Cry1F, Cry2Ab and Cry1Ac toxins from Bacillus thuringinesis, which include WideStrikeŽ and BollgardIIŽ brands, produce proteins that when in the presence of Lepidopteron digestive enzymes, cause microporation of pest gut lining and effectively kill the pest. Variations in environmental conditions may cause changes in Bt gene expression making host plants susceptible to insect damage. Transgenic and a non-Bt isoline were tested in a field trial with shaded and non-shaded sections of three different moisture regimes (normal, flooded and drought). Leaf tissue was used in bioassays infested with Beet Armyworm (Spodoptera exigua) and rated for leaf damage (herbivory) and insect mortality. Additional leaf samples were assayed for toxin production with an ELISA kit specific to each toxin. Results showed that protein expression was not significantly affected by the stresses and that insecticidal activity remained the same.