Transgenic cotton cultivars engineered to express the Cry1F, Cry2Ab and Cry1Ac toxins from Bacillus thuringinesis, which include WideStrikeŽ (Dow AgroSciences, Indianapolis, IN) and BollgardIIŽ (Monsanto Corporation, St. Louis, MO) brands, have been genetically engineered to produce proteins that, when in the presence of Lepidopteron digestive enzymes, cause microporation of the 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. A greenhouse trial using the transgenic and a non-Bt isoline was set up with multiple nitrogen regimes and a field trial with shaded and non-shaded sections of three different moisture regimes (normal, flooded and drought conditions) were grown in Western Fresno County. 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 ELISA kit specific to each toxin (Strategic Diagnostics, Newark DE). Bioassay results have shown the high-nitrogen plants had greater herbivory and lower insect mortality compared to low-nitrogen plants. Also, the high-moisture/shaded plants were subject to greater herbivory versus their drought-stressed/full sun counterparts. ELISA data has shown decreased toxin production correlated to the increased herbivory and decreased mortality. Environmental conditions play a role in Bt toxin expression with extremes in stresses having the potential to effect pest management programs.