The insect specific fungus, Beauveria bassiana (Balsamo) Vuillemin, ATCC 74040, formulated as Naturalis-L, was highly effective for control of cotton insects in an integrated pest management system (IPM) for cotton in the Lower Rio Grande Valley of Texas in 1993. Naturalis-L effectively controlled early season populations of the boll weevil, Anthonomus grandis Boheman, and cotton fleahopper, Pseudatomoscelis seriatus (Reuter). Populations of beneficials were significantly higher in fields treated with Naturalis-L than in fields treated with conventional insecticides. Full season control of insects was obtained for the third consecutive year in fields treated with Naturalis-L only. The lint yield in the IPM program with Naturalis-L was 996 lbs per acre, with Naturalis-L only, 851 lbs and conventional insecticides, 951 lbs.