A lyophilized powder spore - crystal complex of a native Bacillus thuringiensis and an aqueous preparation of killed genetically-engineered cells of the bacterium Pseudomonus fluonescens, which contained B. thuringiensis var. tenebrionis endotoxin crystal toxin was tested for their toxicity to larvae and adults of boll weevil, Anthonomus grandis (Boheman). When the two preparations were incorporated into the diet, their toxicity to larvae was similar. The LC₅₀ value for the powder was 2.1 times greater for adults than for first stage larvae, but when this powder was distributed on the surface of the diet, the LC₅₀ values were lower for adults than larvae. When weevils were dipped into the powder, LC₅₀ values were less than those of the diet surface treatment. Regressions were non-significant for mortalities of adults fed on transgenic preparation in diet. Powder preparation showed LC₅₀ of 6,290 mg per ml. diet after 120 h. Slope values for both preparations to adults were flat. An exotoxin of B. thuringiensis, called thuringiensin, was more toxic to adults than the transgenic endotoxin or a mixture of the two. From a cage test foliar sprays of the transgenic preparation showed an inverse relationship of mortality and rates tested, suggesting that as rates increase the boll weevil ingests less. In a field test yields of cotton treated with transgenic preparation were equal to yields of untreated cotton following application of season-long sprays.