Reduction of resistance of Culex pipiens larvae to the binary toxin from Bacillus sphaericus by coexpression of cry4Ba from Bacillus thuringiensis subsp israelensis with the binary toxin gene

The cry4Ba gene from Bacillus thuringiensis subsp. israelensis and the binary toxin gene from B. sphaericus C3-41 were cloned together into a shuttle vector and expressed in an acrystalliferous strain of B. thuringiensis subsp. israelensis 4Q7. Transformed strain Bt-BW611, expressing both Cry4Ba protein and binary toxin protein, was more than 40-fold more toxic to Culex pipiens larvae resistant to B. sphaericus than the transformed strains expressing Cry4Ba protein or binary toxin protein independently. This result showed that the coexpression of cry4Ba of B. thuringiensis subsp. israelensis with B. sphaericus binary toxin gene partly suppressed more than 10,000-fold resistance of C. pipiens larvae to the binary toxin. It was suggested that production of Cry4Ba protein and binary toxin protein interacted synergistically, thereby increasing their mosquito-larvicidal toxicity.