Scientists in the US have identified a toxin produced by a strain of Bacillus thuringiensis (Bt) which could delay development of resistance to Bt pesticides by insects. Bt produces a class of toxins called CryIV. However, insects had started developing resistance to these toxins. Researchers at the University of California at Riverside tested a strain of Bt that produces another toxin called CryA. This is not very toxic by itself, but enhances the toxicity of CryIV.

The researchers exposed mosquito larvae to a combination of CryA and CryIV. The combination was three to seven times more toxic for mosquitoes that showed no resistance to CryIV, but boosted CryIV's killing power up to 70 times in case of mosquitoes resistant to CryIV ( Proceedings of the National Academy of Sciences , Vol 94).