Bt-transgenic crops: Just another pretty insecticide or a chance for a new start in resistance management?

Transgenic insect-resistant crops carrying genes from Bacillus thuringiensis were grown commercially for the first time in 1996 amid considerable public controversy about resistance management. Several resistance management strategies have been proposed for Bt-transgenic crops. The most promising with currently available technology is the use of refuges of non-transgenic crops, augmented where possible with high toxin expression in the plant and avoiding mosaics of different toxins and pesticides. One problem is that the refuge sizes that are seen as commercially and practically acceptable are generally too small to provide a comfortable margin for the delay of resistance. A promising long-term strategy for delaying resistance, and one which is more forgiving on refuge size, is the pyramiding of two or more insecticidal genes in the same plant. The critical limiting factor to resistance management for transgenic crops will be implementation, which will require cooperation among companies.