BT-TRANSGENIC CROPS - JUST ANOTHER PRETTY INSECTICIDE OR A CHANCE FORA NEW START IN RESISTANCE MANAGEMENT

Transgenic insect-resistant crops carrying genes from Bacillus thuring iensis were grown commercially for the fist time in 1996 amid consider able public controversy about resistance management. Several resistanc e management strategies have been proposed for Bt-transgenic crops. Th e most promising with currently available technology is the use of ref uges 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 comm ercially and practically acceptable are generally too small to provide a comfortable margin for the delay of resistance. A promising longter m strategy for delaying resistance, and one which is more forgiving on refuge size, is the pyramiding of two or more insecticidal genes in t he same plant. The critical limiting factor to resistance management f or transgenic crops will be implementation, which will require coopera tion among companies.