The minefield of genetic engineering will pose many dilemmas before it becomes commonplace. Surprisingly, even those advocating genetic engineering in monocultured crops are calling for alternating belts of unmodified crops to be sown as well in order to provide refuge areas for insects, including the pest species. This apparently counter-intuitive plea was made recently by the US Environmental Protection Agency because of the recognition that pests could adapt to the modified crops and any benefits would be lost. In many of these crops, genetic engineering is employed to insert genes from other species thereby using a natural product in order to obtain an otherwise unnatural advantage. In this case, the inserted genes come from a soil bacterium and express a potent insecticide.
Insects eating the modified crops usually die.
The few survivors will have immunity. If they breed sufficiently, the advantage will be lost because a new strain of insect, tolerant of the insecticide, will have been created. The effects possibly exerted remain unknown. Having unprotected crops nearby means many non-immune insects could swamp the few survivors at breeding time. Therefore nearly all new insect progeny remain susceptible, the modified crop gives good yields and the unmodified crop is sacrificed. .