Gene crops may lose power to kill pests

By Aisling Irwin Science Correspondent

The Electronic Telegraph Wednesday, March 5th, 1997

Crops genetically engineered to wipe out pests may lose their "killing power" after a few years, scientists have found. The discovery comes as the use of transgenic plants is becoming more controversial, with campaigners across Europe trying to prevent them from being grown in Britain.

Scientists in America studied proteins produced by certain genetically-altered maize and cotton plants. The proteins belong to a family of insecticides known as Bt toxins, because they are derived from the soil bacterium Bacillus thuringiensis. The scientists studied the effect of some members of the Bt family on a common pest of vegetables, the diamondback moth. They report in Proceedings of the National Academy of Sciences that the moth became resistant to the insecticides much more swiftly than had been predicted.

Many transgenic crops being grown at the moment have been engineered to produce one Bt toxin. Biotechnologists hope that, by using Bt, they have found an environmentally-friendly method of pest control because it leaves other living things, including humans, undamaged. They have been planning to delay the evolution of resistance to Bt by engineering plants to produce several toxins from the Bt family at once so that even if a pest became resistant to one type of Bt it would still be killed by another type.

Professor Bruce Tabashnik, an entomologist at the University of Arizona, USA, who led the research, made two discoveries. First, the moth requires only a single gene mutation for it to become highly resistant to as many as four different Bt toxins. Second, one in a hundred diamondback moths in the strain he studied already carried this gene mutation. Prof Tabashnik said: "The worst case scenario is that in just a few years there would be widespread resistance. The hope is that they will last at least five to 10 years."

Commercial farming of transgenic crops is not permitted in Europe. However, last month approval was given for four new varieties of genetically engineered maize to be imported into Britain as foods.

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