快猫短视频

THE spread of insect resistance to the toxins in genetically modified crops
will not be slowed by encouraging pests to live in 鈥渞efuges鈥� of weeds around the
edges of farmers鈥� fields, say French scientists. The vulnerable insects that
live there just don鈥檛 mix with their resistant neighbours, the investigators
have found.

Bt maize produces a bacterial toxin that kills pests such as the European
corn borer. But if it鈥檚 used extensively, insects rapidly become immune to the
toxin. The solution in the US, where Bt maize is routinely grown, has been to
plant non-GM refuges near the modified plants. Insects feeding there should
remain sensitive to the toxin, and will help prevent resistance by breeding with
insects emerging from the Bt maize.

Farmers and environmentalists argue about the size and location of the
refuges. At the moment, refuges are planted with non-Bt maize, but corn borers
feed on many plants鈥� including the weeds that often surround
fields鈥攕o it was hoped that these too might act as natural refuges. It
would then be unnecessary to plant areas of non-Bt maize.

Denis Bourguet from the French National Institute of Agricultural Research in
Guyancourt and his colleagues measured the frequencies of different gene
variants in corn borer populations living on maize, sagebrush and hops. Gene
frequencies in corn borers from sagebrush and hop were indistinguishable, but
those in maize-eating insects were different, suggesting the populations were
not mixing freely between the crops and weeds. 鈥淚t won鈥檛 help to have sagebrush
growing at the side of the fields,鈥� says Bourguet.

David Andow of the University of Minnesota agrees with the researchers鈥�
conclusion. 鈥淭hese two wild hosts will probably not be useful as refuges for Bt
corn,鈥� he says, although he would like to see the work repeated in other
locations.