( Genetically modified crops containing t...)Insects develop resistance to engineered crops

A soil bacterium called Bacillus thuringiensis (Bt), whose genes are inserted into crop plants, such as maize and cotton, creates these toxins that are deadly to insects but harmless to humans.

Bt crops were first commercialized in 1996, and scientists, critics and others have been concerned that widespread use of Bt crops would create conditions for insects to evolve and develop resistance to the toxins.

Until now, it has not been shown if neighboring plants producing a single Bt toxic protein might play a role in insect resistance to transgenic crops expressing two insecticidal proteins.

"Our findings suggest that concurrent use of single- and dual-gene Bt plants can put the dual-gene plants at risk if single-gene plants are deployed in the same area simultaneously," said Anthony Shelton, professor of entomology at Cornell's College of Agriculture and Life Sciences and an author of the study, which was posted online June 6 in the Proceedings of the National Academy of Sciences (PNAS) and is in the June 14 print edition of the journal. "Single-gene plants really function as a steppingstone in resistance of two-gene plants if the single gene plants contain one of the same Bt proteins as in the two-gene plant."

Cotton and maize are the only commercial crops engineered with Bt genes. In 2004 these crops were grown on more than 13 million hectares (about 32 million acres) domestically and 22.4 million hectares (more than 55 million acres) worldwide. After eight years of extensive use, there have been no reports of crop failure or insect resistance in the field to genetically modified Bt crops, Shelton said. Still, several insects have develop
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Source:Cornell University News Service