By Rick Callahan
5:30 AM Saturday Dec 31, 2011
When it was introduced in 2003, "Bt corn" seemed like the answer to farmers' dreams. It would enable growers to bring in bountiful harvests using fewer chemicals because the corn naturally produced a toxin to poison a major pest, the western corn rootworm.
The hybrid was such a swift success that it and similar varieties now account for 65 per cent of all US corn hectares - grain that ends up in thousands of everyday foods such as cereal, sweeteners and cooking oil.
But over the last few summers, rootworms have feasted on the roots of Bt corn in parts of four Midwestern states, suggesting that some of the insects are becoming resistant to the crop's pest-fighting powers.
Scientists say the problem could be partly the result of farmers who have planted Bt corn year after year in the same fields.
Most farmers rotate corn with other crops in a method long used to curb the spread of pests, but some have abandoned rotation because they need extra grain for livestock or have grain contracts with ethanol producers.
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