Bt Corn Reduces Insect Damage

WASHINGTONCorn that has been genetically engineered to produce insect-killing proteins isolated from the soil bacterium Bacillus thuringiensis (Bt) provides significant economic benefits even to neighboring farmers who grow non-transgenic varieties of corn, according to new research published in the journal Science.

Agriculture Secretary Tom Vilsack said the study provides important information about the benefits of biotechnology by directly examining how areawide suppression of corn borers using Bt corn can improve yield and grain quality even of non-Bt varieties.

The researchers estimate that farmers in Iowa, Illinois, Minnesota, Nebraska and Wisconsin received cumulative economic benefits of nearly $7 billion between 1996-2009, with benefits of more than $4 billion for non-Bt corn farmers alone. They estimated that in Minnesota, Illinois and Wisconsin, borer populations in adjacent non-Bt fields declined by 28 to 73 percent, with similar reductions recorded in Iowa and Nebraska.

The researchers attribute the collateral benefits enjoyed by non-Bt farmers to areawide suppression of corn borers stemming from long-term plantings of Bt-protected crops. Potato, green bean and other host crops also stand to benefit from areawide reductions of corn borers. The study also highlights the importance of the use of refuge cropsthe planting of non-Bt crops adjacent to fields of Bt crops, providing a refuge to which the pests can retreatand other strategies to slow the corn borer's ability to develop resistance to Bt and thus maintain the insecticidal proteins' long-term effectiveness.

The Bt proteins provide the plant with a built-in defense against attacks by the larvae of European corn borers and other insect pests. Larvae that ingest the protein soon stop feeding and die, typically within 48 hours. In addition to reducing the use of insecticides that also can endanger beneficial insects, the Bt defense strategy helps prevent harmful molds from gaining entry to the plants via wound sites from borer feeding. Some of these molds, like Fusarium, produce mycotoxins that can diminish the value and safety of the crop's kernels.

Bt corn debuted in 1996, and by 2009 was planted on nearly 55 million acres in the United States, accounting for nearly 63 percent of the total U.S. corn crop of 87 million acres. But no research groups had previously investigated the long-term impact of such plantings on corn borer populations on a regional scale, nor had there been any assessment of whether the use of the crop provided any sort of collateral benefit to adjacent or nearby fields of non-Bt crops.