Entomologists across the Midwest and South say a commonly used strategy to preserve the potency of GE corn that makes its own insect-repelling toxins, known as “refuge in a bag,” “may actually increase the risk of Bt resistance in above-ground insects, particularly in the southern United States,” reports DTN. “It’s not the panacea we thought it would be,” said entomologist Pat Porter of Texas A&M.
The idea behind “refuge is a bag” is simple: To keep pests from developing a tolerance for GE corn that contains the Bt gene, a portion of each field is planted with non-Bt seed. Corn earworms, fall armyworm and other corn-damaging insects would constantly interbreed with insects that grew up on non-Bt plants and had no resistance to pass along to offspring. With that in mind, seed companies sell bags of seeds that include 5 percent or 10 percent non-Bt seed, ensuring that every field has its own “refuge” of non-Bt corn.
“However, corn plants pollinate each other freely in a field,” says DTN, so when the ears form, the kernels on the non-Bt plants include a smattering of Bt toxins. It’s a Bt buffet of low or moderate doses, a naturally occurring insecticide, that allows the insects to evolve resistance. The problem was identified more than a decade ago, but only in the past year or so have researchers begun to quantify the threat.
GE seed that includes the Bt trait was planted on three-fourths of U.S. corn land in 2013, says a USDA report.