Is This Sustainable Agriculture? Resistance to Engineered Bt Corn on the Rise

Doug Gurian-Sherman, senior scientist, Food and Environment

December 5, 2011

EPA has responded to reports of resistance by one of the worst insect pests of corn, called rootworm. In the past, about a billion dollars’ worth of chemical insecticides per year were used to control this pest in the U.S.

Starting in 2009, according to EPA monitoring records, possible increases in resistance to the Bt toxin Cry3B were noted. In at least one case, Monsanto appears not to have done needed follow-up studies to determine resistance to its gene.

As I reported earlier, recent research has found strong evidence of Cry3B Bt-resistant rootworms, which is causing failure to control the pest on some farms. One important implication of this is that more chemical insecticides may be used to control the resistant rootworms.

Entomologist Aaron Gassmann (left) of Iowa State University identified rootworms resistant to Bt. Photo by Stephen Ausmus, USDA.

The good news is that the agency is recommending remedial action, maybe for the first time for GE crops, to address the problem. EPA recommends that farmers that experience failure of Bt corn use other means to kill rootworms, rather than exacerbating the resistance problem by continuing to use Bt corn. EPA also recommends beefed-up monitoring of farm fields to better detect resistance.

Unfortunately, EPA’s response may be a case of too little too late. More aggressive action is needed if this problem is to be corralled.

What EPA should do

When EPA was originally considering approving corn containing Cry3B, scientists recommended that only 50 percent of corn acres on a farm contain the Bt gene. This “refuge strategy” was to prevent or delay resistance by increasing the probability that rare resistant insects mated with non-resistant individuals from the non-Bt parts of the farm. The resulting offspring would not be resistant.

EPA instead sided with industry and a minority of scientists and went with a 20 percent refuge, which probably has contributed to the current problem.

EPA should require a larger refuge to delay this problem in areas where resistance has not yet emerged.

EPA should also withdraw the still-smaller five percent refuge for corn that contains two Bts to control rootworm— Cry3B and Cry34/35—so-called “SmartStax”. Where resistance to one Bt already exists, the likelihood of resistance developing to the second Bt is greatly increased.

Widespread loss of both Bts would likely result in greatly expanded use of chemical insecticides.

In discussion with Bruce Tabashnik, entomologist with the University of Arizona and a widely acknowledged expert on Bt, he said that there is currently enough data on rootworm resistance to Cry3B to substantially raise concerns about the use of a five percent refuge for corn containing Cry3B and a second toxin that targets rootworms.

Third, EPA’s focus on remedial action by individual farmers is not likely to prevent the spread of resistance. It is highly likely that the problem is more widespread than has been officially reported. And although rootworm beetles do not move as far as many other insects, they will certainly not stay on individual farms. So EPA needs to consider a regional approach for controlling the spread of resistant insects.

EPA should also convene a Scientific Advisory Panel (SAP) to get more formal input on what to do.

The “root” of the problem—too much corn

The resistant rootworm issue is really just a symptom of a much bigger and more fundamental problem: Midwestern U.S. agriculture is not sustainable. This is because good agroecological practices like alternating, or rotating, crops are not widely practiced due to the drive for shortsighted gains in efficiency.

Crop rotation and other practices greatly reduce pest problems, and rootworm in particular would not even be a big problem if diverse crop rotations were used. But growing demand for ethanol from corn has increased corn acres, pushing more corn-on-corn and fewer corn-soy rotations (let alone more robust rotations that include multiple crops).

Current practices, including genetic engineering, have been pushing us toward greater simplification of our cropping systems—the opposite of diverse, biologically-sound agriculture.

Until we embrace a truly sustainable agriculture, the types of remediation recommended by EPA will merely be a band-aid on a severely wounded patient.

Posted in: Food and Agriculture

About the author: Doug Gurian-Sherman is a widely-cited expert on biotechnology and sustainable agriculture. He holds a Ph.D. in plant pathology.

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