Steps to stop spread of resistant corn rootworms
Planting transgenic corn that produces multiple toxins can also fight resistance, but that technique is less effective if the insects already resist one of those toxins, Cullen says.
In a parallel situation, several weeds have evolved resistance to glyphosate, the active ingredient in Roundup, a herbicide applied to millions of acres of corn and soybean.
In all cases, if only resistant organisms can survive and multiply, resistance becomes widespread. The threat of resistance among insect pests is one reason that organic farmers, who sometimes rely on Bacillus thuringiensis to kill insects, opposed the transgenic Bt crops.
As the threat of insect resistance grows, Cullen says, farmers and their advisors need to take the issue seriously, by planting the appropriate refuges and choosing seeds carefully based on knowledge of insect pest pressure on the farm.
If resistance arises, Cullen suggests rotating to other Bt corn traits, or using conventional seeds and insecticides. This can be difficult because many top corn varieties are only sold as transgenics, and modern corn-planters often lack equipment for applying insecticide.
"Entomologists, biologists and farmers know that when you use one tactic for pest management, whether it's an insecticide or a Bt trait, insects can adapt," says Cullen. "The letter to EPA is an urgent reminder that an integrated approach will serve us best in the long term."
The letter to the EPA is at http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OPP-2011-0922-0013