Recognizing that resistance is not "all or none" and that intermediate levels of resistance can have a continuum of effects on pest control, the authors describe five categories of field-evolved resistance and use them to classify 13 cases of resistance to five Bt toxins in transgenic corn and cotton based on monitoring data from five continents for nine major pest species.
Emerging resistance of the western corn rootworm to Bt corn exemplifies the urgent need for well-defined resistance terms. The cost of this insidious beetle to U.S. corn growers has been estimated at one billion dollars annually. In 2003, to reduce costs and cut back on soil insecticides, U.S. farmers began planting Bt corn that kills rootworms.
"The first evidence of rootworm resistance to Bt corn was discovered in Iowa in 2009," said Dr. Bruce Tabashnik, the study's lead author and head of the entomology department at the University of Arizona. "Nearly five years later, the resistance has spread but decisive regulatory action by the EPA is still stalled, in part because an effective definition of resistance is lacking in this case."
Although some scientists have expressed concern that reports of pest resistance to Bt crops provide 'ammunition' to anti-biotech activists, Tabashnik said "Pests are remarkably adaptable. They usually evolve resistance to any tactic that's used repeatedly to control them, so this problem is not limited to transgenic crops.
|Contact: Dr. Bruce Tabashnik|
Entomological Society of America