Crop Biotech Update

Insect Resistance to Bt Crops Can Be Predicted and Managed

November 27, 2009

Existing theories and strategies can be used to predict, monitor, and manage insect resistance to Bt crops. This was the conclusion of a study Field-Evolved Insect Resistance to Bt Crops: Definition, Theory, and Data published in the December 2009 issue of  the Entomological Society of America's Journal of Economic Entomology. 

The study analyzed insect resistance data from five continents, as reported in 41 studies. Dr. Bruce E. Tabashnik, lead author, says that "Resistance is not something to be afraid of, but something that we expect and can manage if we understand it. Dozens of studies monitoring how pests have responded to Bt crops have created a treasure trove of data showing that resistance has emerged in a few pest populations, but not in most others. By systematically analyzing the extensive data, we can learn what accelerates resistance and what delays it. With this knowledge, we can more effectively predict and thwart pest resistance."

Among the authors' conclusions are:

  •  The refuge strategy (growing non-Bt crops near the Bt crops) can slow the evolution of insect resistance by increasing the chances of resistant insects mating with non-resistant ones, resulting in non-resistant offspring.
  • Crops that are "pyramided" to incorporate two or more Bt toxins are more effective at controlling insect resistance when they are used independently from crops that contain only one Bt toxin.
  • Resistance monitoring can be especially effective when insects collected from the field include survivors from Bt crops.
  • DNA screening can complement traditional methods for monitoring resistance, such as exposing insects to toxins in the lab.
  • Despite a few documented cases of field-evolved resistance to the Bt toxins in transgenic crops, most insect pest populations are still susceptible.

See the Entomological Society of America's press release at