Pests' steady exposure to Bt crops has prompted concern that resistance could develop more quickly than some expect.
But a new study funded by the UDSA and the Special Research Projects for Developing Transgenic Plants in China and completed by Cornell University has a counter to that concern: natural pests.
Cornell research shows that the combination of natural enemies, such as ladybeetles, with Bt crops delays a pest's ability to evolve resistance to these insecticidal proteins.
"This is the first demonstrated example of a predator being able to delay the evolution of resistance in an insect pest to a Bt crop," said Anthony Shelton, a professor of entomology at Cornell University's New York State Agricultural Experiment Station in Geneva, N.Y., and a co-author of the paper.
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Bt is a soil bacterium that produces proteins that are toxic to some species of caterpillars and beetles when they are ingested, but have been proven safe to humans and many natural enemies, including predaceous ladybirds. Bt genes have been engineered into a variety of crops to control insect pests.
Since farmers began planting Bt crops in 1996 with 70 million hectares planted in the United States in 2012, a Cornell announcement said, there have been only three clear-cut cases in agriculture of resistance in caterpillars, and one in a beetle.
"Resistance to Bt crops is surprisingly uncommon," Shelton comments.
To delay or prevent insect pests from evolving resistance to Bt crops, the U.S. Environmental Protection Agency promotes the use of multiple Bt genes in plants and the practice of growing refuges of non-Bt plants that serve as a reservoir for insects with Bt susceptible genes.
"Our paper argues there is another factor involved: the conservation of natural enemies of the pest species," said Shelton. These predators can reduce the number of potentially resistant individuals in a pest population and delay evolution of resistance to Bt.