Crop Pests Abroad Resistant to Controls

A UA researcher says pests that destroy corn and cotton have developed resistance to the most effective and benign method to kill them.

Bruce Tabashnik, University of Arizona research entomologist, said resistance does not pose an immediate threat to the vast acreages of Bt corn and cotton grown with genetically introduced Bt toxins, but argues for continued monitoring.

Tabashnik's study, published this month in the Journal of Economic Entomology, analyzed 41 reports from five continents. It uncovered "strong evidence" of naturally evolved resistance in an obscure journal, an unpublished government report and multiple studies that he said failed to reach the obvious conclusions their data supported.

Officials for Monsanto, which dominates development of the world's genetically modified crops, concede resistance to Bt developed in isolated fields in South Africa and Puerto Rico, but dispute Tabashnik's other claims.

Scientists have long expected corn and cotton pests to develop resistance to Bacillus thuringiensis, or Bt.

Since their introduction as transgenic seed products in 1996, various Bt products have proved effective in reducing damage to cotton bolls and corn crops and have let growers reduce the amount of pesticides sprayed on crops worldwide.

Bt is a naturally occurring soil bacteria that is used by organic farmers to ward off pests. The U.S. Department of Agriculture says "use of Bt cotton reached 65 percent of planted cotton acreage in 2009 and Bt corn use grew from about 1 percent of corn acreage in 1996 to 63 percent in 2009."

Worldwide, about 25 percent of corn and cotton are grown from Bt seed, said Tabashnik, and the incidence of resistance is very small.

Contact name: 
Bruce Tabashnik, Department of Entomology
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Released date: 
Jan 26 2010