Innovative Way to Keep Bollworms Out of Cotton Fields

By Dennis O'Brien
December 28, 2010

ARS scientists in California and Arizona are part of a team that's found an innovative way to keep pink bollworms out of cotton fields in the Southwest and reduce both insecticide spraying and the threat of resistance to genetically modified crops. Their strategy: combining the use of Bt cotton with the release of a sterile version of the voracious pest.

The introduction in 1996 of Bt cotton—which produces insecticidal proteins from the bacterium Bacillus thuringiensis—has greatly reduced pink bollworm populations in Arizona. But the pink bollworm is still one of the world's most destructive cotton pests, and it's developed resistance to Bt cotton in India.

To slow the evolution of resistance by the pest, growers in Arizona were required to set aside "refuges" of conventional cotton that promote survival of pink bollworm caterpillars susceptible to Bt.

But growers were frustrated with the expense and crop losses associated with refuges, so they came up with a plan to replace refuges with releases of sterile pink bollworm moths over Arizona's cotton fields. The U.S. Environmental Protection Agency approved the plan in 2006.

The sterile insect technique (SIT) was originally developed by ARS scientists to control screwworms. This technique has been extensively studied and is now used to control Mediterranean fruit flies and other pests.

In the pink bollworm study, ARS scientists Mark Sisterson, Jeffrey A. Fabrick and their colleagues found for the first time that the SIT can be used to effectively suppress resistance to Bt crops by pests over a large area. Sisterson works in our ARS Crop Diseases, Pests and Genetics Research Unit in Parlier, Calif. and Fabrick works in our ARS ARS Arid-Land Agricultural Research Center in Maricopa, Ariz. ARS is the principal intramural scientific research agency of the U.S. Department of Agriculture (USDA), and this research, published in Nature Biotechnology, supports the USDA commitment to agricultural sustainability.

Our partners on this project include scientists from the University of Arizona, the Arizona Cotton Research and Protection Council and USDA's Animal and Plant Health Inspection Service (APHIS).

Sterile pink bollworm moths were released over all of the state's cotton fields from airplanes two to three times per week for four years. About 2 billion lab-reared moths were released each year during the May-to-October cotton growing seasons from 2006 through 2009. Researchers have been tracking infestation rates in Arizona's 200,000 acres of cotton for the past 13 years and the releases were part of a much larger eradication program that extends from Texas to California and includes parts of northern Mexico.

In the years before the eradication program, about 40 percent of Arizona's cotton acreage was set aside for refuges. But during the four years of the study, growers were able to reduce refuge acreage so that by 2009, it was down to 3.1 percent.

The results show that infestation rates dropped from 15 percent in 2005 to a negligible level in 2009. Tests on field-collected pink bollworms did not detect resistance to Bt cotton. Yield losses and spraying costs also dropped, from about $18 million per year before the eradication program to $172,000 per year from 2006 to 2009. Ideally, the same approach could be used with other pests, but additional research is needed to determine if this is feasible, according to Fabrick.