Insect Birth Control Strategy To Zap Cotton Pests
Using pests as part of an insect birth control program helps to get rid of them, UA researchers find. A new approach that combines the planting of pest-resistant cotton and releasing large numbers of sterile moths has virtually eliminated of the world's most destructive cotton pests from Arizona.
The novel control strategy, published in the November 7 advance online publication of the journal
Nature Biotechnology, has allowed growers to maintain high cotton yields without spraying insecticides to control pink bollworm.
"We are running the pesticide treadmill in reverse," said Bruce Tabashnik, department head of entomology in the UA's College of Agriculture and Life Sciences. "Our new approach has resulted in huge environmental gains. We are using cutting-edge technology to create sustainable cotton farming practices."
The new approach is part of a multi-pronged team effort to eradicate pink bollworm from the southwestern US and Mexico, in which Tabashnik and his coauthors play a leading role.
Caterpillars of the pink bollworm (Pectinophora gossypiella) are one of the most detrimental pests to cotton production worldwide. First detected in the US in 1917, this invasive insect species wreaked havoc on Arizona's cotton growing industry, with larvae infesting as many as every other cotton boll (the fruit capsule containing the precious threads).
The eradication program staff reared large numbers of pink bollworms, sterilized them, and released the sterile moths into cotton fields where they could block reproduction of the wild insects.
"When a sterile moth mates with a fertile wild moth, the progeny won't be fertile," Tabashnik said. "The sterile insects soak up the reproductive potential of the wild population. If you have a high enough ratio of sterile to wild moths, you can drive the reproduction of the wild population to zero."
A limitation of the sterile release strategy is that extremely large numbers of sterile insects can be necessary to block reproduction of the wild population, according to Tabashnik. "It becomes a question of logistics: Can you deliver enough sterile insects to overwhelm the wild population?"
Since the eradication program began in Arizona in 2006, pink bollworm populations have declined dramatically. In 2009, only two pink bollworm larvae were found in 16,600 bolls of non-Bt cotton screened across the state. From 2005 to 2009, the pink bollworm infestation rate dropped by 99.9 percent. Along with the decline, insecticide sprays fell to historic lows. Whereas Arizona cotton growers lost $18 million per year to pink bollworm management between 1990 and 1995, that cost plummeted to an average of $172,000 per year between 2006 and 2009.
Compared with 1995, Arizona growers' insecticide use against all cotton pests, including those not killed by Bt cotton, decreased by 88 percent, saving $200 million between 1996 and 2009.
To test the idea of delaying resistance with sterile insect releases, the researchers conducted computer simulations and analyzed more than a decade of field data from before and after deployment of this strategy statewide in Arizona.
The eradication program and associated research is a partnership among the growers, their organizations, the USDA and the UA, including Peter Ellsworth of the UA's Cooperative Extension Service.
"This has been a team effort from the get-go, with the growers essentially one hundred percent on board," Tabashnik pointed out. "You can tell by the long list of authors -- this wouldn't have happened without teamwork."
Photo: Pink bollworm moth poised on a cotton plant.
Photo: Bruce Tabashnik holding a petri dish with pink bollworm larvae.
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