New Processes Reduce Cotton Pests Without Pesticide

Pink Bollworm Moth (University of Arizona)

Researchers at University of Arizona in Tucson discovered a new strategy for controlling cotton pests that combines the planting of pest-resistant cotton and releasing large numbers of sterile moths. The scientists say this approach has virtually eliminated the pink bollworm, one of world’s most destructive cotton pests, without spraying insecticides.

Caterpillars of the pink bollworm (Pectinophora gossypiella) are a detrimental pest to cotton production worldwide. First detected in the U.S. in 1917, this invasive insect species destroyed much of Arizona’s cotton growing industry, with larvae infesting as many as every other cotton boll — the fruit capsule containing the threads.

With the introduction in 1996 of Bt cotton, a genetically engineered crop containing a gene transferred from the bacterium, Bacillus thuringensis, cotton plants gained a protein that kills some, but not all insects. Unlike typical broad-spectrum insecticides, which kill most insects, pests or not, the Bt toxin only targets certain insect species. Pink bollworm caterpillars that eat Bt cotton die before becoming adults and therefore do not reproduce.

Much like antibiotics, Bt crops have suffered from pests evolving resistance to the toxins, sometimes very rapidly. University of Arizona entomology professor Bruce Tabashnik says the usual strategy to fight resistance of creating refuges with non-modified cotton can manage the pest population, but not eradicate it.

As an alternative to refuges, Tabashnik and his team 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,” says Tabashnik. “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.”

While the release of sterile insects to control pests is not new, this is the first time the sterile insect technique has been used in concert with a Bt crop. Tabashnik’s group discovered that since the tests of combining of Bt cotton and sterile moths started in 2006, pink bollworm survival has become virtually zero.

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