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Yves Carrière's holistic approach to pest control

AAAS Fellow Yves Carrière's research on bug resistance gives farmers practical strategies in planning crops to maximize insecticide effectiveness. (Photo: Lara Herrington Watson)

AAAS Fellow Yves Carrière is something of an entomological Pied Piper. He is experimenting with methods to "lure" crop pests to pesticide-free zones or 'refuges' so that their offspring will remain biologically vulnerable to insecticides on nearby crops. 

A soft-spoken professor of entomology at the University of Arizona, Carrière's main goal is to solve problems within their broad, ecological context. His primary targets are the crop-damaging cotton bollworm and sweet potato whitefly.

His holistic approach to pest control is called landscape ecology, which takes into account the entire ecology affecting a specific crop or pest, because "it's essential to know how ecological processes are affected by local and regional factors," Carrière says.

These research methods only became possible in the last couple of decades, through new technologies, although the importance of a holistic approach was recognized by ecologists as early as the 1950s. 

"We did not have GPS and other mapping technologies; we did not have computers to process large data sets, or many of the statistical tools available now," Carrière says. "Often breakthroughs in science happen when the technology meets the theory. This is a great example of that."

The approach also requires highly organized collaboration and teamwork. Carrière directs complex research among several teams and relies on multiple labs to complete GIS mapping, data analyses and genetic testing of bug samples.

His research has focused on protecting Bt crops, so named because they contain genes of the Bacillus thuringiensis bacterium, a natural insecticide producer. Bt has been used for decades in organic farming, and today it is one of the most common method of pest control. It is permitted—and popular—in organic farming, because it occurs naturally in soil.

"There are many reasons farmers like Bt crops," Carrière says. "One, they can stabilize or increase yields and profits, so farmers are less worried about unpredictability. Also, they can reduce the amount of insecticides [they] spray, so it's simpler to grow the crop."

The problem with continually using Bt and other insecticides is that insects affected by them can evolve resistance. When this happens, it eliminates the benefits of the insecticides and threatens the sustainability of Bt crops and crops that rely on other insecticides.

So far, several pest species have evolved resistance to a Bt crop, including the Western corn rootworm, the fall armyworm and the cotton bollworm. This resistance results in lower crop viability, Carrière says, which "shows that evolution of resistance is a real agricultural threat."

In response to this threat, the EPA introduced a plan to slow the evolution of resistance. Termed a "refuge strategy," the plan entails spacing out fields of genetically modified crops, leaving insecticide-free spaces, or refuges, between them. In practice, a farmer might plant fields of genetically modified corn interspersed with refuge fields of untreated corn.

"These untreated plants act as a refuge, a breeding ground, for insects. Without exposure to such insecticides, pests cannot evolve resistance to them," Carrière explains. Remaining susceptible to insecticides, these pests help keep their offspring, and the whole pest population, vulnerable to crops treated with Bt or other insecticides.

While computer models suggested the refuge strategy would work, there was little empirical evidence backing it. So Carrière started an eight-year field study using landscape ecology to test whether it would, in fact, keep pests from developing resistance to insecticides.

To understand how one crop impacted another, he and his colleagues used satellites and GPS technology to map all crops in an entire 4,000-square-kilometer area in south central Arizona.

"We mapped fields of untreated alfalfa, melons and cotton, and cotton treated with the insecticide pyriproxyfen, an environmentally friendly insecticide, instead of Bt," he says. They then captured live samples of the sweet potato whitefly from various fields and tested resistance to pyriproxyfen.

Carrière's research ultimately confirmed the EPA's resistance management strategies, giving farmers practical strategies to maximize insecticide effectiveness.

"We successfully identified untreated cotton as the only crop that actually does work as a refuge plant in the field," Carrière says.

Carrière has also been an advocate of Bt crops as a viable solution in organic farming. While Bt protein has long been used as insecticide spray, critics have objected to its use in genetically engineered seeds, citing concerns about potential long-term health problems and environmental repercussions.

Carrière, who performed a review on the environmental impacts of these transgenic crops with the National Academy of Sciences, doesn't see a problem with transgenic crops. He argues that genetically modified crops are not only benign, but hugely beneficial.

 "From an environmental point of view, so far, the impacts of Bt crops are largely positive," Carrière says.

The increased use of these crops has caused regional declines in some pests, which benefits both farmers who use Bt crops and farmers who don't. Bt cotton, for example, was used in conjunction with the release of sterile insects to eradicate pink bollworm, a main pest of cotton in the western United States.

"The eradication program eliminated insecticide sprays against pink bollworm and reduced its population density to near zero in Arizona. This would not have been possible without Bt cotton," says Carrière.