(Page 4 of 4)

“The reason I started working with pea aphids is that they are a really great example of biological control. They don’t die natural deaths,” says Ives, a professor of zoology and entomology. Instead, a suite of predators, including ladybugs and parasitoid wasps, keep the aphids in check. When Harmon and Ives covered alfalfa plots with shrink-wrapped plastic boxes to simulate the temperature spikes that might come from global warming, they found that some aphids did suffer. But aphids that harbored particular bacteria suffered less, suggesting that they might evolve symbiotically as temperatures climb. The researchers also found that one of the aphids’ main predators gave up when there weren’t as many of the bugs around, which means that in a real warming scenario, aphids might actually get a reprieve from predator pressure.

The bottom line, says Ives, is that “you can’t simply add the effects together and come up with a conclusion. There are layers of interactions involved, and when you throw evolution on top of that, it produces something that’s quite complicated. But it’s not entirely unknowable.”

That kind of thinking increasingly is finding its way into agricultural policy decisions. “Really, the U.S. government regulation on insecticidal crops is all about resistance management,” says Ives, who has modeled the effects of various regulation schemes in his research. When the U.S. Environmental Protection Agency approved commercial use of Bt corn—a transgenic crop modified to produce the bacterial toxin Bt to deter plant-eating insects—the agency imposed rules that require farmers using Bt corn to plant at least 20 percent of their fields with non-Bt crops to stall the evolution of Bt-resistant bugs. And while farmers and environmentalists have far from settled their differences on the use of Bt-producing crops, Bt resistance has not yet become an issue.

As for corn rootworm beetles, evolutionary biologists are on the case. Scientists are actively searching for the genes that allow western and northern corn rootworm beetles to independently outwit crop rotation. If those genes are identified, they could help biologists devise new strategies to keep the beetle from spreading or forestall its evolutionary development.

But in Eileen Cullen’s lab, the mysteries of evolutionary biology can’t compete with the present demands of economic reality. “Farmers can’t really wait to find that out,” she says. “We know that the insect is changing, and that means we need to change, too.”

That immediacy was apparent on the day that I joined Sarah Schramm to check insect traps in a soybean field south of Darlington. We arrived in late morning, under a blanket of heavy gray clouds that were just beginning to burn off to reveal the high August sun. As we worked our way through the fields, a cacophony of life buzzed around us: grasshoppers, ladybugs and beetles of various colors and sizes. Schramm pointed out a western corn beetle on a nearby leaf, easily distinguishable with its yellow-and-brown striped wings. I wondered if the beetle was getting ready to lay eggs, a small, solitary act of rebellion against farm management practices that might trigger a series of reactions. To alter crop rotations. To treat or not to. The game is on, and it’s our move.

Pages: 1 2 3 4

Tags: Agriculture, Entomology, Evolution, Genetics, Integrated pest management, Pathogens
Posted in Agriculture, Fall 2009, Food, Main feature, On The Cover | 1 Comment »