Jan. 5, 2009 -- Corn syrup, popcorn, corn on the cob, ethanol: The United States is by far the largest corn producer in the world, and the crop is vital to the national economy. As the climate warms, however, corn is likely to suffer from a boom in crop-hungry insects, according to new projections.
At our current rate of greenhouse gas emissions, several of the main pests that target corn will increase in number and expand their ranges by the end of the 21st century, the study suggests.
Already, grain supplies are low and prices are high, said Noah Diffenbaugh, a climate scientist at Purdue University in West Lafayette, Ind. "Increased pressure from pests could exacerbate those conditions," he said, as farmers struggle to control the onslaught of corn-chomping insects.
More than 90 species of insects target corn. But for their study, Diffenbaugh and colleagues focused on four of the bugs that cause the most damage: the European corn borer, the corn earworm, and two kinds of corn rootworm beetles. Every year, American corn producers spend billions of dollars battling these pests.
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From decades of previous studies, scientists knew exactly how each insect responds to temperature changes. Armed with that information, Diffenbaugh's group looked at recent, detailed temperature measurements from around the United States. They also analyzed high-resolution climate model projections.
Together, the data allowed the scientists to estimate where in the country each pest lives now, and where each pest might thrive in the future. Climate projections were based on the concentration of carbon dioxide in the atmosphere.
Right now, atmospheric carbon dioxide concentration is about 380 parts per million, Diffenbaugh said. If greenhouse gas emissions continue to increase at their current rate, that number could rise to 800 ppm by the end of the century, according to one scenario suggested by the Intergovernmental Panel on Climate Change.
Given that scenario and its resulting temperature changes, all four corn pests will spread into new territories, the study found. The insects will also probably be able to squeeze an extra generation into the breeding season -- meaning more pests in more places.
The study, which appeared in November in the journal Environmental Research Letters, found an especially dramatic expansion for the corn earworm. The bug is poised to move into the upper Midwest, parts of the central coast of California, and Washington's Columbia River Basin, among other places. All of those areas are currently too cold for overwintering.
An earworm boom is particularly worrisome because the insect eats other crops, too. The pest is also highly resistant to insecticides and difficult to control.
"Our results indicate that the costs of pest management could go up," Diffenbaugh said. "New pest management strategies may be required."
Farming is already tough work, said Christopher Field, Director of the Department of Global Ecology at the Carnegie Institution in Stanford, Calif. As warming alters the way plants and animals interact, farming will only grow tougher.
"The paper is not saying that things are going to be great or that things are going to be terrible," Field said. "It's saying things are going to get more complicated and more multi-factored as the climate changes."
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