19 December 2008

Study: Global warming could boost crop pests

Chicago Tribune.com from Associated Press, December 16, 2008

WEST LAFAYETTE, Ind. - The milder winters and longer growing seasons predicted under global warming forecasts could boost populations of crop-munching insects in the Midwest's corn country over the coming decades, new research suggests.

Purdue University scientists said their findings could mean lower yields for corn and other crops -- and higher pest control costs for farmers -- as the climate warms up.

The researchers examined how global warming could impact winter's lowest readings and lengthen the growing season across the continental U.S. based on what the study's lead author said is a conservative climate change model.

They then used that data to determine the regions where four insects that feed on corn and other crops could survive until spring, based on forecasts of warmer winter readings.

All four pests, they concluded, would expand their ranges into areas where they are currently not a problem -- or not found at all -- because each would have more spring survivors and more time in the spring and summer to feed, mate and reproduce.

"The range of each of these pests expanded -- not only in areas of the Midwest where corn is the dominant crop but also in areas of the western U.S.," said Noah Diffenbaugh, a Purdue associate professor of earth and atmospheric sciences.

Diffenbaugh, who led the study, said the warmer readings could mean the insects will be capable of producing up to three generations of their kind in a single growing season, filling fields with their hungry offspring.

The findings were recently published online in the Environmental Research Letters.

Diffenbaugh said he knows of no other scientists who have looked at specific insects' response to global warming in the same way his team did.

The key to the team's work, he said, was a high-resolution computer simulation plotting climate changes over the lower 48 states between now and the end of the 21st century.

By 2100, some climate models predict that the amount of carbon dioxide in Earth's atmosphere will have doubled, causing significant increases in global temperatures.

The computer simulation was paired with data showing the lowest survivable temperatures for the corn earworm, the European corn borer, northern corn rootworm and western corn rootworm.

Diffenbaugh said his team predicted the biggest end-of-the-century expansion among the corn earworm, which feeds not just on corn but a wide range of crops that make it a threat well outside the nation's corn states.

The corn earworm is also migratory and pesticide resistant, he said.

"It's clear that we have to look at very fine detail in order to really understand what might happen in the future," he said. "Simply looking at global mean temperatures and gross measures of climate change we could potentially miss a lot of the details that really will determine what human civilization experiences."

Purdue entomologist Christian Krupke said none of the insects looked at as part of the study would be hurt by the higher temperatures expected under global warming. Cold, not heat, is what curtails the pests' success, he said.

"Increases in temperatures, even summer temperatures, generally benefit these pests," Krupke said.

Purdue agricultural economist Corinne Alexander and Utah State University ecological scientist Michael White also took part in the study.

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