CAN GLOBAL WARMING CAUSE CATERPILLAR OUTBREAKS?

John Roach for National Geographic
November 16, 2005

Get ready—the killer caterpillars are coming.

As the weather gets wackier in response to rapid global warming, parasitism against caterpillars will decrease, biologists warn in a new study. This will free the caterpillars to devour agricultural fields and strip leafy forests bare.

"That's really of great concern, especially to agricultural systems where we rely on several of these parasites. They keep outbreaks from occurring," said Lee Dyer, a biologist at Tulane University in New Orleans, Louisiana.

Climate scientists have long predicted that variable and unpredictable weather—for example, intense storms one year, drought the next—will increase as the Earth warms.

How that variability will affect ecosystem functions, like the checks and balances in the food chain, has proven difficult to test.

In search of an answer, Dyer and his colleagues examined data on parasitism in caterpillars from 15 caterpillar-rearing programs in different regions.

Some of the programs are in regions with a highly variable climate, while others are in regions that experience the same weather year round.

The biologists found that parasitism, the greatest control for insect pests such as caterpillars, decreases as climate variability increases.

Dyer and his colleagues report their finding in an upcoming edition of the Proceedings of the National Academy of Sciences. An online early edition of the paper was posted Monday on the journal's Web site.

Caterpillar Killers

Terry Root, an ecologist at Stanford University in California who was not part of the research team, said the study issues a serious warning about the vulnerability of human food supplies to global warming.
"The work [my research group has] been doing shows how some of the bird predators are moving north but the caterpillars aren't," she said.

"So if you have parasites [disrupted] and the higher predators like birds moving out, then the unchecked increase in the caterpillar population could be quite devastating [to crops]."