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CORVALLIS, Ore. - A moth that scientists released into the wild in Oregon mountains to control a poisonous invasive weed has unexpectedly evolved to survive the cooler climate, according to a new study.

The cinnabar moth was introduced in the Cascade and Coast ranges 23 years ago to keep tansy ragwort from overtaking clear-cuts. The insect, which in the caterpillar stage has a voracious appetite for tansy leaves and flowers, was originally used only at lower elevations to control the bright yellow weed, which is toxic to horses and cattle.

Researchers were surprised by how quickly the insect evolved to thrive in the cooler, higher elevations and shortened growing season. They found that through natural selection, its life cycle was altered so that now the insect develops from egg to the overwintering pupa more quickly than its cousins in the warmer Willamette Valley.

"It was commonly assumed that if mobile organisms found themselves in unsuitable environments, they would move rather than stay put and evolve," said one of the study's co-authors, Peter McEvoy, an ecologist at Oregon State University who has studied the moth for 35 years.

The findings have relevance in terms of global climate change, said McEvoy, adding that studies show that species naturally shift to higher latitudes and higher elevations as climates warm.

The results are also significant because the cinnabar moth is just one of more than 70 living organisms - most of them insects - used to control more than 30 types of invasive plants in Oregon. If it's changing, others might, too. But that might have negative effects on the environment, McEvoy said. For example, a previously innocuous insect might evolve into an invader that feeds on valuable crops or native plants in its new setting, he said.

However, he added, after more than two decades of close study, researchers have not detected any negative effects from the cinnabar moth on native plants in mountainous environments.

"Harnessing the potential of insects to provide effective control is a great tool in fighting invasive species," McEvoy said. "And whether an organism must evolve to be effective or whether its evolution could threaten desirable plants are two sides of the same coin and warrant careful study."

McEvoy hopes that one day researchers will be able to predict how an insect might evolve. And if they are able to do that, regulators should take into account any potential changes in insects before they approve them for use in controlling undesirable plants, he said.

The study, published in the July issue of Evolutionary Applications, is online at http://hdl.handle.net/1957/31356.