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CORVALLIS, Ore. - If you want to know how risky it is to use a pesticide, ask a field mouse.

The field mouse - or vole, as it is commonly called - is an excellent model for predicting the impact of pesticides on animals, according to Oregon State University scientists Dan Edge and Jerry Wolff.

Edge and Wolff have a scientific love affair with voles. They've raised thousands and claim to have the world's largest vole research facility. Since 1991, they established 24 populations of voles each year. Each population was kept in a half-acre enclosure.

What they learned in a five-year study supported by the Environmental Protection Agency is that EPA models do not effectively predict pesticide risk. The EPA models use laboratory rats and mice to predict risk in the field.

"For small mammals, like the vole, EPA models are too conservative," Edge said. "They predict a more drastic response to pesticides than actually occurs."

In their studies with the insecticide Guthion, for example, the EPA model projected a 50 percent reduction in vole population when the pesticide was applied 4-6 times the recommended rate. "Instead, we saw just a 10 percent reduction," Edge said.

"We are telling EPA that using laboratory animals to assess pesticides is not enough. Neither is basing a model on a single annual spray application."

Edge and Wolff said the vole is a "fascinating research model," because what effects voles affects many other wildlife.

"The vole is critical to the wildlife food chain," Edge said. "Voles are like candy to virtually every predator, including great horned owls, coyotes and foxes."

The OSU researchers said the vole's susceptibility to a pesticide depends on the height of the vegetation, weather patterns and genetic variations in the field mice.

Vole populations may become inbred, especially in small, isolated fields that don't allow movement among sub populations.

"We found that each succeeding insecticide spray knocked the inbred population down a notch," Edge said. "Voles probably survive pesticides better in larger fields where they have more genetic variation in sex partners."