The EPA models use laboratory rats and mice to predict risk in the field. 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. 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.
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. Voles probably survive pesticides better in larger fields where they have more genetic variation in sex partners.