Gray‐tailed voles do not move to avoid exposure to the insecticide Guthion® 2S

Abstract

AbstractWe used the gray‐tailed vole, Microtus canicaudus, as an experimental model species to test an assumption of the quotient method that nontarget wildlife do not move out of a contaminated area to avoid exposure to potentially harmful agricultural chemicals. In May 1997, we placed voles into 12 0.2‐ha enclosures planted with a mixture of pasture grasses. In late July, we applied 1.5 kg/ha of the insecticide Guthiont 2S (azinphos‐methyl), in three treatments; full spray (all of the habitat sprayed with Guthion 2S), half spray (one half of the habitat sprayed with Guthion 2S and one half sprayed with water), and a control (all of the habitat sprayed with water). Five replicates were used for the half spray and control, and two replicates were used for the full spray. We radio‐tracked 44 female and three male voles before and after the spray treatment. None of the 47 animals moved out of their established home ranges after treatment and no animals moved from the contaminated to uncontaminated areas. Additionally, no biologically meaningful differences occurred in home range size, mean maximum distance moved, or average distance between two successive radio locations. Reproducing adult voles were relatively sedentary and did not leave their established home ranges in response to insecticide exposure. These results suggest that small mammals are not likely to reduce exposure by moving from the contaminated area, which supports the assumption of the quotient method that exposure of small mammals is a function of the spray application. However, behavioral responses such as avoidance of contamination may be specific to the chemical, species, and habitat.