EFFECTS OF GUTHION-2S(R) ON MICROTUS-CANICAUDUS - A RISK-ASSESSMENT VALIDATION

1. An assumption of the quotient method, a risk assessment methodology , was tested by determining if demographic responses of Microtus canic audus Miller to five application rates of Guthion 2S(R) were dose-depe ndent in held enclosures. 2. Vole population sizes in enclosures with application rates of 1.55-4.67 kg ha(-1) were depressed below levels i n enclosures with application rates of 0.0 and 0.77 kg ha(-1) for one trap period. 3. Male and female survival rates were lower in enclosure s with 1.55-4.67 kg ha(-1) application rates than in enclosures with r ates of 0.0 and 0.77 kg ha(-1), and these lower rates persisted for 2- 6 weeks depending on sex and application rate. 4. Populations were fem ale-biased throughout the study, and no effects due to the pesticide a pplication were detected in the proportion of females in the populatio n. 5. No pesticide effects were detected in reproductive performance, recruitment, activity, or male mass change, but a pesticide-related tr end was evident in the cumulative number of recruits. 6. Our predictio ns of effects increasing with application rate were generally supporte d, but effects on M. canicaudus were of short duration, and the higher application rates may have caused a compensatory response in those po pulations.