Deisch, Michele S. 1986. The Effects of Three Rodenticides on Nontarget Small Mammals and Invertebrates. M.S. thesis, South Dakota State Univeristy. 149 p.

Abstract

Mortality of nontarget small mammals and invertebrates using 3 rodenticide treatments (prebaited phosphide, prebaited strychnine, and strychnine alone) was evaluated in western South Dakota. Rodenticides wer applied September 22-24, 1983 on 15 black-tailed prairie dog Cynomys ludovicianus towns. Immediate (September 1983) and long-term (September 1983 through August 1984) rodenticide efficacy and impacts on nontarget wildlife species were evaluated.

None of the 3 rodenticide treatments produced significant (a < 0.10) immediate impacts on deer mice (Peromyscus maniculatus) releative densities. Increases of deer mice densities occurred in 1984 on sites that had been treated with the 2 strychnine treatments. These long-term increases in deer mice densities were due to habitat change associated with the absence of prairie dogs. Overall, comparisons among the 3 rodenticides for efficacy indicated that zinc phosphide reduced deer mice densities greater than either strychnine treatment.
Seven invertebrate taxa were evaluated. Immediate and long-term effects of the 3 rodenticide treatments occurred when significant differences in invertebrate densities were found between control and treated sites. Spider mites (Acarina) and crickets (Orthoptera) were not (a > 0.10) affected by the 3 rodenticides. Immediate impacts of zinc phosphide occurred on ant (Hymenoptera) densities and long-term impacts were found in August 1984. Strychnine alone immediately reduced wolf spiders (Araneae) 13% in September 1983 and densities increased on treated sites as compared to control sites in June 1984.

Densities of darkling beetles (Coleoptera) in September were significantly reduced with zinc phosphide. Ground beetle and dung beetle (Coleoptera) densities were not immediately reduced by the rodenticides in September. Generally, the few long-term changes in invertebrate densities are attributed to biotic and abiotic factors. Changes in vvegetation structure due to prairie dog control may have affected invertebrate densities.

Comparisons among rodenticides for efficacy indicated that zinc phosphide immediately reduced densities of ants and darkling beetles greater than either strychnine treatment. None of the other rodenticide comparisons showed significant differences in immediate reductions of nontarget invertebrates in September 1983.