Toxin metabolism potential in Richardson ground squirrels (<Emphasis Type="Italic">Spermophilus richardsonii)</Emphasis> in the context of chemical control of this pest

Richardson ground squirrels (Spermophilus richardsonii) are prominent pests on the prairies of North America. Rodenticides have been used for their control for several decades, but this pest continues to thrive. In this study we considered the possibility that this apparent lack of success in controlling this pest may be associated with systemic adaptation of Richardson ground squirrels to toxins. Accordingly, we examined the hepatic cytochrome P450 (CYP) enzyme system (phase I biotransformation) in Richardson ground squirrels selected from fields where rodenticides were used (exposed) and from fields where no toxins were distributed (naïve). We found that the content and activity of individual components of the CYP system including CYP, cytochrome b5, and NADPH–CYP reductase in liver microsomes were higher in exposed Richardson ground squirrels than in naïve Richardson ground squirrels. In vitro CYP-mediated activities for generic substrates representing major groups of reactions were found to be highly variable among individuals. However, systemic activity was comparable among the naïve and exposed Richardson ground squirrels. These findings indicate that Richardson ground squirrels may readily develop resistance to toxins by enhancing the functional capacity of enzymes responsible for detoxification. Therefore, it is important to carefully monitor the efficiency of toxicological methods of Richardson ground squirrels control and to revise management strategies accordingly.