Assessment of zinc phosphide bait shyness and tools for reducing flavor aversions

Prairie voles (Microtus ochrogaster Wagner) cause extensive damage in agricultural, suburban, and urban environments. Control of these animals has historically relied on the use of anticoagulant rodenticides and zinc phosphide. However, shyness to zinc phosphide baits has reduced its efficacy. The aim of this study was to evaluate the factors involved in zinc phosphide bait shyness through preference testing. Baits were made using a rolled oat base and contained various combinations of the components of zinc phosphide baits such as lecithin, magnesium carbonate and known flavor modulators sodium cyclamate and zinc sulfate. Encapsulation of zinc phosphide was also tested as a potential means to mask undesirable flavor qualities of the compound. Consumption of test baits was measured in four day laboratory feeding trials. Results demonstrated that numerous components of current bait formulations serve as salient cues during conditioned aversions and therefore may contribute to bait shyness. Vole avoidance of zinc sulfate and sodium cyclamate revealed that these potential additives would not decrease bait shyness. Encapsulation of zinc phosphide may have masked some of the negative flavor cues and therefore should be considered in future bait development. This study suggests that, since voles are able to distinguish components of current bait formulations, varying composition of zinc phosphide baits between applications may serve to reduce bait shyness