Ethyl-iophenoxic acid as a quantitative bait marker for small mammals

Bait markers are indispensable for ecological research but in small mammals,most markers are invasive,expensive and do not enable quantitative analyses of consumption.Ethyl-iophenoxic acid(Et-IPA)is a non-toxic,quantitative bait marker,which has been used for studying bait uptake in several carnivores and ungulates.We developed a bait with Et-IPA,assessed its palatability to common voles(Microtus arvalis),and determined the dose-residue-relation for this important agricultural pest rodent species.Et-IPA concentrations of 40 to 1280μg Et-IPA per g bait were applied to wheat using sunflower oil or polyethylene glycol 300 as potential carriers.In a laboratory study,common voles were offered the bait and blood samples were collected 1,7,and 14 days after consumption.The samples were analyzed with LC-ESI-MS/MS for blood residues of Et-IPA.Sunflower-oil was the most suitable bait carrier.Et-IPA seemed to be palatable to common voles at all test concentrations.Dose-dependent residues could be detected in blood samples in a dose-dependent manner and up to 14 days after uptake enabling generation of a calibration curve of the dose-residue relationship.Et-IPA was present in common vole blood for at least 14 days,but there was dissipation by 33–37%depending on dose.Et-IPA meets many criteria for an“ideal”quantitative bait marker for use in futurefield studies on common voles and possibly other small mammal species.