Effect of Addition of Artificial Flavour on Rodent Bait Attractiveness

Some ready-to-use rodenticide baits against synanthrophic mice and rats exhibit an intense scent of vanilla, chocolate, peanut, or hazelnut. The effects of these additives on bait palatability are unclear. The aim of this study was to test whether flavoured food is more attractive to naïve rodents than natural (untreated) food. The attractiveness of flavoured against natural oat flakes was tested on wild strain groups of rodents. We tested vanilla, chocolate, hazelnut, and peanut flavour. House mice (group size 13 to 23 mice), roof rats (group size 5 to 8 rats) and brown rats (group size 5 to 7 rats) were introduced to test chambers (rats: 6.2 m², mice: 5 m²) for choice experiments. Flavoured and natural food as well as water was offered ad libitum for 12 days. Each day, the amount of consumed food was determined by weighting the remaining food, and food and water were replenished. All flavours that were tested on house mice had a positive effect on bait uptake, and the mice took up more flavoured than untreated food (hazelnut 57.7%, chocolate 61.2%, peanut 62%, and vanilla 73.1% of total food uptake). The effect on food uptake was not significantly different between flavours. Roof rats were repelled by chocolate and hazelnut (7.2% and 30.4% of total food uptake, respectively), whereas vanilla flavour had no clear effect on food consumption (51.6% of total food uptake). Similar effects were observed for bait consumption of brown rats, where chocolate flavour had a negative effect on food uptake (28.2% of total food uptake) and hazelnut flavour was neutral in terms of bait attractivity (50.0% of total food uptake). We conclude that the addition of an artificial flavour may increase the attractiveness of rodent baits to house mice, whereas it can reduce bait uptake in both rat species and has thus a detrimental effect on bait attractiveness. The different reaction of mice and rats to flavoured food is explained by the fact that house mice are neophilic, whereas both rat species avoid new stimuli and are neophobic