Novel edible coatings to improve longevity of rodent baits

Abstract

Rats and mice cause severe biodiversity impacts worldwide, including in New Zealand, where poisoning campaigns are undertaken on the mainland and offshore islands using cereal-based baits. However, bait stations are often irregularly serviced so wildlife managers require a bait that would remain palatable to rodents for at least 6 months in the field. One potential way to improve the field life of baits is by coating them in materials that reduce water uptake and subsequent mould growth. However, these coatings must be palatable to the rodents. This report investigates the palatability to captive Norway rats (Rattus norvegicus) and mice (Mus musculus) of both weathered and unweathered rodent food pellets coated with various polymer solutions. When compared with uncoated alternatives, fresh baits coated with shellac or polyvinyl butyral (PVB) in ethanol solvent were preferred by the rats. The use of acetone rather than ethanol solvent did not affect bait palatability. A combination of shellac and PVB reduced palatability compared with shellac alone. Weathered shellac-coated baits remained more palatable than uncoated fresh pellets to rats for up to 6 months and outperformed the PVB and combination coatings. Overall, the palatability of fresh-coated baits was lower for mice. The PVB-coated baits had lower mean palatability scores than the shellac-coated baits but none of the bait types was significantly less palatable than uncoated baits. The shellac-coated baits remained palatable to mice for up to 4 months. Shellac is recommended as a coating for multi-species rodent baits.