BLOOD-CLOTTING RESPONSE TEST FOR BROMADIOLONE RESISTANCE IN NORWAY RATS

Bromadiolone resistance in Norway rats (Rattus norvegicus) may reduce the efficacy of rodent control measures, and managers need a validated test to detect potential control problems. We developed a test to identify levels of resistance to the rodenticide bromadiolone in warfarin-resistant Norway rats. This test was based on changes in blood-clotting activity 4 days after administering a single dose of bromadiolone in conjunction with menadione sodium bisulphite (vitamin K3). The test procedure identified the degree of bromadiolone resistance in laboratory and wild rats that had anticoagulant resistance genes. In addition, results were available within 5 days, and susceptible animals could be humanely culled rather than dying of anticoagulant poisoning, as occurs with feeding tests. The test was based on an effective dose needed for 99% response (ED99) for rats susceptible to all anticoagulants and results were determined separately for each sex. We report bromadiolone resistance in Norway rats for the first time in the United Kingdom and that rats in central southern England have a higher degree of resistance than do rats from Wales or Yorkshire.