Trials of the anticoagulant rodenticides bromadiolone and difenacoum against the house mouse (Mus musculus L.)

Laboratory and field trials were conducted to determine the efficacy of the anticoagulant rodenticide bromadiolone against the house mouse (Mus musculus). In laboratory feeding tests, family groups of warfarin-resistant mice maintained in pens and conditioned to feeding on plain foods were offered pinhead oatmeal bait containing bromadiolone at 0.005%. Overall mortality in replicated 21-day poison treatments was 55/58 or 94.8%. Six field trials were carried out, using the same poison bait, against mice infesting farm buildings. Treatment success, estimated from the results of census baitings conducted before and after treatment, ranged between 60.4% and 100%, mean 92.4%. In equivalent field trials using difenacoum, another newly developed anticoagulant rodenticide, the control achieved ranged between 70.2% and 100%, mean 96.0%. Five field trials, three involving bromadiolone and two difenacoum, were not completely successful and the surviving mice were removed for laboratory examination. In 21-day toxicity tests, each animal was fed the poison bait offered to it earlier in the field. Bromadiolone and difenacoum gave kills of 12/21 (57.1%) and 9/11 (81.8%) respectively. The possible emergence of mouse populations resistant to these anticoagulants is considered.