Toxicity tests on suspected warfarin resistant house mice (Mus musculus L.)

Abstract

1. Residual populations of wild house mice (Mus musculus L.) were trapped alive in premises where poison treatments with 0·025% warfarin bait had been reported to be ineffective.2. In the laboratory the individually caged mice were fed 0·025% warfarin in a sugar/oil/coarse oatmeal base. In toxicity tests lasting 10 and 21 days, the total mortality was low and the rate of death slow compared with mice drawn from habitats not treated with warfarin.3. It is suggested that tolerance to warfarin in M. musculus either is polygenically based or is controlled by a single major gene influenced by modifiers and that these hard-to-kill populations have arisen through selection during successive control treatments.