Spread of resistance to anticoagulant rodenticides in Germany

Resistance to anticoagulant rodenticides in Rattus norvegicus is now estimated to cover an area of roughly 26 000 km2 in northwest Germany. The chemical compounds involved are warfarin, coumatetralyl, bromadiolone and, to a lesser extent, difenacoum. Recent investigations revealed that the resistance area is extending considerably further east than was previously recorded. The easternmost populations containing resistant individuals are now present in the city of Hannover, whereas it seems that on the southern edge the urbanised Ruhr Basin remains mostly unaffected by resistance problems. Reported control failures with house mice (Mus musculus/domesticus) suggest that resistance to high potency compounds may occur, but these await scientific confirmation. We propose that molecular genetic testing methodology should be exploited to improve monitoring of anticoagulant resistance and provide more accurate information to users of rodenticides.