Figure 1.

Overview of the questionnaire outcome among pest controllers (A) and the outcome of the analysis of tissue samples of R. norvegicus (B) presented on the map of Dutch postal codes (two digits). On map A, the dark-grey areas represent regions where the presence of resistant rats was suspected. On map B, in the dark-grey areas at least one mutation was discovered, based on tail tissue samples, while in the light-grey areas only the wild type (susceptible to anticoagulant rodenticides) was encountered.