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Abstract
A new blood clotting response test was used to determine the susceptibility, to coumatetralyl and bromadiolone, of laboratory strains of Norway rat from Germany and the UK (Hampshire), and wild rats trapped on farms in Wales (UK) and Westphalia (Germany). Resistance factors were calculated in relation to the CD strain of Norway rat. An outbred strain of wild rats, raised from rats trapped in Germany, was found to be more susceptible to coumatetralyl by a factor of 0.5 – 0.6 compared to the CD strain. Homozygous and heterozygous animals of a strain of resistant rats from Westphalia were cross-resistant to coumatetralyl and bromadiolone, with a higher resistance factor for bromadiolone than that found in both UK strains. Our results show that the degree of altered susceptibility and resistance varies between strains of wild rat and between resistance foci. Some wild rat strains may be more susceptible than laboratory rat strains. Even in a well-established resistance area, it may be difficult to find infestations with resistance high enough to suspect control problems with bromadiolone, even after decades of use of this compound.
Acknowledgements
Work in the UK was commissioned by the Rodenticide Resistance Action Committee of CropLife International; work in Germany was part of a Bayer CropScience research program.
Notes
*All animal testing reported in this paper was carried out in accordance with UK and German regulations. Protocols for the use of animals in these experiments carried out in Germany were approved by the Bezirksregierung Düsseldorf, Germany, Laboratory work at the University of Reading was carried out under licenses issued by the UK Home Office and after approval by the University system of Local Ethical Review.