Susceptibility to the anticoagulants bromadiolone and coumatetralyl in wild Norway rats (Rattus norvegicus) from the UK and Germany

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.

The potential of coumatetralyl enhanced by cholecalciferol in the control of anticoagulant-resistant Norway rats (Rattus norvegicus)

“…Prior to the first trial, rats were trapped on the farm, and the frequency of resistance was assessed by BCR resistance tests with coumatetralyl. The tenfold ED 50 of susceptible rats was chosen for these tests, because this dose was considered to be a good discriminating dose for that strain with coumatetralyl resistance factors at 42 to 92 . Five of 12 rats were classified as resistant, which appears to be slightly below the frequency of resistance in the range 45–71% reported elsewhere in populations from this area .…”

“…The dose calculation and BCR test protocol were in accordance with the standard test introduced by the Rodenticide Resistance Action Committee, CropLife International (http://www.RRAC.info), which had been applied previously to determine the susceptibility to coumatetralyl in the Y139C strain of the Norway rat …”

“…It was performed as briefly described below . The active ingredient coumatetralyl was supplied by Bayer CropScience (Monheim, Germany) as a 2.0 g L −1 concentrate in polyethylene glycol PEG 200.…”

“…The dose calculation and BCR test protocol were in accordance with the standard test introduced by the Rodenticide Resistance Action Committee, CropLife International (www.RRAC.info), which had been applied previously to determine the susceptibility to coumatetralyl in the Y139C strain of the Norway rat. 24,25 It was performed as briefly described below. 4,24,25 The active ingredient coumatetralyl was supplied by Bayer CropScience (Monheim, Germany) as a 2.0 g L −1 concentrate in polyethylene glycol PEG 200.…”

“…24,25 It was performed as briefly described below. 4,24,25 The active ingredient coumatetralyl was supplied by Bayer CropScience (Monheim, Germany) as a 2.0 g L −1 concentrate in polyethylene glycol PEG 200. To determine the prevalence of resistance, the 10.0 multiple of the CD strain ED 50 was used.…”