Relationship between resistance factors and treatment efficacy when bromadiolone was used against anticoagulant-resistant Norway rats (Rattus norvegicus Berk.) in Wales

Abstract

We investigated the relationship between the severity and incidence of resistance among Norway rats (Rattus norvegicus) on a farm in Wales and the subsequent outcome of a practical rodent control operation. Bromadiolone resistance factors were estimated for rats trapped on the farm using the blood clotting response test, and were found to be 2 to 3 for male rats and approximately 6 for females. The incidence of resistance in the rat population was high. Infestation size was estimated by census baiting and tracking, and was found to be substantial, with a maximum of 6.5 kg of bait being eaten on a single night. A proprietary rodenticide (Deadline™), containing 0.005% bromadiolone, was used to control the infestation. The duration of baiting was 35 days and, according to the two methods of assessment used, treatment success was in the region of 87 and 93%. No evidence was observed of a significant impact of resistance on the rat control operation, and the remaining rats of this very heavy infestation would probably have been controlled if baiting had continued for longer.

Keywords:

• Anticoagulant resistance
• Welsh anticoagulant resistance focus
• Rattus norvegicus
• bromadiolone
• blood-clotting response test

Acknowledgements

The study was funded by the Rodenticide Resistance Action Committee of CropLife International. The authors wish to express grateful thanks to the RRAC companies (Bayer AG, BASF AG, Liphatech S.A., Rentokil Initial plc, Sorex Limited and Syngenta Crop Protection AG) and to technical representatives Chuck Klein, Mikaeline Billeret, Andy Brigham and Roger Sharples who made significant intellectual contribution to this work.

Notes

*Laboratory animal testing was carried out under licenses issued by the UK Home Office and after approval by the University system of Local Ethical Review. Field work was also carried out under Home Office license and within the framework of the UK Pesticides Safety Directorate's Officially Recognised Efficacy Testing Organisatioin (ORETO) scheme.