A standardised BCR resistance test for all anticoagulant rodenticides

Abstract

This paper presents a reappraisal of the blood clotting response (BCR) tests for anticoagulant rodenticides, and proposes a standardised methodology for identifying and quantifying physiological resistance in populations of rodent species. The standardisation is based on the International Normalised Ratio, which is standardised against a WHO international reference preparation of thromboplastin, and allows comparison of data obtained using different thromboplastin reagents. The methodology is statistically sound, being based on the 50% response, and has been validated against the Norway rat (Rattus norvegicus) and the house mouse (Mus domesticus). Susceptibility baseline data are presented for warfarin, diphacinone, chlorophacinone and coumatetralyl against the Norway rat, and for bromadiolone, difenacoum, difethialone, flocoumafen and brodifacoum against the Norway rat and the house mouse. A ‘test dose’ of twice the ED₅₀ can be used for initial identification of resistance, and will provide a similar level of information to previously published methods. Higher multiples of the ED₅₀ can be used to assess the resistance factor, and to predict the likely impact on field control.

Keywords:

• Anticoagulant resistance
• blood clotting response test
• Rattus norvegicus
• Mus domesticus
• anticoagulant rodenticides
• resistance ratio

Acknowledgement

This work was funded by the Rodenticide Resistance Action Committee of CropLife International (BASF, Bayer, LiphaTech, Rentokil, Sorex and Syngenta).

Notes

*Laboratory animal testing was carried out under licences issued by the UK Home Office and after approval by the University system of Local Ethical Review.