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

BACKGROUND
We evaluated the potential of cholecalciferol as an enhancer of the first-generation anticoagulant coumatetralyl in the Westphalia anticoagulant-resistant strain of the Norway rat (Rattus norvegicus Berkenhout), characterised by the Tyr139Cys polymorphism on the VKOR enzyme. Because today only the most potent, but also most persistent anticoagulant rodenticides of the second generation remain available to control this strain, new rodenticide solutions are required.


RESULTS
Feeding trials in the laboratory confirmed a significant level of efficacy, which was corroborated by field trials in the Münsterland resistance area. After frequency and level of resistance were assessed by blood clotting response tests, field trials were conducted with bait containing coumatetralyl at 375 mg kg-1 and cholecalciferol at 50 mg kg-1 or 100 mg kg-1 . Control success was 94% when a large rat infestation comprising 42% resistant animals was treated. Another field trial applying the combination to a rat population that had survived a preceding treatment with bromadiolone resulted in a 99.5% control success according to the first census day, but with some increase in rat activity during subsequent census days.


CONCLUSION
The combination of coumatetralyl and cholecalciferol is a promising alternative approach to the most potent second-generation anticoagulants in resistance management, particularly in respect of environmental risks, such as secondary poisoning. © 2016 Society of Chemical Industry.