Rodenticide resistance is spreading in the UK's rat and mouse populations – but scientists do not have a clear picture of where best to target control efforts.
To address that knowledge 'vacuum', a free DNA testing initiative has been launched, and a call has gone out to the nation's pest controllers, farmers and gamekeepers – send us your tails.
Campaign for Responsible Rodenticide Use chairman Dr Alan Buckle explained: “Unknown resistance status covers much of Scotland, Wales, Northern Ireland and central England. Elsewhere, we know that an area from Bristol to Dover west-east, and Oxford to Southampton north-south, has multiple locations where genes for resistance have been identified.
"Less clustered pockets have been found in Devon, East Anglia, Greater Manchester, West and North Yorkshire, further north east and along the River Severn valley from Somerset to north west Shropshire. Where resistant rodents are present, some rodenticide products will be ineffective. Equally important is that where resistance genes are still absent, ultra-potent resistance-breaking products may be in use unnecessarily."
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In tandem with the Animal and Plant Health Agency, CRRU is asking anyone who is regularly catching mice or rats to send in two-to-three centimetre tail end samples, taken quickly after death, for DNA analysis.
In areas where resistance has already been confirmed, three-quarters of rats carried a resistance gene but one-in-five had two different genes, known as 'hybrid-resistance'. In house mice, several years of testing has found 93.5% carrying a resistance gene, with many also having hybrid resistance.
Among second generation rodenticide compounds, the two most commonly resisted are bromadiolone and difenacoum, along with first generation compounds, warfarin and coumatetralyl.
For sending tail samples, free packaging kits with instructions are available from CRRU at thinkwildlife.org/anticoagulant-resistance-project/ or bit.ly/3kuBoOW
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