RESEARCH

New data released by The Campaign for Responsible Rodenticide Use (CRRU) UK shows that 73.7% of the Norway rats they sampled were anticoagulant rodenticide resistant.

You can read the full paper here.

122 rodent tissue samples were received for DNA sequencing at the laboratories of the Animal and Plant Health Agency (APHA) from August 2022 to July 2023.

This table shows the number of Norway rat tissue samples received and analysed with their resistance or susceptibility:

*These four animals were heterozygous for each of two the resistance mutations.  Each of these mutations is also counted separately in the records above.

Hybrid resistance (two resistant mutations)

The report states that hybrid resistance was again found in the sample. 

Two rats from West Sussex carried the L120Q and Y139C mutations, and two from Lanarkshire carried the L128Q and Y139C mutations.

House mice

Only five house mouse samples were obtained, but all samples APHA examined were found to be anticoagulant resistant. 

Three were homozygous for the L128S mutation, one homozygous for Y139C, and one animal carried both mutations. 

It is the position of the Rodenticide Resistance Action Group (RRAG) that “all UK house mouse infestations should be assumed to carry resistance and treatments should be conducted against them accordingly”.

Monitoring rodenticide resistance since 2009 

During 2009 and 2023, DNA resistance sequencing was conducted first at the University of Reading and now at APHA. 

A total of 584 Norway rats and 134 house mouse tissue samples were examined, with DNA extracted and sequenced. 

Among these samples, they found that 77.3% of rats and 94.8% of mice carried one or more single nucleotide polymorphisms, which are known to affect the efficacy of anticoagulant rodenticides significantly. 

The report notes:

“These results may not reflect the true frequency of resistance in the two species, however, because samples are generally sent by those experiencing difficulties in obtaining control of rodent infestations with anticoagulants.”

Resistance mapping

The Rodenticide Resistance Action Committee (RRAC) of CropLife International in Brussels publishes online maps showing rodent resistance information.

Resistance trends across the UK suggest:

• L128Q is largely restricted to Scotland and the north of England
• Y139S is found mainly in Wales, on the Anglo-Welsh border and in an expanding focus in North Yorkshire
• L120Q is very widespread across central southern England, but with increasing frequency in East Anglia and the far south-west  
• Y139F is found mainly in Kent, East Sussex and Greater London, but now with an established focus in the north-west.

Advice for pest professionals

Rodenticide Resistance Action Group (RRAG) produced guidance for dealing with resistance in the UK. 

Although the guidance was last revised in January 2021, it is a useful guide for professionals looking to control resistant rodent populations.

FGAR - first-generation anticoagulant rodenticide; SGAR - second-generation anticoagulant rodenticide

GOT RESISTANCE QUESTIONS?

BPCA offers technical pest control support to all BPCA member companies. If you’ve got questions about resistance or any other pest management issues, contact the team today.

technical@bpca.org.uk