Rodenticide resistance

A new study by Reading University states that the study "shows the massive extent of L120Q resistance across the whole of central southern England." Co-author Dr Colin Prescott explains that L120Q is the most severe form of resistance identified to date, effective against first generation anticoagulant rodenticides and one or more of the second generation group.

"Moreover, this doesn't mean the rest of the UK can relax, because lack of sample availability means we just don't have the data," he says. "Another concern is that most rats with L120Q resistance carry the gene from both parents. Where this occurs, it suggests most or even all rats with some susceptibility have been eradicated by widespread use of resisted rodenticides, leaving a population of resistant pure-breds."

The report was commissioned by the Campaign for Responsible Rodenticide Use (CRRU) under its stewardship regime remit to an HSE-led Government Oversight Group (GOG).

CRRU chairman Dr Alan Buckle says the difficulty for farmers, of course, is knowing the resistance status of rats on their own units.

"One effective course of action, but also involving cost, is to employ a professional pest controller with the necessary qualifications to investigate," he suggests.

"For farmers, this exemplifies how there is rather more to rodenticide stewardship than membership of an approved farm assurance scheme or taking a training course. For stewardship to be judged a success by GOG, meaningful and lasting reductions in rodenticide residues carried by non-target wildlife are expected. Without widespread best practice by farmers, enabled and supported by farm assurance and training, this might be an unlikely outcome."

Specifically and immediately, quoting advice from the UK Rodenticide Resistance Action Group, the report advises against using bromadiolone or difenacoum baits against rat populations known to carry the most severe forms of anticoagulant resistance.

It also finds UK leading the world with the highest number of different genes for resistance in rats. Of nine identified, two more in addition to L120Q confer resistance to first generation anticoagulant rodenticides and one or more of the second generation group.

T