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A new study led by researchers at Rutgers University is shedding light on an issue that could affect homeowners, pest management professionals, and even New Jersey’s wildlife.
Many house mice in the state appear to have developed genetic resistance to some of the most commonly used rodenticides.
Published in Pest Management Science in 2026, the research examined nearly 300 rodents collected throughout New Jersey, New York, Pennsylvania, and Washington, D.C. The findings suggest that while traditional rodenticides remain an important tool, they may not always be as effective against house mice as they once were.
What the Researchers Studied
The study focused on a gene known as Vkorc1, which has been linked to resistance against anticoagulant rodenticides. These products work by preventing blood from clotting, ultimately causing internal bleeding in rodents.
Over time, however, some rodents have developed genetic mutations that reduce the effectiveness of these poisons. Researchers analyzed tissue samples from 147 house mice and 143 Norway rats collected between 2021 and 2025 to determine how common these resistance-associated mutations have become.
What They Found in New Jersey
New Jersey produced some of the most notable findings in the entire study.
Researchers collected house mice from communities including:
- New Brunswick
- Paterson
- Trenton
- Branchville
- Newton
- Runnemede
Among the New Jersey mice examined:
- Nearly seven out of every ten carried genetic mutations already known to make anticoagulant rodenticides less effective.
- New Jersey had the highest frequency of one major resistance mutation (known as Y139C) among all states included in the study.
- In Trenton, several mice carried multiple resistance-associated mutations, suggesting some populations may be continuing to evolve.
Overall, researchers found that 84% of all house mice sampled across the study had at least one genetic mutation, while 69% carried mutations already associated with rodenticide resistance.
Mice and Rats Are Telling Different Stories
One of the study’s more surprising discoveries involved Norway rats.
Although researchers found several genetic variations in rats, they did not find the well-established resistance mutations commonly associated with anticoagulant rodenticide resistance.
In other words, while house mice appear to be rapidly developing resistance in parts of the Northeast, Norway rats have not yet shown the same pattern.
The authors note that rats may rely on different survival strategies, including behavioral avoidance of bait, and that additional research is needed to fully understand resistance in rat populations.
Why This Matters
For homeowners, the findings do not mean rodenticides have stopped working altogether.
Instead, the research suggests that in some mouse populations, repeated use of the same type of poison may become less effective over time. When rodents survive treatments, additional bait is often applied, increasing both costs and the amount of rodenticide entering the environment.
That creates another concern: wildlife.
Birds of prey, foxes, raccoons, skunks, opossums, and other animals can be exposed to anticoagulant rodenticides after consuming poisoned rodents. Previous studies have documented these compounds in numerous wildlife species across North America.
The researchers emphasize that reducing unnecessary rodenticide use benefits both effective pest management and environmental conservation.
A Shift Toward Integrated Pest Management
Rather than relying solely on rodenticides, the study recommends an Integrated Pest Management (IPM) approach.
This strategy combines multiple methods to prevent infestations before they become severe, including:
- Sealing gaps and openings that allow rodents to enter buildings
- Eliminating food and water sources
- Improving sanitation around homes and businesses
- Using traps where appropriate
- Reserving rodenticides as one component of a broader control strategy rather than the only solution
Integrated Pest Management is widely recognized as a more sustainable and effective long-term approach because it addresses the underlying causes of infestations instead of simply treating the symptoms.
The Bottom Line
This study provides some of the strongest evidence to date that anticoagulant rodenticide resistance is becoming increasingly common in New Jersey house mice.
While researchers stress that additional monitoring is needed, the findings suggest pest management strategies may need to evolve alongside the rodents themselves.
For New Jersey homeowners, the message isn’t one of alarm—but of adaptation. Preventing rodents from entering buildings, reducing attractants, and using a combination of control methods may prove far more effective than relying on poison alone.
As scientists continue tracking resistance across the Northeast, New Jersey remains an important region for understanding how urban rodent populations are changing—and how communities can respond in ways that protect both public health and local wildlife.
Source
https://scijournals.onlinelibrary.wiley.com/doi/10.1002/ps.70833?af=R
