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Published on: July 23, 2017
Mutation in the RmβAOR gene is associated with amitraz resistance in the cattle tick Rhipicephalus microplus
Sean W Corley1, Nicholas N Jonsson, Emily K Piper
1School of Veterinary Science, University of Queensland, Gatton, QLD 4343, Australia.
Abstract:
We aimed to describe the evolution of resistance to amitraz in Rhipicephalus microplus in the field and to test the association between amitraz resistance and the frequency of a mutation in the β-adrenergic octopamine receptor gene (RmβAOR). We established six populations of Rhipicephalus microplus ticks in similar paddocks by the admixture of ticks from strains known to be susceptible and resistant to amitraz and synthetic pyrethroids. Each population was managed using one of three acaricide treatment regimes: always amitraz, always spinosad, or rotation between amitraz and spinosad. We used microsatellites to elucidate population structure over time, an SNP in the para-sodium channel gene previously demonstrated to confer resistance to synthetic pyrethroids to quantify changes in resistance to synthetic pyrethroids over time, and a nonsynonymous SNP in the RmβAOR, a gene that we proposed to confer resistance to amitraz, to determine whether selection with amitraz increased the frequency of this mutation. The study showed panmixia of the two strains and that selection of ticks with amitraz increased the frequency of the RmβAOR mutation while increasing the prevalence of amitraz-resistance. We conclude that polymorphisms in the RmβAOR gene are likely to confer resistance to amitraz.
Insights
Amitraz resistance in Rhipicephalus microplus ticks evolved with increased frequency of a specific mutation in the beta-adrenergic octopamine receptor gene (RmβAOR). This finding links RmβAOR gene changes to amitraz resistance in cattle ticks.
Area of Science:
- Veterinary Entomology
- Molecular Entomology
- Parasitology
Background:
- Amitraz is a key acaricide used to control Rhipicephalus microplus, a significant cattle parasite.
- Understanding the genetic basis of acaricide resistance is crucial for sustainable tick control strategies.
- Previous studies suggested a potential link between octopamine receptor genes and amitraz resistance.
Purpose of the Study:
- To investigate the field evolution of amitraz resistance in Rhipicephalus microplus populations.
- To determine the association between amitraz resistance and a specific mutation in the RmβAOR gene.
Main Methods:
- Established six Rhipicephalus microplus tick populations by mixing susceptible and resistant strains.
- Implemented three acaricide treatment regimes: continuous amitraz, continuous spinosad, or rotation.
- Utilized microsatellites for population structure, para-sodium channel SNPs for synthetic pyrethroid resistance, and RmβAOR SNPs for amitraz resistance gene analysis.
Main Results:
- Tick populations exhibited panmixia, indicating genetic mixing between the initial strains.
- Selection with amitraz significantly increased the frequency of the RmβAOR mutation.
- Increased RmβAOR mutation frequency correlated with a higher prevalence of amitraz resistance in the tick populations.
Conclusions:
- Polymorphisms within the RmβAOR gene are strongly implicated as conferring resistance to amitraz in Rhipicephalus microplus.
- This study provides field evidence supporting the genetic mechanism of amitraz resistance.
- Findings aid in developing targeted strategies to manage amitraz resistance in cattle ticks.
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