The cattle tick, Rhipicephalus annulatus (Say) is a vector of bovine babesiosis and responsible for direct and indirect losses to cattle producing areas located in temperate and subtropical dry regions. Resistance against pyrethroids has been reported for this species in Asia and Africa, but never before in North America. An outbreak strain, Rio Lado, collected close to the border between Mexico and the United States, in Maverick County, Texas, showed low level of resistance to permethrin, a pyrethroid pesticide. We used genomic material from different strains of cattle ticks collected within the Permanent Quarantine Zone (Rio Lado, Vega and Klein Grass strains) to partially characterize the coding gene of the voltage-gated sodium channel (Na-channel), target-site of pyrethroid pesticides, and search for putative mutations associated with resistance using quantitative PCR high resolution melt (HRM) analysis. The two amplified fragments, corresponding to domains II and III of the Na-channel, were 100 % identical to its ortholog in Rhipicephalus microplus (Canestrini). No nucleotide polymorphisms in the Na-channel gene were observed in the pyrethroid-resistant Rio Lado strain, when compared to the susceptible strains Klein Grass and Vega. This study reports the first case of pyrethroid resistance in R. annulatus collected in the United States. Also, we provide new genomic data for this species of tick that allows for the development of a new method to screen for mutations associated with pyrethroid resistance.

牛tick，Rhipicephalus annulatus（Say）是牛杆状杆菌病的病媒，是造成温带和亚热带干旱地区牛生产区直接和间接损失的原因。在亚洲和非洲，已有报道称该物种对拟除虫菊酯具有抗药性，但在北美却从未有过。在得克萨斯州马弗里克县附近的墨西哥和美国边界附近采集的暴发菌株里约拉多（Rio Lado）对拟除虫菊酯农药菊酯菊酯的抵抗力较低。我们使用了来自永久检疫区内收集的不同牛of菌株的基因组材料（里约热内卢，维加和克莱因草菌株）来部分表征电压门控钠通道（Na通道），拟除虫菊酯的靶位点的编码基因。农药 并使用定量PCR高分辨率熔体（HRM）分析来寻找与抗性相关的推定突变。对应于Na通道结构域II和III的两个扩增片段与其在同源物中的直向同源物100％相同Rhipicephalus microplus（Canestrini）。与易感菌株Klein Grass和Vega相比，在对拟除虫菊酯具有抗性的Rio Lado菌株中未观察到Na通道基因的核苷酸多态性。这项研究报告了在美国收集到的R. annulatus中第一种拟除虫菊酯抗药性病例。此外，我们提供了这种of虫的新基因组数据，从而允许开发一种新方法来筛选与拟除虫菊酯抗性相关的突变。