Tracking the increase of acaricide resistance in an invasive population of cattle fever ticks, Rhipicephalus microplus (Acari: Ixodidae), and implementation of real-time PCR assays to rapidly genotype resistance mutations
2020
Thomas, Donald B. | Klafke, Guilherme | Busch, Joseph D. | Olafson, Pia U. | Miller, Robert A. | Mosqueda, Juan | Stone, Nathan E. | Scoles, Glen | Wagner, David M. | Perez-De-Leon, Adalberto
The invasive southern cattle fever tick, Rhipicephalus (Boophilus) microplus, occurs in the U.S. only in the permanent quarantine zone along the international border in south Texas as incursions from Mexico. Intensive acaricide treatment of cattle herds in Mexico to reduce tick populations resulted in the development of resistance to an array of acaricides. Resistance to permethrin increased both in incidence and level in Texas over the last decade, even though permethrin is not used to control cattle fever ticks on the U.S. side of the border. From 3-4% of tick sample submittals to our laboratory in 2008 to over 50% in 2016 and 2017 showed resistance based on standardized pesticide bioassays. Resistance ratio levels increased from 4 – 6-fold in 2007 to 45-fold by 2017. Moreover, by 2017 the highly resistant southern cattle fever ticks spread to include all five of the southmost Texas counties and have been found on both cattle and wild ruminant hosts. Using DNA fingerprinting markers, we found evidence that separate incursions of ticks with synthetic pyrethroid resistance entered Texas independently, and that ticks on wildlife were a likely source of ticks on cattle. Although one of the resistant populations in Zapata County was eradicated within a year of its discovery in 2008, a second population in Cameron county persisted since 2014. Improved diagnostic tools developed by our group include a panel of DNA-based real-time PCR assays to detect mutations within the voltage-sensitive sodium channel (Vssc) that are involved in permethrin resistance. These assays can be completed within days of receiving field collected ticks providing timely, valuable information to Cattle Fever Tick Eredication Program personnel.
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