Spatiotemporal incidence of acaracide resistance in cattle fever tick, Boophilus spp., outbreaks in the United States

Cattle Fever Ticks Rhipicephalus (Boophilus) microplus and R.(B). annulatus, were eradicated from the U.S. but regularly make incursions along the border with Mexico. The USDA maintains a quarantine buffer zone with surveillance for stray Mexican cattle and inspection of herds in the counties along the Rio Grande. The year 2008, a peak El Nino oscillation year was the worst in decades in termos of the number of fever tick outbreaks with 142 premises infested. With the prevalence of severe drought in the years since, the numbers of outbreaks has declined to only 48 in 2012. Unfortunately, while the number of outbreaks has declined the incidence of acaracide resistance among the ticks has increased. In 2008 only 11% of the outbreaks tested had significant levels of resistance. In 2012 one third of the outbreaks tested showed some level of resistance. The resistance detected in 2008 was to synthetic pyrethroids, however, in recent years resistance to amitraz, fipronil and organophosphates also has been detected. Interception of these ticks and development of strategies for managing resistance are now major foci of the Cattle Fever Tick program.