Detection of Permethrin Resistance and Fipronil Tolerance in Rhipicephalus sanguineus (Acari: Ixodidae) in the United States.

Permethrin is a commonly used acaricide for tick control on domestic animals and in residential environments, while fipronil use is restricted to on-animal treatment. Following widespread reports of permethrin and fipronil application failures to control indoor infestations of Rhipicephalus sanguineus (Latreille), the brown dog tick, 31 tick populations were obtained from Florida and Texas for acaricide resistance screening. These field-collected ticks from kennels and residential facilities were challenged with technical grade permethrin and fipronil to create dose response curves that were compared with an acaricide-susceptible strain. Permethrin resistance was successfully screened in nine populations, all of which were resistant or highly resistant. Tick susceptibility to fipronil was conducted on four populations, which were found to be tolerant, with resistance ratios below 10. This is the first documentation of R. sanguineus permethrin resistance and fipronil tolerance in the United States. Potential causes of resistance development and recommendations on future brown dog tick control management plans are discussed.