© The Authors 2017. Published by Oxford University Press on behalf of Entomological Society of America. All rights reserved. For Permissions, please email: journals.permissions@oup.com 1633 Characterization of a Sodium Channel Mutation in Permethrin-Resistant Rhipicephalus sanguineus (Acari: Ixodidae) Nicholas S.G. Tucker, 1,2 Phillip E. Kaufman, 1 Emma N. I. Weeks, 1 Jessica Rowland, 3 Jason Tidwell, 4 and Robert J. Miller 4 1 Entomology and Nematology Dept., University of Florida, Gainesville, FL 32611 (nicktu@ufl.edu; pkaufman@ufl.edu; eniweeks@ufl.edu), 2 Corresponding author, e-mail: nicholas.s.g.tucker@gmail.com, 3 Environmental and Global Heath Dept., University of Florida, Gainesville, FL 32611 (jekableka@gmail.com), and 4 Cattle Fever Tick Research Laboratory, U.S. Department of Agriculture-Agricultural Research Service (USDA-ARS), Edinburg, TX 78541 (jason.tidwell@ars.usda.gov; Robert.Miller@ARS.USDA.GOV) Subject Editor: Guiyun Yan Received 2 December 2016; Editorial decision 1 June 2017 Abstract The brown dog tick, Rhipicephalus sanguineus (Latrielle) sensu lato, is an important ectoparasite of dogs and occasionally humans, capable of transmitting several pathogens, such as Rickettsia and Ehrlichia, which are of veterinary and medical importance. The brown dog tick is distributed worldwide and has an affinity for human habitations in much of its range. In some populations, lack of integrated pest management plans and overuse of pyrethroid pesticides and other sodium channel inhibitors has resulted in high levels of resistance to per- methrin. Recently, a highly conserved region of the R. sanguineus sodium channel was sequenced, indicating that a single nucleotide polymorphism of thymine to cytosine on domain III segment VI of the sodium channel could confer resistance. A molecular assay targeting a point mutation in the sodium channel was developed and optimized to separate ticks expressing permethrin resistance from those from a susceptible colony. Thereafter, multiple field-collected phenotypically permethrin-resistant populations were evaluated using this molecular assay to determine genotype. As confirmed by DNA sequencing, a point mutation was present at a high rate in phenotypically resistant tick populations that was not present in the susceptible strain. These data suggest an additional permethrin resistance mechanism to metabolic resistance, which has been reported for this tick species, and confirm its association with phenotypic resistance. The results of this study further empha- size the need to preserve acaricide chemistry through rotation of active ingredients used to control ectoparasites. Key words: brown dog tick, acaricide resistance, point mutation, integrated pest management, target site insensitivity The brown dog tick, Rhipicephalus sanguineus Latreille sensu lato, is a three-host tick, but is highly restricted in its preferred host, the do- mestic dog. It is perhaps this close association that has led the brown dog tick to be the only tick known to complete its lifecycle indoors, particularly in temperate climates (Dantas-Torres 2008). This synan- thropic adaptation has allowed for increased exposure to acaricides used both in the environment (residence or kennel) and on the canine host when compared to exophilic tick species. Brown dog ticks spend greater than 95% of their life span in the environment, and dogs serve as the primary dispersal mechanism of this species (Dantas-Torres 2010). Thus, exchange of ticks among locations is largely restricted to dog visitations to common areas, such as veterinary clinics, or when uninfested dogs visit infested homes or vice versa. This restricted genetic exchange along with long-lasting or prophylactic use of acaricides with a similar mode of action provides tremendous opportunity for selection of pesticide resistant populations. Acaricide resistance in R. sanguineus has been observed in several North America populations (Miller et al. 2001; Eiden et al. 2015a, b), and samples from around the world are currently being tested in the Veterinary Entomology Laboratory at the University of Florida. Brown dog ticks are not unique in their expression of pesticide resistance. Worldwide, over 440 instances of arthropods expressing resistance to one or more pesticides have been recorded (Roush and Tabashnik 1990). Physiological pesticide resistance can occur through metabolic detoxification, reduced cuticular penetration, and target site insensitivity. A point mutation conferring target site Vector Control, Pest Management, Resistance, Repellents Journal of Medical Entomology, 54(6), 2017, 1633–1638 doi: 10.1093/jme/tjx127 Advance Access Publication Date: 13 July 2017 Research article Downloaded from https://academic.oup.com/jme/article/54/6/1633/3964504 by guest on 30 November 2022