Veterinary Parasitology 191 (2013) 97–101 Contents lists available at SciVerse ScienceDirect Veterinary Parasitology jo u rn al hom epa ge : www.elsevier.com/locate/vetpar First report of fipronil resistance in Rhipicephalus (Boophilus) microplus of Mexico Robert J. Miller a,∗ , Consuelo Almazán b , Martín Ortíz-Estrada c , Ronald B. Davey a , John E. George d , Adalberto Peréz De León d a USDA, ARS Cattle Fever Tick Research Laboratory, 22675 N. Moorefield Rd., Edinburg, TX 78541, USA b Facultad de Medicina Veterinaria y Zootecnia, University of Tamaulipas, Km 5 carretera Victoria-Mante, Cd Victoria, Tam. CP 87000, Mexico c NOVARTIS Salud Animal México, Pedro Moreno 1677 5o Piso Col. Americana, Guadalajara, Jal. CP. 44 600, Mexico d USDA, ARS, Knipling-Bushland US Livestock Insects Research Laboratory, 2700 Fredericksburg Rd., Kerrville, TX 78028, USA a r t i c l e i n f o Article history: Received 25 February 2010 Received in revised form 14 August 2012 Accepted 16 August 2012 Keywords: Southern cattle tick Resistance Organophosphate Pyrethroid Phenylpyrazole Amidine Macrocyclic lactone a b s t r a c t Five strains of Rhipicephalus (Boophilus) microplus collected from Tamaulipas Mexico were tested for resistance against several classes of acaricides commonly used. All were resis- tant to fipronil. Four of five were co-resistant to permethrin and coumaphos in addition to being resistant to fipronil. One strain, El Zamora was found multi-resistant to perme- thrin, coumaphos, fipronil, and amitraz. Selection with fipronil for 3 generations produced a resistance ratio of 8.3 and 9.4 at the LC 50 and the LC 99 estimates, respectively. Permethrin resistance in El Zamora was possibly linked to elevated esterase (CZEST9) and could be a contributing factor of resistance to fipronil. The implications of resistance for the control of the southern cattle tick in the future are discussed. Published by Elsevier B.V. 1. Introduction The southern cattle tick, Rhipicephalus (Boophilus) microplus (Canestrini), is a major impediment to beef pro- duction in Mexico and while many Mexican ranchers use integrated pest management (IPM) methods to some extent, most must rely heavily on acaricides to control these ticks, especially in the southern and coastal regions of the country where the environmental conditions are ideal for the development of R. microplus (Rodriquez-Vivas et al., 2007). This situation creates the conditions for the rapid ∗ Corresponding author. Present address: USDA, ARS Cattle Fever Tick Research Laboratory, 22675 North Moorefield Rd., Edinburg, TX 78541, USA. Tel.: +1 956 205 7652; fax: +1 965 205 7638. E-mail addresses: robert.miller@ars.usda.gov (R.J. Miller), almazan@uat.edu.mx (C. Almazán), martin.ortiz@novartis.com (M. Ortíz-Estrada), John.george@ars.usda.gov (J.E. George). development of resistance as one of the main driving fac- tors of resistance is the frequency of acaricide application. Beginning in the 1980s, reports of R. microplus resis- tant to acaricides began to emerge in Mexico. Initially, the reports described populations of ticks resistant to a single class of acaricide (Aguirre et al., 1986). Within 10 years, tick populations developed resistance to two different classes of acaricide (multiple resistance), and then three classes of acaricide in 2004 (Santamaría and Fragoso, 1994; Li et al., 2004). Much of the recent reporting has been made with ticks collected within the southern and coastal regions of Mexico especially the Yucatán where acaricide use is most frequent (Rodriquez-Vivas et al., 2007). Because of the progressive development of resistance in Mexico, new classes of acaricides have been introduced. Fipronil and ivermectin are two relatively new chemicals used in Mexico for the control of R. microplus. Almost immediately after its introduction, reports of treatment failures to fipronil were reported (M.O.E., unpublished 0304-4017/$ – see front matter. Published by Elsevier B.V. http://dx.doi.org/10.1016/j.vetpar.2012.08.011