title: First report of fluazuron resistance in Rhipicephalus microplus: a field tick population resistant to six classes of acaricides.
abstract: The control of the cattle tick Rhipicephalus microplus is based mainly on the use of chemical acaricides, which has contributed to the emerging problem of selection of resistant tick populations. Currently, there are six main classes of acaricides commercially available in Brazil to control cattle ticks, with fluazuron, a tick growth regulator with acaricidal properties, being the only active ingredient with no previous reports of resistance. Ticks (designated the Jaguar strain) were collected in a beef cattle ranch located at Rio Grande do Sul state, Southern Brazil, after a complaint of fluazuron treatment failure. To characterise the resistance of this strain against acaricides, larval tests were performed and showed that the Jaguar strain was resistant to all of the drugs tested: cypermethrin (resistance ratio, RR=31.242), chlorpyriphos (RR=103.926), fipronil (RR=4.441), amitraz (RR=11.907) and ivermectin (3.081). A field trial was conducted to evaluate the efficacy of fluazuron treatment in heifers that had been experimentally infested with the Jaguar or a susceptible strain. Between 14 and 28 days after treatment, the average efficacy in cattle experimentally infested with the susceptible strain was 96%, while for the Jaguar strain the efficacy was zero. Additionally, the Jaguar strain response to fluazuron was evaluated in vitro using a modified adult immersion test (AIT) and the artificial feeding assay (AFA). With the AIT, 50 ppm of fluazuron inhibited 99% of larvae hatching in the susceptible strain (POA) and less than 50% in the Jaguar strain. Results of the AFA showed a larval hatching rate of 67% at 2.5 ppm of fluazuron with the Jaguar strain; conversely, only 3% of larvae of the susceptible strain hatched at the same fluazuron concentration. The results showed here demonstrated the first case of fluazuron resistance in R. microplus and the first tick population resistant to six classes of acaricides in Brazil.
authors.affiliation: Instituto de Pesquisas Veterinárias Desidério Finamor (IPVDF), Fundação Estadual de Pesquisa Agropecuária (FEPAGRO), Eldorado do Sul, RS, Brazil.
authors.forename: José
authors.initials: J
authors.lastname: Reck
authors.affiliation: Instituto de Pesquisas Veterinárias Desidério Finamor (IPVDF), Fundação Estadual de Pesquisa Agropecuária (FEPAGRO), Eldorado do Sul, RS, Brazil. Electronic address: gmklafke@gmail.com.
authors.forename: Guilherme Marcondes
authors.initials: GM
authors.lastname: Klafke
authors.affiliation: Instituto de Pesquisas Veterinárias Desidério Finamor (IPVDF), Fundação Estadual de Pesquisa Agropecuária (FEPAGRO), Eldorado do Sul, RS, Brazil.
authors.forename: Anelise
authors.initials: A
authors.lastname: Webster
authors.affiliation: Instituto de Pesquisas Veterinárias Desidério Finamor (IPVDF), Fundação Estadual de Pesquisa Agropecuária (FEPAGRO), Eldorado do Sul, RS, Brazil.
authors.forename: Bruno
authors.initials: B
authors.lastname: Dall'Agnol
authors.affiliation: Instituto de Pesquisas Veterinárias Desidério Finamor (IPVDF), Fundação Estadual de Pesquisa Agropecuária (FEPAGRO), Eldorado do Sul, RS, Brazil.
authors.forename: Ramon
authors.initials: R
authors.lastname: Scheffer
authors.affiliation: Instituto de Pesquisas Veterinárias Desidério Finamor (IPVDF), Fundação Estadual de Pesquisa Agropecuária (FEPAGRO), Eldorado do Sul, RS, Brazil.
authors.forename: Ugo Araújo
authors.initials: UA
authors.lastname: Souza
authors.affiliation: Instituto de Pesquisas Veterinárias Desidério Finamor (IPVDF), Fundação Estadual de Pesquisa Agropecuária (FEPAGRO), Eldorado do Sul, RS, Brazil.
authors.forename: Vivian Bamberg
authors.initials: VB
authors.lastname: Corassini
authors.affiliation: Instituto de Pesquisas Veterinárias Desidério Finamor (IPVDF), Fundação Estadual de Pesquisa Agropecuária (FEPAGRO), Eldorado do Sul, RS, Brazil.
authors.forename: Rafael
authors.initials: R
authors.lastname: Vargas
authors.affiliation: Instituto de Pesquisas Veterinárias Desidério Finamor (IPVDF), Fundação Estadual de Pesquisa Agropecuária (FEPAGRO), Eldorado do Sul, RS, Brazil.
authors.forename: Julsan Silveira
authors.initials: JS
authors.lastname: dos Santos
authors.affiliation: Instituto de Pesquisas Veterinárias Desidério Finamor (IPVDF), Fundação Estadual de Pesquisa Agropecuária (FEPAGRO), Eldorado do Sul, RS, Brazil.
authors.forename: João Ricardo de Souza
authors.initials: JR
authors.lastname: Martins
mesh_terms: D056810:Acaricides / Q000494:pharmacology*; D000818:Animals; D001938:Brazil; D002417:Cattle; D018432:Drug Resistance, Multiple; D007814:Larva / Q000187:drug effects; D048494:Rhipicephalus / Q000187:drug effects*
chemical_list: D056810:Acaricides
keywords: Benzoylphenylurea; Boophilus; Brazil; Cattle tick; Drug resistance; Multiple resistance