title: Multiple resistance to acaricides in field populations of Rhipicephalus microplus from Rio Grande do Sul state, Southern Brazil.
abstract: Acaricide resistance is a major obstacle to the control of Rhipicephalus microplus. Historically, the indiscriminate use of chemical compounds has contributed to the selection of populations resistant to different classes of acaricides. Therefore, multiple acaricide resistance is an important threat to the chemical control of the cattle tick. To investigate the occurrence and extent of multiple resistance to acaricides in Southern Brazil we performed larval tests with cypermethrin, chlorpyriphos, amitraz, fipronil and ivermectin on 104 cattle tick field samples from different ranches in Rio Grande do Sul, between the years 2013 and 2015. Adult immersion tests with a commercial formulation mixture of chlorpyriphos and cypermethrin were performed on 75 samples. Four levels of resistance were established according to the mortality of larvae: Level I: mortality between 82% and 95%; Level II: mortality between 57% and 82%; Level III: mortality between 25% and 57%; and Level IV: mortality lower than 25%. Resistance to cypermethrin was detected in 98.08% of the samples evaluated, mostly at resistance level IV. The frequency of samples resistant to amitraz, chlorpyriphos, ivermectin and fipronil was 76.92%, 60.58%, 60.58% and 53.85% respectively. Multiple resistance to three or more compounds was found in 78.85% of the samples. The results obtained in this study are alarming and reveal a new scenario for the challenge of tick control using chemicals. This is an issue of high importance to cattle production systems where this tick is responsible for a high economic impact.
authors.affiliation: Laboratório de Parasitologia, Instituto de Pesquisas Veterinárias Desidério Finamor, FEPAGRO Saúde Animal, Estrada Municipal do Conde, 6000, 92990-000, Eldorado do Sul, Brazil. Electronic address: guilherme-klafke@fepagro.rs.gov.br.
authors.forename: Guilherme
authors.initials: G
authors.lastname: Klafke
authors.affiliation: Laboratório de Parasitologia, Instituto de Pesquisas Veterinárias Desidério Finamor, FEPAGRO Saúde Animal, Estrada Municipal do Conde, 6000, 92990-000, Eldorado do Sul, Brazil.
authors.forename: Anelise
authors.initials: A
authors.lastname: Webster
authors.affiliation: Laboratório de Parasitologia, Instituto de Pesquisas Veterinárias Desidério Finamor, FEPAGRO Saúde Animal, Estrada Municipal do Conde, 6000, 92990-000, Eldorado do Sul, Brazil.
authors.forename: Bruno
authors.initials: B
authors.lastname: Dall Agnol
authors.affiliation: Laboratório de Parasitologia, Instituto de Pesquisas Veterinárias Desidério Finamor, FEPAGRO Saúde Animal, Estrada Municipal do Conde, 6000, 92990-000, Eldorado do Sul, Brazil.
authors.forename: Endrigo
authors.initials: E
authors.lastname: Pradel
authors.affiliation: Laboratório de Parasitologia, Instituto de Pesquisas Veterinárias Desidério Finamor, FEPAGRO Saúde Animal, Estrada Municipal do Conde, 6000, 92990-000, Eldorado do Sul, Brazil.
authors.forename: Jeniffer
authors.initials: J
authors.lastname: Silva
authors.affiliation: Laboratório de Parasitologia, Instituto de Pesquisas Veterinárias Desidério Finamor, FEPAGRO Saúde Animal, Estrada Municipal do Conde, 6000, 92990-000, Eldorado do Sul, Brazil.
authors.forename: Luiz Henrique
authors.initials: LH
authors.lastname: de La Canal
authors.affiliation: Laboratório de Parasitologia, Instituto de Pesquisas Veterinárias Desidério Finamor, FEPAGRO Saúde Animal, Estrada Municipal do Conde, 6000, 92990-000, Eldorado do Sul, Brazil.
authors.forename: Marcelo
authors.initials: M
authors.lastname: Becker
authors.affiliation: Laboratório de Parasitologia, Instituto de Pesquisas Veterinárias Desidério Finamor, FEPAGRO Saúde Animal, Estrada Municipal do Conde, 6000, 92990-000, Eldorado do Sul, Brazil.
authors.forename: Mateus Felipe
authors.initials: MF
authors.lastname: Osório
authors.affiliation: Laboratório de Parasitologia, Instituto de Pesquisas Veterinárias Desidério Finamor, FEPAGRO Saúde Animal, Estrada Municipal do Conde, 6000, 92990-000, Eldorado do Sul, Brazil.
authors.forename: Melanie
authors.initials: M
authors.lastname: Mansson
authors.affiliation: Laboratório de Parasitologia, Instituto de Pesquisas Veterinárias Desidério Finamor, FEPAGRO Saúde Animal, Estrada Municipal do Conde, 6000, 92990-000, Eldorado do Sul, Brazil.
authors.forename: Rafael
authors.initials: R
authors.lastname: Barreto
authors.affiliation: Laboratório de Parasitologia, Instituto de Pesquisas Veterinárias Desidério Finamor, FEPAGRO Saúde Animal, Estrada Municipal do Conde, 6000, 92990-000, Eldorado do Sul, Brazil.
authors.forename: Ramon
authors.initials: R
authors.lastname: Scheffer
authors.affiliation: Laboratório de Parasitologia, Instituto de Pesquisas Veterinárias Desidério Finamor, FEPAGRO Saúde Animal, Estrada Municipal do Conde, 6000, 92990-000, Eldorado do Sul, Brazil.
authors.forename: Ugo Araújo
authors.initials: UA
authors.lastname: Souza
authors.affiliation: Laboratório de Parasitologia, Instituto de Pesquisas Veterinárias Desidério Finamor, FEPAGRO Saúde Animal, Estrada Municipal do Conde, 6000, 92990-000, Eldorado do Sul, Brazil.
authors.forename: Vivian Bamberg
authors.initials: VB
authors.lastname: Corassini
authors.affiliation: Laboratório de Parasitologia, Instituto de Pesquisas Veterinárias Desidério Finamor, FEPAGRO Saúde Animal, Estrada Municipal do Conde, 6000, 92990-000, Eldorado do Sul, Brazil.
authors.forename: Julsan
authors.initials: J
authors.lastname: Dos Santos
authors.affiliation: Laboratório de Parasitologia, Instituto de Pesquisas Veterinárias Desidério Finamor, FEPAGRO Saúde Animal, Estrada Municipal do Conde, 6000, 92990-000, Eldorado do Sul, Brazil.
authors.forename: José
authors.initials: J
authors.lastname: Reck
authors.affiliation: Laboratório de Parasitologia, Instituto de Pesquisas Veterinárias Desidério Finamor, FEPAGRO Saúde Animal, Estrada Municipal do Conde, 6000, 92990-000, Eldorado do Sul, Brazil.
authors.forename: João Ricardo
authors.initials: JR
authors.lastname: Martins
mesh_terms: D056810:Acaricides / Q000494:pharmacology*; D000818:Animals; D001681:Biological Assay; D001938:Brazil; D007305:Insecticide Resistance; D007814:Larva / Q000187:drug effects; D048494:Rhipicephalus / Q000187:drug effects*
chemical_list: D056810:Acaricides
keywords: Acaricides; Brazil; Control; Multiple resistance; Rhipicephalus microplus