title: Ten years later: Evaluation of the effectiveness of 12.5% amitraz against a field population of Rhipicephalus (Boophilus) microplus using field studies, artificial infestation (Stall tests) and adult immersion tests.
abstract: Using field trials, artificial infestations (Stall tests) and in vitro adult immersion tests, the present study evaluated the acaricidal efficacy of 12.5% amitraz administered via whole body spraying against a Rhipicephalus (Boophilus) microplus population that did not have any contact with chemical products belonging to this acaricide family for 10 years (approximately 40 generations). Two natural infestation trials, two artificial infestation trials (Stall tests) and two adult immersion tests were performed in two different stages in 2005 and 2015. Between 2002 and 2015, the bovine herd of this property was formed by approximately 450 animals from the Simmental breed that were divided into nine paddocks formed by Cynodon dactylon (L.) Pers. For the natural infestation experiments in 2005 and 2015, we selected nearly 70 animals naturally infested with ticks from the same herd that belonged to the "São Paulo" farm located in São José do Rio Pardo, São Paulo, Brazil. Field studies were performed in the same paddock (9). To evaluate anti-R. (B.) microplus activity in the artificially infested cattle (Stall tests) and adult immersion tests, two experiments of each methodology were performed at CPPAR (the Center of Research in Animal Health located on the FCAV/UNESP campus in Jaboticabal, São Paulo, Brazil) in 2005 and 2015. R. (B.) microplus used in the artificial infestation, and adult immersion test experiments were obtained from paddocks 1-9 in 2005 and 2015 from the commercial farm where the field studies were performed. Based on the obtained results, it was possible to conclude that amitraz use in rotation with pyrethroids every 28 days for three consecutive years (2002-2004) previous to the beginning of the first trial (2005) was sufficient to generate a R. (B.) microplus strain resistant to amitraz. Moreover, using field trials, artificial infestations (Stall tests) and adult immersion tests, we verified that 40 generations of the tick species with no contact to the aforementioned compound (amitraz) were not sufficient to revert or modify the efficacy/resistance of amitraz for this analyzed R. (B.) microplus strain. The reversion of amitraz efficacy values in R. (B.) microplus may only occur when resistance of the field strain is incipient. Alternatively, the differences in the results may be due to differences in the Rhipicephalus spp. species between current study locations. Therefore, future studies must be performed to prove this hypothesis.
authors.affiliation: CPPAR-Animal Health Research Center, Faculdade de Ciências Agrárias e Veterinárias, UNESP, Campus de Jaboticabal, Via de Acesso Prof. Paulo Donatto Castellane, s/n° CEP: 14884-900, Jaboticabal, São Paulo, Brazil.
authors.forename: Willian Giquelin
authors.initials: WG
authors.lastname: Maciel
authors.affiliation: CPPAR-Animal Health Research Center, Faculdade de Ciências Agrárias e Veterinárias, UNESP, Campus de Jaboticabal, Via de Acesso Prof. Paulo Donatto Castellane, s/n° CEP: 14884-900, Jaboticabal, São Paulo, Brazil; Instituto de Patologia Tropical e Saúde Pública, Universidade Federal de Goiás, Goiânia, Goiás 74605050, Brazil. Electronic address: wdzlopes@hotmail.com.
authors.forename: Welber Daniel Zanetti
authors.initials: WD
authors.lastname: Lopes
authors.affiliation: CPPAR-Animal Health Research Center, Faculdade de Ciências Agrárias e Veterinárias, UNESP, Campus de Jaboticabal, Via de Acesso Prof. Paulo Donatto Castellane, s/n° CEP: 14884-900, Jaboticabal, São Paulo, Brazil.
authors.forename: Breno Cayeiro
authors.initials: BC
authors.lastname: Cruz
authors.affiliation: CPPAR-Animal Health Research Center, Faculdade de Ciências Agrárias e Veterinárias, UNESP, Campus de Jaboticabal, Via de Acesso Prof. Paulo Donatto Castellane, s/n° CEP: 14884-900, Jaboticabal, São Paulo, Brazil.
authors.forename: Lucas Vinicius Costa
authors.initials: LV
authors.lastname: Gomes
authors.affiliation: CPPAR-Animal Health Research Center, Faculdade de Ciências Agrárias e Veterinárias, UNESP, Campus de Jaboticabal, Via de Acesso Prof. Paulo Donatto Castellane, s/n° CEP: 14884-900, Jaboticabal, São Paulo, Brazil.
authors.forename: Weslen Fabrício Pires
authors.initials: WF
authors.lastname: Teixeira
authors.affiliation: CPPAR-Animal Health Research Center, Faculdade de Ciências Agrárias e Veterinárias, UNESP, Campus de Jaboticabal, Via de Acesso Prof. Paulo Donatto Castellane, s/n° CEP: 14884-900, Jaboticabal, São Paulo, Brazil.
authors.forename: Carolina
authors.initials: C
authors.lastname: Buzzulini
authors.affiliation: CPPAR-Animal Health Research Center, Faculdade de Ciências Agrárias e Veterinárias, UNESP, Campus de Jaboticabal, Via de Acesso Prof. Paulo Donatto Castellane, s/n° CEP: 14884-900, Jaboticabal, São Paulo, Brazil.
authors.forename: Murilo Abud
authors.initials: MA
authors.lastname: Bichuette
authors.affiliation: CPPAR-Animal Health Research Center, Faculdade de Ciências Agrárias e Veterinárias, UNESP, Campus de Jaboticabal, Via de Acesso Prof. Paulo Donatto Castellane, s/n° CEP: 14884-900, Jaboticabal, São Paulo, Brazil.
authors.forename: Gabriel Pimentel
authors.initials: GP
authors.lastname: Campos
authors.affiliation: CPPAR-Animal Health Research Center, Faculdade de Ciências Agrárias e Veterinárias, UNESP, Campus de Jaboticabal, Via de Acesso Prof. Paulo Donatto Castellane, s/n° CEP: 14884-900, Jaboticabal, São Paulo, Brazil.
authors.forename: Gustavo
authors.initials: G
authors.lastname: Felippelli
authors.affiliation: CPPAR-Animal Health Research Center, Faculdade de Ciências Agrárias e Veterinárias, UNESP, Campus de Jaboticabal, Via de Acesso Prof. Paulo Donatto Castellane, s/n° CEP: 14884-900, Jaboticabal, São Paulo, Brazil.
authors.forename: Vando Edésio
authors.initials: VE
authors.lastname: Soares
authors.affiliation: CPPAR-Animal Health Research Center, Faculdade de Ciências Agrárias e Veterinárias, UNESP, Campus de Jaboticabal, Via de Acesso Prof. Paulo Donatto Castellane, s/n° CEP: 14884-900, Jaboticabal, São Paulo, Brazil.
authors.forename: Gilson Pereira
authors.initials: GP
authors.lastname: de Oliveira
authors.affiliation: CPPAR-Animal Health Research Center, Faculdade de Ciências Agrárias e Veterinárias, UNESP, Campus de Jaboticabal, Via de Acesso Prof. Paulo Donatto Castellane, s/n° CEP: 14884-900, Jaboticabal, São Paulo, Brazil.
authors.forename: Alvimar José
authors.initials: AJ
authors.lastname: da Costa
mesh_terms: D056810:Acaricides / Q000008:administration & dosage / Q000592:standards; D000818:Animals; D001938:Brazil; D002417:Cattle; D002418:Cattle Diseases / Q000188:drug therapy*; D007305:Insecticide Resistance; D011722:Pyrethrins / Q000008:administration & dosage; D048494:Rhipicephalus / Q000187:drug effects; D013984:Tick Infestations / Q000188:drug therapy / Q000662:veterinary*; D014052:Toluidines / Q000008:administration & dosage / Q000494:pharmacology / Q000592:standards
chemical_list: D056810:Acaricides; D011722:Pyrethrins; D014052:Toluidines; C014983:amitraz
keywords: Artificial infestations; Natural infestation; Resistance; Spray formulations; Stall test