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Rhipicephalus sanguineussensu stricto (s.s.), the temperate lineage of the brown dog tick, is the most common tick found on dogs from urban areas in Rio Grande do Sul (RS) state, southern Brazil. Chemical treatments against ticks are important to control this pest, but can lead to selection for acaricide resistance. Unfortunately, little is known about acaricide resistance in this tick species in Brazil, although such information is very important to companion animal clinical practice. The objective of this study was to analyze acaricide susceptibility of R. sanguineuss.s. from the metropolitan area of Porto Alegre, RS. Engorged females ticks were collected in ten different locations, from naturally infested dogs or the environment (homes, shelters and kennels). The progenies were used in toxicological larval tests with deltamethrin, fipronil and ivermectin. Mortality data was used to determine the median lethal concentrations (LC50) for each tick population and resistance was characterized based on relative susceptibility of the different tick populations against each acaricide. Seven samples were considered resistant to deltamethrin, with resistance ratios (RR) ranging from 2.32 to 5.67. From five tick populations tested with fipronil, three were considered resistant, with RR varying from 2.56 to 13.83. For ivermectin, resistance ratios were lower, ranging from 1.54 to 2.97. The results reveal a notable variance of susceptibility to deltamethrin, fipronil and ivermectin in the R. sanguineuss.s. populations studied. This study documents for the first time the existence of acaricide-resistant populations of R. sanguineuss.s. in Brazil.

Ticks and tick-borne diseases are a major constraint for a sustainable cattle industry in the tropical and subtropical regions of the world. The development of resistance to most of the commonly used acaricides has led to an assessment of herbal products for acaricidal activity as an eco-friendly tick control alternative. A botanical product, Essentria®IC-3 insect concentrate containing rosemary oil (10%), geraniol (5%) and peppermint oil (2%), acts on target pests by blocking octopamine. Essentria®IC-3 and its active components were evaluated for larvicidal activity against several susceptible and acaricide-resistant strains of the cattle fever tick, Rhipicephalus(Boophilus) microplusCanestrini by Larval Packet test using 14–21 d old unfed larvae. The efficacy was assessed by measuring percent larval mortality and estimating lethal concentrations at 50% (LC50) and 95% (LC95) with 95% confidence limits (CL) using probit analysis. The LC50and LC95(95% CL) values for Essentria®IC-3 against the susceptible strain were estimated as 0.647% (0.59–0.69) and 1.033% (0.94–1.19), respectively, whereas, LC50and LC95values for other strains were variable, ranging from 0.597-1.674% and 0.927–2.236%, respectively. Among the various active ingredients, the larvicidal property of Essentria®IC-3 seem to be attributable mainly to geraniol and the LC50and LC95(95% CL) values for geraniol against the susceptible Deutch strain were estimated as 0.656% (0.61–0.69) and 1.114% (1.03–1.25), respectively. The comparison of LC50and LC95values of acaricide-resistant strains showed susceptibility comparable to Deutch against geraniol except for the Las Palmas strain. We report a low level of resistance in some of the acaricide-resistant strains against the herbal acaricide in the cattle tick for the first time, possibly due to cross-resistance to chemical acaricides.

Amitraz is one of the most used acaricides for the control of ticks of domestic animals, however, extensive use of this active ingredient has favored the development of resistant populations of Rhipicephalus microplusworldwide. The possible mechanisms of metabolic and/or target-site alterations mechanisms of amitraz resistance were investigated in a Brazilian field population of R. microplus(São Gabriel strain). Bioassays with the synergists piperonylbutoxide, triphenylphosphate and diethyl-maleate were used to evaluate the metabolic mechanisms involved. Target-site insensitivity was investigated by amplification and sequencing of a fragment of the octopamine/tyramine (OCT/TYR) receptor gene. Piperonylbutoxide synergism (synergism ratio = 2.8) indicated the participation of the P450 pathway in the detoxification of amitraz. Previously reported single nucleotide polymorphisms that confer amino acid changes in the OCT/TYR receptor, threonine to proline (T8P) and leucine to serine (L22S), were found in the amitraz-resistant strain but not in the susceptible reference strain. The results suggest that amitraz resistance in the studied strain is multi-factorial and may result from cytochrome P450 detoxification and mutations in octopamine receptors.

•Alternatives to control acaricide-resistant ticks are needed.•Plant-derived essential oils have a high potential to be used in tick control.•Laboratory and animal tests were made with a botanical acaricide at 6.25 % in water.•In laboratory tests, 100 % and 94 % mortality were observed against unfed larvae and engorged females of R. microplus.•Animal test showed 70 % overall efficacy of the botanical pesticide against R. microplus.

Rhipicephalus annulatusfield populations collected from small cattle farms in Beni-Suef province in Egypt were evaluated for deltamethrin resistance by toxicological in vitrobioassays (adult immersion test-AIT and larval packet test-LPT). Moreover, a quantitative PCR high resolution melting (PCR-HRM) technique was used to detect nucleotide substitutions in the voltage-gated sodium channel (Na-channel) gene. By the in vitrobioassays, the examined ticks were phenotypically categorized as deltamethrin susceptible (populations El-Wasta - A, and El-Hakamna - C) or resistant (populations El-Wasta - B, El-Hakamna - D, EL-Halabia - E, and Kom-abokhalad - F). Based on LPT findings, the phenotypic resistant populations were found to have a resistance ratio between 6.5 – 10.8. The PCR-HRM genotyping of the ticks showed variable melting curves among the populations in domain II of the Na-channel gene. Analysis of the curves showed the presence of wild type, mutant homozygous, and mutant heterozygous tick individuals. By sequencing the PCR amplified fragments, the C190A mutation was the only detected nucleotide polymorphism of domain II among the phenotypically resistant populations, which was present in 39.5 % (34/86) of the ticks tested. On the other hand, the phenotypically susceptible populations A and C did not show C190A mutant homozygous (RR) individuals. Meanwhile, in domain III all of the examined populations revealed melting curves like the wild type. Furthermore, the sequence analysis of these populations confirmed the absence of SNPs in domain III. The C190A single point mutation was detected for the first time in domain II of the Na-channel gene of deltamethrin-resistant R. annulatusin Egypt using PCR-HRM. Screening for efficacy of chemical compounds used by farmers to control ticks on cattle should be considered as part of animal health programs to manage the emerging resistance to acaricides in R. annulatuspopulations.

Rhipicephalus microplusis responsible for major economic losses in cattle ranching in Brazil, and the development of multiple acaricide resistance is a major concern to control this ectoparasite. To determine the resistance of R. microplusto acaricides in 26 ranches in the semi-arid region of Paraíba State, Brazil, larval assays were performed with cypermethrin, chlorpyriphos, amitraz, ivermectin and fipronil and resistance was observed in all locations. The frequency of populations resistant to cypermethrin, chlorpyriphos, amitraz and ivermectin was, respectively, 96 %, 72 %, 83 % and 92 % while none was resistant to fipronil. Resistance to one, two, three and four acaricides was recorded, respectively, in 4 %, 15 %, 31 % and 50 % of the farms. Errors in the control management of R. microplusdetermined the development of resistance to acaricides in all evaluated properties pointing towards development of new strategies for its control. In order to control multiple acaricide-resistant cattle tick populations in this area it is recommended to apply suppressive treatments with fipronil and/ or fluazuron.

•Rhipicephalus annulatustick is an important vector of diseases to cattle.•Pyrethroid resistance was detected in a field population of R. annulatusin the USA.•Fragments of the voltage-gated sodium channel gene of R. annulatuswere sequenced.•A qPCR-HRM was adapted to detect pyrethroid-resistant mutations in R. annulatus.