Monitoring of evolution of resistance to commercial acaricidal products in Rhipicephalus sanguineus sensu lato (Latreille, 1806) (Acari: Ixodidae) from Goiânia, Goiás State, Brazil

The Brown dog tick Rhipicephalus sanguineus is the most reported and geographically widely spread tick in the world, presenting a great medical and veterinary importance, mainly because the ability to transmit various diseases to its hosts, causing great harm to pets, but also risks to public health, due to the transmission of emerging pathogens to humans. In order to monitor the resistance or susceptibility of R. sanguineus to acaricides, and contribute to integrated control measures for this vector, the activity of 14 commercial acaricidal products on larvae from the city of Goiânia, Goiás, Brazil were studied. Although these products are already sold as acaricides, their cost-benefit efficiency has been questioned by dog breeders and kennel owners. R. sanguineus larvae were obtained from engorged females collected in naturally infested urban environments. The susceptibility of the larvae was evaluated by the larval packet test (lpt) method. Bioassays were carried out in quadruplicate, at 27 ± 1oC, RH ≥ 80% and photoperiod of 12 hours. About 50 larvae, from 14 to 21 days of age, were conditioned in filter paper envelopes, impregnated with different concentrations of acaricide products, obtained from dilution of stock solutions. The control group used the same amount of larvae, submitted to envelopes treated only with distilled water. A status of resistance of R. sanguineus larvae to acaricide formulations was evidenced for Cypermethrin, Cypermethrin + Piperoline Butoxide, Deltamethrin, Permethrin (after 24h of exposure), in the dosages recommended by the manufacturing laboratories, as they promoted a mean mortality of only 58.36%, 71.36%, 48.7%, and 64.5% of the submitted larvae, respectively, Amitraz providedof only 78.8 and 88.00% (After 24 and 48 hours of exposure to the acaricide, respectively), characterizing a status of possible development of resistance to this acaricide. The other evaluated products (Dichlorvos + Cypermethrin, Chlorfenvinphos + Dichlorvos + Alkyl + Xylol, Chlorpyrifos + Cypermethrin hi-cis, Fipronil, Chlorpyrifos, Cypermethrin + Chlorpyrifos + Citronellal, and Trichlorfon + Coumaphos + Cyfluthrin; and Diazinon) showed higherindices, configuring the susceptibility status to these acaricide formulations. No significant mortality was found in the control groups. The ideal concentrations to kill R. sanguineus larvae (CL99) referring to products that showed low acaricidal activity were statically calculated and are presented in this study. The present work, confronted with previous studies, ratified the real evolution of resistance to synthetic chemical acaricides in local populations of R. sanguineus.