Resistance to all chemical groups of acaricides in a single isolate of <i>Rhipicephalus microplus</i> in Mato Grosso do Sul, Brazil
Luiza Mendes Valsoni, Mariana Green de Freitas, Jéssica Teles Echeverria, Dyego Gonçalves Lino Borges, Juliane Francielle Tutija, Fernando de Almeida Borges
Abstract
The aim of the present study was to evaluate acaricide resistance in Rhipicephalus microplus on a ranch in Brazil. Adult immersion tests were performed using commercial formulations containing organophosphorus compounds (OPs), amidines, synthetic pyrethroids (SPs), OP+SP combinations, and fluazuron. The larval immersion test was used to evaluate susceptibility to ivermectin and fipronil. Resistance was detected to all chemical classes with efficacies of 3.2% (Amitraz 12.5 g), 34.2% (Dichlorvos 45 g + Cypermethrin 5 g), 14.6% (Chlorpyrifos 5 g + Cypermethrin 2 g), 72.9% (Deltamethrin 2.5 g), 60.3% (Cypermethrin 15 g), 70.2% and 51.5% (Cypermethrin 15 g + Chlorpyrifos 25 g + Citronella 1 g), 20.5% (Dichlorvos 60 g + Chlorpyrifos 20 g), 0% (Cypermethrin 15 g), 46.2% (Ethion 2 g + Chlorpyrifos 10.6 g + Cypermethrin 6.2 g). Only two associations, one containing two OPs + one SP and another with a high concentration of OP + SP exhibited efficacy of 100% and 96.3%, respectively. Resistance to fluazuron, ivermectin (Resistance ratio [RR] = 3.08), and fipronil (RR = 3.18) was also detected. The present results indicate resistance to all classes of an existing contact or systemic acaricides and combinations of pyrethroids and organophosphates in an isolate of R. microplus.