Detection of coumaphos, fipronil, flumethrin and amitraz susceptibility in Rhipicephalus sanguineus s.l. (Acari: Ixodidae) from Mexico.

Abstract

The brown dog tick, Rhipicephalus sanguineus sensu lato (s.l.), is an important ectoparasite with medical and veterinary significance worldwide. Control mainly relies on acaricides, which can contribute to the development of resistant tick populations. This study aimed to evaluate the susceptibility levels of R. sanguineus s.l. collected from different regions across Mexico, to the acaricides coumaphos, fipronil, flumethrin, and amitraz. Engorged ticks were collected from naturally infested dogs in 13 states across the country. The hatched larvae were tested for susceptibility to coumaphos, fipronil, and flumethrin using larval packet tests, while amitraz was tested using larval immersion tests. Mortality data were analyzed using probit analysis to calculate the median lethal concentrations (LC50), and resistance ratios (RRs) were measured based on LC50 values. The results indicated that 50% of the samples showed resistance to coumaphos, 7% to amitraz, and 4% to fipronil, while none showed resistance to flumethrin. The RRs ranged from 3.37 to 11.63, with two samples demonstrating double resistance. This study is notable for reporting, for the first time in Mexico, the presence of resistance to both coumaphos and fipronil.