Toxicity effect of the acaricide fipronil in semi-engorged females of the tick Rhipicephalus sanguineus (Latreille, 1806) (Acari: Ixodidae): Preliminary determination of the minimum lethal concentration and LC50

Chemical acaricides, especially fipronil (active ingredient of Frontline®), are still the most effective method to control tick populations. In this study, the effectiveness of fipronil was assessed in semi-engorged females of the tick Rhipicephalus sanguineus. A protocol for an in vitro bioassay (AIT) was developed, and the LC50 (lethal concentration 50%) and 95% confidence interval were determined. Ticks were immersed in Petri dishes with different concentrations of fipronil or distilled water for 2 min, dried, and placed in an incubator for 7 days. Dead R. sanguineus females treated with the 14 concentrations of fipronil were counted daily. Mortality results were compared with the Probit analysis, and the LC50 and 95% confidence interval were calculated, g (95): LC50 = 9.647 (4.711 to 13.470). This study was aimed at developing a more appropriate and updated protocol for an in vitro bioassay (AIT - adult immersion test), and providing information on the toxic potential of fipronil (elimination of ectoparasites with lower concentrations) and sensitivity of ticks, especially R. sanguineus, a pest of great interest, due to its occurrence in urban environments.

The present study was aimed at developing a more appropriate and updated protocol for an in vitro bioassay (AIT - adult immersion test), and providing information on the toxic potential of fipronil (elimination of ectoparasites with lower concentrations) and sensitivity of ticks, especially R. sanguineus. The LC50 and the 95% confidence interval were also determined.Research highlights► A more appropriate and updated protocol for an in vitro bioassay (AIT - adult immersion test). ► Providing information on the toxic potential of fipronil (elimination of ectoparasites with lower concentrations). ► Sensitivity of ticks, especially R. sanguineus, a pest of great interest, due to its occurrence in urban environments.