In vitro and in vivo assessment of monoterpene derivatives for controlling cattle tick rhipicephalus (boophilus) microplus

Abstract

Ticks are ectoparasites that significantly impact livestock health and productivity. Phytochemicals, natural compounds derived from plants, have gained attention as potential alternatives in the face of widespread resistance to synthetic acaricides. This study evaluated the in vitro and in vivo acaricidal activity of geraniol (GNL) and thymol (TML). Additionally, GNL exposure in ticks was measured using HPLC. In vitro GNL activity was assessed using the Adult Immersion Test (AIT) with a 1% GNL solution (1% acetone-0.02% Triton X) and an immersion time of 2 minutes. In vivo activity of GNL was evaluated in six calves experimentally infested with Rhipicephalus (Boophilus) microplus. Calves were treated with 1% GNL alone, cypermethrin 20 % alone, or a combination of both. Ticks exposed to GNL in vitro and in vivo (1-3 days post-treatment) were collected for HPLC measurement of GNL concentrations. In vitro TML activity was evaluated using the Larval Immersion Test (LIT) with concentrations ranging from 0.001% to 0.1% TML solution (1% acetone-0.02% Triton X). No significant differences were observed in the oviposition of engorged females after immersion in GNL (efficacy 31%). Similarly, no reduction in tick counts was observed after in vivo treatment with GNL in calves. Although ticks were exposed to similar concentrations of GNL (1%), exposure was significantly higher (P < 0.05) in the in vitro trial. GNL concentrations ranged from 0.96 to 2.60 µg/g in the in vivo trial and from 23.3 to 61.7 µg/g in the in vitro trial. TML showed high larvicidal activity with an LD50 of 0.01% (95% CI: 0.007-0.012) and an LD99 of 0.053% (95% CI: 0.031-0.251). While GNL did not exhibit significant acaricidal activity in vivo or in vitro, TML's effectiveness against tick larvae is promising. Further in vivo trials are necessary to confirm the efficacy of TML against R. microplus.