Assessment and determination of LC₅₀ of carvacrol and salicylic acid analogues with acaricide activity in larvae and adult ticks of Rhipicephalus (Boophilus) microplus

Rhipicephalus (Boophilus) microplus is a tick that causes huge economic losses in cattle. The indiscriminate use of acaricides has generated resistance to most compounds present on the market. Carvacrol and salicylic acid have been widely studied for their biological activities and have been evaluated in different strains of Rhipicephalus. In this research the analogues carvacrol and salicylic acid were evaluated in larvae of R. (B.) microplus with data obtained in larval packet test (LPT) and larval immersion test (LIT). A lethal concentration 50 (LC₅₀) was assessed. The most potent compounds were evaluated in the adult ticks since there are no reports of evaluation in the life state of the parasite. From all the tested compounds, the ethyl 2-methoxybenzoate (91.82 ± 1.66%, 0.91 μmol/mL) and ethyl 2,5-dihydroxybenzoate (89.14 ± 1.61%, 2.04 μmol/mL) showed the highest percentage of mortality and the lowest LC₅₀. They were found to be the best candidates for a study in vivo.