Acaricidal activity of Mexican plants against Rhipicephalus microplus resistant to amitraz and cypermethrin

This study evaluates the acaricidal activity of Mexican native plants against a Rhipicephalus microplus population resistant to both amitraz and cypermethrin. To explore the activities of plants, the larvicidal effects of 72 Kupchan fractions (Hex, DCM, AcOEt and MeOH:H₂O) of 18 plant species collected in Veracruz, Mexico were studied. The evaluation of the Kupchan fractions against double resistant R. microplus indicated that the fractions of Annona globiflora (Hex, LC₅₀ = 0.007% w/v; DCM, LC₅₀ = 0.007% w/v), Annona scleroderma (Hex, LC₅₀ = 0.08% w/v; DCM, LC₅₀ = 0.02% w/v), and Litchi chinensis (Hex, LC₅₀ = 0.79% w/v; DCM, LC₅₀ = 0.54% w/v) showed the greatest larvicidal activities. To identify the presence of additive, synergistic, or antagonistic effects, the acaricidal activity of binary mixtures of the most active fractions of A. globiflora, A. scleroderma, L. chinensis and Citrus sinensis were also evaluated. The latter was chosen as it is easy to obtain due to its substantial presence in agricultural activity locally and globally. The results showed synergistic interaction of the fraction Hex of C. sinensis with the fractions of Hex and DCM of L. chinensis. The most active larvicidal fractions were tested against engorged ticks of R. microplus by adult immersion test at concentration of 2.5% w/v. The Hex and DCM fractions from A. globiflora and A. scleroderma were the most active, causing 100% mortality. The Hex and DCM fractions of L. chinensis exhibited approximately 50% mortality, while the other evaluated fractions did not show efficacy at this concentration. Therefore, it is evident that the fractions of these plants have the potential to be used in either combined or single form as effective alternatives in the control of R. microplus zoonoses.