Ixodicide action of natural products from native Mexican plants

This work determined the acaricidal effect of 18 Mexican plants against Rhipicephalus microplus. The results of the larvicidal assay revealed that 5 methanolic extracts produced high activity (86-100 % mortality), 3 extracts exhibited relatively high activity (71-85 % mortality), 2 extracts displayed moderate activity (56-70 % mortality), 2 extracts presented low activity (31-55 % mortality) and 6 extracts showed non-significant acaricidal activity (0-30 % mortality). Extracts inducing >56 % mortality were subsequently assayed against engorged ticks of R. microplus by adult immersion test at a concentration of 5.0% w/v. In general terms, the results on larvae and adult ticks indicated that the methanolic extracts of Annona globiflora, Annona scleroderma, Litchi chinensis and Azadirachta indica showed the greatest activities. The crude extract of A. indica was subjected to chromatographic purification, which has led to the isolation of 3-O-butyl-(-)-epigallocatechin (1), 3-O-butyl- (-)-epicatechin (2), (-)-epigallocatechin (3), (+)-gallocatechin (4), (-)-epicatechin (5), beta-sitosterol (6), stigmasterol (7), stigmasterol glucoside (8), triolein (9), azadirachtin A (10), and the octadecanoic acid-tetrahydrofuran-3,4-vinyl ester (11). The isolated compounds' chemical structures were identified by the interpretation of NMR and HRESI-MS spectroscopic data. The isolated compounds were assayed against engorged ticks of R. microplus at a concentration of 6 mM. Based on the results obtained, it was concluded that 3-O-butyl-(-)-epigallocatechin (1), 3-O-butyl-(-)-epicatechin (2), azadirachtin A (10), and octadecanoic acid-tetrahydrofuran-3,4-vinyl ester (11) show the highest effectiveness.