Acaricidal Action of Water Extracts from Eysenhardtia polystachya Against Rhipicephalus (Boophilus) microplus

The action of a water extract of Eysenhardtia polystachya on the cattle tick Rhipicephalus (Boophilus) microplus adults and larvae was studied. A stock solution of the extract was serially diluted in distilled, sterile water to obtain test concentrations of 1%, 0.5%, 0.25%, 0.125%, and 0.0625%, and a field trial was carried out on Cebu/Holstein F1 cattle experimentally infected with ticks. The extract was applied by spraying at a rate of 5 liters per animal per day for 7 d. The effectiveness of treatment against engorged females was assessed by measuring mortality and egg production in an adult immersion test. Although the natural extract was found to be nonlethal to adults, it had a significant effect on egg-laying at the highest concentrations, inhibiting 64.58% of oviposition. Using a larval immersion test, the extract was determined to be highly toxic to the larvae at the higher concentrations, killing 100, 99.94 +/- 0.06, 99.35 +/- 0.37, 99.17 +/- 0.14, and 99.03 +/- 0.01 at concentrations of 1%, 0.5%, 0.25%, 0.125%, and 0.0625%, respectively, after 72 hr of immersion. Field trial results also revealed nonadulticidal efficacy. Nevertheless, adult ticks and egg masses recovered from treated calves weighed less than those collected from untreated controls. Also, daily application of the plant extract over 7 d provided 94.82% control as measured by the index of fecundity in engorged females. Aqueous extract from E. polystachya possesses a well-defined acaricidal effect on R. microplus larvae and inhibits oviposition. These findings allow us to suggest that further extraction and characterization of the active compound(s) responsible for the observed acaricidal activity may reveal new xenobiotics for further drug-development and can contribute to our understanding of the larvacidal mechanism of action of E. polystachya extract.