A study was carried out to evaluate the acaricidal activities of crude methanolic extract of leaves of six medicinal plants: Vernonia amygdalina, Calpurnia aurea, Schinus molle, Ricinus communis, Croto6n macrostachys and Nicotiana tobaccum against Rhipicephalus decoloratus and Rhipicephalus pulchellus using in-vitro adult immersion test. Five graded concentrations of the crude extracts; 6.25, 12.5, 25, 50 and 100mg/ml were tested and a change in tick viability was recorded for 24 hours. Diazinon (0.1%) and distilled water were used as positive and negative controls, respectively. Phytochemical screening showed the presence of condensed amount of tannins in all extracts. Starting from 30min post exposure the 100mg/ml concentration of C. aurea and R. communis extracts has caused significantly higher mortality. Significant increase in tick mortality was started 2hr post exposure with diazinon and 50 and 100mg/ml concentrations of S. molle. Vernonia amygdalina extract and diazinon showed significant increase in tick mortality 3hr post exposure with 100mg/ml concentration. At 24hr post exposure, diazinon and 50 and 100mg/ml concentrations of all the extracts have caused significantly higher tick mortality than the rest of the concentrations. Higher concentrations of all the extracts had showed a comparable and strong acaricidal effect on Rh decoloratus and Rh. pulchellus having no significant difference with that of positive control (P>0.05) at 24hr post exposure period. Tick killing activity of all evaluated plant extracts increases with increasing exposure time and concentration as well. Thus, all the tested plants could be used against these ticks as potential alternative to substitute commercially available drugs.
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