Acaricidal Effect of Plumbago zeylanica L. Against Amblyoma variegatum

Abstract : Acaricidal effects of extracts and compounds derived from Plumbago zeylanica L. (Plumbaginaceae) roots against different stages of Amblyoma variegatum were assessed using impregnated filter paper bioassay and compared with that of the commercial gamma benzene hexachloride. The observed responses varied according to the stage in the life cycle. It was noted that 2.0% of the total methanolic extract of P. zeylanica roots applied resulted in 100% (p<0.01) mortality against the larvae while 4.0% resulted in 100% (p<0.01) mortality against the nymphs and adult ticks. Petroleum spirit and ethyl acetate fractions made from the crude methanol extract showed a dose-dependant action on the tick stages with the larva being the most susceptible. Isolation of the biologically active constituent from active fractions was done by using column and thin layer chromatography. The structure of the acaricidal component was analyzed by 1H-NMR, 13C-NMR, 1H-13C COSY-NMR and identified as plumbagin. The acaricidal activity of plumbagin was examined and found to be most pronounced on the larvae and least pronounced on the adult tick with LD50 of 3.7 × 10?2 and 1.37 mg/ml respectively (p< 0.010), while gamma benzene hexachloride (positive control) gave an LD50 values of 2.63 ×10?3 and 2.84 × 10?2 mg/ml against the larvae and adult ticks respectively. The results indicated that the naphthoquinone plumbagin possesses acaricidal properties thus giving scientific justification for the folkloric use of the plant in animal husbandry. ?-sitosterol and stigmasterol isolated alongside plumbagin had no significant action on all stages of the tick.