Acaricidal activity of alkaloid fractions of Leucas indica Spreng against Rhipicephalus (Boophilus) annulatus tick.

The acaricidal activity from alkaloid and non-alkaloid fractions of Leucas indica were studied against Rhipicephalus (Boophilus) annulatus tick using adult immersion test under laboratory conditions. For this purpose, the engorged female R.(B.) annulatus tick were exposed to two fold serial dilutions of alkaloid extract (50 mg/ml, 25 mg/ml, 12.5 mg/ml, 6 mg/ml and 3 mg/ml) using 'dipping method' in vitro. The efficacy was assessed by measuring the percentage of adult mortality, inhibition of fecundity and hatching rate. The alkaloid fraction of the extract produced concentration dependent delayed adult tick mortality. The extract at a concentration of 50 mg/ml demonstrated 66.67 per cent mortality and 55.16 per cent inhibition of fecundity. Nicotine was identified as one of the compounds of alkaloid fraction. However, it did not reveal any acaricidal activity when tested in vitro at concentrations ranging from 62.5-1000 μg/mL. Hence, the acaricidal action of L. indica is not due to nicotine. Non alkaloid fraction also did not reveal any acaricidal effects against R. (B.) annulatus tick.