In vitro acaricidal activity of Murraya koenigii (L.) Spreng (Rutaceae) extracts against synthetic pyrethroid-resistant Rhipicephalus (Boophilus) microplus

Larval packet test was used for detection of resistance status against cypermethrin and deltamethrin, the most commonly used synthetic pyrethroids in Rhipicephalus (Boophilus) microplus collected from Faridkot district, Punjab (India). The slope of mortality, lethal concentration for 50 % (LC₅₀) and resistance levels were determined from the regression graphs of probit mortality of ticks plotted against log values of increasing concentrations of cypermethrin and deltamethrin. Results indicated presence of resistance of levels I and II against cypermethrin (resistance factor (RF) = 2.82) and deltamethrin (RF = 8.44), respectively. Adult immersion test was used to assess the acaricidal activity of aqueous (MLAq), ethanol (MLE), chloroform (MLC), acetone (MLA) and hexane (MLH) extracts of leaves of Murraya koenigii against these synthetic pyrethroid (SP)-resistant engorged adult females of R. (B.) microplus by determination of per cent adult mortality, reproductive index (RI), per cent inhibition of oviposition (%IO) and hatching rate. The per cent mortality caused by various extracts at concentrations ranging from 0.625 to 10.0 % varied from 0.0 to 100.0 % with maximum per cent mortality of 10.0, 100.0, 70.0, 40.0 and 10.0 recorded against MLAq, MLE, MLC, MLA and MLH, respectively. Among all extracts, the highest acaricidal property against SP-resistant R. (B.) microplus was exhibited by the MLE as it showed the minimum LC₅₀[95 % confidence limit (CL)] values of 2.97 % (2.82–3.12 %), followed by MLC as 10.26 % (8.84–11.91 %) and MLA as 18.22 % (16.18–20.52 %). The average egg mass weight recorded in live ticks treated with various concentrations of different extracts was lower than the respective control group ticks and was significantly (p < 0.01) lower in ticks treated with MLH extract. However, no significant effect on hatchability of eggs of treated groups when compared to control was recorded. A significant (p < 0.05) decrease in the RI was recorded in MLH extract-treated ticks, and the %IO varied from 0.07 to 34.73 % with various extracts and was recorded maximum with highest concentration of MLH. The results of the current study indicate that the extracts of M. koenigii can be used for control of SP-resistant ticks.