Synergistic larvicidal activity of Jacquinia ruscifolia flowers and Thuja orientalis strobili petroleum ether extract against Culex quinquefasciatus

Abstract

Objective: Investigating synergistic larvicidal activity by using flowers of Jacquinia ruscifolia and strobili of Thuja orientalis petroleum ether extract against third-instar Culex quinquefasciatus larvae and find out the most effective combination. Methods: After preliminary screening done by crude extract and petroleum ether solvent extract of two plants, J. ruscifolia and T. orientalis were examined separately and in combinations (1:1, 1:2 and 2:1) against filarial vector Cx. quinquefasciatus third-instar larvae with gradually increasing concentration (50 ppm to 250 ppm). To observe the synergistic effect, if any, LC50 values are first estimated. Synergistic factor (SF) can be calculated by using LC50 value of the individual plant extract/ LC50 value of the combined plant extracts at different consecutive periods (24, 48 and 72 hours). SF value > 1 shows presence of synergism. Phytochemical analyses of extract done by IR and GC-MS analysis. Results: 100% mortality was recorded when bioassay experiment was done with petroleum ether extract of J. ruscifolia flower and T. orientalis strobili in their combinations at 250 ppm concentration against third-instar Cx. quinquefasciatus in 72 hours of continuous exposure. For every case SF obtained > 1 showing synergism. The dose-effect curve and combination-index plot suggesting 1:2 combination showing synergism with gradual increased concentration among three. FT-IR analysis suggesting presence of functional groups like alkane, aldehyde, amine salt, aromatics, ether and ester. GC-MS analysis suggest presence of five active compounds, viz., Scopolamine; 1-methyl-7-azabicyclo [4,1,0] heptane; 6-methyl-6-[5-methyl-4-propyl-2-yl] heptane 2-one; Pyrrolidinium 2, carboxy 4-hydroxy-1,1 dimethyl hydroxide and 5-hydroxy pentanamide.