Bioassay-guided fractionation of a dried commercial source, Alpinia galanga (L.) Willd rhizomes extract, against Culex pipiens (Diptera: Culicidae)
2020
Abutaha, Nael | Al-Mekhlafi, Fahd A.
The increasing risk of insecticide resistance in mosquito populations has led to the search for new larvicidal agents. Evaluation of bioassay-guided fractionation of the rhizome extract of Alpinia galanga (L.) Willd against Aedes aegypti was assessed. Bioactive fractions were isolated from the rhizome extract of A. galanga using a Soxhlet extractor and chromatography techniques, and subsequently tested against the fourth instar of Culex pipiens. The lethal concentration (LC) was calculated via log-probit analysis. The active fraction was evaluated by gas chromatography-mass spectroscopy (GC–MS) and infrared (IR) analysis. The highest larvicidal potential obtained from bioassays using the Soxhlet apparatus was observed in dichloromethane (DCM) and ethyl acetate (EtoAc) extracts, with LC₅₀ values of 124.49 and 176.30 ppm, respectively, after 24 h of exposure. Subsequently, the DCM extract was subjected to column and thin-layer chromatography. Results of the DCM extraction and the active TLC fraction (F133) of the Rf value 0.5 revealed that LC₅₀ and LC₉₀ values decreased over time. The F133 fraction of A. galanga exhibited zero hatchability (100% mortality) at LC₅₀ (63.416 ppm) and LC₂₅ (31.70 ppm) against Cx. pipiens eggs. GC–MS analysis of the active thin-layer chromatography TLC fraction (F133) revealed the presence of phenol 2 4-bis (1 1-dimethylethyl), which was identified as the major compound. Alpinia galanga extract is a promising candidate for the control of mosquito populations. Further study is required to determine the effect of the extracts on non-target organisms.
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