Evaluation of larvicidal activity of Senecio laetus Edgew. against the malarial vector, Anopheles stephensi, dengue vector, Aedes aegypti and Bancroftian filariasis vector, Culex quinquefasciatus

The vector-borne diseases caused by mosquitoes are one of the major health problems around the world especially in tropical and sub-tropical countries. The present study was carried out to evaluate the larvicidal potential of petroleum ether, chloroform, ethyl acetate and methanol extracts of root and leaves of Senecio laetus Edgew. against the early fourth-instar larvae of the malarial vector, Anopheles stephensi; dengue vector, Aedes aegypti and the filarial vector, Culex quinquefasciatus. The root and leaf extracts of S. laetus at 200, 100, 50, 25 and 12.5 ppm caused a significant mortality of the tested mosquito species and root extracts showed the highest larvicidal potential than the leaf extracts. After 12 and 24 h of exposure period, the highest larvicidal activities were observed in the methanol extract of root with LC50 = 24.68 and 16.70 ppm and LC90 = 200.42 and 109.19 ppm for An. stephensi; LC50 = 44.25 and 22.30 ppm and LC90 = 266.19 and 144.67 ppm for Ae. aegypti and LC50 = 84.14 and 30.68 ppm and LC90 = 291.17 and 183.84 ppm for C. quinquefasciatus at 200 to 12.5 ppm respectively. Further, gas chromatography-mass spectroscopy (GC-MS) analysis was carried out to identify the bioactive chemical constituents present in the methanol extract of root of Senecio laetus. GC-MS analysis revealed the presence of 29 compounds. The major chemical constituents identified were D:C-Friedours-7-en-3-ol, (3.beta.), Seneciphylline, β-Sitosterol, 5-Hydroxymethylfurfural, 1H-Pyrrolo [2,3-b]pyridine-1-propionitrile, 2-phenyl- and n-Hexadecanoic acid. Further in-depth study is needed to identify and characterize the active molecule responsible for the larvicidal activities which are underway in our laboratory.