Evaluation and toxicity of Indian plant extracts to the larvae of the malaria vector Anopheles stephensi Liston 1901 (Diptera: Culicidae)

The threat posed by mosquitoes has long been a problem in tropical and subtropical areas of the world. Numerous initiatives have been launched to combat mosquitoes, and studies on plant-based products that inhibit mosquito vectors have been proposed as potential substitutes for the widely used synthetic chemical insecticides that are harmful to non-target creatures, human health, and the environment. In this study, the larvicidal efficacy of solvent (hexane, diethyl ether, dichloromethane, ethyl acetate, and methanol) leaf extracts of Indian plants from 44 different families, 83 genera, and 100 species was tested at 1000 mg/L concentration against the early third instar of Anopheles stephensi, the protozoan parasite that causes malaria. Asteraceae family reported highest larvicidal activity with 38.8 %, followed by Fabaceae (27.4 %) and Piperaceae (24.0 %). Thereafter, the extracts of each promising plant (solvent extracts of plants that exhibited 100 % mortality) were tested at lower concentrations of 100, 200, 300, 400 and 500 mg/L for 24 and 48 h. All solvent extracts of Piper longum, Piper nigrum, Piper sarmentosum, Tagetes erecta and Tagetes minuta showed 100 % larval mortality, hence were chosen as the promising plants for further study. LC₅₀ values < 100 mg/L were reported by the diethyl ether, dichloromethane and methanol extracts of Piper nigrum; ethyl acetate extract of Piper sarmentosum; and by the diethyl ether and dichloromethane extracts of Tagetes minuta. For Piper extracts, the dominant phytocompounds identified by GC-MS analysis were limonene, asaricin, phytol, β-asarone, piperine, pipericine, stearic acid, myristic acid, oleic acid, and piperitone; for Tagetes extracts, the dominant phytocompound was piperitone. The larvicidal property of Piper extracts be due to the action of fatty acids and alkaloids present in them, and for Tagetes extracts, due to the presence of flavonoids, tannins and terpenoids. Further, the present study has documented the first scientific report on the larvicidal activity of Piper sarmentosum leaf extracts against Anopheles stephensi.