Active constituent nonacosane from Sphaeranthus indicus (Asterales: Asteraceae) leaves as a potent larvicidal agent against Aedes aegypti (Diptera: Culicidae) and Culex quinquefasciatus (Diptera: Culicidae)

Abstract

Mosquitoes are major carriers of diseases such as dengue, lymphatic filariasis, malaria, chikungunya, and Japanese encephalitis, as they feed on blood and act as ectoparasites. This study focuses on the effectiveness of a plant-derived insecticide, specifically the hexane extract from Sphaeranthus indicus leaves, against Aedes aegypti and Culex quinquefasciatus mosquitoes. By conducting phytochemical extraction, fractionation, and spectroscopic analysis, ten fractions were isolated. One of these fractions showed significant mosquito-killing activity, with nonacosane identified as the primary active component. Various bioassays, including tests for eggs, larvae, and pupae, were conducted. Nonacosane exhibited ovicidal activity, with effectiveness rates of 16.4 % and 17.8 % at 2 ppm against Ae. aegypti and Cx. quinquefasciatus, respectively. Larvicidal and pupicidal tests further confirmed its strong activity, with LC₅₀ values of 2.63 ppm and 2.47 ppm for larvae, and 2.98 ppm and 2.67 ppm for pupae of Ae. aegypti and Cx. quinquefasciatus, respectively. The mosquitocidal effectiveness of nonacosane was comparable to that of established insecticides like azadirachtin and temephos. This research highlights the potential of plant-based compounds in developing effective and environmentally sustainable mosquito control strategies, especially in light of the increasing resistance to synthetic insecticides.