Toxicological effects of Sphaeranthus indicus Linn. (Asteraceae) leaf essential oil against human disease vectors, Culex quinquefasciatus Say and Aedes aegypti Linn., and impacts on a beneficial mosquito predator

Use of environmentally friendly, decomposable natural products for effective vector control has gained considerable momentum in modern society. In this study, essential oil of Sphaeranthus indicus (Si-EO) was extracted and further phytochemical screening revealed fourteen compounds with prominent peak area percentage of 24.9 and 22.54% in 3,5-di-tert-butyl-4-hydroxybenzaldehyde and benzene,2-(1,1-dimethylethyl)-1,4-dimethoxy, respectively. The Si-EO was further evaluated for their larvicidal response against Culex quinquefasciatus and Aedes aegypti at different dosages (62.5, 125, 250 and 500 ppm). The Si-EO displayed prominent larvicidal activity at higher concentration (500 ppm) against both species of mosquitoes. The LC50 and LC90 values of oils were observed at 130 and 350 ppm against C. quinquefasciatus larvae and at 140 and 350 ppm against A. aegypti larvae, respectively. Repellent bioassay established higher protection rate at 200 ppm up to 120 min against both the mosquitoes. However, adulticidal response displayed higher mortality rate only at 700 and 800 ppm against C. quinquefasciatus and A. aegypti, respectively. Toxicological screening against mosquito predator Toxorhynchites splendens revealed that the Si-EO was harmless even at the concentration of 1500 ppm. Overall, these results suggest that the Si-EO plays a significant role as a new bio-rational product against ecological burden mosquito vectors which provides an eco-friendly alternative to synthetic pesticides.