Spatial repellency and molecular docking studies on thymol, oleic acid and naphthalene against the urban malaria vector, Anopheles stephensi (Diptera: Culicidae)

Abstract Background Anopheles stephensi (Diptera: Culicidae) is a primary urban malaria vector in India and neighbouring countries. Spatial repellents are a novel tool for personal protection against bites and curbing malaria transmission. The current study assessed the spatial repellency of thymol (T), oleic acid (O) phytocompounds and naphthalene (N) individually and in blends against adult An. stephensi to estimate the spatial activity index (SAI) and dose-response relationship. In silico interactions of these phytochemicals with 11 target proteins and their associated active toxicity sites were assessed. Results The SAI values ranged from 0 to 0.675 for T, O, and N individually, and from − 0.025 to 0.55 for the blends, indicating promising repellency. The lowest ED 50 (0.052%) and ED 90 (0.485%) were recorded for both thymol and naphthalene. Among the blends, 1T:1O:2 N showed the lowest ED 50 and ED 90 . The lowest binding energies (Kcal/mol) of thymol, oleic acid and naphthalene were observed with the Odorant binding protein (-7.1), M2 muscarine receptors (-7.0) and odorant receptors (-7.5), respectively. Hydrogen bond interactions were stronger between thymol and the odorant binding protein, and between oleic acid and the M2 muscarine receptor. Molecular dynamics simulation plots, including deformability, B-factor, eigenvalue, variance, covariance and elastic network models, showed conformational changes at the atomic level. Toxicity prediction scores of these compounds supported the SAI scores. Conclusion Thymol and naphthalene were the most promising spatial repellents for An. stephensi . Molecular docking studies confirmed protein interactions and bioactivity of these compounds. These spatial repellents can be a potential tool in the management of malaria transmission.