Larvicidal activity of essential oils and nanoemulsions against Culex pipiens larvae (Diptera: Culicidae)

Mosquitoes and mosquito-borne diseases are a growing global challenge. Vector control strategies have recently transitioned from chemical insecticides to botanical products. This study evaluated the larvicidal efficacy of dill, lime, and wormwood essential oils (EOs), along with their combinations and nanoemulsions (NEs), against Culex pipiens third-instar larvae over 48 h. Gas chromatography mass spectrometry (GC-MS) analysis revealed major components for dill EO (Apiol 25.46%, Carvone 24.13%, and D-Limonene 23.47%), lime EO (D-Limonene 24.16%, α-Terpineol 13.12%, and β-Pinene 11.98%), and wormwood EO (davanone 33.8%, and camphor 25.67%). The TEM image showed spherical NE droplets (40-160 nm). The droplet size and polydispersity index (PDI) were (164 nm and 0.2), (211.6 nm and 0.2), and (160.8 nm and 0.6) for dill, lime, and wormwood NEs, respectively. Based on LC₅₀ values after 30 min, the dill EO showed the highest larvicidal activity (LC₅₀ = 286.9 ppm; confidence interval (CI) 226.85-341.52 ppm), followed by dill NE (LC₅₀ = 518.9 ppm; CI 290.4 -765.1 ppm) and then (dill + lime) binary combination (LC₅₀ = 1502 ppm; CI 1403.9-1605.4 ppm). The EO showed faster larvicidal activity than NEs, particularly within 30 min. NEs didn't significantly enhance efficacy over crude EOs. Enzyme assays showed variable effects: dill, lime, and wormwood EOs reduced GST activity, whereas their corresponding NEs generally increased enzyme activity at most exposure times. These findings indicate that botanical formulations, particularly those derived from dill, may serve as promising biodegradable alternatives for vector control. However, optimizing essential oil ratios is needed to maximize synergistic effects, and comprehensive assessments of toxicity and environmental impact are required before large-scale application.