Development of an eco-friendly mosquito larvicide for dengue/chikungunya vector control

Due to increasing insecticide resistance and environment concerns associated with synthetic chemicals, this study evaluates the larvicidal potential of essential oils (EO) extracted from seven plant species using hydro-distillation against Aedes aegypti larvae. The chemical profiles of the volatile oils were characterized through gas chromatography-mass spectrometry (GC-MS). The major constituents identified were thymol (74.93%) in Plectranthus amboinicus leaves, terpinen-4-ol (27.13%) in Myristica fragrans nuts, citral (27.55%) in Citrus limon leaves, caryophyllene oxide (36.11%) in Hyptis suaveolens leaves, and asarone (85.51%) in Acorus calamus rhizomes. Larvicidal bioassays revealed LC₅₀ values below 50 ppm (23.40 to 47.34 ppm), with the order of efficacy being A. calamus > M. fragrans > T. ammi > I. verum > C. limon > H. suaveolens > P. amboinicus. Twenty-one binary and thirty-five ternary combinations were tested to determine synergistic, additive, and antagonistic interactions using Wadley's, Ting-Chao Chou, Co-Toxicity Factor, and Chi-square comparison methods. Binary combinations, such as P. amboinicus and M. fragrans and T. ammi and M. fragrans exhibited better synergism, this combination analysed by GC-MS, P. amboinicus and M. fragrans contains, carvacrol (36.23%), thymol (39.04%), and caryophyllene oxide (3.84%). Similarly, the combination of T. ammi and M. fragrans showed thymol (61.96%) and caryophyllene oxide (7.19%). Based on the EO yield and activity the T. ammi and M. fragrans binary combination formulated as soft-gel capsules, this formulation showed 100% larval mortality. EO mixtures work very well, showing they could be good, eco-friendly options to replace chemical insecticides for controlling mosquito larvae in the future.