Adulticidal activity of essential oils of Ageratum conyzoides L., Hyptis suaveolens L., Ocimum basilicum L. and their synergistic effects against anopheles mosquitoes

This study investigated the insecticidal efficacy of essential oils (EOs) extracted from Ageratum conyzoides, Hyptis suaveolens, and Ocimum basilicum against female Anopheles mosquitoes, aiming to explore their potential as alternatives to synthetic insecticides amidst rising resistance issues. EOs were obtained through steam distillation from freshly harvested plant aerial parts, and their chemical compositions were analyzed using gas chromatography-mass spectrometry. The results revealed significant variations in chemical profiles among the oils, with precocene I dominating in A. Conyzoides, eucalyptol in H. suaveolens, and estragole in O. basilicum. Thin layer chromatography analyses revealed various components with rf values ranging from 0.25 – 0.93. Mosquito bioassay demonstrated varying knockdown effects across the oils, with H. suavolens achieving 77.5% knockdown within six minutes of the observation period. None of the oils or their combinations reached susceptibility status (98–100% mortality), indicating prevalent resistance among the mosquito population in the study area. The combination of A. conyzoides and H. suavolens essential oil gave the highest percentage mortality (70%) at the least time (9 minutes), this is a suggestion of synergistic activity. Despite resistance challenges, this study highlights the promise of botanical insecticides in sustainable mosquito control and underscores the ongoing need for innovation and adaptation in vector management strategies.