Insecticidal activities and comparative efficacy of essential oils of three Citrus species (Sapindales: Rutaceae) against Anopheles gambiae mosquitoes

Essential oils (EOs) from insecticidal plants are becoming prominent again because of their effectiveness in managing disease vectors as well as their eco-friendly nature. The present study evaluated the insecticidal activity of three Citrus species, namely Citrus limon, C. sinensis, and C. aurantifolia, against larvae and adults of Anopheles gambiae. These fully mature Citrus species collected from Ilorin, Nigeria, were extracted, and the chemical components were identified using gas chromatography-mass spectrometry. The EOs extracted were then assessed for toxicity efficacy against larvae and adults of An. gambiae using WHO protocols. Citral was a major component identified in C. aurantifolia, D-limonene in C. limon and Myrtenol in C. sinensis. The highest percentage knockdown was recorded in 0.3 ml of C. limon (95.6±1.15 mosquitoes) against An. gambiae, while the lowest KDT₅₀ and KDT₉₀ were found in 0.5ml of C. aurantifolia (5.79 mins) and C. limon (19.61 mins), respectively. A 100% mortality rate was observed in adult female An. gambiae at concentrations of 0.1 ml of C. limon and 0.3 ml of both C. limon and C. aurantifolia. This result was not significantly different from the 99% mortality rate observed with the control, deltamethrin. Additionally, 100% mortality was recorded in An. gambiae larvae at 0.3 ml of both C. aurantifolia and C. limon after 48 hours of exposure. The lowest LT₅₀ and LT₉₀ values were recorded at 0.5 ml of C. limon, with times of 3.86 hours and 9.49 hours, respectively. The three citrus oils evaluated demonstrated significant adulticidal and larvicidal bioactivities, indicating promising outcomes that can be further developed for An. gambiae management.