Toxic effect of some essential oils and their mixtures on the fourth stage larvae of Culex pipiens mosquitoes

Abstract This study evaluates the efficacy of three essential oils and their combinations against fourth-stage Culex pipiens larvae. In each replicate, 25 larvae were exposed to larvicides, and their status was monitored at 24, 48, and 72-hour intervals. All tested compounds demonstrated varying degrees of toxicity towards the larvae, with LC₅₀ values ranging from 1.28 to 1938.92 mg/L at different time intervals. Z. spina-christi exhibited the highest larvicidal potency with an LC₅₀ value of 903 mg/L after 24 hours, followed by O. basilicum (LC₅₀ = 1114 mg/L), while A. herba-alba showed the least effect with LC₅₀ values of 6470 mg/L.O. basilicum emerged as the most potent larvicide after 48 and 72 hours, with LC₅₀ values of 468 mg/L and 182 mg/L, respectively. Z. spina-christi ranked second in toxicity with LC₅₀ values of 686 and 536 mg/L at 48 and 72 hours. A. herba-alba exhibited the lowest toxicity. The M₃ extract (Z. spina-christi + O. basilicum) demonstrated the highest larvicidal activity; while the M₂ extract exhibited the least toxicity.LT₅₀ results indicated that the combination of Z. spina-christi and O. basilicum in M₃ is the most effective. Some mixtures displayed antagonistic effects, with "synergistic factor; S.F." ranging from 1.05 to 1.6, signifying significant synergistic effects. While some combinations showed no effect, others displayed antagonistic effects against the larvae after 24, 48, and 72 hours. The study underscores the exceptional larvicidal effects of all evaluated botanical extracts, suggesting their potential as natural larvicides for mosquito control operations.