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Abstract
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Abstract: Background: Insect vector control is facing the challenges of resistance development
and environmental hazards caused by synthetic pesticides. This has led to a considerable market
opportunity for botanical insecticides. In this scenario, our study investigated the potential of selected
bioactive monoterpenoids, carvacrol and thymol, as safe and e ective tools to control the West
Nile vector Culex pipiens. Furthermore, the combined e ect of thymol-carvacrol mixtures and their
possible interactions were assessed. Methods: For determining larvicidal and ovicidal 50% lethal
concentration (LC50), each monoterpenoid was tested at di erent concentrations (5–500 mg/L). Then,
the fixed ratio method was used for evaluating their combinational ecacy. Results: Carvacrol was
more toxic against larvae of Cx. pipiens, with a LC50 value of 14 mg/L, whereas thymol exhibited a
LC50 value of 49 mg/L. Comparable trends of ecacy were observed when toxicity on Cx. pipiens
eggs was investigated, with LC50 values of 7 and 13 mg/L for carvacrol and thymol, respectively.
In combinational toxicity assays, the mixture thymol-carvacrol at 1:4 ratio achieved a synergistic
e ect against larvae of Cx. pipiens, whereas an additive e ect was observed on eggs. Other ratios
showed antagonistic e ects. Conclusions: Overall, our findings pointed out that the 1:4 ratio of
thymol-carvacrol blend can enhance the insecticidal ecacy on Cx. pipiens young instars and can be
considered further as active ingredient for developing botanical insecticides to be used in mosquito
control operations.
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