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Efficacy of Two Monoterpenoids, Carvacrol and Thymol, and Their Combinations against Eggs and Larvae of the West Nile Vector Culex pipiens

Department of Veterinary Parasitology, Babol-Branch, Islamic Azad University, Babol 484, Iran
Faculty of Veterinary Medicine, Amol University of Special Modern Technologies, Amol 46131-46391, Iran
Young Researchers and Elite Club, Babol Branch, Islamic Azad University, Babol 484, Iran
Cellular and Molecular Biology Research Center, Health Research Center, Babol University of Medical Sciences, Babol 47176-47745, Iran
Department of Agronomy, Food, Natural Resources, Animals and Environment (DAFNAE), University of Padova, 35020 Legnaro, Italy
Department of Pharmaceutical and Pharmacological Sciences, University of Padova, 35139 Padova, Italy
Department of Agriculture, Food and Environment, University of Pisa, via del Borghetto 80, 56124 Pisa, Italy
School of Pharmacy, University of Camerino, 62032 Camerino, Italy
Authors to whom correspondence should be addressed.
Academic Editor: Derek McPhee
Molecules 2019, 24(10), 1867;
Received: 6 April 2019 / Revised: 30 April 2019 / Accepted: 11 May 2019 / Published: 15 May 2019
(This article belongs to the Special Issue Natural Products as Effective Biopesticides and Antiprotozoal Agents)
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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 effective tools to control the West Nile vector Culex pipiens. Furthermore, the combined effect 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 different concentrations (5–500 mg/L). Then, the fixed ratio method was used for evaluating their combinational efficacy. 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 efficacy 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 effect against larvae of Cx. pipiens, whereas an additive effect was observed on eggs. Other ratios showed antagonistic effects. Conclusions: Overall, our findings pointed out that the 1:4 ratio of thymol-carvacrol blend can enhance the insecticidal efficacy on Cx. pipiens young instars and can be considered further as active ingredient for developing botanical insecticides to be used in mosquito control operations. View Full-Text
Keywords: biopesticide; essential oil; ovicidal activity; larvicidal activity; mosquito vector biopesticide; essential oil; ovicidal activity; larvicidal activity; mosquito vector

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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).

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Youssefi, M.R.; Tabari, M.A.; Esfandiari, A.; Kazemi, S.; Moghadamnia, A.A.; Sut, S.; Dall’Acqua, S.; Benelli, G.; Maggi, F. Efficacy of Two Monoterpenoids, Carvacrol and Thymol, and Their Combinations against Eggs and Larvae of the West Nile Vector Culex pipiens. Molecules 2019, 24, 1867.

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