Mosquitoes and mosquito-borne diseases are a growing global problem. Plant extracts and/or oils can be used as an alternative to synthetic pesticides. In this study, 32 oils (at 1000 ppm) were tested for their larvicidal activity against fourth instar Culex pipiens larvae and the best oils were assessed for their adulticidal activity and analyzed by gas chromatography-mass spectrometry (GC-MS) and high-performance liquid chromatography (HPLC).
Mosquitoes are an ancient pest, and mosquito-borne diseases are an increasing threat to global health, threatening more than 40% of the world’s population. It is estimated that by 2050, almost half of the world’s population will be at risk of mosquito-borne viruses. 1 Culex pipiens (Diptera: Culicidae) is a widespread mosquito that transmits dangerous diseases that cause severe illness and sometimes death in humans and animals.
Vector control is the primary method of reducing public concern about mosquito-borne diseases. Control of both adult and larval mosquitoes with repellents and insecticides is the most effective way to reduce mosquito bites. The use of synthetic pesticides can lead to pesticide resistance, environmental contamination, and health risks to humans and non-target organisms.
There is an urgent need to find eco-friendly alternatives to plant-based ingredients such as essential oils (EOs). Essential oils are volatile components found in many plant families such as Asteraceae, Rutaceae, Myrtaceae, Lauraceae, Lamiaceae, Apiaceae, Piperaceae, Poaceae, Zingiberaceae, and Cupressaceae14. Essential oils contain a complex mixture of compounds such as phenols, sesquiterpenes, and monoterpenes15.
Essential oils have antibacterial, antiviral and antifungal properties. They also have insecticidal properties and can cause neurotoxic effects by interfering with the physiological, metabolic, behavioral and biochemical functions of insects when essential oils are inhaled, ingested or absorbed through the skin16. Essential oils can be used as insecticides, larvicides, repellents and insect repellents. They are less toxic, biodegradable and can overcome insecticide resistance.
Essential oils are increasingly popular among organic producers and environmentally conscious consumers and are suitable for urban areas, homes and other environmentally sensitive areas.
The role of essential oils in mosquito control has been discussed15,19. The aim of this study was to screen and evaluate the lethal larvicidal values of 32 essential oils and to analyze the adenocidal activity and phytochemicals of the most effective essential oils against Culex pipiens.
In this study, An. graveolens and V. odorata oils were found to be most effective against adults, followed by T. vulgaris and N. sativa. The findings showed that Anopheles vulgare is a potent larvicide. Similarly, its oils can control Anopheles atroparvus, Culex quinquefasciatus and Aedes aegypti. Although Anopheles vulgaris demonstrated larvicide efficacy in this study, it was the least effective against adults. In contrast, it has adenocidal properties against Cx. quinquefasciatus.
Our data indicate that Anopheles sinensis is highly effective as a larval killer but less effective as an adult killer. In contrast, chemical extracts of Anopheles sinensis were repellent to both larvae and adults of Culex pipiens, with the highest protection (100%) against unfed female mosquito bites being achieved at a dose of 6 mg/cm2. In addition, its leaf extract also exhibited larvicidal activity against Anopheles arabiensis and Anopheles gambiae (ss).
In this study, thyme (An. graveolens) showed potent larvicidal and adulticidal activity. Similarly, thyme showed larvicidal activity against Cx. quinquefasciatus28 and Aedes aegypti29. Thyme showed larvicidal activity on Culex pipiens larvae at 200 ppm concentration with 100% mortality while LC25 and LC50 values showed no effect on acetylcholinesterase (AChE) activity and detoxification system activation, increased GST activity and decreased GSH content by 30%.
Some of the essential oils used in this study showed the same larvicidal activity against Culex pipiens larvae as N. sativa32,33 and S. officinalis34. Some essential oils such as T. vulgaris, S. officinalis, C. sempervirens and A. graveolens exhibited larvicidal activity against mosquito larvae with LC90 values less than 200–300 ppm. This result may be due to several reasons including that the percentage of its main components varies depending on the origin of the vegetable oil, the quality of the oil, the sensitivity of the strain used, the storage conditions of the oil and the technical conditions.
In this study, turmeric was less effective, but its 27 components such as curcumin and monocarbonyl derivatives of curcumin showed larvicidal activity against Culex pipiens and Aedes albopictus43, and hexane extract of turmeric at a concentration of 1000 ppm for 24 hours44 still showed 100% larvicidal activity against Culex pipiens and Aedes albopictus.
Similar larvicidal effects were reported for hexane extracts of rosemary (80 and 160 ppm), which reduced mortality by 100% in 3rd and 4th stage Culex pipiens larvae and increased toxicity by 50% in pupae and adults.
Phytochemical analysis in this study revealed the main active compounds of the analyzed oils. Green tea oil is a highly effective larvicide and contains a large amount of polyphenols with antioxidant activity, as found in this study. Similar results were obtained59. Our data suggest that green tea oil also contains polyphenols such as gallic acid, catechins, methyl gallate, caffeic acid, coumaric acid, naringenin, and kaempferol, which may contribute to its insecticidal effect.
Biochemical analysis showed that Rhodiola rosea essential oil affects energy reserves, especially proteins and lipids30. The discrepancy between our results and those of other studies may be due to the biological activity and chemical composition of essential oils, which may vary depending on the age of the plant, tissue structure, geographical origin, parts used in the distillation process, type of distillation, and cultivar. Thus, the type and content of active ingredients in each essential oil may cause differences in their anti-harm potential16.
Post time: May-13-2025