Combined toxicity of three essential oils against Aedes aegypti (Diptera: Culicidae) larvae

Authors: Muturi, Ephantus; Ramirez, Jose; Doll, Kenneth - Ken; Bowman, Michael

Submitted to: Journal of Medical Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/21/2017
Publication Date: 10/4/2017
Citation: Muturi, E.J., Ramirez, J.L., Doll, K.M., Bowman, M.J. 2017. Combined toxicity of three essential oils against Aedes aegypti (Diptera: Culicidae) larvae. Journal of Medical Entomology. 54:1684-1691. doi: 10.1093/jme/tjx168.
DOI: https://doi.org/10.1093/jme/tjx168

Interpretive Summary: Essential oils possess insecticidal activity and are currently being evaluated for their potential application as safe alternatives to chemical insecticides. We evaluated the combined toxicity of three essential oils (Manuka, oregano and clove bud) against third instar larvae of the yellow fever mosquito, Aedes aegypti. Our results revealed that a combination of Manuka and oregano essential oils was more toxic to Ae. aegypti larvae compared to either oil alone. In contrast, a combination of Manuka and clove bud essential oils was less toxic to mosquito larvae compared to either oil alone. We further evaluated the interaction between Manuka and one component of oregano essential oil (carvacrol) and two components of clove bud essential oil (eugenol, eugenol acetate). We found that Manuka interacted synergistically with carvacrol and eugenol acetate and antagonistically with eugenol suggesting that carvacrol was responsible for the synergistic interaction between Manuka and oregano essential oils and eugenol was responsible for the antagonistic interaction between Manuka and clove bud essential oils. These findings provide critical insights that may be used to develop safe and effective biopesticides based on the three essential oils.

Technical Abstract: Essential oils are potential alternatives to synthetic insecticides because they have low mammalian toxicity, degrade rapidly in the environment, and possess complex mixtures of bioactive constituents with multi-modal activity against the target insect populations. Twenty one essential oils were initially screened for their toxicity against Aedes aegypti larvae and three out of the seven most toxic essential oils (Manuka, oregano, and clove bud essential oils) were examined for their chemical composition and combined toxicity against Ae. aegypti larvae. Manuka essential oil interacted synergistically with oregano essential oil and antagonistically with clove bud essential oil. GC-MS analysis revealed the presence of 21 components in Manuka essential oil and 3 components each in oregano and clove bud essential oils. Eugenol (84.9%) and eugenol acetate (9.6%) were the principal constituents in clove bud essential oil while carvacrol (75.8%) and m-isopropyltoluene (15.5%) were the major constituents in oregano essential oil. The major constituents in Manuka essential oil were calamenene (20%) and 3-dodecyl-furandione (11.4%). Manuka essential oil interacted synergistically with eugenol acetate and antagonistically with eugenol suggesting that eugenol was a major contributor to the antagonistic interaction between Manuka and clove bud essential oils. In addition, Manuka interacted synergistically with carvacrol suggesting its contribution to the synergistic interaction between Manuka and oregano essential oils. These findings provide novel insights that can be used to develop new and safer alternatives to synthetic insecticides.