Insecticidal activity of Commiphora erythraea essential oil and its emulsions against larvae of three mosquito species

Authors: Muturi, Ephantus; Hay, William; Doll, Kenneth - Ken; Ramirez, Jose; Selling, Gordon

Submitted to: Journal of Medical Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/28/2020
Publication Date: 7/18/2020
Citation: Muturi, E.J., Hay, W.T., Doll, K.M., Ramirez, J.L., Selling, G.W. 2020. Insecticidal activity of Commiphora erythraea essential oil and its emulsions against larvae of three mosquito species. Journal of Medical Entomology. 57(6):1835-1842. https://doi.org/10.1093/jme/tjaa097.
DOI: https://doi.org/10.1093/jme/tjaa097

Interpretive Summary: Plant essential oils have attracted significant interest as promising sources of environmentally-friendly biopesticides. However, their low solubility in water continues to be a major obstacle towards their widespread use in integrated pest and vector management. This study examined the insecticidal activity of opoponax essential oil, its fractions, and emulsions produced with starch-based emulsifiers against mosquito larvae. The influence of opoponax essential oil on expression of selected genes involved in detoxification of toxins was also evaluated. Our results show that the whole essential oil but not its fractions was highly effective against mosquito larvae. One of the two starch-based opoponax essential oil emulsions was more toxic than the bulk essential oil while the other had similar toxicity as the bulk essential oil. Three of the six detoxification genes tested were significantly upregulated in mosquito larvae exposed to opoponax essential oil suggesting their potential involvement in metabolic activation and detoxification of this essential oil. These findings demonstrate that opoponax essential oil is a promising source of mosquito larvicide and that its larvicidal activity is likely due to synergistic interactions among the major and minor constituents. The findings also demonstrate that the use of a starch-based emulsifier can enhance the insecticidal properties of opoponax essential oil.

Technical Abstract: The use of essential oils as ecofriendly tools for vector management is one of the mainstreams for biopesticide research. We evaluated the larvicidal properties of Commiphora erythraea (opoponax) essential oil and its fractions against Culex restuans Theobald, Culex pipiens L., and Aedes aegypti L. The use of bio-based amylose-N-1-hexadecylammonium chloride inclusion complex (Hex-Am) and amylose-sodium palmitate inclusion complex (Na-Palm) as emulsifiers for C. erythraea essential oil was also investigated. Bisabolene was the most abundant chemical constituent in the whole essential oil (33.9%), fraction 2 (62.5%) and fraction 4 (23.8%) while curzerene (32.6%) and alpha-santalene (30.1%) were the dominant chemical constituents in fractions 1 and 3, respectively. LC50 values for the whole essential oil were 19.05 ppm for Cx. restuans, 22.61 ppm for Cx. pipiens and 29.83 ppm for Ae. aegypti and differed significantly. None of the four C. erythraea essential oil fractions were active against mosquito larvae. Two CYP450 genes (CYP6M11 and CYP6N12) and one GST gene (GST-2) were significantly upregulated in Ae. aegypti larvae exposed to C. erythraea essential oil suggesting their potential involvement in metabolic pathways for C. erythraea essential oil. Essential oil emulsions produced with Hex-Am were more toxic than the whole essential oil while those produced with Na-Palm had similar toxicity as the whole essential oil. These findings demonstrate that C. erythraea essential oil is a promising source of mosquito larvicide and that the use of Hex-Am as an emulsifier can enhance the insecticidal properties of C. erythraea essential oil.