Ovicidal and larvicidal effects of garlic and asafoetida essential oils against West Nile virus vectors

Authors: Muturi, Ephantus; Ramirez, Jose; Zilkowski, Bruce; Weiler, Lina; Rooney, Alejandro - Alex

Submitted to: Journal of Insect Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/26/2018
Publication Date: 4/12/2018
Citation: Muturi, E.J., Ramirez, J.L., Zilkowski, B.W., Weiler, L., Rooney, A.P. 2018. Ovicidal and larvicidal effects of garlic and asafoetida essential oils against West Nile virus vectors. Journal of Insect Science. 18(2):43. doi: 10.1093/jisesa/iey036.
DOI: https://doi.org/10.1093/jisesa/iey036

Interpretive Summary: Since World War II, synthetic insecticides have widely been used to control mosquitoes and have played a critical role in reducing the burden of mosquito-borne diseases. However, the persistent use of these chemicals has resulted in rapid and widespread evolution of insecticide resistance in mosquitoes making it necessary to develop alternative vector control strategies. Plant-essential oils are good candidates for use in vector control because they possess diverse bioactive constituents that are less prone to resistance development. This study examined the potential for garlic and asafoetida essential oils to inhibit egg hatch and to kill larvae of two West Nile virus vectors, Culex pipiens and Culex restuans. The results show that both oils are effective at suppressing egg hatch and killing larvae of both mosquito species. Allyl disulfide which accounted for 49% of total garlic essential oil and 7.38% of total asafoetida essential oil was also highly effective at suppressing egg hatch and killing the larvae suggesting it was one of the principal compounds responsible for ovicidal and larvicidal properties of the two essential oils. These findings demonstrate the potential for garlic and asafoetida essential oils to be harnessed as ovicides and larvicides for mosquito control.

Technical Abstract: We examined the chemical composition of garlic and asafoetida essential oils and their individual and combined toxicity against larvae of two West Nile virus vectors, Culex pipiens pipiens and Cx. restuans. The effect of the two essential oils on egg hatch was also examined. Ten and twelve compounds respectively were identified in garlic and asafoetida essential oils. Allyl disulfide (49.13%) and diallyl trisulfide (31.08%) were the most abundant compounds in garlic essential oil accounting for 80.2% of the total oil. In contrast, (E)-sec-butyl propenyl disulfide (30.03%), (Z)-sec-butyl propenyl disulfide (24.32%) and disulfide, methyl 1-(methylthio)propyl (21.87%) were the most abundant compounds in asafoetida essential oil. Allyl disulfide accounted for 7.38% of the total oil in asafoetida essential oil and was one of only three compounds found in both oils. For both mosquito species, garlic essential oil was more toxic than asafoetida essential oil with Cx. restuans (LC50s: garlic = 2.7 ppm; asafoetida = 10.1 ppm) being more sensitive than Cx. pipiens (LC50s: garlic = 7.5 ppm; asafoetida = 13.5 ppm). When combined, the two essential oils had antagonistic effects. The majority of Culex egg rafts exposed to garlic or asafoetida essential oils failed to hatch and larvae of the few that did hatch died as first instars. Allyl disulfide exhibited strong ovicidal and larvicidal activity suggesting its important contribution to the overall toxicity of the two essential oils. These findings demonstrate the potential for garlic and asafoetida essential oils to be harnessed as ovicides and larvicides for mosquito control.