| Summary: | Repellents play a major role in reducing the risk of mosquito-borne diseases by preventing mosquito bites. The present study evaluated the mosquito-repellent activity of β-caryophyllene oxide 1% (BCO), vetiver oil 2.5% (VO), and their binary mixtures (BCO + VO (1:1), BCO + VO (2:1), BCO + VO (1:2)) against four laboratory-colonized mosquito species, <i>Aedes aegypti</i> (L.), <i>Aedes albopictus</i> (Skuse), <i>Anopheles minimus</i> Theobald, and <i>Culex quinquefasciatus</i> Say, using an excito-repellency assay system. In general, the compound mixtures produced a much stronger response in the mosquitoes than single compounds, regardless of the test conditions or species. The greatest synergetic effect was achieved with the combination of BCO + VO (1:2) in both contact and noncontact trials with <i>An. minimus</i> (74.07–78.18%) and <i>Cx. quinquefasciatus</i> (55.36–83.64%). Knockdown responses to the binary mixture of BCO + VO were observed for <i>Ae. albopictus</i>, <i>An. minimus,</i> and <i>Cx. quinquefasciatus</i>, in the range of 18.18–33.33%. The synergistic repellent activity of BCO and VO used in this study may support increased opportunities to develop safer alternatives to synthetic repellents for personal protection against mosquitoes.
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