The efficacy of commercially available essential oil-based candles as spatial repellents against Aedes aegypti mosquitoes - do they actually repel?

Spatial mosquito repellents contain volatile compounds that disrupt mosquito host seeking behavior. Some essential oils have been shown to be effective spatial repellents against biting insects. In this study, we acquired seven batches of commercially available candles containing mixtures of essential oils. Six of these candle labels claim that they repel mosquitoes. We used a taxis cage assay to evaluate the spatial repellency against Aedes aegypti mosquitoes of these and two control candles without essential oils. We used Headspace Solid-phase Microextraction Gas Chromotography-Mass Spectrometry analysis to identify a putative list of volatile organic compounds emitted by heated candle wax. We subsequently correlated individual compounds with spatial repellency. Three types of candles, containing mixtures of various essential oils, showed strong repellent efficacy compared to the controls, while the other three types did not produce significant repellency. The volatile organic compound composition varied between the different types of candles. Candles that were efficient mosquito repellents contained relatively high concentrations of essential oils. We identified several volatile organic compounds that are positively associated with mosquito repellency. The results of this study show that the efficacy of essential oil-based candles as mosquito repellents is based on their formulation.