Abstract

Objective: To determine the bioefficacy of plant essential oils on Aedes aegypti and Anopheles dirus. Repellency was determined by measuring reduction in feeding and mortality. A novel in vitro bioassay apparatus was developed that had a sausage-casing membrane feeding system. Methods: Mixtures of three essential oils were evaluated: turmeric (Curcuma longa), eucalyptus (Eucalyptus globulus), and orange (Citrus aurantium). The oils were mixed in pairs or all together at equal volume for a total of 10% volume and then formulated with 90% virgin coconut oil. Completed formulations were evaluated with and without an additional 5% vanillin. The formulations were applied to the sausage casing membranes and female mosquitoes provided (expose) blood meals (0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5 and 4.0 h) to assess the percentage repellency over time. Results: The strongest repellency was at shorter exposure periods. For Aedes aegypti, the strongest feeding reduction was with the turmeric and eucalyptus combination and with the addition of vanillin (97.6%–99.6%). For Anopheles dirus, the strongest repellency was when all three oils were combined (98.4%–99.6%). Conclusions: Vanillin increased the effects of repellency and mortality for all formulations and demonstrated an increased potential to enhance the bioefficacy of essential oil repellents. This study also demonstrated an in vitro membrane feeding system that can be used to screen essential oils.

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