Evaluation of Essential Oils as Spatial Repellents Against Aedes aegypti in an Olfactometer

Spatial repellents are becoming an integral part of the integrated mosquito management and are considered another tool to prevent mosquito-borne diseases. They are also gaining attention as a potential disease transmission breaking strategy. Current vector control practices are losing their viability due to resistance development in arthropods to synthetic pesticides. Economic feasibility of developing natural products is driving towards search for natural products as spatial repellents evidenced by increase in number of their studies. Different volumes (0.0625, 0.125, 0.25, 0.5 ml) of clove oil, eucalyptus oil, geraniol, Immortelle oil, lemongrass oil, and RepelCare (mixture of turmeric oil and eucalyptus oil) were evaluated for their repellency against Aedes aegypti, replicating each test 5 times. Biogents lure and fresh air were used as control. The evaluations were conducted in a True Choice olfactometer by passing air carrying 2 vapors from 2 different products, i.e., an attractant, repellent, or clean air, through 2 chambers and providing mosquitoes an option to move to the chamber of their choice. For each run, 24-h-starved 15-20 female Ae. aegypti were released into the mosquito release chamber and number of mosquitoes in the 2-choice chambers and the mosquito release chamber were counted after 15 min and recorded. The difference in mosquitoes between 2 chambers indicated presence or absence of repellency. All the natural oils and RepelCare provided ≥70% repellency, except for Immortelle oil which had no repellency. All repellents tested except Immortelle and lemongrass oils showed increase in repellency with increase in application volume. However, minimum application volume to be effective was different for each oil. Lemongrass is the only oil which showed a peak at 0.125-ml volume.