Impact of Pyrethroid Resistance on the Intrinsic Insecticidal Activities of Geraniol Against the Yellow Fever Mosquito, <em>Aedes aegypti</em>

The evolution of resistance in mosquitoes to conventional pesticides such as pyrethroids presents a challenge to vector control. Thus, alternative active ingredients for pesticides to manage pyrethroid resistant populations of mosquitoes are needed. The goal of this study was to evaluate the toxic and repellent efficacies of geraniol, a plant secondary metabolite, as a potential alternative for controlling pyrethroid-resistant Aedes aegypti. We found that addition of geraniol to rearing water of 1st instar larvae caused concentration-dependent mortality within 24 h in both strains. The resistance ratio of geraniol (2.8) was modest compared to that of cypermethrin (435.3). Topical application of geraniol to adult female mosquitoes caused dose-dependent mortality in both strains within 24 h. The resistance ratio of geraniol (1.1) was minimal compared to that for cypermethrin (457). In spatial repellency assays, geraniol repelled adult females from both strains in a dose-dependent manner. The repellency resistance ratio of geraniol (2.6) was modest compared to that for pyrethrum extract (&gt;132). Our findings suggest that geraniol has potential use as a versatile chemical tool for controlling pyrethroid-resistant populations of Ae. aegypti.