Efficacy Evaluation of Medium-Chain Fatty Acids as Skin and Spatial Repellents AgainstAedes aegypti(Diptera:Culicidae) Mosquitoes

Fatty acids derived from natural oils are considered as perspective products for adoption as repellents. Fatty acids derived from coconut oil have shown promise as repellents. This study consisted of an olfactometer evaluation of new formulations containing medium-chain fatty acids for spatial repellency and an in laboratory arm-in cage study for contact repellency against Aedes aegypti L. mosquitoes. Six formulations each of capric acid and lauric acid were evaluated for spatial repellency. These formulations contained 0.28-10% of either capric acid or lauric acid as the active ingredients in a consumer friendly skin care formulation. Base formula without fatty acids was evaluated as control in spatial repellency evaluation. For the arm-in cage evaluations, six formulations of capric acid, one base formulation, and a 7% N,N-diethyl-m-toluamide (DEET) product were tested for contact repellency. For contact repellency, United States Department of Agriculture (USDA) standard repellent test cages were used to determine the complete protection time (CPT) of the different formulated repellents. Among all capric acid formulations tested, the concentration of 2.25% (wt) indicated the best level of spatial repellency, but not significantly different from other concentrations. None of the lauric acid concentrations showed any level of spatial repellency. In the arm-in-cage evaluations, the highest contact repellency resulted from 4.5% capric acid, which was significantly higher than 7% DEET and base formula.