Aedes aegypti (Diptera: Culicidae) Biting Deterrence: Structure-Activity Relationship of Saturated and Unsaturated Fatty Acids

Abstract

In this study we evaluated the biting deterrent effects of a series of saturated and unsaturated fatty acids against Aedes aegypti (L), yellow fever mosquito (Diptera: Culicidae) using theK Dbioassay module system. Saturated(C6:0 toC16:0 andC18:0) and unsaturated fatty acids(C11:1 to C14:1, C16:1, C18:1, and C18:2) showed biting deterrence index (BDI) values signicantly greater than ethanol, the negative control. Among the saturated fatty acids, mid chain length acids (C10:0 to C13:0) showed higher biting deterrence than short (C6:0 to C9:0) and long chain length acids (C 14:0 to C18:0), except for C8:0 and C16:0 that were more active than the other short and long chain acids. The BDI values of mid chain length acids (C10:0 to C13:0) were not signicantly less than N, N-diethyl-metatoluamide (DEET), the positive control. Among the unsaturated fatty acids, C11:1 showed the highest activity (BDI-1.05) andC18:2 had the lowest activity (BDI-0.7). InC11:1, C 12:1, andC14:1 BDI values were not signicantly less than DEET. After the preliminary observations, residual activity bioassays were performed onC11:0, C12:0, C11:1, andC12:1 over a 24-h period. All the fatty acids (C11:0, C12:0, C 11:1, and C12:1) and DEET showed signicantly higher activity at all test intervals than the solvent control. At treatment and 1-h posttreatment, all fatty acids showed proportion not biting (PNB) values not signicantly less than DEET. At 3-, 6-, and 12-h posttreatment, all fatty acids showed PNB values signicantly greater than DEET. At 24-h posttreatment, only the PNB value for C12:0 was signicantly higher than DEET. The dose responses ofC12:0 and DEET were determined at concentrations of 525 nmol/cm2. As in the residual activity bioassays, the PNB values for C 12:0 and DEET at 25 nmol/cm2 were not signicantly different. However, at lower concentrations, the PNB values for C12:0 were signicantly greater than DEET. These results clearly indicate that mid chain length fatty acids not only have levels of biting deterrence similar to DEET at 25 nmol/cm2 in our test system, but also appeared to be more persistent than DEET. In contrast, in vivo cloth patch assay system showed that the mid-chain length fatty acids,C11:0,C11:1C12:0, andC 12:1 had minimum effective dose(MED)values greater than DEET against Ae. aegypti and their relative repellency varied according to species tested. The MED values of 120 (C11:0), 145 (C12:0) and 116 (C 11:1) nmol/cm2 against Anopheles quadrimaculatus Say, indicated that these acids were not as potent as DEET with a MED of 54 nmol/cm2. The MED ratio of the C11:0 and C11:1 for all three mosquito species indicated the C11 saturated and unsaturated acids as more repellent than their corresponding C12:0 and C12:1 homologues. © 2012 Entomological Society of America.