title: 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 the K & Dbioassay module system. Saturated (C6:0 to C16:0 and C18:0) and unsaturated fatty acids (C11:1 to C14:1, C16:1, C18:1, and C18:2) showed biting deterrence index (BDI) values significantly 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 (C14:0 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 significantly less than N, N-diethyl-meta-toluamide (DEET), the positive control. Among the unsaturated fatty acids, C11:1 showed the highest activity (BDI = 1.05) and C18:2 had the lowest activity (BDI = 0.7). In C11:1, C12:1, and C14:1 BDI values were not significantly less than DEET. After the preliminary observations, residual activity bioassays were performed on C11:0, C12:0, C11:1, and C12:1 over a 24-h period. All the fatty acids (C11:0, C12:0, C11:1, and C12:1) and DEET showed significantly 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 significantly less than DEET. At 3-, 6-, and 12-h posttreatment, all fatty acids showed PNB values significantly greater than DEET. At 24-h posttreatment, only the PNB value for C12:0 was significantly higher than DEET. The dose-responses of C12:0 and DEET were determined at concentrations of 5-25 nmol/cm2. As in the residual activity bioassays, the PNB values for C12:0 and DEET at 25 nmol/cm(2) were not significantly different. However, at lower concentrations, the PNB values for C12:0 were significantly 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 nmnol/cm(2) 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, C11:1, C12:0, and C12:1 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 (C11:1) nmol/cm(2) against Anopheles quadrimaculatus Say, indicated that these acids were not as potent as DEET with a MED of 54 nmol/cm(2). 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.
authors.affiliation: The University of Mississippi, National Center for Natural Products Research, University, 38677, USA. aali@olemiss.edu
authors.forename: Abbas
authors.initials: A
authors.lastname: Ali
authors.forename: Charles L
authors.initials: CL
authors.lastname: Cantrell
authors.forename: Ulrich R
authors.initials: UR
authors.lastname: Bernier
authors.forename: Stephen O
authors.initials: SO
authors.lastname: Duke
authors.forename: John C
authors.initials: JC
authors.lastname: Schneider
authors.forename: Natasha M
authors.initials: NM
authors.lastname: Agramonte
authors.forename: Ikhlas
authors.initials: I
authors.lastname: Khan
mesh_terms: D000328:Adult; D000330:Aedes; D000818:Animals; D000852:Anopheles; D005231:Fatty Acids, Unsaturated / Q000737:chemistry*; D005260:Female; D006801:Humans; D007299:Insect Bites and Stings / Q000517:prevention & control*; D007302:Insect Repellents / Q000032:analysis*; D008297:Male; D013329:Structure-Activity Relationship
chemical_list: D005231:Fatty Acids, Unsaturated; D007302:Insect Repellents