Insecticidaland Repellent Activities of Cinnamatesagainst Mosquitoes and Ticks

Three natural flavor and fragrance compounds, n-butyl cinnamate, benzyl cinnamate, and benzyl cinnamate, were evaluated for toxicity and repellency against mosquitoes and ticks in this study. n-Butyl cinnamate showed the highest level of toxicity among the tested cinnamates with LC50value of 7 ppm followed by benzyl cinnamate (LC50= 8.4 ppm) and phenethyl cinnamate (LC50= 10.3 ppm) against 1-d old Aedes aegypti larvae. In Klun & Debboun (K&D) biting deterrence bioassay, these three compounds showed biting deterrent activity above the solvent control. n-Butyl cinnamate and benzyl cinnamate with proportion not biting (PNB) values of 0.8 and 0.74, respectively, were similar to DEET while the activity of phenethyl cinnamate was lower than DEET and the other compounds at a rate of 25 nmol/cm2. In Ali and Khan (A&K) bioassay, n-butyl cinnamate was active at the lowest dose of 5.9 µg/cm2 followed by DEET and benzyl cinnamate that were active at 11.7 µg/cm2 whereas phenethyl cinnamate did not show repellent activity at the highest dose of 93.7 µg/cm2. Based on repellency data, n-butyl cinnamate was tested for residual repellency. Both DEET and n-butyl cinnamate were within the limits of the minimum effective dose (MED) up to 120 min at a dose of 23 .4 µg/cm2. At 11.7 µg/cm2, DEET crossed MED threshold after 30 min whereas n-butyl cinnamate was active up to 120 min. In tick bioassays, the repellent activity of n-butyl cinnamate at the concentration of 2.5% was similar to DEET at 1.25%. n-butyl cinnamate demonstrated reasonably good concentration-repellency response. In contrast, benzyl cinnamate did not demonstrate significant repellency when compared to DEET at the highest dose of 5%. High residual repellency of n-butyl cinnamate indicated its potential to be used as mosquito repellent.