In our natural products screening program for mosquitoes, carrot seed essential oil showed high repellency. The gas chromatography (GC)/flame ionization detector and GC/mass spectrometry analysis of the essential oil revealed the presence of 47 compounds. Carotol was more than 75% w/w, followed by muurolene (4.86%), (Z)-β-farnesene (2.9%), and diepicedrene (1.1%). Systematic bioassay-guided fractionation of the essential oil was performed to identify active repellent compounds. In both Klun and Debboun (K&D) and Ali and Khan (A&K) bioassays, carotol showed biting deterrent activity similar to N,N-Diethyl-3-methylbenzamide (deet) and carrot seed essential oil against both Aedes aegypti and Anopheles quadrimaculatus, while in in vivo cloth patch bioassay, the minimum effective dose (MED) of deet was lower (12.5 μg/cm2) than the essential oil and carotol (25 μg/cm2) against Ae. aegypti. In the A&K bioassay, the MED values were similar, whereas the values of the mixtures of deet with essential oil and carotol was lower (6.25 + 6.25 = 12.5 μg/cm2) than their individual treatments (25 μg/cm2). In direct skin application bioassay, both the essential oil and carotol provided good repellency. The mixtures of deet and essential oil or carotol significantly increased the residual activity, indicating synergism. Mosquito repellency of the essential oil and carotol is reported for the 1st time. These data indicate the potential of these natural products to be developed as commercial repellents.
Keywords: biting deterrent; carotol; carrot seed essential oil; repellent.