Evaluation of the repellent effects of Nepeta parnassica extract, essential oil, and its major nepetalactone metabolite against mosquitoes.

The dichloromethane-methanol extract, the essential oil obtained by hydrodistillation from Nepeta parnassica, and the isolated 4aα,7α,7aβ-nepetalactone were evaluated for their repellent effect against the mosquitoes Aedes (Stegomyia) cretinus Edwards and Culex pipiens pipiens biotype molestus Forskål. The chemical analysis of N. parnassica essential oil, dominated by oxygenated monoterpenes (87 %), revealed 4aα,7α,7aβ-nepetalactone (36.8%), 1,8-cineole (25.5%), and 4aα,7β,7aβ-nepetalactone (11.1%) as the major constituents. The results of the insect bioassays showed that the essential oil and the dichloromethane-methanol extract of N. parnassica were very active against Aedes cretinus for up to 3 h and against Culex pipiens for up to 2 h post application. The isolated 4aα,7α,7aβ-nepetalactone showed very high mosquito repellency for periods of at least 2 h against both species.