Mosquito repellency of essential oils derived from Lao plants
Essential oils or extracts obtained from four plant species growing in Laos were tested foranti-mosquito activity in the field. Solutions of alcohol or acetone containing differentconcentrations of essential oil; 5, 10 or 19 v/v %, were prepared and tested. Mosquitoes werecollected by human baits wearing oil impregnated mosquito nets around their shanks. Thenumber of attracted mosquitoes was compared to the number attracted to positive andnegative controls, i.e., human baits wearing nets impregnated with 19 % N,N-diethyl-metatoluamide (DEET, NN-diethyl-methyl-benzamide) or untreated nets, respectively. A one wayANOVA analysis was conducted on the log-transformed total number of mosquitoes collectedusing each treatment. The statistical analysis showed that significantly fewer mosquitoes wereattracted to the treatment harbouring 19 % oil of Scutellaria angustifolia than to the negativecontrol. No significant decrease in attracted mosquitoes could be detected for the treatmentscontaining oil from the plant Litsea cubeba. However, a tendency of repellency was indicated. Therefore, an investigation running over a longer period of time is desired for Litsea cubeba. No conclusions could be drawn for the remaining two species; Tagetes patula and Citrussinensis.
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