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Background  In the search for plant-based mosquito repellents, volatile emanations were investigated from five plant species,  Corymbia citriodora ,  Ocimum suave ,  Ocimum lamiifolium, Olea europaea  and  Ostostegia integrifolia , traditionally used in Ethiopia as protection against mosquitoes.    Methods  The behaviour of two mosquitoes, the malaria vector  Anopheles arabiensis  and the arbovirus vector  Aedes aegypti , was assessed towards volatiles collected from the headspace of fresh and dried leaves, and the smoke from burning the dried leaves in a two-choice landing bioassay and in the background of human odour.    Results  Volatile extracts from the smoke of burning dried leaves were found to be more repellent than those from fresh leaves, which in turn were more repellent to mosquitoes than volatiles from dried leaves. Of all smoke and fresh volatile extracts, those from  Co. citriodora  (52-76%) and  Oc. suave  (58-68%) were found to be the most repellent,  Os. integrifolia  (29-56%) to be intermediate while  Ol. europaea  (23-40%) and  Os. integrifolia  (19-37%) were the least repellent. One volatile present in each of the fresh leaf extracts of  Co. citriodora ,  Oc. suave  and  Os. integrifolia  was ß-ocimene. The levels of ß-ocimene reflected the mosquito repellent activity of these three fresh leaf extracts. Female host-seeking mosquitoes responded dose-dependently to ß-ocimene, both physiologically and behaviourally, with a maximal behavioural repulsion at 14% ß-ocimene. ß-ocimene (14%) repels mosquitoes in our 6-minute landing assays comparable to the synthetic insect repellent N,N-diethyl-m-toluamide (10% DEET).    Conclusions  Volatiles in the smoke of burning as well as fresh leaves of  Co. citriodora  and  Oc. suave  have significant repellent properties against host seeking  An. arabiensis  and  Ae. aegypti  mosquitoes. ß-ocimene, present in the fresh leaf headspace of  Co. citriodora ,  Oc. suave  and  Os. integrifolia , is a significantly effective volatile mosquito repellent in the laboratory. In addition to its repellent properties, ß-ocimene has long approved safe for use in food and cosmetics, making this volatile an intriguing compound to pursue in further tests in the laboratory and field to validate its mosquito repellent activity and potential for use in a commercial product. Also, the landing bioassay with humanised membranes is a potentially useful repellent screening technique that does not require the exposure of humans to the vectors, however further tests in parallel with conventional techniques are advised.

malaria journal

Fresh, dried or smoked? repellent properties of volatiles emitted from ethnomedicinal plant leaves against malaria and yellow fever vectors in Ethiopia