title: Fresh, dried or smoked? Repellent properties of volatiles emitted from ethnomedicinal plant leaves against malaria and yellow fever vectors in Ethiopia.
abstract: 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.
authors.affiliation: Division of Chemical Ecology, Department of Plant Protection Biology, Swedish University of Agricultural Sciences, 230 53 Alnarp, Sweden.
authors.forename: Fitsum Fikru
authors.initials: FF
authors.lastname: Dube
authors.forename: Kassahun
authors.initials: K
authors.lastname: Tadesse
authors.forename: Göran
authors.initials: G
authors.lastname: Birgersson
authors.forename: Emiru
authors.initials: E
authors.lastname: Seyoum
authors.forename: Habte
authors.initials: H
authors.lastname: Tekie
authors.forename: Rickard
authors.initials: R
authors.lastname: Ignell
authors.forename: Sharon R
authors.initials: SR
authors.lastname: Hill
mesh_terms: D000080462:Acyclic Monoterpenes; D000330:Aedes / Q000187:drug effects*; D000475:Alkenes / Q000032:analysis / Q000737:chemistry; D000818:Animals; D000852:Anopheles / Q000187:drug effects*; D001522:Behavior, Animal; D001681:Biological Assay / Q000295:instrumentation / Q000379:methods; D003671:DEET / Q000737:chemistry; D005002:Ethiopia / Q000453:epidemiology; D005247:Feeding Behavior; D005260:Female; D006801:Humans; D007300:Insect Control / Q000379:methods*; D007302:Insect Repellents / Q000032:analysis / Q000737:chemistry*; D007303:Insect Vectors / Q000187:drug effects; D008288:Malaria / Q000453:epidemiology / Q000517:prevention & control; D008519:Medicine, Traditional; D008566:Membranes / Q000737:chemistry; D031339:Ocimum / Q000737:chemistry; D009812:Odorants; D031658:Olea / Q000737:chemistry; D010936:Plant Extracts / Q000737:chemistry; D018515:Plant Leaves / Q000737:chemistry*; D012906:Smoke / Q000032:analysis; D055549:Volatile Organic Compounds / Q000737:chemistry*; D015004:Yellow Fever / Q000453:epidemiology / Q000517:prevention & control
chemical_list: D000080462:Acyclic Monoterpenes; D000475:Alkenes; D007302:Insect Repellents; D010936:Plant Extracts; D012906:Smoke; D055549:Volatile Organic Compounds; D003671:DEET; C443996:beta-ocimene