title: Discovery of an oviposition attractant for gravid malaria vectors of the Anopheles gambiae species complex.
abstract: BACKGROUND
  New strategies are needed to manage malaria vector populations that resist insecticides and bite outdoors. This study describes a breakthrough in developing 'attract and kill' strategies targeting gravid females by identifying and evaluating an oviposition attractant for Anopheles gambiae s.l.
  
  
  METHODS
  Previously, the authors found that gravid An. gambiae s.s. females were two times more likely to lay eggs in lake water infused for six days with soil from a natural oviposition site in western Kenya compared to lake water alone or to the same but autoclaved infusion. Here, the volatile chemicals released from these substrates were analysed with a gas-chromatograph coupled to a mass-spectrometer (GC-MS). Furthermore, the behavioural responses of gravid females to one of the compounds identified were evaluated in dual choice egg-count bioassays, in dual-choice semi-field experiments with odour-baited traps and in field bioassays.
  
  
  RESULTS
  One of the soil infusion volatiles was readily identified as the sesquiterpene alcohol cedrol. Its widespread presence in natural aquatic habitats in the study area was confirmed by analysing the chemical headspace of 116 water samples collected from different aquatic sites in the field and was therefore selected for evaluation in oviposition bioassays. Twice as many gravid females were attracted to cedrol-treated water than to water alone in two choice cage bioassays (odds ratio (OR) 1.84; 95% confidence interval (CI) 1.16-2.91) and in experiments conducted in large-screened cages with free-flying mosquitoes (OR 1.92; 95% CI 1.63-2.27). When tested in the field, wild malaria vector females were three times more likely to be collected in the traps baited with cedrol than in the traps containing water alone (OR 3.3; 95% CI 1.4-7.9).
  
  
  CONCLUSIONS
  Cedrol is the first compound confirmed as an oviposition attractant for gravid An. gambiae s.l. This finding paves the way for developing new 'attract and kill strategies' for malaria vector control.
authors.affiliation: Department of Chemistry, Royal Institute of Technology, SE-100 44, Stockholm, Sweden. jenlindh@kth.se.
authors.forename: Jenny M
authors.initials: JM
authors.lastname: Lindh
authors.affiliation: Disease Control Department, London School of Hygiene & Tropical Medicine, London, WC1E 7HT, UK. okal.mike@gmail.com.|Behavioural and Chemical Ecology Department, International Centre of Insect Physiology and Ecology, 00100, Nairobi, Kenya. okal.mike@gmail.com.
authors.forename: Michael N
authors.initials: MN
authors.lastname: Okal
authors.affiliation: Disease Control Department, London School of Hygiene & Tropical Medicine, London, WC1E 7HT, UK. manuelahv82@gmail.com.|Behavioural and Chemical Ecology Department, International Centre of Insect Physiology and Ecology, 00100, Nairobi, Kenya. manuelahv82@gmail.com.
authors.forename: Manuela
authors.initials: M
authors.lastname: Herrera-Varela
authors.affiliation: Department of Chemistry, Royal Institute of Technology, SE-100 44, Stockholm, Sweden. akbk@kth.se.
authors.forename: Anna-Karin
authors.initials: AK
authors.lastname: Borg-Karlson
authors.affiliation: Behavioural and Chemical Ecology Department, International Centre of Insect Physiology and Ecology, 00100, Nairobi, Kenya. btorto@icipe.org.
authors.forename: Baldwyn
authors.initials: B
authors.lastname: Torto
authors.affiliation: School of Biological & Biomedical Sciences, Durham University, Durham, DH1 3LE, UK. s.w.lindsay@durham.ac.uk.
authors.forename: Steven W
authors.initials: SW
authors.lastname: Lindsay
authors.affiliation: Disease Control Department, London School of Hygiene & Tropical Medicine, London, WC1E 7HT, UK. ufillinger@icipe.org.|Behavioural and Chemical Ecology Department, International Centre of Insect Physiology and Ecology, 00100, Nairobi, Kenya. ufillinger@icipe.org.
authors.forename: Ulrike
authors.initials: U
authors.lastname: Fillinger
mesh_terms: D000818:Animals; D000852:Anopheles / Q000187:drug effects* / Q000502:physiology*; D005260:Female; D008401:Gas Chromatography-Mass Spectrometry; D007303:Insect Vectors / Q000187:drug effects* / Q000502:physiology*; D007630:Kenya; D010058:Oviposition / Q000187:drug effects*; D010675:Pheromones / Q000737:chemistry / Q000302:isolation & purification* / Q000378:metabolism; D000081223:Polycyclic Sesquiterpenes; D013729:Terpenes / Q000737:chemistry / Q000302:isolation & purification* / Q000378:metabolism
chemical_list: D010675:Pheromones; D000081223:Polycyclic Sesquiterpenes; D013729:Terpenes; C010411:insect attractants; C078669:cedrol