title: Arm-in-cage testing of natural human-derived mosquito repellents.
abstract: BACKGROUND
  Individual human subjects are differentially attractive to mosquitoes and other biting insects. Previous investigations have demonstrated that this can be attributed partly to enhanced production of natural repellent chemicals by those individuals that attract few mosquitoes in the laboratory. The most important compounds in this respect include three aldehydes, octanal, nonanal and decanal, and two ketones, 6-methyl-5-hepten-2-one and geranylacetone [(E)-6,10-dimethylundeca-5,9-dien-2-one]. In olfactometer trials, these compounds interfered with attraction of mosquitoes to a host and consequently show promise as novel mosquito repellents.
  
  
  METHODS
  To test whether these chemicals could provide protection against mosquitoes, laboratory repellency trials were carried out to test the chemicals individually at different concentrations and in different mixtures and ratios with three major disease vectors: Anopheles gambiae, Culex quinquefasciatus and Aedes aegypti.
  
  
  RESULTS
  Up to 100% repellency was achieved depending on the type of repellent compound tested, the concentration and the relative composition of the mixture. The greatest effect was observed by mixing together two compounds, 6-methyl-5-hepten-2-one and geranylacetone in a 1:1 ratio. This mixture exceeded the repellency of DEET when presented at low concentrations. The repellent effect of this mixture was maintained over several hours. Altering the ratio of these compounds significantly affected the behavioural response of the mosquitoes, providing evidence for the ability of mosquitoes to detect and respond to specific mixtures and ratios of natural repellent compounds that are associated with host location.
  
  
  CONCLUSIONS
  The optimum mixture of 6-methyl-5-hepten-2-one and geranylacetone was a 1:1 ratio and this provided the most effective protection against all species of mosquito tested. With further improvements in formulation, selected blends of these compounds have the potential to be exploited and developed as human-derived novel repellents for personal protection.
authors: Biological Chemistry Department, Centre for Sustainable Pest and Disease Management, Rothamsted Research, Harpenden AL5 2JQ, UK. james.logan@bbsrc.ac.uk
authors: James G
authors: JG
authors: Logan
authors: Nina M
authors: NM
authors: Stanczyk
authors: Ahmed
authors: A
authors: Hassanali
authors: Joshua
authors: J
authors: Kemei
authors: Antônio E G
authors: AE
authors: Santana
authors: Karlos A L
authors: KA
authors: Ribeiro
authors: John A
authors: JA
authors: Pickett
authors: A Jennifer
authors: AJ
authors: Mordue Luntz
mesh_terms: D000330:Aedes / Q000187:drug effects; D000447:Aldehydes / Q000494:pharmacology; D000818:Animals; D000852:Anopheles / Q000187:drug effects; D001132:Arm; D009033:Culicidae / Q000187:drug effects; D006801:Humans; D007299:Insect Bites and Stings / Q000517:prevention & control*; D007302:Insect Repellents / Q000008:administration & dosage / Q000494:pharmacology*; D007303:Insect Vectors / Q000187:drug effects*; D007659:Ketones / Q000494:pharmacology; D009032:Mosquito Control / Q000379:methods*
chemical_list: D000447:Aldehydes; D007302:Insect Repellents; D007659:Ketones