Arm-in-cage testing of natural human-derived mosquito repellents

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. CONCLUSION: 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

Residual insecticidal activity of long-lasting deltamethrin-treated curtains after 1 year of household use for dengue control

Objective To evaluate the residual insecticidal activity of the PermaNet((R)) curtains on Aedes aegypti after 1 year of use in Thai households and to assess the influence of sun and dust exposure, washing practices and detergent use. Methods We sampled UV-protected PermaNet((R)) curtains made of a long-lasting deltamethrin-[55 mg/m(2)] treated polyester netting, before (10 curtains) and after 8 (10 curtains) and 12 months (66 curtains) of household use in a field site in Chon Buri, Thailand. We assessed the residual insecticidal activity of the curtains by standard WHO bioassay, using a deltamethrin-susceptible insectarium Aedes aegypti strain. Results Mosquito mortality was 100% before distribution, 100% at 8 months and 98.2% (95% CI 97.9-98.5) at 12 months of use. Sunlight, hand-washing and detergent use had no effect on the residual insecticidal activity after 12 months. However, the mosquito survival rate increased by a factor of 6.4 (95% CI 3.5-11.8) on machine-washed curtains and by a factor of 2.0 (95% CI 1.4-2.9) on curtains not covered by dust. Conclusion The residual insecticidal activity of PermaNet(R) curtains remains high after 12 months use under field condition

Un problème de métalinguistique: L'explication des échecs de communication chez l'enfant de huit à douze ans

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