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

Abstract

BackgroundIndividual 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.MethodsTo 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.ResultsUp 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.ConclusionThe 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.

Smelling your way to food: can bed bugs use our odour?

“…Bed bugs are able to detect C 7 -C 10 aldehydes and sulcatone present in human emanates, similar to other blood-feeding insects (Gikonyo et al, 2002;Birkett et al, 2004;Ghaninia et al, 2008;Logan et al, 2008;Logan et al, 2009;Syed and Leal, 2009;Logan et al, 2010). Quantitative differences in the amount of these compounds in headspace volatile extracts collected from a group of volunteers modulate the behavioural response of bed bugs.…”

“…Aldehydes alone appear to elicit attraction in various blood-feeding insects when presented at relevant doses. For example, tsetse flies, Glossina morsitans, fly upwind in presence of a synthetic blend of six aldehydes (Gikonyo et al, 2003), C. quinquefasciatus is caught in traps baited with nonanal (Syed and Leal, 2009) and the addition of C 8 -C 10 aldehydes significantly increases the number of A. gambiae and C. quinquefasciatus landing on a human arm (Logan et al, 2010). In contrast, sulcatone has been shown to inhibit the final approach and landing of different haematophagous insects such as cattle flies (Birkett et al, 2004), and the mosquitoes A. aegypti, A. gambiae and C. quinquefasciatus (Logan et al, 2008;Logan et al, 2010).…”

Laboratory Studies ofAedes aegyptiAttraction to Ketones, Sulfides, and Primary Chloroalkanes Tested Alone and in Combination with L-Lactic Acid

“…Additional aldehydes (hexanal, octanal, Z-4-decenal) and hexanoic acid, produced by Aethia cristatella Pallas, the crested auklet, have been reported as repellents for mosquitoes (Douglas et al 2005). Logan et al (2008Logan et al ( , 2010 found octanal, nonanal, and decanal as attraction inhibitors and repellents of Ae. aegypti, with decanal as the most potent repellent of the three aldehydes.…”

Reception of odors and repellents in mosquitoes

“…Expression levels and allelic sensitivity of this receptor to 6-methyl-5-hepten-2-one vary across two subspecies of A. aegypti that differ in their preference for humans and correlate positively with preference for human hosts across populations and hybrids of the two subspecies [33]. However, others studies have reported that 6-methyl-5-hepten-2-one is a potent natural repellent found in skin [34,35], and additional studies are required to understand these confounding results.…”

“…Natural repellents have also been identified from a variety of plant sources, and more recently, from volatiles found in the skin of humans found to be minimally attractive to mosquitoes [35,56]. Identical twins are more similarly attractive to mosquitoes than are fraternal twins, suggesting a genetic basis [57].…”