Responses of The Malaria Vector To Plant-And Mammalian Odors.

Abstract

Several studies have shown that odors of plant and animal origin can be developed into lures for use in surveillance of mosquito vectors of infectious diseases. However, the effect of combining plant- and mammalian-derived odors into an improved lure for monitoring both nectar- and blood-seeking mosquito populations in traps is yet to be explored. Laboratory dual choice olfactometer and field assays were used to investigate responses of the malaria vector, Anopheles gambiae, to plant- and mammalian-derived compounds and a combined blend derived from these two odor sources. Using subtractive bioassays in dual choice olfactometer, it was shown that a 3-component terpenoid plant-derived blend comprising (E)-linalool oxide, β-pinene, β-ocimene was more attractive to female An. gambiae than (E)-linalool oxide only (previously found to be attractive) and addition of limonene to this blend antagonized its attractiveness. However antagonistic effect of limonene was not exhibited in field trials in malaria endemic areas probably due to species specificity in odorant perception by different malaria vectors. Likewise, a mammalian-derived lure comprising the aldehydes heptanal, octanal, nonanal and decanal, was more preferred than (E)-linalool oxide. Surprisingly, combining the plant-derived 3-component blend of (E)-linalool oxide, β pinene, β-ocimene with the mammalian derived 4-component blend attracted fewer females of An. gambiae than the individual blends in laboratory assays. However, this pattern was not replicated in field trials, where a dose-dependent effect on trap catches while combining both blends with significantly improved trap catches at higher doses was observed. This indicates the significance of ratio and concentration in formulation of odorant blends for outdoor biting malaria vectors. Therefore, field evaluation of odorant compounds is paramount in the design of vector control strategies involving kairomones from plant- and mammalian-based sources