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
