Malaria is an infectious parasite disease of humans and animals transmitted by the bite of the female Anopheles gambiae
mosquito. In 2015, experts estimate it affected 214 million people,
mostly in Africa, despite decades of mosquito eradication and control
efforts. There is no malaria vaccine, and although the disease is
curable in early stages, treatment is costly and difficult to deliver in
places where it is endemic.
A new study by Johns Hopkins researchers suggests that a specialized
area of the mosquito brain mixes tastes with smells to create unique and
preferred flavors. The findings advance the possibility, they say, of
identifying a substance that makes "human flavor" repulsive to the
malaria-bearing species of the mosquitoes, so instead of feasting on us,
they keep the disease to themselves, potentially saving an estimated
450,000 lives a year worldwide.
‘A specialized area of the mosquito brain mixes tastes with smells to create unique and preferred flavors, suggests a new study.’
A report on the research appeared online in the journal Nature Communications
"All mosquitoes, including the one that transmits malaria, use their
sense of smell to find a host for a blood meal. Our goal is to let the
mosquitoes tell us what smells they find repulsive and use those to keep
them from biting us," says Christopher Potter, assistant
professor of neuroscience at the Johns Hopkins University School of
Because smell is essential to mosquito survival, each mosquito has
three pairs of "noses" for sensing odors: two antennae, two maxillary
palps and two labella. The maxillary palps are thick, fuzzy appendages
that protrude from the lower region of the mosquito's head, more or less
parallel to its proboscis, the long, flexible sheath that keeps its
"feeding needle" under wraps until needed. At the very tip of the
proboscis are the labella, two small regions that contain both
"gustatory" neurons that pick up tastes and olfactory neurons for
To better understand how An. gambiae
mosquitoes that cause
malaria receive and process olfactory information from so many sensory
regions, Potter's team wanted to see where olfactory neurons from those
regions go to in the brain.
They used a powerful genetic technique - never before accomplished
in mosquitoes, according to Potter - to make certain neurons "glow"
green. The green glowing label was designed to appear specifically in
neurons that receive complex odors through proteins called odorant
receptors (ORs), since OR neurons are known to help distinguish humans
from other warm-blooded animals in Aedes aegypti
mosquitoes, which carry the Zika virus.
"This is the first time researchers managed to specifically target
sensory neurons in mosquitoes. Previously, we had to use flies as a
proxy for all insects, but now we can directly study the sense of smell
in the insects that spread malaria," says Olena Riabinina, the
lead author of the study and a postdoctoral fellow now at the Imperial
College London. "We were pleasantly surprised by how well our genetic
technique worked and how easy it is now to see the smell-detecting
neurons. The ease of identification will definitely simplify our task of
studying these neurons in the future."
As expected, Potter says, the OR neurons from the antennae and
maxillary palps went to symmetrical areas of the brain called antennal
lobes, just as they do in flies. But Potter was quite surprised when he
saw that the OR neurons from the labella went to the so-called
subesophageal zone, which, he says, had never before been associated
with the sense of smell in any fly or insect; it had only been
associated with the sense of taste.
"That finding suggests that perhaps mosquitoes don't just like our
smell, but also our flavor," says Potter. "It's likely that the odorants
coming off our skin are picked up by the labella and influence the
preferred taste of our skin, especially when the mosquito is looking for
a place to bite."
Potter says the finding potentially offers researchers one more way
to repel mosquitoes. The antennae and maxillary palps are more
specialized for picking up long-range signals, while the labella come
into direct contact with our skin. In fact, Potter says, before
injecting their needlelike proboscis, mosquitoes use the labella to
probe about on a victim's skin.
"We don't really know why they do that,
but we suspect that they're looking for sensory cues that hint at easy
access to a blood vessel," he says. "This suggests that a combination of
repellants could keep mosquitoes from biting us in two ways. One could
target the antennal neurons and reduce the likelihood that they come too
close, while another could target the labellar neurons and make the
mosquitoes turn away in disgust - before sucking our blood - if they
got close enough to land on us."
The two-part genetic system Potter devised to generate the glowing
neurons will make it much easier for his and other laboratories to mix
and match genetically altered mosquitoes to generate new traits, he
says. His group has already created a strain of An. gambiae
mosquitoes whose OR neurons glow green upon activation. Scientists can
thus see which neurons light up in response to a specific smell.
"Using this method, we hope to find an odorant that is safe and
pleasant-smelling for us but strongly repellant to mosquitoes at very
low concentrations," says Potter.
His group was also able to compare the brains of male and female
mosquitoes. Since only females use their sense of smell to find humans
and males feed only on nectar, it was previously thought that males had
just a rudimentary sense of smell. The Potter group found instead that
males have the same level of complexity in their brains to detect odors
as females but have fewer olfactory neurons. "It appears that males
might just have a scaled-down version of a female's sense of smell. So
they can still smell everything a female smells, just not as well,"
His group plans to study other types of neurons to better understand
how signals from the mosquitoes' three types of olfactory receptors
interact to influence their behavior. For example, why is lactic acid
not attractive on its own but highly attractive when mixed with carbon
"We'd like to figure out what regions and neurons in the brain lead
to this combined effect," says Potter. "If we can identify them, perhaps
we could also stop them from working."