Mosquitoes are troublesome. A mosquito bite is capable of causing pain and irritation and even causes diseases like dengue, malaria and yellow fever.
But what attracts mosquitoes to human blood in the first place?
A study reveals that they are not attracted to “simple flavours like sweet or salty, but only a complex combination of ingredients”.
And what does human blood taste like to mosquitoes? Scientists say that is impossible to understand.
Researchers at The Rockefeller University in New York City have found that only female mosquitoes feed on blood meal to provide nutrients to their eggs to develop.
So, “Aedes aegypti females [the primary spreader of dengue, Zika, yellow fever, and Chikungunya virus] must accurately discriminate blood and nectar because each meal promotes mutually exclusive feeding programs with distinct sensory appendages, meal sizes, digestive tract targets, and metabolic fates”, the study revealed.
The findings were published in the journal Neuron.
“But they survive primarily on nectar-like thousands of other insect species,” a report published in Science focus said.
According to the report, the blood-sucking habit of mosquitoes makes them the “deadliest animal on the planet to humans”. They claim the lives of around “half a million people every year through diseases like malaria, dengue and yellow fever.” it said.
“This innate ability to recognise blood is the basis of vector-borne disease transmission to millions of people worldwide,” the research paper said.
HOW WAS STUDY CONDUCTED?
Researchers used “genetically-modified females to witness which neurons fire when they tasted blood”.
When a nerve cell was activated, a fluorescent tag in the genetically modified insects glowed. This enabled researchers “to track which nerve cells lit up when they were offered different meals,” the report said.
During the course of the study, mosquitoes were offered a mix of four compounds developed to replicate the flavour of blood. They were tricked into switching from nectar-feeding mode to blood-feeding mode.
The mixture contained glucose, sodium chloride, sodium bicarbonate and adenosine triphosphate (ATP) – a compound that provides energy to cells, the report said.
The research revealed that while mosquitoes loved the synthetic “blood”, they were not interested in a mixture of sugar and saline solution.
The study also showed that glucose — found in both nectar and blood — did not “consistently activate any neurons in particular”, but sodium chloride, sodium bicarbonate and ATP each activated specific clusters of Aedes aegypti, the primary spreader of dengue, Zika, yellow fever, and Chikungunya virus.
However, the researchers found that there was one cluster of neurons which was only activated by blood, including both real blood and the synthetic blood prepared by researchers. No other ingredients stimulated this behaviour.
“These neurons break the rules of traditional taste coding, thought to be conserved from flies to humans,” Veronica Jové, one of the lead researchers in the study, was quoted as saying.
The study said: “The distinction between blood and nectar is therefore encoded in specialised neurons at the very first level of sensory detection in mosquitoes.”
The researchers also investigated the “syringe-like blood-feeding appendage, the stylet, and discovered that sexually dimorphic stylet neurons taste blood”.
“We found that blood is detected by four functionally distinct stylet neuron classes, each tuned to specific blood components associated with diverse taste qualities,” the authors of the study said.
WAY TO POSSIBLE ORAL MOSQUITO REPELLENTS
The authors of the study said that this discovery can potentially pave the way for a drug or oral mosquito repellents “that would interfere with their taste for blood”.
But it might be impossible to ever understand exactly what human blood tastes like to mosquitoes, the report quoted Dr Leslie Vosshall, who heads the laboratory at the Howard Hughes Medical Institute at The Rockefeller University, as saying.
WHAT PREVIOUS STUDY SAYS
A research paper published in 2018 said that female mosquitoes use a combination of cues to find their “vertebrate hosts and blood-feed” and that their feeding behaviour “creates a potent pathway for disease transmission”.
It said that the tastants on the skin likely promote blood-feeding once a female mosquitoes land even as “they are guided by other cues to fly towards their hosts”.
After landing, they soon pierce the skin and draw blood from small blood vessels. The mouthparts of the female mosquito are highly specialised for blood feeding and contain sensory hair cells which help locate blood under the skin,” the study revealed.
There are species of mosquitoes which not only respond to taste but also detect thermal cues.
The study also revealed that mosquitoes may also integrate odour with taste cues in response to hosts.
Another study revealed that not all mosquitoes bite humans. The researchers studied Aedes aegypti in specific.
They found two things: “First, they show that mosquitoes living in dense urban cities were attracted to people more than those from more rural or wild places. However, the researchers note that this only applied to especially dense modern cities and therefore isn’t likely to be the original reason that certain population of Ae. aegypti mosquitoes evolved to specialise in biting humans.