Female mosquitoes can distinguish a mix of four unique substances in blood

Overview

• Post By : Kumar Jeetendra


• Source: Howard Hughes Medical Institute


• Date: 13 Oct,2020

Mosquitoes spread diseases like malaria, dengue, and yellow fever that kill at least a half a million people each year. Researchers are learning what people taste like to mosquitoesdown to the individual neurons that sense blood’s distinctive, flavorful taste.

Female mosquitoes have a sense of taste that is especially tuned to detect a combination of at least four different substances in blood, Howard Hughes Medical Institute Investigator Leslie Vosshall’s team at The Rockefeller University and colleagues report October 12, 2020, in the journal Neuron. The team genetically modified mosquitoes so that researchers could see which neurons fire when a mosquito tastes blood.

“This is certainly a technical tour de force,” says neuroscientist Chris Potter of the Johns Hopkins University School of Medicine, who studies mosquito repellents. Identifying the specific taste neurons associated with blood may be something”we could use from the mosquito,” he says.

Vosshall and her team knew a great deal about the insect’s other finely tuned senses. In previous work, for example, they have found that mosquitoes can detect the repellent DEET with their legs and have identified an odorant receptor which mosquitoes use to distinguish between individuals and non-humans.

But little is known about mosquitoes’ sense of taste, despite being crucial to spreading illness. “If mosquitoes were not able to detect the taste of blood, in theory they could not transmit disease,” says Veronica Jové, an HHMI Gilliam Fellow in Rockefeller who led the work in Vosshall’s lab.

Only female mosquitoes feed on blood, which they want for their eggs to grow. That puts females at a special position. They need to distinguish between the sweet nectar they eat for the majority of their meals and the blood they gorge on before laying eggs.

Jové guessed that female Aedes aegypti mosquitoes, unlike men, would have the ability to differentiate between the two materials by flavor. Indeed, in behavioral experiments she discovered that female mosquitoes have two feeding modes which use different mouthparts and detect different flavors.

A nectar-feeding mode detects sugars and a blood-feeding mode employs a syringe-like”stylet” to pierce the skin and taste blood. Jové tricked the mosquitoes to the blood-feeding mode by offering them a mix of four chemicals: glucose (a sugar), sodium chloride (salt), sodium bicarbonate (found in both blood and baking soda), and adenosine triphosphate, or ATP, a compound that offers energy to cells.

Vosshall was curious, so she asked Jové to whip up an ATP solution in the laboratory and then took a sip.

Just as a human has taste buds that differentiate between salty, sweet, bitter, sour, and umami flavors, a mosquito’s stylet has neurons specialized to respond to specific flavors.

To find these taste neurons in action, the researchers genetically modified mosquitoes using a fluorescent tag that glowed when a nerve cell was activated. They then watched which cells at the stylet lit up in response to various meals. Only a subset were activated by blood, including both real blood and the researchers’ artificial mix.

So just what does human blood taste just like to a mosquito? Perhaps the closest we can say is that it is a little salty and a little candy. It is a bit like trying to explain how a honeybee sees a flower in ultraviolet colors invisible to your eye, or the way a bat eavesdrops on sonar waves we can not hear, Vosshall says. Likewise, a female mosquito can taste things we can’t. “There’s nothing like this in the human experience,” she says.

The findings shed light on precisely how specially accommodated the female mosquito is to find blood. Jové and Vosshall say they expect that a better understanding of mosquitoes’ perceptions will finally lead to new approaches to prevent them from biting us and spreading disease.

One possibility might seem like science fiction, Vosshall says, but there is precedent. “I just gave my dogs their monthly flea and tick medication, which is oral,” she says. Maybe something similar could be done for mosquitoes – a drug that humans could take before going to a mosquito-infested area which would interfere with mosquito’s taste for blood.

That idea, which boils down to making people less delicious, raises one final question. Are some people really “tastier” to mosquitoes than others? “We’re all tasty enough for a mosquito,” Jové states. As soon as they detect blood, she says,”we do not have a sense they’re very picky.”