Saturday, October 1

Mosquitoes have a sense of smell that is difficult to fool to find someone to bite

Scientific dogma has held that the sensory systems of animals are exquisitely organized and specialized. Each olfactory neuron has only one type of receptor; however, a new study confirms that this is not the case in mosquitoes, which is why they are able to always smell humans.

“The unexpected result shows that it is even more difficult than previously thought to confuse mosquitoes when they relentlessly seek human blood,” said Leslie Vosshall of the Howard Hughes Medical Institute in the United States. The scientist and her team describe in the journal Cell the neural mechanisms of these insects to ensure that they can always smell – and sting – humans.

The study, in which the Rockefeller University also participates, “upends” the conventional model of the neural circuitry that animals use to detect and distinguish thousands of different odors in their olfactory systems, the authors pointed out.

“We have discovered that Aedes aegypti—the main spreader of dengue, Zika, yellow fever, and chikungunya virus—uses a different organizing principle, with many neurons co-expressing multiple chemosensory receptor genes,” the authors wrote in their article. .

The females of these mosquitoes, which are the ones that bite, are intensely attracted to both the CO2 exhaled by people and their body odour, which they detect through chemosensory receptors.

Until now, the established proposal, based on the research of Linda Buck and Richard Axel, was that the sensory systems of animals were highly specialized; that is, each olfactory neuron had only one type of receptor, which detects a specific set of chemicals and then connects to a single structure in the olfactory bulb.

According to this logic, there would be different types of neurons that respond to the smell of strawberries, for example, others to olive oil, others to peanut butter, others to gasoline, and so on.

However, according to this research, at least in these mosquitoes, each neuronal cell has several types of receptors, not just one. A single mosquito neuron can detect different odors.

“The conventional idea of ​​one receptor per odor and one receptor per neuron was so strong that there was no reason to investigate the existence of multiple receptors,” said Christopher Potter of Johns Hopkins University. “Now we know that we have to look for them,” he said.

The added complexity to the insect olfactory system makes perfect evolutionary sense, the researchers say, especially for mosquitoes that must find humans to survive. Having several types of receptors on each neuron increases their ability to detect exhaled CO2 and the full range of body odours: when it comes to biting avoidance by blocking some of the receptors, mosquitoes can still easily locate blood using their other receptors.

“It’s a very good trick,” Vosshall summed up. “Mosquitoes have plan b after plan b. For me the system is unbreakable”, he highlighted. This is not good news for the effort to reduce the number of mosquito-borne diseases such as malaria, yellow fever and dengue fever. “At least now we have a more realistic view of what we are up against,” he stressed.

“Any future attempts to control mosquitoes through repellants or anything else have to take into account how unyielding their attraction to us is,” said Vosshall, who believes other insects may have a similar mechanism.