Delicious – blood! Researchers have now found out how mosquitoes perceive the special taste of their favorite food. Special types of nerves in the pests’ proboscis react to certain substances in the blood, which, however, only trigger sucking in combination. The results could potentially lead to the development of strategies that spoil the appetite of dangerous disease vectors, the scientists say.
They are the most dangerous animals in the world: mosquitoes spread diseases such as malaria, dengue and yellow fever, from which at least half a million people die every year. In addition to the development of treatment options for the diseases, it is also a goal of research to limit the transmission of pathogens through the bloodsuckers. The specific focus is therefore on the skills and strategies of these insects. Up to now, mosquitoes have paid a lot of attention to their sense of smell, which they use to track down their victims. But the researchers working with Veronica Jové from Rockefeller University in New York have now devoted themselves to investigating a perception system that is only used when the insect has already landed and lowered its sting into the victim.
The taste experience makes them suck
If the mosquito comes across blood, the special taste experience of this substance triggers the further mechanisms of food intake, which are ultimately responsible for the transmission of pathogens. “If mosquitoes weren’t able to recognize the taste of blood, they couldn’t theoretically transmit diseases,” says Jové. As the scientists explain, an important aspect of the mosquito’s sense of taste is that they not only feed on blood – they also ingest nectar from flowers to provide themselves with energy. For the production of eggs, however, the female animals need the nutrients from a blood meal. Different mechanisms of the mouthparts are used with both food sources. A central question of the study was therefore what constitutes the taste of blood or how the female mosquitoes differentiate it from the taste of nectar.
The researchers initially confirmed earlier results by feeding experiments with mosquitoes of the species Aedes aegypti, which provided information about which components of the blood the insects respond to. If they offered them sugar or saline solutions, it was not to the taste of the mosquitoes, even if the warmth and carbon dioxide were present at the same time, which normally signal the animals to the body of a victim. It turned out that only a mixture of glucose, table salt, sodium bicarbonate and adenosine triphosphate animates the mosquitoes to suckle. These are the core components that make up the taste of blood.
Special taste buds emerge
The scientists then devoted themselves to examining the nerves in the mosquito’s proboscis that apparently respond to this recipe. The researchers used genetically modified mosquitoes, whose nerve cells light up when they are active, to investigate the specific stimuli to which they react. “We put tiny drops of different test substances on the tips of the stilettos and recorded which neurons reacted,” explains Jové. The researchers were able to document: In general, the nerves in the proboscis are insensitive to nectar-specific sugars and only react to glucose if the additional core components of the blood taste are also present. The taste of blood is recognized by four functionally different types of nerves that respond to certain components. The entire blood uptake program is only set in motion when all the important ingredients of the blood taste are present together.
The investigation of nerve activity also showed, however, that only half of the forty neurons in the proboscis seem to be activated by blood. In further investigations, the researchers now want to clarify what function the previously inactive nerves have. They suspect that they are involved in recognizing special aromas that are only released the moment the sting pierces a vein in the skin.
As the scientists finally emphasize, the results cannot yet be specifically implemented in an application. They hope, however, that a better understanding of the mosquito’s senses could help develop new methods of preventing bites and thus the transmission of diseases. According to the researchers, a drug that makes human blood less palatable to insects would be conceivable.
Source: Rockefeller University, Howard Hughes Medical Institute, Articles: Neuron, doi: 10.1016 / j.neuron.2020.09.019