Some mosquitoes have an almost unfailing thirst for human blood. Previous attempts to prevent the insects from tracking people by blocking some of the mosquitoes’ ability to smell have failed. A new study hints that it’s because bloodsuckers have built-in solutions to ensure they can always smell us.
For most animals, individual nerve cells in the olfactory system can detect only one type of odor. But Aedes aegypti Each of the mosquito nerve cells can detect many odors, researchers report Aug. 18 in Cell. That means that if a cell were to lose the ability to detect a human scent, it can still detect other scents.
The study provides the most detailed map yet of a mosquito’s sense of smell and suggests that hiding human scents from insects might be more complicated than researchers thought.
Repellents that prevent mosquitoes from detecting odors associated with humans could be especially difficult to manufacture. “Maybe instead of trying to mask them from finding us, we’d be better off finding odors that mosquitoes don’t like to smell,” says Anandasankar Ray, a neuroscientist at the University of California, Riverside, who was not involved in the work. These repellants can confuse either irritate the bloodsuckers and send them flying (serial number: 09/21/11; Serial number: 4/3/21).
Effective repellents are a key tool in preventing mosquitoes from transmitting disease-causing viruses such as dengue and zika (Serial number: 7/11/22). “Mosquitoes are responsible for more human deaths than any other creature,” says Olivia Goldman, a neurobiologist at Rockefeller University in New York City. “The better we understand them, the better we can have these interventions.”
Mosquitoes that feed on people focus on a variety of cues when they hunt, including body heat and body odor. Insects smell using their antennae and small appendages near their mouths. Using three types of sensors in the olfactory nerve cells, they can detect chemicals such as carbon dioxide of exhaled breath or components of body odor (Serial Number: 7/16/15).
In previous work, the researchers thought that blocking some sensors might hide human odors of mosquitoes by disrupting scent messages sent to the brain (Serial number: 5/12/13). But even those sensor-deprived mosquitoes can still smell and bite people, says neurobiologist Margo Herre, also of Rockefeller University.
So Goldman, Herre, and their colleagues added fluorescent labels to A. aegypti nerve cells, or neurons, to learn new details about how the mosquito brain deciphers human scents. Surprisingly, instead of finding the typical single type of sensor per nerve cell, the team found that individual neurons in mosquitoes look more like sensory centers.
Genetic analyzes confirmed that some of the olfactory nerve cells had more than one type of sensor. Some cells produced electrical signals in response to various mosquito-attracting chemicals found in humans, such as octenol and triethylamine, a sign that the neurons could detect more than one type of odor molecule. A separate study published in April in eLife found similar results in fruit fliessuggesting that such a system may be common among insects.
It’s not clear why having redundant ways to detect people’s odors might be helpful to mosquitoes. “Different people can smell very differently from each other,” says study co-author Meg Younger, a neurobiologist at Boston University. “Perhaps this is a setup to find a human, regardless of what variety of human body odor that human emits.”