Secret mosquito ‘sixth sense’ lets them easily find your skin – avoid bites by changing how you dress

THE world’s most notorious blood-sucking insect can seek you out using your body heat.

Mosquitoes have a bad rep, and rightfully so, as they are prominent vectors for disease.

One species, Aedes aegypti, spreads the viruses that cause millions of cases of dengue, yellow fever and Zika each year.

Another, Anopheles gambiae, spreads the parasite that causes malaria, which claims the lives of more than 400,000 people annually according to the World Health Organization.

While males feed on nectar, female mosquitoes need blood for egg development. They have notoriously poor vision – so how do they find suitable victims?

A published Wednesday in Nature proposes an answer: the creepy-crawlies can sense body heat through a process known as infrared detection.

Researchers at UC Santa Barbara took a look at Aedes aegypti, the species most successful at finding hosts.

The bugs use multiple cues including carbon dioxide from exhaled breath and humidity from our bodies. However, these are more volatile than heat sensing, as they can be thrown off by a particularly strong gust of wind.

The best result comes when the insects combine all the weapons in their arsenal.

Scientists found infrared radiation around the temperature of human skin doubled host-seeking behavior when combined with CO₂ and human scent.

From a mere 10 cm away, the insects can detect heat rising from our bodies and directly sense the temperature of our skin upon landing.

But heat energy can travel even longer distances when converted into infrared electromagnetic waves. Scientists were curious to see if mosquitoes could pick up on them, similar to pit vipers.

The researchers put female mosquitoes in a cage and measured their host-seeking activity in two zones.

Each zone was exposed to human odors and CO₂ at the same concentration that we exhale, but only one was also exposed to infrared waves from a source at skin temperature.

The scientists counted how many mosquitoes began probing for a vein.

They found that adding thermal infrared from a temperature source doubled host-seeking activity – and the bugs were effective from up to two and a half feet away.

Co-author Craig Montell explained that “any single cue alone doesn’t stimulate host-seeking activity.”

Rather, infrared waves only have a significant impact when combined with other clues like elevated CO₂ and body odor.

The researchers also sought to determine a mechanism behind the heat sensing.

The tips of mosquito antennae have nerve cells that detect warmth. Earlier studies identified a temperature-sensitive protein called TRPA1 in the end of each antenna.

The UCSB team found that animals without a functional trpA1 gene, which codes for the protein, couldn’t pick up on infrared waves.

However, the researchers suspected the TRPA1 protein might not fully explain how mosquitoes detect infrared over such a long distance.

A previous study identified rhodopsin proteins in fruit flies that were sensitive to infinitesimal temperature increases.

Upon further examination, the researchers discovered that two of the 10 rhodopsins found in mosquitoes are expressed in the same antennal neurons as TRPA1.

Removing TRPA1 eliminated the mosquito’s sensitivity to infrared while issues in either of the rhodopsins, Op1 or Op2, had no impact.

Even knocking out both rhodopsins didn’t entirely eliminate the animal’s sensitivity to infrared, although it weakened their ability to find a host.

Their results suggest that thermal infrared directly activates TRPA1 from a closer range. Meanwhile, Op1 and Op2 can activate at lower levels and set off a chain reaction that triggers TRPA1.

In addition to simply learning more about the humble mosquito, the scientists considered the real-world implications.

“Despite their diminutive size, mosquitoes are responsible for more human deaths than any other animal,” co-lead author Nicolas DeBeaubien said.

“Our research enhances the understanding of how mosquitoes target humans and offers new possibilities for controlling the transmission of mosquito-borne diseases.”

This understanding is crucial as the range of Aedes aegypti continues to extend to countries where it was never seen before.

The results also uncover a practical solution for humans, reinforcing why loose-fitting clothing is particularly good at preventing bites.

Baggy pants and sleeves block the mosquito from latching onto our skin, first and foremost.

But it also allows the infrared waves to dissipate between our skin and the clothing, making it nearly undetectable.