When a mosquito lands on our skin, finding blood requires much more than simply inserting its proboscis.
We know the signals that attract mosquitoes to us: our scent, our warmth and even the gas we exhale. But what happens once the insect has landed on an arm? Researchers from Johns Hopkins University in the United States filmed its movements up close.
A mosquito biting.
Image for illustration purposes, Pixabay
They observed female mosquitoes of the species Anopheles coluzzii, which can transmit malaria. High-speed cameras recorded their movements as they bit a human forearm. At the same time, tiny electrical measurements indirectly tracked what their mouthparts were doing beneath the skin.
The researchers identified five stages. The mosquito begins by piercing the skin, then explores the tissue to find a blood vessel. Once it reaches the blood, it feeds, gradually withdraws its mouthparts and eventually pulls them out completely. This search therefore does not happen in a single movement.
The most surprising aspect is the coordination of its movements. When it pushes its mouthparts in, its front legs bend. When it withdraws them slightly, they straighten again. Two small appendages positioned near its mouth also move during the search, then change their movement when the insect begins to drink.
The team then compared this species with Aedes aegypti, another mosquito known to transmit diseases including dengue. Their strategies are not identical. In the experiments, the former found a blood vessel about 17 seconds faster, while the latter made more exploratory movements.
The researchers also modified certain genes involved in detecting chemical substances. In some mosquitoes, these changes disrupted the beginning of the bite or the taking of blood. But they did not always prevent them from feeding: several detection methods appear to be able to complement one another.
These results show that the mosquito does not simply insert its proboscis at random. It adjusts its movements as it searches for blood. This could help researchers understand how to interrupt a bite once the insect has landed, rather than only how to prevent it from approaching us.
No new repellent has yet been developed as a result of this study. These observations will need to be verified with more people and under different conditions. But understanding each stage of a bite could open up new ways to limit the transmission of diseases.