Malaria Mosquitoes Find Blood Vessels in Two Distinct Steps

Notorious malaria-carrying Anopheles coluzzii mosquitoes are skillful foragers, speedily biting the skin and efficiently probing for blood vessels before feeding, then retracting and withdrawing their mouthparts – all in five distinct steps, new research observes. These blood-hungry insects combine a chemical sensing toolkit with biomechanical coordination that differs from the well-documented strategy used by yellow fever-carrying Aedes aegypti mosquitoes. Female mosquitoes from the Anopheles genus are notorious transmitters of malaria. Until now, how they choose where to munch – finding the juiciest subcutaneous blood vessels – and how they take a bite has remained a mystery. Here, Joanna Konopka and colleagues have described in great detail the biting process of female Anopheles coluzzii mosquitoes, which are endemic to sub-Saharan Africa. Using video, electrophysiological monitoring, and deep learning, they analyzed mosquitoes' behavior before and after the insects bit the same human host. The mosquitoes synchronized their mouthparts with leg movements as they prodded the skin to find the best spot to munch. The insects employed 5 behaviors – piercing, vessel searching, blood ingestion, retraction, and withdrawal – in the subsequent biting and guzzling phases. The team also modified two genes used for chemical sensing to create mutant An. Coluzzii. Doing so caused the mosquitoes to change their biting process slightly, indicating that An. Coluzzii relies on chemical cues as well as innate motor behaviors. Finally, the authors compared An. Coluzzii's biting dynamics with the yellow fever vector, Aedes aegypti, finding that An. coluzzii bites faster and hunts for blood vessels more quickly. "Anopheles coluzzii pierces the skin in an abrupt manner (rapidly stabbing the stylet into the skin), while Ae. aegypti does so more gradually (maintaining rhythmic pattern of piercing)," they write. They note this could be why Anopheles bites can be more painful while Aedes bites go unnoticed.