Mosquitos use different mechanisms depending on the distance to their target.

https://www.npr.org/sections/health-shots/2019/03/28/7068387...

At a distance, its CO2 (30 feet away). Closer in, its the sweat. Even closer to target, its body heat.

The CO2 itself doesn't need to be warm or sweaty. Just when the mosquito is close to a target, it switches from the general vicinity (CO2) approach to one that will give it a better lock on.