How high from the ground do mosquitoes fly?

Insects are found very high in the atmosphere. The are only limited to the altitude that oxygen is still available. We have to use oxygen tanks above 26000-27000 feet. Insects are much smaller and can probably go a little bit higher. Weather balloons have found skeletons of dead insects as high as 45000 feet. I dont think they fly this high because the temperature is at or near freezing.