I never paid much attention to Mosquitoes as a kid in Missouri. Sure I got bit sometimes, but they never seemed to be too big a problem. When I got to young adulthood and starting doing wilderness stuff in a broader area (southern Missouri, northern Arkansas, southern Illinois, western Kentucky, central Tennessee, and then eventually all of Tennessee, northern Alabama, and northern Georgia) I did start to notice them more.
I'd say the rule in that large area I just described is: mosquitoes go wherever they want, though true, on hilltops without much vegetation to break the wind, they might seem more scarce, but I doubt it is because they "don't go there:" they're following your CO2 trail to get a bite of blood . . . hmm, similar to some political parties . . . but then they get caught on a breeze and windup way off course at which point they either find something/someone else to parasitize for a meal or they die.
The first time I went out to the Sierra's I learned how different true alpine conditions can be. At that point, I had probably spent several thousand hours of my life engaged in wilderness activities, either underground or on the surface, so between that and studying the maps I was pretty confident I knew what I was doing. My wife and I had done a few day hikes in Yosemite valley area and we were heading up to Tuolomne (which was way too much elevation gain without some acclimatization, but that is a different story). An older fellow who noticed our gear chatted us up and asked us where our mosquito netting and hats were. Luckily I had the humility to hear him out when he warned that "You REALLY want to have wide-brim hats and mosquito netting for your head" (as well as long sleeves which we had covered already). I forget exactly what we did, but there was a shop that sold gear-probably back in Yo Valley-and we luckily had one last trip back there before we headed up to high elevations.
Lucky thing too, because going to high elevations (like Vogelsang Pass
where we were headed, in the Sierras you find there are about 10-times as many mosquitos higher up than there are lower down!