Anecdotal, but I think there's some kind of immunity component. My parents grew up in a mosquito infested country. When we visited said country, us kids were bitten up while my parents were fine. If it was genetics, you think it would've been passed on to us. The locals commonly joked that mosquitos like "new blood." You could see tourists with itchy red bite reactions while the locals were fine.
I get a welt for about the first half-dozen bites in the spring, then I don't react for the rest of the year. I think there's a histamine response that gives up after a while.
I'm confused by your title and responses. Was there some document somewhere that we were to read to familiarize ourselves with what you already know before we post?