I'm not very tasty to mosquitos to begin with. I used to have the usual reaction to mosquito bites (slight bump, itching). I grew up near a wetland in Minnesota, so I was no stranger to mosquitos, but after getting absolutely mobbed by mosquitos when I took my wilderness survival merit badge course at scout camp, I stopped reacting to mosquito bites.
Though, the downside is that I do have less incentive to protect myself if I'm in malaria/dengue/etc. areas.