Fascinating concept. I like the idea of a race that is considered contemptible for reasons other than their actual behavior (but presumably these guys could parasatize intelligent races if they really wanted to?) Imagine you are a human merchant visiting a hive, and how uneasy you'd feel knowing that you were surrounded by a race of creatures specifically adapted to parasatize you. At the very least these guys would make for a cool "monstrous" race to interact with.
Technically they would be able to parasitize sentient creatures but because of the way they are built it is not a reliable food source on a mass scale. I imagine they were kind of forced into this ideology by their frail body structure and super long proboscis that kind of gets in the way (they don't really have the core strength to do any efficient attacks with it). Their only redeeming quality is their excellent flight and dexterity. It's has been an uphill battle for them for their entire existence, and the only way for their survival is absolute unity and making no enemies. In warfare they rely on traps and siege weapons and if that fails they rely on sheer numbers, coupled with the fact they make their homes on cliff faces, they are usually not attacked by other races. Please tell me if you have any changes or adjustments. (:
Maybe there would be a more developed/beefier form of mosquito people that are more well equipped to parasitize other things that can fight back. They would be like 5-6 feet tall and have a much shorter proboscis, about 1-2 feet long depending on the size of the mosquito. They would probably be a big part of the bastardization of the smaller mosquito people even though they are much rarer than normal mosquitoes. irl mosquito larvae are water born and eat algae, also mosquito larvae are the same size if not bigger than adult mosquitoes. So maybe they would have a lot of their primal agricultural advancements built around breeding pools. I'd also just like to say that it's really cool to be able to do this. If this game turns out, I think it's going to fill a niche a lot of people are looking for. It's just cool to be able to suggest things one on one to the developers of this game that has a decent chance of getting really popular.