Well as a general principle, you don't want to take a species out of the foodchain yeah, but I had heard somewhere or someplace that we can afford to wipe out mosquitos, at least in certain parts of the world, since they're parasitic and their primary role is to be food for fish/frogs/etc that could be filled by a non bloodsucking insect. As for blackflies, I'm referring specifically to the specie(s) that live in the north arctic in the summer and make it almost inhabitable, they proliferate quite readily since the extreme winters deter their main predators so I wonder what would happen if they all got wiped. Maybe replaced by ants.