I remember there being a study done of what would happen if mosquitoes were completely wiped out. The consensus seemed to be that there are a lot of midges and other harmless, non-biting flies whose maggots live in the water that would quickly move in to fill the vacant niche and keep the pond food chains going.
Mosquito abatement is big county business here. They spray, they check peoples pools that don’t maintain them and put fish in them to eat the mosquitos. There will be quite a few people out of a job.