This is a hard topic to find info on so I'm leaving this for anyone else who comes across it and needs help. I had the same problem. No flying insects would spawn. Pond fish were unaffected and spawned normally. Alchemical components from flying insects were still available for purchase. Googling the issue found little but some people affected by this found out it was caused by the current version of the Unofficial Skyrim Patch. I tested the main patch with and without all three of the unofficial add-on patches and did not have any flying insect spawns either time. As soon as I deactivated the patch, all of the flying insects were back. Sometimes its not quickly apparent that they are back - try waiting and running to a new cell. You'll see them shortly. While I was trying to narrow down the troublemaker I found I had a second mod which messes with flying insect spawns: skyBirds - Airborne Perching Birds. Its a cool immersive mod that adds tons of little birds flying around. They'll even land in trees and spawn little nests. Trouble is, the description says the birds will eat insects when hungry. I had 70+ hours on my current save and never saw a single flying insect. If anyone finds a work around to have it and insects without conflict, please give me a heads up. Other people have reported that a mod called Brawl Bugs Patch will also stop insects from spawning. I haven't tried that mod yet. I hope this info helps!
