mozzie larvae are a great live food for fish and can be found in containers of fresh or salt water that might be left in the garden for a few weeks. They don't normally transmit anything if they are in your backyard.
I stay away from all live foods after my sorority betta tank Contracted columnaris. I lost the entire tank. I believe it was bloodworms that did it. I feed quality commercial foods. Insect Bites are a really good choice. Full of protein. I also feed Omega One and New Life Spectrum. Cories get additional sinking shrimp pellets and an occasional veggie/shrimp wafer. Once in a blue moon I’ll feed frozen blood worms as a treat.