Daphnia are NOT mosquito larvae, they are their own species, commonly called Water Fleas. Mosquito larvae are mosquito larvae. They have absolutely nothing to do with each other.
Freeze dried foods can cause constipation, true, but if you soak them before feeding it's much less likely.
Daphnia are the best thing to give for a constipated or bloated betta as the shells serve as roughage and help to get things moving in the digestive tract. I don't feed them regularly, but i do feed frozen bloodworms, mysis shrimp, and brine shrimp, as well as occasional live whiteworms and live daphnia.