Thats a lot of questions, mealworms eat types of bran, wax worms dont eat at the point you buy them. neither do blue bottle flies, unless you are keeping them for a week or more then u need to get some fly food.
I would feed my mantids dubia roaches, flies, crickets and whatever I could catch outside lol. I would make a concoction of a green vegetable, apple slices, bee pollen and I think potato flakes and I would blend them up and freeze little chucks and feed my feeders that. I would feed my flies honey water before I fed my mantises.