I think it seems like a type of fly and how do I treat it
It seems to strip the hedge and leave white fungus.
Pretty hard to say what it is with no description or picture. I will say that when people see a "white fungus," 9 times our of 10, they're seeing mealy bugs, scale, or aphids. And a heavy infestation will cause all the leaves on many plants to drop. So I'm going to give you an article on these pests, so you can see if that might be what you have, and what to do about them: