Answer:
A trees food and air source would be deprived because of this. Trees need leaves to perform photosynthesis, so besides their roots soaking up water and nutrients, they wouldn't have any other form of food until those leaves grow back. If they don't and the locusts continue to eat up the tree, it will eventually starve and die.
Explanation:
Imagine the trees trunk and roots as your body and the leaves as your mouth/food source. God Forbid you catch a cold or some sickness. You probably won't have the appetite to eat. Despite that, you'll still have to. But, if you get so sick to the point that eating just makes you throw it up before your body can take in the nutrients and beneficial stuff, you will eventually get to the point where eating is nearly impossible. This will lead up to the sickness taking over your body, as there's no energy going in to help it fight it off, and you would die.
(Gah, sorry for the dark theme... didn't think it would turn like that lol)
Anyways, hope this helped!
Source(s) used: N/A