Their natural predator in China is a parasitic wasp which, if introduced, would likely decimate native insect populations. The government is considering it as a last resort, but as you can imagine it's not a pretty alternative.
This is true. Actually discovered my first oak gall this season and reading up on the specific wasp that can make an oak make an apple and then the specific wasp that puts parasites into the parasite and so forth. Anyways, fascinating.
For protecting specific trees, you can get sticky wraps that surround the trunk of the tree: https://www.farmanddairy.com/top-stories/how-to-install-stic... . A friend of mine has employed one to great effect.