The bug creates a fungus that it feeds on. It does not eat the tree, but it certainly chews it. You can tell that from the toothpicks hanging on it. I been spraying pesticide every 7 to 14 days, depending on how much it rains. I have not seen one toothpick since i started spraying, and the trees we decided were worth saving are growing well. So, my experience with it tells me a residual pesticide will do some good. The trees that were infested as bad as yours, i pulled up and burnt a mile away from our orchard. One of our crape myrtles here at the house has some damage too. The section with all the toothpicks sticking out of it is almost dead but the rest of the tree is growing well. When i first found them in our orchard, i sprayed the trees with pruner sealer, thinking it might smother them. The next day there were just as many tothpicks as the day before. They had bored their holes back in the trees.