As a general rule, the most damaging tree insects are the ones that bore into the sapwood. Borers cause significant interruption in the conductive vessels of the tree, the plant world’s equivalent to ripping veins and arteries out of a person’s arm.
On the other hand, that’s not a good reason to ignore leaf feeders. These chewers can do quite a bit of damage, especially if they go unnoticed for a year or two before the customer brings them to your attention.
Regularly inspect trees to identify problems before they turn into tree-damaging outbreaks. The prsence of sawdust and holes in tree bark caused by borers are relatively easy to spot. While leaf feeders are normally considered less damaging, they can be nearly invisible, especially on taller trees.
If you’re tasked with caring for clients’ trees and are having trouble with leaf feeders, such as aphids, spider mites, leaf hoppers, sawflies and other unwanted pests, check out the article entitled Leaf-Feeding Insects of Trees by green industry experts John C. Fech and Frederick P. Baxendale.