Proper treatment begins with diagnosis. A professional arborist can help you determine what the bug, or insect, is. Once the insect is identified, it can be determined if it is harmful to the tree, beneficial to the tree, or has no effect whatsoever.
Many bugs are benign while others are beneficial as they control populations of harmful insects through predation or parasitism. You want to avoid any treatments that take out the good bugs with the bad bugs. Most professional arborists operate on the philosophy of treating only when the environmental/economic risk from the insect has reached a certain threshold. If you are unsure, call an arborist before taking any action.
Tree Pesticide Injections
Injections and implants are methods of applying pesticides and nutrients to allow the material direct access into the trunk of the tree. They have been developed to control pests or diseases that have infested or infected the sapwood of a tree, to control tree pests without having to spray pesticides into the environment, or for immediate, short term treatment of nutrient deficiencies.
Injections and implants do require holes to be drilled into the trunk, causing some wounding to the tree. This wounding should be taken into account and weighed against the possible benefits of the injection or implant. Alternatives, such as soil injections or drenches, can also be used. These allow the pesticide to be absorbed by the plant roots and taken into the trunk without having to cause wounds in the trunk.