Wood-boring or wood borer insects describes a whole group of insects known for their tendency to eat their way through the woody parts of trees and shrubs. At best, these insects cause extensive cosmetic damage to your trees; at worst, they can cause tree death. Citrus trees serve as hosts to a wide range of these borer insects, so controlling borer insects is one of the keys to preserving the long-term health of your citrus trees.
Identify the species of wood boring insect attacking your citrus tree. The presence of borer insects is typically confirmed by entry and exit holes in tree bark and other woody parts of the citrus tree. Many borer insects are named after their most distinguishing physical characteristics, such as the red-headed ash borer and metallic wood-boring beetle. Some borers such as the locust borer produce a sawdust-like material called frass where they bore; others do not. Perhaps the easiest way to identify the species of borer that is attacking your citrus tree is to look for the adult form of the insect flying in or near the tree, since borers are almost always the larval form of other insects such as beetles and moths.
Control the borers naturally. Natural control methods begin with keeping your citrus tree in optimal health, since borers always attack trees that are already in a declining state of health more than they attack healthy trees. For small borer populations, you can simply remove the borers by hand when they emerge from feeding beneath the citrus tree wood. If the borers only appear to be taking up residence in parts of the citrus tree, you can prune off those parts and discard or burn them to prevent infestation of the entire tree.
Apply a borer insecticide if natural control measures do not full remove the borers. There are many chemicals used for borer control, but spinosad insecticides are generally recommended for use on citrus trees. Control of borers with insecticides can be difficult since the borers are often protected from contacting any insecticides while they are feeding underneath tree bark. This difficulty underscores the importance of following the manufacturer's printed application instructions in order to achieve total borer control.