Insects can be a serious threat to a tree's health. By examining the symptoms of damage, a reasonable diagnosis can be made and the proper treatment selected, according to the International Society of Arboriculture.
Insects can cause considerable damage. By defoliating trees or sucking out their sap, insects retard their growth, weakening and sometimes killing trees and shrubs. By boring into the trunk and branches, they interfere with sap flow and weaken the tree structure to a point where it may be easily blown over by the wind. Insects may also carry disease by providing an entry way for fungi, bacteria and viruses, according to the ISA.
Insects may be divided into three categories according to their method of feeding: chewing, sucking and boring:
- CHEWING INSECTS. These insects eat plant tissue such as leaves, flowers, buds and twigs. Indications of damage by these insects are often seen by uneven or broken margins on the leaves or other affected plant parts. A few examples from this large insect category are: beetles and their larvae (grubs), webworms, bagworms, larvae of moths and sawflies (caterpillars).
- SUCKING INSECTS. These insects insert a special beak into the tissues of leaves, twigs, branches, flowers or fruit and then suck out the plant's juices. Some typical examples of sucking insects are aphids, mealy bugs, thrips and leaf hoppers. Damage caused by these pests is often indicated by: discoloration, drooping, wilting and a general lack of vigor in the affected plant.
- BORING INSECTS. These insects are characterized by the tunnels they make in the wood of a tree as they eat through it. Because each kind has its own style and tunnel pattern, borers maybe identified by their work even after they have left the scene. One example of borers is the termite. Eventually, most borers eat their way into a tree, making a round opening out of which they eject a characteristic substance called a frass, composed of semi-digested wood.
The treatment method used for a particular insect problem will depend on the species involved, the extent of the problem and a variety of other factors specific to the situation and local regulations.