Insects can destroy a tree within a short time frame, so it's best to stay vigilant for pests. Knowing the signs of a possible infestation can ensure you get professional help from an arborist before it is too late.
Trunk
Symptoms of pests on the trunk of a tree include any type of bark damage. You may notice small to medium-sized holes. These are often caused by boring insects making their way into the trunk to lay eggs. The larva may also make holes when they emerge. In some cases, the bark may also loosen and fall off. If this occurs, you will likely see swirling marks, called galleries, eaten into the wood by the insects. Woodpecker activity also tends to be more severe on trees with insects residing inside the trunk wood.
Leaves
Leaves can show damage in a variety of ways. They may develop holes or ragged edges from the feeding insects. Sometimes weird growths and disfigurations occur due to insect activity. There is also an increased risk of disease to your trees with some insects, as the pests are a vector for infection. Yellowing, spotting, and growth of molds and mildews are the most common side effect. The insects may leave behind a sticky residue on the leaves as they feed, which may further increase the risk of mold and mildew.
Crown
Dieback of the entire crown, including leaves and twigs, is a sign of major infestation. Growth may be reduced from year to year, as the pests put stress on the tree that prevents the proper new flush of spring growth. Part of the crown may die back completely, or it may die back all over depending on the type of insect and whether or not a disease has been introduced by the pest. In severe cases, leaf drop may occur or the tree may begin shedding dead twigs.
Roots
Roots are less prone to insects, but the damage done to other parts of the tree by the pests can leave the roots susceptible to soil pathogens. You may notice fungal growth, including fruiting bodies like mushrooms, around the base of the tree, or from the soil growing over the roots. The roots may also seem to rise to the surface or even lift from the soil as they try to seek out new sources of nutrition due to losses from insect infestation.
Contact an arborist for more help. They can verify the type and severity of a pest infestation, as well as help you develop a plan to eradicate the problem and save the tree.