22 Common Insects Pests That Are Harmful to Trees

Aphids

Leaf-feeding aphids are usually not damaging, but large populations can cause leaf changes and stunting of shoots. Aphids also produce large quantities of a sticky exudate known as honeydew, which often turns black with the growth of a sooty mold fungus. Some aphid species inject a toxin into plants, which further distorts growth.

Asian Longhorn Beetle

This group of insects includes the exotic Asian longhorned beetle (ALB). The ALB was first found in Brooklyn, New York in 1996 but has now been reported in 14 states and is threatening more. The adult insects lay eggs in an opening in a tree's bark. The larvae then bore large galleries deep into the wood. These "feeding" galleries disrupt the vascular functioning of the tree and eventually weaken the tree to the point that the tree literally falls apart and dies.

Balsam Wooly Adelgid

Adelgids are small, soft-bodied aphids that feed exclusively on coniferous plants using piercing-sucking mouthparts. They are an invasive insect and thought to be of Asian origin. The Hemlock Wooly Adelgid and balsam wooly adelgid attack hemlock and firs respectively by feeding on the sap.

Black Turpentine Beetle

The black turpentine beetle is found from New Hampshire south to Florida and from West Virginia to east Texas. Attacks have been observed on all pines native to the South. This beetle is most serious in pine forests that are stressed in some fashion, such as those that have been worked for naval stores (pitch, turpentine, and rosin) or worked for lumber production. The beetle can also affect damaged pines in urban areas and has been known to attack healthy trees. 

Douglas-Fir Bark Beetle

The Douglas-fir beetle (Dendroctonus pseudotsugae) is an important and harmful pest throughout the range of its principal host, the Douglas-fir (Pseudotsuga menziesii). Western larch (Larix occidentalis Nutt.) is also occasionally attacked. Damage caused by this beetle and economic loss if Douglas fir lumber has been extensive in the tree's natural range.

Douglas-Fir Tussock Moth

The Douglas-fir tussock moth (Orgyia pseudotsugata) is an important defoliator of true firs and Douglas-fir in Western North America. Severe tussock moth outbreaks have occurred in British Columbia, Idaho, Washington, Oregon, Nevada, California, Arizona, and New Mexico, but the moth causes notable damage in a much geographic area.

Eastern Pineshoot Borer

The eastern pineshoot borer, Eucosma gloriola, also known as the white pine tip moth, American pine shoot moth, and white pine shoot moth, injures young conifers in northeastern North America. Because it infests the new shoots of sapling conifers, this insect is particularly destructive on planted trees destined for the Christmas tree market.

Emerald Ash Borer

The emerald ash borer (Agrilus planipennis) was introduced into North America sometime in the 1990s. It was first reported killing ash (genus Fraxinus) trees in the Detroit and Windsor areas in 2002. Since then, infestations have been found throughout Midwest, and east to Maryland and Pennsylvania.

Fall Webworm

The fall webworm (Hyphantria cunea) is known to feed late in the season on nearly 100 different species of trees in North America. These caterpillars construct massive silk webs and prefer persimmon, sourwood, pecan, fruit trees, and willows. The webs are unsightly in the landscape and generally more numerous when the weather has been warm and wet for extended periods.

Forest Tent Caterpillar

The forest tent caterpillar (Malacosoma disstria) is an insect found throughout the United States and Canada where hardwoods grow. The caterpillar will consume foliage of most hardwood species but prefers sugar maple, aspen, and oak. Region-wide outbreaks occur at intervals varying from 6 to 16 years in northern areas, while annual infestations occur in the southern range. The eastern tent caterpillar (Malacosoma americanum) is more a nuisance than a threat and is not considered a serious pest.

Gypsy Moth

The gypsy moth, Lymantria dispar, is one of the most notorious pests of hardwood trees in the Eastern United States. Since 1980, the gypsy moth has defoliated close to a million or more forested acres each year. In 1981, a record 12.9 million acres were defoliated. This is an area larger than Rhode Island, Massachusetts, and Connecticut combined.

Hemlock Wooly Adelgid

The eastern and Carolina hemlock is now under attack and in the early stages of being decimated by the hemlock wooly adelgid (HWA), Adelges tsugae. Adelgids are small, soft-bodied aphids that feed exclusively on coniferous plants using piercing-sucking mouthparts. They are an invasive insect and thought to be of Asian origin. The cottony-covered insect hides in its own fluffy secretions and can only live on hemlock.

The hemlock wooly adelgid was first found on ornamental eastern hemlock in 1954 in Richmond, Virginia and became a pest of concern in the late 1980s as it spread into natural stands. It now threatens the entire hemlock population of the eastern United States.

Ips Beetles

Ips beetles (Ips grandicollis, I. calligraphus and I. avulsus) usually attack weakened, dying, or recently felled southern yellow pine trees and fresh logging debris. Large numbers of Ips may build up when natural events such as lightning storms, ice storms, tornadoes, wildfires, and droughts create large amounts of pine suitable for the breeding of these beetles.

Ips populations may also build up following forestry activities, such as prescribed burns that get too hot and kill or weaken pines; or clear-cutting or thinning operations that compact soils, wound trees, and leave large numbers of branches, cull logs, and stumps for breeding sites.

Mountain Pine Beetle

Trees favored by the mountain pine beetle (Dendroctonus ponderosae) are lodgepole, ponderosa, sugar and western white pines. Outbreaks frequently develop in lodgepole pine stands that contain well-distributed, large-diameter trees or in dense stands of pole-sized ponderosa pine. Extensive outbreaks can kill millions of trees.

Nantucket Pine Tip Moth

The Nantucket pine tip moth, Rhyacionia frustrana, is a major forest insect pest in the United States. Its range extends from Massachusetts to Florida and west to Texas. It was found in San Diego County, California, in 1971 and traced to infested pine seedlings shipped from Georgia in 1967. The moth has since spread north and east in California and is now found in San Diego, Orange, and Kern Counties.

Pales Weevil

The pales weevil, Hylobius pales, is the most serious insect pest of pine seedlings in the Eastern United States. Great numbers of adult weevils are attracted to freshly cutover pine lands where they breed in stumps and old root systems. Seedlings planted in freshly cut areas are injured or killed by adult weevils that feed on the stem bark.

Hard and Soft Scale Insects

Scale insects include a large number of insects in the subfamily Sternorrhyncha. They commonly occur on woody ornamentals, where they infest twigs, branches, leaves, fruits, and damage them by feeding on the phloem with their piercing/sucking mouthparts. Damage symptoms include chlorosis or yellowing, premature leaf drop, restricted growth, branch dieback, and even plant death.

Shade Tree Borers

Shade tree borers include a number of insects species that develop underneath the bark of woody plants. Most of these insects can attack only dying trees, felled logs, or trees under stress. Stress to woody plants may be the result of mechanical injury, recent transplanting, over-watering, or drought. These borers often are incorrectly blamed for damage caused by a pre-existing condition or injury.

Southern Pine Beetle

The southern pine beetle (Dendroctonus frontalis) is one of the pine's most destructive insect enemies in the Southern United States, Mexico, and Central America. The insect will attack all southern yellow pines but prefers loblolly, shortleaf, Virginia, pond, and pitch pines. Ips engraver beetles and the black turpentine beetle are frequently associated with southern pine beetle outbreaks.

Spruce Budworm

The spruce budworm (Choristoneura fumiferana) is one of the most destructive native insects in the northern spruce and fir forests of the Eastern United States and Canada. Periodic outbreaks of the spruce bud-worm are a part of the natural cycle of events associated with the maturing of balsam fir.

Western Pine Beetle

The western pine beetle, Dendroctonus brevicomis, can aggressively attack and kill ponderosa and Coulter pine trees of all ages. Extensive tree-killing can deplete timber supplies, adversely affect levels and distributions of tree stocking, disrupt management planning and operations, and increase forest fire danger by adding to available fuels.

White Pine Weevil

In the eastern United States, the white pine weevil, Pissodes strobi, may attack at least 20 different tree species, including ornamentals. However, eastern white pine is the most suitable host for brood development. Two other North American pine weevil species—the Sitka spruce weevil and the Engelmann spruce weevil—also should be classified as Pissodes strobi.