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Borers are a major problem for ornamental trees. Once infested, there is little that can be done to control the insects in the wood. Thus, keeping trees as healthy as possible is the best way to prevent borer damage. Trees that are old, drought stressed,or otherwise unthrifty are most likely to be successfully attacked by borers. Most of the borers we encounter are beetles but some are caterpillars of clearwinged or other moths and others are primitive wasps.

  Poplar and willow borer adult

These weevils emerge around august and lay eggs in stems at least 1" in diameter. It does not attack quaking aspen but a similar borer does.

  Poplar and willow borer larva

The larvae mine the sapwood. Swollen areas on limbs show where the larvae feed and frass can be seen being forced out of holes in the bark as the larva feeds.

  Poplar borer adult

Poplar borers are a serious pest of poplar. Adults emerge and are around from June through august.

  Poplar borer larva and damage

Most of the life cycle is spent as the larva in the tree. They feed for a period of from 2-4 years and bore in the heartwood and sapwood. Infested trees can be weakened and break. A related species, causes galls on smaller limbs of poplars and aspens.

  Locust borer adult

Locust borers attack black locust in Idaho. The strikingly colored adults emerge in the fall and can be seen feeding on goldenrod.

  Locust borer larva and damage

A year is required for the larva to develop in the locust tree. Severe damage can occur from the larval feeding.

  Red headed ash borer adult

The red headed ash borer commonly infests ash trees in southern Idaho. The larvae look like those of the locust borer only smaller. It will attack elm, linden, redbud, and oak as well as ash trees.

  Pine sawyer adult

Pine sawyers attack pine trees and are usually found around homes as a result of being brought in with firewood. They seldom attack pine trees in residential plantings.

  California laurel borer adult

This striking insect, the California laurel borer, mines in dead ash, laurel, and willow. It is not a threat to healthy trees.

  Bronze birch borer adult

Paper birches are frequently attacked by the bronze birch borer. Adults emerge in June and lay eggs in July. Note they have shorter antennae and a different shape than the borers discussed above.

  Bronze birch borer larva in limb

Most of the two year life cyle is spent in the larval stage tunneling in the wood of birch trees. The larvae have a flattened area just behind the head which is characteristic of the flat headed borers. Damage symptoms are usually expressed by some upper limbs of the tree turning yellow and then dying.

  Pacific flatheaded borer adult

There are about 100 species of flatheaded borers represented here by the pacific flatheaded borer. This insect attacks many fruit and ornamental trees and shrubs.

  Pacific flatheaded borer larva

Borers of this type have the typical larval shaped pictured here.

  Bark beetle adults

Although not true borers, bark beetles attack several evergreen trees. The adults usually emerge in mid-summer and lay eggs.

  Bark beetle larvae and gallery

The larvae are legless grubs that feed just under the bark. Enough larvae can girdle a tree. Affected trees have the tops turn red then yellow and brown. Different species can be determined by the shape of the gallery in some cases.

  Shot-hole borer adult

Shot hole borers attack weakened or dead trees and shrubs. They feed deeper in the wood than bark beetles. The larvae are legless grubs.

  Shot hole borer exit holes

Many emergence holes are often present where several adults have emerged. Thus, the "shot hole" appearance on affected trees.

  Carpenter worm larva and damage

Carpenter worms are large caterpillars that grow to almost three inches long. They mine the heart wood of trees. They attack poplars and cottonwoods in Idaho and can attack many other trees as well.

   Carpenter worm adult

The adult carpenter worm is a large grey moth.

  Clear-winged moth adult

Many clear-winged moths bore in trees as larvae. The adults resemble wasps in many cases.

  Clear-winged moth larva and damage

The caterpillars of clear-winged moths can extensively mine limbs of susceptible trees. Poplars, willow, and cottonwood trees are hosts of several species.

  Peach twig borer larva in twig

The peach twig borer is a pest because it mines in the ends of the new twigs of fruit trees and ornamental fruit trees. The new twigs start to grow and then wilt because these larvae are tunneling down the center of them. Adults are small grey moths.