Insects That Bore Holes in Trees

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Pests, like caterpillars or aphids, are straightforward to identify and treat because these insects, and the damage they cause, are visible on your plants. Wood-boring insects, typically beetles, moths or wasps, are more difficult to detect. The immature, or larval, stage of these creatures tunneling through a tree causes the damage, particularly to newly planted or injured trees. Identifying the wood boring pests can help you choose the best treatment for your trees.

Beetles

Jewel Beetles

The shiny, metallic and sometimes brilliantly colored adult jewel beetles (Buprestidae family) range in size from less than 1/8 inch to approximately 3 inches. Their larvae, called flat headed borers because of the enlarged area behind the head, are creamy-white and grow to more than 3 inches long.

The larvae feed inside the tree throughout summer and winter, emerging through oval or D-shaped holes as adults the following spring or early summer. Commons species of flat headed borer include:

  • Flatheaded appletree borer (Chrysobothris femorata) feeds on young
    or drought-stressed fruit, shade and forest trees. The adult insect is 1/2 to 3/4 inch
    long  with metallic green and bronze coloring. Females lay eggs in late
    spring on sun-exposed bark.
  • Emerald ash borer (Agrilus planipennis) is a bright metallic green beetle, with an
    elongated body up to 1/2 inch long  and feeds, as its name suggests, on ash
    trees (Fraxinus spp.). Adult females
    lay eggs soon after emerging in mid- to late May. The larvae hatch and tunnel under
    the bark, often leaving visible trails. 

Tip

  • Ash trees grow in U.S. Department of Agriculture plant hardiness zones 3 through 9 but tens of millions of these shade trees have been destroyed throughout the Eastern and Midwestern U.S. by the invasive, non-native emerald ash borer, which was first detected in Detroit in 2002. If your ash tree is showing signs of distress, this pest could be to blame.

Longhorn Beetles

With antennae at least half as long or longer than the body, adult longhorn beetles (Cerambycidae Family) are easy to identify. These creatures have elongated bodies ranging in size from 1/4 to 3 inches and are common throughout the U.S.

The larvae of the longhorn beetle, known as a round headed borer, have wrinkled, yellowish bodies with brown heads. Adult females typically lay eggs on dying or recently cut trees while a few species seek out healthy trees. The larvae burrow into the wood and feed there for up to three years. They emerge as adults, usually leaving a pile of sawdust at the exit hole. Adult beetles may emerge in spring but can be active throughout the growing season.

Many of the longhorn beetle species are named for their preferred host tree:

  • Locust borer (Megacyllene robiniae) adults are black with yellow bands and are active around the host tree throughout the U.S. in late summer. 
  • Pine sawyer (Monochamus spp.) species are approximately 1 inch long   with a color range from mottled gray to black. They feed on conifers across the U.S. and are active throughout the spring and summer.
  • Red-headed ash borer (Neoclytus acuminatus) beetles usually fly around the host tree in spring and early summer.  These brown and yellow striped, 1/2-inch-long adults are common throughout North America. 

Bark Beetles

Adult bark beetles, members of the Scolytidae subfamily, are tiny, cylindrical beetles with short antennae that terminate in a round club. They bore into the bark of conifer trees and create egg-laying channels. Larvae extend these channels with their feeding, causing trunk girdling and introducing destructive diseases and fungi.

Rust-colored dust patches on the bark near entrance holes, along with discolored leaves at the top of the tree, indicate a bark beetle problem. These pests live all over the U.S. and are particularly problematic in Western states.

Moths

The caterpillars of clearwing moths (Family Sesiidae) and carpenter moths (Family Cossidae) bore into trees. Clearwing moths are often brightly colored and resemble wasps. The peach tree borer (_Synanthedon exitiosa)_, a metallic blue wasplike moth with clear hind wings and an orange abdominal band, is found throughout the U.S. but, as its name suggests, is a serious pest of peach (Prunus persica) and other stone fruit trees (Prunus spp).

Tip

  • Peaches grow in USDA zones 5b through 8b and stone fruit trees grow in USDA zones 3 through 10, depending on species.

Carpenter moths are heavy bodied moths with mottled coloring. Their caterpillars, called carpenterworms, can grow up to 3 inches long and are a pest of shade and fruit trees. Oozing sap with insect droppings and sawdust near bore holes indicate moth borer activity.

Wasps

Horntails (Family Siricidae) are long-bodied wasps with a spearlike, but harmless, appendage at the base of their abdomens. They lack the narrow "waist" typical of other wasp species. Female horntail wasps use their strong ovipositor to pierce through wood and lay eggs within unhealthy or dying deciduous and conifer trees throughout the U.S. The larvae feed inside the tree for up to three years and emerge as adults late in the summer or early fall.

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