University of Illinois Extension

University of Illinois Extension

Hort Answers

Insect Damage

Shot Hole Borer & Other Bark Beetles

4 (1 = rare 5 = annual)
4 (1 = very little damage 5 = plants killed)
There are numerous beetles that attack bark on trees and thus are categorized as bark beetles. Almost any tree is attacked by bark beetles, particularly that part that is dead or dying. Shothole borer (Scolytus rugulosus) attacks dead and stressed trees. It infests most fruit trees, serviceberry, ornamental fruit trees, mountain ash, elm, and mulberry. Corthylus spp. attack maples, dogwood, sasafras, azaleas, rhododendron and other plants.

Many bark beetles are attracted to a plant because their bark is dead but others are attracted to weakened or stressed trees and can be very destructive. The stresses can be due to a wide range of conditions such as weather related, mechanical injury, chemical injury, aging, growing site and planting. The shothole borer (Scolytus rugulosus) makes so many holes in the bark, the bark looks as if it was shot with a buck shot. Many bark beetles overwinter as larvae and emerge as adults in the spring.

Life Cycle
The over-wintering stage can be larvae, pupae or adults. Adults lay eggs in galleries that are mostly in the phloem but a few lay eggs in the xylem. The first beetles attacking a tree often give off a strong scent that attracts other beetles to invade the tree. The eggs hatch, larvae feed, then pupate. Adults eventually emerge to start the cycle all over. Depending on the bark beetle and area of the country, there is from one to six generations per growing season. Shothole borer adults tunnel into the bark to lay their eggs. The entry hole is about the size of a pinhead. The female lays its eggs along a tunnel that is horizontal to the ground. The hatching larvae tunnel outward from the tunnel made by the adult female. Other bark beetles tunnel sideways in the trunk to lay their eggs. Bark beetles pupate under the bark then emerge as adults. Ambrosia beetles are bark beetles that typically tunnel into the sapwood.

Minimize stress factors on the tree. Keep trees healthy, remove infested branches on trees (some bark beetles will attack healthy trees next to dying trees so remove dying trees promptly) and destroy infected material by chipping, burying, or burning (where legal).

Related Resources
Home, Yard & Garden Pest Guide
Illinois Commercial Landscape and Turfgrass Pest Management Handbook
U of IL - Distance Diagnosis through Digital Imaging
U of IL - Plant Clinic