Read
what's new in our current regional forest health updates.
Watch
how to identify and control invasive forest plants.
Learn
about gypsy moth and other spring leaf-eating caterpillars.
Contact information
DNR forest health staff

Bark beetle

Southern pine engraver and other bark beetles attack stressed trees. Tree stress can be caused by drought, flooding, loss of leaves due to insect feeding and other conditions.

Distribution

Southern pine engraver is one bark beetle that has caused damage in southern Wisconsin red pine plantations during dry times.

Biology

How southern pine engraver attacks and kills a tree

Adult southern pine engraver beetle
Adult southern pine engraver beetle.

The adult southern pine engraver, Ips grandicollis, overwinters in the leaves and needles on the forest floor (in the duff layer). In the spring, they come out seeking fresh downed trees, logs, or stressed trees to breed in.

The males start what is called a reproductive attack. They create a nuptial chamber to mate with multiple females inside the tree. The females lay their eggs inside the tree too.

The eggs hatch and small cream colored larvae chew tunnels in the wood just under the bark. This cuts off the flow of water and nutrients through the tree (girdling) and kills the tree. The beetles may go through two to three generations per season.

Egg laying and larval feeding galleries of the southern pine engraver.
Egg laying and larval feeding galleries of the southern pine engraver.

Windstorms or summer tree harvesting operations can cause a lot of breeding places and rapid population build up of the bark beetles. Once trees are dead, with loose bark, they are no longer good material to breed in and pose no risk in beetle population buildup.

Signs and Symptoms

Bark beetles - what to look for

The southern pine engraver, Ips grandicollis, is often found along with attacks caused by the more common pine engraver, Ips pini. The southern pine engraver starts attacks in the upper most portions of red pine crowns, killing individual branches and eventually the entire tree, in the absence of, or prior to, attack by Ips pini. Close inspection of dead branches show nuptial (mating) chambers and tunneling made by bark beetles. As branches in the upper crown die, the bark beetles move into the main trunk and eventually girdle and kill the entire tree. As the population builds, nearby trees are attacked and eventually a "pocket" of dead trees is created.

Other problems that often show up with bark beetles

The fungal shoot blight disease, Diplodia pinea, attacks pines and may be an additional reason why trees are stressed, allowing the southern pine beetle to successfully attack the crown branches of pines. Armillaria root rot and turpentine beetle attacks may also be present in affected stands.

Individual branches in the upper crown of a red pine are dying due to attack by the southern pine engraver.
Individual branches in the upper crown of a red pine are dying due to attack by the southern pine engraver.
A dead branch showing the nuptial chamber and mining caused by the southern pine engraver.
A dead branch showing the nuptial chamber and mining caused by the southern pine engraver.
Shoot blight caused by Diplodia pinea.
Shoot blight caused by Diplodia pinea.
Armillaria mycelial fan under bark of recent dead red pine tree.
Armillaria mycelial fan under bark of recent dead red pine tree.

Management

To prevent bark beetles in the first place

  • Maintain stand vigor. Avoid over-stocking and avoid over-mature stands. If low vigor is due to drought or defoliation, consider pre-salvage harvest.
  • Storm-damaged material should be harvested or monitored for build up of the bark beetle population.
  • Thinning is best done between September and March.

Managing bark beetles if summer thinning is necessary

  • Use all tops of the tree down to 2-inch diameter branches.
  • Leave branches attached to the stem wood to speed drying.
  • Remove cut products from the stand within three weeks of cutting.
  • Monitor the beetle population in the slash: if dangerous levels occur, mangle the bark by driving over it with a tracked vehicle or chip the slash.

To manage bark beetle attacks

If a group of trees are attacked, a well-timed harvest of attacked and nearby low-vigor trees during the growing season may eliminate or help to reduce local populations.

Last revised: Monday March 05 2012