PINE BARK BEETLES

DYING WHITE PINE

FELLED WHITE PINE WITH DEAD BRANCHES

BEETLE EMERGENT HOLES IN BARK

LARVAL GALLERIES UNDER BARK

STUMP GROWTH RINGS

Sunday,  8:00 AM.  80 degrees F, unusually warm for early morning.  The wind is N, light with strong gusts.  The sky is mostly clear but very hazy at present,  but it had been filled with beautiful fish-tail clouds earlier when Buddy and I went to the beach.  The humidity is 70% and the barometer is down, at 29.89".  It looks and feels like we will get  a thunderstorm sometime soon.

   A white pine has been declining for several years on S Ninth St., and the property owner recently had it cut down.  It was for all intents and purposes dead.  I counted the growth rings of the stump and they indicate the tree was about forty-five years old, probably the same age as the house on the property.  I had been observing the tree, and was eager to examine it once it was on the ground.

  I found that an infestation of bark beetles had finished the tree off,  but  they seldom attack healthy trees, and my assumption is that this tree was badly damaged by the drought of recent summers and  that it had outgrown its environment as well.  Poor soils, drought and other environmental factors weakened the tree and made it a target for the tiny beetles, the adult males of which excavate chambers in which the males and females mate, and in which eggs are laid.  When the eggs hatch the larvae feed under the bark, creating tunnels that girdle branches and eventually the entire tree.  The infestation begins at the top of the tree and proceeds downward over several growing seasons.  

   In the above photo of the galleries the larvae have pupated into adults and left the tree to attack another weakened pine tree.  The photo of the branch with the bark still intact shows the very small (smaller than a pin head) exit holes produced by the emerging young adult beetles.  Red pine plantations are sometimes seriously damaged by bark beetles, but the insects are  probably  only a secondary threat in ornamental pines, and once the bark falls off the dead trees and their branches the beetles are gone and the tree is no longer  a source of infection.  There are two species of pine bark beetles in Wisconsin, and they often are both present in infected trees.  For further information on pine beetle life cycles, their biology and control, visit the WDNR web site.