Bug of the Month: Bark Beetles

It’s going to be another hot summer, and a dry one, too.  Our trees are really feeling the increased heat, and when trees are stressed, they are more likely to be invaded by pests and diseases.  An example is bark beetles and blue stain fungus attacking pine trees stressed by both urban conditions generally, and increased heat specifically.  These sneaky little beetles can quickly overcome and kill such stressed trees.

Bark beetles cue in on the chemical signature, the “smell”, of a tree that is suffering from drought.  These trees are not able to make enough of their own defensive chemistry, making them a good target for attack.  Once the first beetles get into a tree, they secrete pheromones that attract others, mating occurs, and the new host is under attack.  

The larva tunnel through and feed on the phloem, or living inner bark, of the tree.  The phloem is critical vascular tissue that moves sugars made by photosynthesis (as well as important plant hormones) to wherever they are needed.  The larvae also consume the vital cambium and even some shallow sapwood.  The roots begin to die from lack of food, the leaves begin to dry from lack of water, and the tree can’t make new tissues to replace what has been lost.  Very often, fungi spread into the rest of the sapwood, plugging up the whole vascular flow. There are many species of bark beetle, each with a particular set of host species and characteristic tunneling damage, but in almost all cases the result is the same – once they are in the tree, it’s their tree.  

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