The Pine Beetle
EC member and acting environment steward for the Juniper Point Cottage Owners' Association, Jennifer Darling breaks down the growing threat posed in our region by the pine beetle.
PINE BARK BEETLES
The Species
Dendroctonus ponderosae: Mountain pine bark beetle
Dendroctonus frontanalis: Southern pine bark beetle
Dendroctonus frevicomis: Western pine bark beetle
Dendroctonus valens: Red Turpentine pine bark beetle
The Problem
Outbreaks of pine bark beetles around the world are erupting due to pine trees weakened from heat, drought and climate change. Here in our area we are also experiencing these effects and the lack of colder temperatures in the winter prevents the winter die off of these insects.
The world’s forests have survived beetle attacks for thousands of years because of their defense mechanisms. When the beetles burrow into the bark, trees release a sap rich with volatile toxic chemicals to flush the insects and prevent them from sending pheromone signals, which call other beetles to the tree. Increasingly, long and intense droughts have weakened these defenses. Without sufficient water, trees can’t produce enough sap thus making it easier for the beetles to overwhelm the tree.
Biology of the Beetle
Adult females search for a weakened tree. Once found, pheromones are released which can attract hundreds to the tree. The tree’s defenses are overwhelmed and the female beetles tunnel into the inner bark of the tree to lay eggs, the newly hatched larvae eat further into the tree. Each mated pair can produce up to 60 young, an exponential growth rate with each hatching. Larvae usually spend the winter in the tree and complete their development the following spring, pupating in June or July to repeat the cycle, although in higher populations and favourable conditions there can be several generations of adults that fly from mid April through to mid September.
As populations increase, the bark beetles are better able to overwhelm the defences of larger healthier trees through a rapid, coordinated group or mass attack. This results in a positive feedback and rapid population growth. Landscape level epidemics only decline once most of the large diameter host trees have been killed or unfavourable weather causes catastrophic insect mortality.
Right, the mountain pine beetle., a wood boring insect native to western Canada.
How the tree is killed
The beetles can attack trees when they reach around 3 inches in diameter and larger. They lay eggs under the bark and also disperse a fungi that turn the trees tissue into food for the young developing beetle. This disrupts and destroys the tree’s vascular system.
How to tell if the tree has been attacked:
1) Trees react by releasing pitch as their natural defense against bark beetle attacks. This response will leave small white or reddish-brown pitch tubes on the outside of the bark. A white pitch tube means the tree successfully repelled the beetle. If it is reddish brown, most likely the beetle was successful in penetrating the tree.
2) A sawdust like substance, called frass, created by bark beetles and their larvae as they bore through the bark, accompanies the pitch.
Prevention
Unfortunately, it is unclear which species we are dealing with in our area. I have discussed the situation with MNR and the Great Lakes Forestry Scientists and unless there is a beetle that is captured, we will not know the particular species.
Thus at this point, control measures are limited and we are left with preventative measures.
1) Water the trees: The trees defences depend on the formation of sap as discussed above. In order to produce sap, the tree must have water. In our area, we have seen drought after drought years and our trees have been struggling. It makes them much more susceptible to these attacks. Water at the drip line of the tree, this is where the feeder roots are; watering at the trunk is not effective. Another method is drip irrigation, the cheap way to do it is a 19l bucket with two 1/8 inch drill bit holes in the bottom and fill the bucket with water. A large tree may need 2-3 around the perimeter of the drip line and a tree needs 1” of water per week. I know this will be difficult to do for many because of the number of trees but I wanted to let you know of the methods available.
2) Provide nutrients to the trees in the form of compost. The forestry scientists recommended nitrogen free fertilizers but I have concerns with using them around the lake due to run off.
3) Removing infested trees. Approximately 40 attacks per metre square of the tree will be fatal. The tree can remain green for approximately 12 months then will start to turn yellow. It is important not to wait for the tree to die to remove it. Removing it early on will prevent the next generation of beetles from emerging.
4) Avoid making pruning cuts. The scent of fresh cut wood is an attractant.
5) There is anecdotal evidence that ASA can improve the immune system of trees. Willow bark mulch (which contains ASA) can be used or 2 tablets in a large bucket watered at the drip line of the trees might help. And finally, what would also help is to positively identify which species we are dealing with. If you have an infected tree that you are going to take down, please let me know and hopefully we could harvest the larvae or the adult beetle for identification.
Jennifer Darling
The image below reveals the inner destruction of a fallen tree caused by the mountain pine beetle, a native of BC. Climate change has paved the way for its migration east.
