Forestry Friday … Bug Kill!

“Bug kill” or “beetle kill” are the terms we use for insect killed trees. Bark beetles kill more trees in our forest than any other insects. They are always present in the forest. At low population levels, the dead trees or snags they create are left for wildlife. When beetle populations spike up, we salvage most of the dead trees.

salvage timber, bark beetles, forestry

We salvage dead and dying trees to capture their value while the wood is still sound. Red or fading tops signal the problem areas.

bark beetle, pitch tube, ponderosa pine

This pitch tube is the entry point where the beetle first bored into the tree. If the pitch tube is amber in color, the tree successfully fended off the attack. When the pitch tube is pinkish like this one, the beetles successfully penetrated into the tree.

adult red turpentine beetle, Dendroctonus valens

This is the culprit, a red turpentine beetle, Dendroctonus valens. They bore into the trees to lay eggs. Trees in a weakened state, such as during severe drought, attract these beetles.

Red turpentine beetle, Dendroctonus Valens, bark beetle, Ponderosa pine

The red turpentine beetle adult, Dendroctonus valens,  normally attacks the base of the tree. Such a tiny creature can do so much damage.

bark beetle, larva, Dendroctonus valens

The larva of bark beetles are what kill the tree. The adult beetle chews a nursery gallery into the tree to lay her eggs. The larva hatch and spread out from that gallery creating more galleries as they feed. During this feeding process the larva girdle the cambium of the tree causing it to die.

bark beetle, Ips

The top of this Ponderosa pine is dead. This in an indication of a different beetle, Ips sp. Location of the attack on the tree can be a diagnostic tool for identification of the insect attacker. There a many species of bark beetles that attack trees.

I’ve been asked over the years what can be done to protect the trees from these beetles. The answer is very little. Keeping your trees thinned out reduces competitive stress between the trees. Reducing stress on the trees is the only effective way to reduce attack by the beetles. However, in years when the beetle populations peak, they will even attack healthy trees. Once you see evidence of beetle attack, it is already too late. Salvaging the dead and dying trees is all that can be done. You have to “log the problem away.”

21 thoughts on “Forestry Friday … Bug Kill!

  1. Whenever I take the train to Colorado we go past areas in the mountains that look like they’ve been hit pretty hard by pine beetles, with some spots having more dead trees than not.

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    • It’s true, some timber stand suffer total collapse during severe drought when the beetle population explode. Certain species of trees, such as lodge pole pine are particularly susceptible to this phenomenon.

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  2. I’m so terribly familiar with this. Our beetles were mountain pine beetles or Dendroctonus ponderosae and they pretty much killed the entire forest in central BC. They’re still logging the salvage wood. But in my yard (and elsewhere) we have hundreds of new young lodgepole waist high. It’s all a cycle.

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    • Yes, the exuded pitch is the tree’s defense mechanism. Good sticky pitch traps the beetles. When the trees are dry it’s hard to generate pitch. We have to depend on Mother Nature to do our watering in the woods.

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  3. Fascinating Tim. Presumably the beetles have a useful role of some kind when everything is kept in balance, but take hold when the balance slips. There was an interesting situation I heard about a few years ago here in Australia. Some eucalypts were dying in large numbers in one area, attacked by Christmas beetles. It turned out that a lot of tea trees in the area had been cleared, where gliders (a kind of small possum) lived, so they had gone elsewhere, and normally they would keep the Christmas beetles to a manageable level. So a knock-on effect!

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    • They are a natural part of the forest ecosystem. When they kill trees they create snags. These snags are important habitat to cavity dwelling wildlife. Also, the woodpeckers and other birds love to eat them. There populations cycle over time and when they are high we have a lot of dead tree. When the are changes such as you had with the Christmas beetles there are ripple effects. It all comes back into balance in time. A forest environment can be very dynamic.

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  4. Just love your informative blogposts Tim – I fully respect the work you do, leaving a lasting positive impression on the land and optimising sustainable offtake at the same time. Those beetles (or an equivalent species) are ubiquitous in the indigenous forests of Africa… We used to have to oil our wooden furniture regularly to keep them at bay when I was a little guy. Looking forward to your next post – regards – metiefly

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    • Thanks M. Nature is remarkably good at exploiting every opportunity to use available habitat. Not to mention relentless. Even if it is furniture! As stewards of the land we just have to be diligent and flexible.

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  5. We had quite a problem with the “scale” insect a couple of years ago. If you walked under the trees, it was raining #@$%. The trees also had been stressed by a couple of years of drought. We lost dozens of tulip poplars. We had a very cold winter this year and I think it helped kill the insects. Right now, the ash borer beetle is making inroads into the state and is worrying a lot of foresters.

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    • We have black scale out here the kills the tops of sugar pine. Fortunately, it only cycles through about every 20 years. With drought that is going on out here, we are gearing up for lots of bug kill the next few years.

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  6. Tim, it has been awhile since I stopped by to read your posts. Great information, have been aware of beetles in general and the damage they can cause but did not know the particular kinds of beetles and how they were able to kill a tree. I just hit the button for notifying me of your posts via email. Take care.

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