BARK BEETLE BOY!!!: ACT II

Jan. 21, 2016: In Act I, I introduced our antagonist, the bark beetle and the dramatic question -how will our forests be saved from this rapacious beast? In any good suspense story, I would now portray that villain in a most maleficent light so you would hate it and thereby root for the protagonists (the trees). When you look at how bark beetles interact with their prey, it's pretty tough to paint a black and white picture. For something the size of a mouse dropping , they are remarkably "clever" (if I may use that anthropomorphic term).

Our three biggest bark beetle pests, (the Ips, mountain pine and western pine beetles), are all native to North America. This is no alien invader introduction. They have co-evolved with western pines for millenniums. Why now are they such a plague? That is the dramatic question that will be answered in Act III.

Pitch tubesPitch tubesMany years ago I had a student, in my horticulture program in South Carolina (where they have southern pine beetles), that managed the grounds of a shopping complex. He asked me to come out and look at a group of Loblolly pines that looked like they were dying. They were located in a parking lot island surrounded by other healthy pines. Four trees out of that group of twenty or thirty were showing decline (browning and dropping needles) and little white irregular bumps, or pitch tubes, on the trunk. These trees were under attack by the southern pine beetle but why only four trees and not all the trees surrounding them? When I started questioning the groundskeeper, he told me that one of the trees had been struck by lightning in a storm two weeks before. Lightning often does more damage underground to roots than is exhibited aboveground and more than likely the four trees all had root damage due to the lightning grounding out. That explains why beetles attacked these trees but did not explain how they can detect stressed trees. When I'm stressed, I swear a lot and snap at people, but I've never seen that with trees.

The reason why bark beetles attack stressed trees is that stressed trees are less able to defend themselves. When a bark beetle attacks a pine, the adult must first chew through the outer bark into the nutritious inner bark, which contains the phloem, the food bearing "arteries" of the tree. The trees defense is to produce large quantities of pine pitch in an effort to drown the invading beetles. Those are the pitch tubes you see on an attacked tree. Healthy trees are very effective in this defense and any bark beetles that attacked healthy trees would not fare well in this world. So in the constant evolutionary cat and mouse game, the beetles have developed a way to sense stress in trees and thereby improve their success. That was something that was widely known, even by me, back in the stone . . . well awhile ago.

But how do they do that? How? How? That question bothered me for years. Alot! Not such that I lost a marriage or jobs or took to excessive drinking over it (though I think that would be a great idea for the protagonist in the movie), but I thought about it frequently. One day I was at a seminar, and an entomologist was talking about bark beetles and he revealed the secret . . . they hear it! Talk about a hosanna moment! And (this is even more amazing!) what they hear is cavitation within the tree! "Really?"you're saying"Cavitation? That's amazing! What the h. .. is cavitation?"

I'm glad you asked. There is cavitation in pumps and there's cavitation in the xylem (water conducting tubes) of the tree. Both types of cavitation, the pump kind and the tree kind, involve air bubbles getting into the stream of fluids. In a mechanical pump, it causes a rattling. In a tree, it cause causes a rattling, though not at a decibel that you or I or any animal can hear, but the bark beetles do. Trees that are healthy don't have air bubbles in their sap, trees that are drought stressed or having dying roots, say from lightning strikes, do. There is even a branch of science research called acoustic ecology.

For me, the answer to that long vexing question filled that void in my soul that nothing else before could, even the excessive drinking . . .well, forget that last part. (Note to Marvel: Final Climactic Battle Scene: Large army flatbeds pull up with huge megaphones mounted on them and atop them are mounted megaton bug zappers. Our sober protagonist hero/ine stands in front as the beetle horde approaches. Pretty dramatic, eh.)

Once the bark beetle detects the stressed tree what happens next is even more, or, at the very least, AS amazing. And this time, its involves the sense of smell. And that, most patient reader, I will reveal when next I blog : Pine Beetle Boy!!! Act II-B. Until then, don't excessively drink and go into the forest alone.

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