Conifers

ODE TO THE WHITE PINE WEEVIL

 

When we talk about preserving biodiversity by preserving our native plants, part of the reason is so that our native insects with specialized diets will have something to eat. This statement may puzzle the gardener who thinks that bites out of the roses are a bad thing. After all, who needs bugs? Yeah, some of the “bugs” pollinate the flowers so that we have fruits and vegetables, some till the soil, some make the honey, some spin the silk, and some break dead things down into their original components for re-use, but…well, who cares about the rest of them?

Our small creepy-crawlies actually come from several families. There are the eight-legged spiders and mites, the six-legged the insects, the zero-legged worms, the centipedes and millipedes with too many legs to count, the armor-plated pill-bugs (related to shrimp), and a whole host of microscopic guys. For our purposes, they are all “bugs”, even if to a biologist “bug” means just one kind of “insect” and “spiders” aren’t “insects”…

The white pine weevil (Pissodes strobe) seems as good a candidate as any to start The Monday Garden native bug-appreciation day movement. Chances are you’ll be much more likely to see this critter’s work than the critter, which may be a good thing seeing that the bug is an ugly as an orc. You can tell all weevils by their long, downward curving snouts, good for poking holes in plant tissue. The white pine weevils are small beetle-types with splotchy, hard shells and the characteristic long snouts. Their children are pasty white legless grubs. Yuk.

However, this little bug’s whole job is to go around topping out our native eastern white pine trees. According to the Ohio State University Extension these little guys “prefer” eastern white pine and various spruces, but, it is said, that in a pinch they’ll also attack about 20 other pines, including, on rare occasion, a Douglas-fir or two. In other parts of the country, due to a difference in diet, the white pine weevil is called “Sitka spruce weevil” and “Engelmann spruce weevil”.

What the white pine weevil does, as a larva and adult, is feed on the new soft leaders at the top of the tree. They seldom kill a tree but can significantly change its shape.

Left to their own devices, eastern white pines grow tall and straight. When they loose their top leader, due to while pine weevils, utility companies, severe weather or other cause, they usually develop the soft, wind-swept shapes with which the trees grace many a New England sky-line.

If you look around the Northeast, here and there, you’ll see a white pine grown to adulthood tall and straight, but most have developed multiple leaders and wonderful individualized shapes. There’s no way to say for sure that a particular pine got its shape from a weevil rather than other cause but the weevils do a lot of the work.

Interesting, sources pretty much agree that the only white pines likely to be killed by weevils are the under 4-footers growing in full sun, particularly if a bit over-watered (that means in a tree farm, tree nursery or front yard, rather than in natural part-shade understory conditions).

Equally interesting, they say that if the weevil population is in balance, usually only one weevil per tree will lay her eggs in the holes she makes right under the white pine’s top bud cluster. In this case, most of the grubby larva will get smothered by the white pine’s thick, plentiful resin, provided for exactly this purpose, and the tree’s leader is likely to survive even if gets a bit (artistically) bent.

If there are too many adult weevils, multiple females will compete for egg-laying space on the same tree. If simultaneously attacked by several weevil broods, the tree is sure to loss its terminal (top) leader and possibly also the next rung down, which will change is its shape and stunt its growth, making it ugly for a year or two while it sheds the dead top and makes new leaders. (If this happened to your tree, prune out the dead parts.)

The weevil population is kept in balance naturally through the white pine’s own defenses, predators, weather conditions, and the like. The weevil population will increase in monocultures (one-kind-of-plant places) of its chosen food plant, especially if any of the trees are unhealthy. The weevil population will also increase when the predators have been killed off by chemicals, unusual weather conditions, destruction of habitat or some other ecological disturbance.

Tree nurseries, of course, hate white pine weevils, because the nurseries are trying to sell “prefect” little trees, grown quickly, packed together in full sun, and the weevils are actually taking a bite out of the cashier register’s contents. The lumber folk don’t like the weevils either because a severely bent tree is worthless for lumber.

Once white pines were dominant in northeast forests but they lost significant population due to lumbering over the past 200 years. So to the extent that the white pine weevil prevents the trees from being cut down by their worse predator, lumbering humans, this is so bad? While the weevils make life difficult for the (non-organic?) tree farmers (according to the growers’ way of thinking), for the rest of us, though, the white pine weevil is one of nature’s great pruners, toiling hard to beautify the roadsides and hilltops. Who knew?