What's In A Log? Forest Insect Pests!

Besides Ornithology, I am teaching a Forest Entomology class this quarter. Getting students to recognize damage caused by certain insects is one of the main objectives for those majoring in Forest Management. It's one thing to roll over a log and see what is underneath, it's another to go digging inside.

Looking at bark or wood, one may notice lots of very small holes, or what we call "pinhole borers". These can consist of many different types of wood dwelling insects, though mostly created by beetles.

These white and orange piles of dust, soft as baby powder, are created by Powderpost Beetles. Lyctid and Bostrichid beetles are the guilty parties.

Powderpost Beetles prefer old 'seasoned' wood. Furniture and antiques without protection can be reduced to piles of powder. These beetles seek out wood with a high starch content. For that reason, you will notice the holes are concentrated in the light sapwood, not the dark heartwood.

While not unique to this group, many powderpost beetles can be recognized by the helmet-like thorax, which keeps the head hidden below.

Another group of pinhole borers are the Ambrosia Beetles. Look on the outside for black stained exit holes. Sometimes the side galleries create what look like little railroad tracks. These beetles do not eat wood, they create galleries to raise and eat Ambrosia fungus. It's the fungus that causes the black stain.

Not only does the boring of galleries reduce the value of the wood, the fact that trees transport nutrients up and down causes the fungus stain to be carried with it.

Another group of pinhole makers are the bark borers, or more properly called Inner Bark Borers. They do not attack into the wood, but chew on the surface, or the cambium layer. These are the galleries of Ips pini, the Pine Bark Borer beetle.

Depending upon the species, the males usually carve out the main gallery, and send out a pheromone to attract a female. Some species of bark beetle males may let in from one to three females, then block the entrance with his body so no others can enter. After the eggs are laid, the young grubs chew outward and create these side galleries.

After the grubs have finished eating, they will carve out a rounded pupal chamber where they will metamorphose into adults, then chew their way out of the bark. Since beetles do not spin silk, what you are looking at here are cocoons, the result of an Ichneumon Wasp that parasitized the beetle grubs.

These guys are tough to photograph, especially when alive and moving. They total 1/8th of an inch. The key feature to recognize Ips bark beetles is the appearance of what looks like a cut off abdomen. Part of the elytra is missing and it ends in these sharp points. Ips beetles are known as secondary pests, which means they usually attack weakened or injured trees. Another genus of bark beetles are called Dendroctonus, which means 'tree killer'. This group will attack en mass entire stands of healthy pine trees.

These are shots from an article in the Orlando Sentinel of Ormond Beach Florida, a community near Daytona, suffering from the Southern Pine Beetle. The Rocky Mountains, Canada, and Alaska, all have bark beetle species devastating their pine forests.

Moving up in size is what I refer to as the medium sized holes. Looking like a shotgun blast, these are from the Oak Timberworm.

Members of the Brentidae family, the Oak Timberworm is another true wood boring beetle. This is a female.

The female will seek out a wounded area of the tree. She will not lay eggs in a healthy tree where the wood hasn't been exposed. It takes her 2 hours to chew a little cavity where she will lay only one egg per hole.

You can see why it takes her so long to excavate the wood. What appears as a piercing beak is actually an elongated snout with chewing mandibles. Timberworms are closely related to Weevils, and sometimes put in the same family.

Don't come sniffing around for timberworm eggs to eat. The male has intimidating short jaws, and he will use them to protect the female while she is laying eggs.

Moving up to the large exit holes, these are usually oval or egg shaped.

This group of borers often inflict some of the most serious damage in regards to lumber quality. Most are Cerambycidae, or Long-horned Beetles. This one in particular is the Painted Hickory Borer, one of which is sitting in the upper most gallery.

The damage is also visible from the outside, and no, this is not from a Yellow-bellied Sapsucker.

Here is evidence of the Sugar Maple Borer.

This is one of the long-horned beetle larva, probably from the genus Rhagium. Its thick sclerotized jaws make it easy for boring into heartwood. These are very similar looking to the Buprestidae larvae. The Buprestids, or Flat-head Borers have a much reduced abdomen in comparison to the enlarged thorax.

Another way you can be sure. Flat-head borers only occur under the inner bark. These were all boring holes into solid wood.

Long-horned Beetles are so named because of the long antennae. Here is one of the species in our area, the White Spotted Sawyer. Look for it around freshly cut White Pine.

Not exactly a good pic, but I just wanted to show the variety of Long-horns, and their representative host plants. From left up top, Red Oak Borer, Locust Borer, Painted Hickory Borer, Chestnut Oak Borer. Second row, Cottonwood Borer, Elderberry Borer, Elm Borer, Banded Ash Borer.

So what exactly then does Flat-head borer damage look like? Flathead, Fatheads, or Metallic Wood Borers eat the cambium layer, much the way bark beetles do. Due to their larger size, the galleries are much more evident. They look as if someone took a router across the wood surface.

Here are what the metallic wood borers look like. These are from both North and South America. Take the second one on the left and reduce its size, and you have what the Emerald Ash Borer somewhat resembles.

So what makes the Emerald Ash Borer so fatal?  Unlike other members of the family which mine the wood randomly, the Emerald Ash larva leaves NO cambium untouched. You can see it literally girdles the entire tree.

Emerald Ash Borer adults hatch out in May, so start looking for skinny little green beetles the length of a penny. Check your ash trees for holes that differ from most, they have a D shaped exit hole. These samples came to me from Cincinnati. Once restricted to Lake Erie counties, they have spread through half the state and continue to move.

A couple others I'd like to add before closing. Perhaps the fattest galleries in wood are created not by a beetle, but a moth! Most moth caterpillars feed on leaves, but the Carpenterworm of the Cossidae family is a wood borer. Galleries can be an inch and a half wide, sometimes stained black, sometimes not.

I have found the pupal shells of Carpenterworms sticking half way out of trees from which they wiggled out of. I have also caught many at lights. The female is larger, and the males have yellow hindwings.

Swiss Cheese anyone? This is caused by Carpenter Ants. They move in on already dead or decaying trees. They don't eat wood, but chew holes to create living quarters for the colony. If your house has had termites, these guys may come next.

With the exception of the Emerald Ash Borer, all the above mentioned are native species. Nature has checks and balances, and these creatures have always existed in our woods. When we introduce an economic value to our forest products, which is perfectly fine, then these are some of the issues forest managers must contend with. By the way, there are no easy methods of which to control these particular insect outbreaks.

The marks above were not made by a pocket knife, they are from a beetle. We do know the above bark borer is a native species to America, notice it carves out galleries in the shape of U-S-A.    :-)