Mary Allen
Bark beetles are a group of beetles. Most bark beetles eat through the bark of a coniferous tree from the outside and reproduce there. They are known because they can kill entire forests.
There are about 6,000 species of bark beetles around the world. They are brown or black. Individual species are a little over an inch long. You can see three parts of her body from above: the two elytra and the pronotum. Underneath is the head, which cannot be seen from above. Bark beetles are part of the forest ecosystem. They help with the removal of dead trees so that new humus can be created from them. When they appear in large numbers, people count them among the pests.
We have almost only one special species of bark beetle called the book printer. It grows about five millimeters long. The name comes from this: the larvae dig tunnels under the bark. If you remove the bark from the tree, you will discover a relief that looks like the printing plates used in letterpress printing in the past. Forest workers and even foresters sometimes talked about bark beetles and sometimes about book printers and always meant the same beetle.
There is another bark beetle that causes the same damage. It’s the engraver. It is only about three millimeters in size. It doesn’t happen that often with us.
How does the printer live?
A printer can fly up to three kilometers. But the wind can carry it even further. Then he prefers to sit on a spruce, a silver fir, or a pine. There it bores through the bark. The tree tries to defend itself against the intruder with its sap, the resin. It can only do this if not too many bugs attack it.
The male digs a cave under the bark, the rambling chamber. After fertilization, the female lays her eggs under the bark. About forty larvae then dig their own passage. They will pupate and fly out. That’s called a generation. About ten females manage to continue to multiply. So at the end of the second generation, there are about a hundred females. After the third generation, there are a thousand. So far it can come in a year if it suits the printers.
The males know special tricks: They can convert part of the resin into scents. They “call” other males to them. In this way, suitable trees are quickly infested. When things start to get tight, the males produce a different scent that signals the end. Then no more beetles will come and the tree will not die before the young have fledged.
Why do bark beetles cause so much damage?
Bark beetles exploit the weaknesses of the trees. Storms help them with this. When trees are on the ground, they begin to wither. This allows you to produce less resin and use it to fight bugs. Dry years also favor this. Due to climate change, dry years are increasing in our country.
In many places, people have planted unnatural forests. They are monocultures, which mostly consist exclusively of spruces. These forests are generally less resilient. Spruces in particular fall over more easily in storms than, for example, beeches or oaks. With their short roots, spruce trees can hardly withstand drought.
The printer has few enemies such as certain woodpeckers. It is also not bad for nature if an entire forest perishes. Then the printers will die too. The birds bring seeds or seeds that were still in the ground sprout. A heavy infestation is only really bad for the forest owners. If you get the damaged trees out of the forest quickly, you can still sell them. But they are worth less than healthy trees.
Sometimes you can see traps with attractants for the printer in the forest. But you can’t defeat him with that. You can only tell if there are a lot or a few on the road. Chemical sprays do exist, but they are rarely used because of their poisons.