The Swedish Forest Agency reports in a Article that ant beetles, stylt flies and parasitic wasps are some of the main enemies of spruce bark beetles. Favouring these can help in the fight against spruce bark beetles.
Natural enemies of spruce bark beetles are important because they reduce the number of spruce bark beetles and therefore the infestations they can cause. These enemies cannot prevent spruce bark beetle outbreaks after, for example, a storm or a summer of extreme drought, but they can influence the size of the outbreaks and help to reduce damage more quickly.
The main enemies are various beetles, flies or parasitic wasps that feed on spruce bark beetles. Other species, such as the common bark beetle, the double-eyed bark beetle and the six-toed bark beetle, compete with spruce bark beetles for space under the bark. The woodpecker is also considered an important enemy, as it likes to eat spruce bark beetles.
How can you favour your enemies?
- Save small trees and parts of trees, both spruce and other species that spruce bark beetles do not like. This will favour other bark beetle species, which in turn will increase the number of natural enemies as they will have more to eat.
- Increase the proportion of pine. This favours, among other things, the ant beetle, which is one of the most important enemies of the spruce bark beetle.
- Forest management that allows more light into spruce stands can favour pollen- and nectar-producing plants. These food sources allow parasitic wasps to live longer and produce more eggs.
- Avoid control methods that reduce the number of enemies in relation to the number of spruce bark beetles. In winter felling, for example, there is a risk that more stilt flies than spruce bark beetles will be killed.
- Act quickly when you detect new spruce bark beetle infestations. If you mill away all the bark on parts of the trunk larger than 10-15 cm, you will kill the spruce bark beetles before their natural enemies have time to lay their eggs. The natural enemies will then seek out other infested spruces (that you have not detected) and lay their eggs there.
- Leave the spruce bark beetle-killed spruce trees that you did not find in time if it is not economically viable to utilise the wood. Felling these trees risks hitting the enemies harder than the bark beetles.
- To favour woodpeckers, save old trees that are starting to develop nest holes. Woodpeckers particularly like aspen, but also coarse stumps and coarse dead standing trees of all species.
You can read more about the enemies of the spruce bark beetle and see more pictures of the insects in Fakta skog on SLU's website and at skogskunskap.se
