The bark beetle: an insect at the heart of forest dynamics
A small, inconspicuous yet ubiquitous insect, the bark beetle has become one of the main symbols of the changes observed in mountain forests. Although it occurs naturally in forest ecosystems, its proliferation is now drawing particular attention due to its effects on certain stands. Understanding its role and the mechanisms that influence its populations provides a better understanding of current forest dynamics.
Bark beetle: one name, a wide variety of species
The term “bark beetle” actually refers to many species of small beetles belonging to the subfamily Scolytinae. Behind this common name lies great biological diversity: some species are generalists and can colonize different types of trees, while others are highly specialized and attack only a specific tree species. This is the case with the best-known species in Europe, the spruce bark beetle ( Ips typographus), which is highly specialized in spruce trees. It is responsible for the majority of the pest outbreaks observed in spruce forests.
Beneficial insects that can become destructive
Bark beetles are naturally present in forests. By feeding on dead wood, they contribute to its decomposition and the recycling of organic matter, thereby playing a role in the dynamics of forest regeneration.
However, under certain conditions, they can attack living trees. They burrow under the bark to lay their eggs; the larvae then develop there, boring tunnels and feeding on the tree’s vascular tissue, which can weaken the tree or even kill it.
Why is it growing so much?
In the Chamonix Valley, the forests are regularly affected by bark beetle infestations. This phenomenon is now exacerbated by rising temperatures and periods of drought linked to climate change. Under these conditions, the insects develop much more rapidly: at 30°C, their development rate is about three times higher than that observed at 15°C (Wermelinger and Seifert, 1999). As a result, they can produce an additional generation within a single summer season, leading to these outbreaks of overpopulation. During the scorching summer of 2003, up to three generations succeeded one another, causing significant damage in certain forest areas.
Managing these outbreaks relies on regular monitoring of forest stands to identify affected areas. Whenever possible, measures are implemented to cut down infected trees—known as “dead trees”—to limit the spread of the populations. Owners of the affected plots may also be subject to regulated measures, particularly through prefectural orders mandating the felling of infected trees.
The bark beetle: a resource for other forest species
Bark beetle populations are part of broader ecological networks and serve as a food source for many species. This is the case with the ant-trumpeter, a beetle whose larvae develop in the tunnels dug by the bark beetle and feed on its broods. The three-toed woodpecker also plays an important role in controlling bark beetle populations: a single woodpecker can consume up to 670,000 insects per year!
