Alder bark beetle

The Alder bark beetle (Dryocoetes alni) is a small beetle belonging to the order Coleoptera and the family Curculionidae (subfamily Scolytinae). This species is well-known in forestry as a secondary pest that primarily targets various deciduous trees. By inhabiting the inner bark and cambium, these beetles interfere with the tree's vital functions, often leading to decline in wood quality and overall forest health.

While their primary host is alder (Alnus), these beetles can also be found on other hardwood species such as hazel, hornbeam, and birch when the host trees are under stress. They typically select trees that are physiologically weakened by drought, disease, or mechanical damage, although they can reach outbreak levels in healthy stands under favorable climate conditions.

The life cycle of the Alder bark beetle is typical for the Scolytinae subfamily. They usually overwinter as adults in the bark or forest floor litter. In spring, when temperatures rise, the adults emerge to seek host trees. The female initiates the gallery construction, laying eggs in niches along the main tunnel. The larvae feed on the cambial tissue, extending perpendicular galleries that girdle the tree's conductive systems.

Damage caused by this beetle manifests as a distinct network of galleries under the bark, which eventually leads to the detachment of the bark and the death of the cambium layer. Early indicators include the presence of fine wood dust (frass) around the entrance holes and the discoloration of foliage on individual branches. If left unchecked, persistent attacks can cause systemic dieback of the host tree.

Effective management and protection strategies focus on maintaining forest vigor and sanitation:

• prompt removal and destruction of infested trees (sanitary logging) before the next generation of beetles emerges;
• clearing logging residues that provide breeding grounds for the pests;
• monitoring tree health to ensure early detection of infestations;
• utilizing trap logs or pheromone attractants to manage population spikes in vulnerable areas.