Bark beetles

Bark beetles (Scolytinae)

1. Identification

• Common name: Bark beetles, bark beetles or engraver beetles.
• Scientific name: Several species of the subfamily Scolytinae (e.g.:Dendroctonus frontalis Zimmermann, Dendroctonus micans Kugelann, Dendroctonus ponderosae Hopkins, Euwallacea fornicatus Eichhoff, Hylastes ater Paykull, Hylurgus ligniperda Fabricius, Hypothenemus eruditus Westwood, Hypothenemus hampei Ferrari, Ips typographus L., Phloeosinus armatus Reitter, Polygraphus poligraphus L., Scolytus multistriatus Marsham, Scolytus scolytus Fabricius, Xyleborus dispar Fabricius, Xyleborus glabratus Eichhoff).
  
• Order: Coleoptera.
• Family: Curculionidae (subfamily Scolytinae).

2. Description of the group

• Adults: Small cylindrical beetles, generally 1–6 mm, brown to black coloration, compact body and geniculate antennae; many species show an elytral declivity with characteristic teeth.
• Larvae: Apodous, whitish, with a curved body and brown head; they develop in galleries excavated under the bark or in the surface wood.
• Pupae: Formed in pupal chambers inside the bark or wood.
• Eggs: Deposited in nuptial galleries or egg-laying chambers.
• Behaviour: Many species are aggregative and use pheromones; some carry symbiotic fungi (ambrosia).

3. Main hosts

• Various conifers, including pines, firs, spruces and larches.
• Broadleaved trees such as oaks, chestnut trees, elms and other woody species.
• A preference for weakened, recently felled or stressed trees, although some species attack healthy trees.

4. Symptoms and damage

• Fine borings in the bark, frequently accompanied by the expulsion of sawdust.
• Characteristic subcortical galleries, interrupting the flow of sap and causing cambial necrosis.
• Drying of branches and crown, yellowing and premature fall of leaves or needles.
• Progressive decline of the tree, which may culminate in death in severe attacks.
• Introduction of associated pathogenic fungi, which aggravate the decline and accelerate mortality.
• High economic importance in forests and production stands.

5. Biological cycle

• One to several generations per year, depending on the species and climatic conditions.
• Adults emerge in spring or summer and begin excavating egg-laying galleries.
• Eggs deposited in nuptial galleries; larvae excavate radial galleries.
• Pupation under the bark or in the surface wood.
• Development favoured by high temperatures, prolonged droughts and an abundance of weakened wood.

6. Monitoring

• Observation of fine borings and expulsion of sawdust on the bark.
• Inspection of branches and trunks to detect subcortical galleries.
• Evaluation of the crown for signs of drying or loss of vigour.
• Traps with specific pheromones for detection and population monitoring.
• Reinforced monitoring after storms, cuts, prunings or periods of water stress.

7. Management measures

• Cultural: Removal and destruction of infested wood; appropriate management of forest residues; avoid prolonged storage of fresh wood.
• Preventive: Maintenance of the vitality of the stand; reduction of water stress; avoid injuries to the trunk.
• Integrated protection: Regular monitoring; use of traps with pheromones for early detection; intervention only when necessary; practices that reduce the availability of attractive wood.
• Legal framework: Some bark beetle species, including invasive exotic species and quarantine pests, are regulated in the European Union under Regulation (EU) 2016/2031 and Implementing Regulation (EU) 2019/2072, which establish mandatory surveillance and control measures.

Bibliographic references

• EPPO Global Database – Scolytinae.
• CABI Invasive Species Compendium – Scolytinae.
• EFSA  – Scientific Opinions on forest pests and bark beetles.
• European Commission – Regulation (EU) 2016/2031 on protective measures against quarantine pests.
• European Commission – Implementing Regulation (EU) 2019/2072.
• Lieutier, F. et al. (2004). Bark and Wood Boring Insects in Living Trees in Europe.
• Wermelinger, B. (2004). Ecology and management of bark beetles in European conifer forests.