The larger European elm bark beetle
Fig. 1. A large Europan elm bark beetle, Scolytus scolytus, adult
Fig. 2. A typical S. scolytus gallery
Fig. 3. A sign of the large European elm bark beetle maturation feeding on an elm twig
Fig. 4. Damage caused by the large European elm bark beetle
Fig. 5. A sign that the elm is infected by fungi causing the Dutch elm disease
Adults are shiny, reddish brown to black beetles. Usually, the pronotum is black and elytrae are reddish brown. The body is compact, oval, 3–6 mm long. After mating (monogamy) in spring (May – June), females bore a mating chamber in the bark (phloem), where mating occurs. Each mated female excavates a maternal gallery, which is uniramous and straight, running vertically. It is approximately 4–6 cm long and 2–3 mm wide. The female lays about 50 eggs, one by one on the side walls of the gallery. Larvae feed on the phloem, by which they create dense, long galleries that start perpendicular to the maternal gallery and end widening and winding upwards or downwards. Larval tunnels are 5–15 cm long and they cross each other only very rarely. Larvae are white, C-shaped, with a brown head. S. scolytus overwinter in a larval stage. The pupa is white and about the size of an adult. After emerging through a round exit hole in the bark, young beetles find another host to feed on young twigs (typically in twig forks) to sexually mature (maturation feeding). In Europe, S. scolytus generally develops two generations per season. Beetles of the first generation swarm in August – September. The second generation starts developing in autumn. Larvae of the second generation overwinter.
Natural habitats, nurseries, plantations and urban areas. Beetles develop in the bark of elm trees (Ulmus spp.), rarely on other woody plant species (ash, walnut, oaks, willows, poplar and aspen, stone fruits). They mainly attack old, large-sized elm trees that are weakened by various stress factors, such as drought, pruning, diseases, defoliators, … Brood development generally takes place in the lower part of the trunk. Young beetles choose healthy and vigorous trees for maturation feeding.
The larger European elm bark beetle, S. scolytus, is a Eurasian species that is common in Europe. It can be found throughout the ReFOCUS area.
The larger European elm bark beetle is a serious pest of elms (Ulmus spp.) throughout Europe. It causes tree death and wood loss. Damage is caused by larvae, which feed on phloem and create extensive galleries in the bark. The beetle is also a vector of phytopathogenic fungi that cause Dutch elm disease (Ophiostoma ulmi, O. novo-ulmi). Minor damage is caused by maturation feeding on twigs. Damage is caused throughout the season.
Scolytus species are morphologically very similar and with similar life histories. The differences are in small morphological characteristics that are difficult to see to an untrained eye. Different Scolytus species can be distinguished by the shape and size of their galleries.