THE EUROPEAN SPRUCE BARK BEETLE
European spruce bark beetle (Ips typographus L.) is around half centimeter long dark brown bark beetle. The species is endemic to Finland, and it is ecologically significant. For forest owners the European spruce bark beetle causes economic losses by drying Norway spruce trees (Picea abies (L.) Karst.) in the span of one summer season. Thus, the economic value of the mature forest can decline quickly.
After hibernating in the soil or under the bark the European spruce bark beetle swarms in May and June, when the air temperature rises above +18 degrees Celsius. After that, they start to attack spruces for reproductive purposes. Windthrown and weakened tree trunks are the most attractive reproduction materials. When colonizing a new host, the European spruce bark beetle usually selects large tree individuals with thick bark for reproduction purposes. The infestation of the bark beetle can be visually detected from brown sawdust and resin flow spots on the tree trunk.
The characteristic shape of the gallery begins to build from the mating chamber where the mother tunnel starts and where females lay their eggs. Larvae, that develop from the eggs, engrave individual tunnels parallel to the radius of the tree. As the larvae grow the tunnel gets wider until the larvae pupate. The development of larvae, happening under the bark, cuts the fluid flow of a tree from the roots to the canopy and the tree begins to dry.
A young spruce bark beetle is light brown.
The species is endemic to Finland, and it is ecologically significant.
The adults that have been overwintered, form the first sister generation of the upcoming summer season. Sister broods are common in areas, where the development of the second generation is rather uncertain. After reaching 700-degree days the first generation of the season maturate. Depending on the summer, it can happen until mid-July. Mid-July is also the time when breeding trees need to be cut down and transported from the forest to prevent larger infestation of bark beetles. Maturation of the sister generation happens at the end of August.
The first generation of the summer season will swarm and lay their eggs weather there is enough heat. Probably, some individual starts to overwinter. If the degree days go over 1500 this second generation of the season can reach maturity stage. As the larvae from the second generation are eating the bark, they already cause symptoms in the tree trunk and the canopy.
A mating chamber under the bark.
Spruce bark beetles on the top of the pheromone trap.
When the spruce tree is infested, the color of tree crown starts to change, and eventually the needles fell down.
A damage spot.
Mother- and larval galleries on the tree trunk.
Referenssit
Blomqvist, M., Kosunen, M., Starr, M., Kantola, T., Holopainen, M., & Lyytikäinen-Saarenmaa, P. (2018). Modelling the predisposition of Norway spruce to Ips typographus L. infestation by means of environmental factors in southern Finland. European Journal of Forest Research, 137, 675-691.
Pouttu A., Annila E. (2011). Kirjanpainajalla kaksi sukupolvea kesällä 2010. Metsätieteen aikakauskirja vuosikerta 2010 numero 4 artikkeli 6951. (In Finnish).
Terhonen,E. ym. 2023. Metsätuhot vuonna 2022. Luonnonvara- ja biotalouden tutkimus, Luonnonvarakeskus. Viitattu 15.8.2023. (In Finnish).
Uotila, A., Kasanen, R. & Heliövaara, K. 2020. Metsätuhot. Tapio. 206 s. (In Finnish).