PINE SHOOT BEETLES
Pine shoot beetles, i.e. the common and the lesser pine shoot beetles (Tomicus piniperda and T. minor) belong to bark beetles and are among the worst pests of pine trees in Finland. These species cause growth losses to the trees and spread the blue stain fungus. Growth losses occur when adult beetles eat the shoots’ cores growing at the tree’s top. These hollow shoots break off and fall to the ground. The species especially worsen the condition of pine trees weakened by the defoliators, i.e. pine sawflies, and increase the intensity of growth loss with their shoot feeding. Pine shoot beetles are considered the worst secondary pests of pine sawflies. Pine trees weakened by fungal diseases or drought are also suitable for the reproduction of pine shoot beetles. The common pine shoot beetle can also kill a weakened tree after boring under the bark to reproduce. The lesser pine shoot beetle only reproduces in dead wood or lumber.
Pine shoot beetles are early swarmers, as they fly early in spring when the air temperature exceeds 10⎼12 degrees. The beetles breed in weakened trees, windbreaks and timber. The common pine shoot beetle reproduces under a thick bark, and the lesser pine shoot beetle under a thin one. The larvae become adults at the end of June and fly to the crowns of nearby pine trees for eating purposes. The species hibernate on the ground or under the bark at the base of a tree.
For the preservation of pine timber piles and weakened pines in the forest, the Forest Pests Act stipulates removal dates and maximum quantities of the weekend wood
Pines affected by the beetles can often be found in the vicinity of long-term timber storage. For the preservation of pine timber piles and weakened pines in the forest, the Forest Pests Act (read more about the Forest Pests Act – in Finnish) stipulates removal dates and maximum quantities of the weekend wood; when there is more than 20 m3/ha of timber, it must be transported away before the maturation of the beetles.
Horizontal mother galleries of the lesser pine shoot beetle, with short larval galleries (left). The mother gallery of the common pine shoot beetle is made vertically (right).
Annila, E.; Långström, B.; Varama, M.; Hiukka, R.; Niemelä, P. 1999. Susceptibility of defoliated Scots pine to spontaneous and induced attack by Tomicus piniperda and Tomicus minor. Silva Fennica, 33, 93–106.
Langström, B., Annila, E., Hellqvist, C., Varama, M., & Niemelä, P. 2001. Tree mortality, needle biomass recovery and growth losses in Scots pine following defoliation by Diprion pini (L.) and subsequent attack by Tomicus piniperda (L.). Scandinavian Journal of Forest Research, 16, 342–353.
Tuhonaiheuttajat, Metsäinfo, Luonnonvarakeskus. Viitattu 7.12.2023. https://metsainfo.luke.fi/cms/opas/tuhonaiheuttajaluettelo [In Finnish].