Open access publications in the SLU publication database

Abstract

Damage caused by the pine weevil, Hylobius abietis (L) feeding on conifer seedlings is a major problem in reforested areas in many parts of Europe. The adult weevil feeds on the stem-bark of young seedlings, frequently killing a large proportion of newly planted seedlings. The aims of the studies underlying this thesis were to investigate whether additional food supplies could decrease the damage caused by pine weevil to seedlings, and to determine whether access to extra food might explain why seedlings beneath shelter trees receive less damage from pine weevils compared to seedlings planted in a clear-cutting. A survey was conducted to study what effect removing shelter trees has on the level of damage pine weevils cause to seedlings. Finally, the influence of factors including fertilization, establishment and soil scarification on the growth and tolerance of Norway spruce seedlings to pine weevil feeding was studied. Pine weevil damage to seedlings was significantly reduced when extra food (fresh branches of Scots pine) was regularly provided nearby. Feeding by pine weevils in the crowns of large trees occurred during a limited period following their migratory flight but did not seem to be sufficient enough to explain the lower feeding pressure observed on seedlings in shelterwoods over the entire season. During the first year after cutting, roots in the humus layer seemed to be an important food source but were utilized to similar extent in both clear-cuts and shelterwoods. Thus, findings reported provided valuable knowledge about pine weevil feeding on seedlings and other food sources but could not fully explain why seedlings planted beneath shelter trees receive less pine weevil damage compared to seedlings planted on an open clear-cutting. Before the removal of shelter trees, Norway spruce and Scots pine seedlings need to have reached diameters of 10-12 mm in order to avoid lethal levels of damage from pine weevil attack. Loading Norway spruce seedlings with nutrients in the autumn before plantation did not lead to more feeding from pine weevils. Treatments that postpone the start of pine weevil feeding enhanced the ability of seedlings to sustain pine weevil damage later on, probably as a result of reduced stress allowing a more rapid establishment of seedlings.