Current issue: 56(1)
Under compilation: 56(2)
Bark beetles are amongst the most aggressive pest agents of coniferous forests. Due to this, many boreal countries have designated laws aiming to lower the risk of bark beetle epidemics. Finland’s forest legislation has pre-emptive measures targeted against bark beetles, and for Scots pine (Pinus sylvestris L.), the law concerns pine shoot beetles (Tomicus spp.). This study used data collected around 25 piles of Scots pine roundwood that were harvested in the winter but left in the forest until the following November. Thus, the pine shoot beetles were able to use the piles for breeding. We assessed the number of emerged insects from the piles and the cascading damage they caused in the surrounding forests. All roundwood piles, regardless of their volume, were used by the beetles for breeding. Highest densities of beetle exit holes were found from the parts of the log with thick and intact bark. If the bark of the log was damaged by the harvester head, the number of beetles decreased significantly. Depending on the volume of the roundwood pile, the cascading damage (fallen shoots) was noticeable up to ca. 40–60 m from the roundwood pile. Storing of piles smaller than 50 m3 did not cause excess damage. The number of fallen shoots per tree was generally below the known thresholds for when growth losses can occur. However, the study was conducted in mature forests, and it can be assumed that the recorded damage levels would severely affect the growth of young pines, raising the question of where to store the roundwood. As with other bark beetles, the role of Tomicus beetles as damage agents may change in the future, but based on this as well as past studies, the species can be viewed as a notable damage agents only around long-term wood storage sites in the current northern conditions.
Three most promising protection methods of pine pulp wood stacks against the attacks of Tomicus piniperda L. were compared. The methods were the covering of stacks by fibreglass-strengthened paper or twofold achrylene netting, removing the upper parts of stacks, and enhanced planning of the placement of the timber store using ARC/INFO GIS-software. T. piniperda was observed to strongly prefer the upper parts of the stacks: 90 % of the beetles occurred within 0.5 meters of the top of the stacks. Covering of the stacks decreased the attack density of T. piniperda, and the protection effect of covering was 80 %. Due to long transport distances and fragmentation of forest landscape the relocation of timber store was found to be an unsuitable method in the practical level. Also, taking into account the costs of the method, removing of the upper parts of stacks was considered to be the optimal solution.
Shoot losses due to maturation feeding by pine shoot beetles (Tomicus piniperda (L.) and T. minor (Hart.), Col., Scolytidae) and subsequent growth losses were studied in Scots pine (Pinus sylvestris L.) stands growing at different distances from a timber yard, where pine timber was stored during the years 1982–84. In autumn 1985, pine trees were felled at 20, 40, 80, 500 and 1,500 m distance from the timber yard, five trees in each distance class. Trees were analysed for beetle attack, needle biomass and growth. In autumn 1988, increment cores were taken from 20 trees in each distance class.
In 1985, different damage estimates showed that beetle damage was more than 10-fold in the crowns of pine trees growing close to the timber yard as compared to less damaged trees in greater distance. Crude needle biomass estimates indicated that the trees attacked most had lost more than half of the total foliage. Following three years of attack, basal area growth decreased for 2–3 years and recovered during the subsequent 3 years, the total period of loss thus being 5–6 years. The loss in volume growth during 1983–85 was ca. 70, 40, 20 and 10% at 20, 40, 80 and 500 m distance from the beetle source, respectively, compared to the stand at 1,500. Growth losses did not occur until the number of beetle-attacks, ”pegs”, exceeded ca. 200 per tree. The highest observed growth losses occurred in trees with more than 1,000 pegs per tree.
The PDF includes an abstract in Finnish
In the 1980 and 1981, windthrown and felled Scots pine (Pinus sylvestris L.) were examined at 8 localities in Sweden. The number and length of egg galleries as well as the number of exit holes of Tomicus piniperda (L.) and T. minor (Hart.) were recorded on sample sections (30 m in length) distributed at 3 m intervals on the 37 fallen pine stems, which were successfully colonized by the beetles. In addition, 78 uprooted pines were surveyed in 6 localities. Most trees were attacked by T. piniperda, but only a few by T. minor. Successful colonization often resulted in the production of several thousand beetles per tree, the maximum being approximately 1,800. The attack density of T. piniperda seldom exceeded 200 egg galleries/m3 bark area, and the brood production usually remained below 1,000 beetles/m3. Much higher figures were obtained or T. minor. In T. piniperda, the rate of reproduction (i.e. the number of exit holes /egg gallery) decreased rapidly with increasing attack density, whereas T. minor seemed to be less sensitive to intraspecific competition.
The PDF includes a summary in Finnish.
The aim of the study was to investigate the abundance of bark beetle species and their damage in Finland. The bark beetle populations were studied in several areas in Finland, both in sites with known beetle damage and without. Two-meter wide lines were measured in the sample plots, where all trees were studied for bark beetle damage in the stem and the crown of the trees. The abundance of bark beetle species and the beetle damages in 25 study areas, and 52 different species are discussed in detail.
Divided by their lifestyle, the most important groups of bark beetles are the pine shoot beetles (Tomicus sp.), beetles reproducing in Scots pine (Pinus sylvestris L.) stems and branches under the bark, beetles reproducing in Norway spruce (Picea abies (L.) H. Karst.) stems and branches under the bark, beetles living in the other coniferous trees, beetles reproducing in roots, beetles reproducing under the Betula sp. bark, beetles reproducing in other deciduous trees and beetles reproducing inside of the stems. Of individual species, Blastophagus piniperda (now Tomicus piniperda) and B. minor cause worst damage to pine and Ips typographus (L.) and Pityogenes chalcographus (L.) to spruce. Serious damage is caused also by Xyloterus lineatus to coniferous trees, Polygraphus polygraphus and P. subopacus to Norway spruce and Scolytus Ratzburgi to Betula sp.The PDF includes a summary in German.
Blastophagus piniperda L. (now Tomicus piniperda) life cycle, especially temperature effects at various stages, has been studied in laboratory, outdoor development experiments and in natural conditions in the field in Finland, 1961–1970.
It was established that when a tree with overwintering beetles in its base is felled during the winter, the overwintered insects can establish an egg gallery into the stump without leaving for swarming flight. The egg gallery can be established in this case already about a month before swarming starts. Swarming starts after temperature in the shade exceeds 10° C. It is at its maximum at a temperature over 12° C and in conditions of no wind. The swarming starts in Southern Finland generally in the latter half of April, and in Lapland two to four weeks later than in Southern Finland, and it lasts from a few days to a few weeks. As the temperature rises, the rate of egg gallery construction and the rate of egg laying increase. The characteristics of the galleries and pupal stage are described in detail.
In Finnish conditions, B. Piniperda does not have a diapause. Movement into overwintering sites starts after the minimum daily temperature goes below 0° C. About 10% of the insects found in the overwintering sites in spring were estimated to have died during the winter. With increasing density, the number of new beetles which developed from each egg gallery decreased.
The PDF includes a summary in Finnish.