Publications
NIBIOs employees contribute to several hundred scientific articles and research reports every year. You can browse or search in our collection which contains references and links to these publications as well as other research and dissemination activities. The collection is continously updated with new and historical material.
2016
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Kirsten TørresenAbstract
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Kirsten TørresenAbstract
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The Eurasian spruce bark beetle Ips typographus is a major forest pest in Europe, capable of mass-attacking and killing mature Norway spruces over extensive areas during outbreaks. Recurring outbreaks over the last few centuries have affected Central and Northern Europe. Outbreaks tend to be periodic and are in many cases triggered by large wind-felling events. For example in Scandinavia several large outbreaks have been triggered by storm disturbances in the last 50 years. In Europe I. typographus is widespread where spruce hosts are found except for in the British Isles. Here we review the identification and biology of this insect and present information about its invasiveness and the potential of success in early detection and control of outbreaks. There are indications that a warmer climate will increase the risk for outbreaks in the northern range of spruce in Europe, where outbreaks so far have been rare. More outbreaks are also expected at the southern margin of the spruce distribution in Europe, where lower than average precipitation seems to generally favor infestations. Establishments outside Eurasia have not been found despite frequent interceptions at ports of entry. Our experiments showed that North American spruce species may be suitable hosts and we conclude that it cannot be ruled out that future establishment can result from repeated imports. The most efficient control option of storm-triggered outbreaks is removal of wind-felled trees before the new generation beetles emerge.
Authors
Bjørn ØklandAbstract
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The purpose of this study is to increase the basic understanding of outbreak dynamics in order to improve the management of bark beetle outbreaks. The spruce bark beetle Ips typographus is a major disturbance agent of European forests and is the continent’s most economically and environmentally damaging bark beetle. Outbreaks of the spruce bark beetle are often triggered by large windfall episodes, and we have utilized a unique opportunity to study a Slovakian outbreak where little salvage logging was performed in some areas after a 2.5 million m3 storm-felling in 2004. Our analyses focused on the first five years after the windfall, and we used a combination of empirical data and simulation models to understand the spatial patterns of beetle-killed forest patches developing during the outbreak. The univoltine beetle population used an increasing proportion of the windfelled trees during the two first seasons after the storm, but from the third season onwards our comparisons of inter-patch distance distributions indicated a transition from beetle production largely in windfall areas to a self-sustaining outbreak with infestation patches developing independently of the windthrows. The size of new infestation patches formed after this transition was modeled as a function of beetle pressure, estimated by the proportion of a circle area surrounding new patches that was covered by infestation patches the previous year. Our model results of patch size distribution did not correspond well with the empirical data if patch formation was modeled as a pure dispersal–diffusion process. However, beetle aggregation on individual trees appears to be important for patch development, since good correspondence with empirical data was found when beetle aggregation was incorporated in the modeled dispersal process. The strength of correspondence between the beetle aggregation model and the empirical data varied with the density of aggregation trees in the modeled landscape, and reached a maximum of 83% for a density of three aggregation trees per infestation patch. Our results suggest that efficient removal of windfelled trees up until the start of the second summer after a major windfall is important to avoid a transition into a patch-driven bark beetle outbreak that is very difficult to manage. Our results also indicate that the outcome of a patch-driven outbreak is difficult to predict, since the development of new infestation patches is not a simple function of beetle pressure but is also affected by beetle behavior and local forest conditions.
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No abstract has been registered
Authors
R. Venancio G.J. Moraes R.C. Castilho N.S. Iwanicki G.F. Moreira Lise Grøva Karin Westrum Ingeborg KlingenAbstract
Tick-borne diseases, such as anaplasmosis and babesiosis, are of major concern for Norwegian sheep farmers. Ticks can be controlled on and off the host, usually with the long-term, high-rotation use of chemicals. Fungal pathogens, predatory mites and ants are thought to be important tick killers in nature. However, the prevalence and diversity of predatory mites in tick habitats has barely been evaluated. It is known that most soil mite species of the cohort Gamasina (order Mesostigmata) are predators. Until now, 220 mesostigmatid species have been reported from Norway, most of them belonging to the Gamasina. One of the first recommended steps in a biological control program involves the determination of the fauna in the pest habitat. The objective of this study was to determine the groups of gamasines co-occurring with I. ricinus in sheep grazing areas in Isfjorden and Tingvoll in Western Norway. A total of 2,900 gamasines of 12 families was collected. The most numerous families were Parasitidae (46.9%) and Veigaiidae (25.7%), whereas the most diverse families were Laelapidae, Macrochelidae, Parasitidae and Zerconidae. Our results showed that the tick density was significantly related only to locality, elevation and rainfall. Differences in the prevailing environmental conditions resulted in more outstanding differences between Gamasina abundances than diversities. Based on our present knowledge of the potential of different gamasine groups as biological control agents, the results suggested that laelapid mites should be among the priority groups to be further evaluated for their role in the natural control of I. ricinus in Norway.