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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.

2024

To document

Abstract

Ascospores discharged at rainfall and dispersed by wind can provide long-distance spread of the European canker fungus, Neonectria ditissima. Ascospores are produced by perithecia which are the sexual reproductive stage. Diffuse knowledge exists on the seasonal pattern of perithecium formation under different climatic conditions. Therefore, the development of perithecia was observed for several successive seasons at five sites in three Northern European countries. In Norway and Finland, ripe perithecia were commonly recorded throughout the year, and on individual cankers continuously for up to 28 months. In contrast, asexual reproductive structures (sporodochia) were confined to the growing season in both countries. In Northern Germany an average of 51% of cankers developed ripe perithecia by late winter, and perithecial senescence ensued in late spring. On average, ripe perithecia were present on cankers for 22 weeks. In contrast, sporodochia were observed all year round. The timing of perithecium maturation correlated with the number of days with > 2 mm rainfall in July–September. The presence of mature perithecia and sporodochia for different lengths of time in different countries has implications for regional disease management strategies.

To document

Abstract

Six species of Ips de Geer (Coleoptera: Curculionidae; Scolytinae) occur in Europe. They attack weakened or dead conifers but may become aggressive and mass-attack living trees. All species have expanded their ranges in Europe since the late 19th century. Here, we analyse the patterns of this spread and discuss the factors at play. Starting with an assessment of distribution changes of the insects and of their host trees since the nineteenth century, we describe how and, when known, why territorial changes occurred in Fennoscandia (Norway, Sweden, Denmark, and Finland), Central Europe (Czechia, Slovakia, Hungary, Poland, Austria, Germany), the Netherlands, Belgium and Great Britain. Based on these country narratives, we discuss the conditions for, and causes of, territorial expansion. A necessary condition is the presence of host trees of vulnerable ages and sizes, resulting from the post-glaciation expansion of host range. Population changes and territorial expansion are influenced by environmental or anthropic drivers: climatic events (droughts and storms), silvicultural practices and trade. Three main factors favour or hamper the response of the different species to these drivers: active and passive flight capacity, dispersal upon emergence and response to pheromones after take-off, and pre-dispersal mating. These criteria enable identification of differences in the invasive capacities of the six species. In particular, Ips typographus appears to be a poor invader worldwide because of its wide dispersal upon emergence and its delayed response to pheromones. Finally, we discuss the risks to the Irish forests so far uncolonised by Ips species.