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.
2011
Authors
Anna Maria Jönsson Susanne Harding Paal Krokene Holger Lange Åke Lindelöw Bjørn Økland Hans Peter Ravn Leif Martin SchroederAbstract
The Eurasian spruce bark beetle, Ips typographus, is one of the major forest insect pests in Europe, capable of mass-attacking and killing mature Norway spruce trees. The initiation and development of a new generation are strongly controlled by temperature and a warmer climate may affect the number of generations that is produced per year and hence the outbreak dynamics. Experimental knowledge regarding reproductive diapause adaptations is, however, too sparse for largescale assessments of future trends. We developed a model description of diapause induction, and used gridded observational temperature data to evaluate multiple combinations of day length and temperature thresholds to find the model parameterisation most coherent with I. typographus monitoring data from Scandinavia. The selected model parameterisation is supported by European literature data, though further experimental studies are required to analyse population specific adaptations and capacity for adjustments to changing climate conditions. Implementing the model description of reproductive diapause in a temperature driven model of bark beetle phenology (swarming activity and development from egg to mature bark beetle), enabled us to assess the length of the late summer swarming period that is a critical determinant of the risk of forest damage. By using regional climate model data we show that higher temperatures can result in increased frequency and length of late summer swarming events, producing a second generation in southern Scandinavia and a third generation in lowland parts of central Europe. Reproductive diapause will not prevent the occurrence of an additional generation per year, but the day length cues may restrict the length of the late summer swarming period.
Authors
Tao Zhao Paal Krokene Jiang Hu Erik Christiansen Niklas Björklund Bo Långström Halvor Solheim Anna-Karin Borg-KarlsonAbstract
Background: Tree-killing bark beetles (Coleoptera, Scolytinae) are among the most economically and ecologically important forest pests in the northern hemisphere. Induction of terpenoid-based oleoresin has long been considered important in conifer defense against bark beetles, but it has been difficult to demonstrate a direct correlation between terpene levels and resistance to bark beetle colonization. Methods: To test for inhibitory effects of induced terpenes on colonization by the spruce bark beetle Ips typographus (L.) we inoculated 20 mature Norway spruce Picea abies (L.) Karsten trees with a virulent fungus associated with the beetle, Ceratocystis polonica (Siem.) C. Moreau, and investigated induced terpene levels and beetle colonization in the bark. Results: Fungal inoculation induced very strong and highly variable terpene accumulation 35 days after inoculation. Trees with high induced terpene levels (n = 7) had only 4.9% as many beetle attacks (5.1 vs. 103.5 attacks m22) and 2.6% as much gallery length (0.029 m m22 vs. 1.11 m m22) as trees with low terpene levels (n = 6). There was a highly significant rank correlation between terpene levels at day 35 and beetle colonization in individual trees. The relationship between induced terpene levels and beetle colonization was not linear but thresholded: above a low threshold concentration of ,100 mg terpene g21 dry phloem trees suffered only moderate beetle colonization, and above a high threshold of ,200 mg terpene g21 dry phloem trees were virtually unattacked. Conclusion/Significance: This is the first study demonstrating a dose-dependent relationship between induced terpenes and tree resistance to bark beetle colonization under field conditions, indicating that terpene induction may be instrumental in tree resistance. This knowledge could be useful for developing management strategies that decrease the impact of tree-killing bark beetles.
Authors
Ermias Deribe Bjørn Olav Rosseland Reidar Borgstrøm Brit Salbu Zinabu Gebremariam Elias Dadebo Hans Ragnar Norli Ole Martin EkloAbstract
No abstract has been registered
Abstract
No abstract has been registered
Authors
Vladimir Shulaev DJ Sargent RN Crowhurst TC Mockler O Folkerts AL Delcher P Jaiswal K Mockaitis A Liston SP Mane P Burns TM Davis JP Slovin N Bassil RP Hellens C Evans T Harkins C Kodira B Desany OR Crasta RV Jensen AC Allan TP Michael JC Setubal JM Celton DJG Rees KP Williams SH Holt JJR Rojas M Chatterjee B Liu H Silva L Meisel A Adato SA Filichkin M Troggio R Viola TL Ashman H Wang P Dharmawardhana J Elser R Raja HD Priest DW Bryant SE Fox SA Givan LJ Wilhelm S Naithani A Christoffels DY Salama J Carter EL Girona A Zdepski WQ Wang RA Kerstetter W Schwab SS Korban Jahn Davik A Monfort B Denoyes-Rothan P Arus R Mittler B Flinn A Aharoni JL Bennetzen SL Salzberg AW Dickerman R Velasco M Borodovsky RE Veilleux Kevin M. FoltaAbstract
No abstract has been registered
Abstract
In a series of tritrophic-level interaction experiments, the effect of selected host plants of the spider mites, Tetranychus evansi and Tetranychus urticae, on Neozygites floridana was studied by evaluating the attachment of capilliconidia, presence of hyphal bodies in the infected mites, mortality from fungal infection, mummification and sporulation from fungus-killed mite cadavers. Host plants tested for T. evansi were tomato, cherry tomato, eggplant, nightshade, and pepper while host plants tested for T. urticae were strawberry, jack bean, cotton and Gerbera. Oviposition rate of the mites on each plant was determined to infer host plant suitability while host-switching determined antibiosis effect on fungal activity. T. evansi had a high oviposition on eggplant, tomato and nightshade but not on cherry tomato and pepper. T. urticae on jack bean resulted in a higher oviposition than on strawberry, cotton and Gerbera. Attachment of capilliconidia to the T. evansi body, presence of hyphal bodies in infected T. evansi and mortality from fungal infection were significantly higher on pepper, nightshade and tomato. The highest level of T. evansi mummification was observed on tomato. T. evansi cadavers from tomato and eggplant produced more primary conidia than those from cherry tomato, nightshade and pepper. Switching N. floridana infected T. evansi from one of five Solanaceous host plants to tomato had no prominent effect on N. floridana performance. For T. urticae, strawberry and jack bean provided the best N. floridana performance when considering all measured parameters. Strawberry also had the highest primary conidia production. This study shows that performance of N. floridana can vary with host plants and may be an important factor for the development of N. floridana epizootics.
Abstract
No abstract has been registered
Abstract
odronia canker (Godronia cassandrae f. sp. vaccinii) is a severe disease in young plantings of highbush blueberry (Vaccinium corymbosum L.) in Norway. In Europe, only the imperfect stage (Topospora myrtillii) has been reported, and thus conidia produced in pycnidia are assumed to be important for dissemination of the fungus. The seasonal pattern of production of conidia was investigated in a commercial planting of ‘Jersey" in 1998 and a research planting of ‘Bluecrop" in 1998 to 2000. The disease became apparent in March on shoots infected the preceding growing season, and lesions started to form pycnidia containing conidia in April. Samples of stems with distinct lesions of Godronia canker were collected from the bushes every two to three weeks from early spring to autumn. Stem pieces with lesions were shaken in water to release conidia from the pycnidia, and the numbers of conidia were determined by microscopy. Conidia were present throughout the growing season, but the highest numbers occurred during May, with 106 to more than 107 conidia per lesion. The numbers generally decreased during July to 20 % or less of that found in May, and decreased further during September to around 4 %. Ability to germinate remained high throughout the period conidia were trapped, from April to November/December. Options to manage the disease are discussed.
Abstract
Frequent bark beetle outbreaks cause biome-scale impacts in boreal and temperate forests worldwide. Despite frequent interceptions at ports of entry, the most aggressive bark beetle species of Ips and Dendroctonus in North America and Eurasia have failed to establish outside their original home continents. Our experiments showed that Ips typographus can breed in six North American spruce species: Engelmann spruce, white spruce¸ Sitka spruce, Lutz spruce, black spruce and red spruce. This suggests that differences between the Eurasian historical host and North American spruce species are not an insurmountable barrier to establishment of this tree-killing species in North America. However, slightly diminished quality of offspring beetles emerged from the North American spruces could reduce the chance of establishment through an Allee effect. The probabilistic nature of invasion dynamics suggests that successful establishments can occur when the import practice allows frequent arrivals of non-indigenous bark beetles (increased propagule load). Model simulations of hypothetical interactions of Dendroctonus rufipennis and I. typographus indicated that inter-species facilitations could result in more frequent and severe outbreaks than those caused by I. typographus alone. The potential effects of such new dynamics on coniferous ecosystems may be dramatic and extensive, including major shifts in forest structure and species composition, increased carbon emissions and stream flow, direct and indirect impacts on wildlife and invertebrate communities, and loss of biodiversity.
Abstract
No abstract has been registered