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.
1996
Abstract
In the present study the predation rate of Chrysoperla carnea (Stephens) on eggs and larvae of the lepidopterous species Mamestra brassicae (L.) was investigated including the prey"s influence on survival and development. The experiments were done at 20 +/- 1 degrees C and L:D = 16:8. C. carnea larvae were fed on eggs and first instar larvae of M. brassicae, respectively. In both cases the daily predation rate of C. carnea increased slowly during the two first instars and reached a peak in the third larval instar. During the third instar 87% and 85% of the total numbers of M. brassicae eggs and larvae, respectively, were consumed. C. carnea preyed on a mean total of 312 M. brassicae eggs and 232 M. brassicae larvae during its larval development. The mean daily predation rate of C. carnea reached a maximum of 106.6 eggs of M. brassicae and 46.1 larvae of M. brassicae. C. carnea consumed a total of 32 mg of M. brassicae eggs and 70 mg of M. brassicae larvae during its larval development. The developmental time of C. carnea fed on M. brassicae eggs and larvae was 27.4 and 21.5 days, respectively. Almost 10% of C. carnea died when reared on M. brassicae eggs and 15% died when reared on M. brassicae larvae. The quality aspect of the prey is discussed.
Authors
Paal KrokeneAbstract
Aggressive bark beetles kill healthy conifers through pheromone-mediated mass attacks. The exact mechanism by which trees are killed is still disputed, but phytopathogenic blue-stain fungi associated with the beetles are probably involved in most cases. This thesis compares the blue-stain flora of five bark beetle species that colonize Norway spruce of different resistance. The aggressive Ips typographus can kill healthy trees, while the other species are non-aggressive and colonize either severly stressed or dying trees (the facultatively parasitic Ips duplicatus, Polygraphus poligraphus and Pityogenes chalcographus), or dead trees (the saprophagic Hylurgops palliates). Ips typographus and I. duplicatus were both found to carry very high frequencies of the phytopathogenic fungus Ceratocystis polonica. This fungus has previously been found associated only with I. typographus, and has been shown to be pathogenic to Norway spruce in experimental mass inoculations. The other bark beetles carried no known pathogenic fungi. The phytopathogenicity of four of the isolated blue-stain fungi were evaluated through mass and low-density inoculation in young Norway spruce trees. Mass inoculations confirmed C. polonica\"s pathogenicity, while the other fungi, which are associated with non-aggressive beetles, were not pathogenic (Ophiostoma piceae, cfr. Ambrosiell sp., Dark sterile sp.A). Low-density inoculations revealed only small differences between the four fungi in phloem necrosis length. Necrosis length is used as a standard criterion of fungal pathogenicity, but it was not useful for assessing the pathogenicity of the fungi in the fungus-host tree system under study here. Ceratocystis polonica was found to penertrate deeper into the sapwood and induce deeper sapwood desiccation than the other fungi. The ability to invade sapwood is probably more important for fungal pathogenicity than the ability to colonize phloem, and may thus be a better criterion for assessing the pathogenicity of blue-stain fungi. General aspects of the association between bark beetles and blue-stain fungi are discussed.
Abstract
No abstract has been registered
Abstract
No abstract has been registered
Authors
Torild Wickstrøm W. Lund R. ByeAbstract
It is shown, by using ICP-AES, that some Ni, Co, Fe and Cr is transported, probably as an aerosol, with the hydrides to the atom cell during a hydride generation process. The amount of matrix elements introduced to the atom cell depends on the concentrations of the sodium tetrahydroborate and the acid used for the hydride generation. For solutions containing 5000 mg l(-1) of Ni and Co, the signals obtained are equivalent to those obtained from 1-5 mg I-1 metal solutions nebulized in the ordinary way. A glass filter Frit placed between the gas-liquid separator and the torch reduces the transport of metal to the plasma by 50-80%. When HGAAS is used, a decrease in sensitivity is observed for As in samples containing high concentrations of Ni and Co. This may be owing to the presence of Ni and Co in the quartz tube atomizer.
Authors
Sondre SkatterAbstract
No abstract has been registered
Authors
Bjørn ØklandAbstract
The relationship between the mycetophilid fauna and a set of environmental variables was studied in spruce forests of southeastern Norway. At the stand level, the continuous presence of wood in all decay stages combined with a tree cover appeared to be a major factor for increasing the species richness of mycetophilids. However, the spatial representation of suitable stands in the landscape seems to be particularly important, since the % area of oldgrowth in the surrounding 100 km showed the strongest influence on both species richness and abundance within individual species. The present findings indicate that conservation of a species-rich mycetophilid fauna requires networks of stands within dispersal distances. A reserve network in southern Norway should give special priority to little disturbed forests in the more remote sub-montane areas, since they appear to be very species-rich, and since their strong populations may provide a long-term viability of many mycetophilid species.
Authors
Gro HylenAbstract
No abstract has been registered
Authors
Tonje ØklandAbstract
No abstract has been registered
Authors
Tonje ØklandAbstract
Vegetational and environmental monitoring of boreal spruce forest was initiated in 1988, as a part of the programme “Contrywide Monitoring of Forest Health” at the Norwegian Institute of Land Inventory (NIJOS). As a basis for monitoring, relationships between trees, understory vegetation and environmental conditions (vertical relationships) were analysed for each of ten reference areas. The reference areas were selected to span regional gradients, in climatic conditions and deposition of airborne pollutants, in old-growth, so-called “bilberry-dominated”, “small-fern” and “low-herb”, also paludified, spruce forests south of the Polar Circle. Fifty 1-m2 meso sample plots, randomly chosen within ten 50-m2 macro sample plots in each reference area, were subjected to vegetation analysis, using frequency in subplots as species abundance measure. Environmental (including soil chemical) and tree parameters were recorded for meso as well as macro sample plots. The main vegetational gradients were found by parallel use of DCA and LNMDS ordination methods and subjected to environmental interpretation, mainly by means of non-parametric correlation analyses. DCA and LNMDS in most cases revealed the same main gradients in vegetation, but outliers were more frequent in LNMDS ordinations, due to higher vulnerability of this method to plots with deviating number of species. A complex-gradient in nutrient conditions, with pH and the concentration of nitrogen as the most constantly contributing variables, but with considerable between-area variation with respect to important cations, was evident in nine reference areas. Soil moisture varied along the second vegetational gradient in most areas. In the three most humid reference areas, the Ca concentration was related to variation in soil moisture and gradients from below to between trees, while unrelated or inversely related to the same vegetational gradient as pH. Species abundances were plotted on plot positions in DCA ordinations in order to summarize the species´ responses to environmental variation in each area. Variation in vegetation in the total data set (500 meso sample plots) was partitioned onto two sets of explantory variables (environmental and climatic/geographical) by use of CCA, in order to find the relative importance of environmental and climatic/geographical variation. The fraction of variation exclusively explained by environmental variables was about 17%, while only 5% of the variation was explained exclusively by climatic variables. The variation shared by both sets of variables was about 8%. The main vegetational gradients and environmental/climatic/geographical complex-gradients in the total data set were found by DCA and subsequent interpretation of axes. The main complex-gradients found by separate analyses of data from each reference area, were reflected along the DCA axes in total ordinations, but differences between areas with respect to positions along both environmental and climatic/geographical gradients were also evident. Meso plot occurrences of selected species were plotted in a DCA ordination of the total data set, with variation exclusively due to climatic/geographical variables removed, in order to express regional similarities and differences in the species´ responses to the environment. The different patterns of species´ distributions in the DCA ordination were discussed in the light of their use as indicators of specified environmental conditions.