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The pinewood nematode, Bursaphelenchus xylophilus, is the most harmful plant parasitic nematode on trees in Asia and Europe and is the causal agent of the so-called pine wilt disease of susceptible conifer species, mainly Pinus spp. The disease has occurred only outside its natural range of distribution (North America) or on nonnative pine species. In greenhouse trials using saplings, Pinus sylvestris was one of the most susceptible European pine species. To examine the significance of these sapling-based analyses concerning the population dynamics and pathogenicity for mature P. sylvestris trees, investigations using seven- to eight-year-old trees were carried out. The trees were artificially inoculated using a suspension of 10,000 B. xylophilus in 600 µl of tap water per tree. For the population dynamics investigation, the pines were divided into 48 segments for nematode extraction. The development of wilt symptoms as well as physiological changes were observed until tree death. During the population dynamics investigation, B. xylophilus was located at the inoculation site and in adjacent segments during the first 11 days after inoculation. On day 16, B. xylophilus was distributed throughout the entire stem, adjacent branch segments, root collar and roots before any external wilt symptoms appeared. With increasing pine wilt disease, B. xylophilus was finally found in all wood and root segments. High nematode densities appeared. Shortly before tree death, the treetop showed several nematode-free segments. The rest of the stem and adjacent branch segments and root collar were highly nematode-infested. During the pathogenicity investigation, all B. xylophilus-inoculated pines died within 84 days. The significant decline in the water potential in the needles was steeper and more strongly correlated with increasing wilt symptoms compared to a droughtstressed variant. However, the decline in the water potential in the needles started earlier in the drought-stressed pine variant. In conclusion, the population dynamics of B. xylophilus in seven- to eight-year-old P. sylvestris trees and the pathological reactions of the pines were comparable to those observed in assays with saplings, although delayed in reaching a population peak and developing wilt symptoms. Therefore, P. sylvestris saplings are good indicator trees for B. xylophilus population dynamics and pathogenicity investigations. [ABSTRACT FROM AUTHOR]

Investigations with pitfall traps into the influence of crop species on the dynamics of arthropod communities are presented. They included four perennial crops (extensive grassland, miscanthus and poplar and willow tree species) as well as winter barley as annual crop. The cultivars determined the diversity (Shannon-Weaver-Index) of arthropod communities, whereby the diversity of the tree species was mostly statistically different from the diversity in agricultural crops. This finding was due to temporal changes in the species stock (species identity) and the species dominance (dominance identity) and demonstrates high dynamics of arthropod presence within and between crops. The crop species lead to temporally and locally separated metapopulations. Possible driving forces stimulating the adaptation of arthropod communities to crops were analyzed by recording the energy status of the cropping systems. It was based on management data, plant yields and accompanying information about biomass accumulation. The term "agricultural energy gain" summarizes these influences on the energy level. The return of biomass to the cultivation system was described as "ecosystem energy gain". Both parameters elucidate the arthropod presence within the crops. Increasing agricultural energy gain was negatively related in contrast to the energy gain of the entire ecosystem. Furthermore, the splitting of arthropods into functional groups helped to explain the species and dominance variation of arthropod communities between crops. This is based on the need for energy dissipation and influences the energy flow across trophic levels. The position of arthropod species within the food web gets modified. The results show that energy-based data serve to evaluate the biodiversity status of cropping systems. They can be the basis for derivation of indirect status or impact indicators. In addition, the findings promote the understanding of ecosystem processes and the meaning of "intensity" in the context of ecologically sustainable land use. [ABSTRACT FROM AUTHOR]