Spinnen als Prädatoren von landwirtschaftlich schädlichen Blattläusen

Direct observations in grasslands and cereal fields near Zurich (Switzerland) have shown that aphids constitute an essentiel component in many spiders' prey. Spiders were observed to be predators of the agricultural harmful aphidsRhopalosiphum padi L.,Sitobion avenae F.,Metopolophium dirhodum Walck.,Hyalopterus pruni Geoffr.,Myzus persicae Sulz. andAphis fabae Scop.     

Planting materials for warm tropic potato production: growth and yield of transplanted seedlings or rooted cuttings and tuber materials in the field

Expansion of potato production in lowland tropical regions has been constrained by the lack of planting materials, given that adapted genotypes and suitable field management practices now exist.

The respective performance of transplanted materials (i.e., true potato seed (TPS) seedlings or rooted stem cuttings) produced in situ in the warm tropics were compared with that of genetically identical seedling tubers (tubers produced from seedlings) or seed tubers. Seed and seedling tubers had been previously produced under optimal cool conditions. Transplanted materials achieved lower maximum leaf area index than did tuber materials (1.3–2.2 vs. 2.7) but relative growth rates of cuttings and seedlings were greater. This was in part due to the greater net assimilation rate of cuttings and to greater leaf:stem ratio for both compared with plants originating from tubers. Stolon and tuber formation were greater in seed tubers than in cuttings and in seedlings versus seedling tubers. On average, seedlings produced 14 tubers per plant, apical cuttings 12, seedling tubers 8, and stem cuttings 6.

Tuber yields within a genotype were statistically similar for crops from seed tubers or cuttings and for crops from seedling tubers or seedlings. However, the proportion of marketable (i.e., > 3.5 cm diameter) tubers was approximately 12% less in the crops from seed tuber and seedlings compared with those from cuttings and seedling tubers, respectively. Within a genotype, the crop duration in the field was similar whatever the type of planting material. Maximum yields, at 23 t/ha in warm sites, were still below those of temperate potato crops, but could be achieved equally well with transplanted in situ-produced materials or imported cool-climate seed tubers.     

Analyse von Konkurrenzbeziehungen bei der Vegetationsentwicklung eines Grünlandbestandes mit Hilfe eines populationsdynamischen Modells

Analysis of Competitive Interactions in Grassland Stands by a Population Dynamical Model
The potential yield of permanent grassland is highly influenced by dynamical interactions within its plant species. The possibility to recognize and to quantify these interactions opens a wide field of applications in grassland management. A mathematical simulation model was chosen to meet this aim. The base of the model is a simple population dynamic arrangement. The competition between the species or species groups is described by a linear function. A long time trial is used as a data base. The productivity and the floristic changes in this trial were recorded for 12 years. By reason of the limited data base the species were aggregated into 5 groups consisting of species with similar behaviour. The model proofed to be useful, to simulate the important interactions between the species groups and to quantify their significance with regard to the dynamic development of the grassland. Because of the small data set used in the sample, the model is limited in its validity. The model can be improved by incorporation of a larger data base.     

Anthelmintic activities of ivermectin against immature and adult Dictyocaulus viviparus

Eighteen calves about 3 months old were inoculated with 3,000 Dictyocaulus viviparus infective larvae. Three groups of 6 calves each were formed. Thirteen days after inoculations, 3 of the 6 group 1 control calves were given vehicle subcutaneously (SC) and the group 2 calves were given ivermectin at the dose rate of 200 micrograms/kg, SC. Thirty-five days after inoculation, the remaining 3 calves in group 1 were given vehicle SC and the group 3 calves were given ivermectin at the dose rate of 200 micrograms/kg, SC. Necropsies were performed 42 days after inoculations. A total of 474 D viviparus was recovered from the group 1 control calves, whereas none was recovered from the calves treated when the nematodes were in the 4th stage of development (group 2) or adult stage (group 3).     

Extrasolar planets: constraints for planet formation models

Since 1995, more than 150 extrasolar planets have been discovered, most of them in orbits quite different from those of the giant planets in our own solar system. The number of discovered extrasolar planets demonstrates that planetary systems are common but also that they may possess a large variety of properties. As the number of detections grows, statistical studies of the properties of exoplanets and their host stars can be conducted to unravel some of the key physical and chemical processes leading to the formation of planetary systems.