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The arthropod predator community of an organically cultivated 0.3 ha field was sampled by pitfall trapping during 1 year and analysed for small-scale spatial distribution patterns and their seasonal variation. Due to the small size of the study site, most of the investigated species were able to colonise the whole field. Ordination analyses revealed significant differences in community composition (i) between field centre and margin in summer and (ii) between field parts adjacent to meadows or conventionally cultivated arable land in all seasons. Results changed considerably if only adult carabids or spiders were used instead of the whole predator community.During summer the following significant differences in community parameters were found: (i) total catches in the centre were nearly twice as high as near the margin, (ii) predator richness did not differ between centre and margin while significantly more species were found close to meadows and (iii) evenness and heterogeneity were significantly higher at the margin versus the centre.The arthropod predator community even of a small field site showed distinct spatial distribution patterns with seasonal changes. Selecting appropriate taxonomic groups is crucial for the outcome of such studies and should be tailored to the aim of the investigation. [Copyright &y& Elsevier]

• Landscape had a lower effect on aphids and their parasitoids than fertilisation. • Fertilisation affected plants positively. • Fertilisation affected aphids and primary parasitism rate negatively. • Fertilisation had no effect on secondary parasitism rate. • H 2 ' and generality between parasitoids are affected by landscape and fertilisation. Agricultural intensification can impact agrobiodiversity in several ways such as in terms of population densities, community composition and food web interactions across all trophic levels. This effect can be investigated at two scales: field-scale and landscape scale. Here it was assessed how the impact of fertilisation (within field) and landscape complexity (within landscape) impact cereal aphid-primary parasitoid-secondary parasitoid systems in winter wheat in Germany. A newly developed molecular technique was used to quantify species-specific linkages between aphids, primary parasitoids and secondary parasitoids sampled in fertilised and unfertilised plots in either simple or complex structured landscapes. The results show a stronger effect of fertilisation than landscape complexity on the groups: fertilisation positively affected the crop plants while it negatively affected both the density of the cereal aphid Sitobion avenae and its primary parasitism rates whereas no effect on the level of secondary parasitism rates was observed. Landscape complexity had no effect on plants, aphids, as well as on primary parasitism rate. In case of secondary parasitism rate there was an effect in interaction with sampling date. Field identity accounted for the strongest effect on parasitoid community composition (10.6% of the variance) from all tested variables, while fertilisation and landscape complexity had almost no effect (1.1% and no effect). Nevertheless, a weak cascading effect of both environmental factors could be observed as the primary-secondary parasitoid network structure responded to both. However, these observed effects on food webs strongly depended on species identity, highlighting the need of species-level food web assessment. [ABSTRACT FROM AUTHOR]

Abstract: Organic farmers cannot use most commonly available synthetic insecticides to control crop pests and reduce economic losses due to pest outbreaks. Instead, they rely heavily on the activities of naturally occurring predators and parasitoids, particularly in broad-acre crops such as cereals. It is still unclear whether organic farms which typically support greater levels of biodiversity also experience greater levels of pest control services. We assess whether organic farming systems were better able to control cereal aphids due to a greater diversity and activity of naturally occurring parasitoid species. We anticipated greater parasitism rate of aphids in organic arable fields due to closer proximity to plants that provide resources for adult parasitoids and places that are suitable for overwintering, and the presence of alternate aphid hosts when cereals are absent. Aphids were collected from organic and conventional cereal crops, and screened for parasitoid DNA using diagnostic polymerase chain reaction (PCR). Aphid abundance was low across the season, however organic cereal fields had significantly greater aphid abundance. From the 1446 aphids screened we detected 12 parasitoid taxa. There was no difference in parasitism rate between the farming systems (org. mean mortality 20.9±3.3% s.e., con. 29.8±4.9%). Furthermore, there was no difference between farming systems in hyperparasitoid attack and multiparasitism rates, parasitoid richness and parasitoid community diversity. The most abundant species recorded on organic and conventional farms was the generalist aphid primary parasitoid Ephedrus plagiator. It appears that the extra plant diversity and greater area of semi-natural habitats on organic farms offer no advantage for increasing cereal aphid parasitoid diversity, at least at the aphid abundances encountered during the sampling period. [Copyright &y& Elsevier]