Fields of winter wheat on organic and conventional farms were sampled for weeds and invertebrates in June/July in 1990 and 1991. Organic fields were paired with adjoining conventional ones and their invertebrate fauna compared with a D-vac vacuum suction sampler. Weed counts showed greater percentage cover of broad-leaved weeds in organic fields than in conventional ones, with three times as many species present where herbicides were not used.Significantly higher densities of nematoceran and acalypteran Diptera, Hemiptera (especially aphids), aphid-specific predators, parasitic Hymenoptera and cryptophagid and cantharid Coleoptera were found in conventionally grown fields. Significantly higher densities of weevils, spiders, springtails, plant hoppers and sawfly larvae were found in organic fields. Reasons for these differences or the lack of them are discussed. SED = approximate standard error of the difference. (NS = not significant, ' = P < 0.05, ** = P<0.101,

Summary1. The spatial dynamics of farmland invertebrates can provide essential information relevant to their management for pest control and biodiversity conservation in sustainable agriculture. Carabid beetles are one of the most important groups contributing to biological control in arable fields. Previous studies have focused on spatial dynamics within single fields and years. In this study we examined their larger scale, long-term dynamics, thereby taking into account the impact of changes in crop rotation and the influence of field size. 2. The spatial distributions of four beetle species were investigated at an unprecedented spatial scale in a grid of 973 pitfall trap locations across six fields encompassing 64 ha of arable land. Week-long trapping was conducted four times in the first year and twice in the two following years. 3. All species showed strong aggregation but the size and location of patches differed among species. The distribution of Pterostichus melanarius was stable within and between years, with a single large patch close to the field boundaries. Patches of Poecilus cupreus were also located close to field boundaries but their location changed between years. Pterostichus madidus and Philonthus cognatus distributions extended across field boundaries and were less stable, with patch locations changing between years. 4. Synthesis and applications . The spatial extent of a population patch for a given species was species-specific. Species overwintering in field boundaries remained in proximity to these throughout the summer, whereas patches of mid-field overwintering species were more extensive. Patches were generally stable within years but varied for some species between years. Species therefore differ in their response to crop management practices and consequently blanket management approaches for these important generalist predators of crop pests are inappropriate. For spatially stable species (e.g. Pterostichus melanarius ) it may be possible to determine their specific habitat requirements and to devise predictive and protective measures to preserve populations or manipulate them at the farm-scale. More mobile species may be better at responding to pest aggregations at the farm-scale. However, operations that deplete populations, e.g. soil cultivations, should be spatially and temporally desynchronized at the farm-scale to conserve populations and enable functional biocontrol.

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In many European countries agri-environment funding can improve ecosystem services, including the adoption of conservation biocontrol, through the creation of habitats that encourage beneficial arthropods. Predatory beetles are amongst the most numerous and diverse arthropods present in arable fields. The primary ecosystem services provided by predatory beetles are in biological control and food chain maintenance as they are a key resource for many higher organisms. However, to be effective biological control agents, able to respond quickly to wherever a pest infestation occurs, then they must be sufficiently abundant and widely distributed. Conservation biocontrol utilising predatory beetles has focussed on the impact of species that overwinter in adjacent field boundaries, although those overwintering within fields are often more abundant. If the abundance and distribution of predatory beetles is to be maximised then further knowledge of their spatial dynamics is required to ensure habitats are arranged appropriately. The spatio-temporal dynamics of boundary and field overwintering species was measured across 64 ha encompassing six fields and for three consecutive years using a grid of 973 pitfall traps. Boundary species were more numerous in spring (May and June) whereas more field species were captured in July. The species composition was comprised of relatively few taxa. Boundary species occurred in small patches that were distributed across the fields in spring, but were only found close to the margins in July. Patches persisted in some locations over two years. Field species occurred in larger patches, spread across particular fields and these were stable within years and to some extent between years. Game-cover strips were attractive to boundary species in the spring and summer and did not effect predator distribution in the adjacent crop.