Importance of arthropod pests and their natural enemies - HGCA

the margins may not benefit pest control directly within the field, although they may reduce pests utilisingmargins. Araneae especially were shown to have different species composition in margins compared to thecrop (Kromp & Steinberger, 1992) while some carabid species, especially spermophagous species, remainstrongly associated with margins (Cardwell et al., 1994; Holland et al.,1999; Thomas et al., 2001;). Furtherinformation on the species composition of sown margins and the impact of cutting, scarification andherbicides will be gained from the SAFFIE project.The establishment of grassy margins is one the most widely adopted ES options (Boatman, et al., 2007), buttheir value for natural enemies has received only limited attention in the UK. In the Arable Stewardship PilotScheme, the abundance and species richness of carabids was the same grassy margins, beetle banks and theopen field, however, the community composition differed reflecting the differences in the environmentalconditions and preferences of individual taxa (Gardner et al., 1999). Grassy margins were recommended as away of enhancing carabid diversity in cereal dominated landscapes (Anon, 2001). The margins were,however, relatively new at the time of sampling and further changes in their invertebrate composition wouldbe expected (Thomas & Marshall, 1999). In the Netherlands, emergence traps placed in grassy marginsrevealed that during the growing season the fauna was comprised mostly of dipteran flies, followed byparasitic wasps, spiders, carabid beetles and staphylinid beetles (Canters & Tamis, 1999). Numbers ofStaphylinidae abd Carabidae were higher in the winter showing that they were used as an overwintering site.Mowing lead to increases in parasitic wasps, hoverflies and Staphylinidae, but also aphids. Spiders werereduced by mowing.Potential to improve biocontrolMost biocontrol related research on uncultivated habitats has focussed on determining whether naturalenemies were enhanced in the adjacent crop rather than the impact on the pest. Furthermore, because therelationship between the level of predation and abundance of natural enemies remains unquantified, knowingthe abundance of natural enemies does not allow their impact to be determined.Natural enemies overwintering in field margins were shown to move outwards from field margins in twoways. For those species that walked a wave of dispersal was identified, but those that flew achieved rapidcoverage across the whole field (Coombes & Sotherton, 1986; Kromp & Nitzlader, 1995). Even so thedistribution of natural enemies across fields is rarely even, with most showing some degree of aggregationinto patches (Holland et al., 1999, 2004b, 2005). Moreover, as the ratio of edge to field will decrease as fieldsize increases, so the impact of boundary overwintering natural enemies would be expected to diminish.When the distribution of boundary overwintering ground-active predators (Carabidae, Staphylinidae andLycosidae) was examined in the 3D Farming project, they were found throughout the smaller study fieldsduring May and June where the distance to the field centre from the boundary was no more than 150 m.However, they did not penetrate the larger fields and most patches were located within 100 m of the fieldboundary. By July, most were located within 60 m of the field boundary (Powell et al., 2004; Holland et al.,49