Using a multi-scale approach to examine the effects of field margins and landscape features on predatory carabid communities in crop fields

Carabid beetles are major predators in agro-ecosystems. The composition of their communities within crop environments governs the pest control services they provide. Field margins and landscape features are known to affect carabid community composition, yet evidence is currently lacking that can be used to support land management decisions targeted at optimising predation services at the farm scale. We used experimental margins across a farm site to test carabid communities in crop areas, margins, and adjacent habitats sampled in the summer. We used novel subterranean trapping with standard pitfall trapping, to distinguish above ground and below ground activity of adults and larvae in different farm habitats. Crop type was the major influence on carabid communities in crop areas. This was followed by landscape influences in terms of adjacent habitat and boundary features, and whilst significant, margin type explained relatively little variance in summer carabid communities in-field. Trap type revealed differential activity by species. Responses to crop type, landscape factors, and margin type also varied by species. Overall, abundances were less in association with margins than control of no margin. Particularly, abundances were lower in the spillover zone adjacent to grass margins, and in the wildflower margins themselves. Carabid larvae showed notably higher abundances in association with an absence of field margins. Measures to boost key carabid species in crop areas should be considered at a farm scale, taking into account potential barrier effects, and potential buffer effects.