Effects of landscape composition on carabids and slugs in herbaceous and woody field margins

• We investigated habitat and landscape effects on carabid beetles and slugs.
• Herbaceous semi-natural habitats higher numbers of carabids than woody ones.
• Predatory carabid abundances tended to increase in structurally rich landscapes.
• Pest slugs responded differently to semi-natural habitats and landscape composition.
• Our results indicate that Arion spp. could be controlled by carabids.

Field margin vegetation can provide shelter and complementary resources for both agricultural pests and their natural enemies. Thus, simplification of agricultural landscapes can either reduce or enhance pest pressure, depending on the habitat preferences and mobility of the relevant organisms. The promotion of field margin vegetation that selectively enhances natural enemies but not pests, would be desirable for the optimization of pest control services. Unfortunately, the majority of existing studies on the effects of field margins and landscape focussed on either natural enemies or (less often) on pests, but very rarely on both. This study evaluates the influence of herbaceous and woody semi-natural habitats and landscape composition on carabid beetles as natural enemies of the pest slugs Deroceras reticulatum and Arion spp. We found effects of semi-natural habitats on carabids and slugs at the field and landscape scale. While most carabids and D. reticulatum preferred herbaceous over woody habitats, Arion spp. oppositely showed highest activity-densities in woody habitats. With increasing amount of semi-natural habitats in the landscape activity-densities of predatory carabids tended to increase while activity-densities of Arion spp. decreased. This, and a negative correlative trend between Arion spp. and carabid densities indicate favourable conditions for natural slug control by carabids in landscapes with a high amount of semi-natural habitats. Our results confirm that different response of pest and their natural enemies to the landscape context can indeed alter the predator-prey ratio. However, our study also revealed that pests such as Arion spp. and D. reticulatum prefer different types of field margins, complicating the optimization of agricultural landscapes for pest management.