Positive effects of local and landscape features on predatory flies in European agricultural landscapes

Provisioning of suitable habitats for predatory insects in agricultural landscapes can improve natural pest control and hence the sustainability of agriculture. Apart from Syrphidae, the spatial ecology of predatory flies remains little studied. We investigated the response of Dolichopodidae, Empididae and Syrphidae to local features of seminatural habitats and to the composition of the surrounding landscape. We sampled adult predatory flies with pan traps in 183 field-bordering seminatural habitats along gradients of landscape composition in Italy, Germany and Switzerland. Local habitat type, the composition of the surrounding landscape and proximity to watercourses affected the abundance of predatory flies. Across countries, Empididae and Syrphidae were more abundant in woody (i.e. forests and in particular hedgerows) than in herbaceous habitats, whereas Dolichopodidae had lowest abundance in forests. The abundance of Dolichopodidae in Italy and Empididae in Germany were furthermore enhanced by the proximity of watercourses. Abundance of Dolichopodidae increased with the proportion of seminatural habitats in 1 km radius. Empididae were more abundant in landscapes with higher proportion of forests. We identified hedgerows as favorable habitats for predatory flies in agricultural landscapes. Moreover, our study reveals the importance of proximity to watercourses, which has rarely been considered when studying natural enemies of pests in agroecosystems. The varying responses indicate that preserving or restoring habitat-diverse, heterogeneous landscapes guarantees high numbers of predatory flies across families.