The contribution of CAP greening measures to conservation biological control at two spatial scales

To promote a more sustainable agricultural production, the European Commission implemented direct payments that require farmers to implement greening measures aimed at reducing negative effects of agriculture on the environment and biodiversity. These greening measures (including fallows and permanent grasslands) have been criticised for their potential inability to conserve biodiversity and promote associated ecosystem services. In this study, we investigate if the presence of old or recently established fallows and permanent grassland in the landscape are beneficial for the emergence, activity density and spillover of ground-running natural enemies and as a result aphid biological control in cereal fields. Lycosidae and Theridiidae were more numerous in fallows (emergence & activity density) compared to crop fields, while Staphylinidae and Linyphiidae showed opposite patterns. Spillover of Lycosidae was significantly higher from fallows into cereal fields, than between cereal fields. As a result of the opposite patterns in activity density in fallows between different groups of predators, a spillover from fallows did not result in a significantly higher aphid control in crop fields adjacent to them. A high proportion of permanent grassland in the landscape resulted in lower emergence of Linyphiidae and Carabidae. Our results support the assumption that a higher emergence and activity density of ground-running predators generally results in higher spillover to adjacent fields. However, patterns of emergence and activity density differed between individual natural enemy groups. Fallows, independent of age, can therefore act as source or sink depending on the focal predator group and more permanent grassland in the landscape can result in lower local emergence. Fallows at the local scale and permanent grassland at larger spatial scales therefore did not generally promote aphid biological control services provided by ground-running natural enemies.