Pesticide-free fields under minimum tillage and flower strips enhance carabid beetles and spiders through increased overwintering and spill over processes

Enhancing generalist arthropod predators in arable farming can contribute to pest control and pesticide use reduction, and be achieved through a diversity of management options at field and farm scales. Most studies however link management options to densities of circulating adults, which gives little insight into potential source-sinks dynamics and the occurrence of ‘source’ habitats enabling overwintering. In this study, we assessed the assemblages of emerging and circulating ground-dwelling carabids and spiders during four months in a continuous mosaic of pesticide-free winter-sown crops under contrasted tillage regimes (minimum vs. conventional tillage) and sown flower strips bordering fields. We detected clear patterns, with high in-field carabid and spider overwintering densities than in adjacent flower strips, which were rarely a preferred overwintering habitat. Our results nevertheless indicate that within both taxa, different species exhibit different responses and source-sink dynamics. Our results also demonstrate the key role of pesticide-free fields under minimum tillage, acting both as a high-quality overwintering site for some dominant carabid species and as a source habitat, as several predator species activity-density responded positively to the increased area of minimum tillage fields in the surroundings. We detected a comparable positive effect of the area of flower strips in the surrounding for some species, suggesting that these linear features could also act as a temporary refuge and source. These findings highlight that sustaining diverse communities of carabid beetles and spiders probably requires adopting several and complementary management options and that in-field farming practice represent a powerful lever to foster natural enemies populations. • High carabid and spider overwintering densities were found in pesticide-free fields. • Carabid beetles benefitted more from minimum-tillage fields than flower strips. • Flower strips sheltered numerous agrobiont and rare overwintering spider species. • Spillover towards fields occurred both from minimum-tilled fields and flower strips.