Effects of undersowing maize with a diverse annual flower mixture on insect abundance and diversity

• Undersowing maize enhances flower-visiting wild bee abundance and diversity. • Ground beetles showed no significant response to the undersowing system. • Rove beetle activity density was increased, while diversity remained unchanged. Biodiversity is declining globally, largely driven by anthropogenic land use. In Germany, maize occupies a large proportion of arable land and its cultivation is often viewed critically from an ecological perspective. Maize undersown with a diverse annual flower mixture represents a novel approach aimed at improving biodiversity. We investigated the effects of this undersowing system on the abundance, species richness, and diversity of wild bees (Hymenoptera: Apoidea: Anthophila), ground beetles (Coleoptera: Carabidae), and rove beetles (Coleoptera: Staphylinidae). We hypothesized that the flower mixtures would positively affect these insect groups. Insect sampling was conducted at four trial sites in 2022 and eight trial sites in 2023 across Baden-Württemberg, Germany. At each trial site, two cropping systems were compared: pure maize and maize intercropped with a flower mixture, cultivated on adjacent plots within the same experimental field. Flower strips implemented at six trial sites in 2023 served as additional reference, representing an established conservation measure. Undersowing maize with a flower mixture significantly increased wild bee abundance, species richness, and Shannon diversity index H‘ (SDI) compared to pure maize. However, ground beetles showed no significant differences between cropping systems. Rove beetles exhibited an intermediate response, with activity density significantly higher under undersowing, while species richness and SDI remained unaffected. Flower strips supported even higher diversity per unit area across all insect groups, as well as higher abundance of wild bees and rove beetles. However, when considering a scenario with 5 % flower strip coverage, abundance was lower compared to undersown maize. The positive effect of the undersowing system – especially for wild bees – highlights its potential to enhance habitat quality in agricultural landscapes and to complement more traditional conservation measures such as flower strips. To maximize their benefits for biodiversity, such systems should be integrated into a broader, landscape-scale conservation strategy.