Organic agricultural landscapes promote the conservation and diversity of cavity-nesting solitary bees

Solitary bees are important pollinators and maintain biodiversity in agricultural landscapes, yet their populations are declining due to habitat loss, intensive farming and pesticide use. Organic farming offers a sustainable alternative to conventional systems, benefiting pollinators through reduced chemical inputs and greater habitat diversity. While effects on social bees such as honeybees and bumblebees are well documented, little is known about how farming practices and landscapes influence communities of cavity-nesting solitary bees. We investigated these effects across 17 sites in Germany using standardized cavity nests (“bee hotels”). This approach enabled us to assess number of brood cells, species diversity, the abundance of females and males and the proportion of undeveloped bees, revealing how solitary bee populations respond to different farming systems and landscape features. Landscape composition was analyzed within a 500 m radius to quantify the extent of organic farming and forest cover within the bees’ foraging range. We found that organic farming had a beneficial effect on solitary bee brood cells and female production. Organic landscapes were positively correlated with increase in bee abundance, species richness, and diversity, while forest cover had no strong effects. Still at the landscape level, the abundance of both females and males increased with the extent of organic farming, while at the local scale, the abundance of both sexes was higher in organic farms than in conventional sites. The findings highlight the potential ecological benefit of organic farming in supporting cavity nesting solitary bee populations and underscore its potential to mitigate biodiversity loss in agriculture. • Organic farming enhances cavity-nesting solitary bee communities, increasing abundance, species richness, and diversity across agricultural landscapes. • Both female and male solitary bees respond positively to organic management, with higher abundances at local (farm) and landscape scales. • Landscape-level organic farming extent is a key driver of solitary bee population metrics Forest cover showed no strong influence on cavity-nesting solitary bee abundance or diversity in agricultural settings. • Organic farming has clear potential to mitigate biodiversity loss, supporting solitary bees in intensively managed agroecosystems.