Exploring bee functional trait response to the agro-environment: a possible contribution to the future design of a farm-level indicator

Pollination is essential for agriculture and food production. In Europe, the upcoming Common Agricultural Policy (CAP) will assess pollinator status and the effectiveness of Rural Development Programmes (RDPs) in supporting pollinator populations. While wild bees are recognized as key contributors, more clarity is needed on the ecological, agricultural and biological factors crucial for their conservation. This study aims to support the design of an indicator reflecting the impact of RDP measures on bees by selecting crucial variables. We conducted field monitoring in Emilia-Romagna (Italy) across five farms with different regimes (conventional and organic) and landscape contexts (altitude and complexity). We analysed 36 variables at transect level, including agri-environmental (landscape, farming and geography) and bee-related biodiversity (taxonomy and eco-functional traits). Agri-environmental data came from databases and farmers, while biodiversity data derived from field monitoring. Our findings suggest that agri-environmental variables related to altitude and farm management can consolidate these two factors into effective proxies for broad landscape structure and composition. Notably, eusocial bees, especially Halictus and Lasioglossum species, responded strongly to altitude, being more abundant in lowland farms. Some variables we combined under the eco-functional group, such as phenology, distribution in Italy, and rarity also emerged as promising candidates for a future biological indicator based on wild bees. This approach aligns with evolving European agri-environmental policies, which emphasise the protection of pollinators and the promotion of sustainable farming practices, with RDPs playing a central role in biodiversity monitoring and enhancement.