Floral resource maps: a tool to explain flower-visiting insect abundance at multiple spatial scales

International audience

anglais. Context : Flower-visiting insects depend on floral resource availability from both cultivated and semi-natural habitats in agricultural landscapes. Landscape studies exploring insect abundance mainly focus on land cover maps without considering plant species within. Highlighting the functional role of landscapes through the potential floral resources they provide is an overlooked innovative approach. Objectives : We aimed to identify traits of floral communities that are important, across several spatial scales, for explaining the abundance of flower-visiting insects. Mapping and quantifying potential floral resources according to their attractivity, accessibility and profitability in both crop and non-crop habitats was performed to gain insights into flower-vising insect requirements. Methods : We translated land-cover maps of 39 landscapes of 250 m, 500 m and 1000 m radius into potential floral resource maps, using pre-existing vegetation surveys and floral traits databases. In the centres of the landscapes, the abundance of flower-visiting insect groups (domestic and wild bees, bumblebees and hoverflies) were recorded in organic winter cereal fields. We then fitted Generalized Linear Models (GLMs) to investigate the effects of flower trait variables (pre-selected with conditional random forests) at both field and landscape scales on the abundance of each flower-visiting insect group. Results : Floral resource maps explained the abundances of flower-visiting insect groups. Small wild bees (< 1 cm) responded positively to the relative amount of attractive and accessible floral resources at 250 m. The abundance of domestic bees and bumblebees was positively correlated with the relative amount of high nectar producing plants at 1000 m. The abundance of hoverflies was positively influenced by the relative amount of actinomorphic flowers (i.e., those with radial symmetry), at 1000 m.Conclusion : Resource maps could explain flower-visiting insect abundances, identify which category of floral resources organisms require, and determine in which habitat types these resources prevail. These results open a new research area related to managing the environment by optimising floral resources for flower-visiting insect conservation and pollination maintenance.