Given the predicted expansion of cities throughout the world, understanding the effect of urbanization on bee fauna is a major issue for the conservation of bees. The aim of this study was to understand how urbanization affects wild bee assemblages along a gradient of impervious surfaces and to determine the influence of landscape composition and floral resource availability on these assemblages. We chose 12 sites with a proportion of impervious surfaces (soil covered by parking, roads, and buildings) ranging from 0.06% to 64.31% within a 500 m radius. We collected using pan trapping and estimated the landscape composition of the sites within a 500 m radius and the species richness of plant assemblages within a 200 m radius. We collected 1104 bees from 74 species. The proportion of impervious surfaces at the landscape scale had a negative effect on wild bee abundance and species richness, whereas local flower composition had no effect. Ground‐nesting bees were particularly sensitive to the urbanization gradient. This study provides new evidences of the impact of urbanization on bee assemblages and the proportion of impervious surfaces at the landscape scale emerged as a key factor that drives those assemblages.

Bee hotels are increasingly set up by land managers in public parks to promote wild bee populations. However, we have very little evidence of the usefulness of bee hotels as tools to help the conservation of wild bees within cities. In this study, we installed 96 bee hotels in public parks of Marseille (France) for a year and followed their use as a nesting substrate by the local fauna. The most abundant species that emerged from bee hotels was the exotic bee species Megachile sculpturalis, representing 40% of all individuals. Moreover, we only detected four native bee species all belonging to the Osmia genus. More worryingly, we found a negative correlation between the occurrence of M. sculpturalis in bee hotels and the presence of native bees. One hypothesis to explain this result might be linked to the described territorial and aggressive behaviour of M. sculpturalis toward the nests built by the native fauna. This study raises the question about the usefulness of bee hotels for the conservation of native bees especially within cities harbouring high abundance of exotic bees. We provide here concrete advices to land managers to build bee hotels that can both host native bees and prevent the installation of M. sculpturalis.