Insights into the ecology of early leaf-cutter bees revealed through synchrotron X-ray tomography

During the Paleogene, bees diversified extensively after expanding from tropical regions into northern forests surrounding the future Baltic Sea, evolving alongside diverse angiosperms. Most fossil bee diversity is preserved in amber, which captures morphology but rarely behavior or ecology. Using synchrotron X-ray imaging, we describe a new leaf-cutter bee species, † Protolithurgus acarophorus sp. nov., from two specimens in Baltic amber. This is only the second known record of the extinct tribe †Protolithurgiini, which displays both ancestral and derived megachilid traits. The holotype preserves exceptional anatomical detail and reveals ecological insights, including compacted floral rewards in the hind-leg scopa, a pollen-carrying strategy rare in living Megachilidae. We also document the first fossil bee-mite association, suggesting unspecialized kleptoparasitic interactions, and reconstruct thoracic musculature dimensions. Together, these findings provide rare evidence of the foraging ecology, parasite relationships, and biomechanics of the earliest leaf-cutter bees.