Photoreceptor recordings reveal remarkable acuity in small solitary bees compared with larger species

Bees rely strongly on visual cues for essential tasks such as avoiding predators, targeting mates, and navigating their environment. However, physiological measures of photoreceptor acuity in bees remain scarce. Here, we used intracellular recordings in light-adapted eyes to estimate photoreceptor receptive fields (angular sensitivity, Δρ) and detectability thresholds in compound eyes of both sexes in four bee species. We recorded from the bumblebee Bombus terrestris; two closely related but biogeographically distant apid species, Anthophora quadrimaculata and Amegilla murrayensis; and the solitary species Anthidium manicatum. To place these physiological measurements in an optical context, we quantified interommatidial angles (Δφ) in corresponding eye regions to assess spatial sampling resolution and compared our results with previously published data for both sexes of Apis mellifera. Photoreceptors of both sexes and all species show significantly better resolution than female forager honeybees, with highest acuity in both sexes of Amegilla and in males of Anthophora and Anthidium. Despite small body size, Amegilla shows impressive photoreceptor detectability thresholds, matched only by much larger honeybee drones. Optical sampling revealed very small interommatidial angles (Δφ_V < 1°), indicating high spatial resolution, with more than twofold variation across species and particularly high resolution in solitary bees and honeybee drones. By correlating photoreceptor acuity with maximal corneal facet diameter and distal rhabdom diameter, we reveal morphological adaptations underpinning physiological performance. These findings provide evidence for functional adaptation in early visual processing across bee species and highlight mechanisms supporting the detection of moving targets.