In Japan, Japanese native honeybee Apis cerana japonica coexists with the exotic honeybee A. mellifera. Apis mellifera is kept for beekeeping, and it forages wild flowers in the field, although it does not make feral colony in Japan. Both honeybees are generalist flower visitors and they are similar in morphology. We predicted that there are different foraging preferences related to flower color, nectar, and plant origin (endemic vs. exotic). We captured A. cerana japonica and A. mellifera on 20 plant species, including three exotics, under semi-natural conditions in Nara, Japan, from April to August 2012. We also measured flower color (color angle, brightness, and chroma), based on bee color vision (15 flower spp.), nectar volume (9 spp.), and nectar concentration (8 spp.). Flower color measurements were conducted with a digital camera set three color filters that transmittance properties are close to the spectral sensitivity curves of the three kinds of A. mellifera’s photoreceptors. We also measured nectar volume and concentration with microcapillary tubes and hand-held brix refractometer, respectively.
Results/Conclusions
Flowers colored white, pink, red, purple, and cream for human eyes were classified as bee-blue-green, and yellow was classified as bee-green, for bee eyes. These results accord with the color measurements with a spectrometer. Apis cerana japonica visited 14 species of plants and A. mellifera visited 11. The plant species that these two Apis species visited were overlapped, whereas A. cerana japonica more intensively visited native plant species than A. mellifera did. Both Apis species visited not only flowers that secrete nectar, but also those without nectar. We also detected different visitation patterns between A. cerana japonica and A. mellifera: A. cerana japonica more often visited flowers with smaller color angle (bee-blue-green), lower chroma, higher brightness, and nectars of higher concentration and smaller volume, while A. mellifera did flowers with larger color angle (bee-green), higher chroma, lower brightness, and nectars of lower concentration and greater volume. The differences at their foraging preferences may play an important role on their coexistence.