Takahashi, Keigo, and Takao Itino. “Visitation Frequencies of Bumblebees and Swallowtail Butterflies to Flowers and the Nectar Sugar Concentration of Rhododendron Kaempferi and R. Japonicum in Mountains of Central Japan”. Journal of Pollination Ecology 21 (December 20, 2017). Accessed April 20, 2024. https://pollinationecology.org/index.php/jpe/article/view/438.