E. China, Taiwan, Japan
Honey produced from this plant is toxic. 
"P. japonica is known as “Ma-Zui-Mu” in Chinese, which originated from the fact that horses became intoxicated after eating the leaves and branches, indicating their anesthetic effects. In addition, P. japonica is a well-known Traditional Chinese Medicine to treat tinea and scabies." 
"[I]t is urgent to find novel analgesics with high efficiency and low toxicity. Natural products from medicinal plants are tremendous sources of new drug candidates... and morphine, a μopioid receptor agonist, is the first naturally occurring analgesic. The Ericaceae plants are famous not only for their beautiful flowers but also for the structurally novel diterpenoids with significant biological activities..." 
Fifteen grayanane diterpenoids were isolated from P. japonica, and "all the isolated grayanane diterpenoid glucosides showed significant analgesic activities." 
"Pieris brassicae is a pernicious and oligophagous insect, with the larvae feeding dominantly on members of the Brassicaceae family.20 The adults feed on the sap of a variety of crop and vegetable plants, thus resulting in great economic loss to farmers." Ten compounds isolated from P. japonicus "showed potent antifeedant activity against P. brassicae." 
 Zheng, G., Zhou, J., Huang, L., Zhang, H., Sun, N., Zhang, H., ... & Yao, G. (2019). Antinociceptive grayanane diterpenoids from the leaves of Pieris japonica. Journal of Natural Products, 82(12), 3330-3339.
 Zheng, G., Jin, P., Huang, L., Sun, N., Zhang, H., Zhang, H., ... & Yao, G. (2020). Grayanane diterpenoid glucosides as potent analgesics from Pieris japonica. Phytochemistry, 171, 112234.
 Chen, X. Q., Gao, L. H., Li, Y. P., Li, H. M., Liu, D., Liao, X. L., & Li, R. T. (2017). Highly Oxygenated Grayanane Diterpenoids from Flowers of Pieris japonica and Structure–Activity Relationships of Antifeedant Activity against Pieris brassicae. Journal of agricultural and food chemistry, 65(22), 4456-4463.
 Scott, P. M., Coldwell, B. B., & Wiberg, G. S. (1971). Grayanotoxins. Occurrence and analysis in honey and a comparison of toxicities in mice. Food and Cosmetics toxicology, 9(2), 179-184.