(Fig. 20)
Geometra dieckmanni: Beljaev & Mironov 2019: 253 (Sakhalin).
Material examined. 2 ♀, S Kholmsk, 17.VIII.2017, 27.VII.2021; 5 ♂, 1 ♀, Yasnomorskoe and Sokhonda mount., 18, 20, 26.VII.2019; 1 ♂, Yasnomorskoe and Sokhonda mount., 11–13.VIII.2020.
Distribution. Russia (S RFE: SW Sakhalin, S Kurils—Kunashir, S Khabarovskii Krai, S Amurskaya Oblast, Primorskii Krai; SE Siberia: extreme SE Zabaikalskii Krai), Japan (Hokkaido, Honshu, Shikoku, Kyushu, Tsushima), North Korea, South Korea, NE China.
Remarks. The finding of G. dieckmanni in Sakhalin significantly expands its distribution range to the northeast. The host plants of the larvae are various species of Quercus (Fagaceae). In Sakhalin the moths fly from mid-July to mid-August, the species develops in one generation.