"Ambulyx sericeipennis tobii Inoue was synonimyzed with A. s. sericeipennis Butler by Kobayashi, Wang and Yano (2006). However, tobii is distinguished from sericeipennis in appearance as follows: a little smaller than the nominotypical subspecies (expanse of male 95-102 mm, 111-112 mm in the nominotypical subspecies); head, thorax and abdomen slightly tinged with brown; patagia deeper greenish; forewing rather pale brownish instead of grayish in the nominotypical subspecies. Thus I treat here tobii as an independent subspecies of sericeipennis (stat. rev.).
As the population of Hokkaido is clearly different from subsp. tobii, it is described as a new subspecies as follows.
Ambulyx sericeipennis pirika ssp. nov.
Same as in expanse to subsp. tobii. Head, thorax and abdomen darker. Patagia darker, more remarkably tinged with brown. Forewing more blackish, with maculation slightly tinged with green. Hindwing darker, rather blackish, with median transverse band rather less obvious. The male genitalia are identical with those of subsp. tobii.
Holotype. ♂, Japan, Hokkaido, Kamikawa, Sounkyo, 28. vi. 2018, Y. Kishida leg., preserved in the University Museum, The University of Tokyo, Tokyo. Paratypes. Same data as holotype, 8♂1♀. Kamikawa, Aizankei, 1♂, 1-4. vii. 2016 (Y. Kishida). Rumoi, Chibaberi, 2♂1♀, 5. vi. 1914 (H. Nonaka). Obihiro, Iwanaisenkyo, 1♂, 7. vi. 2016 (A. Nakajima). Kamishihoro, Nukabiragensenkyo, 6♂, 30. v. 2015 (A. Nakajima). Yufutsu, Shimukappu, 1♂, 6. vi. 1999 (H. Kobayashi). Sapporo, Jozankei, 2♂, 23. vi. 2005 (H. Kobayashi).
Distribution. Japan (Hokkaido).
Etymology. The subspecific name "pirika" means good or beautiful in the language of Ainu people, an ethnic group of in Hokkaido."