Question: What is the smallest of the four main islands of Japan where the Acronicta digna moth can be found?

Context articles: Acronicta digna
Acronicta caesarea
Shikoku
Acronicta subochrea
Miller (moth)
Acronicta parallela
Acronicta hasta
Invasion of Shikoku (1585)
Jost Van Dyke
Takydromus tachydromoides

Acronicta digna is a moth of the Noctuidae family.
 It is found in the Korean Peninsula, China, Japan (Honshu, Shikoku, Kyushu), the Russian Far East (Primorye, southern Khabarovsk, Amur region) and Taiwan.
Acronicta caesarea was a species of moth of the Noctuidae family, it is now considered a synonym of "Acronicta retardata".
 It is found in North America, including New Jersey, New York and Pennsylvania.
Shikoku (四国 , "four provinces") is the smallest (225 km long and between 50 and wide) and least populous (3.8 million as of 2015 ) of the four main islands of Japan, located south of Honshu and east of the island of Kyushu.
 Its ancient names include "Iyo-no-futana-shima" (伊予之二名島 ), "Iyo-shima" (伊予島 ), and "Futana-shima" (二名島 ).
 The current name refers to the four former provinces that made up the island: Awa, Tosa, Sanuki, and Iyo.
The Puzzling Dagger Moth ("Acronicta subochrea") was a species of moth of the Noctuidae family, it is now considered a synonym of "Acronicta hamamelis".
 It is found in North America, including New York, Virginia, Iowa and Florida.
The miller ("Acronicta leporina") is a moth of the family Noctuidae.
 It is found throughout Europe apart from the far south-east.
The range extends from the South of Spain, Central Italy and Bulgaria to Scotland and Central Scandinavia, crossing the Arctic circle in Finland and Norway.
 Outside Europe it is only known in North Africa.
 In the Eastern Palearctic and the Nearctic ecozone it is replaced by "Acronicta vulpina," (Grote, 1883) formerly known as "Acronicta leporina" subspecies "vulpina"
The Parallel Dagger Moth ("Acronicta parallela") is a species of moth of the Noctuidae family, it was considered a synonym of "Acronicta falcula" but reinstated as a valid species in 2011.
 It is found in North America, including Colorado and Oklahoma.
The forked dagger moth, speared dagger moth, cherry dagger moth or dart dagger moth ("Acronicta hasta") is a moth of the Noctuidae family.
 It is found in the eastern deciduous woodlands, ranging west across southern Saskatchewan and Alberta into central southern British Columbia, south to Tennessee, Wisconsin and Kansas.
In the 1585 invasion of Shikoku, Toyotomi Hideyoshi seized Shikoku, the smallest of Japan's four main islands, from Chōsokabe Motochika.
Jost Van Dyke (sometimes colloquially referred to as JVD or Jost) is the smallest of the four main islands of the British Virgin Islands, measuring roughly 8 km2 .
 It rests in the northern portion of the archipelago of the Virgin Islands, located in the Atlantic Ocean and Caribbean Sea.
 Jost Van Dyke lies about 8 km to the northwest of Tortola and 8 km to the north of Saint John.
 Little Jost Van Dyke lies off its eastern end.
Takydromus tachydromoides, the Japanese grass lizard, is a wall lizard species of the genus "Takydromus".
 It is found in Japan.
 Its Japanese name is 'kanahebi' (カナヘビ).
 'Hebi' means 'snake' in Japanese, although this lizard is not a snake.
 There are three lizards found in the four main islands of Japan.
 The other two are the Japanese gekko (also, Schlegel's Japanese gekko, "Gekko japonicus"), and the Japanese five-lined skink ("Eumeces latiscutatus", also "Plestiodon latiscutatus"; this skink shows five lines only as a juvenile).