Origin(Koishimaru(Sericultural Experiment Station of Japan))
Neriki Kizo said that Koishimaru had existed among the Shinshu strains since the era of Kyoho(1716-1736). It was said that Koishimaru was bred from Kanamaru race that was kept by a man named Maruyama at Koisawa of Kai(Yamanashi Prefecture at the present time). The Koishimaru was easy to rear. The cocoon was short circular shaped. And it was said that Odanaka Genemon selected the race which was circular shaped like peanut from Matamukashi race, and named it "Koishimaru". It was written in "Kaiko No Shuruigo" as follows:
Odanaka Genemon of Nagano Prefecture obtained the especially good quality race from Chunyorai in the beginning of Kansei era(1789-1801). It had large healthiness of larvae and evenness in exuviation. The cocoon was slightly small, but had glossy face, good reelability and hard cocoon shell. Odanaka Gengoro said that Koishimaru changed the cocoon shape for a long time. The cocoon shape was small at first, and grew slightly larger in the era of Tenpo(1830-1844). Namely, it was about 450 grains/Sho(1.8l). And then, it was about 370 grains/Sho(1.8l) in the 1st year of Meiji(1868), about 300 grains /Sho(1.8l) in the 20-30the year of Meiji(1887-1897) and about 270 grains/Sho(1.8l) in the end of the Meiji era(1912). The nature of the silkworm had not changed for those long periods. It had large healthiness of larvae. The rate of cocooning was large, though the intake of mulberry leaves was small. Namely, Koishimaru was excellent race.
And it was written in "Kaiko No Shuruigo" that Furuya Tansaku of Yamanashi Prefecture had reared Koishimaru since the 9th year of Meiji(1876). The cocoon was 300 grains/Sho(1.8l) in size and was uneven in shape. But, after selecting the eggs, bodies of larvae, mother moths and parent silkworms for hybridization, the excellent race that had large healthiness of larvae and high cocoon quality was developed. There are a variety of views about the origin of Koishimaru. The opinion of Odanaka Genemon, however, is dominant. One way or the other, Koishimaru was considerably popular among sericulturist in the era of Kansei(1789-1801). And then, it was widely used again in the era of Tenpo(1830-1844) to Kaei(1848-1854). And, afterwards, it was widely used through the Meiji era(1868-1912).
In conclusion, these facts showed that Koishimaru was the excellent race for practical use. Koishimaru had been used since around the 20th year of Meiji(1887). Afterwards, as excessive miniaturizing cocoon shape of Koishimaru was promoted in around the 35th year of Meiji(1902), the cocoon became too small shaped, deep wrinkle faced, bad reeled and bad in cleanness and neatness. The improvement of cocoon for making big shaped and shallow wrinkle faced was unsuccessful, because of yielding of unhealthy silkworm and getting out of cocoon shape. Accordingly, Koishimaru, the race of small shaped and white colored cocoon, was replaced by Matamukashi and Aojuku strains.
Koishimaru was widely used in Japan in the Taisho era(1912-1926), however, the improvement of the race did not move forward. Koishimaru did not exceed Matamukashi and Aojuku in the needs of the times.
Production of Koishimaru in the 1st year of Taisho(1912): 89,000 moths
(It is presumed that one moth will hatch 400 eggs.)
1) Eikichi HIRATSUKA(1961) : History of Modern Silkworm Race Breeding, Dainippon Silk Foundation, Silk Science Research Institute, pp236
2) Eikichi HIRATSUKA(1969) : Genealogy of Japanese Silkworm Races for Practical Use, Dainippon Silk Foundation, Silk Science Research Institute, pp335