「はくぎん」は繭糸繊度が2デニールを下回る極細繊度品種であるが，蚕種製造における問題点として母蛾の産卵性が悪いことが指摘されたため，繭糸繊度を維持しながら産卵性を改善した中516号×中517号（愛称:「白麗」）を育成した。しかしながら「白麗」の欠点として，登蔟性が悪いことが明らかとなったため，登蔟性を改善するための選抜法の開発と品種改良を行った。白麗の原種である中516号と中517号を樹脂製の山型蔟を3段重ねて自然上蔟させ，上段に結繭した個体のみを選抜した。選抜を複数世代で行った結果，上段に結繭する個体数が増え，それらの交雑種である「白麗」においても登蔟性の向上が見られた。

 The microsporidium, Pleistophora sp. NIS-M27, is a representative strain isolated from silkworms in rearing rooms, and Pleistophora sp. NIS-M27 along with Nosema bombycis NIS-001 and Vairimorpha sp. NIS-M11 is a standard strain for pébrine inspection. However, the molecular phylogenetic analysis of Pleistophora sp. NIS-M27 has not yet been performed. Thus, we performed a molecular phylogenetic analysis of Pleistophora sp. NIS-M27 (LC649920) based on the small subunit ribosomal RNA gene sequence. Additionally, we re-examined the relationship between small spore-producing microsporidian strains reported in previous studies and Pleistophora sp. NIS-M27. Phylogenetic analysis suggested the classification of Pleistophora sp. NIS-M27 into the genus Endoreticulatus. In particular, Pleistophora sp. NIS-M27 showed a high genetic homology of 99.83% with Endoreticulatus sp. BM-2018-2, and no other strain showed high genetic homology with the strain derived from the rearing room. This suggests that there are no strains genetically close to Pleistophora sp. NIS-M27 in the rearing room in recent years. From these results, we believe that Pleistophora sp. NIS-M27 should be classified in the genus Endoreticulatus. To accurately classify this strain in the future, multifaceted investigations, such as host infectivity and analyses based on other gene sequences, are required.