Populations of European corn borer (Ostrinia nubilalis Hübner) from Krasnodar Territory (Southwestern Russia) become regularly infected with Nosema-like microsporidia. To identify the parasite, it was subjected to electron microscopy and small subunit ribosomal RNA (SSU rRNA) gene sequencing. The spore ultrastructure of the parasite was highly similar to Nosema bombycis from China and Nosema pyrausta from the USA. The nucleotide sequence of SSU rRNA gene was identical to a microsporidium isolated from O. nubilalis in southern France (GenBank accession no. HM566196) and closely related to Nosema bombycis (no. AY209011, 99.7 % sequence similarity) from Bombyx mori of Chinese origin and N. pyrausta (no. AY958071) from O. nubilalis of North American origin. As the molecular haplotype of SSU rRNA is fixed for the parasite infecting O. nubilalis across Europe and N. pyrausta was initially described in France as Perezia pyraustae (Paillot CR Acad Sci Paris 185: 673-675, 1927), we conclude that the parasite examined under the present study correspond to the type isolate of N. pyrausta. The microsporidium from O. nubilalis in North America (no. AY958071) corresponds therefore to a closely related, yet distinct haplotype.