Nosema ceranae n. sp. (Microspora, Nosematidae), morphological and molecular characterization of a microsporidian parasite of the Asian honey bee Apis cerana (Hymenoptera, Apidae)

Based on light microscopic and ultrastructural characteristics as well as on the nucleotide sequence of the small subunit ribosomal RNA coding region, the microsporidium Nosema ceranae n. sp., a parasite of the Asian honey bee Apis cerana is described. Merogonial stages and sporonts are diplokaryotic. Merozoites are mostly formed by cytoplasmic fission in quadrinucleate meronts and the number of merogonial cycles may vary. The sporogony is disporoblastic. The living mature spore is ovocylindrical, straight to slightly curved and measures 4.7 × 2.7 μm whereas fixed and stained spores measure 3.6 × 1.7 μm. The polar filament is isofilar with a diameter of 96–102 nm and is arranged in 20–23 coils in the posterior and mid-part of the spore. In the anterior part of the polaroplast there are closely packed approximately 11 nm thick lamellae. The lamellae of the posterior polaroplast are thicker and less regular. In the posterior part of the mature spore a well fixed posterior body interpreted as a posterosome was often observed. Phylogenetic analysis, based on the sequence of the small subunit ribosomal RNA, places Nosema ceranae in the Nosema clade, as defined by Nosema bombycis, the type species of the Nosema genus.