In this study, a microsporidian pathogen of the date moth (Apomyelois (Ectomyelois) ceratoniae, Zeller, 1839) also known as the carob moth, is described based on light microscopy, ultrastructural characteristics and comparative molecular analysis. The pathogen infects the gut and hemolymph of A. ceratoniae. All development stages are in direct contact with the host cell cytoplasm. Fresh spores with nuclei arranged in a diplokaryon are oval and measured 3.29 +/- 0.23 mu m (4.18-3.03 mu m, n = 200) in length and 1.91 +/- 0.23 mu m (2.98-1.66 mu m, n = 200) in width. Spores stained with Giemsa's stain measured 3.11 +/- 0.31 mu m (3.72-2.41 mu m, n = 150) in length and 1.76 +/- 0.23 mu m (2.16-1.25 mu m, n = 150) in width. Spores have an isofilar polar filament with 10-12 coils. An 1110 bp long alignment of the current microsporidium showed an SSU rRNA gene difference of only 0.0009, corresponding to >99.91% sequence similarity with Nosema fumiferanae, while RPB1 gene sequences were 98.03% similar within an alignment of 969 bp. All morphological, ultrastructural and molecular features indicate that the microsporidian pathogen of A. ceratoniae is the new isolate of the N. fumiferanae and is named here as Nosema fumiferanae TY61.