The ultrastructure of three microsporidia from winter moth,Operophtera brumata (L.), and the establishment of a new genus Cystosporogenes n.g. for Pleistophora operophterae (Canning, 1960)

Summary The ultrastructure of three species of microsporidia in winter moths, Operophtera brumata (L.), has been used to consolidate taxonomic assessments previously based on light microscopy. The characters formerly used to assign Nosema operophterae Canning, 1960 to a new genus Orthosoma Canning, Wigley & Barker, 1983, namely that the nuclei are isolated and that sporoblasts are separated from ribbon-shaped multinucleate (2, 4, 8 or rarely 12 nuclei) sporonts, were upheld at the ultrastructural level. Development was in contact with the cell cytoplasm but all stages, which must have included meronts, had an electron dense surface coat. Nosema wistmansi Canning, Wigley & Barker, 1983, was found to be ultrastructurally typical of the genus Nosema Naegeli, 1857. An unusual feature of this species was the close association of cysternae of host endoplasmic reticulum with the surface of meronts, an association lost in sporogony. Pleistophora operophterae (Canning, 1960) has been transferred, on ultrastructural criteria, to a new genus Cystosporogenes n.g. Nuclei are isolated; all stages develop in a vesicle bounded by an envelope of enigmatic origin; this envelope persists around the spores as a sporophorous vesicle; division of the sporont within this vesicle is by budding and the number of sporoblasts, and therefore spores, is variable up to about 60.Microsporidia which undergo multisporous sporogony in sporophorous vesicles are now distributed among seven genera. These are: Glugea Thélohan, 1891; Pleistophora Gurley, 1893; Pseudopleistophora Sprague, 1977; Vavraia Weiser, 1977; Baculea Loubès & Akbarieh, 1978; Polydispyrenia Canning & Hazard, 1982 and Cystosporogenes n.g. New genera would appear to be needed for Pleistophora sp. of Sandars & Poinar (1976) and Pleistophora sp. of Percy, Wilson & Burke (1982). ac]19840404