The Light and Electron Microscopic Cytology of Janacekia adipophila N. Sp. (Microspora, Tuzetiidae), a Microsporidian Parasite of Ptychoptera paludosa (Diptera, Ptychopteridae)

ABSTRACT. The microsporidium Janacekia adipophila n. sp., a parasite of Ptychoptera paludosa larvae in Sweden, is described based on light microscopic and ultrastructural characteristics. Merogonial stages and sporonts are diplokaryotic. Merozoites are formed by rosette-like division. Sporonts develop into sporogonial plasmodia with isolated nuclei. These plasmodia give rise to 8–16 sporoblasts by rosette-like budding. A sporophorous vesicle is initiated by the sporogonial plasmodium. Sporoblasts and spores are enclosed in individual sporophorous vesicles. Granular inclusions of the vesicles, visible using light microscopy, discriminate sporogonial stages from stages of the merogony. The monokaryotic, fresh spores are oval with blunt ends, measuring 4.2-6.3 × 9.1-11.2 μm. Macrospores are formed in small numbers. The spore wall has three subdivisions and the exospore is electron-dense. The polaroplast has two parts: closely arranged lamellae anteriorly, wider sac-like compartments posteriorly. The isofilar polar filament, 191–264 nm wide, has 12-13 coils, which are arranged in one layer in the posterior half of the spore. The electron-dense inclusions of the sporophorous vesicle are modified during sporogony, and vesicles with mature spores are traversed by 21–27 nm wide tubules, which connect the exospore with the envelope of the vesicle. The walls of the tubules, the envelope of the vesicles, and the surface layer of the exospore are all identical double-layered structures. The microsporidium is compared to microsporidia of Ptychopteridae and Tipulidae and to related microsporidia of the family Tuzetiidae.