[Refinement of the diagnosis of Issia globifera (Microsporidia: nosematidae) based on ultrastructural data].

An ultrastructure of a microsporidian belonging to the aberrant and poorly studied genus Issia is discribed in this paper. The first description of Issia globulifera (Issi, Pankova, 1983) was made on the basis of light microscopic analysis of midgut smears of the infected insects. Both late merogonic and sporogonic stages can be met on the sections from midguts of Anopheles messae. Meronts are ameba-like cells (3.0-3.5 x 2.0-2.5 microns) forming conglomerates of cells without any regular organization. Meronts and sporonts directly contact with the host cell cytoplasm; they are surrounded by numerous mitochondria. Sporonts divide into 2 sporoblasts, but remain connected with each other by posterial ends. In the vicinity of the contact the paramural bodies (structures, presumably participating in the formation of the exospore) can be seen. Sporoblast morphogenesis is accompanied by the rapid grow of electron dense layer in the region of the contact of two sister sporoblasts. Due to such intensive growth the sporoblasts are finally located at sharp angle to each other. Envelopes of sporonts and sporoblasts possess typical 2-membrane structure. Their nuclei lay in pairs like in Nosema species. Sporoblasts (unlike meronts and sporonts) are surrounded by the electron lucid zone of the cytoplasm with numerous tubule-like and spherical inclusions. Host mitochondria are closely adjacent to the periphery of this zone. The formation of characteristic spherical structures (globules), in which the posterior ends of two (in rare cases of 1 or 4) sister spores are downsinked, starts immediately after the sporont division. Globules rapidly increase in size during the sporogenesis. The homogenous globule (6-8 microns), which is essentially larger than a spore, seems to represent the modified exospore; it is not limited by any visible membrane. Fine structure of spores (2.5-3.0 x 2.0-2.3 microns) is typical for the nosems: spherical polar disk; lamellas polaroplast; nuclei located along the long spore axis; basal part of a polar tube forming a fork. A thin (25-40 nm) heterophilar polar filament forms 12 rows of various structure (8 + 4) packed in two rows. The posterior vacuole was no revealed. Endospore is very thick up to 250-400 nm in mature spores. The exospore covering the 2/3-4/5 of the spore length passes into the globule on the posterior end. The refined diagnosis of Issia globulifera: type host species--Anopheles messae (larvae, pupae); tissue localization: mitgut epithelium; terra typica: Siberia, Tomsk region, Ob river basin; developmental stages: multicellular merogonial plasmodium, sporont gives rise to 2 (rarely 1 or 4) sporoblasts connected with each other by a "globule", a specific formation homologous to an exospore of other microsporidians; globule (6-8 microns) possesses a homogenous inner structure of average electron density; sporophorous vesicle not formed; spore structure is typical for Nosematidae. Embeddings, negatives (## 2301, 2303, 2308, 2311-2313, 2532, 2533) and photos of type material in the collection of All-Russian Institute for Plant Protection.