An ultrastructural and molecular study of Tubulinosema kingi Kramer (Microsporidia: Tubulinosematidae) from Drosophila melanogaster (Diptera: Drosophilidae) and its parasitoid Asobara tabida (Hymenoptera: Braconidae)

Tubulinosema kingi is a pathogen of Drosophila spp. that was originally described 40 years ago. Although Drosophila melanogaster is widely used as a model organism for biological research, only limited data about microsporidia infecting Drosophila have been published so far and very little is known about the ultrastructure of T. kingi. In this study, we present the results of ultrastructural and molecular examinations of T. kingi. The whole life cycle took place in direct contact with the host cell cytoplasm and all examined life cycle stages contained a diplokaryon. Very few membrane elements were present in early merogonial stages, but their number and order of arrangement increased as the life cycle proceeded. The cell membrane of meronts had a surface coat of tubular elements that encircled the cell. Later, numerous electron-dense strands without any ornamentation accumulated on the plasma membrane, indicating that cells had entered sporogony. The cell membrane of sporonts was covered by electron-dense material. The polar filament in the spores was slightly anisofilar with the last three or four coils being smaller in diameter. The polar filament has 10 to 14 coils which were arranged predominantly in a single row, but in many spores, one winding of the coiled polar filament was located inside the outer coils. In some spores, the polar filament was irregularly arranged in two or even three rows. Molecular analysis showed that all Tubulinosema spp. are closely related and form a clade of their own that is distinct from the Nosema/Vairimorpha clade. All these ultrastructural and molecular features are in concordance with the family Tubulinosematidae and the genus Tubulinosema which reinforces the recent reclassification of this microsporidium.     

Sporogony of Tetracapsuloides bryosalmonae in the brown trout Salmo trutta and the role of the tertiary cell during the vertebrate phase of myxozoan life cycles

Tetracapsuloides bryosalmonae is the myxozoan that causes the commercially and ecologically important proliferative kidney disease of salmonid fish species. Immunohistochemistry and electron microscopy were used to examine the development of this parasite within the kidney of the brown trout Salmo trutta. The main replicative phase of T. bryosalmonae is a cell doublet composed of a primary cell and a single secondary cell. Engulfment of one secondary cell by another to form a secondary-tertiary doublet (S-T doublet) heralded the onset of sporogony whereupon the parasite migrated to the kidney tubule lumen. Within the tubule, the parasite transformed into a pseudoplasmodium and anchored to the tubule epithelial cells via pseudopodial extensions. Within each pseudoplasmodium developed a single spore, composed of 4 valve cells, 2 polar capsules and 1 sporoplasm. The pseudoplasmodia formed clusters suggesting that large numbers of spores develop within the fish. This examination of T. bryosalmonae suggests that the main replicative phase of freshwater myxozoans within vertebrates is via direct replication of cell doublets rather than through the rupturing of extrasporogonic stages, while tertiary cell formation relates only to sporogony. Taken in conjunction with existing phylogenetic data, 5 distinct sporogonial sequences are identified for the Myxozoa.     

Ultrastructure of Enteromyxum leei (Diamant, Lom, & Dyková, 1994) (Myxozoa), an Enteric Parasite Infecting Gilthead Sea Bream (Sparus aurata) and Sharpsnout Sea Bream (Diplodus puntazzo)

ABSTRACT. The ultrastructure of the developmental stages of the myxozoan Enteromyxum leei parasitizing gilthead seabream ( Sparus aurata ) intestine and sharpsnout sea bream ( Diplodus puntazzo ) intestine and gallbladder are described. The earliest stage observed was a small dense trophozoite located among enterocytes. Proliferative stages, observed intercellularly in the epithelium of the intestine and gallbladder as well as in the lumen, possessed the typical cell-in-cell configuration throughout their development. Secondary cells were seen undergoing division within a common vacuolar membrane that also encompassed pairs of tertiary cells. Cytochemical studies showed that primary cells stored mainly lipids whereas secondary cells stored abundant β-glycogen granules. Sporogonic development resembled that described for other disporous myxozoans. Within sporogonic stages, nonsporogonic secondary cells were observed accompanying two developing spores. Mature spores had a binucleated sporoplasm in which glycogen stores were abundant and no sporoplasmosomes were found. Our observations are discussed in relation to our knowledge on other myxozoans of the genus Enteromyxum .     

Ultrastructural and Cytochemical Observations on Sporogenesis of Myxobolus sp. (Myxosporida: Myxobolidae) from the Common Shiner Notropis cornutus*

SYNOPSIS. The structure and cytochemistry of spores of Myxobolus sp. from plasmodia which occur in the gill filaments of the common shiner Notropis cornutus were studied by light microscopy and by scanning and transmission electron microscopy. The thin-walled valves of the pyriform spores are thickened in the lateral sutural and apical regions. Mucous material is associated predominantly with the posterior end of many spores. The plasmodium is surrounded by a syncytial wall bounded by 2 membranes. Pinocytotic channels are formed by the inner membrane and numerous dense vesicles are pinched off at the distal ends of the channels. Sporogenesis is initiated by the envelopment of one vegetative cell by another. The larger, enveloped cell divides to form a disporous pansporoblast, which contains 2 pairs of capsulogenic and valvogenic cells and 2 binucleate sporoplasm cells. Each capsular primordium and connecting external tubule gives rise to a polar capsule which houses a helically coiled polar tubule. The apical end of each polar capsule is plugged by a stopper. The valvogenic cells surround the capsulogenic and posteriorly situated sporoplasm cells to form the spore valves. Iodinophilic (glycogen) inclusions were not seen in spores stained with iodine or Best's carmine. A darkly stained band was observed around the posterior region of most spores stained with Best's carmine. In the electron microscope large aggregates of β glycogen particles were seen in the cytoplasm of sporoplasm cells in mature spores.     

Ultrastructural studies of Henneguya rhamdia n. sp. (Myxozoa) a parasite from the Amazon teleost fish, Rhamdia quelen (Pimelodidae)

Henneguya rhamdia n. sp. is described in the gill filaments of the teleost fish Rhamdia quelen, collected from the Peixe Boi River, State of Pará, Brazil. This myxosporean produced spherical to ellipsoidal plasmodia, up to 300 microm in diameter, which contained developmental stages, including spores. Several dense bodies up to 2 microm in diameter were observed among the spores. The spore body was ellipsoidal (13.1 microm in length, 5.2 microm in width, and 2.5 microm in thickness) and each of the two valves presented a tapering tail (36.9 microm in length). These valves surrounded the binucleated sporoplasm cell and two equal ellipsoidal polar capsules (4.7 x 1.1 microm), which contained 10-11 (rarely 12) polar filament coils. The sporoplasm contained sporoplasmosomes with a laterally eccentric dense structure with a half-crescent section. Based on the data obtained by electron microscopy and on the host specificity, the spores differed from previously described Henneguya species, mainly in their shape and size, number and arrangement of the polar filament coils, and sporoplasmosome morphology.     

Structure and Development of a Marine Actinosporean, Sphaeractinomyxon ersei n. sp. (Myxozoa)

ABSTRACT This is the first ultrastructural study of the development of a marine actinosporean and of a species belonging to the genus Sphaeractinomyxon Caullery & Mesnil, 1904. S. ersei n. sp. is described from a limnodriloidine oligochaete, Doliodrilus diverticulatus Erséus, 1985, from Moreton Bay. Queensland, Australia. Development is asynchronous, there being all stages from two-celled pansporoblasts through to mature spores present simultaneously within a host. Spores develop in groups of eight within pansporoblasts in the coelom and when mature are located also in the intestinal lumen. The primordial spore envelope and sporoplasm develop separately in the pansporoblast until the polar filament is formed within the polar capsule and the capsulogenic cell cytoplasm has begun to degrade. The sporoplasm then enters the spore through a separated valve junction. Mature spores are triradially symmetrical with three centrally located polar capsules and a single binucleate sporoplasm with about 46 germ cells. Swellings or projections of the epispore do not occur when spores exit the host and contact sea water.     

Henneguya adiposa Minchew (Myxosporida) in the channel catfish: ultrastructure of the plasmodium wall and sporogenesis.

Wall ultrastructure and sporogenesis were studied in plasmodia of Henneguya adiposa Minchew which infects the channel catfish, Ictalurus punctatus (Rafinesque). Plasmodia were located among connective tissue bands of the adipose fin and were always separated from host fibrocytes by collagen fibers. The plasmodium wall consisted of a single unit membrane which was continuous with numerous pinocytic canals extending into the parasite's ectoplasm. The membrane was highly convoluted, producing an irregular parasite surface, and was covered by a fine granular coat of almost uniform thickness. Early sporogenic stages were located in a zone of cytoplasm rich in mitochondria, just interior to the zone of pinocytic canals. Later sporogenic stages, including mature spores, were concentrated in the center of the plasmodia. Sporogenesis began with the envelopment of one generative cell, the sporont, by a 2nd, nondividing, cell--the enveloping cell. The sporont and its progeny proceeded through a series of divisions until 10 cells were present within the enveloping cell. Once divisions were completed, the 10 cells became arranged into 2 indentical spore-producing units, each consisting of one binucleate sporoplasm and 2 capsulogenic cells, all surrounded by 2 valvogenic cells. Later stages of spore development indicated that capsulogenesis, valvogenesis and sporoplasm maturation occurred concimitantly.     

Ultrastructure of Enteromyxum leei (Diamant, Lom, & Dyková, 1994) (Myxozoa), an enteric parasite infecting gilthead sea bream (Sparus aurata) and sharpsnout sea bream (Diplodus puntazzo).

The ultrastructure of the developmental stages of the myxozoan Enteromyxum leei parasitizing gilthead seabream (Sparus aurata) intestine and sharpsnout sea bream (Diplodus puntazzo) intestine and gallbladder are described. The earliest stage observed was a small dense trophozoite located among enterocytes. Proliferative stages, observed intercellularly in the epithelium of the intestine and gallbladder as well as in the lumen, possessed the typical cell-in-cell configuration throughout their development. Secondary cells were seen undergoing division within a common vacuolar membrane that also encompassed pairs of tertiary cells. Cytochemical studies showed that primary cells stored mainly lipids whereas secondary cells stored abundant beta-glycogen granules. Sporogonic development resembled that described for other disporous myxozoans. Within sporogonic stages, nonsporogonic secondary cells were observed accompanying two developing spores. Mature spores had a binucleated sporoplasm in which glycogen stores were abundant and no sporoplasmosomes were found. Our observations are discussed in relation to our knowledge on other myxozoans of the genus Enteromyxum.     

Henneguya adiposa Minchew (Myxosporida) in the Channel Catfish: Ultrastructure of the Plasmodium Wall and Sporogenesis*

Wall ultrastructure and sporogenesis were studied in plasmodia of Henneguya adiposa Minchew which infects the channel catfish, Ictalurus punctatus (Rafinesque). Plasmodia were located among connective tissue bands of the adipose fin and were always separated from host fibrocytes by collagen fibers. The plasmodium wall consisted of a single unit membrane which was continuous with numerous pinocytic canals extending into the parasite's ectoplasm. The membrane was highly convoluted, producing an irregular parasite surface, and was covered by a fine granular coat of almost uniform thickness. Early sporogenic stages were located in a zone of cytoplasm rich in mitochondria, just interior to the zone of pinocytic canals. Later sporogenic stages, including mature spores, were concentrated in the center of the plasmodia. Sporogenesis began with the envelopment of one generative cell, the sporont, by a 2nd, nondividing, cell—the enveloping cell. The sporont and its progeny proceeded through a series of divisions until 10 cells were present within the enveloping cell. Once divisions were completed, the 10 cells became arranged into 2 identical spore-producing units, each consisting of one binucleate sporoplasm and 2 capsulogenic cells, all surrounded by 2 valvogenic cells. Later stages of spore development indicated that capsulogenesis, valvogenesis and sporoplasm maturation occurred concomitantly.     

Presentation by scanning electron microscopy of the life cycle of microsporidia of the genus Encephalitozoon

This paper presents, for the first time, documentation by detailed scanning electron microscopy of the life cycle of microsporidia of the genus Encephalitozoon. Phase 1 is represented by the extracellular phase with mature spores liberated by the rupture of host cells. To infect new cells the spores have to discharge their polar filament. Spores with everted tubes show that these are helically coiled. When the polar tubules have started to penetrate into a host cell they are incomplete in length. The infection of a host cell can also be initiated by a phagocytic process of the extruded polar filament into an invagination channel of the host cell membrane. After the penetration process, the tube length is completed by polar tube protein which passes through the tube in the shape of swellings. A completely discharged polar tube with its tip is also shown. The end of a polar tube is normally hidden in the cytoplasm of the host cell. After completion of the tube length the transfer of the sporoplasm occurs and phase 2 starts. Phase 2 is the proliferative phase, or merogony, with the intracellular development of the parasite that cannot be documented by scanning electron microscopy. The subsequent intracellular phase 3, or sporogony, starts when the meronts transform into sporonts, documented as chain-like structures which subdivide into sporoblasts. The sporoblasts finally transform directly into spores which can be seen in their host cell, forming bubble-like swellings in the cell surface.     

Paranucleospora theridion n. gen., n. sp. (Microsporidia,Enterocytozoonidae) with a Life Cycle in the Salmon Louse (Lepeophtheirus salmonis,Copepoda) and Atlantic Salmon (Salmo salar)

ABSTRACT. Paranucleospora theridion n. gen, n. sp., infecting both Atlantic salmon (Salmo salar) and its copepod parasite Lepeophtheirus salmonis is described. The microsporidian exhibits nuclei in diplokaryotic arrangement during all known life‐cycle stages in salmon, but only in the merogonal stages and early sporogonal stage in salmon lice. All developmental stages of P. theridion are in direct contact with the host cell cytoplasm or nucleoplasm. In salmon, two developmental cycles were observed, producing spores in the cytoplasm of phagocytes or epidermal cells (Cycle‐I) and in the nuclei of epidermal cells (Cycle‐II), respectively. Cycle‐I spores are small and thin walled with a short polar tube, and are believed to be autoinfective. The larger oval intranuclear Cycle‐II spores have a thick endospore and a longer polar tube, and are probably responsible for transmission from salmon to L. salmonis. Parasite development in the salmon louse occurs in several different cell types that may be extremely hypertrophied due to P. theridion proliferation. Diplokaryotic merogony precedes monokaryotic sporogony. The rounded spores produced are comparable to the intranuclear spores in the salmon in most aspects, and likely transmit the infection to salmon. Phylogenetic analysis of P. theridion partial rDNA sequences place the parasite in a position between Nucleospora salmonis and Enterocytozoon bieneusi. Based on characteristics of the morphology, unique development involving a vertebrate fish as well as a crustacean ectoparasite host, and the results of the phylogenetic analyses it is suggested that P. theridion should be given status as a new species in a new genus.     

Experimental detection of the actinospores of Myxobolus pseudodispar (Myxosporea: Myxobolidae) in oligochaete alternate hosts

The development of Myxobolus pseudodispar Gorbunova, 1936, an intracellular myxosporean muscle parasite of the roach Rutilus rutilus L., was studied in experimentally infected oligochaetes. In one experiment, uninfected Tubifex tubifex Müller and Limnodrilus hoffmeisteri (Claparéde) were exposed to mature spores of M. pseudodispar. Triactinomyxon spores developed both in T. tubifex and L. hoffmeisteri specimens. Triactinospores were first released from the oligochaetes 76 d after initial exposure. At that time, pansporocysts containing 8 triactinospores were located in the gut epithelium of experimentally infected oligochaetes, but free actinosporean stages were also found in their gut lumen. Each triactinospore had 3 pyriform polar capsules and an elongated cylindrical sporoplasm with 8 secondary cells. The spore body joined the 3 caudal projections with a relatively long style. One of the 3 caudal projections was shorter than the other two. The total length of the triactinospore was on average 206.5 microns.     

Enterocytozoon salmonis n. sp.: an intranuclear microsporidium from salmonid fish

The developmental stages of a recently described microsporidian from the nucleus of hematopoietic cells of salmonid fish were found to be unique among the Microsporida. All observed stages, including meronts, sporonts, and spores were in direct contact with the host cell nucleus (principally hematopoietic cells) of chinook salmon (Oncorhynchus tshawytscha). There is no parasitophorous vacuole and sporogony does not involve formation of a pansporoblastic membrane as with other members of the suborder Apansporoblastina. The extrusion apparatus differentiates prior to division of sporogonial plasmodia. The spores are ovoid (1 x 2 microns) and uninucleate, and possess a coiled polar tube with 8-12 turns. Developmental stages of the salmonid microsporidian are similar to those described for Enterocytozoon bieneusi as found in the intestinal mucosa of human AIDS patients. However, the intranuclear development, different cell types, and host infected clearly separate the salmonid and human parasites. Accordingly, the intranuclear parasite of salmonids is given the name Enterocytozoon salmonis n. sp. within the suborder Apansporoblastina.     

Ultrastructural study on a novel microsporidian, Endoreticulatus eriocheir sp. nov. (Microsporidia, Encephalitozoonidae), parasite of Chinese mitten crab, Eriocheir sinensis (Crustacea, Decapoda)

A microsporidian pathogen, infecting the epithelial cells of the hepatopancreas of Chinese mitten crab, Eriocheir sinensis, was studied by electron microscopy. The detailed ultrastructure of life cycle of the pathogen including proliferative and sporogonic developmental stages are provided. All stages of the parasite are haplokaryotic and develop in a vacuole bounded by a single membrane in contact with host cell cytoplasm. Sporogenesis is synchronous with the same developmental stage in one vacuole. Sporogony shows a characteristic of multinucleate sporogonial plasmodia divided by rosette-like division, producing 4 or 8 sporoblasts. The mature spore is ellipsoidal, length (mean) 1.7 microm, width 1.0 microm, with a uninucleate in the center of the sporoplasm, 7 turns of the polar filament, a bell-like polaroplast of compact membranes and obliquely positioned posterior vacuole. The morphological characteristics of this novel microsporidian pathogen have led us to assign the parasite to a new species of Endoreticulatus, E. eriocheir sp. nov., that has not been reported previously from crab.     

Life Cycle of Culicospora magna (Kudo, 1920) (Microsporida: Culicosporidae) in Culex restuans Theobald with Special Reference to Sexuality1

The life cycle of Culicospora magna (Kudo, 1920) Weiser, 1977, consists of two major developmental sequences that alternate in host individuals of successive generations, each of the sequences starting with a sporoplasm and ending with spores. The first sequence occurs in larval, pupal, and adult stages of a parental generation of the host mosquito, Culex restuans Theobald; it begins with a sporoplasm from an ingested uninucleate spore and progresses through stages in gametogony, plasmogamy, nuclear association, merogony, karyogamy, and disporous sporulation with production of binucleate spores that discharge sporoplasms into the oocytes. The second sequence occurs in egg and larval stages of a filial generation of the same host species; it begins with the binucleate sporoplasm that entered the egg, includes stages in merogony, nuclear dissociation, and mictosporous sporulation, and ends with uninucleate spores. These spores are released into the environment following death of the host and are capable of infecting new parental generation host individuals. The life cycle is conceived as an alternation of generations related to haploidy and diploidy in the nuclei, the transition from haploidy to diploidy occurring with nuclear association and the transition from diploidy to haploidy occurring with nuclear dissociation.     

Fine Structure of Triactinomyxon Early Stages and Sporogony: Myxosporean and Actinosporean Features Compared

ABSTRACT. The first ultrastructural study of the actinosporean genus Triactinomyxon was carried out on Triactinomyxon legeri from the intestinal epithelium of Tubifex tubifex. The developmental cycle starts with bi- and uninucleate cells. We propose that these cells may be an early proliferative phase of the cycle and may unite to give rise to the four-cell stage, initiating pansporoblast formation. Valvogenic cells transform in the long stylus and anchor-like projections of the spore. In the capsulogenic cells, the primordium of the polar capsules originates as a simple, dense, club-shaped structure not observed in other actinosporeans. In all other respects, actinosporean ultrastructure follows more or less similar patterns. Comparison of actinosporean and myxosporean species gives evidence of considerable structural similarity, exemplified in both classes by the occurrence of cell junctions in their multicellular spores, identical polar capsules and their morphogenesis, cell-in-cell condition, pansporoblast formation, and presence of dense bodies (sporoplasmosomes) primarily in the sporoplasm. This unity of patterns speaks in favor of the postulated actinosporean-myxosporean transformation, which warrants further study.     

Ultrastructure of Myxobolus brycon n. sp. (Phylum Myxozoa), parasite of the piraputanga fish Brycon hilarii (Teleostei) from Pantanal (Brazil)

Light and electron microscopy studies of a myxosporean, parasitizing the gill filaments of the freshwater fish Brycon hilarii (Valenciennes, 1850) (Characidae) collected in the Paraguay River (18°49'S, 57°39'W) (Pantanal), Brazil, is described. This parasite produces spherical to ellipsoidal polysporic histozoic plasmodia (Pmd) (up to ～180 μm in diameter) delimited by a double membrane and with several pinocytic channels. The plasmodial cyst contained the youngest developmental stages at the cortical periphery and immature and mature spores more internally. The Pmd developed near the cartilaginous structure of the gill filament, forming a prominent deformation where the gill lamellae disappear. Pyriform spores measured 6.9±0.6 (range 6.5-7.2) μm long, 4.2±0.5 (range 3.9-4.8) μm wide, and 2.5±0.7 (range 1.9-2.8) μm thick. The spores composed of two equal shell valves (～70 nm thick), adhering together along the straight suture line, surrounded two equal symmetric and elongated to pyriform polar capsules (PC) 4.2±0.6 (range 3.8-4.7) × 1.9±0.6 (1.7-2.5) μm; each PC contained a coiled polar filament with eight or nine (rarely 10) turns and a binucleated sporoplasm cell. Dense irregular masses were observed among the polar filaments coils. An intercapsular appendix was not observed. The sporoplasm contained several globular sporoplasmosomes randomly distributed among an extensive rough endoplasmic reticulum system with numerous vesicles and cisternae. Based on the morphological and ultrastructural differences and specificity of the host, we establish the new species, Myxobolus brycon n. sp.     

圆形碘泡虫孢子发生的超微结构研究

寄生于鲫的圆形碘泡虫的孢子发生过程中,最早可认识阶段的营养体是一个单核原初细胞,原初细胞通过分裂直接在细胞内产生生殖细胞,形成一个细胞包围另一个细胞的状态,在以后的过程中,包围细胞不再分裂,生殖细胞进行一系列的分裂,形成双孢子型泛孢子母细胞.生殖细胞分化成10个细胞,形成二个产孢子单元,每个产孢子单元由5个细胞组成,两个壳瓣原细胞位于两边包围着两个极囊原细胞和一个双核孢子质细胞,最后形成两个孢子.       

Ultrastructural study of the microsporidian chytridiopsis typographi (Chytridiopsida: Microspora) infecting the bark beetle,Ips typographus (Scolytidae: Coleoptera), with new data on spore dimorphism

Two types of sporogony of the microsporidian Chytridiopsis typographi in the midgut of adult bark beetle, Ips typographus, have been examined by means of light and electron microscopy. New data are reported on spore dimorphism and on the formation of pansporoblasts in two types of sporogony. Thin-walled spores, larger in size, are formed in a parasitophorous vacuole in the host columnar cells. Thick-walled spores are formed in a minimal vacuole in the host. The ultrastructure of the spore walls and the cyst wall are different from the organization in other microsporidia. Both spore types have identical internal structures and viable spores.     

Ultrastructural characteristics and small subunit ribosomal DNA sequence of Vairimorpha cheracis sp. nov., (Microspora: Burenellidae), a parasite of the Australian yabby, Cherax destructor (Decapoda: Parastacidae)

This is the first record of a species of Vairimorpha infecting a crustacean host. Vairimorpha cheracis sp. nov. was found in a highland population of the Australian freshwater crayfish, Cherax destructor. The majority of spores and earlier developmental stages of V. cheracis sp. nov. were found within striated muscle cells of the thorax, abdomen, and appendages of the crayfish. Only octosporoblastic sporogony within sporophorous vesicles (SPVs) was observed. Diplokaryotic sporonts separated into two uninucleate daughter cells, each of which gave rise to four sporoblasts in a rosette-shaped plasmodium, so that eight uninucleate spores were produced within the persistent ovoid SPV. Ultrastructural features of stages in the octosporoblastic sequence were similar to those described for Vairimorpha necatrix, the type species. Mature spores were pyriform in shape and averaged 3.4x1.9 microm in dimensions. The anterior polaroplast was lamellar in structure, and the posterior polaroplast vesicular. The polar filament was coiled 10-12 times, lateral to the posterior vacuole. The small subunit ribosomal DNA (SSU rDNA) of V. cheracis sp. nov. was sequenced and compared with other microsporidia. V. cheracis sp. nov. showed over 97% sequence identity with Vairimorpha imperfecta and five species of Nosema, and only 86% sequence identity with V. necatrix. The need for a taxonomic revision of the Nosema/Vairimorpha group of species is discussed.