Development, ultrastructure, and mode of transmission of Amblyospora sp. (Microspora) in the mosquito

Amblyospora sp. in Culex salinarius (Coquillett) is transovarially transmitted and has 2 developmental sequences, one in each host sex. In females, the entire life cycle is restricted to oenocytes which become greatly hypertrophied due to the multiplication of diplokaryotic cells during merogony and come to lie next to ovaries. Sporulation occurs only after a blood meal is taken and is shortly followed by infection of the oocytes and subsequent transmission to the next host generation. In the male host, infections spread from oenocytes to adipose tissue where diplokaryotic cells undergo a 2nd merogony. During this merogonic cycle, the number of diplokaryotic cells greatly increases and the infection is spread throughout the body of the larval host. Sporulation is initiated with the physical separation of the 2 members of the diplokaryon and the simultaneous secretion of a pansporoblastic membrane. Subsequent meiotic division and morphogenesis result in the formation of 8 haploid spores enclosed with a pansporoblastic membrane. Buildup of spores and subsequent destruction of host adipose tissue prove fatal to the male host during the 4th larval stage.     

Life Cycle and Epizootiology of Amblyospora sp. (Microspora: Amblyosporidae) in the Mosquito,Aedes cantator1

In Aedes cantator, Amblyospora sp. is transovarially transmitted and has two developmental sequences. The life cycle is initiated in the adult female with the release of sporoplasms from binucleated spores not bounded by membranes, lying free within host oenocytes. Sporoplasms infect the developing oocytes and are transmitted to the filial generation when the eggs are laid. In some of the female progeny that hatch from infected eggs, diplokaryotic cells infect host oenocytes and divide by binary fission during merogony. Sporulation and spore formation do not occur until a blood meal is taken by the host and they coincide with the development and maturation of the oocytes to complete the cycle. In other female and all male progeny, pathogen development occurs within fat body tissue of the host where diplokaryotic cells divide by multiple fission during merogony to spread the infection. Sporulation in this developmental sequence is characterized by the secretion of an accessory membrane and the meiotic division of diplokaryotic sporonts, which result in the formation of octonucleated plasmodia that undergo cytokinesis to form eight haploid spores which are not perorally infectious to other mosquito larvae. There is no increase in the prevalence of either type of infection in field populations during juvenile development, indicating that there is no direct horizontal transmission of the pathogen within any one generation. Data obtained from laboratory rearings of infected progeny, however, show that infections cannot persist relying solely upon maternal-mediated transmission and that some other mode of transmission must be operative for continued maintenance of this microsporidium in A. cantator.     

Life cycle of a new species of Amblyospora (Microspora: Amblyosporidae) in the mosquito Aedes taeniorhynchus

A new species of Microspora, Amblyospora polykarya, is described from the mosquito Aedes taeniorhynchus. The parasite is transovarially transmitted for one generation only. Spores in adult females extrude binucleate sporoplasms which infect developing eggs. Merogony occurs in larval oenocytes with diplokaryotic stages in early instars giving rise to plasmodia with many diplokarya. Plasmodia undergo cytokinesis to form diplokaryotic sporonts. In fat body cells, these sporonts secrete pansporoblastic membranes and undergo two nuclear divisions to form octonucleate sporonts. Cytokinesis and differentiation result in uninucleate spores in packets of eight. These spores are not transmissible per os and are of different morphotype from those in adult females. Infected larvae die in the fourth stadium.     

Development of Amblyospora campbelli (Microsporida: Amblyosporidae) in the Mosquito Culiseta incidens (Thomson)

The complete life cycle of Amblyospora campbelli (Kellen and Wills, 1962) (Microsporida: Amblyosporidae) requires a two-host system involving the mosquito host, Culiseta incidens (Thomson), and an obligatory intermediate copepod host. The parasite has dimorphic spore development producing meiospores (haploid condition) and binucleated spores (diploid condition), either as an exclusive infection or simultaneously (within females only). This is the 1st known report of concurrent spore development within an adult mosquito host, and, therefore, shows the Amblyospora campbelli system to be uniquely different from other Amblyospora spp. cycles previously described. The significance of dimorphic spore development is discussed. In females, diplokaryotic meronts may invade oenocytes, causing a benign-type of infection. A blood-meal is required to initiate sporulation of the binucleate spore. The binucleate spore contains the sporoplasm involved in transovarial transmission. A 2nd sporulation sequence, primarily in adipose tissue, may involve both males and females. In this sequence, repeated merogonic division greatly increased the density of diplokaryotic meronts and generally involved most of the body of the host. Production of meiospores, unlike that for the binucleate spore, appeared to be spontaneous (i.e. no obligatory blood meal). Survivorship of male and female larval mosquitoes was nearly equal. Adult females spread the parasite in three ways: transovarial, transovum, and by meiospore deposition.     

Development of Amblyospora campbelli (Microsporida: Amblyosporidae) in the mosquito Culiseta incidens (Thomson)

The complete life cycle of Amblyospora campbelli (Kellen and Wills, 1962) (Microsporida: Amblyosporidae) requires a two-host system involving the mosquito host, Culiseta incidens (Thomson), and an obligatory intermediate copepod host. The parasite has dimorphic spore development producing meiospores (haploid condition) and binucleated spores (diploid condition), either as an exclusive infection or simultaneously (within females only). This is the 1st known report of concurrent spore development within an adult mosquito host, and, therefore, shows the Amblyospora campbelli system to be uniquely different from other Amblyospora spp. cycles previously described. The significance of dimorphic spore development is discussed. In females, diplokaryotic meronts may invade oenocytes, causing a benign-type of infection. A blood-meal is required to initiate sporulation of the binucleate spore. The binucleate spore contains the sporoplasm involved in transovarial transmission. A 2nd sporulation sequence, primarily in adipose tissue, may involve both males and females. In this sequence, repeated merogonic division greatly increased the density of diplokaryotic meronts and generally involved most of the body of the host. Production of meiospores, unlike that for the binucleate spore, appeared to be spontaneous (i.e. no obligatory blood meal). Survivorship of male and female larval mosquitoes was nearly equal. Adult females spread the parasite in three ways: transovarial, transovum, and by meiospore deposition.     

Life Cycle of Culicosporella lunata (Hazard & Savage, 1970) Weiser, 1977 (Microspora) as Revealed in the Light Microscope with a Redescription of the Genus and Species1

Light microscopy studies of Culicosporella lunata (Hazard & Savage), a parasite of the mosquito Culex pilosus (Dyar & Knab), revealed two sporogonial sequences. One sequence begins with diplokaryotic meronts that undergo repeated nuclear divisions to produce sporogonial plasmodia with nuclei in diplokaryotic arrangement. These plasmodia form rosette-like clusters of sporoblasts during incomplete cytokinesis and, eventually, binucleate spores. These spores initiate infections in healthy larvae when they ingest spores. The second sequence begins with diplokaryotic meronts that undergo karyogamy and meiosis to form Thelohania-like sporonts and haploid spores. Anomalies are often observed in these sporonts which result in aberrant spores, usually fewer than eight, in an accessory (pansporoblastic) membrane. Normal haploid spores are morphologically similar to those of species of Amblyospora. The genus and the type species are redefined based on new information presented here and it and the type species are placed in the family Amblyosporidae.     

Occurrence of a New Microsporidan: Enterocytozoon bieneusi n. g., n. sp., in the Enterocytes of a Human Patient with AIDS1

A new microsporidium is reported infesting the enterocytes of a Haitian patient with AIDS. The stages observed were diplokaryotic cells, sporogonial plasmodia, unikaryotic sporoblasts, and spores. Neither a sporophorous vesicle (pansporoblastic membrane) nor parasitophorous vacuole were differentiated around the developmental stages, which were in direct contact with the host cell cytoplasm. The polar tube (5-6 coils) was differentiated before fission of the sporogonial plasmodium. The mature spores measured 1.5 m?m × 0.5 m?. The spore wall was very thin as the endospore was absent or poorly differentiated. The organism is named Enterocytozoon bieneusi n. g., n. sp. and is assigned to the suborder Apansporoblastina.     

Life cycle,epizootiology, and horizontal transmission of Amblyospora (Microspora: Amblyosporidae) in a univoltine mosquito, Aedes stimulans

Amblyospora infections in Aedes stimulans are transovarially transmitted by females infected in the previous year. Pathogen development in progeny is dimorphic and host sex dependent. In males, the pathogen invades fat body tissue and undergoes an extensive developmental sequence which kills the host and results in the formation of eight haploid spores enclosed in an accessory membrane that are not infectious to other larvae. In females, the pathogen invades host oenocytes and undergoes a simple developmental sequence which has no detrimental affect on longevity, fecundity, oviposition, or egg hatch, and results in the formation of binucleated spores that infect the ovaries and ensure transmission to the next generation. Transovarial transmission is continuous and is the major way in which these microsporidia are maintained from year to year, but is incapable of maintaining infections in breeding populations because of low transmission rates and is not sufficient to account for the types and levels of infection observed in the field. Horizontal transmission is reported for the first time. It occurs sporadically during the early stages of larval subsequently disseminated to oenocytes of adult hosts and are transovarially transmitted by females to filial host generations. This pathway of transmission provides the necessary mechanism whereby these microsporidia can reenter the mosquito population and thus perpetuate themselves.     

Life cycle of Amblyospora indicola (Microspora: Amblyosporidae), a parasite of the mosquito Culex sitiens and of Apocyclops sp. Copepods

The life cycle of Amblyospora indicola, a parasite of the mosquito Culex sitiens, was revealed by field observations and laboratory infection experiments conducted in Australia. In northern Queensland, infected C. sitiens larvae were often found breeding in association with two cyclopoid copepods: Apocyclops dengizicus and an undescribed species of the same genus. The latter species was found to be an intermediate copepod host of this microsporidium whereas A. dengizicus was not. One complete cycle of the parasite extends over two mosquito generations (by transovarial transmission from females with binucleate spores to their eggs) and by horizontal transmission between mosquitoes and copepods. The latter involves horizontal transmission from mosquitoes to copepods via meiospores produced in larval fat body infections and horizontal transmission from copepods to mosquitoes via uninucleate spores produced within infected copepods. Uninucleate clavate spores were formed in Apocyclops sp. nov. copepods 7-10 days after exposure to larval meiospores and were infectious to larvae of a microsporidian-free colony of C. sitiens. The development of A. indicola within mosquito larvae exposed to infected copepods is similar to that of A. dyxenoides infecting C. annulirostris. It proceeds from stages with a single nucleus to diplokaryotic binucleate cells in oenocytes. These stages persist through pupation to adult emergence after which time a proportion of male mosquitoes and female mosquitoes may develop binucleate spores without the need for a blood meal. A proportion of both male and female larval progeny of infected females with binucleate spores develop patent fat body infections via transovarial transmission and die in the fourth larval instar.(ABSTRACT TRUNCATED AT 250 WORDS)     

Occurrence of a new microsporidan: Enterocytozoon bieneusi n.g., n. sp., in the enterocytes of a human patient with AIDS

A new microsporidium is reported infesting the enterocytes of a Haitian patients with AIDS. The stages observed were diplokaryotic cells, sporogonial plasmodia, unikaryotic sporoblasts, and spores. Neither a sporophorous vesicle (pansporoblastic membrane) nor parasitophorous vacuole were differentiated around the developmental stages, which were in direct contact with the host cell cytoplasm. The polar tube (5-6 coils) was differentiated before fission of the sporogonial plasmodium. The mature spores measured 1.5 micron X 0.5 micron. The spore wall was very thin as the endospore was absent or poorly differentiated. The organism is named Enterocytozoon bieneusi n. g., n. sp. and is assigned to the suborder Apansporoblastina.     

Heterovesicula cowani N. G., N. Sp. (Heterovesiculidae N. Fam.), a Microsporidian Parasite of Mormon Crickets, Anabrus simplex Haldeman, 1852 (Orthoptera: Tettigoniidae)

ABSTRACT. Heterovesicula cowani , n. g., n. sp., is a dimorphic microsporidium described from the adipose tissue of the Mormon cricket, Anabrus simplex Haldeman. Proliferation of the microsporidium is by karyokinesis of uninucleate and binucleate cells to form binucleate and tetranucleate cells, respectively. These cells will undergo binary fission (merogony). Ultimately, the meronts undergo karyokinesis without subsequent cytokinesis producing spherical multinucleate plasmodia that are transitional to 2 types of sporogony. Transitional to disporoblastic sporogony, a fragile interfacial envelope delaminates from the plasmodium with morphogenesis to a monfiliform plasmodium consisting of fusiform binucleate diplokaryotic sporonts. These undergo karyokinesis to form tetranucleate diplokaryotic sporonts that undergo cytokinesis during disintegration of the plasmodium into isolated binucleate sporonts. Transitional to octosporoblastic sporogony, multinucleate plasmodia disintegrate into short monofiliform plasmodia of diplokaryotic sporonts which then segregate while undergoing gradual nuclear dissociation (haplosis by nuclear dissociation). These undergo two sequences of karyokinesis and subsequent multiple fission to form eight uninucleate (haploid) sporoblasts in a fusiform arrangement within a persistent envelope. Binucleate spores are ovocylindrical, about 5.4 × 1.7 μm (fresh), with an isofilar polar filament singly coiled about 11 turns. Uninucleate spores are ovoid to slightly pyriform, 4.0 × 1.7 μm (fresh), with an isofilar filament singly coiled about 9 turns. A new family, Heterovesculidae, is proposed for the new genus.     

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.     

Nosema helminthorum Moniez, 1887 (Microspora,Nosematidae):A Taxonomic Enigma1

ABSTRACT. The microsporidian parasite known as Nosema helminthorum Moniez, 1887, parasitic in the tapeworm Moniezia expansa (Rudolphi, 1810), has been shown by electron microscopy to have two cycles of development, one with isolated nuclei, the other with paired nuclei (diplokarya). Both merogony and sporogony of the two separate sequences take place in direct contact with the host cell cytoplasm and ultimately give rise to unikaryotic and diplokaryotic sporoblasts. Sporogony is disporoblastic. The nuclear condition of the spores was not seen. The sequences, corresponding to those of the genera Unikaryon and Nosema, may be part of a single dimorphic life cycle and, if so, the species will have to be transferred to a new genus.     

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.     

Food utilization values of gypsy moth Lymantria dispar (Lepidoptera: Lymantriidae) larvae infected with the microsporidium Vairimorpha sp. (Microsporidia: Burenellidae)

Infection of the gypsy moth, Lymantria dispar, with the microsporidium Vairimorpha sp. strongly influences the development of the host in ways typical of many species of terrestrial entomopathogenic Microsporidia; growth is reduced while development time is extended in infected insects. The appearance of the different stages of the parasite in the host relative to the elapsed time after oral infection, as well as the influence of the parasite proliferation on food utilization of the host, were examined. At 3 days postinfection, midgut muscle cells were infected with primary spores, and the fat body tissues contained meronts, sporonts, and primary spores. Many more fat body cells contained vegetative stages and primary spores at 4 and 5 days postinfection, and diplokaryotic spores and immature octospores were also present. Approximate digestibility of infected larvae increased during this time period, whereas the conversion of ingested and digested food to body substance decreased. The relative growth rate of infected and uninfected groups did not differ significantly between 4 and 5 days postinfection, although the relative consumption rate in infected L. dispar larvae was higher. Between 8 and 10 days postinfection, the relative growth rate of uninfected larvae increased. The infected group did not demonstrate this increase at a time period characterized by maturation of diplokaryotic spores and octospores in larval fat body tissues. Total body weight of uninfected larvae remained higher than that of infected larvae after 8 days postinfection.     

Development, ultrastructure, natural occurrence, and molecular characterization of Liebermania patagonica n. g., n. sp., a microsporidian parasite ot the grasshopper Tristira magellanica (Orthoptera: Tristiridae)

A new microsporidium, Liebermannia patagonica n. gen., n. sp., is described from midgut and gastric caecum epithelial cells of Tristira magellanica, an apterous grasshopper species of southern Patagonia, Argentina. L.patagonica is diplokaryotic, apansporoblastic, homosporous, and polysporoblastic. Transitional (from merogony to sporogony) stages and sporonts of L. patagonica were surrounded by host rough endoplasmic reticulum. The ovocylindrical spores measured 2.9 +/- 0.09 x 1.2 +/- 0.04 microm (fresh, n = 50), and they had an isofilar polar filament of only three coils and a cluster of tubules instead of a classical posterior vacuole. Prevalence was high (up to 80.6%) at the type locality for the four years sampled . Maximum likelihood , neighbor joining, maximum parismony analyses of the small submit rDNA all placed L.patagonica(Accession No. DQ 239917) in one with Orthosomella operophterae.     

On the Cytology of Toxoglugea chironomi (Debaisieux, 1931) Jírovec 1936 (Microspora, Thelohaniidae)

ABSTRACT. The light microscopic and ultrastructural characteristics of a microsporidium provisionally identified as Toxoglugea chironomi (Debaiseux, 1931) Jírovec, 1936, is described. It was isolated from oenocytes and adipose tissue of a midge larva of the genus Dicrotendipes . Merozoites are diplokaryotic. The sporogony produces, by fragmentation, eight monokaryotic spores in a sporophorous vesicle. Mature spores are horse-shoe shaped. The total length is about 5.8 μm, the width 0.8-0.9 μm, the external height of the curve 2.3-3.5 μm, and the external width of the curve 3.5-5.2 μm. The polaroplast has lamellar compartments of two types: narrow and closely packed anteriorly, and wider and more loosely arranged posteriorly. The isofilar polar filament is arranged in 8–10 coils in the posterior fourth of the spore. The external nuclear membrane is sometimes continuous with the endoplasmic reticulum. Lamellar and tubular material of exospore construction are present in the episporontal space from the beginning of sporogony. Teratological and normal spores sometimes occur together in the sporophorous vesicle. The identification of the species is discussed and the ultrastructure is compared to Toxoglugea variabilis , the only further species of the genus with known ultrastructural cytology.     

Fine Structure and Development of Pilosporella chapmani (Microspora: Thelohaniidae) in the Mosquito,Aedes triseriatus (Say)1

ABSTRACT. New information on the life cycle and fine structure of Pilosporella chapmani, a microsporidium of the mosquito Aedes triseriatus, is presented. Pilosporella chapmani is shown to have two sporulation sequences, one of them being involved in transovarial transmission. One sequence, involving meiosis and production of a moniliform sporogonial plasmodium, occurs in the larval fat body, resulting in eight uninucleate, spherical, and fully developed spores. The other occurs in oenocytes of adult mosquitoes and results in isolated, binucleate, elongate, and thin-walled spores. Also, for the first time, metabolic products are shown to be expelled into the surrounding host tissues through the wall of the sporocyst.     

A Light and Electron Microscopical Study of Trichoduboscqia epeori Léger (Microspora: Duboscqiidae)1

Trichoduboscqia epeori Léger was found to parasitize nymphs of the mayfly Rhithrogena iridina Kolenati in southwest Germany for a new host record. It was studied by light and electron microscopy. The pansporoblast membrane is evaginated at several points, usually four, to produce long needle-like appendages >20 μm in length with a resilient inner core superficially resembling collagen, which is thought to maintain their orientation. It is suggested that the pansporoblast appendages may play a role in host infection. The structure and ultrastructure of developmental stages are recorded for the first time. Apart from the pansporoblast appendages, the ultrastructure of T. epeori conforms to the general pattern seen in many other pansporoblastic Microspora. Typically 16 spores are produced per pansporoblast but 32-spore pansporoblasts were also found, and the taxonomic significance of this is discussed.     

Moulting hormone,juvenile hormone and the ultrastructure of the fat body of adult Sarcophaga bullata (Diptera)

Summary In the ovoviviparous fly, Sarcophaga bullata, vitellogenesis is cyclic; a process reflected in ultrastructural changes in the fat body cells and oenocytes. At eclosion the larval fat body has not yet completely disappeared. During vitellogenesis the fat body cells are specialized for intensive protein synthesis showing a very extensive RER and numerous invaginations of the plasma membrane. These features disappear when the eggs descend into the oviducts to complete embryogenesis. The predominant feature of the oenocytes is their very prominent SER. The fat body cells of the males are never as specialized for protein synthesis as those of the females. Feeding of ecdysterone to males for 3 or more days induces a rather extensive subcellular apparatus for protein synthesis, i.e., invaginations of the plasma membrane and an extensive RER. Juvenile hormone is completely ineffective in this respect. Both ecdysterone and juvenile hormone have pronounced but different effects on the oenocytes of males.