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.     

Karyogamy and meiosis in an Amblyospora sp. (Microspora) in the mosquito Culex salinarius

Stages of merogony and sporogony are illustrated in photomicrographs of lacto-aecto-orcein stained smears of an undescribed species of Amblyospora in male Culex salinarius larvae. Karyogamy was observed to take place in diplokaryotic meronts followed by an unusual meiosis-like process in young sporonts. Karyogamy was confirmed by DNA measurements in the nuclei of meronts. DNA measurements at mingling indicate that tetrads may not be formed during “pachytene.” Therefore, structures previously reported to be synaptonemal complexes and meiotic configurations of chromosomes may not actually represent true pachytene chromosomes. It is further shown that karyogamy has been either misplaced or overlooked by numerous investigators and that the behavior of chromosomes during the meiosis-like process was misinterpreted by previous researchers studying chromosomes in microsporidian sporonts.     

Significance of transovarial infections of Amblyospora sp. (Microspora:Thelohaniidae) in relation to parasite maintenance in the mosquito Culex salinarius

Adult females of Culex salinarius, transovarially infected with the microsporidium Amblyospora sp., showed no significant differences in overall fecundity, physiological longevity, and preoviposition periods when compared to healthy adults under laboratory conditions. Development times and survival rates for congenitally infected young to reproductive age were also indistinguishable from those of healthy controls. A significant reduction of 52% in egg hatch was observed for infected eggs when compared to healthy eggs. Prevalence rates of infection for progeny produced by infected females declined with each successive gonotrophic cycle and averaged 90%. Transovarial transmission is not sufficient for the maintenance of the microsporidium in a population of mosquitoes. An alternate host is suggested as a mechanism whereby the microsporidium can reenter a healthy mosquito population.     

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.     

Amblyospora sp. (Microspora, Amblyosporidae) infecting nerve ganglia of Culex pipiens (Diptera, Culicidae) from Egypt.

A species of Amblyospora-infecting neurones of Culex pipiens is described. Diplokaryotic meronts, which divided by binary fission, were distinguished at the electron microscope level by their unthickened plasma membranes. Sporonts with an electron-dense surface coat gave rise to eight uninucleate sporoblasts within a sporophorous vesicle, cytoplasmic division occurring at the quadrinucleate or octonucleate stages. Indications that nuclear fusion and chromosome reorganization occurred in merogony and sporogony were obtained by light microscopy but meiosis was not detected at the ultrastructural level. Spores were typical of Amblyospora, being ovoid when fresh, truncate when stained, and having an exospore of two membranous layers subtended by a thick amorphous layer, an electron-lucent endospore, an anisofilar polar filament, and a polaroplast comprised of an anterior region of close-packed lamellae and a posterior region of expanded sacs. The metabolic products in the sporophorous vesicle took the form of large globules, small globules with electron-dense borders, and fine granules. These were depleted in mature sporophorous vesicles, though a surface layer of fine granules on the spores may have been derived from them. Many stages were degenerate and it is suggested that C. pipiens may be an accidental host in which the parasite could develop suboptimally in nervous tissue only. Infections in larvae hatched from eggs in the laboratory indicate that vertical transmission occurs.     

Amblyospora trinus N. sp. (Microsporida: Amblyosporidae) in the Australian mosquito Culex halifaxi (Diptera: Culicidae)

A new species of Amblyospora, a parasite found in wild populations of the predacious Australian mosquito Culex halifaxi, was investigated with light and electron microscopy. This species was found to be heterosporous with two concurrent sporulation sequences in the host larvae, both arising from diplokaryotic meronts and ending with haploid spores. One sequence was dominant and involved meiosis to produce eight thick-walled, broadly oval meiospores in a sporophorous vesicle (SV). The other sequence involved nuclear dissociation to produce lanceolate, thin-walled spores in a subpersistent SV. Horizontal transmission to the mosquito host, by one or both of two distinctly different pathways (one via an intermediate host, the other by cannibalism of infected individuals) and by vertical transmission, are postulated but have not been demonstrated. A new species, Amblyospora trinus, is proposed and its affinities to other heterosporous microsporidia in mosquitoes are discussed.     

Chromosomal Evidence on the Sporogony of Amblyospora californica (Microspora: Amblyosporidae) in Culex tarsalis (Diptera: Culicidae)

ABSTRACT. Amblyospora californica is a polymorphic, eukaryotic microsporidian. Three types of sporogony producing three types of spores occur in male larvae and female adults of its mosquito host, Culex tarsalis , and an alternate copepod host, Acanthocyclops vernalis. Development of A. californica in male larvae includes merogony and sporogony. Karyogamy and meiosis was observed in sporogony in male larvae but not in the female adult or in the copepod. Chromosomal evidence showed that sporogony included two consecutive meiotic divisions and a subsequent mitosis forming an octosporont, ultimately containing eight haploid, uninucleate mature spores. In this species, the haploid number of chromosomes is nine. Macrosporoblasts and macrospores, containing 1, 2 or more nuclei, can be seen in infected male larvae. The stage of sporogony in which cytokinesis was arrested seems to determine the number of nuclei. Those with only one nucleus, we believe are due to failed nuclear division at meiosis. Although A. californica displayed a process of karyogamy and meiosis similar to that of the species from Cx. salinarius , they may not be the same species because of the difference in their chromosome numbers.     

Life cycle and description of Amblyospora camposi n. sp. (Microsporidia: Amblyosporidae) in the mosquito Culex renatoi (Diptera, Culicidae) and the copepod Paracyclops fimbriatus fimbriatus (Copepoda, Cyclopidae)

The life cycle of Amblyospora camposi n. sp. is described from the mosquito Culex renatoi and the copepod Paracyclops fimbriatus fimbriatus collected in the leaf axils of the plant Eryngium cabrerae in Argentina. Meiospores of A. camposi (5.8 x 4.1 microm) were infectious per os to female adults of the copepod P. f. fimbriatus. All developmental stages in the copepod had unpaired nuclei, with sporulation involving the formation of a sub-persistent, sporontogenic, interfacial envelope and the production of a second type of uninucleate spore. These spores, formed in the ovaries of P. f. fimbriatus, were large, pyriform, and measured 10.70 x 3.85 microm. When ingested they infected C. renatoi larvae to initiate a sequence that involves schizogony and gametogony and ends with plasmogamy and nuclear association to form diplokaryotic meronts. Oblong ovate binucleate spores (7.86 x 2.96 microm) are formed in the adult mosquito and are responsible for vertical transmission to the filial generation. This is the first report of an Amblyospora species from a mosquito that inhabits the small-water bodies held in parts of terresterial plants (phytotelmata).     

Laboratory experiments on infection rates of Amblyospora dyxenoides (Microsporida: Amblyosporidae) in the mosquito Culex annulirostris

Laboratory observations were made of the microsporidian parasite Amblyospora dyxenoides in its natural mosquito host, Culex annulirostris. There were no differences in the numbers of eggs laid and in the proportions which hatched between infected and uninfected females, indicating that the parasite did not affect fecundity. Unlike other species of Amblyospora which have been studied the development of binucleate spores in adult mosquitoes increase with age of the host in both sexes and in females it proceeds independently of egg development and blood feeding. The same trend is apparent for adult mosquitoes which acquired the infection in the larval stage by horizontal transmission from the intermediate copepod host as well as for mosquitoes which acquired oenocytic infections by transovarial transmission. There was considerable variation in the proportion of mosquitoes which became infected after exposure to A. dyxenoides infected copepods. Infections in larval progeny of female mosquitoes infected via spores produced in copepods ranged from 0 to 100% in individual batches and averaged 45.6% with meiospore infections, 19.3% with oenocytic infections, with the remaining 35.7% being uninfected. Similar variability was observed in the progeny of infected female mosquitoes in the second generation after exposure to infected copepods. During experiments in which the microsporidium was maintained in C. annulirostris through 9 successive transovarially transmitted cycles (by selectively rearing the progeny of females infected with binucleate spores after an initial exposure to infected copepods) the proportion of infected progeny with oenocytic infections increased from 25 to around 50% whereas the incidence of meiospore infections declined from 50 to 10%.(ABSTRACT TRUNCATED AT 250 WORDS)     

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.     

Intermediate host for an Amblyospora sp. (microspora) infecting the mosquito, Culex annulirostris

Experiments conducted in Australia are described which show that there is an intermediate host involved in the life cycle of an Amblyospora sp. infecting the mosquito, Culex annulirostris. Microsporidian spores produced in the cyclopoid copepod, Mesocyclops albicans, are infectious to laboratory colony C. annulirostris larvae and produce developmental stages identical to those of natural Amblyospora infections in this mosquito. These larval infections result in uninucleate spores in progeny mosquitoes which, in turn, are infectious to M. albicans. Subsequent studies conducted with Amblyospora, copepods, and mosquitoes in the United States to replicate and reconfirm results obtained in Australia were successful. This is the first substantiated evidence of the involvement of intermediate hosts in the life cycles of microsporidia, and the discovery now provides us with information needed to evaluate these organisms as biological control agents for mosquitoes and other disease vectors.     

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.     

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.     

Amblyospora trinus N. Sp. (Microsporida: Amblyosporidae) in the Australian Mosquito Culex halifaxi (Diptera: Culicidae)

ABSTRACT. A new species of Amblyospora , a parasite found in wild populations of the predacious Australian mosquito Culex halifaxi , was investigated with light and electron microscopy. This species was found to be heterosporous with two concurrent sporulation sequences in the host larvae, both arising from diplokaryotic meronts and ending with haploid spores. One sequence was dominant and involved meiosis to produce eight thick-walled, broadly oval meiospores in a sporophorous vesicle (SV). The other sequence involved nuclear dissociation to produce lanceolate, thin-walled spores in a subpersistent SV. Horizontal transmission to the mosquito host, by one or both of two distinctly different pathways (one via an intermediate host, the other by cannibalism of infected individuals) and by vertical transmission, are postulated but have not been demonstrated. A new species, Amblyospora trinus , is proposed and its affinities to other heterosporous microsporidia in mosquitoes are discussed.     

Epizootiology of Amblyospora stimuli (Microsporidiida: Amblyosporidae) infections in field populations of a univoltine mosquito, Aedes stimulans (Diptera: Culicidae), inhabiting a temporary vernal pool.

The epizootiology of the microsporidium Amblyospora stimuli was studied in natural populations of a univoltine mosquito, Aedes stimulans, inhabiting a temporary vernal pool over an 18-year period. The yearly prevalence of benign oenocytic infections in adult females was variable, ranging from 1.0 to 9.6% (mean = 5.1%). The yearly prevalence of transovarially transmitted meiospore infections in larval populations was consistently lower but less variable, ranging from 1.3 to 5.9% (mean = 3.5%). Meiospore infections in F(1)-generation larvae were significantly correlated with infections in parental-generation females, thus suggesting that larval infection rates could be substantially increased if methods were available to facilitate transmission of A. stimuli to a larger portion of the female population via inundative or inoculative release of infected copepods. No correlation was found when infections in filial-generation adult females were measured against meiospore infections in larvae from the preceding year. Analysis of yearly prevalence data using Fine's Fundamental Vertical Transmission Equation revealed low rates of horizontal transmission from the intermediate copepod host to female larvae in most years, ranging from 0.1 to 8.7% (mean = 3.1%). A. stimuli is enzootic, persists at a very low level, and has minimal impact on Ae. stimulans populations at this site. The low incidence rate of horizontal transmission to larvae appears to be due largely to a paucity of copepods and is a major factor that limits the abundance and subsequent proliferation of A. stimuli in Ae. stimulans populations at this locale. Results support the view that host-parasite cospeciation is an important mechanism of evolution in this group of mosquito/copepod microsporidia.     

Life cycle of Brachylaima mascomai n. sp. (Trematoda: Brachylaimidae), a parasite of rats in the Llobregat delta (Spain)

The terrestrial triheteroxenous life cycle of Brachylaima mascomai n. sp. (Trematoda: Brachylaimidae) is elucidated. Operculated, assymetric, embryonated eggs (25.4 x 12.7 microm) are passed with feces of the natural (Rattus norvegicus and R. rattus) and experimental (albino and wild mice, albino rats, Apodemus sylvaticus, Mus spretus [Muridae] and the golden gerbil) definitive hosts and ingested by the helicid gastropod Pseudotachea splendida, the only natural and experimental first intermediate host. Microcaudate cercariae harbored in branched sporocysts in the digestive gland emerge from this snail and contact P. splendida, Otala punctata, Theba pisana, and Helix (C.) aspersa snails developing into unencysted infective metacercariae in the kidney. Definitive hosts are infected by ingestion of infected snails; the adult parasites inhabit the small intestine. Chaetotaxic cercarial pattern specific at acetabular (S(II) 8-10 papillae) and cephalic (C(III) 13-15 papillae, H 16 papillae) levels. Three types of cercarial papillae are observed by scanning electron microscopy (SEM) and their arrangement is correlated with chaetotaxy for the first time in trematodes: argentophilic papillae with fingerlike process (cephalic, body, and acetabular levels), argentophilic papillae with opening (2 papillae in the M body level), and nonargentophilic dome-shaped papillae (alternated with argentophilic S(II) papillae on the ventral sucker). SEM detected interlacing network of ridges covering the metacercarial body. Adults with multidigitate tegumentary spines were observed by SEM. Subequal suckers; the acetabulum located in the posterior part of anterior fifth of body. Vitellaria extend from between middle level and anterior margin of anterior testis to between middle level and posterior margin of acetabulum. Uterus almost reaches the intestinal bifurcation.     

Six new species of microsporidia of the genus Amblyospora (Microspora: Amblyosporidae) from blood sucking mosquitoes (Diptera: Culicidae) from the west Siberia

Microsporidia of the genus Amblyospora parasiting the adipose body of mosquito larvae of the genus Aedes and Culex has been studied with both light and electron microscopy. Six new species of microsporidia are described based on ultrastructural characteristics of spores and sporogony stages. Amblyospora flavescens sp. n. Mature spores are egg-shaped. The spore wall with three layers, about 165 nm. Exospore is two-membranous. Subexospore is absent. Endospore is electron-translucent. Polaroplast consists of three parts: lamellar, large vesicular, lamellar. The anisofilar polar filament with 10--11 coils (3 1/2 + 2 1/2 + 4-5). Fixed spores are 6.3 +/- 0.1 x 4.24 +/- 0.1 microm. Amblyospora kolarovi sp. n. Mature spores are egg-shaped. The spore wall with three layers, about 265-315 nm. Exospore shapes tucks on the surface of spore. It is two-membranous. Subexospore is quagge, structural. Endospore is electron-translucent. Polaroplast consists of two parts: lamellar and large vesicular. The anisofilar polar filament with 11-13 coils (3 + 8-10). Fixed spores are 5.4-5.6 x 3.5-4.2 microm. Amblyospora orbiculata sp. n. Mature spores are widely egg-shaped. On a back pole there is a small concavity. The spore wall with three layers, about 155 nm. Exospore is shapes tucks on a surface of spore. It is two-membranous. Subexospore is absent. Endospore is electron-translucent. Polaroplast consists of three parts: lamellar, vesicular, lamellar. Polar filament is anisofilar, with 11 1/2 coils (4 1/2 + 1 + 6). Fixed spores are 6.3 +/- 0.1 x x 4.0 +/- 0.1 microm. Amblyospora rugosa sp. n. Mature spores are egg-shaped. On a back pole there is a small concavity. The spore wall with three layers, about 225 nm. Exospore is shapes tucks on a surface of spore. It is two-membranous. Subexospore is quaggy, structural. Endospore is electron-translucent. Polaroplast lamellate. Polar filament is anisofilar, with 17 1/2 coils (3 1/2 + 1 + 13). Fixed spores are 5.3 +/- 0.1 x 3.7 +/- 0.1 microm. Amblyospora undata sp. n. Mature spores are egg-shaped. The spore wall is three-layered, about 220 nm. Exospore is shapes tucks on a surface of spore. It is two-membranous. Subexospore is quaggy, structural. Endospore is electron-translucent. Polaroplast lamellate. The anisofilar polar filament with 8 coils (3 + 5). Fixed spores are 5.0 +/- 0.1 x 3.0 +/- 0.1 microm. Amblyospora urski sp. n. Mature spores have widely oval form. The back pole is concave. The spore wall with three layers, about 280 nm. Exospore is shapes tucks on a surface of spore. It is two-membranous. Subexospore is quaggy, structural. Endospore is electron-translucent. Polaroplast lamellate. Polar filament is anisofilar, with 6 coils (2 + 4). Fixed spores are 4.4 +/- 0.1 x 2.9 +/- 0.1 microm.