Epizootiological studies of Amblyospora albifasciati (Microsporidiida: Amblyosporidae) in natural populations of Aedes albifasciatus (Diptera: Culicidae) and Mesocyclops annulatus (Copepoda: Cyclopidae) in a transient floodwater habitat

The epizootiology of the microsporidium Amblyospora albifasciati was studied in natural populations of its definitive host, a multivoltine, neotropical, floodwater mosquito, Aedes albifasciatus, and its intermediate copepod host, Mesocyclops annulatus, in an ephemeral floodwater habitat during a 12-month period. A. albifasciati was enzootic in mosquitoes. Vertically (transovarially) transmitted meiospore infections occurred regularly and were detected in five of eight larval broods but the prevalence of infection was always low, ranging from 0.5 to 6.9% with an overall average of 0.7%. Horizontal transmission of A. albifasciati infection from copepods to mosquitoes was nominal and limited. It was detected at levels of 6.4 to 20% in larval Ae. albifasciatus populations on two occasions, the month of August and late September through early October. The low levels of horizontal transmission of infection to mosquito larvae appeared to be the principal limiting factor that prevented the proliferation of A. albifasciati in Ae. albifasciatus populations. Copepod populations were abundant from May through September and weekly prevalence rates of A. albifasciati averaged over 50% (range = 5.8 to 100%). The moderately high infection rates in M. annulatus copepods were inconsistent with the low prevalence of meiospore infection in Ae. albifasciatus mosquito larvae. Results suggest that either meiospores of A. albifasciati produced in the mosquito host are highly infectious to copepods or they are long-lived and remain viable within the pool as long as some standing water is present. Observations further indicate that A. albifasciati has a significant detrimental impact on M. annulatus copepod populations but minimal impact on larval populations of Ae. albifasciatus at this site.     

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.     

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.     

Ultrastructural Characterization of Meiospores of Six New Species of Amblyospora (Microsporida: Amblyosporidae) from Northern Aedes (Diptera: Culicidae) Mosquitoes

ABSTRACT. The ultrastructure of meiospores of six different species of Amblyospora found infecting larval mosquitoes of Aedes abserratus, Aedes aurifer, Aedes cinereus, Aedes excruciates, Aedes sticticus , and Aedes stimulans are described. Meiospores of all species exhibited characteristics typical for the genus Amblyospora including: a single nucleus, a large posterior vacuole, a thick undulating exospore and thinner endospore, a bipartite and lamellate polaroplast with more tightly stacked membranes in the proximal region, and an anisofilar polar filament with distal coils reduced in thickness. Distinct differences were found in the arrangement and number/ ratio of coils formed by the broad basal and narrow distal portions of the polar filament. These differences, when quantified and averaged, were unique from all other mosquito-parasitic species that have been examined ultrastructurally. Information on parasite development, natural field prevalence and transmission to suspected intermediate copepod hosts is presented. The creation of six new species, Amblyospora abserrati, Amblyospora auriferi, Amblyospora cinerei, Amblyospora excrucii, Amblyospora stictici , and Amblyospora stimuli is proposed. Synonymies and complete host lists of all forms and species of Amblyospora described from mosquitoes are given.     

Epizootiology of Amblyospora connecticus (Microsporida) in field populations of the saltmarsh mosquito, Aedes cantator, and the cyclopoid copepod, Acanthocyclops vernalis

The natural ecology of a heterosporous microsporidium, Amblyospora connecticus was investigated at three different salt marsh habitats during 1986-1989. The parasite has a well-defined seasonal transmission cycle that occurs regularly each year and intimately involves the primary mosquito host, Aedes cantator, and the intermediate copepod host, Acanthocyclops vernalis. In the spring, the microsporidium is horizontally transmitted from the copepod, where it appears to overwinter, to the mosquito via the ingestion of haploid spores produced in the copepod. Mosquitoes develop a benign infection, and females transmit the microsporidium transovarially to their progeny via infected eggs. Oviposition occurs during the summer and infected eggs hatch synchronously in the fall causing widespread epizootics. Infected larvae die, and the cycle is completed when meiospores are released into the pool and subsequently are eaten by A. vernalis, which reappears in the fall and early winter. Amblyospora connecticus thereby persists by surviving in one of two living hosts throughout most of its life cycle rather than in the extra-corporeal environment. This represents an important survival strategy for A. connecticus as results show the salt marsh habitat to be a relatively unstable environment that is subject to periodic flooding and drying. The adaptive significance of utilizing an intermediate host in the life cycle is discussed as it directly facilitates transmission and enhances survival of the microsporidium.     

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.     

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)

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.     

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).     

Development of Edhazardia aedis (Kudo, 1930) n. g., n. comb. (Microsporida: Amblyosporidae) in the mosquito Aedes aegypti (L.) (Diptera: Culicidae)

A microsporidium of the mosquito Aedes aegypti (L.), identified as Nosema aedis Kudo, 1930, was found to be a heterosporous species with 3 sporulation sequences. Usually, 1 sequence developed in a parental generation host individual that was infected per os as a larva and the other 2 developed concurrently in a filial host larva that was infected transovarially. Under some conditions there were deviations from the parental host-filial host alternation. The 1st sporulation sequence was diplokaryotic (diploid in a particular sense) throughout; the other 2 arose from diplokaryotic meronts, developed concurrently and ended with haploid spores. Haplosis in 1 case was by means of dissociation of the diplokaryon. In the other case it was by meiosis. Conflicting reports about whether the members of the diplokaryon in the latter sequence separate and undergo meiosis individually or coalesce and undergo meiosis as 1 nucleus were resolved in favor of the latter idea. A new genus in family Amblyosporidae was created to contain this species, which then became Edhazardia aedis (Kudo, 1930) n. g., n. comb.     

Infection of the western treehole mosquito,Aedes sierrensis (Diptera: Culicidae), with Lambornella clarki (Ciliophora: Tetrahymenidae)

Lambornella clarki was a common parasite of Aedes sierrensis immatures collected from treeholes in Mendocino County, California, in 1982–1983. The ciliate was not found in mosquitoes from treeholes with water having the most extreme values of electrical conductivity (<0.23 and >1.74 mmhos/cm) and pH (<6.5 and >7.7). Infection rates for individual monthly samples from L. clarki-positive treeholes ranged from 1 to 75%; 67% of all infections were observed in 4th-instar larvae. Infection with pathogens and parasites such as L. clarki, Ascogregarina clarki, Octomyomermis troglodytis, and unidentified bacteria and fungi, appeared responsible for high mortality rates (21–76%). Parasitism with L. clarki did not always result in death of the mosquito host; 7% of adults emerging from samples held in the laboratory were found to be infected. Ciliates were restricted to the host hemocoel except in older females where they invaded the ovaries, resulting in parasitic castration. This phenomenon may be associated with parasite dispersal.     

Reduced productivity in adult yellowfever mosquito (Diptera: Culicidae) populations

Male and female Aedes aegypti (L.) mosquitoes of the laboratory strain ROCK were irradiated with 130 mw of argon 514.5 nm laser microbeams for 0.04, 0.25, 0.4, and 0.5 s, respectively. Egg production, percentage hatch, and productivity (average number of adults surviving after 3 wk) were used to assess mutagenic effects. Mortality was high for males in all laser radiation groups and increased with time of exposure. Except for the group treated for 0.25 s, significant reductions in total F1 progeny also were demonstrated for all other experimentals when male parents were exposed to laser radiation. Females showed a high mortality when subjected to 0.4- and 0.5-s laser radiation. No F1 progeny were produced when parental females were exposed for 0.25, 0.4, and 0.5 s. Numbers of F1 progeny from females exposed to 0.04 s of laser radiation were significantly reduced. A comparison of weekly mean number of progeny showed that the important differences in productivity occurred during the first and second week, respectively, when either male or female adult parents were subjected to laser radiation.     

Behavioural functions of grooming in male Aedes albopictus (Diptera: Culicidae), the Asian tiger mosquito

Flight, walking and resting behaviours of male Aedes albopictus (Skuse) were observed in a flight cage. These behaviours were also associated with repetitive acts of grooming. The effects of sugar meal and period of the day on the total duration, the frequency and the duration of each individual grooming behaviour were studied. Fed or unfed males were individually released in a transparent plastic flight cage and direct visual observations using Observer software were carried out for 2?h during the morning and 2?h in the afternoon. There was no significant difference in the grooming behaviour between morning and afternoon observations. Fed male mosquitoes groomed longer than unfed males. The sugar meal seemed an important influencing factor of the grooming behaviour by giving more energy and making different parts of the mosquito sticky. The functions of grooming behaviour are discussed in regard to other behaviours such as mating, copulation, sensory detection and flight.     

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.     

Epizootiology of Hyalinocysta chapmani (Microsporidia: Thelohaniidae) infections in field populations of Culiseta melanura (Diptera: Culicidae) and Orthocyclops modestus (Copepoda: Cyclopidae): a three-year investigation

The epizootiology, transmission dynamics and survival strategies employed by the microsporidium Hyalinocysta chapmani were examined in field populations of its primary mosquito host, Culiseta melanura and its intermediate copepod host, Orthocyclops modestus over a three-year period in an aquatic subterranean habitat. H. chapmani was enzootic and was maintained in a continuous cycle of horizontal transmission between each host. There were three distinct periods during the summer and fall when developing mosquito larvae acquired infections; each was preceded by or coincident with the detection of infected copepods. Results were corroborated in laboratory bioassays, wherein transmission was achieved in mosquito larvae that were reared in water and sediment samples taken from the site during the same time periods. The highest infection rates, ranging from 60% to 48%, were repeatedly observed during the first six weeks of larval development. These were coincident with the most sustained collections of infected copepods obtained during the year and highest levels of infection achieved in the laboratory transmission studies. The high prevalence rates of lethal infection observed in larval populations of C. melanura at this site are among the highest recorded for any mosquito-parasitic microsporidium and clearly suggest that H. chapmani is an important natural enemy of C. melanura. H. chapmani appears to overwinter in diapausing mosquito larvae but may also persist in copepods. The absence of vertical transmission in the life cycle of H. chapmani and the sole reliance on horizontal transmission via an intermediate host are unique survival strategies not seen among other mosquito-parasitic microsporidia. The epizootiological data suggest that this transmission strategy is a function of the biological attributes of the hosts and the comparatively stable environment in which they inhabit. The subterranean habitat is inundated with water throughout the year; copepods are omnipresent and C. melanura has overlapping broods. The spatial and temporal overlap of both hosts affords abundant opportunity for continuous horizontal transmission and increases the likelihood that H. chapmani will find a target host. It is hypothesized that natural selection has favored the production of meiospores in female host mosquitoes rather than congenital transfer of infection to progeny via ovarian infection as a strategy for achieving greater transmission success.     

Morphology, biology and geographical distribution of the mosquito Aedes (Ochlerotatus) sergievi (Diptera, Culicidae)

New data on morphology and differential diagnosis of adults (variability of the pattern of mesonotum and wings, difference from all other species of the cantans group of the Palaearctic fauna by the spot of the scales on the mesepimeron reaching its lower edge, difference of its male genitalia from those of Ae. montchadskyi Dub.), biology (period of activity and predomination indices of the females attacking man, breeding places and period of occurrence of preimaginal phases in the south of the East Transbaikalia and Krasnoyarsk Region), and geographical distribution (from the Tuva ASSR and south of Krasnoyarsk Region in the west to the south of the Chita Region in the east, misidentification in East Kazakhstan, confinement of the range to the Mongolian district of the Kazakhstan-Mongolian province of the Central Asian subregion of the Holarctic that suggests that the main part of its distribution range is situated in Mongolia) are given for the recently described species of mosquitoes, Aedes sergievi Danilov, Markovich et Proskuryakova, 1978 from the south of East Siberia.