DsRNA-mediated targeting of ribosomal transcripts RPS6 and RPL26 induces long-lasting and significant reductions in fecundity of the vector Aedes aegypti

Ribosomal transcripts produce critical proteins that are involved in most cellular production processes. Targeting ribosomal transcripts has produced mortality in mites and ticks but the effect of ribosomal transcript knockdown has not been thoroughly examined in mosquitoes. We examine the effects of triggers targeting four ribosomal proteins (RP) transcripts. Although no significant mortality was observed after dsRNA microinjection and subsequent blood feeding, significant contrasts were observed on fecundity. Triggers targeting RPS6 and RPL26 effectively reduced gene expression but more importantly, reduced reproductive output by more than 96% and 91% at the first oviposition while triggers targeting RPL1 and RPS2 did not cause a reduction although gene expression was reduced. Significantly reduced fecundity continued through a second oviposition cycle in dsRPS6 and dsRPL26 cohorts, although the effect was not as strong. Relative gene expression levels confirmed specific transcript knockdown up to 20days post-injection in mosquitoes that did not oviposit or produced reduced clutch sizes. Dissections at 36h post-blood meal indicated defects in oocyte provisioning. The strong phenotype produced by dsRPS6 allowed us to examine the effects in various tissues as well as the dose response, trigger format, delivery method and trigger specificity in Aedes aegypti. Strong knockdown was observed in the abdomen and the ovaries. Greater than 50ng of dsRPS6 significantly reduced fecundity but not when delivered in a sugar meal or as an siRNA. Similar bioassays with mutated dsRPS6 triggers indicates that up to three mismatches per possible siRNA are still effective in reducing fecundity. These studies indicate that while active and effective triggers can be developed for vector species, the lack of an efficient delivery method is the biggest barrier to use as a potential control method.

Microsporidia - Emergent Pathogens in the Global Food Chain

Intensification of food production has the potential to drive increased disease prevalence in food plants and animals. Microsporidia are diversely distributed, opportunistic, and density-dependent parasites infecting hosts from almost all known animal taxa. They are frequent in highly managed aquatic and terrestrial hosts, many of which are vulnerable to epizootics, and all of which are crucial for the stability of the animal-human food chain. Mass rearing and changes in global climate may exacerbate disease and more efficient transmission of parasites in stressed or immune-deficient hosts. Further, human microsporidiosis appears to be adventitious and primarily associated with an increasing community of immune-deficient individuals. Taken together, strong evidence exists for an increasing prevalence of microsporidiosis in animals and humans, and for sharing of pathogens across hosts and biomes.

Influence of temperature on microsporidia infections in a natural population of Simulium pertinax Kollar, 1832 (Diptera; Simuliidae)

During the studies involving the correlation between the water temperature of the breeding site of Simulium pertinax larvae and the infection prevalence by microsporidia, developed in the Andorinhas river, Magé, RJ, weekly samples of blackfly larvae were taken within a two-year period (2001-2002 and 2003-2004), and it was noticed that the infections by Amblyospora sp. were more prevalent when compared to infections by Polydispyrenia sp. in larvae. It was also observed that the infections do not follow the same pattern, since the genus Amblyospora was recorded almost every month during the study with the exception of December, 2001. In the results of correlation between the environmental water temperature and the microsporidia infection rates, it was observed that for the first period studied, there was a high negative correlation, while during the second period there was absence correlation. On the other hand, the Amblyospora sp. infection rates prove that the correlation was high and significant in the first period, but was not significant in the second sampling period and Polydispyrenia sp. showed absence correlation in both periods.

Effects of temperature, pH and salinity on the infection of Leptolegnia chapmanii Seymour (Peronosporomycetes) in mosquito larvae

The effects of temperature, pH, and NaCl concentrations on the infectivity of zoospores of Leptolegnia chapmanii (Argentine isolate) were determined for Aedes aegypti and Culex pipiens under laboratory conditions. Zoospores of L. chapmanii were infectious at temperatures between 10 and 35 degrees C but not at 5 or 40 degrees C. At the permissive temperatures, mortality rates in young instars were much higher than in older instars and larvae of Ae. aegypti were more susceptible to L. chapmanii than larvae of Cx. pipiens. At 25 degrees C, Ae. aegypti larvae challenged with L. chapmanii zoospores resulted in 100% infection at pH levels ranging from 4 to 10. Larvae of Cx. pipiens exposed to similar pH and zoospore concentrations resulted in increasing mortality rates from 62% to 99% at pH 4 to 7, respectively, and then decreased to 71% at pH 10. Aedes aegypti larvae exposed to L. chapmanii zoospores in NaCl concentrations ranging from 0 to 7 parts per thousand (ppt) at 25 degrees C resulted in 100% mortality while mortality rates for Cx. pipiens decreases from 96% in distilled water to 31.5% in water with 6 ppt NaCl. Control Cx. pipiens larvae died when exposed at a NaCl concentration of 7 ppt. Vegetative growth of L. chapmanii was negatively affected by NaCl concentrations. These results have demonstrated that the Argentinean isolate of L. chapmanii tolerated a wide range of temperatures, pH, and salinity, suggesting that it has the potential to adapt to a wide variety of mosquito habitats.

Morphological and molecular characterization of a new microsporidian species from the predatory mite Metaseiulus occidentalis (Nesbitt) (Acari, Phytoseiidae)

A new microsporidian species is described from the predatory mite Metaseiulus (formerly Typhlodromus or Galendromus) occidentalis (Nesbitt) (Acari, Phytoseiidae). The ultrastructure of this new species is presented together with the first molecular characterization for a microsporidium of mites. All stages of this new microsporidium are haplokaryotic and develop in direct contact with the host-cell cytoplasm. Sporogony is disporoblastic and spores are formed in eggs, immature stages, and adults of M. occidentalis. There are two morphological classes of spores, one with a short polar filament (3-5 coils) that measured 2.53 x 1.68 microm and one with a longer polar filament (8-9 coils) that measured 3.14 x 1.77 microm. Horizontal transmission of this new species occurs by cannibalism of eggs and other stages and perhaps involves the spores with the long polar filament. Spores with the short polar filament may play a role in autoinfection and vertical (transovarial) transmission that is highly efficient in transferring the microsporidium from adults to progeny. Analysis of the small subunit ribosomal DNA indicated that this species from M. occidentalis is most closely related to the Nosema/Vairimorpha clade of microsporidia. A conflict between the morphological and molecular data is discussed. The species is compared to previously described microsporidia of arachnids resulting in creation of Oligosporidium occidentalis n. sp. in the family Unikaryonidae.

Genome sequence of a baculovirus pathogenic for Culex nigripalpus

In this report we describe the complete genome sequence of a nucleopolyhedrovirus that infects larval stages of the mosquito Culex nigripalpus (CuniNPV). The CuniNPV genome is a circular double-stranded DNA molecule of 108,252 bp and is predicted to contain 109 genes. Although 36 of these genes show homology to genes from other baculoviruses, their orientation and order exhibit little conservation relative to the genomes of lepidopteran baculoviruses. CuniNPV genes homologous to those from other baculoviruses include genes involved in early and late gene expression (lef-4, lef-5, lef-8, lef-9, vlf-1, and p47), DNA replication (lef-1, lef-2, helicase-1, and dna-pol), and structural functions (vp39, vp91, odv-ec27, odv-e56, p6.9, gp41, p74, and vp1054). Auxiliary genes include homologues of genes encoding the p35 antiapoptosis protein and a novel insulin binding-related protein. In contrast to these conserved genes, CuniNPV lacks apparent homologues of baculovirus genes essential (ie-1 and lef-3) or stimulatory (ie-2, lef-7, pe38) for DNA replication. Also, baculovirus genes essential or stimulatory for early-late (ie-1, ie-2), early (ie-0 and pe-38), and late (lef-6, lef-11, and pp31) gene transcription are not identifiable. In addition, CuniNPV lacks homologues of genes involved in the formation of virogenic stroma (pp31), nucleocapsid (orf1629, p87, and p24), envelope of occluded virions (odv-e25, odv-e66, odv-e18), and polyhedra (polyhedrin/granulin, p10, pp34, and fp25k). A homologue of gp64, a budded virus envelope fusion protein, was also absent, although a gene related to the other category of baculovirus budded virus envelope proteins, Ld130, was present. The absence of homologues of occlusion-derived virion (ODV) envelope proteins and occlusion body (OB) protein (polyhedrin) suggests that both CuniNPV ODV and OB may be structurally and compositionally different from those found in terrestrial lepidopteran hosts. The striking difference in genome organization, the low level of conservation of homologous genes, and the lack of many genes conserved in other baculoviruses suggest a large evolutionary distance between CuniNPV and lepidopteran baculoviruses.

Evidence of intracolony transmission of Thelohania solenopsae (Microsporidia: Thelohaniidae) in red imported fire ants (Hymenoptera: Formicidae) and the first report of spores from pupae

Red imported fire ant, Solenopsis invicta, colonies were infected horizontally by introducing live brood (mainly larvae and pupae) infected with Thelohania solenopsae. Live, infected brood introduced into uninfected colonies were adopted and raised to adulthood instead of being executed by the recipient colony. Introductions of infected larvae with uninfected pupae, which eclose into adult worker caste fire ants, resulted in an 80% infection rate of the inoculated colonies. Infections from introductions of infected pupae with uninfected larvae resulted in a 37.5% infection of inoculated colonies. Infections were also detected in 11.6 and 3.7% of the adult worker caste ants that eclosed from uninfected large larvae and pupae, respectively, that were held with infected adult workers. Microscopic examination of infected brood revealed sporoblasts and large numbers of spores of T. solenopsae in S. invicta pupae.

In vivo and in vitro development of the protist Helicosporidium sp

We describe the discovery and developmental features of a Helicosporidium sp. isolated from the black fly Simulium jonesi. Morphologically, the helicosporidia are characterized by a distinct cyst stage that encloses three ovoid cells and a single elongate filamentous cell. Bioassays have demonstrated that the cysts of this isolate infect various insect species, including the lepidopterans, Helicoverpa zea, Galleria mellonella, and Manduca sexta, and the dipterans, Musca domestica, Aedes taeniorhynchus, Anopheles albimanus, and An. quadrimaculatus. The cysts attach to the insect peritrophic matrix prior to dehiscence, which releases the filamentous cell and the three ovoid cells. The ovoid cells are short-lived in the insect gut with infection mediated by the penetration of the filamentous cell into the host. Furthermore, these filamentous cells are covered with projections that anchor them to the midgut lining. Unlike most entomopathogenic protozoa, this Helicosporidium sp. can be propagated in simple nutritional media under defined in vitro conditions, providing a system to conduct detailed analysis of the developmental biology of this poorly known taxon. The morphology and development of the in vitro produced cells are similar to that reported for the achorophyllic algae belonging to the genus Prototheca.

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).

Molecular characterization and taxonomy of a new species of Caudosporidae (Microsporidia) from black flies (diptera: simuliidae) with host-derived relationships of the North American caudosporids

A new species of microsporidium, Caudospora palustris (Microsporidia: Caudosporidae), is described from 3 species of black flies (Cnephia ornithophilia and diploid and triploid cytospecies of Stegopterna mutata), bringing to 7 the total species of caudosporids recorded from North America. This new species of caudosporid is recorded from swamp streams of the Coastal Plain from New Jersey to Georgia, with single records from the New Jersey mountains and the Upper Peninsula of Michigan. Densities of patently infected larvae (up to 10,600/m2) and spore production (nearly 8x10(11)/m2) are the greatest recorded for any microsporidium of black flies. The ultrastructure of this new species is presented, along with the first molecular characterization for a microsporidium of black flies. The phylogenetic position of black fly microsporidia within the phylum Microsporidia is presented; however, the analysis does not support the inclusion of C. palustris in any clade. Key features of all North American caudosporids are provided, and possible evolutionary trajectories are proposed based on optimization of caudosporid species on the phylogeny of their 22 known host species, including 16 that represent new host species records.

Horizontal transmission of Amblyospora albifasciati García and Becnel, 1994 (Microsporidia: amblyosporidae), to a copepod intermediate host and the neotropical mosquito, Aedes albifasciatus (Macquart, 1837)

The life cycle of Amblyospora albifasciati is characterized by three sporulation sequences involving the definitive mosquito host and a copepod intermediate host. Meiospores of A. albifasciati were infectious per os to adult females of the copepod Mesocyclops annulatus. All developmental stages in the copepod had unpaired nuclei, with sporulation involving the formation of a sporontogenic interfacial envelope and the production of a second type of uninucleate spore. These spores, formed in the ovaries of M. annulatus, were large, pyriform, and measured 10.4 x 4.8 microm. They infected Aedes albifasciatus larvae when ingested to initiate a sequence that involves schizogony and gametogony and ends with plasmogamy and nuclear association to form diplokaryotic meronts. Oval binucleate spores (9.3 x 3.1 microm) are formed in the adult mosquito and are responsible for vertical transmission to the filial generation.

Pathogenicity Tests on Nine Mosquito Species and Several Non-target Organisms with Strelkovimermis spiculatus (Nemata Mermithidae)

Nine species of mosquitoes and several species of non-target aquatic organisms were tested for susceptibility to the mernaithid nematode, Strelkovimermis spiculatus. All species of Anopheles, Aedes, Culex, and Toxorhynchites exposed to S. spiculatus were susceptible. Of the nine mosquito species tested, C. pipiens quinquefasciatus had the greatest tolerance to initial invasion and the highest percent infection of those that survived. High levels of infection were also achieved with Aedes taeniorhynchus and A. albopictus, but these mosquitoes were significantly less tolerant to parasitism than C. pipiens quinquefasciatus. Strelkovimermis spiculatus did not infect or develop in any of the non-target hosts tested.

Horizontal transmission of amblyospora dolosi (Microsporidia: amblyosporidae) to the copepod metacyclops mendocinus (Wierzejski, 1892)

This study documents the involvement of a copepod intermediate host in the life cycle of Amblyospora dolosi from the neotropical mosquito Culex dolosus in Argentina. Meiospores of A. dolosi from the mosquito host were infectious per os to female adults of the copepod Metacyclops mendocinus. All developmental stages in the copepod were haplophasic (unpaired nuclei), with sporulation producing a second type of uninucleate spore. These spores, formed in the ovaries of M. mendocinus, were lanceolate, curved, and measured 14.3 x 3.8 &mgr;m. This study supports previous life cycle studies which demonstrate that most if not all Amblyospora spp. in mosquitoes require an obligate intermediate copepod host to complete the life cycle.

Analysis of the ribosomal DNA sequences of the microsporidia Thelohania and Vairimorpha of fire ants

Sequences of the 16SrRNA gene of three microsporidia pathogenic to imported fire ants, Solenopsis invicta and Solenopsis richteri, were determined and compared to each other and 15 other species of microsporidia. The sequences of 2 Thelohania species are nearly identical (99.2% identity), supporting light-microscopic and ultrastructural evidence that Thelohania solenopsae and Thelohania sp. are closely related but probably not conspecific. Sequence comparisons further revealed that Vairimorpha sp. has a sequence identity of about 73% with the two Thelohania species and Vairimorpha necatrix, the type species of the genus Vairimorpha. This, together with information on spore morphology, suggests that Vairimorpha sp. represents a genus distinct from that of the fire ant Thelohania. Its placement in the genus Vairimorpha must also be reevaluated. Two new sister taxa, one containing T. solenopsae and Thelohania sp. and one containing Vairimorpha sp., were found to have diverged early in the microsporidian lineage.

Phylogeny of amblyospora (Microsporida: amblyosporidae) and related genera based on small subunit ribosomal DNA data: A possible example of host parasite cospeciation

Small subunit ribosomal RNA (SSU rRNA) gene sequences were analyzed for six species and four genera of microsporidia from mosquito hosts; Amblyospora stimuli (Aedes stimulans), Amblyospora californica (Culex tarsalis), Amblyospora sp. (Culex salinarius), Edhazardia aedis (Aedes aegypti), Culicosporella lunata (Culex pilosus), and Parathelohania anophelis (Anopheles quadrimaculatus). Comparison of these sequences to those of other microsporidia show that these sequences are longer with the SSU rRNA gene of E. aedis being the longest microsporidia sequenced to date (1447 base pairs). Parsimony, maximum likelihood, and distance methods produced identical trees, suggesting that the above microsporidian taxa, contrary to current classification schemes, form a monophyletic group. Relationships within this group are further supported by high bootstrap and decay analysis values. Based on the molecular analysis, P. anophelis is the most divergent species in this group of mosquito parasites. Amblyospora is paraphyletic with A. californica and Amblyospora sp., forming a sister taxon to a clade composed of E. aedis and A. stimuli. Culicosporella lunata comprises a sister taxon to the Amblyospora/Edhazardia clade. The pattern of host relationships on the tree provides preliminary evidence that the branching pattern seen here may indicate that host-parasite cospeciation is an important mechanism of evolution in this group.

Amblyospora salinaria n. sp. (Microsporidia: amblyosporidae), parasite of Culex salinarius (Diptera: culicidae): its life cycle stages in an intermediate host

Horizontal transmission testing with an Amblyospora species from the mosquito Culex salinarius has documented the involvement of a copepod intermediate host. Meiospores (one type of uninucleate spore) of the Amblyospora sp. were infectious per os to female Macrocyclops albidus adults. All developmental stages in the copepod had unpaired nuclei (were haplophasic), starting with the sporoplasms from the meiospore, continuing as a succession of schizonts undergoing binary division and ending with sporulation, producing a second type of uninucleate spore. These spores, formed in the ovaries of M. albidus, were lanceolate, slightly curved and measured 13.23 x 3.85 microm. They infected C. salinarius larvae, both male and female, when ingested. In addition, cross-infectivity testing was conducted and demonstrated that while A. californica from C. tarsalis will infect C. salinarius, it does not complete its life cycle in this host. Based on these findings, we conclude that Amblyospora sp. from Culex salinarius is a distinct species and assign it the name Amblyospora salinaria n. sp.

Discovery of thelohania solenopsae from the red imported fire ant, solenopsis invicta, in the united states

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Phylogenetic position of Amblyospora Hazard & Oldacre (Microspora:Amblyosporidae) based on small subunit rRNA data and its implication for the evolution of the microsporidia

Sequences of the small subunit rRNA genes of Amblvospora california and an Amblyospora sp. from Culex salinarius were determined. These sequences were compared phylogenetically with 16 other microsporidia. The results suggest Amblyospora forms a sister taxon to the rest of the microsporidia examined. The basal position of Amblyospora is discussed with respect to the evolution of microsporidian life cycles. These sequences represent the longest microsporidian small subunit rRNA genes sequenced to date, 1,359 and 1,358 bp. respectively. Structural features and GC content (49% for both) are comparable to those of other microsporidia which have been sequenced.

Effects of three larvicides on the production of Aedes albopictus based on removal of pupal exuviae

The production of adult Aedes albopictus from tires in northcentral Florida was monitored for 169 days by the daily removal of pupal exuviae. More than twice as many adults emerged from tires located in the shade (1.74 adults/tire/day) compared to tires in the sun (0.64 adults/tire/day). The effect of 3 larvicides on the production of adult Ae albopictus was evaluated. The fungal pathogen Lagenidium giganteum was ineffective. A liquid formulation of Bacillus thuringiensis israelensis (Acrobe) provided significant control for 47 days, whereas a slow-release pellet formulation of the insect growth regulator methoprene (Altosid) provided almost complete control for 116 days.

Edhazardia aedis (Microspora: Culicosporidae) effects on the reproductive capacity of Aedes aegypti (Diptera: Culicidae)

The influence of the microsporidium Edhazardia aedis (Kudo) on the survival and reproduction of its mosquito host, Aedes aegypti (L.), was studied in the laboratory. Survival, fecundity, egg hatch, and percentage of emergence for 4 gonotrophic cycles were compared for control and infected mosquitoes. Control females oviposited an average of 123.1 eggs over 4 gonotrophic cycles, 86.1% of which hatched, whereas infected females laid an average of 38.0 eggs with a 69.3% hatch. Emergence in progeny of infected female Ae. aegypti was significantly less than for control mosquitoes in all gonotrophic cycles. The reproductive capacity (Ro) for control and infected adults was 168.4 and 4.1, respectively, representing a decrease of 98.2%. Overall infection levels in progeny of infected females was 95.7%, of which 46.6% were lethal, larval infections. Infected female survivors were capable of initiating infections in F2 progeny. Wing length, often used as an indicator of fitness, was not significantly different between infected and control adults.

Seasonality, prevalence and pathogenicity of the gregarine Ascogregarina taiwanensis (Apicomplexa: Lecudinidae) in mosquitoes from Florida

Aedes albopictus larvae collected in Gainesville, FL, were infected with the gregarine Ascogregarina taiwanensis. Natural prevalence varied from 68 to 100%. Eight mosquito species were tested in the laboratory for susceptibility to A. taiwanensis isolated from field-collected Ae. albopictus. Aedes aegypti, Aedes albopictus, and Aedes taeniorhynchus became 100% infected in the larval stage, whereas Aedes triseriatus was less susceptible; Culex quinquefasciatus, Culex nigripalpus, Culex territans, and Anopheles quadrimaculatus were not susceptible. Viable A. taiwanensis oocysts from adults were recovered from Ae. taeniorhynchus (30%) and Ae. albopictus (100%); no oocysts were produced in the other exposed hosts. Mortality induced by A. taiwanensis infection was low in all mosquitoes except Ae. taeniorhynchus. We conclude that A. taiwanensis has little short-term impact on the mortality of the 3 most common container-inhabiting mosquito species in Florida; however, the long-term impact on overall host population regulation has yet to be determined.

A device for monitoring populations of larval mosquitoes in container habitats

A device was developed for repetitive sampling of mosquito larvae without undue disruption of the larval habitat. The sampler is a 3-oz. (ca. 100-ml capacity) transparent plastic cup with a hole in the center of its convex bottom. The device is buoyed by corks so that the water level is 15 mm above the bottom rim of the cup and 5 mm above the hole. There was significant correlation between 24-h samples of Aedes albopictus and Culex quinquefasciatus 4th-instar larvae in the larval sampling device and populations in tires. Greater numbers of immature mosquitoes were found per unit surface area of the sampling device than the tire as a whole, demonstrating that immature mosquitoes were trapped by the sampler.

Mosquito host range and specificity of Edhazardia aedis (Microspora: Culicosporidae)

Edhazardia aedis was transmitted horizontally to its natural host, Aedes aegypti, and to 6 alternate hosts: Ae. albopictus, Ae. triseriatus, Ae. taeniorhynchus, Anopheles quadrimaculatus, Orthopodomyia signifera and Toxorhynchites rutilus rutilus. The microsporidium produced both binucleate and uninucleate spores in all susceptible hosts. Transovarial transmission, however, was only successful in Ae. aegypti. Therefore, while E. aedis can infect a variety of mosquito species from diverse genera, it is specific for its natural host, Ae. aegypti. Five other mosquito species were not susceptible to E. aedis.

Influence of temperature on developmental parameters of the parasite/host system Edhazardia aedis (Microsporida: Amblyosporidae) and Aedes aegypti (Diptera: Culicidae)

Larvae of Aedes aegypti, transovarially infected with Edhazardia aedis, were reared between 20 and 36 degrees C to determine the influence of temperature on the development of the parasite and the infected host. Development of the parasite was evaluated based on spore yield and size. The predicted optimum temperature for maximum spore production of E. aedis in A. aegypti was 30.8 degrees C. The results demonstrate that the E. aedis-A. aegypti system has a wide temperature tolerance; whereas spore yield will be lower at unfavorable temperatures, the host will remain infected. Additionally, spores were significantly smaller from individual reared at 34 degrees C than those reared at either 20 or 27 degrees C. Development of the infected host was evaluated based on pupal weight and time of pupation. Infected pupae were significantly larger than uninfected pupae. There was also a significant difference in the pupation rate between controls and infected A. aegypti larvae. Controls had a 50% cumulative pupation time (CPT50) of 65.7 degree days and infected individuals a CPT50 of 76.6 degree days.

Potential of microsporidia for the biological control of mosquitoes

The use of larvicides for the control of disease vector mosquitoes is not always practical. Tony Sweeney and Jimmy Becnel discuss prospects for the use of microsporidio, particularly Edhazardia aedis, as biocontrol agents.

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.

Nolleria pulicis n. gen., n. sp. (Microsporida: Chytridiopsidae), a microsporidian parasite of the cat flea, Ctenocephalides felis (Siphonaptera: Pulicidae)

A new species of microsporidium, Nolleria pulicis, is described and named here from the cat flea, Ctenocephalides felis. The genus Nolleria is created and placed within the family Chytridiopsidae. The family is slightly modified to accommodate certain features of intracellular development seen in N. pulicis, which is otherwise very similar to other species in the family Chytridiopsidae. Sporulation is described from ultrastructural analysis of infected midgut epithelial cells of adult C. felis. The term "multiple division by vacuolation" is proposed for describing sporogony as it occurs in this species and certain related species of microsporidia. The probable mode of transmission and apparent absence of merogony are discussed.

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.

Fine structure and development of Pilosporella chapmani (Microspora: Thelohaniidae) in the mosquito, Aedes triseriatus (Say)

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.