Nosema algerae: Infection of the white mouse by a mosquito parasite

Spores of Nosema algerae, a microsporidan parasite of mosquitoes, were subcutaneously injected into the ears, tail, and feet of white mice. Infections were transient and localized at the injection sites. Spore germination tests in blood plasma indicated that it is unlikely that spores injected by an infected mosquito bite would result in an infection.     

Hyperparasitism of intrasnail stages of Fasciola hepatica by a mosquito microsporidian parasite

Laboratory studies were conducted to investigate the infective behavior of Nosema algerae spores when ingested by Fasciola hepatica free of F. hepatica-infected snails (Lymnaea cubensis). Among the F. hepatica-infected snails exposed to N. algerae, 38.09% harbored microsporidia-infected F. hepatica rediae. The F. hepatica-free snails exposed to N. algerae as well as the controls did not become infected. Light microscopical studies of Giemsa-stained microsporidia distinguished this organism from microsporidia previously described in trematode larvae. Based on the infectivity studies and morphological data, it was concluded that N. algerae, a mosquito pathogen, was transmitted to intrasnail stages of F. hepatica.     

The effect of the microsporidan, Nosema algerae, on Anopheles stephensi

A bioassay method was established to examine infectivity differences between different batches of Nosema algerae spores. The IC₅₀ of N. algerae spores produced in one unusual host, Heliothis zea, was the same as for spores from the normal mosquito host, Anopheles stephensi. Soil and sand bottoms caused an approximate 200–400 fold increase in the IC₅₀. Nosematosis had little effect on the survival of larvae and pupae but the adult life span was reduced to the extent that malaria transmission would be doubtful.     

Susceptibility of spores of the microsporidian Nosema algerae to sunlight and germicidal ultraviolet radiation

Spores of the microsporidian Nosema algerae exposed to 1, 2, and 4 hr of sunlight and 121 μW/cm² of germicidal ultraviolet light were fed to first-instar Anopheles albimanus. Twenty days after feeding, the incidence and intensity of infection (spores/mosquito) were recorded from adult mosquitoes. While sunlight-treated spores showed no significant decline in incidence of infection after 1-, 2-, and 4-hr exposures, intensity of infection decreased significantly after the 2- and 4-hr exposures. Incidence of infection of mosquitoes fed bactericidal ultraviolet light-treated spores declined 48.2, 76.2, and 99.9% after 1-, 2-, and 8-min exposures, respectively. Measured by intensity of infection, activity of bactericidal light-treated spores decreased 87.2% after 1 min, 91.7% after 2 min, and 99.9% after 8 min. Levels of radiation required to inactivate spores of N. algerae fell within the range reported for other Microsporidia.     

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.     

Growth of Nosema algerae in Pig Kidney Cell Cultures*

SYNOPSIS. Nosema algerae, a microsporidan parasite of mosquitoes, can infect pig kidney cell cultures. Spores germinated in the culture medium, infected the cells within 30 min of germination, multiplied, and produced spores. The early developmental stages in the N. algerae life cycle are described.     

Factor Affecting Sex Ratios of a Mermithid Parasite of Mosquitoes

The ratio of male to female Reesimermis nielseni Tsai and Grundmann, a nematode parasite of mosquito larvae, increased as the number of parasites per host increased. Hosts with a single nematode produced 9% males compared with essentially 100% males in hosts with more than 7 parasites; hosts with 3 nematodes produced about equal numbers of males and females. Males of R. nielseni generally emerged before females because of the earlier death of multiple-infected mosquitoes. The species of the host mosquito influenced the sex ratio, but the size of a specific host at the time of invasion did not. Host diet also had a noticeable influence on the sex ratio of the nematode: singly infected hosts from a starved population produced 92% males compared with 13% in the normally fed group. The importance of these factors in the mass rearing of R. nielseni is discussed.     

Infectivity of a microsporidium of mosquitoes (Nosema algerae) to larval stages of Schistosoma mansoni in Biomphalaria glabrata

Lai P. F. and Canning E. U. 1980. Infectivity of a microsporidium of mosquitoes (Nosema algerae) to larval stages of Schistosoma mansoni in Biomphalaria glabrata. International Journal for Parasitology10: 293–301. Nosema algerae derived from a closed colony of Anopheles stephensi was fed to Biomphalaria glabrata infected with Schistosoma mansoni. Mother and daughter sporocysts became hyperinfected but the snail tissues remained free of the microsporidia except for rare small aggregates of spores. These lay close to the sites occupied by mother or daughter sporocysts and were probably liberated from them. Irrespective of dose, fewer snails contained infected sporocysts when spores were given at 7 days post-miracidial infection than when given at 14 days. These periods corresponded respectively to stages when mother sporocysts only or daughter sporocysts as well were present in the snails. Infection of the sporocysts began in the tegumental cells, spread to the brood chamber and ultimately to the cercariae themselves. Heavily infected sporocysts contained fewer developing embryos. Doses of 10⁶ and 10⁷ spores/snail caused significant depression of cercaria output when given at 14 days but not at 7 days.     

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)     

Coelomomyces dodgei: Establishment of an in vivo laboratory culture

An in vivo laboratory culture of the fungus Coelomomyces dodgei (Chytridiomycetes: Blastocladiales) was established, using the copepod Cyclops vernalis as an intermediate host and the larvae of the mosquito Anopheles quadrimaculatus as the definitive host. The culture was perpetuated by infecting copepods and mosquitoes using separate procedures. Copepods were infected by being combined with dehiscing sporangia. Patently infected copepods, which contained either light amber, bright orange, or both light amber and bright orange mycelia, were collected daily beginning 12 days later. Mosquitoes were infected by combining 100 first-instar larvae for 48 hr with a mixture of 12 infected copepods, four of each of the above types. The mean rate of infection for the first 100 trials was 41%. When groups of 100 first-, second-, third-, and fourth-instar larvae were exposed to a similar mixture of infected copepods for 48 hr, the mean rates of infection were 37.4, 27.0, 17.8, and 2.4%, respectively. Observations and experimental evidence suggest that the differentially pigmented mycelia found in infected copepods are gametophytes which develop into gametangia that subsequently release gametes of opposite mating types, the light amber gametangia producing female and the bright orange gametangia producing male gametes. Zygotes resulting from the fusion of these gametes lead to the infection of mosquito larvae. Thus, C. dodgei appears to have an Euallomyces type of life cycle with sporophyte and gametophyte generations alternating between mosquito and copepod hosts, respectively, with differentially pigmented sexual structures present in the gametophyte phase.     

Plasmodium infection brings forward mosquito oviposition

Invertebrate hosts often bring forward their reproductive effort in response to a parasitic infection. This is widely interpreted as a host-driven response aimed at compensating for the expected losses in future fitness as a result of parasitism. Here we report that mosquitoes bring forward their oviposition schedule when they are infected with Plasmodium, a parasite known to severely curtail mosquito fecundity. This response could aim at compensating for a negative time-dependent effect of the parasite on mosquito fitness, as infected mosquitoes seem to display a strong and progressive decrease in the quality of the eggs they lay. In addition, we show that this shift in oviposition date is dependent on mosquito strain: a comparison of several isogenic mosquitoes strains, one insecticide-susceptible and two insecticide-resistant ones, reveals that only the former shift their oviposition strategy when infected. This pattern suggests the existence of a costly host-driven response to parasitism, as insecticide-resistant mosquitoes have been shown to be in generally poorer condition.     

Stored Bacillus popilliae spores and their infectivity against Popillia japonica larvae

Bacillus popilliae spores were stored for about 7 years under three separate conditions: frozen in sterile distilled water, smeared on glass microscope slides, and stored in loam soil at room temperature. In separate experiments, each of the 7-year-old preparations was fed to Popilla japonica larvae at concentrations of 10³, 10⁵, 10⁷, and 10⁹ spores/g of soil. A significant decrease in the percentage of larvae infected occurred in all of the aged spore tests. B. popilliae spores stored in soil, for the extended period, produced 3% larval infection only at the 10⁹ spores concentration; similar results were obtained from frozen spores. When P. japonica larvae were fed spores stored dried on slides, about 20% of the larvae developed milky disease. When aged frozen spores were artificially injected into larvae, 12% became infected at concentrations of 1 × 10⁶ spores/larvae; dried spores at the same concentration infected about 38% of the insect larvae. We conclude from these data that aged B. popilliae spores are significantly less infective against P. japonica larvae than young spores.     

Development and fine structure of Pleistophora sp. (Cnidospora: Microsporida) in the mosquito, Aedes sierrensis

The development and fine structure of a Pleistophora sp. from larvae of Aedes sierrensis was investigated. The usual site of infection was the posterior midgut epithelium, and small uni- and binucleate forms were the first stages observed. There was no evidence of autogamy or the production of uninucleate sporonts. Binucleate sporonts produced prosporoblasts with two and four nuclei. Cellularization of the prosporoblasts resulted in sporoblasts which matured into spores. Heavily infected larvae have less fat body than healthy hosts and usually die when infected in the first or second instar. The pathogen could remain chronic and be carried into the adult host. Although natural infections were low, the pathogen could serve as a biological control agent.     

Changes in body tissues and hemolymph composition of Culex pipiens in response to infection by Romanomermis culicivorax

Hemolymph composition of fourth instar larvae of an autogenous strain of Culex pipiens was examined to determine the effects of parasitism by a mermithid nematode, Romanomermis culicivorax. Mosquitoes were reared under two different pH regimens: 4.5 and 7.3. Wet and dry weight of infected mosquitoes reared at either pH were significantly lower than controls. The effects of parasitism in the development of C. pipiens were evaluated from paraffin sections of mosquito larvae 2, 4, and 6 days postinfection. At 2 days postinfection, the infected larvae showed no apparent effects of parasitism; at day 4, the fat body tissue was reduced and imaginal disc development was retarded; and at day 6, parasitized mosquitoes were smaller in cross section, fat body tissue was found only in isolated clumps, and there was a complete absence of imaginal discs. Concentrations of total carbohydrates in hemolymph from infected fourth instar mosquitoes reared at pH 7.3 were reduced. Trehalose and glucose were each reduced by more than half. Total α-amino nitrogen was significantly lower in infected mosquitoes reared at pH 7.3. However, total amino acid concentrations for hemolymph from control and infected larvae reared at pH 7.3 were the same. Methionine sulfoxide decreased 63% and proline increased 2.5 times in infected mosquitoes. Hemolymph protein concentrations were reduced 80% in infected mosquitoes reared at both pHs. The number of hemolymph proteins also declined from 35 to 22 during infection. Two host proteins, 82,000 and 158,000 daltons, remained prominent throughout the mermithid infection.     

Avian malaria infection intensity influences mosquito feeding patterns

Pathogen-induced host phenotypic changes are widespread phenomena that can dramatically influence host–vector interactions. Enhanced vector attraction to infected hosts has been reported in a variety of host–pathogen systems, and has given rise to the parasite manipulation hypothesis whereby pathogens may adaptively modify host phenotypes to increase transmission from host to host. However, host phenotypic changes do not always favour the transmission of pathogens, as random host choice, reduced host attractiveness and even host avoidance after infection have also been reported. Thus, the effects of hosts’ parasitic infections on vector feeding behaviour and on the likelihood of parasite transmission remain unclear. Here, we experimentally tested how host infection status and infection intensity with avian Plasmodium affect mosquito feeding patterns in house sparrows (Passer domesticus). In separate experiments, mosquitoes were allowed to bite pairs containing (i) one infected and one uninfected bird and (ii) two infected birds, one of which treated with the antimalarial drug, primaquine. We found that mosquitoes fed randomly when exposed to both infected and uninfected birds. However, when mosquitoes were exposed only to infected individuals, they preferred to bite the non-treated birds. These results suggest that the malarial parasite load rather than the infection itself plays a key role in mosquito attraction. Our findings partially support the parasite manipulation hypothesis, which probably operates via a reduction in defensive behaviour, and highlights the importance of considering parasite load in studies on host–vector–pathogen interactions.     

Susceptibility of Anopheles messeae Fall. and Culex pipiens pipiens L. Larvae to entomopathogenic Fungi Metarhizium

The mortality rate of Anopheles messeae Fll. and Culex pipiens pipiens L. mosquito larvae infected with entopathogenic fungi Metarhizium brunneum and M. robertsii has been studied in laboratory conditions. It was shown that C. pipiens larvae are more susceptible to a water suspension of fungal conidia treatment while A. messeae larvae are more susceptible to treatment with dry conodia. The mortality of mosquito larvae infected with the most virulent strain and dose of 2 × 10⁶ conidia per cm² was 87.5–92.5%. Prospects for the use of fungi in the biocontrol of bloodsucking mosquitoes are discussed.     

The effect of parasitism by the mermithid Romanomermis culicivorax on the dry weight and hemolymph soluble protein content of three species of mosquitoes

The dry weight, hemolymph soluble protein composition, and content of three species of mosquitoes, Culex pipiens, Aedes taeniorhynchus, and Anopheles quadrimaculatus were examined to determine the effects of parasitism by the mermithid nematode Romanomermis culicivorax. The dry weights of infected fourth-stage larvae of all three species were significantly lower than controls. The differences in weight found between infected early and late C. pipiens and A. quadrimaculatus larvae were attributed to the weight of the parasite itself. This difference was not noticeable in A. taeniorhynchus larvae. Hemolymph proteins were severely depleted in all three mosquito species during parasitism by R. culicivorax. Analysis of protein composition by PAGE showed that these depletions were accompanied by a reduction in the number of proteins. Differences between protein composition concentrations were evident between early and late fourthstage control larvae of C. pipiens and A. quadrimaculatus. The concentration of some low-molecular-weight proteins (below 68,000) remained constant between infected and control samples of all three mosquito species.     

Biology of Octomyomermis muspratti,a parasite of mosquitoes as it relates to mass production

The first- and second-instar larvae of Culex pipiens quinquefasciatus were equally susceptible to parasitism by the mermithid nematode Octomyomermis muspratti; the third-instar hosts were significantly less susceptible. The yield of postparasitic nematodes was higher from hosts exposed as second instars then from hosts exposed as first or third instars at comparable levels of parasitism. Mortality of the host prior to emergence of the nematode occurred most frequently among first- and third-instar hosts. About 4% of the infected hosts exposed as first and second instars and 37% of the infected hosts exposed as third instars pupated prior to emergence of the postparasitic nematodes. The exposure of mosquitoes as second instars was the most efficient for mass rearing and resulted in the highest yields of postparasitic O. muspratti.     

Recycling potential and selective retrieval of Bacillus sphaericus from soil in a mosquito habitat

A selective medium containing a combination of starch, milk proteins, and streptomycin was used as a reliable indicator for the presence of Bacillus sphaericus in soil samples collected from a mosquito habitat where this pathogen was previously applied. The medium can also be used as an indicator substrate to retrieve B. sphaericus from infected mosquito larvae. Results show that B. sphaericus remains viable and infective 9 months after application as a larvacidal agent of mosquitoes in a roadside ditch.     

Bioassays for comparative infectivity of mermithid nematodes (Romanomermis iyengari,Romanomermis culicivorax and Strelkovimermis spiculatus) for culicine mosquito larvae

Two improved bioassays were developed to establish infectivity baselines for selection experiments using mermithid nematode variants. Comparative infectivity of Romanomermis iyengari, Romanomermis culicivorax and Strelkovimermis spiculatus using larvae of three mosquito spp. Aedes sierrensis, Aedes aegypti and Culex pipiens were evaluated with “plate” and “tray” bioassays at selected intensity of infections. Using the “plate” bioassay, single mosquito larvae were immersed in 2 ml of water within individual depressions of 12-well, polystyrene tissue culture plates. One, three, or five preparasitic juveniles (J2) were added to each well. In the “tray” bioassay, polyethylene trays containing 500 ml water and 100 mosquito larvae were exposed to 500 (5:1, nematode:insect host) or 1000 (10:1) J2s. Percentage infection (PINF, infectivity) and intensity of infection (IINF, #nematodes per infected larvae) number were determined only after emergence of post-parasitic J3 juveniles. Under the bioassay conditions, all three species of nematodes resulted in infections in all mosquito hosts, but R. iyengari exhibited better effectiveness in the parasitism of mosquito larvae. The three species of mosquitoes presented high levels of susceptibility to each of the three species of nematodes, but in general Cx. pipiens and Ae. sierrensis were slightly more susceptible than Ae. aegypti. The “plate” bioassay was more efficient in measurement of infectivity of the mermithid species and in establishing baseline characteristics for these mosquito-parasitic nematodes. The “tray” bioassay was an effective bioassay for large cohorts of both infective juveniles and host larvae and, potential for field interactions.