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PubMed1993

Molecular characterization of lengthy mitochondrial DNA duplications from the parasitic nematode Romanomermis culicivorax.

Complete nucleotide sequences, precise endpoints and coding potential of several 3.0-kilobase mitochondrial DNA (mtDNA) repeating units derived from two isofemale lineages of the mermithid nematode Romanomermis culicivorax have been determined. Endpoint analysis has allowed us to infer deletion and inversion events that most likely generated the present day repeat configuration. Each amplified unit contains the genes for NADH dehydrogenase subunits 3 and 6 (ND3 and ND6), an open reading frame (ORF 1) that represents a cytochrome P450-like gene, and three additional unidentified open reading frames. The primary nucleotide sequences of the R. culicivorax mt-repeat copies within individual haplotypes are highly conserved; three nearly complete copies of the repeat unit vary by 0.01% at the nucleotide level. These observations suggest that concerted evolution mechanisms may be active, resulting in sequence homogenation of these lengthy duplications.

Amino Acid Sequence↗
PubMed1991

Mermithid (Nematoda: Mermithidae) parasitism of Simulium damnosum s.l. (Diptera: Simuliidae) in Sierra Leone and the need for vector control.

Females of Simulium damnosum Theobald s.l. were systematically collected at four sites in the Gorawa Chiefdom of Sierra Leone, West Africa, over a period of 15 mo from July 1986 to September 1987. The prevalence of mermithids infecting parous females varied from 0 to 7.9%, whereas the prevalence of mermithids in nulliparous females varied from 0 to 42.8%. The peak incidences of mermithid infection in nulliparous females occurred during the rainy season (15.2% in October 1986, 42.8% in August 1987). The high incidence of mermithids was associated with a high monthly biting rate, particularly during the month before the peak mermithid period (5,240 in September 1986, 4,878 in July 1987).

Animals↗
PubMed1996

Release of Romanomermis iyengari (Nematoda:Mermithidae) to control Aedes taeniorhynchus (Diptera:Culicidae) in Punta del Este, Isla de la Juventud, Cuba.

Preparasites of Romanomermis iyengari Welch were applied at the rate of 1,000 preparasites per square meter of surface area in 5 natural breeding sites in carbonate rock depressions to control Aedes taeniorhynchus Wiedeman larvae. Larval parasitism averaged 100, 97, 81, and 80% in 1-4 instars, respectively. Three of 5 sites produced parasitism in excess of 90%. The range of salinity and water depth had little influence on the levels of parasitism. Ae. taeniorhynchus density was reduced from 78 to 96% at the 5 sites 8 d posttreatment.

Aedes↗
PubMed1997

Reduction of mosquito larval densities in natural sites after introduction of Romanomermis culicivorax (Nematoda:Mermithidae) in Cuba.

Romanomermis culicivorax Ross & Smith became established in 4 of 6 treated sites and produced high levels of infection in Anopheles albimanus Wiedemann, Culex atratus Theobald, Psorophora confinnis Lynch-Arribálzaga, and Uranotaenia sapphirina Oster-Sacken mosquitoes for 9 wk in 1993. Mean levels of southern house mosquito parasitism ranged from 82 to 83% for Culex quinquefasciatus Say, at 2 sites, from 89 to 95% for An. albimanus at 4 sites, and from 78 to 80% at 2 sites for Cx. atratus, Ps. confinnis, and Un. sapphirina. Results indicated that R. culicivorax has potential use as biological control agent against mosquitoes in several different habitats in Cuba.

Animals↗
PubMed1997

Improved rearing methods for Heleidomermis magnapapula (Nematoda: Mermithidae), a larval parasite of Culicoides variipennis sonorensis (Diptera: Ceratopogonidae).

Improvements in rearing techniques have decreased maintenance needs and have increased the parasitism rate of larval Culicoides variipennis sonorensis Wirth & Jones by the mermithid nematode, Heleidomermis magnapapula Poinar & Mullens. In colony pans with 2,500-3,000 larval C. v. sonorensis, H. magnapapula adults emerged from 22.5% of hosts, with an average yield of 159 female H. magnapapula per pan. H. magnapapula females refrigerated for 1 wk showed no decline in preparasite infectivity compared with nonrefrigerated females. Female insemination did not differ with various mating combinations of 1 or 2 females with 1 or 2 males; 37-47% of these pairs failed to produce fertilized eggs. In 9-cm petri dishes, the optimal preparasite/host ratio was 900 infective preparasites (1 female's entire clutch) to 650-700 C. v. sonorensis larvae. Overall, parasite production was more time- and labor-efficient when larvae were parasitized in regular colony pans compared with petri dishes.

Animals↗
PubMedDate not supplied

Effect of temperature on different stages of Romanomermis iyengari, a mermithid nematode parasite of mosquitoes.

The effect of temperature (20 degrees-35 degrees C) on different stages of Romanomermis iyengari was studied. In embryonic development, the single-cell stage eggs developed into mature eggs in 4.5-6.5 days at 25-35 degrees C but, required 9.5 days at 20 degrees C. Complete hatching occurred in 7 and 9 days after egg-laying at 35 and 30 degrees C, respectively. At 25 and 20 degrees C, 85-96% of the eggs did not hatch even by 30th day. Loss of infectivity and death of the preparasites occurred faster at higher temperatures. The 50% survival durations of preparasites at 20 and 35 degrees C were 105.8 and 10.6 hr respectively. They retained 50% infectivity up to 69.7 and 30.3 hr. The duration of the parasitic phase increased as temperature decreased. Low temperature favoured production of a higher proportion of females which were also larger in size. The maximum time taken for the juveniles to become adults was 14 days at 20 degrees C and the minimum was 9 days at 35 degrees C. Oviposition began earlier at higher temperature than at lower temperature. However, its fecundic period was shorter at 20 degrees C than at 35 degrees C indicating enhanced rate of oviposition at 20 degrees C. Fecundity was adversely affected at 20 degrees C and 35 degrees C. It is shown that the temperature range of 25 degrees-30 degrees C favours optimum development of R. iyengari.

Animals↗
PubMedDate not supplied

Limnomermis subtropicalis n. sp. (Nematoda:Mermithidae) a parasite of larvae of Simulium orbitale Lutz (Diptera:Simuliidae) in Argentina.

Limnomermis subtropicalis n. sp. (Nematoda:Mermithidae) a parasite of Simulium orbitale Lutz (Diptera:Simuliidae) found in Argentina is described and illustrated. This species is characterized by having medium sized amphids, pocket-shaped, medium sized vagina, sculptured spicule, and by having 9 preanal, 7 postanal papillae in the ventral row, and 12 papillae in the lateral rows.

Animals↗
PubMed2003

Mortality in immatures of the floodwater mosquito Ochlerotatus albifasciatus (Diptera: Culicidae) and effects of parasitism by Strelkovimermis spiculatus (Nematoda: Mermithidae) in Buenos Aires Province, Argentina.

Life tables were constructed for six cohorts of immature stages of the floodwater mosquito Ochlerotatus albifasciatus (Macquart) in a park in Buenos Aires, highlighting the mortality attributable to the parasitic nematode, Strelkovimermis spiculatus Poinar & Camino. Two cohorts were selected to compare parasite incidence in all mosquito stages when low and high parasitism occurred. Development time of Oc. albifasciatus from first instar to adult was 7.7-10 days in the spring, 6 days in the summer, and 10.9-21.9 days in the fall. Survival was estimated as 0-1.4% in the spring, 2% in the summer and 0.2-4.4% in the fall. The highest "K" value (Killing power) occurred during a fall cohort when prevalence of the parasite was 86.9%, and the lowest in a spring cohort. Parasitism occurred during all seasons, but S. spiculatus persisted to adult only in the summer and fall, when adult mosquitoes developed from parasitized third and fourth instars larvae. The abundance of S. spiculatus differed between old and young larvae only when parasite prevalence was the highest. Although pupae and adults of Oc. albifasciatus were parasitized, no pupal mortality attributable to parasitism was recorded. The proportion of parasitized adults ranged from 14.2% and 5.7% in the two cohorts compared. Pupal wet weight and adult wing lengths did not differ between parasitized and unparasitized individuals.

Animals↗
PubMed1999

The Romanomermis iyengari parasite for Anopheles pseudopunctipennis suppression in natural habitats in Oaxaca State, Mexico.

In September and November 1996 Romanomermis iyengari Welch, a parasite of larval mosquitoes, was released in 44 natural larval habitat sites of Anopheles pseudopunctipennis Theobald in an attempt to reduce the larval populations of this important malaria vector. The selected treatment sites ranged in size from 5 to 500 m2. The study was carried out in Pochutla District of Oaxaca State, on the Pacific coast of Mexico. Chemical pesticides to reduce vector populations have been the principal tool in malaria suppression campaigns. However, the excessive use of these chemicals has created pesticide resistance and other serious collateral problems. Therefore, a biological control project using agents that are pathogens of Anopheles larvae was initiated in 1996. The principal objective was to establish mass rearing capacities for R. iyengari. Detailed methodology for rearing and introducing these nematodes into mosquito larval habitats was established at the National Polytechnic Institute of Oaxaca State. Before application of the parasites to larval habitats, site characteristics were determined, including size, depth, aquatic vegetation, salinity, pH, conductivity, temperature, and pretreatment larval density. With a compressed air sprayer, infective mermithid parasites were released at rates of either 2,000 or 3,000/m2, and the parasites produced high levels of infection. Anopheles populations were sampled 72 h posttreatment, and the larvae obtained were taken to the laboratory and examined through microscopic dissection to determine infection levels and mean parasitism. Nematode parasitism ranged from 85 to 100% at all the treatment sites, even though no previous information concerning field parasitism of An. pseudopunctipennis by R. iyengari has been reported. In addition, a significant reduction of mosquito larval density at the treatment sites was found five days after the nematode application. Levels of parasitism were indicative of the number of mosquito larvae killed by the treatment since infected larvae never progressed to the pupal stage. Results from sampling nine of the sites 2 months after the initial application of nematodes indicated that a high number of mosquito larvae were infected by parasites that had emerged from eggs previously deposited in the stratum. This work suggests the potential of this mermithid to reduce An. pseudopunctipennis populations in Oaxaca State.

Animals↗
PubMed2000

[Mass production of Romanomermis iyengari (Nematoda: Mermithidae) applied to anopheline breeding sites in Boa Vista (Roraima), Brazil].

In order to begin mass producing the nematode Romanomermis iyengari Welch, a bioprocessing plant was designed and set up on the grounds of Universidad Federal in the State of Roraima, Brazil, after reaching an agreement with the State's Health Department. The objective of this paper was to establish the basic process for mass breeding the parasite in order to apply it to anopheline breeding sites. Cultures were obtained at a rate of 68 during every seven-day cycle, making for a total of 272 cultures a month. Before treatments were applied in the field, laboratory tests were conducted that showed the great susceptibility of anopheline larvae to infestation by R. iyengari, with parasitism rates ranging from 71 to 98%. In order to assess the parasitizing capacity of R. iyengari in actual field conditions, 12 natural anopheline breeding sites were chosen, each ranging in size between 50 and 450 m2. The species Anopheles albitarsis Lynch-Arribálzaga and Anopheles rondoni Neiva-Pinto were detected there, at densities that ranged from 34 to 66 larvae/m2. The biolarvicide was sprayed in all 12 breeding sites with a domestically manufactured pump set at a pressure of two atmospheres and a dose of 2,000 preparasites/m2. Seven days after treatments were performed, anopheline populations were markedly reduced (85 to 97%). Results obtained point to the feasibility of using R. iyengari to control larval populations of both species of anophelines.

Animals↗
PubMed2000

[Susceptibility of Aedes aegypti larvae to parasitism by Romanomermis culicivorax in laboratory and field conditions in Oaxaca, Mexico].

In June 1996 in the state of Oaxaca, Mexico, larvae of the mosquito species Aedes aegypti were exposed to infective preparasites of the nematode Romanomermis culicivorax, Ross and Smith, in the laboratory and in the field. For the laboratory experiments larvae in instars I-IV were used; they had been collected in natural reservoirs. The laboratory experiments were carried out in triplicate, with 100 larvae of each larval stage per experiment. Three preparasite application dosage ratios were tested: 5, 10, or 15 preparasites per mosquito larva. For the field studies 13 A. aegypti outdoor breeding sites were used, with larvae in instars I-IV and a 15:1 preparasite dosage ratio. With the laboratory experiments, an increase was observed in the average infestation of the larvae as the preparasite application ratio was increased from 5:1 to 15:1. With a 10:1 ratio, the rates of parasitism were 100%, 100%, 85%, and 74% in the larvae in instars I, II, III, and IV, respectively; for the 15:1 preparasite ratio, parasitism rates were 100%, 100%, 90%, and 79%, respectively. The field tests with the 15:1 preparasite dosage ratio in the 13 outdoor reservoirs produced parasitism rates of 80% to 98%, thus demonstrating the susceptibility of this species of mosquito to parasitism by R. culicivorax in Oaxaca, Mexico.

Aedes↗
PubMed2003

Strelkovimermis papillosus n. sp. (Nematoda: Mermithidae), a parasite of chironomid (Insecta: Diptera) adults from the headwaters of the Mississippi River in northern Minnesota.

On 18 August 2002, chironomid imagoes of Rheotanytarsus sp. emerged from the upper Mississippi River in Minnesota and yielded distinctive mermithid nematodes of a new mermithid species. Strelkovimermis papillosus n. sp. is distinguished from the other 14 species of the genus by the presence of unusually large cephalic papillae encircling the mouth and forming a rosette with the mouth in the center and by the absence of a fixator muscle in the males. Additionally, both sexes have very acute posterior ends, long amphids, and a long stoma. Strelkovimermis is revised by eliminating nondiscriminating parameters and accommodating the 15 known species. Intrageneric characteristics useful in separating species of Strelkovimermis are listed. Intensity of infection and intensity of infection versus sex were determined from 41 hosts. Where known, the hosts and geographical distribution are given for all 15 Strelkovimermis species.

Animals↗
PubMed2004

Lanceimermis palustris n. sp. and Telomermis palustris n. sp. (Nematoda: Mermithidae) parasites of chironomid (Insecta: Diptera) adults from Lake Alice Bog in northern Minnesota.

In the summer of 2003, chironomid imagoes eclosing from Lake Alice Bog in Minnesota yielded mermithid nematodes of 2 new species. Lanceimermis palustris n. sp. is distinguished from the other 14 species of the genus by the subventral mouth position, thinness of the hook-shaped spicule, body index, and structure of the male tail muscles. Telomermis palustris n. sp. is distinguished from the only other species of the genus by the structure of the amphids, body length, maximum body width, length of the esophagus, and the presence of a minute larval terminal horn. Lanceimermis palustris n. sp. hosts were Chironomus maturus Johannsen and T. palustris n. sp. hosts were Tanytarsus mendax Kieffer, Paratanytarsus nr. dissimilis n. sp., and Micropsectra polita (Malloch). In both mermithid species, the percent of mermithid males per host increased with the intensity of the infection.

Animals↗
PubMed2006

Population interactions between Culex vishnui mosquitoes and their natural enemies in Pondicherry, India.

Population interactions among mosquitoes in the Culex vishnui subgroup, which are vectors of Japanese Encephalitis, and their natural enemies were studied in Pondicherry, India. We tested the hypothesis that the breakdown of interactions between the larvae and their natural enemies due to drought followed by rain was responsible for the sudden increase in the vector population above the threshold for disease transmission during the heavy rainy period. We randomly sampled mosquito larvae and their predators in different breeding habitats and subjected the mean densities of prey, predator, and mosquito larvae infected with parasites/pathogens to covariate analysis to understand the interaction between prey and their natural enemies in relation to environmental factors. In rice fields, neither prey nor predator showed any positive correlation with temperature, RH, or the number of rainy days. However, the pathogen/parasite of mosquito immatures showed a positive correlation with RH. Among the mosquito predators, notonectids exhibited a significant positive correlation with Cx. vishnui larvae. The parasitic Romanomermis iyengari and pathogenic Coelomomyces anopheliscus also showed positive correlations with immatures. No parasites and pathogens of mosquito larvae were recorded in shallow water pools (SWP) or cement tanks (CT) during the study period. Important predators recorded in SWP were notonectids, damselfly nymphs, Diplonychus indicus, and hydrophilids. Dragonfly nymphs, gerrids, and tadpole shrimps were recorded in CT. In CT, prey and their predators were positively correlated with RH and rainy days. In SWP, there was a highly significant correlation between prey, predators and environmental factors. We conclude that rice fields are a stable ecosystem where regular interaction occurs between larvae and their natural enemies and a sudden increase in mosquito populations is uncommon. In transient habitats, no such stability is present and they become more important as breeding habitats in terms of seasonality and number. Shallow water pools should be seriously considered for the control of these vectors.

Animals↗