Susceptibility of the floodwater mosquito Aedes albifasciatus from eggs of different dormancy times to the nematode parasite Strelkovimermis spiculatus.

This study aimed to evaluate the effects of egg dormancy times on susceptibility of larvae of the floodwater mosquito Aedes albifasciatus (Diptera: Culicidae) to parasitism by their natural enemy Strelkovimermis spiculatus (Nematoda: Mermithidae) and on their life history traits. Aedes albifasciatus eggs stored for 2, 4, 6, 8 and 10 months were hatched, and the larvae either exposed to S. spiculatus (treatment group) or not exposed (control group). Egg dormancy time had a negative effect on the retention of parasites, but no effect on the prevalence and intensity of parasitism or the melanization of nematodes. The survival to adulthood of control individuals decreased as dormancy time increased, whereas that of exposed individuals that remained uninfected was constant and low. A trend towards increasing development times with longer dormancy times was detected in the control group, but not in the exposed noninfected group. The results suggest nonconsumptive effects of parasites in exposed but not infected larvae from eggs with short dormancy times. In contrast, the relatively low fitness of larvae from eggs with long dormancy times regardless of their contact with the nematodes may be the result of the nutritional deprivation during the egg stage.

Prevalence of parasitism and adult survival time of Aedes albifasciatus (Diptera: Culicidae) parasitized by Strelkovimermis spiculatus (Nematoda: Mermithidae).

We described the carryover of Strelkovimermis spiculatus (Poinar and Camino) (Nematoda: Mermithidae) from mosquito larvae, the primary site of maturation, to adults. We analyzed the survival time of male and female Aedes albifasciatus (Macquart) (Diptera: Culicidae) parasitized by S. spiculatus, the time of emergence of nematodes from adult mosquitoes, and the state of parasitism in the same mosquito cohorts during the immature stages. Mosquito larvae with single and multiple parasitism (up to 11 parasites) were observed. The mortality of mosquito larvae and adults was produced in all cases where at least one mermithid emerged. The mortality of S. spiculatus showed an increasing trend in mosquito larvae with larger numbers of nematodes and was higher in larvae parasitized by eight or more nematodes. Maximum survival of parasitized adult females of Ae. albifasciatus was 38 days, while non-parasitized adult males and females survived 39 and 41 days, respectively. Strelkovimermis spiculatus mortality was observed in Ae. albifasciatus larvae with single or multiple parasitisms. The spread of mermithid parasitism in adult mosquito populations is discussed.

Mermithid nematode infection in a colony of blue-winged grasshoppers (Tropidacris collaris).

A die-off occurred in a captive colony of blue-winged grasshoppers (Tropidacris collaris) at the Toronto Zoo. One fourth of the colony died within a year due to infection with worms initially mistaken for nematomorphs but later identified as nematodes belonging to the Mermithidae, genus Mermis. Mortality persisted and the grasshopper population dwindled over the following years. Mermithid larvae developed in the hemocoel of the insects until they eventually emerged from a hollowed-out exoskeleton. Circumstantial evidence suggests that the parasites were introduced with raspberry browse that was grown on site and contaminated with mermithid eggs.

First extant records of mermithid nematode parasitism of Auchenorrhyncha in Europe.

Parasitic nematodes of the family Mermithidae were found within four specimens of Auchenorrhyncha from two families (Cicadellidae and Delphacidae). This appears to be the the first extant example of mermithid parasitism of Auchenorrhyncha in Europe. The insect hosts were collected from agricultural grassland field margins at three locations in Ireland during a farmland biodiversity study in 2007.

[Pathogenic effect of 3 parasitic nematodes in Aedes aegypti larvae under laboratory conditions in Cuba]. / Efecto patogénico de 3 nematodos parásitos en larvas de Aedes aegypti en condiciones de laboratorio, en Cuba.

The pathogenic effect of three parasitic nematodes, Romanomermis culicivorax Ross y Smith, 1976, Romanomermis iyengari Welch, 1964, and Strelkovimermis spiculatus Poinar and Camino, 1986, was evaluated at different application doses in larvae of Aedes aegypti. For each experimental unit, one hundred second instar larvae of this mosquitoe were infested with preparasites of the three nematode species in the following proportions: 3:1, 5:1, 10:1, 15:1 and 20:1. Both infestation mean and parasitism rate increased as the doses augmented. Romanomermis culicivorax proved to be more effective at low doses when compared to other species; however, with the 10:1 proportion, all the nematodes caused 100% of mortality. S. spiculatus showed the highest infestation rate. For this reason, a proportion of 10:1 could be recommended to evaluate these nematodes under natural conditions in useless artificial containers as a biological alternative for Aedes aegypti control.

Mermithid parasitism of Hawaiian Tetragnatha spiders in a fragmented landscape.

Hawaiian Tetragnatha spiders inhabiting small forest fragments on the Big Island of Hawaii are parasitized by mermithid nematodes. This is the first report of mermithid nematodes infecting spiders in Hawaii, and an initial attempt to characterize this host-parasite interaction. Because immature mermithids were not morphologically identifiable, a molecular identification was performed. A phylogenetic analysis based on 18S small ribosomal subunit nuclear gene sequences suggested that Hawaiian spider mermithids are more closely related to a mainland presumptive Aranimemis species that infects spiders, than to an insect-infecting mermithid collected on Oahu, HI, or to Mermis nigrescens, also a parasite of insects. Measured infection prevalence was low (ranging from 0 to 4%) but differed significantly among forest fragments. Infection prevalence was associated significantly with fragment area, but not with spider density nor spider species richness. Results suggest that mermithid populations are sensitive to habitat fragmentation, but that changes in infection prevalence do not appear to affect spider community structure.

Chromosomal polymorphism is associated with nematode parasitism in a natural population of a tropical midge.

A natural population of a tropical midge, Chironomus ramosus (Diptera: Chironomidae), was found to be polymorphic for a paracentric inversion (IV: 18C-19D). Based on the characteristic banding pattern of the fourth chromosome in the larval salivary gland polytene nuclei, individuals were classified as either structural homozygotes or heterozygotes. Isofemale lines were obtained and subsequently standard (S/S) and inversion (I/I) homozygotes were characterised by careful progeny testing in the laboratory. While exploring various biotic and abiotic factors that might be responsible for the maintenance of inversion polymorphism, we detected nematode (Family: Mermithidae) infections among the larval population. A detailed study indicated that the inversion polymorphism in the natural population of C. ramosus was apparently being maintained as a result of the selective pressure exerted by the nematode parasite. The corresponding pattern of increase and decrease in genotype frequencies and the relative fitness values indicated a selective advantage of inversion heterozygotes (S/I) over both homozygous types (S/S and I/I). Both empirical and experimental data suggest the strong heterotic nature of adaptation in this C. ramosus population towards nematode infection. This is the first report of its kind where inversion polymorphism has been shown to be associated with nematode parasitism.

[Pathogenic effect of the nematode parasite Romanomermis iyengari(Nematoda: Mermithidae) in Aedes aegypti mosquito larvae (Diptera: Culicidae) under laboratory conditions in the state of Oaxaca, Mexico]. / Efecto patogénico del nematodo parásito Romanomermis iyengari (Nematoda: Mermithidae) en larvas del mosquito aedes aegypti (Diptera: Culicidae) en condiciones de laboratorio en el Estado de Oaxaca, México.

Laboratory tests with waters from Aedes aegypti Linneaus (1762) breeding places were made to determine the pathogenic effect of the mermithid nematode Romanomermis iyengari Welch 1964 in mosquito larvae of this species. According to the results obtained, the administration of a dosage of 10:1 (10 preparasitics per mosquito larvae) showed levels of parasitism of 90, 93, 91, and 85% in mosquito larvae in the I, II, III, and IV stage, respectively. With the highest dosage of 20:1 (20 preparasitics per mosquito larvae) there were obtained levels of parasitism with values of 98, 97, 93 and 89% among larvae in the I, II, III, and IV stage, respectively. Generally, the values of the physical and chemical parameters such as pH, conductivity, oxygen, and chlorides calculated in these waters did not affect apparently the infective capacity of the preparasitics of R. iyengari.

[The susceptibility of Anopheles pseudopunctipennis larvae to parasitism by the nematode Romanomermis iyengari (Nematoda: Mermithidae), the state of Oaxaca, Mexico]. / Susceptibilidad de las larvas de Anopheles pseudopunctipennis al parasitismo del nematodo Romanomermis iyengari (Nematoda: Mermithidae), Estado de Oaxaca, México.

Mosquito larvae of the species Anopheles pseudopunctipennis Theobald 1901 were studied under laboratory and field conditions to evaluate the level of susceptibility to the parasitism of nematode Romanomermis iyengari Welch 1964. Doses of 5:1 and 10:1 and development stage II larvae collected in natural reservoirs were used for the laboratory assays. A dose of 1,000 preparasitic agents/m2 was applied to field trials. The results of the lab and field tests yielded high levels of infestation in larvae with values ranging from 90 to 100% and from 85 to 95%, respectively. A marked reduction of the larval densities was observed in the 5 treated reservoirs seven days later, which showed an elevated susceptibility of the anopheline species to mermithid parasitism.

Experimental host range studies with Heleidomermis magnapapula (Mermithidae), a parasite of Culicoides variipennis (Ceratopogonidae).

Infectivity of the mermithid nematode Heleidomermis magnapapula, a parasite of Culicoides variipennis variipennis and C. v. sonorensis in dairy wastewater pond habitats, was tested against larvae of aquatic Diptera in the laboratory. Observations were made on preparasite penetration. If the host species could be reared after parasitization, further observations determined nematode development and emergence. Genera in the families Syrphidae (Eristalis), Psychodidae (Psychoda), and Chironomidae (Tanypus), common in wastewater pond habitats, were not attacked. Larvae of Bezzia and Dasyhelea (Ceratopogonidae) also were not attacked. Larvae of Chironomus (Chironomidae) were penetrated, but rapidly encapsulated the nematodes. All Culicoides spp. exposed were readily penetrated by H. magnapapula preparasites. The nematodes successfully emerged from C. v. occidentalis. Some nematode maturation was seen in C. lahontan, and limited adult nematode emergence was seen in C. boydi and C. cacticola. No nematode development was observed in 5 other Culicoides spp. penetrated.

[The evaluation of the infectious capacity of the parasitic nematode Romanomermis iyengari (Welch, 1964) (Nematoda: Mermithidae) in natural mosquito larval breeding areas]. / Valoración de la capacidad infectiva del nematodo parásito Romanomermis iyengari (Welch, 1964) (Nematoda: Mermithidae) en criaderos naturales de larvas de mosquitos.

Field tests were carried out with the nematode parasite Romanomermis iyengari (Welch, 1964) to fight 3 species of mosquito larvae Anopheles albimanus (Wiedeman, 1821); Culex nigripalpus (Theobald, 1901); and Culex quinquefasciatus (Say, 1823) in three ecologically different natural mosquito reservoirs. The release of the nematode embryos (infective stage) in the above-mentioned reservoirs was carried out with a Holder-planta 5 manual sprayer, at 2 atm, and an application dose of 1000 parasite embryos/m2. The parasite embryos were obtained from 6 nematode cultures, soaked in distilled water. Results showed that mosquito larvae were parasitized by R. iyengari as follows: 100% of the A. albimanus and 85% of the C. nigripalpus, in the first reservoir; 85% of the C. nigripalpus, in the second reservoir; and 80% of the C. nigripalpus and 75% of the C. quinquefasciatus in the third one. Thus, the potential use of the nematode parasite Romanomermis iyengari as a biological control agent of mosquito larvae was shown.

[Infective capacity of the parasitic nematoda Romanomermis iyengari (Welch, 1964) (Nematoda: Mermithidae) in mosquito larvae in natural conditions]. / Capacidad infestiva del nematodo parásito Romanomermis iyengari (Welch, 1964) (Nematoda: Mermithidae) en larvas de mosquitos en condiciones naturales.

The effectiveness of the parasitic nematoda Romanomermis ivengari (Welch, 1964) was proved in 3 breeding sites of Anopheles albimanus (Wiedman, 1821) and Culex Nigripalpus (Theobald, 1901) and 2 spillways for 2 oxidation ponds with Culex quinquefasciatus (Say, 1823) larvae, in the Isle of Youth. The results of the experiments showed the infesting capacity of this nematoda species with 80-100% parasitism in A. albimanus and C. nigripalpus larvae, and 75-80% mortality for C. quinquefasciatus. Besides, the recycling capacity of R. invengari, after its introduction, was proved, confirming its possible use in the control of mosquito larvae of medical-epidemiological importance in the Cuban tropical conditions.

Infectivity of a mermithid nematode Romanomermis iyengari (Welch) in different conductivity levels under laboratory and field conditions.

Infectivity of R. iyengari was examined by exposing mosquito (Culex quinquefasciatus) larvae to the preparasite at different conductivity levels. The preparasite infected 63.5, 30, 11, 1.5 and 0.5% of the mosquito larvae respectively at 2000, 2500, 3000, 3300 and 3600 mu ho/cm. Although, 62-69% of the preparasite survived at 4000-5400 mu ho/cm, it did not infect. Application of preparasite to tree-holes resulted in 53-63% infection of Aedes albopictus larvae initially. On 6th day the infection level was 40% which decreased further to 7% by 15th day. The infection reappeared on 38th day indicating that R. iyengari has not only infected mosquito larvae as soon as they were applied to tree-holes in which the conductivity was 600-2800 mu ho/cm but also got established there.

[The infective capacity of the nematode Romanomermis culicivorax Ross et Smith, 1976 (Rhabditida: Mermithidae) in mosquito larvae of the species Anopheles albimanus Wiedemann, 1821 (Diptera: Culicidae) under natural conditions]. / Capacidad infestiva del nematodo Romanomermis culicivorax Ross y Smith, 1976 (Rhabditida: Mermithidae) en larvas de mosquitos de la especie Anopheles albimanus Wiedemann, 1821 (Diptera: Culicidae) en condiciones naturales.

An experimental study was carried out in two natural breeding sites of Anopheles albimanus Wiedemann, 1821 in Havana City, in order to test the effectiveness of the nematode Romanomermis culicivorax Ross and Smith, 1976. In one of the breeding sites fresh preparasiticals from eggs recently hatched in cultures were applied at a 10:1 dose, a mean infestation rate being found of mean = 3 with a 97 +/- 0.86% mortality. The second breeding site was treated with preparasiticals 30 hours after their obtention, and a decrease was seen in the larva infestation levels mean means = 1.1 and 76 +/- 0.76% mortality rate.

[A trial of Romanomermis iyengari and R. culicivorax mermithids as a means for controlling blood-sucking mosquitoes in the Tadzhik SSR]. / Ispytanie mermitid Romanomermis iyengari i R. culicivorax kak sredstva bor'by s krovososushchimi komarami v Tadzhikskoi SSR.

Field trials of R. iyengari and R. culicivorax in the biological control for the mosquito larvae were conducted in Parkhar, Kuibyshevsk, Gissar districts and the outskirts of the city of Dushanbe, the Tadjik SSR. Larvae of Anopheles superpictus, An. pulcherrimus and An. hyrcanus in a dosage of 1-5 thousand intact larvae per sq. m were invaded by mermithids. The mean infection rate was 46 per cent. The maximum infection rate was 98 per cent. It depended on several factors: the dosage of intact larvae, temperature, water salinity, water flowage in the waterbodies and their overgrowth with plants. Slow-flowed rice paddies and flow-free fresh waterbodies turned to be the proper sites for mermithids. The effect was higher in Anopheles than in Culex mosquitos.