Mermithid Infection Research Articles

Role of Mermithid Nematodes in the Management of Agricultural and Household Insect Pests: A review

The increasing challenges associated with using chemicals in managing agricultural and household insect pests has prompted a re-evaluation of previous approaches and the search for new ones as alternatives or supplements to the present management programmes. The introduction and release of bio-agents, like fungi, bacteria, viruses, nematodes, and insects for the control of pests is a novel biological control strategy. Among bio-agents, the role of mermithid nematodes in insect-pest management has been considered. Mermithids are prime candidates for biocontrol of insects due to their adaptability to the life cycle of the host, a high degree of host specificity often limited to one or more species of insects, high reproductive potential, free swimming behavior making dissemination of pre-parasitic stage easy, pathogenic ability and high levels of parasitism. Another useful trait favoring their employability is their non-feeding habit soon after emerging from the host body, making their handling simple. The morphological, physiological, and behavioral responses of host insects are significantly disrupted by mermithid infective juveniles often the J2 stage. Many mermithid infections cause abdominal distortion, discolored cuticle/integument, and a decrease in total fat body content of the host. The parasitism by these nematodes can lead to formation of intersexual conditions in the host insects which also create distortion to endocrine system. Owing to such mechanism of parasitism of mermithids, these nematodes are one the best considerations as bio-control agents.

Agamermis sp. (Nematoda: Mermithidae) parasitizing Armadillidium vulgare (Crustacea: Isopoda) in Argentina.

The Mermithidae is a family of nematodes parasitic in many kinds of insects, spiders, leeches, crustaceans and other invertebrates throughout the world. While conducting an assay with entomopathogenic nematodes, we found Armadillidium vulgare (Crustacea: Isopoda) individuals to be infected with Agamermis sp., marking the fourth known discovery of a mermithid infection in the order Isopoda. In this work, we contribute with an 18S rDNA sequence of the isolated nematode and the morphological and morphometrical characterization of the juveniles.

Natural infections and distributions of parasitic mermithids (Nematoda: Mermithidae) infecting larval black flies (Diptera: Simuliidae) in tropical streams of Malaysia

Mermithids are parasites of black flies that cause host mortality along with physical and behavioural changes in infected hosts. However, there is a lack of knowledge on the distribution of mermithids infecting black fly larvae and the factors that influence these distributions in Asia, including Malaysia. A total of 13,116 mid- to late-instar black fly larvae belonging to 42 species were collected from 138 streams across East and West Malaysia and screened for the presence of mermithid parasites. Overall, 121 mermithids were obtained from 107 (0.82%) larvae of nine (21.4%) black fly species. The average number of mermithids per black fly host was 1.10 ± 0.04 (SE), ranging from one to three mermithids per host. Mermithid infection was highest in Simulium trangense, with a frequency of occurrence of 6.5%, followed by S. cheongi (5.8%) and S. angulistylum complex (2.9%). Infection was lowest in S. brevipar and S. tahanense, with a frequency of occurrence of 0.7% each. Regression analysis indicated that mermithid infections in larval black flies were significantly associated with cooler and shallower streams with more canopy cover, dense riparian vegetation, high dissolved oxygen, and lower conductivity and complete pH. Forward logistic regression further indicated that infections in S. cheongi were associated with shaded, cooler, slightly acidic streams with higher conductivity and dissolved oxygen. These findings suggest that mermithid infections in larval black flies in Malaysia are not randomly distributed and are influenced by the breeding habitat of their hosts.

Review and contribution to the stonefly (Insecta: Plecoptera) fauna of Azerbaijan.

Known Plecoptera data published from Azerbaijan are critically reviewed. New records of 28 species are enumerated on the basis of specimens collected between 2017 and 2019, among them 16 are new for the fauna of Azerbaijan. Nemoura irani Aubert, 1964 is new for the whole Caucasian region, Leuctra sanainica Zhiltzova, 1960 and Plesioperla sakartvella (Zhiltzova, 1956) are new for the Greater Caucasus. The female and larva of an unknown Protonemura Kempny, 1898 species, collected in the Talysh Mts, are illustrated and described under temporary name Protonemura sp. AZE-1. A new species of Protonemura, collected both in the Azerbaijan and Georgian areas of the Greater Caucasus, will be formally described in a further paper. A male Protonemura specimen was found to be infected by mermithid worms, morphological lesions are illustrated and commented; this is the second documented case of mermithid infection in stoneflies. Subspecies level identity of Azerbaijani populations of Leuctra fusca (Linnaeus, 1758) proved to be problematic, morphological characters of the specimens are illustrated. Synonymy of Isoperla caucasica Balinsky, 1950 and I. pulchra Balinsky, 1950 under I. bithynica (Kempny, 1908) is disputed, the two names are combined under I. grammatica (Poda, 1761) sensu lato.

Sexually anomalous individuals of the black fly Simulium trangense (Diptera: Simuliidae) infected with mermithid parasites (Nematoda: Mermithidae)

Sexually anomalous individuals, typically intersexes or gynandromorphs, bear a mixture of male and female traits. Twelve sexually anomalous individuals of the black fly Simulium (Gomphostilbia) trangense Jitklang, Kuvangkadilok, Baimai, Takaoka & Adler were discovered among 49 adults reared from pupae. All 12 sexually anomalous adults were parasitized by mermithid nematodes, although five additional parasitized adults had no overt external anomalies. Sequence analysis of the 18S rRNA gene revealed that the mermithids, possibly representing a new species, are related to Mesomermis spp., with genetic distances of 5.09-6.87%. All 12 anomalous individuals had female phenotypical traits on the head, thorax, forelegs, midlegs, and claws, but male features on the left and right hind basitarsi. One individual had mixed male and female genitalia. The findings are in accord with the trend that mermithid infections are associated with sexually anomalous adult black flies.

First report on Mermithidae (Mermithida) infection in Ligidium sp. (Isopoda, Ligiidae).

Specimens of Ligidium sp. (Crustacea, Isopoda, Oniscidea) collected from Kanagawa Prefecture in Japan were found to be infected with parasitic nematodes. We have obtained two Mermithidae (Nematoda) by dissecting the fresh specimen and from the dead specimen of Ligidium, which marks the second known discovery of a mermithid infection in the order Isopoda. Herein, a report on the nuclear 28S rDNA and 18S rDNA sequence of the isolated Mermithidae nematodes and on the morphology of the juveniles is provided.

Survey of entomopathogenic organisms of the Cantharis livida Linnaeus, 1758 (Coleoptera: Cantharidae) in Turkey

In the present study, one cephaline (septate) gregarine and mermithid infections were reported from the Cantharidae family for the first time. These infections were determined from different populations of Cantharis livida L. 1758 (Coleoptera: Cantharidae) in Turkey. During the observations, the main life stages of the current gregarine like trophozoite, gamont associative form (syzygy) and gametocyst stages were observed. The gamont stage which separated into two parts by septum as protomerite and deutomerite was the most common stage in the host gut and ovocylindrical gamonts measured 240.4 ± 29.0 (154.5-306.2; n=40) μm in length. The mermithid infection was observed only in two samples which were collected from Rize (total infection rate 3.22%). The determined juvenile forms were measured 270-281 μm in width and 68.6-79.98 mm in length.

Survey of mermithid nematodes (Mermithida: Mermithidae) infecting fruit-piercing stink bugs (Hemiptera: Pentatomidae) in Japan

Mermithid nematodes (Mermithida: Mermithidae) infect and kill many different invertebrates and have been investigated for their potential as a biological control agent of insect pests. In this study, we conducted a survey of mermithid nematodes infecting fruit-piercing stink bugs (Hemiptera: Pentatomidae) in Japan. We collected fruit-piercing stink bugs in four different prefectures (Shizuoka, Mie, Tokushima, and Saga) and investigated the distribution and infection ratio by mermithid nematodes. The results indicate that the nematode infection ratio of Glaucias subpunctatus (Walker) was higher than that of Plautia stali Scott or Halyomorpha halys (Stal). Furthermore, significant differences in mermithid infection percentages were observed among regions and seasons, with the highest being in G. subpunctatus in Mie during May–June. Of note, all mermithid nematodes were isolated from stink bugs collected from plants, and no nematodes were isolated from stink bugs attracted to store lights. This implies that parasitism of mermithid nematodes may affect the behavior of the host stink bugs. Furthermore, we obtained DNA sequences and simple morphological characteristics for the nematodes isolated. This study indicates that the mermithid nematodes obtained from stink bugs belong in the genus Hexamermis.

Amphimermis enzoni n. sp. (Nematoda: Mermithidae) parasitizing damselflies and dragonflies in Argentina.

A mermithid nematode was found parasitizing nymphs of dragonflies and damselflies. The host specimens were collected from the stream Cajaravilla, Magdalena, Buenos Aires state, Argentina. In this work, we described Amphimermis enzoni n. sp., a nematode new to science. Nematodes were identified through morphological and molecular methods. The combination of the following characters separates A. enzoni n. sp. from other members of the genus Amphimermis Steiner: long and S-shaped vagina, twisted spicules for proximal 34% of their length, untwisted for 12%, again twisted for 30%, and untwisted for the last 24%; genital papillae arranged in three rows, medial row marginally longer than sub-medial rows; medial row bifurcated immediately anterior and posterior to cloaca, with 111 genital papillae (73 pre-anals and 38 post-anals). The sequences of 18S rDNA regions from A. enzoni formed a well-supported monophyletic clade with two GenBank sequences of Amphimermis spp. (EF617354 and EF617355) with 0.63 to 1.26% divergence and two Mermithidae spp. (LC512371 and LC512370) with 0.63 to 1.1% divergence, respectively. To our knowledge, this is the first example of mermithid infection in nymphs of dragonflies and damselflies for South America.

A molecular war: convergent and ontogenetic evidence for adaptive host manipulation in related parasites infecting divergent hosts.

Mermithids (phylum Nematoda) and hairworms (phylum Nematomorpha) somehow drive their arthropod hosts into water, which is essential for the worms' survival after egression. The mechanisms behind this behavioural change have been investigated in hairworms, but not in mermithids. Establishing a similar mechanistic basis for host behavioural change between these two distantly related parasitic groups would provide strong convergent evidence for adaptive manipulation and insight into how these parasites modify and/or create behaviour. Here, we search for this convergence, and also contrast changes in physiology between hosts infected with immature and mature mermithids to provide the first ontogenetic evidence for adaptive manipulation by disentangling host response and pathology from the parasite's apparent manipulative effects. We used SWATH-mass spectrometry on brains of Forficula auricularia (earwig) and Bellorchestia quoyana (sandhopper), infected with the mermithids Mermis nigrescens and Thaumamermis zealandica, respectively, at both immature and mature stages of infection, to quantify proteomic changes resulting from mermithid infection. Across both hosts (and hairworm-infected hosts, from earlier studies), the general function of dysregulated proteins was conserved. Proteins involved in energy generation/mobilization were dysregulated, corroborating reports of erratic/hyperactive behaviour in infected hosts. Dysregulated proteins involved in axon/dendrite and synapse modulation were also common to all hosts, suggesting neuronal manipulation is involved in inducing positive hydrotaxis. Furthermore, downregulation of CamKII and associated proteins suggest manipulation of memory also contributes to the behavioural shift.

First Record of a Species of Mermithidae Braun, 1883 Infecting a Decapod, Palaemon paludosus (Palaemonidae)

The hemocoel of 26 of 30 (86%) eastern grass shrimps, Palaemon paludosus (Gibbes, 1850) (Decapoda: Palaemonidae), captured during June 2017 from several freshwater lakes near Leesburg and Lake Kissimmee, Florida, was infected by juveniles of a nematode species (Mermithidae sp.). Some infected eastern grass shrimps were preserved whole for histopathology, whereas others were dissected to excise parasitic juvenile nematodes, and still others were kept alive in glass aquaria such that post-parasitic (emerged) juvenile nematodes could be opportunistically observed alive and ultimately preserved. Parasitic and post-parasitic juvenile nematodes had cuticle cross-fibers, cephalic papillae, cup-shaped amphids, a horn-shaped vagina, a trophosome, and a caudal appendage, which collectively diagnosed them as Mermithidae sp. They differed from those of nematomorphs (Nematomorpha) by lacking 4 giant cells anteriorly, tegumental bristles, scale or plate-like areoles, a bifurcate or trifurcate posterior end, and an anus. A phylogenetic analysis of the small subunit rDNA (18S) that included all of the available mermithid sequences corresponding to morphologically diagnosed specimens recovered Mermithidae sp. within the clade of mermithids and sister to Ovomermis sinensis Chen, Jian, and Ren, 1991 . This is the first record of a mermithid infection in a decapod and first report of a mermithid infection in an aquatic crustacean from North America (another mermithid infects a terrestrial isopod there). The high prevalence of infection and the multiple geographic localities harboring infected eastern grass shrimps indicated that these infections were not spurious. Because no other decapod is confirmed as a mermithid host, we suspect that these specimens likely represent a new species with a life cycle worth studying, since none for a mermithid involving a decapod nor a crustacean has been elucidated to date. We also provide a table of all mermithid and nematomorph infections in crustaceans.

The mermithid species Isomermis lairdi (Nematoda, Mermithidae), previously only known in Africa, found in Europe

The present work contributs to the knowledge on the aquatic mermithids (Nematoda, Mermithidae) occurring in black flies – an insufficiently studied group of parasitic nematodes. Isomermis lairdi Mondet, Poinar & Bernadou, 1977, described from larvae of Simulium damnosum Theobald, 1903 in Western Africa, is reported to occur in Bulgaria. The species was isolated from larvae of Simulium ornatum Meigen, 1818 in a local population of simuliids in a mountain stream near Jeleznitsa Village, Sofia district. Postparasitic juveniles of mermithids were obtained from the hosts and reared to the adult stage. The species was identified by morphological and morphometrical characters of postparasitic juveniles, and of male and female individuals. In the summer of 2012 a relatively high rate of mermithid infection in a local host population was detected (prevalence up to 44.1%). In August of the next year host abundance had considerably declined and other simuliid species, Simulium variegatum Meigen, 1818 and Simulium reptans (Linnaeus, 1758), predominated in the investigated locality. In West Africa, Isomermis lairdi is considered to be a potential biological agent for reducing the population density of the Simulium damnosum complex – the main vector of human onchocerciasis. In Europe, species of the Simulium ornatum complex are among the vectors of onchocerciasis of cattle and deer. The mermithids presumably play a certain role in the epidemiology of these diseases. A brief discussion on the taxonomy of the genus Isomermis Coman, 1953, and of the feasibility of molecular methods in mermithid taxonomy is provided. The species Isomermis lairdi is reported for the first time from Europe.

Chiasmate meiosis in male black fly (Diptera: Simuliidae) larvae associated with mermithid infections (Nematoda: Mermithidae)

Mermithid nematodes (Nematoda: Mermithidae) parasitize larval, pupal, and adult black flies (Diptera: Simuliidae) and may result in the development of intersex adults, generally considered to be feminized males. Simuliid gonad morphology and meiotic chromosome condition were examined in both early-instar larvae and late-instar larvae (≈ pharate pupae) to determine the developmental stage at which mermithid-associated feminization was initiated. We found that feminization occurred in early-instar larvae prior to gill histoblast formation. Infected larvae were morphologically male (rounded testes present) or female (elongated ovaries present), with morphological males exhibiting either male (achiasmate) or female (chiasmate) meiotic chromosomes; morphological females only had chiasmate chromosomes. Mermithid infection can also inhibit simuliid gonad development completely.

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).

The efficacy of melanotic encapsulation as a defense against parasite-induced mortality in snowpool mosquitoes (Diptera: Culicidae) infected by mermithid nematodes

The effects of host reactions to parasitism were studied in two species of mosquitoes (Diptera: Culicidae) infected with mermithid nematodes (Romanomermis sp.). No immune reactions were observed in Aedes impiger and virtually all (98.5%) infected larvae died before pupation. Mermithid infections of Aedes nevadensis resulted in high host mortalities (99.3% failed to pupate) when none of the parasites were encapsulated. Melanotic encapsulations of the nematodes were found in 67% of infected Aedes nevadensis, and larvae of this species that encapsulated all of their parasites had the same rate of survival as uninfected conspecifics. Survivorship of Aedes nevadensis larvae that encapsulated some but not all of their Romanomermis parasites was intermediate. Encapsulation also suppressed parasite-induced reductions in host size, and larvae that encapsulated all parasites were significantly larger than other Aedes nevadensis. This is the first quantitative demonstration of the efficacy of mosquito immune responses as defenses against mermithid parasites.

A Field Study of Parasitism of Larval Black Flies (Diptera: Simuliidae) by Neomesomermis flumenalis (Nematoda: Mermithidae) in Southern California

The prevalence of Neomesomermis flumenalis (Welch) parasitism in late-instar larvae of black fly populations was investigated in two California oak woodland streams in the foothills of the San Gabriel Mountains. A permanent stream in San Dimas Canyon was sampled from July 1982 through January 1984. The age-specific attack rate was documented in Simulium aureum Fries and Simulium piperi Dyar & Shannon populations during an epizootic in the fall of 1982. Sporadic infections of larvae were found throughout the year; however, high rates of parasitism developed only in association with substantial S. aureum populations. Mermithid infections were also documented in S. argus Williston, S. arcticum Malloch, S. vittatum Zetterstedt, and S. virgatum Coquillett. Study of an intermittently dry stream in Lodi Canyon suggests that free living N. flumenalis survive periods of summer drought in the stream bed and infect invading Simulium larvae when fall rains flood the channel.

Suppression of immune responses of locusts to trypanosomatid flagellates by concomitant mermithid infection

Suppression of immune responses of locusts to trypanosomatid flagellates by concomitant mermithid infection

Naididae (Oligochaeta) as hosts for mermithid nematodes (Enoplida: Mermithidae)

Naidid species Chaetogaster diaphanus, Chaetogaster diastrophus, Chaetogaster limnaei limnaei, Dero digitata, Dero nivea, Nais communis, Nais simplex, Nais variabilis, Pristina leidyi, Slavina appendiculata, and Stylaria lacustris were observed as paratenic and possibly intermediate hosts for larval mermithid nematodes from field collections. Mermithids were generally found in the anterior, dorsal region of the oligochaetes. Individual naidids were at most infected with two nematodes. No seasonal prevalence patterns could be firmly established owing to the sporadic occurrence of mermithid infections in the naidids.

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.

Distribution and specificity of Mermithidae (Nematoda) infecting Simuliidae (Diptera) in Newfoundland

A number of simuliid populations infected with mermithids were studied to elucidate the nematode's life history patterns and the effect of this on the infected host's distribution. Some of the mermithids were very host specific, while others infected all simuliid species exposed to some degree. An extensive study showed that mermithids infecting Prosimulium mixtum failed to infect Stegopterna mutata which may have been due to the preparasites inability to recognize St. mutata as a potential host, or due to host behaviour, rather than microdistribution or physiology.In mermithid species where the majority complete their parasitic phase and emerge from the larval simuliid, the heaviest infections occur towards the downstream end of the host distribution. On the other hand those mermithid species which emerge only from adult simuliids have a high infection rate in the larval simuliids at the upstream end of host distribution. Infection occurs in the early simuliid instars, primarily first and second, with perhaps some in the older larvae. The rate of infection and the number of larvae per host changed between the time of simuliid hatch and the final host instar at most sites. However, the infection pattern in late instar larvae in any one stream appeared to be relatively stable from year to year.In the present study all mermithid infections of adult hosts were confined to the female fly irrespective of the mermithids life history pattern.