Research Article |
Corresponding author: Denis Gradinarov ( dgradinarov@abv.bg ) Academic editor: Hans-Peter Fagerholm
© 2014 Denis Gradinarov.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Gradinarov D (2014) The mermithid species Isomermis lairdi (Nematoda, Mermithidae), previously only known in Africa, found in Europe. ZooKeys 454: 1-11. https://doi.org/10.3897/zookeys.454.7577
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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, S. variegatum Meigen, 1818 and S. reptans (Linnaeus, 1758), predominated in the investigated locality. In West Africa, I. lairdi is considered to be a potential biological agent for reducing the population density of the S. damnosum complex – the main vector of human onchocerciasis. In Europe, species of the S. 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 I. lairdi is reported for the first time from Europe.
Entomoparasitic nematodes, morphology, taxonomy, parasite ecology, distribution, Simulium ornatum , disease vectors, black fly control, Bulgaria
Mermithids (Nematoda, Mermithidae) are lethal parasites of arthropods, mainly insects. Species of at least 15 different orders of insects are among the hosts of the family (
Mermithids may play an important role in the regulation of population densities of simuliid hosts (
The aim of the present study was to i) perform identification of newly isolated mermithids from a local population of Simuliidae in Bulgaria, ii) analyze the taxonomic position of these species within the genus and their geographical distributions, and iii) provide original data on the rate of mermithid infection in the investigated host population and discuss the host–parasite relationships at population level.
Larvae and pupae of Simuliidae were collected from (1) the Selska Reka River (mountain stream) just above Jeleznitsa Village, Vitosha Mts. (42°32.04'N; 23°21.79'E, 1050 m a.s.l.), and (2) from a channel which diverts the water from the river and supplies barrage ponds in the village square (42°32.05'N; 23°21.91'E, 1030 m a.s.l.). The sampling was carried out in July-September of 2012 in both localities and in August-September of 2013 in the second locality only. Denotations of nematode individuals used for measurements and species identification are: July (25.07., 1♀), August (03.08., 4♂♂, 1♀, 1♂J, 3♀♀Js; 12.08., 2♂♂, 2♀♀, 1♂J) and September (22.09., 1♂J) of 2012.
Simuliids were collected along with grasses and branches of trees which were dipping in the water. The host larvae were kept in shallow dishes with tap water and were examined periodically for the emergence of postparasitic juveniles of mermithids (
Mermithid identification was performed according
The rate of mermithid infection is given for the second locality. Host larvae of middle and late instars (body length of 3 mm or more) were examined individually under the stereomicroscope for the presence of parasitic juveniles of nematodes. In suspicious cases host larvae were dissected. Black flies were determined by larvae and pupae (after
Larvae of Simuliidae infected with mermithids were established in July, August and September of 2012 and August and September of 2013. Mermithids were found in both localities examined mainly in larvae of Simulium ornatum Meigen, 1818 (Fig.
Simuliid species and the rate of their infection with mermithids in the supply channel of the Selska Reka River, Vitosha Mts., July – August of 2012 and August – September of 2013.
Date | Simuliids | Number larvae | Infected larvae | |
---|---|---|---|---|
N | % | |||
25.07. 2012 | S. ornatum | 179 | 79 | 44,1 |
S. variegatum | 7 | 1 | 14,3 | |
Total (% infected) | 186 | 80 | (43,0) | |
03.08. 2012 | S. ornatum | 391 | 150 | 38,4 |
S. variegatum | 2 | 0 | 0,0 | |
Total (% infected) | 393 | 150 | (38,2) | |
12.08. 2012 | S. ornatum | 239 | 22 | 9,2 |
25.08. 2012 | S. ornatum | 340 | 6 | 1,8 |
16.08. 2013 | S. variegatum | 182 | 0 | 0,0 |
S. reptans | 50 | 2 | 4,0 | |
S. ornatum | 10 | 6 | 60,0 | |
Total (% infected) | 242 | 8 | (3,3) | |
27.08. 2013 | S. variegatum | 110 | 1 | 0,9 |
S. reptans | 77 | 3 | 3,9 | |
S. ornatum | 11 | 9 | 81,1 | |
Total (% infected) | 198 | 13 | (6,6) | |
12.09. 2013 | S. reptans | 50 | 2 | 4,0 |
S. ornatum | 32 | 20 | 62,5 | |
S. variegatum | 16 | 0 | 0,0 | |
Simulium sp. | 1 | 0 | 0,0 | |
Total (% infected) | 99 | 22 | (22,2) |
The emergence of postparasitic juveniles of mermithids was observed only from larvae of S. ornatum in the summer and early autumn of 2012. Six males and three females, suitable for measurements, were reared to adult stages. The period of maturation and release from the cuticle remains of postparasitic juveniles under rearing conditions was from 20 to 40 days. The attempts to obtain postparasitic juveniles in the second year were unsuccessful. Based on morphological characteristics of postparasitic juveniles, as well as males and females, all mermithids were identified as belonging to genus Isomermis Coman, 1953. These characteristics are the presence of: eight hypodermal chords, six cephalic papillae, terminal position of mouth opening (Fig.
Main morphological characters of Isomermis lairdi from Jeleznitsa (A–H). A, B Mature male, anterior region with terminal mouth opening (A) and amphid (B), lateral view. C Female postparasitic juvenile, posterior end with tail appendage D Mature female, posterior end E Female, vulvar region with vagina F Male, spicules G Male postparasitic juvenile, tail region with tail appendage H Mature male, tail region. Scale bars: A, B: 50 µm; C–F: 70 µm; G, H: 100 µm.
Males (n=6): body length: 10.81 mm ± 1.51 (9.10–13.26), width of the head at the level of cephalic papillae: 52 µm ± 5 (47–59), width of the body at the level of nerve ring: 93 µm ± 11 (82–105), greatest width of the body: 148 µm ± 16 (127–163), width of the body at cloaca: 123 µm ± 15 (106–141), distance from the head to the nerve ring: 191 µm ± 27 (158–231), tail length: 277 µm ± 37 (238–332), length of amphidial pouch (n=2): 24 µm ± 1 (24–25), width of amphidial pouch (n=2): 17 µm, number of the genital papillae: 18–21 in lateral rows and 56–62 in ventral row, arrangement of the papillae as follows: precloacal – 11–14 in lateral rows and 31–38 in ventral row, postcloacal – 7–8 in lateral rows and 23–26 in ventral row, length of spicules (measured along median): 203 µm ± 10 (191–218), length of spicules (measured along chord): 179 µm ± 8 (168–193). Spicules yellowish-colored, clearly separated at the base and close towards the tip, with elongate distal and arcuate proximal part.
Females (n=3): body length: 17.44 mm ± 3.95 (12.96–20.42), width of the head at the level of cephalic papillae: 71 µm ± 5 (67–77), width of the body at the level of nerve ring: 113 µm ± 19 (94–131), greatest width of body: 251 µm ± 39 (208–285), width of the body at vulva: 233 µm ± 42 (186–267), distance from head to the nerve ring: 191 µm ± 26 (171–220), width of the body at posterior end of the trophosome: 111 µm ± 5 (106–116), length of vagina: 219 µm ± 22 (205–245), width of vagina: 54 µm ± 2 (52–57), length of amphidial pouch (n=1): 20 µm, width of amphidial pouch (n=1): 16 µm, V%: 52.1 (50.2–54.8). Vagina is slightly curved, with the first bend extended posteriorly.
Color of the trophosome of the living individuals of both sexes varies from pale pink to brownish red, more intense in parasitic and postparasitic juveniles (Fig.
After a detailed comparison with the original descriptions of the species the mermithids were identified as Isomermis lairdi Mondet, Poinar & Bernadou, 1977, originally described from West Africa. The main reasons for the identification were good conformity with most morphometric characters of the species, the compliance of morphology of the caudal region of the males with the figure in the original description, as well as the morphology of caudal appendage of postparasitic juveniles (
No other mermithids, except I. lairdi, emerged from larvae of S. ornatum or were received from them at the selective dissections. Sporadic infection of S. reptans and S. variegatum larvae (Table
The genus Isomermis, as well as the whole family Mermithidae (
Isomermis lairdi resembles most closely three species of the genus. These are I. rossica Rubzov, 1968, described from Russia, I. benevolus Poinar & Takaoka, 1979 from Guatemala and I. wisconsinensis Welch, 1962 from North America. Among the diagnostic characters of I. lairdi
Isomermis rossica is the only repeatedly reported species of Isomermis from Europe. It was found in different regions of Russia, Belarus, (
Isomermis lairdi was described in Cote d’Ivoire from larvae of S. damnosum Theobald, 1903 (
Simuliids of the S. damnosum complex are among the main vectors of human onchocerciasis in Africa (
According to previous research on simuliid fauna in Bulgaria, S. ornatum and S. variegatum are common in the rivers on Vitosha Mts., while S. reptans is relatively rare (