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

Denis Gradinarov

doi:10.3897/zookeys.454.7577

Abstract

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.

Highlights

Mermithids (Nematoda, Mermithidae) are lethal parasites of arthropods, mainly insects
The host larvae were kept in shallow dishes with tap water and were examined periodically for the emergence of postparasitic juveniles of mermithids (Rubzov 1974)
Mermithids were found in both localities examined mainly in larvae of Simulium ornatum Meigen, 1818 (Fig. 1A, B)

Summary

Introduction

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 (Nickle 1972). Mermithids occurring in black flies (Diptera, Simuliidae) are an insufficiently studied group with problematic taxonomy (Molloy 1981, St-Onge et al 2008). Descriptions of many species are not satisfactory and many described species are considered as species inquirendae (Curran and Hominick 1981, Poinar and Takaoka 1979). The adult nematodes, essential for a correct morphological identification (Poinar 1979), need in most cases to be obtained by laboratory rearing of emerged postparasitic juveniles. Morphology-based taxonomy requires significant time and effort. Molecular methods have been introduced in the taxonomy of the group (St-Onge et al 2008, Crainey et al 2009)

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