Mermithids (Nematoda: Mermithidae) Parasitizing Different Blackfly (Diptera: Simuliidae) Populations in Quebec: Environmental Parameters Related to Their Presence or Absence in the Studied Brooks

Abstract

Specimens of Isomermis wisconsinensis, Gastromermis viridis, Mesomermis flumenalis, and Mesomermis camdenensis have been found in 14 out of 28 studied sites. Their hosts were the following blackfly species: Cnephia dacotensis, Cnephia mutata, Prosimulium sp., Simulium decorum, Simulium tuberosum, Simulium venustum/verecundum complex, and Simulium vittatum. Superparasitism was observed in several simuliid larvae and, occasionally, with 2 different mermithid species. The prevalence of different mermithid species varies according to seasons: Mesomermis genus is more abundant during winter, whereas Isomermis and Gastromermis are found in higher number during summer. The study of environmental parameters related to mermithid presence or absence shows that only stream depth makes a difference.

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

“…Camino (1987) accepts as valid approximately 12 species of the genus, without listing them, and describes three new species (Camino 1987, 1994). Species of Isomermis have been reported from Europe (Coman 1961, Rubzov 1968, Rubzov and Doby 1970, Katyukha and Lukhovoz 2008), North America (Welch 1962, St-Onge and Charpentier 2008, St-Onge et al 2008), Central (Poinar and Takaoka 1979, 1981) and South America (Camino 1987, 1994, Ginarte et al 2003), Africa (Rubzov 1972, Mondet et al 1977, Maduabum and Iwuala 1990, Crainey et al 2009) and Asia (Poinar and Takaoka 1986). The host range of the genus includes different species of Simuliidae (Crosskey and Poinar 2002) and rarely Chironomidae (Rubzov 1968, Camino 1987).…”

“…Mermithids may play an important role in the regulation of population densities of simuliid hosts (Rubzov 1974, Molloy 1981, Crainey et al 2009), but problems in taxonomy and insufficient data on the biology and ecological requirements (St-Onge and Charpentier 2008) complicate the use of mermithids for black fly control. The difficulties in the identification of immature stages of the hosts, as well as unsolved taxonomic problems in the Simuliidae (Molloy 1981, Adler and Crosskey 2013) further discourage research on the host–parasite relationships within this group.…”

Ecology of Symbiotes of Larval Black Flies (Diptera: Simuliidae): Distribution, Diversity, and Scale

“…Studies of macrodistributions of simuliid symbiotes typically are based on samples from fewer than 30 sites and usually from restricted geographic areas where biogeographic factors would not play a signiÞcant role, as with mermithids (Ezenwa 1973(Ezenwa , 1974aBruder and Crans 1979;Colbo and Porter 1980;Colbo 1990), microsporidians (Ezenwa 1973(Ezenwa , 1974a(Ezenwa , 1974bVávra and Undeen 1981;St-Onge and Charpentier 2008), and trichomycetes (Nelder et al 2009). A few studies have sampled a large number of sites or a broad geographic region.…”

“…The occurrence of mermithids in S. tuberosum and S. ubiquitum Adler, Currie & Wood (as S. tuberosum F.) over a large area of South Carolina is correlated with stream oxygen levels (McCreadie and Adler 1999), and the presence of mermithids in larval hosts in Quebec is associated with stream depth (St-Onge and Charpentier 2008).…”