Mermithid and microsporidan parasitism of blackflies (Diptera: Simuliidae) in the vicinity of Churchill Falls, Labrador

Neomesomermis flumenalis (Welch) infected 11.2% of 3144 blackfly larvae from five localities. Thelohania bracteata (Strickland) and Pleistophora simulii (Lutz &Splendor) and P. multispora (Strickland) parasitized 4.9% of the larval population. The mermithid infected the larvae of Prosimulium mixtum Sime &Davies and Simulium corbis Twinn, S. decorum Walker, and S. venustum Say. The larvae of the last three species were also infected with at least one of the species of Microsporida. Joint infections of T. bracteata and P. simulii occurred in S. venustum. Only 5 of 18 localities had infected blackfly populations. One nematode per host occurred most often, and emergence was from the host abdomen.