Observations on the occurrence and collection of mermithid nematodes from blackflies (Diptera: Simuliidae)

Abstract

From 1973 through 1975 larval blackflies were sampled for mermithid nematodes in 83 streams in Newfoundland. Prosimulium mixtum/fuscum and Simulium venustum were the predominant hosts of the mermithid Neomesomermis flumenalis but rates of infection in late-instar larvae were generally low (4.3 ± 0.7% and 5.4 ± 1.2% for P. mixtum/fuscum and S. venustum respectively). Mermithid infection in the streams studied showed temporal fluctuations and varied among and within host breeding sites. When numbers of parasitized larvae were judged adequate, mass collections of larvae were made and held in the laboratory for emergence of mermithids. Nematode emergence was in two distinct peaks, one for the Prosimulium generation the other for the first generation of S. venustum. The temporal separation of the peaks varied from year to year owing to weather. Observations on the bionomics of both mermithids and blackfly hosts made during the course of the surveys and technical problems inherent to such studies are discussed.