Notes on mermithid parasitism of Newfoundland blackflies, with the first record of Neomesomermis flumenalis from adult hosts.

Field-collected pupae of Simulium venustum and Prosimulium mixtum were allowed to eclose in the laboratory and the adults were dissected to reveal the presence or absence of mermithid parasites. Twenty-six (11.7%) of 221 female P. mixtum were found parasitized; all 187 males examined were unparasitized. Nematodes emerged from 10 (14.3%) of 70 female P. mixtum when placed in water-filled dishes. The nematodes recovered from P. mixtum were Neomesomermis flumenalis (66.6%), Isomermis sp. (26.7%), and Gastromermis viridis (6.7%). Forty-three (22.2%) of 194 female S. venustum were parasitized; all 134 males examined were unparasitized. Three (5%) of 60 male pupae of S. venustum were parasitized; 7 (8%) of 86 females were found to harbour mermithids. The nematodes recovered from S. venustum were Hydromermis sp. (75%), G. viridis (12.5%), and N. flumenalis (12.5%).