The mermithid (Nematoda) and other endoparasites of simuliidae (Diptera) in insular Newfoundland

Ebsary, B. A. (Barry Alan) (1973) The mermithid (Nematoda) and other endoparasites of simuliidae (Diptera) in insular Newfoundland. Masters thesis, Memorial University of Newfoundland.

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Abstract

In 1971 and 1972, 198 streams in insular Newfoundland were examined for blackfly endoparasites. Forty streams yielded one or more species of the microsporida-- Thelohania bracteata, T. fibrata, Plistophora simulii, Caudospora simulii and C. brevicauda. The fungus Coelomycidium simulii was found in 14 streams. The blackfly mermithids Gastromermis viridis, Isomermis, wisconsinensis and Neomesomermis flumenalis were recovered from 59 streams. Central Newfoundland had higher frequencies of mermithid infections (47.3-75.0%) than the more coastal areas (11.7-36.3%). The longitudinal distribution of mermithid infected blackflies within the stream showed that the upper 400 m. of the stream were devoid of mermithids, while the lower reaches of the stream harboured mermithids. Current, depth and chemical parameters of the stream water in streams with and without mermithids were examined. Mermithid parasitism did not appear to be significantly affected by these factors. Neomesomermis flumenalis was redescribed in light of the finding of eggs and pre-parasites. Adult males of G. viridis and I. wisconsinensis were also redescribed. The life cycle of N. flumenalis was described. Following emergence from the host, male and female post-parasites molt to adults in 9-15 days at 12°C., 10-13 days at 18°C., 37-40 days at 6°C., and failed to molt at 22-24°C. A double pre-adult molt and a parasitic molt were noted. Mating lasted for 12-24 hours, and usually occurred within a few hours of molting to adults. Eggs were laid 36-59 days after mating. Females laid 600-650 eggs over 3 days. The incubation period was 35-55 days at 12°C.; heaviest egg hatching occurred 4-11 days after the onset of hatching. No eggs were laid at 3°, 7°, 18°, or 22-24°C. Pre-parasites live 2-3 days. The period from emergence from the host to egg laying was 45-74 days, and from emergence to egg hatching, 80-129 days. Mixed infections involving microsporida, mermithids and coelomycidians were noted. Seasonal fluctuations of host/parasite populations in Half Moon Brook and Long Pond Tributary were studied, Neomesomermis flumenalis infected the Prosimuliums in October and the early summer Simuliums in late May-early June. Carryover of mermithids to adult simuliids, based on extrapolated data from late larval and pupal infections, indicated that N. flumenalis probably carried over to the Prosimuliums and Simuliums at a rate of .026 and .062% respectively. Gastromermis viridis and I. wisconsinensis probably infect 1.3-26.8% of their adult simuliid hosts. Host specificity appeared to be related to the asynchronous life cycles of the host parasite populations. Sex ratios of 1.4:1 males to females were noted for the mermithids from the Prosimuliums in Half Moon Brook. Female to male mermithid ratios of 1.33:1 and 9.2:1 for the Prosimuliums and Simuliums in Long Pond Tributary and 2.7:1 for the Simuliums in Half Moon Brook were also noted in 1972.

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