Studies on Host-Parasite Relationships of Simuliidae with Mermithids and Microsporidans

Abstract

Neomesomermis flumenalis infected Prosimulium mixtum/fuscum, Simulium venustum, S. corbis, and S. latipes. Gastromermis viridis infected the first 3 blackfly hosts, and Isomermis wisconsinensis, the first 2 hosts. Caudospora simulii infected P. mixtum/fuscum, and Caudospora brevicauda, Cnephia mutata. Pleistophora simulii infected S. venustum, S. vittatum, S. tuberosum, and S. latipes, and Pleistophora multispora, the first 2 hosts. Thelohania bracteata parasitized S. latipes, S. venustum, and S. vittatum, and Coelomycidium simulii, the last 2 hosts. Mermithids, microsporidans, and fungus infected 9.42% of 24,964 larval blackflies. Mermithids infected 5.02% and 94.8% of that infection was N. flumenalis. Incidence of mermithids was limited by lack of infection of the 2nd generation of Simulium species. Microsporidans and fungus infected 4.4% of (24,964) the blackfly larvae. Majority (96.4%) of this infection was microsporidans. Larvae of C. dacotensis, S. aureum, S. decorum, and S. gouldingi, totaling 1.97% of the 24,964 blackfly larvae, were not infected. First-stage juveniles of N. flumenalis resemble preparasites, but the former are shrunken and have larger trophosomes than the latter. Secondstage parasites are sickle-shaped. The 1st phase of the 3rd stage assume sinuous form, and their cuticles are pervious to water. The 2nd phase of the 3rd stage maintains the sinuous form, but the cuticle is impervious to water. Up to the 3rd instar, both blackfly larvae and mermithids developed slowly. In the 4th instar, both the blackfly larvae and the mermithids grow rapidly and the latter emerges from 5th-instar hosts. Mermithid and microsporidan parasites of blackflies are receiving more attention as potential biological control agents. Welch (1962) noted that prior to his publication about 40 cases of mermithid parasitism of blackflies were recorded in North America. He also (1963) noted that at least 153 records of mermithid parasites of blackflies exist in the world literature with hosts in the genera of Simulium, Prosimulium, Eusimulium, and Cnephia. This investigation sought to determine the feasibility of employing both groups of parasites for control of blackflies. Data were gathered on simuliid hosts, factors that influence host-specificity, total effect of all the parasites on blackfly population, most promising candidate species of the parasitic groups for biological control, and relationship between parasites and other freshwater invertebrates in blackfly larval habitats. MATERIALS AND METHODS Twenty-seven streams in Avalon Peninsula, Newfoundland, were sampled between July and August 1972 for larval blackflies infected with mermithid and/or microsporida. Five of the 18 streams with infected larvae were selected from different watersheds to include several species of blackflies and Received for publication 26 October 1973. their endoparasites. These streams were subsequently sampled at regular intervals (with some irregularities in the months of December up to February due to adverse winter conditions) up to the end of August 1973. The key of Wood et al. (1963) was adopted for blackfly larval identification with reference to species previously identified by Peterson (pers. comm., 1972). Microsporidan parasites were identified using Thomson (1960), Weiser (1961, 1969), and with reference to species that had been identified by Weiser (pers. comm., 1972, 1973). Mermithids were identified using Welch (1960, 1962), Phelps and Defoliart (1964), Nickle (1972a), Johnson (1963), Poinar (1968), Hominick and Welch (1971), and with reference to species previously identified by Nickle (pers. comm., 1972). Fully developed larval blackflies with histoblasts, pupae, and adults were examined for mermithid, microsporidan, and fungal infections. These observations were used to determine if the parasites from larvae were passed to adult blackflies, and what influence this might have on dispersal of the parasites.