A survey of the prevalance and study of the effects of an ovariam phycomycete in some Newfoundland blackflies

Yeboah, Daniel Owusu (1980) A survey of the prevalance and study of the effects of an ovariam phycomycete in some Newfoundland blackflies. Masters thesis, Memorial University of Newfoundland.

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Abstract

The ovarian phycomycete parasitizes Stegopterna mutate and prosimulium mixtum. The rate of infection in St. mutate was found to be 40%, but the rate in P. mixtum could not be accurately determined because of insufficient data. Simulium verecundum is a suspected host because the fungus is found on its egg masses. – The spore released by the fly during oviposition did not withstand desiccation and did not develop on the artificial media tested; development occurred only in water. At 4°C development was slow, and sporangia took between 5 and 7 days to develop. Above 10°C, the sporangia developed faster, within 2-3 days. The developmental process included the formation of sporangia from which discharge tubes formed, from these structures zoospores were presumed to be released. Evidence suggested that discharge tube development coincided with egg development, and that the life cycle of the fungus coincided with that of the host. A dormancy period equivalent to egg diapause of the host, of the involvement of an inte3rmediate host in the life cycle of the fungus is discussed. Evidence collected suggest there were two seasonal forms of the fungus – winter and summer – each form parasitizing the simuliid species present in the appropriate season. Based on the evidence collected to date, it is thought that infection occurs during the host’s early instars. Parasitism does not produce any detectable external symptoms in the host for results in a complete destruction of the ovarian tissues and eggs. Infected flies did not bite after the first gonotropic cycle and did not oviposit again. The infection rate in an ovipositing fly population was found to decrease with time. Longevity of the host did not appear to be affected by the presence of the fungus.

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