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Patterns of covert infection by invertebrate pathogens: iridescent viruses of blackflies
Article first published online: 28 JUN 2008
Volume 4, Issue 4, pages 447–458, August 1995
How to Cite
WILLIAMS, T. (1995), Patterns of covert infection by invertebrate pathogens: iridescent viruses of blackflies. Molecular Ecology, 4: 447–458. doi: 10.1111/j.1365-294X.1995.tb00238.x
Since 1990 I have been studying various aspects of the ecology of viral diseases in invertebrate populations at the IVEM, Oxford with particular emphasis on iridescent viruses. I am currently involved with the Iridovirus subgroup of the International Committee for the Taxonomy of Viruses and have made suggestions for changes to the taxonomy and nomenclature of these viruses. I hope to be able to continue this work and to develop additional lines of bioconhol-related research in my new job here at ECOSUR, Mexico.
- Issue published online: 28 JUN 2008
- Article first published online: 28 JUN 2008
- Received 19 December 1994 accepted 27 March 1995
- fluctuations in incidence;
- inapparent infection;
- iridescent viruses;
- Simulium variegatum
Recently, it has been recognized that blackfly populations may host two forms of infection by iridescent viruses (IVs); a covert (inapparent, nonlethal) form which was common in springtime populations in the River Ystwyth, Wales, and a patent (obvious, lethal) form which was rare. This study aimed to investigate the changes in frequency of the two types of infection in blackfly populations over the reproductive period of the flies, April-September 1992. Blackfly larvae sampled from three different sites along the river were bioassayed for the presence of covert IV infection. Of 870 larvae assayed, 17 were found to be infected. All the infected larvae appeared to be Simnulium variegatum, the dominant species during the sampling period. IV infections were common in the spring (17–37% depending on site) but appeared absent in the S. variegatum population for most of the summer months, reappearing again in the autumn (0–20% infected). These fluctuations were concurrent with biotic and abiotic factors: elevated levels of covert infection occurred at low population densities, high water flow rates, low temperatures (and presumably slower growth rates), although it is not clear if any cause-and-effect relationship exists. Patent infections occurred immediately after the peak of covert infection in the spring, and again in the autumn. Virus characterization of isolates from covertly infected larvae showed that three distinct groups of isolates were present in the blackfly population. Isolates from the springtime populations were mostly variants of an isolate found in patently infected blackfly larvae in the 1970s (Aberystwyth IV). Isolates from the autumn populations were mostly variants of an isolate from a patently infected larva found in September the previous year. A third group comprised a single novel isolate which was detected in a covertly infected larva. The mechanisms by which IVs persist in blackfly populations remain unknown, although the role of alternative hosts is a possibility which needs to be studied.