Behavioral effects of the entomopathogenic fungus, Entomophthora muscae on its host Musca domestica: Postural changes in dying hosts and gated pattern of mortality

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Abstract

Videotaped records of house flies dying from infection with the fungus Entomophthora muscae showed that flies typically die on the fourth or fifth day post-infection in elevated positions, with the proboscis extended and attached to the substrate, the legs spread, the abdomen angled away from the substrate and the wings raised above the thorax. Four events occurring before or shortly after death were identified, the last locomotory movement (LM), the last extension of the proboscis to the substrate (PD), the start of upward wing movement (WS) and the end of upward wing movement (WU). Progression through this sequence was essentially unidirectional and highly stereotyped. The median elapsed time between WS and WU was 15 min. The median time between LM and WU was 1.25 h. The mortality of diseased flies, observed over several days, exhibited a distinct diel periodicity under both natural and artificial photoperiodic regimes with most flies dying 0–5 h before the onset of darkness. The mortality of flies held in the dark from the time of exposure until death did not exhibit rhythmicity; however, a circadian periodicity of mortality was observed in a population of infected flies exposed to a L12:D12 photoperiod for 3 days following infection and then held in continuous darkness. These findings indicate that mortality in E. muscae-diseased flies is a gated phenomenon governed by a biological clock, that, it is argued, is most probably a property of the fungus.

Keywords

Musca domestica L.
Entomophthora muscae Cohn (Fresenius)
Entomopathogenic fungus
Circadian

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