|WATSON D W|
|KWAN E C|
Submitted to: Journal of Intervertebrate Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/2/1995
Publication Date: N/A
Interpretive Summary: Fungi that specifically infect insect pests hold great potential as highly selective environmentally benign biological control agents. In order to use these fungi more effectively, we need to understand how they use their insect hosts for their survival. In this study, the manipulation by a fungus of the behavior of its house fly host has been documented. By manipulating the posture of the dying house fly (raising the wings and the abdomen) the fungus turns the host into a more effective launching pad for spreading the fungal spores. Also, mortality occurred at specific times under the control of a biological clock. The most likely source governing the biological clock appears to be the fungus alone. This report provides the first documented evidence of a biological clock involved in the fungal pathogen-insect interaction, and provides a defined system to monitor the relative effectiveness of fungi as biocontrol agents.
Technical Abstract: The behavior of house files infected with entomopathogenic fungus Entomophthora muscae was recorded on videotape and analyzed quantitatively. 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). The median elapsed time between WS and WU was 15 minutes. The median time interval between the LM and WU was 1.25 h. Also, the mortality of diseased flies observed over several days, exhibited a distinct diel periodicity with most flies dying 0-5 hours before the onset of darkness. The mortality of flies held in the dark from the time of exposure until just before death did not exhibit rhythmicity; however, a circadian periodicity of mortality was observed in a population of infected flies exposed to a 12:12 (light:dark) photoperiod for three 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. It is argued that the most likely source of the governing clock is the fungus alone.