Fungal artillery of zombie flies: infectious spore dispersal using a soft water cannon. Issue 159 (30th October 2019)

• Record Type: Journal Article
• Authors: de Ruiter, Jolet; Arnbjerg-Nielsen, Sif Fink; Herren, Pascal; Høier, Freja; De Fine Licht, Henrik H.; Jensen, Kaare H.
• Is Part Of: Journal of the Royal Society interface. Volume 16:Issue 159(2019)
• Publication Date: 2019-10-30
• Subjects: fungal spore ejection -- Entomophthora muscae -- biomimetic soft cannon -- high-speed videography -- dispersal range -- force-balance model; Physical sciences -- Research -- Periodicals; Life sciences -- Research -- Periodicals; Interdisciplinary research -- Periodicals; 570.5
• DOI: 10.1098/rsif.2019.0448
• Languages: English
• ISSNs: 1742-5689

Abstract

Abstract : Dead sporulating female fly cadavers infected by the house fly-pathogenic fungus Entomophthora muscae are attractive to healthy male flies, which by their physical inspection may mechanically trigger spore release and by their movement create whirlwind airflows that covers them in infectious conidia. The fungal artillery of E. muscae protrudes outward from the fly cadaver, and consists of a plethora of micrometric stalks that each uses a liquid-based turgor pressure build-up to eject a jet of protoplasm and the initially attached spore. The biophysical processes that regulate the release and range of spores, however, are unknown. To study the physics of ejection, we design a biomimetic 'soft cannon' that consists of a millimetric elastomeric barrel filled with fluid and plugged with a projectile. We precisely control the maximum pressure leading up to the ejection, and study the cannon efficiency as a function of its geometry and wall elasticity. In particular, we predict that ejection velocity decreases with spore size. The calculated flight trajectories under aerodynamic drag predict that the minimum spore size required to traverse a quiescent layer of a few millimetres around the fly cadaver is approximately 10 µm. This corroborates with the natural size of E. muscae conidia (approx. 27 µm) being large enough to traverse the boundary layer but small enough (less than 40 µm) to be lifted by air currents. Based on this understanding, we show how the fungal spores are able to reach a new host.