Scientists at the University of Copenhagen wanted to know how the 'zombie fungus' Entomophthora muscae spreads in a fly population, because the fungus does so incredibly quickly. They observed infected and dead flies, analysed the odours emitted by the insects, and studied the genome of the fungus. They discovered that the fungus uses a very devious and deliberate strategy to spread: necrophilia.
When a female housefly becomes infected with the fungus, it slowly eats her from the inside out. Just before she dies after about six days, the fungus takes control of the fly. It forces her to sit on a high spot. Once the fly is dead, the fungus bursts out, spreading not only its spores but also a chemical signal. These so-called sesquiterpenes act as pheromones to 'enchant' the male flies.
These pheromones encourage the male flies to mate with the corpses of infected females. During mating, the male becomes covered in fungal spores. The fungus shoots these at the fly at a speed of 10 metres per second - one of the fastest movements in nature.
More attractive with time
The researchers also found that the fly corpses became more attractive as the hours passed. In the experiment, 73 per cent of the male flies mated with females that had died from the fungal infection 25 to 30 hours earlier. Only 15 per cent of males mated with female corpses that had been dead for only 3 to 8 hours. This is because the number of fungal spores increases with time, reinforcing the enticing odours.
Biological fly control
In addition to understanding this fascinating fungal behaviour, the scientists state that the research could also provide answers in the field of fly control. Flies can spread all kinds of pathogens. By using the sesquiterpenes of this zombie fungus as biological control, male flies can be lured to a fly trap. This prevents them from spreading diseases.
Naundrup, et al. The ISME Journal, 2022. Pathogenic fungus uses volatiles to entice male flies into fatal matings with infected female cadavers. https://www.nature.com/articles/s41396-022-01284-x