Entomophthora muscae is a common fungus that attacks domestic flies, like the ones we find in summer swarming around the house. The pathogen has a somewhat cruel way of working and it is that it infects the females turning them into something similar to ‘zombies’ and forces them to be located in high areas, from where it is more effective that they spread the spores of the fungus once they die. The thing does not end here and it turns out that the fungus makes the dead females irresistible and attracts the males to copulate with them , infecting them too.
Once E.muscae infects a female housefly, it spends approximately six days spreading through her body, killing her from within. At this point, the fungus takes control of the fly, as if it were a ‘zombie’, and guides it to a high place. The reason for this is that from the heights and once it dies it will better release chemical signals that will attract the male . These irresistible signals that will lead the male to death are known as sesquiterpenes. The fungus is capable of expelling its infected spores up to 10 meters per second, a prodigious speed in nature.
“The chemical signals act as pheromones that cast a spell on the male flies, giving them an incredible urge to mate with dead female corpses,” explains Henrik H. De Fine Licht, from the Department of Environment and Plant Sciences at the University of Copenhagen. and one of the study authors. After the sexual act, the spores are deposited on the male, who will follow the same path as the female. In this way, the fungus continues to thrive.
The scientists carried out a chemical analysis of the pheromones and a genetic analysis of the flies. They found that as time passed, the dead females became more attractive to the males. Specifically, 73% of the male flies in the study copulated with dead females killed by the fungus at 25-30 hours. 15% did so 3-8 hours after the female died. The reason researchers give for this behavior is that the number of fungus spores increases over time , making the aroma they give off more seductive.
The study, in addition to revealing this curious mechanism of nature, could give ideas to manufacture more effective repellents in the future. “Flies are quite unhygienic and can make humans and animals sick by spreading coli bacteria and any diseases they carry. Therefore, there is interest in limiting housefly populations, in areas where food is produced, for example. This is where E. muscae could come in handy, he says. We could use these same fungal fragrances as a biological pest control that attracts healthy males to a fly trap, rather than to the carcasses of their female counterparts.”
The study has been carried out by researchers from the University of Copenhagen and the Swedish University of Agricultural Sciences in Alnarp and has recently been published in The ISME Journal .
Referencia: Naundrup, A., Bohman, B., Kwadha, C.A. et al. 2022. Pathogenic fungus uses volatiles to entice male flies into fatal matings with infected female cadavers. The ISME Journal. DOI: https://doi.org/10.1038/s41396-022-01284-x
