INSECTS A rare fungus survives by luring male flies into mating with dead female flies. The greater the male’s lust, the longer a female fly carcass has lain and rotted. This is according to a new study led by University of Copenhagen researchers.

A male fly attempting to mate with a female corpse held in place with Vaseline. The fungus has spread from the back body segment and can be seen as large white patches from which spores are ejected (credit: Filippo Castelucci)
A male fly attempting to mate with a female corpse held in place with Vaseline. The fungus has spread from the back body segment and can be seen as large white patches from which spores are ejected (credit: Filippo Castelucci)

Entomophthora muscae is a pathogenic fungus that spreads by infecting common houseflies with lethal spores. According to new research, the fungus employs a novel strategy to ensure its survival. With the fungal-infected corpses of dead females, the fungus ‘bewitches’ male houseflies and drives them to necrophilia.

The fungus spreads after infecting a female fly with its spores until the host is slowly consumed alive from within. After about six days, the fungus takes over the female fly’s behavior and forces it to the highest point, whether it’s on vegetation or a wall, where it dies. When the fungus has killed the zombie female, it begins to emit sesquiterpenes, which are chemical signals.

“The chemical signals act as pheromones that bewitch male flies and cause an incredible urge for them to mate with lifeless female carcasses,” explains Henrik H. De Fine Licht, an associate professor in the Department of Environment and Plant Sciences at the University of Copenhagen and one of the study’s authors.

When male flies copulate with dead females, the fungal spores are splattered on the males, who then die. Entomophthora muscae spreads its spores to new victims in this manner, ensuring its survival.

This is the finding of a new study by researchers at the University of Copenhagen and the Swedish University of Agricultural Sciences in Alnarp.

“Our observations indicate that the fungus is using this strategy on purpose. It is a true manipulator, and this is incredibly fascinating “Henrik H. De Fine Licht concurs.

Fly corpses become more attractive as the hours’ pass

The researchers were also able to demonstrate that dead female flies become more attractive over time by tracking their behavior.

In particular, 73% of the male flies in the study mated with female fly carcasses that had died from the fungal infection between 25 and 30 hours earlier. Only 15% of the males mated with female corpses that had been dead for three to eight hours.

“We can see that the longer a female fly is dead, the more appealing she becomes to males. This is due to the fact that the number of fungal spores increases over time, enhancing the seductive fragrances “Henrik H. De Fine Licht explains.

Aside from providing new insight into nature’s fascinating mechanisms, the study also provides new information that could lead to effective fly repellents in the future. Henrik H. De Fine Licht continues:

“Flies are filthy and can make humans and animals sick by spreading Coli bacteria and any diseases they carry. As a result, there is an incentive to reduce housefly populations, for example, in areas where food is produced. This is where the Entomophthora muscae fungus can help. These same fungal fragrances could be used as biological pest control that attracts healthy males to a fly trap rather than a corpse “Finally, he says.

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