The fungus Entomophthora flies has a survival strategy that is both fascinating and likely to put you off your next meal: it infects and ‘zombifies’ female houseflies before sending out irresistible chemical signals that encourage male houseflies to become necrophiliacs.
By enticing these male flies to mate with zombified females, the fungus can be transferred to the male fly and, in theory, have a better chance of further spread. The unfortunate male fly is then taken over E. flies in the same way.
Important to the process is the release of sesquiterpenes, or chemical messages, which are synthesized in the female cadaver and sent out as a seductive signal. Based on the experiments conducted by the researchers, the longer the corpse has been dead, the more attractive it appears to be to the men.
“The chemical signals act as pheromones that mesmerize male flies and cause them an incredible urge to mate with lifeless female carcasses,” says evolutionary biologist Henrik H. De Fine Licht, from the University of Copenhagen in Denmark.
Once E. flies infected a female fly with its spores, it begins to multiply. After about six days, it can control the behavior of the insect and send it to the highest possible point (on a wall or a plant) before it dies. Fungal spores are then emitted from the dead fly, hoping to land on another.
But as this new study shows, by persuading a man, E. flies can ensure that it passes into at least one more host, which will once again carry its tracks far and wide.
The team used a variety of chemical analysis and genetic sequencing techniques to figure out exactly what the fungus was doing, as well as exposing male flies to female partners at different stages of fungal infection, or who had died from other causes.
“Our observations indicate that this is a very deliberate strategy for the fungus,” says H. De Fine Licht. “It’s a true master of manipulation – and it’s incredibly fascinating.”
Tests showed that female flies that had been dead for 3-8 hours attracted 15 percent of male flies, while with corpses that had been dead for 25-30 hours, that figure shot up to 73 percent. The more time that passed, the more chemical signals were released.
This is not the only time scientists have seen sesquiterpenes used to attract the attention of insects. As chemical signals go, it seems to be one of the most effective at manipulating these little creatures.
There are many opportunities for further research here, not least on effective fly repellents – flies can infect humans with various diseases, and sesquiterpenes can be used to attract flies away from certain areas, such as where food is prepared.
“This is where the Entomophthora flies fungus can be useful,” says H. De Fine Licht. “It may be possible for us to use these same fungal odors as a biological pest control that attracts healthy males to a fly trap instead of a corpse.”
The research was published in the ISME Journal.