Flies have a bizarre mating ritual, which is instigated by a fungus. Scientists who have studied the mating behaviour of flies inform us not only of their shocking mating ritual but also of how humans can apply that knowledge practically for pest control.
“It’s almost like an aphrodisiac, maybe driving his sexual behaviors to a supernormal level,” said Andreas Naundrup Hansen, a PhD student at the University of Copenhagen. He is describing the effects of an intriguing fungus, Entomophthora muscae, and the individual here is a male fly.
“If you see a dead housefly on a windowsill surrounded by a ghostly halo of tiny white spores, it is a death trap,” reported Science, commenting on the findings of a recent research paper published on bioRxiv. Scientists from the University of Copenhagen looked into a deadly fungus, at least for the pests.
The fungus infiltrates the bodies and brains of the female flies, manipulating them to reach the highest spot. The fungus then released its spores into the air, infecting as many healthy flies as possible. Once dead, the fungus does a strange thing. It attracts male flies to copulate with the dead bodies of females! It seems to emit some kind of “love potion,” which seduces the male flies into having sex with dead females.
Previously, scientists had noticed flies attracted to female corpses who died from the infection of Entomophthora muscae. They were not sure if the fungus was the reason behind this sexual attraction. However, a new study explores the effects of the fungus and proves that the fungus causes the attraction. The intimacy serves the purpose of the fungus spread to reach as many flies as possible.
To test the effects of the fungus, Henrik de Fine Licht, a well-known ecologist from the University of Copenhagen and Naundrup, experimented. They collected dead female flies infected with Entomophthora muscae in a petri dish and introduced healthy males.
The scientists noted whether the females attracted males, whether they mated, and the time they spent in the petri dish. They also compared the results with an experiment that included corpses of female flies that did not die from the fungus.
The new research published reported that the males were “five times as likely to try to mate when the female had died of the fungus.”
In a different experiment, scientists placed two types of corpses of female flies, one affected by the fungus and the other unaffected. They wanted to see if males were more likely to have sex with the ones affected by Entomophthora muscae. The healthy males could not tell the difference. However, the researchers did conclude that the males wanted sex with corpses more in the presence of the fungus, which explains the stimulant character.
It must be the strong smell of the fungus that influences the flies. According to the study team, the grassy and sweetish odour was part of the attraction. The fungus generated an electrical current in the fly’s brain, which Naundrup detected using an electrode put on the fly’s antennae.
“It really is a beautiful study,” said West Virginia University’s Matthew Kasson, an expert on insect-killing fungus. Because of its propensity to fatally infect house flies, the fungus has previously been researched as a possible biological control agent. The current research lends support to that possibility.
The potential of a fungus acting as an insecticide is a promising development towards producing and using natural insecticides. Chemical-based pesticides and insecticides have received much criticism over time. Studies show that they pollute the environment, can be dangerous to animals consuming plants treated with chemicals and are even injurious to the human neurological system, endocrine system, and reproductive system.
Entomophthora muscae adds to the sustainable list of potential natural insecticides. The new study is “a big step forward,” explained Carolyn Elya, a Harvard molecular biologist and postdoctoral research fellow.
However, controlling flies with Entomophthora muscae presents technological challenges. The fungus is temperature-sensitive, and the disease’s prevalence drops to extremely low levels in high temperatures. Houseflies infected were also noted to clear the infection by resting at temperatures that impeded the fungus’s development.
Lastly, the fungus is difficult to store in a viable form and cannot be readily cultivated in the laboratory. Captive colonies must be kept alive by direct transfer from fly to fly, and there is no commercial source of the pathogen.
Working with chemical ecologists at Sweden’s University of Agricultural Sciences, the researchers discovered that fungus-infected flies had many more chemical compounds than healthy flies. The quantity and concentration of the chemicals changed depending on how long the fly had been infected.
The researchers could not identify the exact chemical that made the fungus attractive, but if it could be isolated and synthesised, it may be used as a housefly trap bait.
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