Diabolical Fungus Makes Male Cicadas Act Female To Attract Hosts

Deceptively simple in appearance, fungi are known to be ingenious biological terrorists. Just ask the zombie ants with giant spore stalks erupting from their brains, or in the latest bizarre example, sexually confused male cicadas.

According to a study published in Scientific Reports, ecologists from the University of Connecticut have discovered that a parasitic fungus that has evolved to complete its lifecycle in the bodies of cicadas actually alters the insects’ behavior in order to spread itself to a greater number of hosts.

While researching the mating habits of healthy cicadas, the team inadvertently observed that males infected with Massospora cicadina were noisily clicking their wings together in response to the mating songs of other males. This signaling is normally only performed by female cicadas as a signal that she is ready to mate.

Consequently, the infected males were being physically bombarded by other males looking for females – an ideal situation for the fungus because infectious spores leaking from the bugs’ torn-open abdomens and genitalia are rubbed all over the would-be suitors.

This naturally led to the hypothesis that the fungus is somehow responsible for the wing-flick signaling. But considering that the bugs are literally falling apart at this point thanks to the fungal filaments exploding out of them, the ecologists needed to disprove that the altered behavior was simply a side effect of a dying insect’s addled brain. 

Their investigation involved collecting healthy and Massospora-infected male and female cicadas, playing them recordings of mating calls, and seeing how they responded.

Now, to appreciate the study’s findings, you need to know some more about Massospora. The infection progresses through two phases: Stage I and Stage II. During the former, the fungus produces spores that can enter and colonize new cicadas. But when the fungus reaches Stage II, the spores it produces are no longer dangerous to others; they are specialized to remain dormant in the soil, waiting to infect the next generation of cicadas as they molt from underground juveniles into flying adults.

Fascinatingly, the only group that produced abnormal wing flicks during the experiment were Stage I males. None of the Stage II males did so, and no infected females did anything unusual. Coincidence? The authors think not.

“If both fungal stages caused males to express sexual behaviors normally observed in females only, then the changes might be more easily dismissed as mere byproducts of the physical damage suffered by infected cicadas,” they wrote. The fact that males stopped flicking their wings after progressing to Stage II makes this very unlikely. 

“Thus, Massospora functions at least partly as a sexually transmitted disease and the novel behaviors of infected males are complex manipulations instigated by the fungus for its own benefit,” added the researchers. 

Uninfected male Magicicada septendecim (left) with genitalia torn from a female infected by Stage I of Massospora cicadina (right). Despite extensive injuries, infected individuals mate with enthusiastic fervor. Cooley et al./Nature, 2018

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