Strange fungus could turn emerging cicadas into ‘death cultivators,’ scientists say

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This spring, billions of cicadas will emerge after more than ten years underground, ready to climb into the trees and make a ruckus by singing to attract others. But some of these insects will not succeed in their goal of procreation – instead, they will be controlled like zombies to spread a strange fungus that hijacks the cicadas’ body and behavior.

Details of the fungus’ attack on the bugs – destroying the insects’ genitalia, replacing their abdomen with a cavity full of fungal spores, manipulating the bugs into hypersexual behavior to spread the fungus further and changing the cicadas as “saltshakers”. of death” — they might look like they belong in a horror feature film. But regarding the fungus Massospora cicadina, said Dr. John Cooley, associate professor in residence of ecology and evolutionary biology at the University of Connecticut, Hartford, “truth is really stranger than science fiction.”

Period cicadas lay their eggs in tree branches, and when those eggs hatch, the baby cicadas, or nymphs, drop to the ground and burrow into the soil. Depending on their species, they spend 13 or 17 years underground, drinking sap from tree roots, until it is time for the almost vegetative cicadas to emerge. At some point, the insects are exposed to the spores of the fungus Massospora cicadina. It is not clear to scientists whether it happens when the cicadas enter or leave the soil, or how that exposure occurs.

How Massospora cicadina controls cicadas

The spores make their way into the body of the cicadas, and from that point on, the cicadas are at the mercy of the fungal parasite. A mass of fungal spores build up in the abdomen of each infected cicada. Eventually, the backside of the cicada – including its genitalia – falls off. In its place, a white fungal plug is exposed, “a collection of spores that are erupting from where the genitals and abdomen once were,” said Dr. Matt Kasson, associate professor of mycology and forest pathology at West Virginia University. “It looks like there’s a gumdrop covered in chalk dust, stuck to the back of these cicadas.”

Researchers have infected cicadas with the fungus Massospora cicadina.  - Courtesy of Angie Macias/WVU

Researchers have infected cicadas with the fungus Massospora cicadina. – Courtesy of Angie Macias/WVU

Despite having a calcareous spore gumdrop instead of genitalia, the infected cicadas still attempt to mate, with gusto. The fungus manipulates the behavior of the cicadas, causing what researchers including Kasson refer to as hypersexualization. The infected males keep trying to mate with females, and they also change their behavior to attract their mates. Healthy female cicadas will flap their wings to indicate they are ready to mate. Both male and female cicadas infected with Massospora flap their wings to attract ugly, soon-to-be-infected males.

But trying to mate is only one part of how infected cicadas spread the fungus.

“Periodic cicadas have interlaced genitalia. So when they pull apart, guess what happens? RIP. And then there’s a cicada walking around with someone else’s genitalia stuck to them,” Cooley said. “And now the infected cicada is busted open.”

Once the chalky fungal plug is ripped apart, the infected and disfigured cicada flies around, raining down fluffy brown spores. “We call them death salts,” Kasson said. The spores spread by these salts in flight catch the next generation of chickadees that will emerge more than ten years later and start the cycle all over again.

Zombie cicadas induced by amphetamine?

There is a lot of moving around and mating of animals whose bodies have been torn apart. Kasson and his colleagues have found a possible explanation for what keeps these cicadas going. “We found amphetamine in those fungal plugs, which provides a plausible explanation for why the behavioral modification is occurring,” Kasson said. After all, amphetamines are powerful stimulants in humans.

Cooley noted that while amphetamines stimulate the central nervous systems of vertebrate animals, insects (which are all invertebrates) such as cicadas have different nervous systems, and it is unclear whether these stimulants would affect them in the same way.

“We’re left with this problem, that it’s making a powerful psychoactive chemical, but the powerful psychoactive chemical may not do anything to the insects,” Cooley said. He suggested that the fungus may have other ways of controlling the behavior of the cicadas, and that the amphetamines it produces may instead serve vertebrate predators of cicadas (and thus, cicada-dwelling fungi), such as birds.

This spring’s periodic cicada emergence is notable because two different broods will emerge simultaneously in neighboring regions – 17-year cicadas concentrated in northern Illinois, and 13-year cicadas across much of the Midwest and Southeast . These two broods have not been above ground at the same time since 1803; However, scientists expect little geographic overlap between the two broods.

Kasson said he hopes to study infected insects from the two different broods and see if there are genetic differences between the M. cicadina infecting the 17-year and 13-year broods.

Although cicadas are edible, Kasson said people hoping to taste the bugs should be very choosy about the ones they eat. If you find adult cicadas near the end of their lives, or already dead, Kasson said, “you don’t want to put those in your mouth,” regardless of whether they’re infected with M. cicadina. If a person, dog or cat ate an infected cicada, the amphetamines in it would not affect them – the dose is too small. And for fans of “The Last of Us”, M. cicadina is only able to infect cicadas (and only the 13 and 17 year types of these bugs), so humanity is probably safe from zombification .

Kasson said that while he understands the horror people may have about the impending emergence of cicadas, not to mention the grotesque fungal infection that up to 10% of them may develop, he noted , “It’s a biological scene. And I think we should understand this as one of the natural wonders of the world.”

Kate Golembiewski is a freelance science writer based in Chicago with special interests in zoology, thermodynamics and death.

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