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This spring, billions of crickets will emerge after more than a decade underground, ready to climb trees and make noise as they sing to attract mates. But some of these insects will not succeed in their reproductive goal. Instead, they will be controlled as zombies to spread a strange fungus that hijacks the bodies and behavior of crickets.
The details of the fungus’ attack on the insects: destroying the insects’ sexual organs, replacing their abdominal cavity with a cavity full of fungal spores, manipulating the insects into hypersexual behavior to further spread the fungus, and transforming the crickets in what some scientists call ‘salt spreaders’. of death” – might seem like they belong in a creature horror film. But when it comes to the fungus Massospora cicadina, said Dr. John Cooley, associate professor of ecology and evolutionary biology at the University of Connecticut, Hartford, “the truth is actually much stranger than science fiction.”
Periodical crickets lay their eggs in tree branches, and when those eggs hatch, the resulting baby crickets, or nymphs, drop to the ground and burrow into the soil. Depending on their species, they spend 13 to 17 years underground, drinking sap from tree roots, until it’s time for the nearly fully grown crickets to emerge. At some point the insects are exposed to spores of the fungus Massospora cicadina. It’s not clear to scientists whether this happens when the crickets enter or leave the soil, or how that exposure occurs.
How Massospora cicadina controls crickets
The spores find their way into the crickets’ bodies, and from that moment on the crickets are at the mercy of the fungal parasite. A mass of fungal spores accumulates in the abdomen of each infected cicada. Eventually, the back of the cicada – including the genitals – falls off. Instead, it exposes a white fungal plug, “a clump of spores that erupt where the genitals and abdomen once were,” says Dr. Matt Kasson, associate professor of mycology and forest pathology at West Virginia University. “It looks like a bubble gum drop fell into chalk dust and stuck to the back of these crickets.”
Despite having a chalky gumdrop of spores instead of genitalia, the infected crickets still attempt to mate with enthusiasm. The fungus manipulates the crickets’ behavior and causes what researchers, including Kasson, call hypersexualization. The infected males continue to try to mate with females, and they also change their behavior to attract their fellow males. Healthy female crickets wave their wings to indicate they are ready to mate. Both male and female crickets infected with Massospora flap their wings to attract amorous, soon-to-be-infected males.
But trying to mate is only part of how infected crickets spread the fungus.
“Periodic crickets have interlocking genitalia. So when they fall apart, guess what happens? Rest in peace. And then there’s a cicada walking around with someone else’s genitals stuck to it,” Cooley said. “And now the infected cicada is being broken open.”
Once the chalky fungal plug is torn apart, the infected and lacerated cicada flies around, raining down fluffy, brown spores. “We call them the salt shaker of death,” Kasson said. The spores spread by these flying salt shakers then infect the next generation of crickets, which will emerge more than a decade later and start the cycle again.
Zombie crickets stimulated by an amphetamine?
It’s a lot of moving and mating for animals whose bodies have been torn apart. Kasson and his colleagues have found a possible explanation for what keeps these crickets alive. “We found an amphetamine in those fungal plugs, which provides a plausible explanation for why the behavioral change is happening,” Kasson said. After all, amphetamines are powerful stimulants in humans.
Cooley noted that while amphetamines stimulate the central nervous systems of vertebrates, insects (which are all invertebrates) such as crickets have different nervous systems, and it is not clear whether those stimulants would affect them in the same way.
“We have the problem that it produces 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 some other means of controlling the cicadas’ behavior, and that the amphetamines it produces might instead serve to kill vertebrate predators of cicadas (and thus of cicada-dwelling fungi), such as birds, to ward off.
The periodic emergence of cicadas this spring is notable because two different broods will appear simultaneously in adjacent regions: 17-year-old cicadas concentrated in northern Illinois, and 13-year-old cicadas in much of the Midwest and Southeast Asia. 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 that infects the 17-year-old and 13-year-old broods.
Although crickets are edible, people who want to taste the insects should be picky about which ones they eat, according to Kasson. If you find adult crickets near the end of their lives, or already dead, Kasson says, “You don’t want to put those in your mouth,” regardless of whether they are infected with M. cicadina. If a human, dog, or cat were to eat an infected cicada, it would not be affected by the amphetamines it contains; the dose is too small. And for fans of “The Last of Us,” M. cicadina is only capable of infecting crickets (and only the 13- and 17-year-old varieties of these insects), so humanity is probably safe from zombification.
Kasson said that while he understands the concern people might have about the coming rise of cicadas, not to mention the grotesque fungal infection that up to 10% of them could develop, he noted: “It’s a biological spectacle. And I think we just have to appreciate this as one of the natural wonders of the world.”
Kate Golembiewski is a freelance science writer based in Chicago who is particularly interested in zoology, thermodynamics and death.
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