Massospora cicadina is a unique example of a fungal pathogen that specifically targets periodical cicadas. This specialized fungus interacts with its insect hosts, influencing their biology and behavior for its propagation. The fungus infects 13- and 17-year periodical cicadas, synchronizing with their infrequent emergence from underground.
Infection and Physical Transformation
Cicada nymphs acquire the initial infection from Massospora cicadina as they burrow through the soil to emerge as adults after their subterranean development. Resting spores, which remain dormant for years, are present in the soil and attach to the emerging nymphs, initiating fungal growth within their bodies.
The fungal infection progresses through two distinct stages. In Stage I, the fungus grows internally, consuming the cicada’s tissues and replacing the posterior segments of its abdomen with a chalky white plug of asexual spores called conidia. During this period, the infected cicada remains alive and active, continuing to fly and interact with healthy cicadas.
Later in the emergence period, some cicadas develop a Stage II infection, acquired from contact with Stage I infected adults. In this stage, the fungus produces thick-walled resting spores, not immediately infectious to other adult cicadas. These resting spores fall back into the soil, where they will await and infect the next generation of cicada nymphs during their emergence 13 or 17 years later.
Behavioral Manipulation for Spore Transmission
The fungus alters the cicada’s actions, turning the infected insects into “zombie cicadas.” Despite having a significant portion of their abdomen replaced by fungal spores, these cicadas continue to fly, dispersing thousands of microscopic spores into the environment. This has been described as the “salt shaker of death,” as the cicada showers its surroundings with infectious particles.
A behavioral change is the induction of hypersexuality. Infected male cicadas begin to exhibit wing-flick signals used by sexually receptive females to attract mates. This lures healthy male cicadas to attempt copulation with the infected males, facilitating direct spore transfer. Infected cicadas of both sexes also continue to attempt mating with healthy individuals, ensuring the fungus’s spread through physical contact, even though their reproductive organs have been consumed.
The Psychoactive Chemical Arsenal
The behaviors induced by Massospora cicadina are attributed to a chemical arsenal produced by the fungus. Research has identified psychoactive compounds within the infected cicadas. These compounds are the underlying mechanism behind the fungus’s ability to manipulate its host.
One compound found in Massospora cicadina-infected periodical cicadas is cathinone, an amphetamine-like stimulant. This chemical maintains the cicada’s high energy levels and sustained flight, even as its body deteriorates. The stimulant allows the mutilated cicada to remain active and continue spore-dispersing flights, maximizing the fungus’s reproductive success.
Another compound detected in infected cicadas is psilocybin, the psychedelic substance commonly associated with “magic mushrooms.” This hallucinogen is theorized to contribute to the cicada’s hypersexual behaviors and its apparent indifference to its severe physical injuries. The presence of these compounds represents a unique instance of a fungus producing such chemicals to manipulate the behavior of an insect host for its parasitic benefit.
Ecological Role and Safety
Massospora cicadina serves as a natural population control agent for periodical cicadas. While it infects a portion of emerging cicada broods, it does not threaten the overall survival of the cicada population. The fungus’s life cycle is linked to the cicadas’, ensuring its persistence without causing host extinction.
A common concern relates to the safety of Massospora cicadina for humans and pets. This fungus is not considered harmful to either. Even if a pet or other animal consumes an infected cicada, the concentrations of psychoactive compounds like cathinone and psilocybin are not sufficient to cause noticeable effect in vertebrates. The fungus itself is non-toxic to humans and animals, making accidental ingestion of an infected cicada largely benign.