Entomopathogenic Fungi: Insect Mind-Control Masters

Entomopathogenic fungi: insect mind-control masters

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We’ve all seen horror movies where a zombie virus takes over, and humans start committing mindless acts of violence. But that’s all just make-believe, right? To a degree, yes. As far as science is aware, there’s no risk of a zombie apocalypse any time soon. But there are fungi out there that have body-controlling effects on their hosts, eventually leading to their death.

What are Entomopathogenic Fungi?

What are entomopathogenic fungi?
Locust Parasitized by Cordyceps

An entomopathogenic fungus is a species of parasitic fungus that usually attaches to an insect host and eventually kills or at least seriously damages it. Many insects can be affected by these fungi, including ants, beetles, flies, and caterpillars and, when the fungi parasitizes the host, it will begin to slowly take over and suppress the insect’s immune system so it doesn’t put up a fight.

The process begins with the attachment of a spore, called a conidium, which then starts to germinate before penetrating the cuticle of the host. After this, the fungus reaches the insect’s blood and starts budding out, creating a yeast-like structure known as a blastopore. The proteins within these blastophores are sent to the immune system cells to coat them and prevent them from working.

Depending on the type of fungus, this process can happen very quickly, leading to the death of the insect or, may take time which gives the fungus a chance to fully manipulate its host. In these cases, it’s not uncommon for the fungus to affect the behavior of its host for its own benefit. This might include causing the insect to position itself in a certain way.

But what’s the benefit of all this? Well, essentially, it all comes down to reproduction. If the fungi can manipulate its host into a specific location or position, this better enables further spores to be released so the process can be repeated, ensuring the survival of the fungi. Of course, the cycle can vary between fungi species, including different infection durations, different stages, and different ways of manipulating the host.

Entomopathogenic Fungi Examples

It’s thought that there are around 750 species of zombie fungi, and while I can’t possibly include them all in this article, I’d like to discuss some of the most weird and wonderful examples.

1. Ophiocordyceps

The Ophiocordyceps unilateralis more commonly known as the zombie ant fungus is, as its name suggests known for infecting ants.
Ophiocordyceps unilateralis Sprouting from an Ants Exoskeleton in Borneo – (Dr. Alexey Yakovlev / Flickr / CC BY-SA 2.0)

Ophiocordyceps is a genus of fungi from the Ophiocordycipitaceae family, which was first discovered in 1931. The genus is more commonly referred to as the zombie fungus and is typically found in tropical regions, particularly the rainforests of Asia and the Amazon. While only recently discovered, this is an ancient genus with fossilized records dating back as far as 48 million years!

When an insect is infected by the Ophiocordyceps fungi, this usually begins with spores attaching to the host which then have to go through a process of germination. After this, special chitin breaking proteins enable the parasite to enter the host’s body. While inside, it will feed on the bodily tissues, but these are smart fungi that avoid essential organs in order to avoid killing its host prematurely. This gives the fungi optimal time to grow.

What Are Its Effects?

When a host is infected, the Ophiocordyceps fungi is able to manipulate its behavior in order to maximize the dispersal of new spores. This can include causing the insect to climb to a higher position, causing it to bite down on plants, or even causing it to convulse. These behaviors are typically out of character for the host, who no longer has control over its own functions.

What Does It Infect?

The Ophiocordyceps genus infects a variety of different insects depending on the species. This can include ants, which is one of the most common hosts for this genus as well as caterpillars and various species of arthropods.

Are There Different Species?

The Ophiocordyceps genus is one of the most diverse in terms of species, with several different types that affect many different insects. In fact, it is thought that there are around 140 species within this genus. Let’s take a closer look at some of them.

1. The Zombie Ant Fungus – Ophiocordyceps unilateralis

The Ophiocordyceps unilateralis more commonly known as the zombie ant fungus is, as its name suggests known for infecting ants. Most commonly, this species affects carpenter ants, but there are several subspecies of Ophiocordyceps unilateralis, around 1.5 million in fact, each infecting its own subspecies of carpenter ant.

When this happens, the fungus gets inside the ant using the method I described earlier and is able to alter the ant’s behavior. Typically, the ant will be forced to attach itself to vegetation using a death grip. Once in this elevated position, the fungus is then able to grow back out of the ant’s body before releasing its spores. The benefit of this raised position is that the released spores will fall down and hopefully land on new ant hosts.

For optimal growth, these tropical fungi require temperatures between 68ºF and 86ºF (20ºC and 30ºC). They’re common in areas like Thailand, Brazil, and parts of Africa.

2. Ant-Infecting Cordyceps – Ophiocordyceps camponoti-rufipedis

The Ophiocordyceps camponoti-rufipedis, also known as the ant-infecting Cordyceps is another species of fungi from the Ophiocordyceps genus that affects carpenter ants (Camponotus rufipes). In this case, the infected host’s central nervous system is taken over, causing the ant to latch onto a piece of vegetation in the understory of the forest.

It is here that the host dies, but its body remains in place on the vegetation so that the fungus can continue growing on the outside of its body. A round protrusion emerges before more infectious spores are released towards the forest floor to attach to new hosts, and so the process continues.

Ophiocordyceps camponoti-rufipedis was first discovered in Brazil at the high elevation of 2,300 feet (701 meters) in the tropical rainforests. Interestingly, there are four further subspecies, each of which attacks a different type of carpenter ant.

3. Vegetable Caterpillar Fungus – Ophiocordyceps robertsii

Ophiocordyceps robertsii is a type of fungus that attacks the caterpillar of the Porina moth, known as the vegetable caterpillar. As the caterpillar goes about its business on the forest floors of New Zealand, Ophiocordyceps robertsii makes its invasion, wrapping the body of the moth in its growth and essentially turning it into a mummified version of its former self.

From here, a fruiting spike emerges, allowing the fungus to disperse its spores so that the process can start again.

While this might seem like a strange aspect of nature, the Maori tribes of New Zealand see the good in it and are known to eat the parasitized caterpillars. What’s more, they will also burn the caterpillars and mix them with fat to make a traditional tribal ink.

2. Massospora

The Massospora cicadina entomopathogenic fungi is sometimes called the cicada-killing fungus.
Cicada Infected with Massospora cicadina – (G. Edward Johnson / Wikimedia Commons / CC BY 4.0)

Massospora is a genus of fungi from the Entomophthorales family. The genus contains around a dozen species, and there are some that not only infect their hosts but also produce a psychoactive reaction. The chemical responsible for this is called psilocybin and can also have similar effects on humans.

What Are Its Effects?

As I have mentioned, the Massospora genus of fungi are well known for their psychoactive effects. But let’s take a look at what happens when it attaches to its host.

The species that have psychoactive effects do this for a very good reason. These compounds cause the host to lose their appetite and, even though they may lose portions of their bodies to the infection, these ‘drugs’ keep them mobile and continuing with their normal activities like breeding.

Why is breeding important? Well, in order for this type of fungus to pass onto its next host, it must be transmitted sexually, which occurs when the cicadas mate. It’s at this point that some of the abdomen of the cicada may break away, leaving an open wound through which the fungal spores can pass.

However, there are other species of non-psychedelic Massospora that attack their hosts in different ways. For example, some will alter the behavior of their host in order to expose themselves to the most favorable conditions, including making the host averse to light (as we know, fungus thrives in dark conditions.)

While living inside its host Massospora feeds on the internal tissues, eventually resulting in the death of the insect. When this happens, the fungus will release its spores, and the process starts again.

What Does It Infect?

Most commonly, the Massospora fungus infects various species of cicada. However, it is also known to affect other similar species, including crickets and grasshoppers.

Are There Different Species?

Within the Massospora genus, there are several subspecies which include the following:

  • Massospora diminuta
  • Massospora carinetae
  • Massospora levispora
  • Massospora pahariae
  • Massospora dorisianae
  • Massospora fidicinae
  • Massospora spinosa
  • Massospora ocypetes
  • Massospora platypedaie
  • Massospora tettigatis

However, one of the most interesting is the Massospora cicadina, sometimes called the cicada-killing fungus.

This particular species is something of a trickster and will use the breeding habits of its cicada host to spread its spores. It does this by altering the behavior of an infected male, causing him to display similar signals to a female that is ready to mate. 

This naturally attracts the attention of other males who will attempt to mate only to be infected, via close contact, with the original host through its disintegrated abdomen.

3. Furia

Furia ithacensis typically affects snipe flies, causing them to attach to the underside of a leaf.
Snipe Fly Infected with Furia ithacensis – (Katja Schulz / Wikimedia Commons / CC BY 2.0)

Furia, likely named because of the stress that it causes its victims, is a genus belonging to the Zygomycota family which is found primarily in Europe and America. It is most commonly recorded in the United Kingdom and Spain and is most easily able to produce spores between 50ºF and 68ºF (10ºC and 20ºC).

What Are Its Effects?

Furia has a very complex lifecycle and has to go through various stages once it infects its host. Even before this, the fungus must go through several phases. When it’s ready to infect its host, this is usually done either via direct contact or if the host is unlucky enough to consume the spores.

Once inside the host, typically a fly, Furia has the ability to alter its behavior and will cause the insect to grip onto the underside of a leaf. This usually happens in the evening and the insect will quickly die. By this point, it is covered in a fungal mass which releases spores over the course of the night.

Unusually, some male flies are attracted to these fungus-covered corpses and will come to take a look at whether there is a mating opportunity. Unfortunately for them, there is no such offer. Instead, they make direct contact with the fungus, contract the spores, and become the next sorry victim.

While the host is still alive, the Furia fungus not only alters its behavior but can also interfere with its function. This includes reducing its ability to reproduce and shortening its lifespan.

What Does It Infect?

Furia most commonly affects flies and specifically the snipe fly. However, it has also been recorded to infect species from the Malacosoma disstria genus, including the forest tent caterpillar.

Are There Different Species?

There are several species of Furia, each having their own unique traits. I’d like to look at Furia ithacensis in a little more detail but first, here is a list of some of the other common types:

  • Furia fumimontana
  • Furia shadongensis
  • Furia americana
  • Furia creatonoti
  • Furia zabri
  • Furia gastropachae
  • Furia montana
  • Furia pieres
  • Furia virescens
  • Furia ellisiana
  • Furia fujiana

Furia ithacensis is more commonly known as the grasshopper parasite and causes its host to turn into something of a zombie. It typically affects snipe flies, causing them to attach to the underside of a leaf, as I described earlier.

When this happens, the fungus encases the fly in hundreds of hyphae, which are powerful enough to latch onto the leaf so the fly won’t fall off. It’s at this point that other flies of the same species come to investigate and end up with nothing more than a nasty infection of their own.

4. Metarhizium

Metarhizium is an asexual genus of fungi from the Clavicipitaceae family that contains a whopping 55 different species.
Metarhizium robertsii Secretes Enzymes and Compounds that Weaken an Insect’s Cuticle – (CSIRO / Wikimedia Commons / CC BY 3.0)

Metarhizium is an asexual genus of fungi from the Clavicipitaceae family that contains a whopping 55 different species. It attacks a variety of different pests, but this has come in handy for humans who have cultivated this type of fungus as a form of pest control, particularly against bugs like weevils and thrips.

What Are Its Effects?

When Metarhizium sporesinitially attach to their host, they will land on the exterior of the insect. These spores then begin to germinate and before long, are able to penetrate the cuticle, getting inside the body, thus the infection begins. From here, the fungus continues to grow, feeding on the bodily tissues of its host, slowly causing it to die.

Death can take anywhere from just a few days to several weeks, and this largely depends on the species of Metarhizium as well as the conditions.

Once infected, Metarhizium affects the behavior of its host, causing it to move to a particular location, for example, on vegetation. The benefit of this is that from here, spore dispersal will  be more uniform and successful. What’s more, spores remain present on the host, which can be passed onto other insects through direct contact.

What Does It Infect?

Being such a widespread genus of fungi, it’ll likely come as no surprise that Metarhizium has a large range of potential insect hosts.

Are There Different Species?

There are 55 known species of Metarhizium including the following:

  • Metarhizium rileyi
  • Metarhizium robertsii
  • Metarhizium viride
  • Metarhizium yongmunense
  • Metarhizium owariense
  • Metarhizium phasmatodae
  • Metarhizium taii
  • Metarhizium rongjiangense
  • Metarhizium carneum
  • Metarhizium brittlebankisoides

However, one species that I find of particular interest is the Metarhizium acridum which is more commonly known as the locust parasite.

This fungal species, as its name suggests, usually affects locusts but is also known to use grasshoppers as a host. However, this isn’t necessarily a bad thing since the fungus has been used in various applications relating to locust control.

When Metarhizium acridum takes hold of its host, it has the capacity to alter its behavior. This is usually displayed by sluggish movement and a greater tendency to climb plants, which puts it in a better position for spore dispersal.

In any case, Metarhizium acridum ends up killing the host but even before this, spores present on its body can be transmitted to any other insects that make direct contact with it. That said, it is important to note that Metarhizium acridum does not have the ability to infect anything other than locusts or grasshoppers due to its genetic make up.

Can Zombie Fungi Infect Humans?

Can zombie fungi infect humans?
Cordyceps militaris a Entomopathogenic Fungus

If you’ve seen the HBO series, The Last Of Us, then you’ll be familiar with the concept of a zombie fungus taking over humans. But is there any truth to this?

It’s a scary thought, but there is good news. The simplest answer to this question is that while zombie fungus could affect humans, the results would be no worse than any other fungal infection you’ve experienced. No need to worry about zombification, then. 

But let’s go a little deeper and look at the science behind this. The show is based around the Cordyceps genus of fungi, and what’s interesting is that this is a species that has been used in traditional Chinese medicine for thousands of years, with no signs of zombies. 

That’s quite simply because of our physiology. The physiology of, let’s say, an ant, is very different to that of a human. These fungi have adapted over the course of millions of years to use ants (and other insects) as their hosts and, as such, have adapted to these creatures’ unique bodies. Even if the fungi could infect humans, it just wouldn’t have the capacity to take over our much more complex bodily systems.

Not only this, but each subspecies of fungus is specialized to a particular type of insect whose immune systems are very different to that of a human. The fungi just aren’t well adapted enough to take over our immune systems. And while you might argue that they adapted to take over the immune systems of insects, you have to keep in mind that this took millions of years. Moreover, there have been no reported cases of human zombification as a result of fungi.

Potential Uses for Entomopathogenic Fungi

Uses for entomopathogenic fungi
Ophiocordyceps Have Been Used in Traditional Chinese Medicine for their Reputed Health Benefits

As I mentioned earlier on, there are some entomopathogenic fungi that have been used in traditional Chinese medicine for many years, and this is not something that’s dwindling in popularity. In fact, there are some dedicated Chinese people that will travel hundreds of miles each year just to pick these seemingly miraculous fungi that are used for everything from kidney infections to treating sexual dysfunction. 

But even in western medicine, there is hope that these fungi could hold the key to treating many conditions.

There’s a lot of ongoing collaboration between medical researchers and entomopathogenic fungi researchers with the aim of finding new uses for these organisms.

It seems like the Chinese idea of using entomopathogenic fungi for the treatment of kidney-related diseases might not be as far-fetched as many westerners would believe. In fact, studies in rat models have shown promising results. Additionally, other studies have demonstrated the effectiveness of Cordyceps sinensis as a treatment for heart arrhythmia, which has even been approved for use in China. 

There may even be the possibility of using certain species of Cordyceps for the treatment of diabetes, although studies into this are ongoing.

What’s more, certain types of entomopathogenic fungi have been successfully used as pesticides such as the locust-killing fungi I talked about earlier. Not only are these pesticides incredibly effective, but they’re also an eco friendly and organic alternative to chemicals, especially in agriculture. On top of this, because each type of fungus is specifically adapted to attack a certain species of insect, humans can be much more selective about what they attack, leaving other, beneficial bugs out of it.

Additionally, some types of entomopathogenic fungi are effective at managing nematode populations without causing any damage to the surrounding soil. As researchers look further into the use of fungus as a pesticide, further advances are being made, and there’s even the possibility of enhancing their genetics to make them even more effective.

The potential health care benefits of entomopathogenic fungi are seemingly endless. There is a suggestion that these fungi may aid in wound healing owing to their antimicrobial properties as well as their regeneration properties. In research, there has also been hope of the potential to use properties from these fungi for the treatment of cancer.

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