The Good Side of Fungi

You have probably heard the word fungi, and you may think of them as organisms that can cause diseases in plants, animals, and humans. You may also know that some fungi are helpful to us, because they are a food source or are used in medicine. For example, the antibiotic called penicillin comes from a fungus. One important group of beneficial fungi are called entomopathogenic fungi. Entomo means insects in Greek, and pathogen means something that causes disease. In other words, an entomopathogenic fungus is a microorganism that invades an insect, reproduces, and spreads to infect other insects.

Entomopathogenic fungi live in the soil, mainly in organic matter, and can be spread by the air or by rain. So, these fungi are like little helpers that keep insect pests away, making harmful insects sick and sometimes even killing them. In this way, the entomopathogenic fungi can help farmers to grow food crops. Apart from causing diseases in insect pests, entomopathogenic fungi can also directly protect plants. How do they do this? Some species penetrate into the plant’s roots and travel to the stem and leaves, where they can live and multiply. These fungi are called endophytic, which means they live inside a plant without hurting it [1].

The Battle Between Entomopathogenic Fungi and Insect Pests

Entomopathogenic fungi are super tiny, so small that sometimes we cannot even see them! They are made of many long, thin structures that are similar to threads of cloth, called hyphae. A large group of hyphae, called the mycelium, forms the body of the fungus.

The reproductive phase of entomopathogenic fungi involves structures called spores (similar to very small dust particles). Even though they are microscopic, just one spore hitching a ride on an insect can kick-start a whole infection. But for a fungus to infect an insect, it needs the right environment, like really warm temperature (25–28°C) and high humidity (75%-90%). At first, a spore sticks to the insect’s body and germinates (Figures 1A, B). Next, the fungus forms a structure called an appressorium, like a small tail that tries to penetrate the insect’s body (Figure 1C). However, sometimes, the insect’s body is quite tough to break through. So, the fungi have another surprising invasion strategy: they release substances called enzymes that break down proteins and chitin (the insect’s skin), destroying layers of the insect’s body until the fungi can get inside the insect (Figure 1C).

The battle between entomopathogenic fungi and insect pests is very interesting. Once inside the insect’s body, the fungus multiplies rapidly. However, the insect senses a foreign agent inside and activates its defenses to defeat the fungus. The fungus fights back by producing substances called secondary metabolites, which are even more toxic to the insect, suppressing the insect’s defenses (Figure 1D). The fungus then spreads quickly, taking over and eventually killing the insect (Figure 1E). When an insect dies from a fungus infection, the fungi try to find a way out of the insect, usually through tiny natural openings through which the insect breathes (Figure 1F). Once outside, the fungi are spread by pollinating insects, air, or water, leading to infection, disease, and death of other harmful insects. One great thing about entomopathogenic fungi is that they do not seem to harm pollinators or other beneficial insects that act as natural enemies of plant pests!

Friendship Between Plants and Fungi

Entomopathogenic fungi enter plants mainly through the roots (Figure 2A), and they then live in one part of the plant or distributed throughout the whole plant (Figure 2B). Some entomopathogenic fungi enter plants through small natural openings on the leaves, or through any wounds the plant may have. These fungi have a symbiotic relationship with the plants they colonize, meaning that the plant and the fungus benefit each other. The plant provides food for the fungus (e.g., sugars), while the fungus protects the plant from harmful insects. To protect the plant, the fungus releases secondary metabolites, similar to those released when fungi infect insect pests (Figure 2C). Some secondary metabolites include alkaloids, which are natural compounds known for their insect-killing properties.

When plants die, their tissues are incorporated into the soil as organic matter. Similarly, any fungi that lived inside the plant return to the soil from which they came [2].

Preparing a Fungal Warrior

There are many species of entomopathogenic fungi, and among them, the most effective against agricultural pests are grouped into two major types: Beauveria and Metarhizium. For example, Botanigard®; is a commercial product made from the fungus Beauveria bassiana, used for controlling insect pests. Particularly, the species Metarhizium rileyi, causes the death of larvae feeding on maize crops, such as the fall armyworm, the main pest of maize worldwide [3]. Fall armyworms feed on the tender inner parts of the maize plant, creating large holes and reducing the plant’s ability to produce ears, lowering crop yield.

How did scientists prepare M. rileyi to be a warrior for protecting maize? Our team did many searches for fall armyworm larvae in maize fields in the state of Michoacán, Mexico. Some of the larvae were found dead and covered by the M. rileyi fungus, which had a dusty consistency and was light green. Larvae were collected and taken to our laboratory in the Universidad Michoacana de San Nicolás de Hidalgo. We grabbed a tiny bit of the fungus using a sterile loop and put it into a special growth mix (Figure 3A). This mix had all sorts of nutrients for the fungus, like maltose, peptone, yeast extract, and agar. These nutrients promote fungal growth, just like fruits and vegetables help you grow.

After 20 days, we took a 5 cm piece of this fungus and added it to a sterilized liquid culture medium (Figure 3B). We placed it on a machine that gently shook it constantly for 3 days. Next, we added 100 mL of the culture medium containing the fungus to 200 g of pre-sterilized rice (Figure 3C). Then, we placed it in a warm chamber (28°C) with high humidity (75%). The fungus thrived and multiplied, producing millions of spores. Next, we submerged this rice-fungus mixture in water, using a strainer to separate the rice from the fungus. What remained was water containing the diluted fungus. We loaded this mixture into a backpack sprayer and sprayed it onto the maize plants when they reached the six-leaf stage (Figure 3D). When the water with the fungus contacts the larva’s body, the infection process explained earlier begins. At the end of this process, the fungus spores covered the insect’s body completely. Depending on the fungus species, these spores can look green (Figure 3E) or white (Figure 3F).

With this method, we could reduce the number of fall armyworm larvae in corn by up to 50%. In addition, using entomopathogenic fungi does not cause any pollution to the environment or harm to humans. So, the entomopathogenic fungi are really environmentally friendly.

Right now, scientists worldwide are very interested in finding ways to get rid of pests that wreck our crops, and they hope to do so in a way that is kind to the environment. Entomopathogenic fungi like M. rileyi are a great help. Much research has shown that this fungus is very safe for humans. So, they can help us out in a big way without causing any harm. Now it is your turn! Please help us to spread this interesting information to your family, teachers, and friends.

Glossary

Hyphae: ↑ Tiny thread-like parts of a fungus that grow and help it get food and water.

Mycelium: ↑ A network of tiny thread-like parts (hyphae) of a fungus that spread out to get food and water.

Spores: ↑ Tiny, seed-like structures produced by fungi. Spores can be spread by wind, water, or animals, and when they land in a suitable place, they can grow into a new fungus.

Appressorium: ↑ A small, tail-like structure that some fungi use to attach themselves to insects.

Enzymes: ↑ Special proteins that help speed up chemical reactions in living organisms.

Secondary Metabolites: ↑ Chemicals made by plants, fungi, and some bacteria that help them survive. They can protect against pests, attract pollinators, or help the organism compete for resources.

Alkaloids: ↑ Compounds found in some plants that can strongly affect living things. They often help plants protect themselves from pests and can also be used in medicine.

Conflict of Interest

The author(s) declared that this work was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Acknowledgments

We thank the Coordinación de la Investigación Científica of the Universidad Michoacana de San Nicolás de Hidalgo and the Instituto de Ciencia, Tecnología e Innovación for supporting this basic science research (project FCCHTI23_ME-4.1.-0064).

AI Tool Statement

The author(s) declared that generative AI was not used in the creation of this manuscript.

Any alternative text (alt text) provided alongside figures in this article has been generated by Frontiers with the support of artificial intelligence and reasonable efforts have been made to ensure accuracy, including review by the authors wherever possible. If you identify any issues, please contact us.