What are Entomopathogenic Fungi?

Fungi are found in practically every environment on the planet. They live both on land and in water, and they can often be confused with plants. But, unlike plants, fungi cannot produce their own food from sunlight. Fungi are essential for life on Earth because they play several critical roles in nature—they are decomposers and nutrient recyclers, and they can even help some other organisms grow and thrive.

One special group of fungi, called entomopathogenic fungi, can cause disease in arthropods such as insects (like caterpillars and bugs), mites, and ticks. Arthropods are a big animal group that includes many creatures with legs and hard outer shells. Insects are just one part of this group—so all insects are arthropods, but not all arthropods are insects. Mites and ticks, for example, are arthropods but not insects.

The name of our special group of fungi comes from “entomo”, which means insect, and “pathogenic”, which means causing disease. The action of these fungi was discovered even before microorganisms were known. Insects that died were soon covered with a white or green powder (depending on the species of fungus that was attacking the arthropod) [1].

In nature, entomopathogenic fungi can be found in arthropods or in soils. The ideal temperature for their growth ranges from 25 to 30°C, and high humidity is also necessary for their development. Among the best-known species are the green and the white fungi that cause muscardine, a special sickness that makes insects stiff and covered in the fungus (Figure 1).

For more than a century, entomopathogenic fungi have been used to kill insects that attack crops, offering an alternative to chemical pesticides. More recently, scientists discovered that these fungi can also help plants in surprising ways. For example, entomopathogenic fungi can sometimes enter a plant and help it grow or protect it from insects that feed on it [2].

How do Entomopathogenic Fungi Kill Arthropods?

Entomopathogenic fungi can cause the death of different types of arthropods, such as insects, ticks, and mites. The action of these fungi begins with attachment. Their spores, which are tiny “seeds” of the fungus that help it spread and reproduce, attach to the arthropod’s body. In the next step, called penetration, the fungus enters the arthropod’s body using its appressorium—a tiny, sticky tentacle used to latch onto surfaces. The appressorium basically grabs hold and breaks into the arthropod’s cuticle, which is the protective covering on the outside of the arthropod’s body. Once inside, the fungus develops within the arthropods’ hemolymph and spreads, stealing nutrients and producing toxins that damage the arthropod’s organs and cause death. After death, the arthropod is no longer useful to the fungus, so the fungus spreads to the outermost part of the arthropod’s body, releasing new spores into the environment. Spores are carried by water or wind until they reach a new arthropod (Figure 2).

Are Entomopathogenic Fungi Better Than Pesticides?

In Brazil, entomopathogenic fungi have been used against spittlebugs in sugarcane for many years [3]. Pesticides can also be used to control pests such as banana weevils and coffee berry borers. Most of the pesticides sold today are man-made, not natural. But natural products, like mycoinsecticides (fungus-based bug killers made with the green and the white fungi that cause muscardine) have great potential. Right now, they make up only about 6% of pesticides sold in Brazil. In addition to killing insects that cause problems for crops, these fungi can kill the mosquitos that carry dengue virus, the kissing bugs that transmit Chagas disease, and the ticks that spread Lyme disease. Despite solid evidence that entomopathogenic fungi can kill these arthropods, there are still no commercially available fungus-based products specifically targeting mosquitoes, kissing bugs, or ticks.

Entomopathogenic fungi can be mass produced in several ways. First, they are grown on solid substances, such as rice, or they can be grown in liquid. Second, they are fine-tuned to improve their effectiveness in the field. Some fungal products are sold as powders; others are basically rice with fungi growing on it. The farmer just needs to add water, stir well, and spray the liquid over the crops. Oil-based products are also manufactured. The oil can protect the fungi from drying out, working as a sunscreen. This strategy helps farmers since, when applied to the field, fungi can be killed by sunlight or by very high or very low temperatures. Besides protecting the fungus, the oil can also help it kill arthropods faster, by easing the interaction of the fungus with the host’s cuticle.

Mycoinsecticides cause no harm to humans or to other vertebrates, even when ingested. Our bodies are too different, so the fungi cannot attach, grow, or cause disease in us. This is explained because entomopathogenic fungi are specific for arthropods. This means that the fungi can only target arthropods, not mammals, fish, birds, reptiles or amphibians, which makes them safe to use in the environment. Beneficial insects, such as bees, lady beetles, and green lacewings, are important for pollination and pest control. Although these beneficial insects are directly affected by chemicals, according to the scientific literature, entomopathogenic fungi kill fewer beneficial insects than man-made pesticides do [4]. In this way, mycoinsecticides are safer for insects that are not the target.

Entomopathogenic fungi can also be used to help plants grow [5]. Most entomopathogenic fungi are present in soil and can interact with the plant in a way that benefits both. This relationship provides nourishment and shelter for the fungi and protects the plants from harmful pests by preventing the pests from feeding or laying eggs on the plants. The fungi also help the plants obtain nutrients and resist variations in temperature and humidity. Entomopathogenic fungi can also help clean up pollutants like heavy metals from water and soil.

Bringing it all Together

In this article, we explored entomopathogenic fungi—organisms that offer a natural and often safe way to fight bugs that harm crops, reducing the need for chemical pesticides. These fungi can also help plants grow stronger. Because they are easy to produce and use, entomopathogenic fungi are a great eco-friendly tool for farmers. However, “often safe” does not mean “always safe”. Some studies have found important problems. For example, even though these fungi are safer than pesticides for helpful insects like bees, farmers still need to be careful not to spray them where bees are looking for food. We also do not fully understand what happens to the environment when we use these fungi over long periods of time, so more research is needed. To use entomopathogenic fungi in agriculture in a sustainable and responsible way, we must consider both their advantages and their limitations.

Glossary

Entomopathogenic  Fungi: ↑ Fungi that can make arthropods sick.

Arthropods: ↑ Animals with hard shells on the outside of their bodies and jointed legs. Insects, mites and ticks are different types of arthropods.

Muscardine: ↑ A disease caused by entomopathogenic fungi, which makes the insect stiff and covered in a fungal growth.

Pesticides: ↑ Chemical products used to kill bugs that harm plants, but which can be dangerous for people and nature.

Appressorium: ↑ A specialized structure that helps a fungus to penetrate the cuticle of an arthropod.

Cuticle: ↑ Tough outer layer that covers an arthropod’s body.

Hemolymph: ↑ A special liquid that moves around inside an arthropod’s body, similar to blood.

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

This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brasil (CAPES) - Finance Code 001, providing a Ph.D. scholarship for T.A. Corrêa. The Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) of Brazil provided undergraduate scholarships and a Ph.D. scholarship for V.S. Bório. The paper was published using funds from CNPq/INCT Innovative Bioinputs (#406803/2022-6).

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