Entomopathogenic Fungi in agriculture: natural enemies of insect pests

Entomopathogenic fungi are microorganisms that live in the soil and natural environments. They are known for their ability to parasitize pest insects, causing disease and ultimately death. This gives them great potential as biopesticide agents, and they are increasingly being considered worldwide as an alternative in integrated pest management (IPM) programs.

My first experience with an entomopathogenic fungi was in the field, when I observed a pest insect covered in a white coating. It was Beauveria bassiana, parasitizing a beetle. For some time, I dedicated myself to evaluating the quality of products based on entomopathogenic fungi and became a great admirer of their benefits.

What exactly are entomopathogenic fungi?

They are a group of beneficial fungi that naturally inhabit the soil. Their main advantage is their ability to parasitize and cause disease in pest insects that affect crops. It sounds like a breakthrough in a world where farmers are constantly battling increasing pest resistance and an ever-growing list of insect threats.

Currently, more than 170 strains with bioinsecticidal potential have been identified worldwide, with the most recognized genera being Metarhizium, Lecanicillium, Paecilomyces, Beauveria, Isaria, and Hirsutella [1].

How do they work?

The mechanism of action of entomopathogenic fungi is fascinating due to its complexity, and it is relatively consistent across different species.

The mechanism of action of entomopathogenic fungi is remarkably sophisticated—so precise and effective that it's almost hard to believe that it occurs naturally. 

1. Adhesion:
The first stage is adhesion, where the fungal spore attaches to the insect’s body. Research has identified several factors that favor this process. Some hypotheses point to electrostatic and hydrophobic forces that facilitate adherence to the insect's surface. In addition, certain proteins (such as MAD1 and MAD2) can help the entomopathogenic fungus to recognize the insect pest.

2. Spore Germination:
Once on the insect’s body, the spore germinates when environmental conditions are suitable (particularly temperature and humidity). This leads to the formation of a specialized structure called an appressorium, which enables the fungus to penetrate the insect’s cuticle.

3. Penetration:
The appressorium exerts mechanical pressure on the insect’s cuticle while secreting enzymes that break down its layers [2].

Once inside, the fungal mycelium spreads throughout the insect’s hemocoel (body cavity), feeding on its tissues. In some cases, the fungus produces secondary metabolites that are toxic to the insect, contributing to its death.

4. Colonization:
The final stage occurs when the mycelium has fully colonized the insect and begins to emerge externally. At this point, the fungus enters a reproductive phase, producing spores that disperse through the wind to infect other insects, starting the cycle again [2a].

Where are these species isolated from?

They are typically isolated from infected insects collected in the field. The most common method involves collecting the insect, taking it to the laboratory, and isolating the fungus using selective agar designed for these microorganisms [3].

Among the pest insects affected by entomopathogenic fungi are aphids, mites, thrips, mosquitoes, whiteflies, rootworms, moths, and many others.

Why aren’t they more widely used?

In my opinion, their use has not expanded significantly due to a lack of awareness and training. Many farmers are unfamiliar with their use and mode of action and may assume they are less effective in field conditions 

The fungi’s slower action compared to chemical insecticides can be a drawback, as they require time to establish, infect, and ultimately kill the pest. Multiple applications may be necessary to achieve effective control, making them less appealing under time-sensitive conditions [4].

They also tend to have limited specificity. Each fungus typically targets a specific pest or group of pests, so crops affected by multiple insects may require combinations of several control agents.

In addition, mass production and formulation of these fungi can be costly and demand specialized infrastructure. Their availability in the commercial market remains limited when compared to conventional insecticides.

What does the success of entomopathogenic fungi depend on?

Despite their potential, the effectiveness of entomopathogenic fungi depends on several critical factors, which may explain some growers' skepticism:

• Temperature

• Humidity

• Interaction with other chemicals

These fungi are sensitive to temperature, and applying them during the hottest part of the day (such as noon) is not recommended. Each species has an optimal temperature range for growth, and high temperatures can reduce spore viability.

They also require high relative humidity to germinate and penetrate the insect cuticle. If humidity is too low, spores will not germinate, and infection cannot occur. For example, Beauveria bassiana and Isaria fumosorosea spores require at least 70% relative humidity for the first 14 hours after application to germinate (this is a very narrow window in which the fungi must act to be successful). [5].

Furthermore, mixing entomopathogenic fungi with certain agrochemicals can inhibit or reduce their effectiveness. This is mainly due to their sensitivity to various fungicides, insecticides, and herbicides.

To wrap up 

Entomopathogenic fungi represent a viable alternative to chemical pesticides, offering effective pest control while supporting environmental sustainability. Their integration into pest management practices could play a crucial role in reducing reliance on synthetic chemicals.

However, addressing the challenges associated with their use is essential for maximizing their potential. Continued research into the biology, ecology, and application methods of these fungi will further support their adoption in sustainable farming systems.

Sources

[1] Bamisile, B. S., Akutse, K. S., Siddiqui, J. A., & Xu, Y. (2021). Model application of entomopathogenic fungi as alternatives to chemical pesticides: Prospects, challenges, and insights for next-generation sustainable agriculture. Frontiers in Plant Science, 12, 741804. https://doi.org/10.3389/fpls.2021.741804

[2] Pucheta Díaz, M., Flores Macías, A., Rodríguez Navarro, S., & de la Torre, M. (2006). Mecanismo de acción de los hongos entomopatógenos. Interciencia, 31(12). https://ve.scielo.org/scielo.php?script=sci_arttext&pid=S0378-18442006001200006

[2a] Altinok, H. H., Altinok, M. A., & Koca, A. S. (2019). Modes of action of entomopathogenic fungi. Current Trends in Natural Sciences, 8(16), 117–124.

[3] Servicio Nacional de Sanidad Agraria - SENASA. (2017). Manual de producción y uso de hongos entomopatógenos. Ministerio de Agricultura y Riego del Perú. Recuperado el 9 de abril de 2025, de https://www.senasa.gob.pe/senasa/wp-content/uploads/2017/09/Manual-de-Producción-y-Uso-de-Hongos-Entomopat%C3%B3genos.pdf

[4] Redagrícola. (s.f.). Hongos entomopatógenos, una opción biológica para superar las barreras de la agroexportación. Recuperado el 9 de abril de 2025, de https://redagricola.com/hongos-entomopatogenos-una-opcion-biologica-para-superar-las-barreras-de-la-agroexportacion/

[5] Ortiz-Catón, M., Alatorre-Rosas, R., Valdivia-Bernal, R., Ortiz-Catón, A., Medina-Torres, R., & Alejo-Santiago, G. (2011). Efecto de la temperatura y humedad relativa sobre el desarrollo de los hongos entomopatógenos. Revista Biociencias, 1(2), 42–53. Recuperado de https://revistabiociencias.uan.edu.mx/index.php/BIOCIENCIAS/article/download/14/12/28