Endophytic entomopathogenic fungi can support plant health in multiple ways. Their metabolites and the plant’s activated systemic defenses work together to strengthen resistance to insects and diseases. In addition, plant‑released volatiles can attract natural enemies of herbivores, providing an indirect layer of pest suppression. Fungal colonization also boosts the plant’s access to key nutrients, including iron, phosphorus, nitrogen, and calcium, which enhances overall growth and vigor. (Figure created using BioRender.com, originally published in Panwar and Szczepaniec 2024, Pest Management Science, CC BY-NC-ND 4.0)

By Neha Panwar, Kadie Britt, Ph.D., and Adrianna Szczepaniec, Ph.D.

Ada Szczepaniec, Ph.D.

Kadie Britt, Ph.D.

Neha Panwar

Entomopathogens are beneficial microbes that can infect and kill insects. Various entomopathogenic fungi, such as Beauveria bassiana or Metarhizium spp., are widely used by growers as insect-killing biological controls: These fungal strains can be formulated into sprayable insecticidal products that growers can apply to crops in controlled environments (greenhouses or nurseries) or open fields to aid in management of insect pests.

When a fungal insecticide is applied to a crop, the spores land on pest insects and germinate on their exoskeleton, or the tough outer surface of the body. From there, the fungus slowly invades and eventually kills the insect, a process that typically takes one to two weeks. Entomopathogenic fungi may also be introduced to plants via wind- or rain-dispersed spores, transported by insects or other animals, and, in some cases, carried within seeds, enabling transmission of beneficial fungi from parent plants to their next generation.

The interesting part about this story is that these organisms don’t just exist on the surface of plants after being applied as an insecticide. Some versions of these fungi are also naturally occurring and can live inside plants as endophytes—essentially, friendly microbes that live within plant tissues without causing visible harm to the plant. Most endophytes are beneficial or neutral, though a few can become pathogenic under certain conditions. These endophytic strains generally originate from the plant’s surrounding ecosystem, especially from soil and the rhizosphere, where these fungi persist and can enter plants through their root systems. These are known as endophytic entomopathogenic fungi (EEPFs). In July 2024, we published a review in Pest Management Science that detailed current research on EEPF use in biological control of insect pests.

Working From the Inside

You can think of EEPFs as undercover agents embedded in the structure of the plant: They can protect plants from insect pests, boost plant growth, improve stress tolerance, and even help plants recruit natural enemies. Once inside plants, EEPFs can tune plant physiology by shifting plant hormones to promote stronger root systems, further improving water and nutrient uptake. During stressful periods, endophytic fungi may help plants cope by boosting tolerance and producing stress-associated protective compounds.

Endophytic entomopathogenic fungi can affect herbivores directly and indirectly (Fig 1). Directly, EEPFs retain their capacity to act as insect pathogens when they become established in plant tissues. They can significantly reduce the number of pests on a crop, overall fitness of the pest, and amount of injury to the plant. Insects feeding on plants colonized with EEPFs often show reduced survival, slower development, lower body weight, and decreased egg production. Indirectly, EEPFs can also alter the plant’s physiology. Plant colonization by EEPFs can increase naturally occurring plant defenses even before plants sense an herbivore. Finally, they can also influence how plants interact with other plants, herbivores, and even beneficial insects by altering the plant produced odors intended to attract predators. In short, EEPFs can serve as living fungal “bodyguards” inside of plants.

Beneficial, insect-killing fungi can naturally infect a wide range of insect pests in the field. These naturally occurring fungi are important allies in sustainable pest management because they can help suppress pest populations without relying only on chemical control. Here, a white fungal growth associated with entomopathogenic fungal infection is visible on an infected insect on a plant stem. (Photo by Brian Little, University of Georgia, Bugwood.org)

Beneficial, insect-killing fungi can naturally infect a wide range of insect pests in the field. These naturally occurring fungi are important allies in sustainable pest management because they can help suppress pest populations without relying only on chemical control. Here, a white fungal growth associated with entomopathogenic fungal infection is visible on infected larval stages (left and middle) on a leaf surface alongside a healthy larva (right). (Photo by Keith Weller, USDA Agricultural Research Service, Bugwood.org)

Beneficial, insect-killing fungi can naturally infect a wide range of insect pests in the field. These naturally occurring fungi are important allies in sustainable pest management because they can help suppress pest populations without relying only on chemical control. Here, a white fungal growth associated with entomopathogenic fungal infection is visible on infected wood-boring insect larva. (Photo by James Solomon, USDA Forest Service, Bugwood.org)

These EEPFs are multi-functional: The same strain can suppress insect pests, reduce the severity of some plant diseases, improve nutrient uptake, and increase plant tolerance to abiotic stress. Since the EEPFs live inside of plant tissues, they can provide systemic protection that is not limited to an insecticide application on plant surfaces or one single insecticide application window. Endophytic entomopathogenic fungi are a great option for low-input and organic crop production systems where synthetic insecticide options are limited.

Of course, it’s not always smooth sailing. The effectiveness of EEPFs in real-life field conditions can be hit or miss. Successful colonization depends on the specific fungus-plant combination, inoculation method (seed coating, soil drench, or foliar spray), and environmental conditions such as temperature and moisture. Because these fungi can alter plant chemistry, they might also influence behavior of beneficial insects, sometimes in undesirable ways, so their compatibility with other biocontrol methods isn’t always guaranteed.

Fighting a Stem-Boring Fly in Quinoa

Low-input and organic crops often stand to gain the most from endophytic biocontrol tools, and quinoa provides a useful example of how these fungi could help address pests that are difficult to manage. Quinoa has been cultivated in Colorado since the early 1980s, and by 2021 the crop reached roughly 3,000 acres statewide. That growth continued until a stem-boring fly emerged as a major constraint for quinoa in the state and beyond.

Larvae of Amauromyza karli (in the family Agromyzidae) feed inside of quinoa stems where they are well protected from insecticides, making management incredibly difficult. As of 2025, the acreage of quinoa shrunk dramatically owing to the severity of A. karli’s impact on the crop. Because endophytic fungi can establish in plant stems, which is the same tissue attacked by the pest, the fly larvae can (in theory) be vulnerable to EEPFs. Our preliminary experiments with B. bassiana have shown promising results, but we still need field validation. Any reduction in A. karli numbers will be a win towards keeping quinoa production viable in this region.

In parallel, we also investigated whether the rhizosphere (soil) fungal communities present in quinoa fields can help explain why A. karli outbreaks are worse in some fields than others. So far, we see a clear pattern: fields with higher fly pressure tend to be dominated by fungi commonly associated with plant stress or disease, while fields with lower fly pressure were enriched with fungi considered beneficial for plant health. These patterns point to practical applications such as promoting beneficial fungi, including candidate EEPF strains. By improving soil health, organic amendments and intercropping may encourage beneficial fungi to persist in and around quinoa plants. Over time, supporting these microbial allies could potentially reduce A. karli pressure and promote sustainable quinoa production in Colorado.

A Useful Tool for IPM Programs

EEPFs hold great potential as an aid for our pest management work. Refining strain selection, inoculation methods, and furthering our understanding of how these fungi interact with plants, pests, and natural enemies can help in establishing these EEPFs as reliable tools in integrated pest management programs.

These fungi are more than just insecticide applications to crops; they should be viewed more as partners in our efforts, living inside plants, offering systemic plant protection and a whole host of other benefits mentioned here.

For quinoa growers battling A. karli in Colorado, these fungal bodyguards could be the ultimate protectors. Stay tuned as we learn more from our field experiments and explore how to turn this science into a sustainable pest management solution.

Neha Panwar is a Ph.D. candidate in the lab of Ada Szczepaniec, Ph.D., associate professor of horticultural entomology at Colorado State University in Fort Collins, Colorado. Kadie Britt, Ph.D. is the integrated pest management program manager at Colorado State University. Email: [email protected], [email protected], [email protected].