Entomopathogenic Fungi: An Unlikely Alliance with Life

by Andrew Zhou, Biology

Abstract: From moldy bread to yeast infections, fungi have acquired a reputation as unsightly, unsavory organisms. Nasty and nugatory… the negativity never expires. These common generalizations reduce the fungal kingdom to repulsion, yet there is a rarer, refined perspective that defends some species as an unusual desideratum. It is this contrary view, entomopathogenic fungi, that depicts a moving embodiment of nature. By killing insects, these fungi are an anchor of life. A genuine scrutiny of these species unveils how ubiquitously rooted death is in the environment altogether. And despite antipathy being the prevailing sentiment held toward fungi, they persist in their large-scale maintenance nonetheless. Their contributions have value beyond external recognition: they work hidden from the light, and their responsibility is grey. Also functioning as endophytes, these insect pathogenic fungi tend to share a symbiotic relationship with plant life. Importantly, besides serving as protection against pests, they extract crucial resources to support plant growth. The magnitude of their unconventional capacities and alliance with life may be invisible at first glance, but the culmination of their partnership is tangible. To regulate the pest population is to stir the rest of the ecosystem into fruition. Naturally, researchers want to harness their promising properties; genetic modification offers an avenue for scientists to tailor the fungi to fit within a vast array of applications ranging from agriculture to medicine.

entomopathogenic, mycology, fungi, symbiotic, endophyte

True Nature

In a garden teeming with life, there lies an underworld of death and decay. Of the creatures that inhabit this realm, there are crawlers, fliers, and then those that kill both. These agents of mortality go by the alias of entomopathogenic fungi, but like most things in mycology, they are lamentably underappreciated and unconscionably misrepresented. Though its name, entomopathogenic, suggests that the fungus merely causes disease to insects, it is more than just a pest exterminator: it is a plant protector, an environmental warden, a ferry between life and death.

In life, organisms are classified into kingdoms, and entomopathogenic fungi are no different, encompassing a multitude of species across the fungal kingdom. Yet, one species by the name of Beauveria bassiana has a particular history, and to appreciate the breathtaking depth of these fungi, it is important to consider their context within the scientific community. Before the end of the 19th century, the accepted theory for disease transmission held that bad-smelling vapor, or miasma, was the vehicle of infection. Nevertheless, miasma would soon evanesce and draw its final breath at the hands of an Italian entomologist. An irrepressible intellectual curiosity and a steadfast commitment to research: these were Agostino Bassi’s colleagues when he inadvertently set into motion a new understanding of pathogenic microorganisms. Looking to revive the declining silk industry, Bassi devoted nearly a third of his life to studying a species of fungus that caused devastating illness in silkworms. His revolutionary conclusion—that living organisms rather than miasma were pathogenic—marked the emergence of the germ theory of disease.

The germ theory has been the definitive basis for modern medicine, and Bassi’s work set the novel precedent for farmers taking preventative measures against diseases. Because he urged for a standard of disinfection, the European silk industry underwent an economic reinvigoration, and from its rebirth sprung the widespread practice of preventative medicine. He even catalyzed future scientists such as the renowned Louis Pasteur to build upon Bassi’s research and eventually enable the replacement of the erroneous miasma theory. His revelations from the fungus, now recognized in his honor as B. bassiana, illustrate entomopathogenic fungi’s relevance in providing insight into a broader sense of biology. Such research underscores that studying these fungi is not exclusively reserved for incapacitating pests; rather, the lessons derived from these mechanisms are key to understanding pathogenic microorganisms and their implications within the natural world.

In death, however, Bassi’s story is relatively unsung compared to the legacy of Pasteur. Yet, Bassi’s contributions to science cannot be understated; his findings with B. bassiana manifest across countless aspects of current medicine, microbiology, and mycology. In an ironic twist, approbation for Bassi and entomopathogenic fungi are eerily similar from their unrequited presence in the germ theory and environment, respectively. Despite being the substratum in their fields, they are alike in their affliction of lingering obscurity: Bassi’s enduring research lacks the commendation it should receive, and insect pathogenic fungi’s versatile capabilities suffer the neglect they should not.

To Kill an Insect

The trademark ability of entomopathogenic fungi is its namesake: a type of fungus that causes disease in insects. In most species, they utilize spores or enzymes to burrow through the insect cuticle into the bloodstream. Such fungal-insect relationships coincide with Dr. Brian Lovett’s research interests of navigating their pathogenic mechanisms through a biotechnological lens. Lovett is not only a mycologist but also an entomologist and genetic engineer—a combination well-equipped to investigate the species that belong in Metarhizium. Conducting trials with genetically modified fungi, he worked with a team to leverage insect-specific neurotoxins rendering malaria mosquitoes incapacitated. Within five days of infection of roughly six spores, the transgenic fungi displayed incredible efficacy with an almost complete reduction of blood-feeding behavior in mosquitos (Bilgo et al., 2017). These results demonstrate that the successful application of engineered Metarhizium not only kills mosquitoes but also prevents them from blood-feeding and transmitting disease to humans.

Showing immense promise for the agricultural industry, they “have been applied to millions of hectares of land to control pests,” explains Lovett. These fungi are ubiquitous in the world; species like B. bassiana or Metarhizium are generalists—they do not discriminate, colonizing a wide variety of plants or infecting an abundance of insect hosts. Due to their higher yields, Metarhizium in Brazil has been successfully integrated with sugarcane through plant protection and biocontrol of herbivore pests (Iwanicki et al., 2019). But this is not an isolated occurrence. Along with Metarihizium, B. bassiana and other fungal species were used to support cash crops on the other side of the world in Malawi, East Africa (Kasambala et al., 2021). If there are insects, and if there is soil, then entomopathogenic fungi will be there to capitalize. Think about it: insects are everywhere, so their pathogens would be everywhere, too. The hordes of insects are essentially a reservoir of free food, so long the pathogens can crack their genetic code and dive into it.

To Live in a Plant

Interestingly, the common theme behind these examples is that concealed under every death is the nourishment of life. As stated earlier, Metarhizium kills mosquitoes but even restrains blood-feeding behavior. Along with those abilities, genetic modification exhibits obstruction of the disease binding to the mosquito’s salivary glands, preventing the transmission of malaria altogether (Fang et al., 2011). This alone could create a possibility of life without malaria mosquito-associated suffering.

And within the agricultural industry, although insect suppression receives the outward attention and recognition for its success, there are other moving parts behind the scenes. Bamisile et al. (2021) show that, in addition to regulating pest populations, these fungi remove toxic compounds from the ecosystem and foster unique symbiotic relationships with plants. Yet, even with such functional diversity, applications of the fungi have been primarily contracted to their role as a biopesticide. Indeed, the practical overtones of a natural living pesticide are pertinent in human agricultural contexts, but the other auxiliary counterparts are equally as compelling. Their capacity as plant symbionts covers a myriad of independent interactions but is still astonishingly understudied, meaning that scientists have only grazed the surface of what truly occurs beneath the soil. In a way reminiscent of Bassi, the fungi parallel their researchers in being unseen.

Undaunted by its unfamiliarity to the masses, modern mycology has made steady progress in research regardless. A remarkable example is tripartite scientist Dr. Lovett with his cross-disciplinary background in mycology, entomology, and applied biotechnology. In a study he took part in, the fungus M. robertsii and even B. bassiana were observed to produce auxin plant hormones, which increase virulence to insects and promote lateral plant root development (Liao et al., 2017). So although entomopathogenic fungi are decorated with the title of insect destroyer, the categorization is by no means exhaustive. Instead, these fungi are found in the soil across many regions of the world. They occupy and colonize the plant root systems as a defender and safeguard of overall ecosystem health. Awareness of these functions is imperative to move away from the caricature that the fungi singularly seek the destruction of insects; in this case, practicing good science comes full circle to Bassi—to build upon knowledge of the antecedent—and a desire to inquire about the true nature of things.

Plant Protection

The production of auxin is a fascinating, lesser-known example of how fungi are a major force in their environment. Lovett’s inquiry shows that auxin not only enhances insect virulence but also stimulates root proliferation; fungi not only kill insects but also support life. By living within their plant hosts (endophytes), these symbiotic alliances can perform an abundance of interactions that support the fungal-plant relationship and the ecosystem together. In fact, it is not certain whether entomopathogenic fungi evolved initially as insect pathogens but rather as root-colonizing endophytes first (Moonjely et al., 2016). At any rate, the phylogenetic evidence seems to agree, given that pathogenic fungi are closely related to grass endophytes (Barelli et al., 2015). This speculation appears to align with Lovett’s understanding of their prevalence in nature, “Fungi have so many different roles, and depending on the species, some are much more likely to form an interaction with a plant than infect an insect anyway.” Entomopathogenic fungi could arguably be considered a misleading hypernym because, in reality, their species are incredibly diverse, and their endophytic interactions deserve to be given equal consideration. Because the roots and soil lay the groundwork of a connected landscape, the interplay between vegetation and an endophytic-entomopathogenic fungus reverberates across every direction of the trophic network. By facilitating plant development and defense against pests, insect pathogenic fungi protect life; they maintain control, order, and balance in the overall health of the ecosystem. In a profound sense, these natural interactions are the essence of life.

Environmental Warden

Explicit evidence of their diverse responsibilities is the latest discovery of fungi and plants engaging in the trade of nitrogen and sugar. The unearthing was unanticipated yet obvious in hindsight; of course, the biological exchange of resources is necessary in a world of propinquity. Fungi need sugar for metabolism and energy; plants need nitrogen as a crucial macronutrient for growth. However, nitrogen extracted from the soil is scarce, making it the limiting factor for plant life. Conveniently for the fungal-plant relationship, insects are a source of nitrogen too, and fungal virulence to insects is an indemnity for plants. As Behie and Bidochka (2014) frame it, the fungi “act as a conduit to provide insect-derived nitrogen to plant hosts,” with both M. robertsii and B. bassiana increasing plant productivity compared to plants without endophytes. Mutualism is perfectly represented here: the transfer of nitrogen from fungi to plants provides an economic advantage in the soil, and in turn, sugar from photosynthesis is passed on from plant to fungus. As if the protection against insects was not already enough, the nitrogen-sugar exchange is more than remunerative for both participants in this ecological cycling. Fungi’s role as security and biofertilizer with plants is a microscopic yet touching personification in which fungi are entrusted by nature herself as killers, bodyguards, and stewards.

That steward responsibility surpasses expectations, extending to entire environments by removing toxic pollutants. Litwin et al. (2020) list dozens of unsafe compounds and synthetics such as heavy metals, estrogen, dibutyltin, and carcinogenic triazine being filtered from contaminated waters. In a study carried out by Gola et al. (2016), B. bassiana was observed to reduce metal contamination in water by up to 75%. Similarly, genetically modified M. robertsii can even bioremediate mercury, an extremely toxic metal, from both soil and water to support plant growth (Wu et al., 2022). It is hard to conceive that a microorganism, especially a fungus, would be able to do such a thing. But there is no need to imagine it. Having an extraordinary aptitude for ecosystem maintenance, these fungi have the potential to ameliorate the growing issue of environmental pollution. Most scientists affiliate this threat with conditions worsened by global warming, yet entomopathogenic fungi already possess a counteraction. Mantzoukas et al. (2022) report that these fungi can increase plants’ tolerance to environmental stresses by aiding drought tolerance. These abilities present a straightforward solution by strengthening plant durability to withstand the rising temperatures associated with climate change.

Disadvantages with Solutions

Entomopathogenic fungi do have their drawbacks. Firstly, despite being known for hundreds of years, the collective understanding of these fungi is extremely limited. Far more is known about the species B. bassiana and M. robertsii because they were the first among the group to be discovered. Secondly, socioeconomic factors come into play; Metarhizium and B. bassiana are widely used because they are multifaceted in lifestyle and region. They both perform numerous functions and are host generalists. Being able to study and replicate fungi in a lab, especially multipurpose ones, will typically dictate whether a species can translate into practical use. Hence, generalist species are suited better. But even then, pathogenic fungi are interested in their self-preservation, so they will attempt to extract as many nutrients as possible and maximize the duration to proliferate, prolonging the insect from dying beyond what agricultural contexts can sustain. The final challenge resides in the fact that entomopathogenic fungi are living things—they die. Their death can come from unfavorable abiotic elements such as the exposure of fungal spores to low humidity, high temperature, and solar radiation conditions (Bamisile et al., 2021). These possible points of failure are precisely what scientists like Lovett are up against.

In this new era of science, the restrictions in self-preservation strategies and practical hurdles can be circumvented. Given the abiotic factor of radiation, scientists can genetically engineer fungi to be more resistant to UV light. By using other organisms that can better handle radiation, the insertion of their photoreactivation systems into a fungus led to higher UV tolerance while retaining its virulence (Fang & Leger, 2012). As a result, the fungi can survive longer under harsh environmental stresses and continue to regulate pest populations. As for self-preservation strategies, Zhao et al. (2016) explain that protein engineering can form insecticides with extremely high virulence that overcome fungal survival instincts. This hypervirulence makes them excessively lethal to the point that the desire to exploit the insect’s resources does not matter. The assortment of possibilities that genetic engineering can unravel makes the fungi uniquely customizable in a way that the current standard of chemical insecticides cannot match.

Comparisons to Chemicals

Nathan East, a microbiology undergraduate at the University of Georgia, is keenly aware of the concerns about agriculture’s overreliance on chemicals. “They have food safety concerns, adverse effects on non-target organisms, and are impractical in the long run of the evolutionary arms race,” he clarifies on the movement to decrease dependence on chemicals in agriculture. Chemical insecticides may intentionally target pest insects but can frequently harm non-targets such as birds and fish. Unlike fungi, chemicals do not die, so their negative effects can be perpetuated repeatedly. Contaminants persist in the ecological cycles by drifting into the soil and water in the environment leading to a decrease in soil fertility and agricultural productivity. The disadvantages do not end at immortality: insect survival selects for traits resistant to chemical pesticides, and over time, the application of a particular insecticide will have a significant reduction in efficacy. This phenomenon is becoming increasingly worrisome with recent applications of chemical pesticides proving ineffective as a consequence of resistant populations. In contrast, entomopathogenic fungi are living participants of the arms race, so they will coevolve with the targeted insects.

The resistance concerns that chemical pesticides face do not exist with mycopesticides. Lovett affirms that insects forced to become resistant in the lab must develop a distinctly thick cuticle to avoid pathogenic penetration. This adaptation is unrealistic in nature; an insect with an extremely thick cuticle would be severely impaired compared to wild insects. Because survival depends on many factors, predation or nutrition subsistence would prevent exceedingly thick cuticles from propagating in nature. Hence, such a trait can only be attained through artificial conditions with a singular purpose in mind. Moreover, fungi are not contingent on a single enzyme or protein but instead are complex microorganisms with several means to overcome an insect. Like any other form of life, fungal populations evolve to elude extinction. Their survival depends on it. While chemical insecticides require routine monitoring and active development, scientists can rely on inherent fungal affinities. It would be foolish not to use the natural enemies of insects—to repudiate a timeless precedent of their triumphs in history. Even with imperfections, genetic modification compensates and forges the fungi to accommodate societal needs. All things considered, less micromanagement is involved, which makes them an appealing and accessible form of biocontrol.

Concerning the apprehension for safety and biodiversity in ecosystems, Lovett adds that the fungi are already “ubiquitously present in nature and follow cycles, so it is unlikely to wipe out a population, insect or not.” He reassures that entomopathogenic fungi only have an appetite for insects due to their genetic composition. The infection pathways are specific to its natural prey, and they discretely target them without interfering with other species. So no, there is no need to fear a Cordyceps zombie scenario portrayed in the popular show The Last of Us. Fungi are inherently safer than chemicals for most living things, especially humans, as Mantzoukas et al. (2022) indicate that they have low mammalian toxicity. Recalling back to the abiotic conditions, high temperatures are hostile for entomopathogenic fungal growth; and accordingly, these fungi especially cannot grow at human body temperature. Pesticides derived from insect pathogenic fungi are environmentally sustainable and human-friendly, which is desperately needed in the modern circumstances of chemical overdependence and destructive human habits.

The Cultivation of Knowledge

Chemicals may have many pitfalls, but so do entomopathogenic fungi. They parallel each other: fungi die and chemicals never live, but neither dying nor inanimate pesticides are optimal in isolation. Finding a balance is key. Because of their shared deficiencies, Lovett emphasizes employing a comprehensive integrated approach to pest control: “All forms of pest management have their merits and their circumstances where they can work together. An intelligent integrated pest management plan would incorporate multiple modes of control.” In conclusion, an ideal agricultural practice would leverage chemicals, fungi, and other pesticides in combination. A diversified attack not only provides the greatest pest suppression but also prevents insecticide resistance simultaneously. Using both chemical pesticides and various mycoinsecticides is a transformative shift in how agriculture has been conducted, and to no surprise, their designs work synergistically. Lovett hopes to see this formidable arsenal more commonly in the future.

Bassi planted the seeds for understanding entomopathogenic function, but now the endophytic alliance has finally germinated in the fields of science. Considering the growing challenges of today’s society with pollution and pesticide resistance, scientists and farmers alike need only look into the garden of life where nature’s instruments have been restoring balance in the environment since their existence. These fungal wardens preserve homeostasis in their ecosystems, overlapping between parasitism of insect death and mutualism with plant life. It would be misguided to believe that they are one-dimensional killing machines because, in truth, they are the antithesis of death.

These fungi are the sine qua non of an environment; without them, nature would come to a halt. As the driver of insect disease and a prophylactic for everything else, the intimacy of all living things on Earth is much more apparent when one realizes that this ensemble of fungi is intertwined with the very machinations of nature. It may be bittersweet or perhaps counterintuitive, but every organism has its place, even insects, and entomopathogenic fungi happen to be more than an emissary of death but a champion of life.


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Acknowledgements: This paper would not have been possible without the mentorship that Dr. Gallagher has lent throughout the many stages of revisions. Similarly, Dr. Lovett was very generous in sharing his expert opinion—imparting a more nuanced outlook of the relationship between fungi and the world.

Citation Style: APA7