Insect-Killing Fungi Secretly Arm Crops Against Drought, Salt and Toxic Metals

For decades, entomopathogenic fungi have earned their reputation the hard way: by infecting and killing insects. Species such as Beauveria bassiana and Metarhizium anisopliae have been formulated as biological pesticides that attach to the insect cuticle, breach the exoskeleton and proliferate inside the host’s body cavity, wiping out pests from larvae to adults. But a comprehensive new review published in Crop Health argues that this insect-killing talent is only half the story. When these same fungi slip inside plant tissues as endophytes, they transform into quiet biochemical engineers, rewiring the physiology of their hosts to withstand drought, salinity and heavy metal contamination, three of the most damaging abiotic stresses in modern agriculture.

The review, led by Ya-Qiang Zheng of Guizhou University of Traditional Chinese Medicine together with Komivi Senyo Akutse, Song Mei, Artemio Mendoza-Mendoza and Bin Chen, is the first systematic synthesis to unite the drought, salt and heavy metal literature on endophytic entomopathogenic fungi within a single mechanistic framework. The timing could hardly be more pressing. Abiotic stresses are estimated to cause global yield losses exceeding fifty percent, and climate change is intensifying drought frequency while more than 800 million hectares of soil worldwide are already affected by salinity. Heavy metal pollution from mining, sewage irrigation and industrial emissions adds a third, largely irreversible threat to arable land.

The authors begin with an evolutionary observation that reframes how these fungi should be seen. Rather than being mere insect parasites that occasionally wander into plants, entomopathogenic fungi appear deeply entwined with the plant root mycobiome. Genomic analyses show that Metarhizium and Beauveria species are close relatives of established endophytes and plant-associated fungi such as Fusarium. The Metarhizium lineage may even have travelled the opposite evolutionary route: starting as saprophytes attracted to root exudates, becoming plant endophytes, and only later acquiring the machinery to kill insects. Many Metarhizium species retain the flexibility to switch between all three lifestyles, which is precisely what makes them so attractive as dual-purpose agricultural agents.

Under drought, the mechanisms these fungi deploy are remarkably layered. In red oak seedlings, B. bassiana colonisation maintained higher leaf relative water content and stomatal conductance while promoting root growth, giving trees better access to scarce water. In tomato, the same fungus pushed plants toward what researchers call a water spender strategy, growing larger and drawing more water through improved root function and stomatal regulation. In onion, colonisation enhanced uptake of phosphorus, calcium, magnesium and iron, nutrients central to energy transfer, membrane stability and chlorophyll synthesis. Wheat seeds primed with M. anisopliae MetA1 showed improved photosynthesis, growth and yield under drought, while maize plants colonised by M. robertsii grew taller under water stress, although the authors caution that results in maize have been inconsistent, likely because inoculation method strongly determines whether the fungus establishes at all.

Beneath these visible improvements lies a concerted molecular campaign against oxidative damage. Drought triggers the accumulation of reactive oxygen species, which shred membranes and proteins. The review documents how endophytic entomopathogenic fungi consistently boost the plant’s enzymatic arsenal, elevating superoxide dismutase, catalase, peroxidase and ascorbate peroxidase activity across species as diverse as tomato, onion, wheat and mallow. These enzymatic gains are mirrored by reductions in malondialdehyde, a chemical fingerprint of lipid peroxidation, indicating genuinely preserved membrane integrity. In parallel, the fungi stimulate non-enzymatic defences: polyphenols, flavonoids and ascorbic acid accumulate, most dramatically under severe drought, when fungal support matters most.

Osmotic adjustment, the accumulation of compatible solutes such as proline, soluble sugars and free amino acids, forms a third pillar of drought resilience, though the review is careful to note that this response is species-specific. Proline rose in colonised tomato, onion and wheat, helping cells retain turgor pressure, yet in red oak the fungus conferred drought tolerance without raising proline at all, suggesting alternative strategies such as enhanced root growth can substitute. Hormonal rewiring completes the picture: B. bassiana upregulated genes governing stomatal behaviour and abscisic acid signalling in tomato, elevated ABA in colonised maize, and in mallow increased gibberellins while suppressing ethylene, the senescence hormone that accelerates tissue damage under stress. The precise molecular dialogue between fungus and host under drought, the authors stress, remains largely unmapped and represents a major frontier.

Under salinity, the fungal playbook shifts toward ion management. The central challenge for salt-stressed plants is maintaining a favourable potassium-to-sodium ratio, and here the evidence is striking. Rice seeds primed with M. anisopliae MetA1 accumulated less sodium and more potassium in both roots and shoots, while B. bassiana strain BeauA1 improved the same ratio under both saline and non-saline conditions. The fungi also promoted proline and carbohydrate accumulation to maintain cell turgor, activated antioxidant enzymes including glutathione S-transferase, and in soybean reprogrammed hormone balance by lowering abscisic acid while raising jasmonic acid. Growth gains followed: improved shoot length, chlorophyll content, leaf area and even stolon production in potato, all under salt concentrations that would normally suppress them. One Metarhizium pinghaense strain even sustained indole-3-acetic acid production at up to 200 millimolar sodium chloride in vitro, sustaining root growth when it mattered most.

The heavy metal findings are arguably the most surprising, revealing the fungi as both detoxification engines and ecological regulators. On the fungal side, B. bassiana immobilises cadmium, lead, zinc and copper on its cell wall through carboxyl, phosphate, hydroxyl and amino groups, removing up to 84.5 percent of total metals from multi-metal wastewater. Inside fungal cells, cadmium entering through calcium channels is bound by glutathione and processed by upregulated cytochrome P450 enzymes, whose inhibition cuts cadmium removal by 45 percent. Some Metarhizium species acquired a bacterial gene, methylmercury demethylase, through horizontal gene transfer, allowing M. robertsii to convert highly toxic methylmercury into volatile elemental mercury that escapes the rhizosphere. Others, such as Beauveria caledonica, excrete oxalic acid that precipitates metals as insoluble oxalate crystals, locking them away from plant roots.

On the plant side, colonised hosts activate their own cadmium efflux pumps and metal-binding proteins while suppressing uptake transporters: in rice, M. robertsii silenced the cadmium importer OsNramp5, cutting cadmium in roots by up to 44.3 percent and in grains by 24.7 percent. In an especially timely result, M. anisopliae seed treatment disrupted what researchers describe as a Trojan Horse effect, in which nanoplastics act as carriers that smuggle lead into rice roots, reducing the soil-to-root transfer of lead by roughly a third while restoring antioxidant balance and rebuilding a beneficial rhizosphere microbiome rich in Sphingomonas and Burkholderia. The fungi even stabilise metals in soil itself, with B. bassiana FE14 cutting bioavailable cadmium from 26.23 to 5.41 milligrams per kilogram through organic acid secretion.

The review closes with a sober assessment of what stands between laboratory promise and field reality. Effectiveness depends on specific plant-fungus combinations and environmental contexts, so systematic strain screening across crops, climates and soils is paramount. Stable endophytic colonisation under fluctuating temperature, humidity, ultraviolet radiation and microbial competition remains difficult to achieve, demanding better formulations such as microencapsulation and optimised seed coating methods. The authors also urge rigorous ecological risk assessment: these fungi are potent insect pathogens, and their effects on pollinators and other beneficial insects must be evaluated before deployment, while growing concern frames all microbial inoculants as potential neomicrobiota that could disrupt native ecosystems. Yet if molecular tools such as CRISPR gene editing, multi-omics profiling and improved regulatory frameworks can unlock these fungi’s full potential, the authors argue, agriculture could gain a single microbial ally that fights pests, buffers climate extremes and cleans contaminated soils simultaneously, a combination no chemical input has ever offered.

Subject of Research: Mechanisms by which endophytic entomopathogenic fungi enhance plant tolerance to abiotic stresses including drought, salinity and heavy metal toxicity

Article Title: Entomopathogenic fungi: beyond biocontrol-unravelling mechanisms of enhanced plant abiotic stress tolerance

Article References: Zheng, Y.-Q., Akutse, K. S., Mei, S., Mendoza-Mendoza, A., & Chen, B. (2026). Entomopathogenic fungi: beyond biocontrol-unravelling mechanisms of enhanced plant abiotic stress tolerance. Crop Health, 4(1), Article 14. https://doi.org/10.1007/s44297-026-00077-4

Image Credits: AI Generated

DOI: 10.1007/s44297-026-00077-4

Keywords: entomopathogenic fungi, fungal endophytes, abiotic stress, drought tolerance, salinity, heavy metals, Beauveria bassiana, Metarhizium, plant-microbe interaction, bioremediation, sustainable agriculture, phytohormones