Insect-killing fungi yield silver nanoparticles with larvicidal and antimicrobial power

In laboratories on the Indonesian island of Java, two of nature’s most accomplished insect assassins have been recruited for a second career: manufacturing tiny spheres of metallic silver that kill mosquito larvae and cripple disease-causing bacteria. Researchers at Indonesia’s National Research and Innovation Agency (BRIN), together with a collaborator at Periyar University in India, grew the entomopathogenic fungi Trichoderma asperellum and Metarhizium anisopliae—both separately and, unusually, in combination—filtered out their cells, and mixed the remaining protein-rich broth with silver nitrate. From that mixture self-assembled three distinct batches of mycosynthesized silver nanoparticles, described in a study published on 29 August 2026 in Environmental Science and Pollution Research. The standout performer was the dual-fungal formulation: it killed Aedes aegypti larvae, the principal vector of dengue, Zika and yellow fever, at the lowest dose of any preparation tested, and it posted the study’s highest larval mortality of 87.69 percent. The same particles also suppressed the growth of Pseudomonas aeruginosa, an infamous multidrug-resistant opportunist, and of Bacillus megaterium, with the antibiotic chloramphenicol serving as the benchmark. In an era of spreading insecticide resistance and rising antimicrobial resistance, the message from the fungi is strikingly simple: let biology build the weapon, and it may outperform what either mold achieves alone.

The urgency behind the work is hard to overstate. Mosquito-borne pathogens impose a global burden measured in hundreds of millions of infections every year, and Aedes aegypti has expanded its footprint dramatically over recent decades, carried along by urbanization, international trade and a warming climate. The conventional response—synthetic chemical insecticides—is showing its age. Resistance to the organophosphate larvicide temephos has been documented across Southeast Asia and beyond, with resistant larvae overproducing detoxification enzymes such as cytochrome P450 monooxygenases and esterases. Residual insecticides can persist in soils and sediments, poison non-target aquatic organisms and accumulate along food chains, prompting health agencies to call for larvicides that are biodegradable, targeted and affordable. Researchers have responded by mining the living world for alternatives: plant extracts, bacterial metabolites, actinobacterial filtrates and, increasingly, the secretions of fungi that spend their lives attacking insects. The new study argues that these entomopathogenic fungi, long valued as living biocontrol agents, are also superb chemical factories for green nanotechnology.

Silver’s antimicrobial pedigree reaches back to antiquity, but its nanoscale incarnation behaves very differently from the metal in jewelry and tableware. Shrink silver to a few dozen nanometers and the proportion of atoms sitting on the particle surface skyrockets; those surface atoms interact directly with biological membranes and steadily release silver ions, the species responsible for much of the toxicity. Chemists can force this transformation with reagents such as sodium borohydride or citrate, but those routes typically demand hazardous chemicals, elevated temperatures and organic solvents. Biosynthesis sidesteps the problem. Filamentous fungi secrete a rich cocktail of extracellular enzymes, proteins and polysaccharides; when their cell-free culture filtrate meets an aqueous silver nitrate solution, those biomolecules reduce silver ions (Ag+) to neutral metallic atoms (Ag0), which nucleate into nanoparticles. Other proteins then adsorb onto the nascent particle surfaces and cap them, arresting further growth and stabilizing the colloid against aggregation. The fungus, in effect, performs the reduction, the shaping and the stabilization in a single, room-temperature step, using nothing more exotic than its own metabolism.

The two species were not chosen at random. Trichoderma asperellum is a soil-dwelling workhorse of agricultural biocontrol, famed for parasitizing plant pathogens and secreting an arsenal of secondary metabolites. Metarhizium anisopliae, the agent of the so-called green muscardine disease in beetles, actively infects insects and has served for more than a century as a mycoinsecticide. Where most previous mycosynthesis studies tested a single organism, the team also combined the two cultures, harvesting a mixed filtrate containing the proteins and metabolites of both before the reduction step. This combined system, designated Ta Ma AgNPs, yielded particles with properties distinct from either single-species batch—and, as the bioassays later confirmed, distinct biological behavior. The rationale, the authors suggest, is that pooling two different fungal secretomes can produce a more diverse biomolecular coating on the nanoparticle surfaces, potentially enhancing colloidal stability and biological activity in ways that neither organism achieves alone.

Characterization followed a demanding, multi-instrument protocol. Ultraviolet–visible spectroscopy detected the characteristic surface plasmon resonance of silver nanoparticles—the collective oscillation of conduction-band electrons that absorbs light in the visible spectrum—confirming that reduction had succeeded in all three systems. Attenuated total reflectance Fourier-transform infrared spectroscopy, or ATR-FTIR, mapped the functional groups of the proteins, carbohydrates and other biomolecules adsorbed onto the particle surfaces, direct evidence that fungal metabolites were acting as capping agents. Cryogenic field-emission scanning electron microscopy and cryogenic transmission electron microscopy—techniques that image flash-frozen specimens close to their native, hydrated state—revealed uniformly spherical particles in every preparation. The mean diameters measured by TEM were 9.17 nanometers for the Trichoderma-derived particles (Ta AgNPs), 11.25 nanometers for the Metarhizium-derived particles (Ma AgNPs) and 12.54 nanometers for the combined-fungal particles (Ta Ma AgNPs), all squarely within the size range associated with potent biological activity. Dynamic light scattering characterized the hydrodynamic dimensions of the particles in suspension, while zeta potential measurements, which quantify the effective surface charge of a colloid, ranged from −23 to −26.9 millivolts. Values of that magnitude imply strong electrostatic repulsion between particles, keeping them dispersed in water rather than clumping and settling—an indispensable property for any nanoparticle intended to be applied to mosquito breeding habitats.

With the materials verified, the team turned to the mosquito. Following World Health Organization guidelines for laboratory larvicidal testing, they exposed Aedes aegypti larvae to each formulation at four concentrations—25, 50, 100 and 150 micrograms per milliliter—and scored mortality at 24 and 48 hours, correcting for control mortality with Abbott’s formula and computing lethal concentrations by probit analysis. All three preparations proved potently larvicidal, but the combined-fungal particles led at every time point. Their 24-hour median lethal concentration (LC50) was 52.32 micrograms per milliliter, against 58.61 for Ta AgNPs and 63.39 for Ma AgNPs; by 48 hours the values had fallen to 39.50, 43.60 and 51.46 micrograms per milliliter, respectively. Equally telling, the nanoparticles outperformed the raw fungal filtrates from which they were made: mortality reached 82.50 percent for Ta AgNPs, 80.44 percent for Ma AgNPs and 87.69 percent for Ta Ma AgNPs, all higher than the killing achieved by unmodified fungal extracts. The silver was no passive carrier of fungal toxins; the particles themselves were the weapons.

How exactly do these particles dispatch a larva? The leading mechanisms assemble into a coherent picture. At nine to thirteen nanometers, the spheres can adhere to and penetrate the larval cuticle, the chitinous armor through which the insect breathes and senses its world. Once inside, silver nanoparticles and the ions they liberate attack a battery of cellular targets simultaneously: they bind sulfur- and phosphorus-rich biomolecules such as proteins and DNA, inhibit respiratory and antioxidant enzymes, and catalyze the generation of reactive oxygen species that oxidize membrane lipids and structural proteins. Studies of biosynthesized silver particles in mosquito larvae have documented disruption of the midgut epithelium, deranged ion regulation and characteristic aberrant swimming before death, typically within hours to days of exposure. The negative zeta potentials measured here suggest each particle carries a corona of anionic fungal proteins, which may promote adhesion to positively charged membrane surfaces—and may help explain why the dual-species corona of the combined batch proved most lethal of all. Mortality climbed steadily with both dose and exposure time, a pattern consistent with progressive, cumulative toxicity rather than any single-point kill mechanism.

The same particles were then pitted against four bacterial pathogens representing both major cell-envelope architectures: the Gram-negatives Escherichia coli and Pseudomonas aeruginosa and the Gram-positives Bacillus megaterium and Staphylococcus aureus. Using the zone-of-inhibition well diffusion method and benchmarking against the antibiotic chloramphenicol, the researchers found that all three formulations inhibited P. aeruginosa and B. megaterium, with the clearest effect at the highest dose of 150 micrograms per milliliter. Activity against Pseudomonas is particularly noteworthy. P. aeruginosa is an opportunistic pathogen shielded by a restrictive outer membrane and a formidable talent for biofilm formation, and it ranks among the multidrug-resistant bacteria for which new agents are most urgently sought. Silver nanoparticles are believed to act through multiple, simultaneous mechanisms—membrane disruption, ion release, protein denaturation, oxidative stress and interference with DNA replication—which together make comprehensive bacterial resistance far harder to evolve than it is against single-target antibiotics. The differences observed among the four species likely reflect their contrasting cell-wall structures and the distinct biomolecular coatings of each nanoparticle batch, and the authors suggest that this dual larvicidal and antibacterial profile positions the formulations as a two-in-one tool for mosquito-borne disease control and antimicrobial applications alike.

None of this means silver-spiked water will be sprayed across tropical neighborhoods tomorrow. The work remains laboratory-scale, and the road from beaker to breeding ground is long. Silver nanoparticles can themselves harm non-target aquatic organisms, and questions of environmental persistence, accumulation and dose escalation in real water bodies must be resolved before any field deployment; the formulations would also need to survive sunlight, dilution and microbial degradation in open habitats, and to be manufactured at scale at tolerable cost. The authors do not claim otherwise. What the study does establish is that fungal biosynthesis can reliably deliver nanoparticles of tightly controlled size, negative surface charge and robust colloidal stability—and that combining two entomopathogenic species produces a particle that outperforms those made by either fungus alone, both as a larvicide and as an antibacterial. As dengue incidence climbs across Asia, Africa and Latin America and insecticide resistance erodes the frontline tools of vector control, the image of two humble molds, grown side by side in a culture flask, quietly manufacturing a dual-purpose weapon against mosquitoes and bacteria alike is precisely the kind of biological ingenuity the field has been hunting for. Corresponding author Titik Kartika and colleagues conclude that the combined Ta Ma nanoparticles, above all, stand out as a candidate alternative strategy for mosquito-borne disease control—and, from the same flask, a possible ally in the broader fight against antimicrobial resistance.