Destructive Crop Caterpillar's Gut Fungi Show Potential to Break Down Styrofoam
- Marc Violo
- 1 minute ago
- 4 min read
Researchers from the Federal University of São Carlos (UFSCar) and São Paulo State University (UNESP) have isolated four fungi from the gut of the cotton bollworm caterpillar (Helicoverpa armigera) and shown, using scanning electron microscopy, that each one can alter the surface of polystyrene film.
When fed expanded polystyrene, the caterpillar's gut microbiome shifted, with the yeast genus Diutina declining and potentially plastic-degrading genera including Aspergillus, Talaromyces, and Penicillium becoming more prominent.
The findings, published in BMC Microbiology, suggest that insect gut fungi — long overlooked in favour of bacteria — could provide enzymes or genes useful in developing biological approaches to polystyrene waste treatment.
A Pest With an Unexpected Role
Polystyrene accounts for roughly 5.2% of the 400 million tonnes of plastic produced globally each year, yet it remains one of the harder materials to recycle or break down. Its recalcitrant chemical structure, a long chain of carbon atoms with aromatic side groups, resists most biological attack. Most of what is discarded ends up in landfills or the open environment, where it may persist for centuries.
Into this problem steps an unlikely candidate: Helicoverpa armigera, the cotton bollworm. In agricultural terms, it is a significant pest of soybean, cotton, maize, tomato, and other crops across Europe, Africa, Asia, Australia, and South America. In laboratory terms, it now emerges as a potential reservoir of fungi capable of degrading expanded polystyrene (EPS),
the foamed form of the polymer used in packaging and food containers.
The research, led by Flávio Henrique-Silva of UFSCar's Molecular Biology Laboratory and published in BMC Microbiology in 2026, is described by the authors as likely the first study in Brazil to examine fungi from insect gut microbiota specifically in the context of polystyrene biodegradation.
What the Experiments Found
Third-instar larvae of H. armigera were divided into three feeding groups: one receiving only EPS blocks, one a mixed diet of 50% EPS and 50% conventional food, and one a conventional diet alone. After seven days, the gut contents were analysed using ITS metabarcoding, a DNA-sequencing technique that identifies fungal communities by a genetic barcode region.
In all groups, the yeast genus Diutina dominated. However, its relative abundance fell notably in the EPS-fed group, and the overall fungal community became more diverse. Genera including Aspergillus, Talaromyces, Metarhizium, and Trematosphaeria were more prominent in EPS-fed larvae than in controls. The authors suggest this shift reflects a microbial community adapting to a new carbon source, though they acknowledge this interpretation requires further investigation.
Four filamentous fungi were then isolated from the larval gut by culturing gut contents on agar plates: one Aspergillus species, one Talaromyces species, and two Penicillium species, designated FFHA01 through FFHA04. Each was cultured on a low-carbon medium overlaid with a thin polystyrene film for 60 days. Scanning electron microscopy of the washed films revealed that all four fungi had grown on the polymer surface and produced structural alterations, including the formation of trails and cavities. The Talaromyces isolate (FFHA02) showed the most pronounced surface changes.
The result indicates that the fungi interacted with and altered the polymer, which the authors interpret as evidence of potential use of polystyrene as a carbon source. They stop short of claiming full mineralisation, noting that further chemical characterisation using Fourier-transform infrared spectroscopy is needed to confirm the nature and extent of the changes.
A Parallel Finding in a Sugarcane Pest
A companion paper by the same research group, published in Frontiers in Microbiology in March 2026, reports complementary results from a different insect. The sugarcane weevil, Sphenophorus levis, harboured a bacterium, Paenibacillus lautus, that also modified polystyrene films. In that study, more rigorous chemical analysis, including Fourier-transform infrared spectroscopy, energy-dispersive X-ray spectroscopy, and gel permeation chromatography, confirmed surface oxidation and a measurable reduction in the polymer's molecular weight, with a mass loss of 3.73% over 60 days. Whole-genome sequencing of the bacterium identified candidate genes encoding enzymes relevant to plastic degradation, including cytochrome P450 oxygenases, glutathione peroxidases, and ring-cleaving dioxygenases.
Together, the two studies point to insect guts as a relatively underexplored source of plastic-degrading microorganisms, with both fungi and bacteria potentially contributing to the process.
Limitations and the Road Ahead
The BMC Microbiology study has explicit limitations. The degradation evidence is qualitative, based on surface morphology rather than chemical confirmation of bond cleavage or mineralisation. The larvae used were laboratory-reared on a standardised commercial diet, which the authors note may have suppressed certain gut microorganisms. Additionally, two of the four isolated fungi did not appear in the metabarcoding data, most likely due to methodological biases in DNA extraction or culture selectivity.
The UFSCar group plans to analyse insect frass to determine whether the polymer is fully broken down or merely reduced to micro- or nanoplastic fragments. They are also building a collection of efficient plastic-degrading microorganisms with the longer-term goal of engineering a highly capable degradation system. Whether that ambition can be realised at meaningful scale remains an open question, but the gut of a crop pest has, at minimum, widened the search.