The research team, working with incipient colonies collected at the Federal University of São Carlos and experimented on at the Luiz de Queiroz College of Agriculture in Piracicaba, São Paulo, set out to quantify a behaviour that is easy to observe but hard to weigh. They housed miniaturised colonies in plaster-lined Petri dishes, each containing half a gram of symbiotic fungal garden, one larva, one pupa, and ten medium-sized ants, and let them acclimate for 48 hours. Three treatments followed: a Tween 80 control, a suspension of the entomopathogenic fungus Metarhizium anisopliae, and a suspension of Escovopsis phialicopiosa, the notorious garden parasite. Suspensions were adjusted to 10^8 conidia per millilitre and applied with an airbrush spray. Cameras recorded four hours of behaviour per replicate at 30-minute intervals, with five-minute focal sampling analysed in BORIS software, allowing the researchers to measure, in seconds, how much time workers spent on self-grooming versus allogrooming.

The behavioural data revealed a striking asymmetry. Under the control treatment, maximum allogrooming reached 1701 seconds, with a mean of 330 seconds. When Metarhizium anisopliae was present, those figures collapsed to a maximum of 169 seconds and a mean of just 54 seconds, suggesting that workers facing a virulent pathogen pull back from social contact, likely to avoid horizontal spore transmission between nestmates. Escovopsis phialicopiosa, by contrast, produced allogrooming values close to the control, with a maximum of 1639 seconds and a mean of 82 seconds. Self-grooming, meanwhile, remained relatively stable across treatments, with means hovering between 12 and 14.4 seconds. The largest difference among treatments appeared between the maximum and mean allogrooming values, hinting that social hygiene is the more behaviourally plastic of the two defences.

To translate these seconds into colony-scale consequences, the team built on a mathematical framework originally developed by Kang and colleagues in 2011 to describe biomass dynamics in Acromyrmex ants, a genus that typically cultivates its fungus in a single chamber. Two coupled differential equations track ant biomass and fungal biomass over time: ant growth depends on fungal biomass consumed through a Holling Type I functional response, while fungal growth depends on the labour ants allocate to harvesting and processing leaves, modelled with a Type III numerical response and a half-saturation constant. Mortality rates for both partners, plus a conversion rate of fungus into ant biomass, close the loop. The new study extended this single-chamber model into a two-chamber system, because Atta sexdens cultivates its symbiotic fungus across multiple underground chambers rather than one.

The extension introduced two crucial innovations. First, grooming was written directly into the mortality terms: pathogen-induced mortality for ants and fungus is scaled by the factor one minus the grooming time divided by its maximum, so the longer workers spend grooming, the lower the pathogen’s lethal intensity. The same structure was applied to allogrooming by substituting the allogrooming time. Second, a one-way transfer rule was added between chambers: when fungal biomass in chamber A exceeds its carrying capacity, a density-dependent flux moves ants and fungus to chamber B, mimicking how real Atta workers relocate brood and fungal biomass to newly excavated chambers as the colony expands. This directional flow reflects the colony’s developmental trajectory, in which older chambers act as sources of biomass for new compartments, and it embodies the organisational immunity that compartmentalised nests provide by limiting pathogen dissemination.

Simulations solved with the deSolve package in R, using the lsoda numerical method, produced sigmoidal growth curves for both partners, consistent with classical models of obligate mutualism. When the one-way transfer parameter was set to 0.1 per day, biomass decreased in the source chamber while increasing in the receiving chamber, and inflection points in the growth curves, identified from the second derivative of the biomass trajectories, were delayed. Those delayed inflection points mark a critical growth shift: the moment when accelerating growth gives way to deceleration. Under pathogen pressure, the timing of these shifts became diagnostic. In the Metarhizium treatment, ant and fungal biomasses dropped significantly compared with the control, and inflection points moved to higher values, producing a time-delayed effect. In the Escovopsis treatment, curves closely resembled the control, with only minor shifts in inflection values.

The most sobering result concerned Metarhizium anisopliae’s resilience to grooming. Even when the model was fed the maximum measured self-grooming and allogrooming durations, the pathogen still significantly reduced the biomasses of both ants and symbiotic fungus. The reason lies in the pathogen’s direct virulence to workers: Metarhizium infects insects through conidia that adhere to the cuticle, germinate, and penetrate the integument, so self-grooming alone may be insufficient to prevent infection even though it reduces spore quantity and viability. Infection may also impair worker activity, and empirical studies have shown that Metarhizium can disrupt essential tasks such as foraging, destabilising the social homeostasis that keeps a colony functioning. Escovopsis phialicopiosa, an opportunistic pathogen that attacks the cultivated fungus rather than the ants themselves, had minimal impact unless fungal mortality exceeded a critical threshold, roughly above 0.5 per day in the simulations, suggesting the strain’s lower virulence fails to trigger strong defensive responses.

Bifurcation diagrams, which map how equilibrium states change as parameters vary, exposed the system’s stability landscape. The proportion of workers allocated to fungus cultivation, denoted q, proved decisive: when q approached zero, too few workers tended the garden and biomass collapsed; when q approached one, workers neglected other essential tasks to the detriment of colony function. Intermediate values between 0.4 and 0.6 maximised stability by balancing competing demands. Ant and fungal mortality rates produced non-linear declines in most simulations, with a pronounced threshold near 0.5 per day for ant mortality, beyond which worker losses exceeded the colony’s replacement capacity and fungal biomass accelerated its decline. Self-grooming proved more effective than allogrooming in mitigating Metarhizium’s effects, likely reflecting the prioritisation of individual defences under high pathogen pressure, and ant biomass associated with self-grooming was significantly higher than biomass associated with allogrooming, although fungal biomass did not follow this pattern.

These findings carry practical weight well beyond ecology. Atta species are dominant herbivores in Neotropical biomes, capable of consuming up to 17 percent of available foliar biomass, and they inflict substantial damage on Eucalyptus and Pinus plantations as well as crops such as cassava and coffee. Biological control with entomopathogenic fungi has long struggled against these ants precisely because their multi-chambered nests and layered behavioural defences hinder uniform application of control agents. By identifying the behavioural and structural factors that limit or enhance pathogen effectiveness, the model suggests that targeted interventions could exploit critical mortality thresholds and worker allocation dynamics, minimising environmental impacts while optimising population control. The framework also provides a useful tool for understanding epidemiological dynamics in natural nests, integrating behavioural defences and spatial strategies to safeguard a mutualism that has persisted for 66 million years, and pointing toward future studies that could extend the two-chamber model into interconnected multi-chamber networks to reveal how full nest topology shapes ecological stability.

Subject of Research: Grooming behaviour and nest architecture regulating biomass growth of leafcutter ants and their symbiotic fungus under entomopathogenic fungal infection

Article Title: The role of grooming in regulating biomass growth of ants and symbiotic fungi under entomopathogenic fungal infection: experiments and mathematical modelling

Article References: Bueno, I., Toledo, J. V. M. F. D., Canuto, L. S., & Godoy, W. A. C. (2025). The role of grooming in regulating biomass growth of ants and symbiotic fungi under entomopathogenic fungal infection: experiments and mathematical modelling. BioRisk, 23, 17-43. https://doi.org/10.3897/biorisk.23.151538

Image Credits: AI Generated

DOI: 10.3897/biorisk.23.151538

Keywords: leafcutter ants, Atta sexdens, symbiotic fungus, grooming, Metarhizium anisopliae, Escovopsis phialicopiosa, entomopathogenic fungi, mathematical modelling, bifurcation analysis, mutualism, social immunity, biological control

The study was led by researchers from the Faculty of Medicine at the University of Peradeniya, including Jananie Abeygunasekera, Anushka Sachini, Malindi Kulathunga, Chathurika Abeysekara, Dulanjana Senavirathna, and microbiologist Veranja Liyanapathirana. Drawing on a descriptive cross-sectional design, the team surveyed 351 adult visitors attending the outpatient department of a tertiary care hospital. Participants were recruited consecutively using convenience sampling, meaning the researchers enrolled eligible adults as they presented, and data were collected through a structured self-administered questionnaire. The instrument probed perceptions of physicians’ attire and grooming, as well as beliefs about infection-related risks tied to what doctors wear. Statistical associations between perceptions and sociodemographic characteristics were tested using Pearson’s chi-square test or Fisher’s exact test, with significance set at a p-value below 0.05.

The headline result is unambiguous: scrubs dominate patient preferences. Some 200 participants, or 57.0 percent, identified scrubs as the preferred attire for male doctors, while 194, or 55.3 percent, said the same for female physicians. This preference was not uniform across the age spectrum. Among young adults, 65.5 percent favored scrubs for male doctors, compared with 54.2 percent of middle-aged adults and only 34.1 percent of older adults, a difference that was highly statistically significant. The same generational gradient appeared for female doctors, with 63.0 percent of young adults, 52.8 percent of middle-aged adults, and 34.1 percent of older adults preferring scrubs.

As enthusiasm for scrubs waned with age, preference for traditional attire climbed. The saree, a garment with deep cultural resonance in Sri Lanka, was favored for female physicians by 18.2 percent of young adults, 35.9 percent of middle-aged adults, and 54.5 percent of older adults, a pattern that reached strong statistical significance. The authors interpret this shift through a sociocultural lens: younger patients appear to associate modern, standardized clinical dress with professionalism and hygiene, while older patients may read traditional attire as a marker of respectability, identity, and trustworthiness. In other words, what counts as an appropriate doctor’s look is not a fixed visual code but one negotiated between global medical conventions and local cultural expectations.

Beyond aesthetics, the study tapped into a growing scientific concern: clothing as a fomite. Textiles in clinical environments can harbor bacteria and other microorganisms, and several studies worldwide have documented contamination of white coats, neckties, and sleeves. The Sri Lankan patients surveyed were notably aware of this risk. Fully 283 participants, or 80.6 percent, knew that microorganisms could survive on clothing, and 192, or 54.7 percent, perceived physicians’ attire as a potential source of infection. That more than half of ordinary outpatients independently view clothing as an infection vector underscores how far public awareness of cross-contamination has penetrated, even outside hospital wards.

When it came to ranking garments by infection risk, patients again converged on scrubs. Among those who viewed attire as a potential infection source, 136, or 70.8 percent, judged scrubs the lowest-risk option for male physicians, and 135, or 70.3 percent, said the same for female physicians. A remarkable 164 participants, or 85.4 percent of this subgroup, also considered short-sleeved attire more favorable for effective hand hygiene. This detail aligns neatly with infection control doctrine: bare forearms allow thorough hand and wrist washing, whereas long sleeves can dip into sinks, contact patients, and retain moisture and microbes. Patients, it seems, have internalized the same practical logic that guides hospital hygiene protocols.

The study fills a conspicuous gap in the literature. Much of the existing research on physician attire has been conducted in high-income settings such as the United Kingdom, the United States, and Japan, where debates have swung from the traditional white coat to bare-below-the-elbows policies. Evidence from South Asia and other low- and middle-income contexts has been sparse, despite the fact that cultural norms, climate, laundry infrastructure, and hospital resourcing differ substantially. By documenting patient perspectives at a major Sri Lankan hospital, the Peradeniya team provides data that hospital administrators and professional bodies in the region can use to ground attire policies in patient sentiment rather than imported assumptions.

The findings carry practical implications for hospitals weighing dress codes. Because scrubs are simultaneously the most preferred attire and the garment perceived as carrying the lowest infection risk, they occupy a rare sweet spot where patient preference and infection prevention goals coincide. Uniform scrub programs could, in principle, strengthen both patient confidence and hygiene practice, particularly if paired with short sleeves and institutional laundering, which reduces the burden on individual clinicians to maintain garment cleanliness. At the same time, the age-dependent preference for traditional attire suggests that any transition toward standardized dress should be communicated sensitively, since older patients may experience such changes as a loss of familiarity or respect. Grooming, too, emerged as part of the equation, with tidy appearance functioning in patients’ eyes as a proxy for both professionalism and safety.

The researchers caution that their findings come from a single tertiary care outpatient department and used convenience sampling, so the results may not generalize to all Sri Lankan patients or to inpatient settings. Still, the study, which received no external funding and was approved by the Ethics Review Committee of the Faculty of Medicine at the University of Peradeniya under protocol number 2024/EC/SP/02, adds an important data point to a global conversation about how doctors should dress. Its central message resonates well beyond Central Sri Lanka: a physician’s appearance is never merely cosmetic. To the patients who watch clinicians walk into the examination room, clothing communicates competence, cleanliness, and care, and it can either reassure or quietly alarm. As hospitals worldwide refine attire policies in the name of infection control, this study is a reminder that patients are not passive observers of those choices. They bring their own expectations, shaped by generation and culture, about what a safe and trustworthy doctor looks like, and those expectations deserve a seat at the policy table.

The symbolic weight of the white coat is worth recalling when interpreting these results. The garment entered medical fashion in the late nineteenth century, when physicians adopted laboratory dress to signal that medicine was becoming a scientific discipline grounded in germ theory and antiseptic practice. Over the following century the coat became so entrenched that many institutions staged formal ceremonies in which students received their first coat as a rite of passage. The Sri Lankan findings suggest that this historical emblem no longer commands automatic deference, at least among younger outpatients, who appear to associate standardized clinical uniforms rather than traditional professional dress with modern, hygienic care.

The study’s methodology merits some attention for readers weighing its conclusions. Because participants were surveyed with a self-administered questionnaire in an outpatient waiting area, the results capture stated perceptions rather than observed behavior. Perception and behavior can diverge: a patient may prefer scrubs yet still trust a physician in a saree once a consultation begins. The cross-sectional design also means the age gradient documented by the researchers could reflect either generational differences that will persist as younger cohorts age, or a life-stage effect in which attitudes toward traditional dress shift with maturity. Longitudinal work would be needed to separate these possibilities.

The finding that 80.6 percent of participants knew microorganisms can survive on clothing is striking given that textile contamination is a relatively technical concept. Research in other settings has recovered pathogenic bacteria, including staphylococci and enteric organisms, from the sleeves, pockets, and lapels of clinical garments, and contamination rates appear to rise with the frequency of patient contact and the interval between laundering. Whether contaminated attire translates into actual transmission of infection to patients remains difficult to prove, and direct evidence linking physician clothing to hospital-acquired infections is limited. This uncertainty has shaped policy debates, since some national guidance has restricted long sleeves and neckties on precautionary grounds even without definitive transmission data.

The Sri Lankan context adds further nuance. In tropical climates, lightweight and easily laundered garments offer practical advantages, and institutional laundering of hospital-owned scrubs can guarantee washing temperatures and detergent standards that home laundering of personal coats may not achieve. For hospitals in resource-constrained settings, however, supplying multiple sets of scrubs to every clinician carries real costs, which helps explain why traditional attire and personal white coats remain widespread across South Asia. Any move toward uniform programs must therefore balance patient preferences and infection control logic against procurement, laundry capacity, and staff acceptance.

Finally, the study highlights how patients themselves have become sophisticated participants in infection prevention culture. Public experience with hand hygiene campaigns and, more recently, pandemic-era messaging has familiarized ordinary people with concepts such as fomites and cross-contamination. That more than half of surveyed outpatients spontaneously identified clothing as a potential infection source indicates that hospitals can no longer assume attire is a neutral or invisible element of care. Patient-facing communication about dress codes, including why particular garments are chosen, may itself become a tool for building confidence in outpatient settings.

Subject of Research: Patient perceptions of physician attire and grooming and their perceived infection risks in outpatient care in Sri Lanka

Article Title: Patient perceptions of physician attire and perceived infection risk associated with attire and grooming in outpatient care at a tertiary care hospital in Central Sri Lanka

Article References: Abeygunasekera, J., Sachini, A., Kulathunga, M., Abeysekara, C., Senavirathna, D., & Liyanapathirana, V. (2026). Patient perceptions of physician attire and perceived infection risk associated with attire and grooming in outpatient care at a tertiary care hospital in Central Sri Lanka. Discover Social Science and Health. https://doi.org/10.1007/s44155-026-00481-9

Image Credits: AI Generated

DOI: 10.1007/s44155-026-00481-9

Keywords: physician attire, patient perceptions, infection control, cross infection, scrubs, ambulatory care, hand hygiene, cultural factors, Sri Lanka, developing countries, tertiary care hospital, grooming