https://orcid.org/0000-0002-2998-8716
Figures
Abstract
In Malaysia, anecdotal accounts have linked the household casebearer (Lepidoptera: Tineidae) to skin lesions and localized inflammation; however, scientific evidence is lacking, and the species’ taxonomic identity remains unclear. This study aimed to confirm the species identity and examine the bacteria associated with larvae that may be linked to skin irritation. Larvae were collected from three locations in Peninsular Malaysia and preserved. DNA was extracted from the larvae, and species identification was conducted by analyzing the cytochrome c oxidase subunit I (COI) gene through DNA barcoding. To study the bacteria present, the bacterial 16S rRNA gene was amplified and sequenced using Next-generation sequencing technology. The DNA sequences were analyzed to determine the species and profile the bacterial communities. The results identified the specimens as Phereoeca sp., suggesting they may represent an undescribed lineage. Microbiome analysis revealed that Proteobacteria (40.18%) and Actinobacteriota (32.13%) were the dominant bacterial phyla, with Cutibacterium acnes, Enterobacter, and Pseudomonas among the taxa previously associated with skin irritation or opportunistic infections. Several unclassified but potentially relevant taxa were also identified. These findings provide new insights into the microbial ecology and taxonomy of Phereoeca and underscore its potential role in medically significant interactions within human environments.
Citation: Yaakop S, Senen MA, Adila Rosli NA, Mohammed MA (2026) Molecular identification and microbiome profiling of household casebearer, Phereoeca sp. (Lepidoptera: Tineidae) from Malaysia: Potential implications for human skin irritation. PLoS One 21(4): e0346590. https://doi.org/10.1371/journal.pone.0346590
Editor: Naji Arafat Mahat, Universiti Teknologi Malaysia - Main Campus Skudai: Universiti Teknologi Malaysia, MALAYSIA
Received: November 29, 2025; Accepted: March 20, 2026; Published: April 9, 2026
Copyright: © 2026 Yaakop et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Data Availability: The DNA barcoding sequences generated in this study have been deposited in GenBank under accession numbers PP961802-PP961804, PQ882320, and PQ885044-PQ885048. The metagenomic 16S rRNA sequence data are available in the NCBI Sequence Read Archive (SRA) under the accession number PRJNA897111.
Funding: The authors received no specific funding for this work.
Competing interests: The authors have declared that no competing interests exist.
Introduction
Casebearers (Lepidoptera: Tineidae) are small moths commonly encountered in domestic environments and known for their larval habit of constructing silk cases adorned with fibers, debris, and other environmental materials [1]. These insects, often referred to as “plaster bagworms” or “household casebearers,” or locally known as “kamitetep,” are widespread in Malaysia and are frequently observed on walls, ceilings, and household fabrics. While their presence is mostly viewed as a nuisance due to fabric damage, there is growing concern over their potential role in causing allergic skin reactions.
Social media reports and anecdotal accounts have linked contact with these larvae to skin irritation and inflammatory responses in humans. Despite these claims, no scientific studies have confirmed the dermatological effects or identified the specific species involved. Moreover, the taxonomy of Phereoeca species in Southeast Asia remains poorly resolved, with limited molecular data available for accurate identification.
Insects, including moths, harbor diverse microbiomes that play key roles in host biology, digestion, immunity, and environmental interactions [Zhang et al., 2022]. Microbial communities may include bacterial taxa capable of producing bioactive compounds such as histamine, a biogenic amine implicated in immune regulation, allergic reactions, and inflammation [2]. Several bacterial genera, including Pseudomonas, possess the enzymatic capacity to convert L-histidine into histamine through histidine decarboxylase activity [3]. These associations suggest that the microbiota of household insects may be medically relevant.
Recent advances in Next-generation sequencing (NGS) have enabled comprehensive profiling of microbial communities associated with insects through metagenomic approaches [4]. Metagenomic sequencing allows the identification of both culturable and unculturable microbes, offering insights into host–microbe interactions and potential health implications [5,6]. However, no studies to date have applied these methods to the casebearer in Malaysia, leaving a gap in our understanding of its microbiome and possible effects on human health.
This study aims to address these gaps by combining DNA barcoding and 16S rRNA-based microbiome profiling of Phereoeca sp. collected from Malaysian households. The objectives are to (i) confirm species identity using the COI gene, (ii) characterize the associated bacterial community, and (iii) identify microbial taxa potentially involved in skin irritation. The findings are expected to provide both taxonomic clarity and novel insights into the possible medical relevance of this common household insect.
Materials and methods
The overall experimental workflow used for molecular identification and microbiome analysis of Phereoeca sp. larvae is summarized in Fig 1. The procedure included sample preparation, DNA extraction, PCR amplification, library preparation, and Illumina MiSeq sequencing, followed by bioinformatic analysis.
The process includes sample preparation, DNA extraction, DNA quality control, amplicon PCR, two-stage PCR amplification, PCR clean-up steps, library quality control, library normalization and pooling, followed by Illumina MiSeq sequencing.
Sampling location and household casebearer collection
Sampling was conducted at three locations in the western part of Peninsular Malaysia: Bangi (Selangor), Benut (Johor), and Nilai (Negeri Sembilan). These sites were selected to provide an overview of microbial composition. Visual observations were carried out in indoor residential environments by examining the surfaces of ceilings and walls with the naked eye. The larval stage of the moth, found within portable cases, was collected and preserved in 70% alcohol. Some larvae were reared in a plastic container (10 × 8 × 6 cm; dry sample) until adult emergence. Larval sampling was conducted within private residential premises with homeowner consent. The study did not involve protected species or protected areas; therefore, no specific collection permit was required for this study. Representative voucher specimens of Phereoeca sp. from this study were deposited in the Centre for Insect Systematics, Universiti Kebangsaan Malaysia (UKM) collection to support future taxonomic work.
Morphological identification
Each individual larval sample was recorded and photographed using an Image Analyser (Zeiss Stereo Discovery V20) with AxioVision software, and a representative image is presented in Fig 2. Only samples with similar structures were assumed to belong to the same species. Selected individuals that were successfully reared to the adult stage were identified to species level using a stereo microscope (Zeiss, Germany) at 40× magnification. To further support the identification, DNA barcode analysis was conducted using a minimum of three samples from each location.
The larva is enclosed within a portable case constructed from silk, dust particles, and environmental debris. Scale bar = 0.5 mm.
DNA Barcoding Analysis
DNA extraction and PCR amplification.
DNA was extracted from nine larval samples of the household casebearer (Table 1). To minimize external contamination, all specimens were handled using sterile forceps and transferred into sterile containers. Prior to DNA extraction, larvae were carefully removed from their cases and rinsed three times with 70% ethanol followed by sterile distilled water to reduce surface-associated contaminants. Microbiome analysis was performed on larval material only, and the external casing was not included in downstream DNA extraction unless otherwise stated. All dissections were conducted under clean laboratory conditions. Only the larval portion was collected for extraction, which was performed using the Macherey-Nagel DNA Kit (Germany) according to the manufacturer’s protocols.
PCR analysis targeted the cytochrome c oxidase subunit I (COI) gene using primer pairs from Folmer et al. [7]: LCO1490 (5′-GGTCAACAAATCATAAAGATATTGG-3′) and HCO2198 (5′-TAAACTTCAGGGTGACCAAAAAATCA-3′). Each 25 μL PCR reaction contained 12.5 μL Mastermix (Promega), 5.5 μL ddH₂O, and 5 μL of DNA template (4–6 μL). PCR conditions followed Mohammed et al. [8], Yaakop et al. [9], and Mohammed et al. [10]. PCR products were subjected to electrophoresis for 30 min at 90 V using a 1.5% agarose gel.
DNA sequencing, editing, and BLAST analyses.
PCR amplicons were purified and sequenced commercially by Apical Scientific Sdn. Bhd. (Malaysia). Raw sequence chromatograms were inspected and edited using Sequencher version 5.4.6 (Gene Codes Corporation, USA). Consensus sequences were subsequently compared against reference sequences in the National Center for Biotechnology Information (NCBI) database using the Basic Local Alignment Search Tool (BLAST) [11] to verify species identity. Successful amplification of the mitochondrial cytochrome c oxidase subunit I (COI) gene was confirmed through agarose gel electrophoresis (Fig 3a). DNA barcoding analyses were conducted on nine specimens collected from three localities in Malaysia (Table 2). The validated COI sequences were deposited in GenBank under accession numbers PP961802–PP961804, PQ882320, and PQ885044-PQ885048.
(a) Amplification of the mitochondrial cytochrome c oxidase subunit I (COI) gene used for DNA barcoding. (b) Amplification of the bacterial 16S rRNA gene (V3-V4 region) used for microbiome analysis. Sample codes correspond to specimens collected from three localities: Nilai (1A-3A), Benut (1B–3B), and Bangi (1C-3C).
Tree reconstruction.
Sequences were analyzed using the Neighbor-Joining (NJ) method based on Kimura 2-Parameter (K2P) distances in PAUP 4. Bootstrap analysis was performed with 1,000 replications. Maximum Parsimony (MP) analysis was also conducted using heuristic search with TBR and 1,000 bootstrap replicates. Additional sequences from expected species in GenBank were included (Table 2).
Metagenomic analysis
Larvae extraction.
Nine larvae collected from three locations (Table 1) were dissected from their cases with sterile forceps. Samples were rinsed three times with 70% alcohol. DNA was extracted using the Macherey-Nagel DNA Kit. Samples <40 mg were placed in NucleoSpin® Bead Tubes with buffers BE, MG, and proteinase K. Samples were vortexed, centrifuged, washed with BW and B5 buffers, dried, and eluted with BE buffer.
DNA quality control.
DNA purity and concentration were assessed using the Implen NanoPhotometer® N60/N50 and the iQuant™ Broad Range dsDNA Quantification Kit. Only high-quality DNA proceeded to downstream applications.
Amplicon PCR of bacterial 16S rRNA.
DNA extracted from nine Phereoeca sp. larval specimens was subjected to amplification prior to bacterial 16S rRNA gene metabarcoding analysis. The V3-V4 hypervariable regions of the bacterial 16S rRNA gene were amplified using primers Bakt_341F and Bakt_805R [12]. PCR reactions were performed using REDiant 2 × PCR Master Mix (1st BASE, Malaysia) following the manufacturer’s recommendations. Amplification products were verified by agarose gel electrophoresis before downstream metabarcode sequencing analysis (Fig 3b).
Library construction
First PCR.
Overhang adapters were attached during amplification. Reactions were conducted using KOD-Multi & Epi DNA polymerase in 30 cycles.
Second PCR (Indexing).
Dual indices were added using the Illumina Nextera XT Index Kit v2. Library quality was verified using an Agilent Bioanalyzer 2100 and Helixyte Green™.
Next-generation sequencing.
Libraries were normalized and pooled before sequencing on the Illumina MiSeq (300 PE). Raw sequences (PRJNA897111) were processed in R v3.6.2. Using DADA2 [13], sequences were quality-filtered, denoised, spliced, and checked for chimeras. Taxonomy was assigned using RDP’s Naïve Bayesian Classifier with SILVA v138.1 [14] in QIIME2 [15].
Relative abundance was visualized using phyloseq [16]. Venn diagrams, rarefaction curves, and phylogenetic trees (FastTree2; [17]) were constructed. Sequences <150 bp or >600 bp were removed.
Statistical analyses
Alpha diversity metrics (Chao1, Observed ASVs, Shannon, Simpson) were calculated in R v3.6.2. Samples were rarefied to the lowest depth. Differences among localities were tested using Wilcoxon rank-sum tests (p ≤ 0.05). Beta diversity was examined using Bray–Curtis and UniFrac distances. PCoA and UPGMA analyses were conducted. ANOSIM tested for community composition differences.
Results
DNA barcoding
Sequence similarity analysis of nine individuals collected from three localities in Malaysia revealed that the obtained sequences shared only 89.26–90.08% identity with available Phereoeca uterella sequences in GenBank, suggesting that the specimens do not represent the same species. Accordingly, the Malaysian material is provisionally designated as Phereoeca sp., pending further taxonomic confirmation.
This distinction is further supported by phylogenetic analyses using both Neighbor-Joining (NJ) and Maximum Parsimony (MP) methods, with the Malaysian specimens forming a separate clade from P. uterella individuals from other countries (Figs 4a and 4b). The NJ and MP trees provided strong statistical support for this separation, with bootstrap values of 100% and 99%, respectively. These findings suggest that the Malaysian population may represent a distinct, previously undescribed lineage within the genus Phereoeca. Given the significant genetic divergence and phylogenetic separation, the species is currently referred to as Phereoeca sp. Malaysia. Further morphological and molecular investigations are required to clarify its taxonomic status and determine whether it constitutes a novel species.
(a) Neighbor-Joining (NJ) tree constructed using Kimura 2-parameter genetic distances. (b) Maximum Parsimony (MP) tree reconstructed from the same dataset. Bootstrap support values are indicated at the nodes. Malaysian Phereoeca specimens form a distinct clade separate from reference sequences retrieved from GenBank.
Genetic distance
Fig 4a presents the Neighbor-Joining (NJ) tree constructed from the COI dataset, with bootstrap values indicated on the corresponding branches. The analysis revealed that genetic divergence between different genera ranged from 0.15959 to 0.19355, indicating substantial intergeneric variation (Tables 3 and 4). In contrast, intraspecific divergence between individuals of the same species was considerably lower, ranging from 0.00000 to 0.06112, consistent with expected values for conspecific populations. Notably, the Phereoeca sp. specimens from Malaysia exhibited a genetic divergence of 0.10357 to 0.10526 when compared with P. uterella sequences from other geographic regions. This level of divergence is significantly higher than what is typically observed within a single species, suggesting that the Malaysian specimens may represent a distinct taxonomic entity. These findings support the hypothesis that the Phereoeca population in Malaysia constitutes a potentially undescribed species, warranting further taxonomic investigation through morphological and additional molecular analyses.
Bacterial community diversity
Sequencing of the V3-V4 hypervariable regions of the bacterial 16S rRNA gene yielded a total of 996,762 raw reads, with an average of 110,751 reads per sample. Rarefaction curves for all three biological replicates approached asymptotes, indicating sufficient sequencing depth and sampling effort to capture the majority of bacterial diversity across all localities (Fig 5). Following quality filtering and removal of low-quality and short reads, final read counts were 163,137 for Johor (J), 142,090 for Negeri Sembilan (S), and 123,284 for Selangor (U) samples (Table 1). A total of 461 Amplicon Sequence Variants (ASVs) were identified and used for clustering and downstream taxonomic classification.
The curves represent the number of observed amplicon sequence variants (ASVs) as a function of sequencing reads across samples from Johor, Negeri Sembilan (Nilai), and Selangor (Bangi). Curves approaching a plateau indicate adequate sequencing coverage.
Alpha diversity metrics, including observed ASVs, Chao1 richness estimator, Shannon index, and Simpson index, revealed variation in microbial diversity across samples. The sample from Negeri Sembilan (S2) exhibited the highest alpha diversity (observed ASVs = 176; Shannon index = 3.89; Simpson index = 0.95), while Selangor (U3) showed the lowest diversity (observed ASVs = 24). Comparatively, the median Shannon index across locations was highest in Johor (3.12), followed by Negeri Sembilan (2.83), and lowest in Selangor (2.29) (Table 5). Statistically significant differences in bacterial community diversity across localities were evident in all diversity indices, as visualized in Figs 6 and 7.
Samples cluster according to similarities in microbial community structure.
Diversity metrics include ACE, Chao1, Inverse Simpson, Observed ASVs, Shannon index, and Simpson index.
Among the 461 ASVs, four bacterial taxa were shared across all three populations, namely Paraburkholderia (Proteobacteria), Methylobacterium (Alphaproteobacteria), and Cutibacterium (Actinobacteria). The highest ASV richness was recorded in samples from Nilai (S, 151 ASVs), followed by Johor (J, 123 ASVs), and Selangor (U, 72 ASVs) (Fig 8). Taxonomic classification revealed that the dominant phylum was Proteobacteria (40.18%), followed by Actinobacteriota (32.73%) and Firmicutes (21.22%) (Fig 9). At the class level, Actinobacteria (31.77%), Alphaproteobacteria (21.76%), and Gammaproteobacteria (18.42%) were most abundant, with other classes distributed among remaining phyla (Table 6). At the family level, Pseudonocardiaceae (15.53%), Beijerinckiaceae (12.97%), and Burkholderiaceae (11.24%) were the most prevalent (Fig 10). Although Enterobacteriaceae was present, its relative abundance was low (1.7%). Genus-level analysis identified Methylobacterium and Methylorubrum (combined 11.4%), Burkholderia-Caballeronia-Paraburkholderia (10.7%), and Pseudonocardia (5.7%) among the most dominant genera (Fig 11). The genus Enterobacter, of particular interest in this study, was detected at a relative abundance of 0.71%.
Each bar represents an individual sample, and colors indicate the proportion of major bacterial phyla identified through 16S rRNA gene sequencing.
Each bar represents the microbial composition of individual samples.
Bars represent individual samples, showing the distribution of dominant genera across different sampling sites.
At the species level, Cutibacterium acnes (3.11%) emerged as one of the top 10 most abundant species and was among the top seven families. Other notably abundant species included Enhydrobacter aerosaccus and Mesorhizobium loti, ranked 14th and 15th among the top 25 most abundant taxa, respectively (Table 7). Several unidentified or unclassified species were also present and are discussed in the context of their potential ecological or medical relevance. Taxonomic assignments were conducted using the SILVA reference database, which revealed a total of 15 bacterial phyla, including one unclassified group. Taxonomic composition across samples was visualized through taxa boxplots, which consistently showed Proteobacteria as the most dominant phylum across all Phereoeca specimens.
Discussion
Taxonomic uncertainty of Phereoeca sp. in Malaysia
The household casebearer, Phereoeca sp., remains underrepresented in entomological research, both in Malaysia and globally, despite its common presence in household environments (Villanueva- Jimenez and Fasulo 2010). Public attention in Malaysia was recently sparked by viral social media posts alleging that this insect causes skin irritation or bites, although no empirical data have validated such claims. The species status of Malaysian Phereoeca specimens remains unclear due to slight morphological differences compared to the globally accepted P. uterella. DNA barcoding in this study revealed that Malaysian samples did not cluster with known Phereoeca species such as P. uterella from the USA, P. praecox from Malta (MW305963), or the Brazilian Phereoeca sp. (MH540351.1), the latter of which was associated with Rickettsia felis (de [18,19]. These findings suggest the possibility of a distinct or previously undescribed species in Malaysia, underscoring the need for further taxonomic revision and molecular confirmation.
To investigate potential species divergence, phylogenetic comparisons were made with other Lepidoptera in the family Tineidae, including Pelecystola spp. from China [Yang and Li 2021] and Monopis longella from South Korea [20]. Additionally, comparisons included agriculturally relevant species such as Mahasena corbetti and Metisa plana, bagworms that cause economic damage in Malaysian oil palm plantations [21,22]. These broader comparisons help clarify genus-level relationships and highlight the genetic divergence of the Malaysian Phereoeca sp. from its closest relatives. The genetic distance observed among these species points toward potential cryptic speciation or geographic divergence in Phereoeca populations. Future studies using full mitochondrial genomes and morphological reassessment could help resolve these taxonomic ambiguities. Given the observed genetic divergence, formal taxonomic assessment in collaboration with tineid specialists will be necessary to determine the species status of the Malaysian population.
Microbiome composition of Phereoeca sp.
This study provides the first comprehensive profile of the bacterial microbiome of Phereoeca sp., marking a significant contribution to understanding urban lepidopteran microbiota. The casebearer’s microbial community is shaped by its unique habitat which is the human household that differs from the microbiomes of agriculturally associated Lepidoptera such as Metisa plana and Bombyx mori [23,24]. Proteobacteria was the most dominant phylum in Phereoeca sp. (40.18%), followed by Actinobacteriota (32.13%) and Firmicutes (21.22%), a distribution that aligns with patterns found in other insects but with unique ratios. The prevalence of these phyla suggests they play critical roles in nutrient cycling, host physiology, and interactions within the urban environment [25]. Minor phyla such as Bacteroidota, Cyanobacteriota, and Actinomycetota were also detected and are notable for their potential involvement in histamine production and immune modulation [3].
At the family level, Pseudonocardiaceae, Beijerinckiaceae, and Burkholderiaceae were highly abundant, particularly within the Actinobacteriota and Proteobacteria phyla. These bacteria are typically associated with soil, plants, and environmental surfaces, suggesting potential transfer from household dust, textiles, or decaying organic matter. Enterobacteriaceae, though found in low abundance, remains a family of interest due to its relevance in both entomological and medical contexts, including gut symbiosis and pathogenicity [26]. Similar bacterial families have been recorded in lepidopterans such as Galleria mellonella and Spodoptera frugiperda, supporting the commonality of core gut bacteria across species. However, the differences in abundance and composition highlight how habitat and diet strongly influence microbial communities in urban versus agricultural insects.
The comparatively higher alpha diversity observed in the Negeri Sembilan samples may reflect local environmental or microhabitat differences influencing the microbial exposure of Phereoeca larvae. Variations in indoor humidity, household cleaning practices, building materials, or surrounding environmental conditions could contribute to differences in microbial acquisition, as environmental exposure is known to shape insect-associated microbial communities [24]. However, given the limited sample size and geographic coverage of the present study, these interpretations remain tentative. More systematic spatial sampling and environmental metadata collection will be necessary to determine the drivers of microbiome variation across locations.
It should be noted that the present microbiome profile primarily reflects bacteria associated with the processed larval material. Environmental or casing-associated microbes may also contribute to the detected community and should be examined separately in future studies.
Histamine-associated bacteria and public health implications
A key focus of this study was the identification of histamine-associated bacteria, which could provide insights into anecdotal reports of skin irritation linked to Phereoeca larvae. Several genera detected such as Enterobacter, Pseudomonas, and Streptomyces are known histamine producers in both environmental and foodborne contexts [3]. For example, Enterobacter hormaechei produces histamine and can cause dermal toxicity, including severe lesions in mammals [27]. Ting et al. [24] also reported the presence of this bacterium in insect larvae, where it supports larval growth and digestion. Although Enterobacter spp. were not dominant in Phereoeca sp., their presence, even at low abundance, raises questions about their role in potential allergic reactions when the larvae interact with human environments.
The detection of Mycobacterium tuberculosis at a relative abundance of 2.46% was unexpected and warrants further attention. While it may result from environmental contamination, previous research has shown that ants and insects in hospital settings can act as vectors for Mycobacterium spp., including M. tuberculosis [28]. If Phereoeca sp. serves as a passive carrier, it could contribute to bacterial dispersion within households, although the direct transmission risk remains speculative. Furthermore, bacteria like Pseudomonas fluorescens and Streptomyces griseus were known histamine producers and were not found at the species level, but their genera were detected, indicating the potential presence of other histamine-active strains. These findings underscore the importance of future functional assays to confirm bacterial activity and their possible link to skin sensitivity or allergies in humans.
It is important to emphasize that the present study does not establish a direct causal relationship between the detected bacterial taxa and human dermatological or inflammatory outcomes. The microbiome data generated here should be interpreted as exploratory and hypothesis-generating. Many of the identified bacteria are known environmental or commensal taxa that are widely distributed across indoor surfaces and arthropods. Therefore, their detection in Phereoeca larvae does not by itself demonstrate species-specific medical relevance. Targeted functional assays, controlled exposure studies, and clinical correlation will be necessary to determine whether any of these microbial associates contribute meaningfully to reported skin irritation cases.
The absence of environmental surface controls or comparative household insect samples in the present study limits our ability to determine whether the observed microbiome profile is unique to Phereoeca sp. or reflects broader indoor microbial backgrounds. Future investigations incorporating parallel sampling of household surfaces and sympatric indoor insects would provide valuable context for interpreting host specificity.
In addition, the assignment of M. tuberculosis based on short-read 16S rRNA data should be interpreted with caution, as this marker region may not reliably discriminate among closely related Mycobacterium taxa. The present study did not assess epidemiological links to tuberculosis exposure, and confirmatory approaches (e.g., targeted PCR, culture-based methods, or longer-read sequencing) would be required to validate this identification.
Possible histamine transmission via saliva or chewing activity
The idea that histamine or histamine-producing bacteria may be transmitted via insect oral secretions onto surfaces is plausible, especially considering larval feeding and movement patterns. Radwan-Oczko et al. [29] demonstrated the presence of histamine in saliva, particularly in autoimmune-related oral conditions, suggesting that oral bacteria can synthesize or trigger histamine release. If Phereoeca larvae deposit histamine on surfaces such as carpets, curtains, or clothing during feeding or pupation, human contact could lead to localized allergic reactions. Ribeiro [30] and Coutinho-Abreu et al. [31] have also shown that lepidopteran saliva can contain bioactive compounds with immunological effects. Additionally, Nässel [32] reported that histamine functions as a neurotransmitter in insects, indicating that it is physiologically active in their nervous systems and potentially present in body secretions.
This raises the hypothesis that bacterial symbionts in Phereoeca sp. may convert environmental or dietary histidine into histamine, which could accumulate on larval casing materials. Histamine production could be enhanced under certain environmental conditions, such as increased temperature or microbial load. As larvae often remain in fixed locations within households, repeated contact with contaminated casings may increase the likelihood of skin exposure. While this hypothesis is speculative, it aligns with the pattern of allergic symptoms reported online, though more rigorous clinical and biochemical testing is needed to establish causality. These insights provide a new direction for exploring insect-human interactions in urban ecosystems.
Prevalent and unidentified microbial species
Among the top 25 species identified in this study, the two most abundant were Methylobacterium-Methylorubrum (11.79%) and Burkholderia-Caballeronia-Paraburkholderia (10.99%), both classified as unknown at the species level. These bacteria are typically associated with environmental sources such as soil, plants, and water systems, suggesting potential environmental acquisition by Phereoeca larvae. Their roles in histamine production remain unclear, but their high abundance may indicate ecological importance in the larval microbiome. Additionally, Propionibacterium acnes (now classified as Cutibacterium acnes) was found at 3.11% and is a known human skin commensal linked to acne. Its presence on Phereoeca larvae suggests possible contamination from human contact or shared living environments.
Other environmental bacteria, such as Enhydrobacter aerosaccus and Mesorhizobium loti, were also detected, although their relevance to human or insect physiology is limited. These species are more commonly associated with aquatic environments and plant nodules, respectively, and may reflect incidental microbial colonization. While their functional role in Phereoeca sp. remains uncertain, their detection adds to the complexity of the insect’s microbiome, which appears to integrate both environmental and host-derived bacteria. The presence of these species highlights the need for future studies using metatranscriptomics or metabolomics to better understand their biological significance. Overall, these findings lay the foundation for further exploration of microbial diversity and its implications for insect ecology and human health.
Barcoding and metagenomic analyses revealed that the household casebearer species studied, Phereoeca sp., may pose potential health risks to humans due to the presence of histamine-producing bacteria. These bacteria are likely capable of synthesizing bioactive compounds, such as histamine, which can trigger irritation and inflammatory responses upon contact with human skin. However, further investigation is essential to identify the specific bacterial strains involved, their enzymatic pathways, and the exact mechanisms through which these compounds exert physiological effects. Confirming the species identity of Phereoeca sp. will not only contribute to taxonomic clarity but also support the development of effective and environmentally safe household pest management strategies.
From an applied perspective, the present findings provide a preliminary basis for improving household pest awareness and management of casebearer infestations in indoor environments. Although direct health impacts remain to be experimentally validated, the detection of bacteria with potential dermatological relevance highlights the importance of routine household hygiene, monitoring of casebearer presence, and proper cleaning of wall and fabric surfaces where larvae commonly occur. Enhanced taxonomic resolution of Malaysian Phereoeca populations may also support more targeted pest management strategies in the future. At the public health level, these results primarily serve as an early evidence framework to guide further interdisciplinary investigations rather than to justify immediate intervention measures.
It is important to note that this study was based on a limited number of samples collected from selected locations in Peninsular Malaysia and therefore does not aim to represent the full geographic diversity of Phereoeca populations across Malaysia, including Malaysian Borneo. The findings should thus be interpreted as an initial baseline assessment. Future studies incorporating larger sample sizes and wider geographic coverage are needed to better resolve population-level patterns [33,34,35,36,37].
Despite its small size, this casebearer species may represent an under-recognized component of indoor arthropod communities, underscoring the need for deeper ecological, microbiological, and toxicological studies to better understand its role in the urban environment.
Conclusions
This study presents the first combined molecular identification and microbiome survey of household casebearers collected from residential settings in Malaysia. COI barcoding indicates that the examined specimens form a distinct lineage within the genus Phereoeca, suggesting that the Malaysian population may represent an unresolved or potentially undescribed taxon. The 16S rRNA analysis revealed a diverse bacterial community dominated by Proteobacteria and Actinobacteriota, including several taxa that have previously been reported in contexts involving skin irritation or opportunistic infections. However, the present data do not demonstrate a direct causal link between Phereoeca larvae and human dermatological reactions, and many of the detected bacteria are commonly found in indoor environments and on other arthropods. The findings should therefore be viewed as preliminary. Further work, particularly functional assays, culture-based validation, and clinical correlation will be necessary to determine whether these insects contribute in any meaningful way to reported cases of household skin sensitivity. This study establishes a baseline for the taxonomy and microbial associations of Phereoeca in Malaysia and highlights the species as a still poorly studied member of indoor arthropod communities. Broader sampling and interdisciplinary follow-up studies will be important to better understand its ecological role and to clarify whether it has any verified relevance to indoor environmental health.
Supporting information
S1 Fig. Original uncropped and unadjusted gel image underlying Fig. 3a.
https://doi.org/10.1371/journal.pone.0346590.s001
(PDF)
S2 Fig. Original uncropped and unadjusted gel image underlying Fig. 3b.
https://doi.org/10.1371/journal.pone.0346590.s002
(PDF)
Acknowledgments
We also would like to thank Ms. Aqilah Sakinah Badrulisham and Mr. Muhammmad Ikhwan Idris for their help during the DNA extraction of samples.
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