Gut bacteria of the silkworm Bombyx mori facilitate host resistance against the toxic effects of organophosphate insecticides

Exposure to spaceflight enhances the virulence of Purpureocillium lilacinum against Tetranychus cinnabarinus: modulation of the host's enzyme activities and microbiome

Multiple studies have been conducted to investigate the impact of space conditions on human, plant, and microbial life. This research investigated the virulence of spaceflight mutants of the entomopathogenic fungus Purpureocillium lilacinum (HP7, HP36, HP52) and its original strain (SP535) against Tetranychus cinnabarinus as well as examination of the T. cinnabarinus immune response, including alterations in enzyme profiles and microbiome composition post fungal application. Our observations revealed contrasting, time-specific differences in pathogenicity and tissue infection between the ground-based isolate and spaceflight mutant isolates. Analysis of detoxifying and antioxidant enzymes showed a significant reduction in enzyme activities T. cinnabarinus infected with the most virulent spaceflight mutants at 36 h post-fungal infection, compared to ground-based isolates. Additionally, the microbiota was reduced due to a fungal infection, partly due to decreased antioxidant enzyme activities. Our findings indicate that changes in the microbiota of T. cinnabarinus following infection with P. lilacinum (both ground-based and spaceflight mutant isolates) resulted in variations in metabolism and genetic information-related KEGG pathways. This data can help identify potential changes in the host immune system that drive increased virulence after spaceflight mutation.

Enhanced bioaccumulation and toxicity of Fenpropathrin by polystyrene nano(micro)plastics in the model insect, silkworm (Bombyx mori)

BACKGROUND

Nano(micro)plastics (NMPs) and agrochemicals are ubiquitous pollutants. The small size and physicochemical properties of NMPs make them potential carriers for pollutants, affecting their bioavailability and impact on living organisms. However, little is known about their interactions in terrestrial ecosystems. This study investigates the adsorption of Fenpropathrin (FPP) onto two different sizes of polystyrene NMPs and examines their impacts on an insect model, silkworm Bombyx mori. We analyzed the systemic effects of acute exposure to NMPs and FPP, individually and combined, at organismal, tissue, cellular, and gut microbiome levels.

RESULTS

Our results showed that NMPs can adsorb FPP, with smaller particles having higher adsorption capacity, leading to size-dependent increases in the bioaccumulation and toxicity of FPP. These effects led to higher mortality, reduced body weight, delayed development, and decreased cocoon production in silkworms. Additionally, the pollutants caused physical and oxidative damage to the midgut and altered gene expression related to juvenile hormone (JH) and silk protein synthesis. The gut microbiome analysis revealed significant changes and reduced abundance of potentially beneficial bacteria. Thus, the aggravated toxicity induced by NMPs was size-dependent, with smaller particles (NPs) having a greater impact.

CONCLUSIONS

This study demonstrates the role of NMPs as carriers for contaminants, increasing their bioavailability and toxicity in terrestrial ecosystems. These findings have significant implications for ecosystem health and biodiversity.

Fungi on the cuticle surface increase the resistance of Aedes albopictus to deltamethrin

Aedes albopictus (Ae. albopictus) is widely distributed and can transmit many infectious diseases, and insecticide-based interventions play an important role in vector control. However, increased insecticide resistance has become a severe public health problem, and the clarification of its detailed mechanism is a matter of urgence. This study found that target-site resistance and metabolic resistance could not fully explain insecticide resistance in field Ae. albopictus, and there were likely other resistance mechanisms involved. The 16S and internal transcribed spacer sequencing revealed significant differences in the species compositions of the cuticle surface symbiotic bacteria and fungi between deltamethrin (DM)-resistant (DR) and DM-susceptible (DS) Ae. albopictus. Additionally, the abundances of Serratia spp. and Candida spp. significantly increased after DM treatment. Furthermore, 2 fungi (Rhodotorula mucilaginosa and Candida melibiosica) and 3 bacteria (Serratia marcescens, Klebsiella aerogenes, and Serratia sp.) isolated from DR Ae. albopictus can use DM as their sole carbon source. After reinoculation onto the cuticle surface of DS Ae. albopictus, R. mucilaginosa and C. melibiosica significantly enhanced the DM resistance of Ae. albopictus. Moreover, transcriptome sequencing of the surviving Ae. albopictus after DM exposure revealed that the gene expression of cytochrome P450 enzymes and glutathione-S-transferases increased, suggesting that besides the direct degradation, the candidate degrading microbes could also cause insecticide resistance via indirect enhancement of mosquito gene expression. In conclusion, we demonstrated that the cuticle surface symbiotic microbes were involved in the development of insecticide resistance in Ae. albopictus, providing novel and supplementary insights into insecticide resistance mechanisms.

The symbiont Wolbachia increases resistance to bifenthrin in Ectropis grisescens by regulating the host detoxification function

The global issue of insecticide resistance among pests is a major concern. Ectropis grisescens Warren (Lepidoptera: Geometridae), is a highly destructive leaf-eating pest distributed in tea plantations throughout China and Japan, and has exhibited resistance to various insecticides. Recent studies suggest that insect symbionts play a role in influencing insecticide resistance, however, their specific involvement in E. grisescens remains unclear. Here, we initially selected appropriate antibiotic mixtures at a concentration of 300 μg ml-1. The bioassay results showed that the insecticide susceptibility of the E. grisescens population treated with antibiotic mixtures significantly increased exposed to bifenthrin. Comparative analysis revealed that the LC50 value, survival rate, P450 enzyme activity, and relative content of Wolbachia in the E. grisescens population treated with 300 μg ml-1 tetracycline were notably lower than those treated with other antibiotics (ampicillin, gentamicin, and streptomycin). Moreover, the population treated with 2.5 mg ml-1 tetracycline exhibited even greater reductions in these parameters than the 300 μg ml-1 tetracycline-treated group. Additionally, 16S rRNA sequencing results showed a significant decrease in xenobiotics metabolism by cytochrome P450 in the E. grisescens population treated with 2.5 mg ml-1 tetracycline. Transcriptome analysis showed a significant down-regulation of two cytochrome P450 genes in E. grisescens population without Wolbachia. These results suggest that Wolbachia may contribute to the resistance of E. grisescens to bifenthrin by regulating cytochrome P450 genes, providing a foundation for further study on the mechanism of symbiont-mediated host detoxification metabolism in insect pests.

De Novo Genome Assembly and Annotation for the Synanthropic Webbing Clothes Moth (Tineola bisselliella): A Globally Distributed, Economically Important Pest

Tineola bisselliella, the webbing clothes moth, is an economically important, globally distributed synanthropic pest species and member of the basal moth lineage Tineidae. These moths are facultatively keratinophagous, and their larvae can cause extensive damage, particularly to clothing, textiles, and museum specimens. Despite the economic and phylogenetic importance of T. bisselliella, there is a lack of quality genomic resources for this, or for other species within the Tineidae family. The T. bisselliella genome assembly presented here consists of 30 pseudochromosomes (29 autosomes and 1 Z chromosome) produced using synteny alignment of a preliminary contig-level assembly (256 contigs) to a closely related species, Tinea pellionella. The resulting final pseudochromosome-level assembly is 243.630 Mb and has an N50 length of 8.708 Mb. The assembly is highly contiguous and has similar or improved quality compared to other available Tineidae genomes, with 93.1% (91.8% single copy and 1.3% duplicated) of lepidopteran orthologs complete and present. Annotation of the pseudochromosome-level genome assembly with the transcriptome we produced ultimately yielded 11,259 annotated genes. Synteny alignments between the T. bisselliella genome assembly and other Tineidae genomes revealed evidence for numerous small rearrangements with high synteny conservation. In contrast, a synteny alignment performed between T. bisselliella and Melitaea cinxia, which is thought to have retained the ancestral karyotype (n = 31), revealed a fusion of the ancestral autosome 30 and Z chromosome that led to a reduction in T. bisselliella karyotype size. The reference quality annotated genome for T. bisselliella presented here will advance our understanding of the evolution of the lepidopteran karyotype by providing a chromosome-level genome for this basal moth lineage and provide future insights into the mechanisms underlying keratin digestion in T. bisselliella.

Insects and microbes: best friends from the nursery

Insects host microbes and interact with them throughout their life cycle. This microbiota is an important, if not essential, partner participating in many aspects of insect physiology. Recent omics studies have contributed to considerable advances in the current understanding of the molecular implications of microbiota during insect development. In this review, we present an overview of the current knowledge about the mechanisms underlying interactions between developing insects and their microbial companions. The microbiota is implicated in nutrition, both via compensating for metabolic pathways lacking in the host and via regulating host metabolism. Furthermore, the microbiota plays a protective role, enhancing the insect's tolerance to, or resistance against, various environmental stresses.

Root inoculation with soil-borne microorganisms alters gut bacterial communities and performance of the leaf-chewer Spodoptera exigua

Soil-borne microorganisms can impact leaf-chewing insect fitness by modifying plant nutrition and defence. Whether the altered insect performance is linked to changes in microbial partners of caterpillars remains unclear. We investigated the effects of root inoculation with soil bacteria or fungi on the gut bacterial community and biomass of the folivore Spodoptera exigua. We also explored the potential correlation between both parameters. We performed herbivory bioassay using leaves of tomato plants (Solanum lycopersicum), measured caterpillar weight gain and characterized the gut bacterial communities via 16S rRNA gene metabarcoding. All soil microbes modified the gut bacterial communities, but the extent of these changes depended on the inoculated species. Rhizophagus irregularis and Bacillus amyloliquefaciens had opposite effects on S. exigua weight. While plant inoculation with the fungus influenced gut bacterial diversity, B. amyloliquefaciens also affected the community composition. A reduced abundance of two S. exigua enterococcal symbionts correlated with decreased insect biomass. Our results show that soil microorganisms can induce plant-mediated changes in the gut bacterial community of foliar-feeding caterpillars. We propose that the impact of these alterations on insect performance might rely on specific adaptations within the gut bacteria, rather than solely on the occurrence of changes.

Improving the mechanical property of silk by feeding silkworm with chiral carbon dots

The influence of chiral materials on organisms is crucial. However, there is little research on the impact of chiral carbon dots (CDs), a kind of typical chiral materials, on biology. Herein, chiral CDs (L-/D-CDs) were synthesized using the thermal polymerization method from citric acid and chiral cysteine. The effect of chiral CDs on silkworms was explored through feeding silkworms with chiral CDs. The breaking strength of silk fibers (667.9 MPa) in D-CDs group exhibit a 71.4 % increase compared with control-silk (389.5 MPa), while the breaking strength of silk fibers in L-CDs group increases by 51.6 %. In addition, Fourier transform infrared spectra display CDs can prevent the transformation from random coil/α-helix structures to β-sheet structures. Furthermore, D-CDs group exhibit the highest percentage of four primary amino acids (glycine, alanine, serine, and tyrosine) relative to the total amino acids in silkworm hemolymph. This percentage is elevated by 70.5 % compared to the control group, thereby furnishing an ample supply of raw materials for the synthesis of silk proteins. In contrast, L-CDs group exhibit increase by 39.3 %. Our work provides new ideas and approaches for studying the effects of chiral materials on living organisms.

Functions and regulations of insect gut bacteria

The insect gut is a complicated ecosystem that inhabits a large number of symbiotic bacteria. As an important organ of the host insect, the symbiotic bacteria of the insect gut play very important roles in regulating physiological and metabolic processes. Recently, much progress has been made in the study of symbiotic bacteria in insect guts with the development of high-throughput sequencing technology and molecular biology. This review summarizes the primary functions of symbiotic bacteria in insect guts, such as enhancing insecticide resistance, facilitating food digestion, promoting detoxification, and regulating mating behavior and egg hatching. It also addresses some possible pathways of gut bacteria symbiont regulation governed by external habitats, physiological conditions and immunity of the host insect. This review provides solid foundations for further studies on novel theories, new technologies and practical applications of symbiotic bacteria in insect guts. © 2024 Society of Chemical Industry.

Adaptability of the gut microbiota of the German cockroach Blattella germanica to a periodic antibiotic treatment

High-throughput sequencing studies have shown that diet or antimicrobial treatments impact animal gut microbiota equilibrium. However, properties related to the gut microbial ecosystem stability, such as resilience, resistance, or functional redundancy, must be better understood. To shed light on these ecological processes, we combined advanced statistical methods with 16 S rRNA gene sequencing, functional prediction, and fitness analyses in the gut microbiota of the cockroach Blattella germanica subject to three periodic pulses of the antibiotic (AB) kanamycin (n=512). We first confirmed that AB did not significantly affect cockroaches' biological fitness, and gut microbiota changes were not caused by insect physiology alterations. The sex variable was examined for the first time in this species, and no statistical differences in the gut microbiota diversity or composition were found. The comparison of the gut microbiota dynamics in control and treated populations revealed that (1) AB treatment decreases diversity and completely disrupts the co-occurrence networks between bacteria, significantly altering the gut community structure. (2) Although AB also affected the genetic composition, functional redundancy would explain a smaller effect on the functional potential than on the taxonomic composition. (3) As predicted by Taylor's law, AB generally affected the most abundant taxa to a lesser extent than the less abundant taxa. (4) Taxa follow different trends in response to ABs, highlighting "resistant taxa," which could be critical for community restoration. (5) The gut microbiota recovered faster after the three AB pulses, suggesting that gut microbiota adapts to repeated treatments.

The humoral immune response of the lepidopteran model insect, silkworm Bombyx mori L., to microbial pathogens

Insects are valuable models for studying innate immunity and its role in combating infections. The silkworm Bombyx mori L., a well-studied insect model, is susceptible to a range of pathogens, including bacteria, fungi, viruses, and microsporidia. Their susceptibility makes it a suitable model for investigating host-pathogen interactions and immune responses against infections and diseases. This review focuses on the humoral immune response and the production of antimicrobial peptides (AMPs), the phenoloxidase (PO) system, and other soluble factors that constitute the primary defense of silkworms against microbial pathogens. The innate immune system of silkworms relies on pattern recognition receptors (PRRs) to recognize pathogen-associated molecular patterns (PAMPs), which then activate various immune pathways including Imd, Toll, JAK/STAT, and RNA interference (RNAi). Their activation triggers the secretion of AMPs, enzymatic defenses (lysozyme and PO), and the generation of reactive oxygen species (ROS). Collectively, these pathways work together to neutralize and eliminate pathogens, thereby contributing to the defense mechanism of silkworms. Understanding the innate immunity of silkworms can uncover conserved molecular pathways and key immune components shared between insects and vertebrates. Additionally, it can provide valuable insights for improving sericulture practices, developing strategies to control diseases affecting silk production, and providing a theoretical foundation for developing pest control measures.

Role of Enterococcus mundtii in gut of the tomato leaf miner (Tuta absoluta) to detoxification of Chlorantraniliprole

Chlorantraniliprole (CAP) is applied worldwide for the control of caterpillars (Lepidoptera). However, with the overuse of CAP, the resistance problem in pest control is becoming increasingly serious. Recent studies have indicated a central role of the gut symbiont in insect pest resistance to pesticides and these may apply to the tomato leaf miner Tuta absoluta, is one of the most destructive insects worldwide. Here, we successfully isolated seven strains of tolerant CAP bacterium from the CAP-resistant T. absoluta gut, of which Enterococcus mundtii E14 showed the highest CAP tolerance, with a minimum inhibitory concentration (MIC) of 1.6 g/L and CAP degradation rate of 42.4%. Through transcriptomics and metabolism analysis, we studied the detoxification process of CAP by the E. mundtii E14, and found that CAP can be degraded by E. mundtii E14 into non-toxic compounds, such as 3,4-dihydroxy-2-(5-hydroxy-3,7-dimethylocta-2,6-dien-1-yl) benzoic acid and 2-pyridylacetic acid. Additionally, 2-pyridylacetic acid was detected both intracellular and extracellular in E. mundtii E14 treated with CAP. Meanwhile, we identified 52 up-regulated genes, including those associated with CAP degradation, such as RS11670 and RS19130. Transcriptome results annotated using KEGG indicated significant enrichment in up-regulated genes related to the glyoxylate cycle, nitrogen metabolism, and biosynthesis of secondary metabolites. Additionally, we observed that reinfection with E. mundtii E14 may effectively enhance resistance of T. absoluta to CAP. The LC50 values of the antibiotic treatment population of T. absoluta reinfection with E. mundtii E14 is 0.6122 mg/L, which was 18.27 folds higher than before reinfection. These findings offer new insights into T. absoluta resistance to CAP and contribute to a better understanding of the relationship between insecticide resistance and gut symbionts of T. absoluta, which may play a pivotal role in pest management.

Composition and Diversity of Gut Bacterial Community in Different Life Stages of Osmia excavata Alfken (Hymenoptera: Megachilidae)

Osmia excavata is an excellent pollinator in nature and plays a vital role in the conservation of agro-ecosystems and food security. Given the important role of the gut bacterial community in host health and regulation of host growth and development, using 16S rRNA gene sequencing data, the present study explored the composition of the gut bacterial community and its diversity at different life stages (eggs, young larvae, old larvae, young pupae, old pupae, and 1-day-old adults in cocoons) of the solitary bee Osmia excavata. The results showed that the core phyla in the gut of O. excavata at different life stages were Proteobacteria, Firmicutes, Bacteroidota, and Actinobacteriota, and the core genera were Sodalis, Tyzzerella, and Ralstonia. The highest intestinal bacterial diversity was found in the Egg period, and the lowest bacterial alpha diversity was found in the 1-day-old Adult period; the bacterial diversity of O. excavata showed a process of decreasing, as it was growing from the Egg period to the 1-day-old Adult period. Our study found that O. excavata undergoes a significant change in the structure of the gut flora when it grows from the young pupae to old pupae stage, a period of growth that coincides with the process of cocooning and isolation from the external environment after food depletion. This suggests that food and environmental factors are key contributors to the structure of the bacterial community in the gut of solitary bees.

Bacterial Symbionts Contribute to Insecticide Susceptibility of Diaphorina citri via Changing the Expression Level of Host Detoxifying Genes

Insecticide susceptibility is mainly determined by the insect host, but symbiotic bacteria are also an important affecting factor. In this study, we investigate the relationship between the structure of gut bacterial symbionts and insecticide susceptibility in Diaphorina citri, the important carrier of Candidatus Liberibacter asiaticus (CLas), the causal agent of Huanglongbing (HLB). Our results indicated that antibiotic treatment significantly increased the susceptibility of D. citri to bifenthrin and thiamethoxam, and significantly decreased the relative abundance of Wolbachia and Profftella, enzyme activities of CarEs, and expression level of multiple CarE genes. The relative loads of Wolbachia and Profftella were positively correlated with DcitCCE13, DcitCCE14, DcitCCE15, and DcitCCE16. RNAi and prokaryotic expression revealed that DcitCCE15 is associated with bifenthrin metabolism. These results revealed that bacterial symbionts might regulate DcitCCE15 expression, which is involved in the susceptibility of D. citri to bifenthrin.

Effects of baculovirus infection on intestinal microflora of BmNPV resistant and susceptible strain silkworm

Bombyx mori L. (Lepidoptera: Bombycidae) nucleopolyhedrovirus (BmNPV) is a serious pathogen causing huge economic losses to sericulture. There is growing evidence that the gut microbiota of silkworms plays a critical role in shaping host responses and interactions with viral infection. However, little is known about the differences in the composition and diversity of intestinal microflora, especially with respect to silkworm strain differences and BmNPV infection-induced changes. Here, we aim to explore the differences between BmNPV-resistant strain A35 and susceptible strain P50 silkworm and the impact of BmNPV infection on intestinal microflora in different strains. The 16S rDNA sequencing analysis revealed that the fecal microbial populations were distinct between A35 and P50 and were significantly changed post BmNPV infection in both strains. Further analysis showed that the BmNPV-resistant strain silkworm possessed higher bacterial diversity than the susceptible strain, and BmNPV infection reduced the diversity of intestinal flora assessed by feces in both silkworm strains. In response to BmNPV infection, the abundance of Muribaculaceae increased in P50 and decreased in A35, while the abundance of Enterobacteriaceae decreased in P50 and increased in A35. These results indicated that BmNPV infection had various effects on the abundance of fecal microflora in different silkworm strains. Our findings not only broadened the understanding of host-pathogen interactions but also provided theoretical help for the breeding of resistant strains and healthy rearing of silkworms based on symbiotic bacteria.

Toxic mechanism in Daphnia magna due to phthalic acid esters and CuO nanoparticles co-exposure: The insight of physiological, microbiomic and metabolomic profiles

Various phthalic acid esters (PAEs) such as dibutyl phthalate (DBP) and butyl benzyl phthalate (BBP) co-exist with nanopollutants in aquatic environment. In this study, Daphnia magna was exposed to nano-CuO and DBP or BBP at environmental relevant concentrations for 21-days to investigate these combined toxic effects. Acute EC50 values (48 h) of nano-CuO, DBP, and BBP were 12.572 mg/L, 8.978 mg/L, and 4.785 mg/L, respectively. Results showed that co-exposure with nano-CuO (500 μg/L) for 21 days significantly enhanced the toxicity of DBP (100 μg/L) and BBP (100 μg/L) to Daphnia magna by 18.37% and 18.11%, respectively. The activities of superoxide dismutase, catalase, and glutathione S-transferase were enhanced by 10.95% and 14.07%, 25.63% and 25.91%, and 39.93% and 35.01% in nano-CuO+DBP and nano-CuO+BBP treatments as compared to the individual exposure groups, verifying that antioxidative defense responses were activated. Furthermore, the co-exposure of nano-CuO and PAEs decreased the population richness and diversity microbiota, and changed the microbial community composition in Daphnia magna. Metabolomic analysis elucidated that nano-CuO + PAEs exposure induced stronger disturbance on metabolic network and molecular function, including amino acid, nucleotides, and lipid metabolism-related metabolic pathways, as comparison to PAEs single exposure treatments. In summary, the integration of physiological, microflora, and untargeted metabolomics analysis offers a fresh perspective into the potential ecological risk associated with nanopollutants and phthalate pollution in aquatic ecosystems.

Insects to the rescue? Insights into applications, mechanisms, and prospects of insect-driven remediation of organic contaminants

Traditional and emerging contaminants pose significant human and environmental health risks. Conventional physical, chemical, and bioremediation techniques have been extensively studied for contaminant remediation. However, entomo- or insect-driven remediation has received limited research and public attention. Entomo-remediation refers to the use of insects, their associated gut microbiota, and enzymes to remove or mitigate organic contaminants. This novel approach shows potential as an eco-friendly method for mitigating contaminated media. However, a comprehensive review of the status, applications, and challenges of entomo-remediation is lacking. This paper addresses this research gap by examining and discussing the evidence on entomo-remediation of various legacy and emerging organic contaminants. The results demonstrate the successful application of entomo-remediation to remove legacy organic contaminants such as persistent organic pollutants. Moreover, entomo-remediation shows promise in removing various groups of emerging contaminants, including microplastics, persistent and emerging organic micropollutants (e.g., antibiotics, pesticides), and nanomaterials. Entomo-remediation involves several insect-mediated processes, including bio-uptake, biotransfer, bioaccumulation, and biotransformation of contaminants. The mechanisms underlying the biotransformation of contaminants are complex and rely on the insect gut microbiota and associated enzymes. Notably, while insects facilitate the remediation of contaminants, they may also be exposed to the ecotoxicological effects of these substances, which is often overlooked in research. As an emerging field of research, entomo-remediation has several knowledge gaps. Therefore, this review proposes ten key research questions to guide future perspectives and advance the field. These questions address areas such as process optimization, assessment of ecotoxicological effects on insects, and evaluation of potential human exposure and health risks.

Cereal leaf beetle-associated bacteria enhance the survival of their host upon insecticide treatments and respond differently to insecticides with different modes of action

The cereal leaf beetle (CLB, Oulema melanopus) is one of the major cereal pests. The effect of insecticides belonging to different chemical classes, with different mechanisms of action and the active substances' concentrations on the CLB bacterial microbiome, was investigated. Targeted metagenomic analysis of the V3-V4 regions of the 16S ribosomal gene was used to determine the composition of the CLB bacterial microbiome. Each of the insecticides caused a decrease in the abundance of bacteria of the genus Pantoea, and an increase in the abundance of bacteria of the genus Stenotrophomonas, Acinetobacter, compared to untreated insects. After cypermethrin application, a decrease in the relative abundance of bacteria of the genus Pseudomonas was noted. The dominant bacterial genera in cypermethrin-treated larvae were Lactococcus, Pantoea, while in insects exposed to chlorpyrifos or flonicamid it was Pseudomonas. Insecticide-treated larvae were characterized, on average, by higher biodiversity and richness of bacterial genera, compared to untreated insects. The depletion of CLB-associated bacteria resulted in a decrease in larval survival, especially after cypermethrin and chlorpyrifos treatments. The use of a metagenome-based functional prediction approach revealed a higher predicted function of bacterial acetyl-CoA C-acetyltransferase in flonicamid and chlorpyrifos-treated larvae and tRNA dimethyltransferase in cypermethrin-treated insects than in untreated insects.

Multiomics analysis reveals the molecular basis for increased body weight in silkworms (Bombyx mori) exposed to environmental concentrations of polystyrene micro- and nanoplastics

INTRODUCTION

Micro- and nanoplastics (MNPs) are emerging environmental pollutants that have raised serious concerns about their potential impact on ecosystem and organism health. Despite increasing efforts to investigate the impacts of micro- and nanoplastics (MNPs) on biota little is known about their potential impacts on terrestrial organisms, especially insects, at environmental concentrations.

OBJECTIVES

To address this gap, we used an insect model, silkworm Bombyx mori to examine the potential long-term impacts of different sizes of polystyrene (PS) MNPs at environmentally realistic concentrations (0.25 to 1.0 μg/mL).

METHODS

After exposure to PS-MNPs over most of the larval lifetime (from second to last instar), the endpoints were examined by an integrated physiological (growth and survival) and multiomics approach (metabolomics, 16S rRNA, and transcriptomics).

RESULTS

Our results indicated that dietary exposures to PS-MNPs had no lethal effect on survivorship, but interestingly, increased host body weight. Multiomics analysis revealed that PS-MNPs exposure significantly altered multiple pathways, particularly lipid metabolism, leading to enriched energy reserves. Furthermore, the exposure changed the structure and composition of the gut microbiome and increased the abundance of gut bacteria Acinetobacter and Enterococcus. Notably, the predicted functional profiles and metabolite expressions were significantly correlated with bacterial abundance. Importantly, these observed effects were particle size-dependent and were ranked as PS-S (91.92 nm) > PS-M (5.69 µm) > PS-L (9.7 µm).

CONCLUSION

Overall, PS-MNPs at environmentally realistic concentrations exerted stimulatory effects on energy metabolism that subsequently enhanced body weight in silkworms, suggesting that chronic PS-MNPs exposure might trigger weight gain in animals and humans by influencing host energy and microbiota homeostasis.

Purple acid phosphatase promoted hydrolysis of organophosphate pesticides in microalgae

When organophosphate pesticides (OPs) are not used and handled in accordance with the current rules and standards, it results in serious threats to the aquatic environment and human health. Phaeodactylum tricornutum is a prospective microalgae-based system for pollutant removal and carbon sequestration. Genetically engineered P. tricornutum, designated as the OE line (endogenously expressing purple acid phosphatase 1 [PAP1]), can utilize organic phosphorus for cellular metabolism. However, the competencies and mechanisms of the microalgae-based system (namely the OE line of P. tricornutum) for metabolizing OPs remain to be addressed. In this study, the OE line exhibited the effective biodegradation competencies of 72.12% and 68.2% for 30 mg L-1 of dichlorvos and 50 mg L-1 of glyphosate, accompanied by synergistic accumulations of biomass (0.91 and 0.95 g L-1) and lipids (32.71% and 32.08%), respectively. Furthermore, the biodiesel properties of the lipids from the OE line manifested a high potential as an alternative feedstock for microalgae-based biofuel production. A plausible mechanism of OPs biodegraded by overexpressed PAP1 is that sufficient inorganic P for adenosine triphosphate and concurrent carbon flux for the reduced form of nicotinamide adenine dinucleotide phosphate biosynthesis, which improved the OP tolerance and biodegradation competencies by regulating the antioxidant system, delaying programmed cell death and accumulating lipids via the upregulation of related genes. To sum up, this study demonstrates a potential strategy using a genetically engineered strain of P. tricornutum to remove high concentrations of OPs with the simultaneous production of biomass and biofuels, which might provide novel insights for microalgae-based pollutant biodegradation.

From phyllosphere to insect cuticles: silkworms gather antifungal bacteria from mulberry leaves to battle fungal parasite attacks

BACKGROUND

Bacterial transfers from plants to insect herbivore guts have been well investigated. However, bacterial exchanges between plant phyllospheres and insect cuticles remain unclear, as does their related biological function.

RESULTS

Here, we report that the cuticular bacterial loads of silkworm larvae quickly increased after molting and feeding on the white mulberry (Morus alba) leaves. The isolation and examination of silkworm cuticular bacteria identified one bacterium Mammaliicoccus sciuri that could completely inhibit the spore germination of fungal entomopathogens Metarhizium robertsii and Beauveria bassiana. Interestingly, Ma. sciuri was evident originally from mulberry leaves, which could produce a secreted chitinolytic lysozyme (termed Msp1) to damage fungal cell walls. In consistency, the deletion of Msp1 substantially impaired bacterial antifungal activity. Pretreating silkworm larvae with Ma. sciuri cells followed by fungal topical infections revealed that this bacterium could help defend silkworms against fungal infections. Unsurprisingly, the protective efficacy of ΔMsp1 was considerably reduced when compared with that of wild-type bacterium. Administration of bacterium-treated diets had no negative effect on silkworm development; instead, bacterial supplementation could protect the artificial diet from Aspergillus contamination.

CONCLUSIONS

The results of this study evidence that the cross-kingdom transfer of bacteria from plant phyllospheres to insect herbivore cuticles can help protect insects against fungal parasite attacks. Video Abstract.

Effects of Habitual Dietary Change on the Gut Microbiota and Health of Silkworms

Diet plays a crucial role in shaping the gut microbiota and overall health of animals. Traditionally, silkworms are fed fresh mulberry leaves, and artificial diets do not support good health. The aim of this study was to explore the relationship between the dietary transition from artificial diets to mulberry leaves and the effects on the gut microbiota and physiological changes in silkworms as a model organism. With the transition from artificial diets to mulberry leaves, the diversity of the silkworm gut microbiota increased, and the proportion of Enterococcus and Weissella, the dominant gut bacterial species in silkworms reared on artificial diets, decreased, whereas the abundance of Achromobacter and Rhodococcus increased. Dietary transition at different times, including the third or fifth instar larval stages, resulted in significant differences in the growth and development, immune resistance, and silk production capacity of silkworms. These changes might have been associated with the rapid adaptation of the intestinal microbiota of silkworms to dietary transition. This study preliminarily established a dietary transition-gut microbial model in silkworms based on the conversion from artificial diets to mulberry leaves, thus providing an important reference for future studies on the mechanisms through which habitual dietary changes affect host physiology through the gut microbiome.

Toward an Integrated Understanding of the Lepidoptera Microbiome

Research over the past 30 years has led to a widespread acceptance that insects establish widespread and diverse associations with microorganisms. More recently, microbiome research has been accelerating in lepidopteran systems, leading to a greater understanding of both endosymbiont and gut microorganisms and how they contribute to integral aspects of the host. Lepidoptera are associated with a robust assemblage of microorganisms, some of which may be stable and routinely detected in larval and adult hosts, while others are ephemeral and transient. Certain microorganisms that populate Lepidoptera can contribute significantly to the hosts' performance and fitness, while others are inconsequential. We emphasize the context-dependent nature of the interactions between players. While our review discusses the contemporary literature, there are major avenues yet to be explored to determine both the fundamental aspects of host-microbe interactions and potential applications for the lepidopteran microbiome; we describe these avenues after our synthesis.

Lactic acid bacteria modulate the CncC pathway to enhance resistance to β-cypermethrin in the oriental fruit fly

The gut microbiota of insects has been shown to regulate host detoxification enzymes. However, the potential regulatory mechanisms involved remain unknown. Here, we report that gut bacteria increase insecticide resistance by activating the cap "n" collar isoform-C (CncC) pathway through enzymatically generated reactive oxygen species (ROS) in Bactrocera dorsalis. We demonstrated that Enterococcus casseliflavus and Lactococcus lactis, two lactic acid-producing bacteria, increase the resistance of B. dorsalis to β-cypermethrin by regulating cytochrome P450 (P450) enzymes and α-glutathione S-transferase (GST) activities. These gut symbionts also induced the expression of CncC and muscle aponeurosis fibromatosis. BdCncC knockdown led to a decrease in resistance caused by gut bacteria. Ingestion of the ROS scavenger vitamin C in resistant strain affected the expression of BdCncC/BdKeap1/BdMafK, resulting in reduced P450 and GST activity. Furthermore, feeding with E. casseliflavus or L. lactis showed that BdNOX5 increased ROS production, and BdNOX5 knockdown affected the expression of the BdCncC/BdMafK pathway and detoxification genes. Moreover, lactic acid feeding activated the ROS-associated regulation of P450 and GST activity. Collectively, our findings indicate that symbiotic gut bacteria modulate intestinal detoxification pathways by affecting physiological biochemistry, thus providing new insights into the involvement of insect gut microbes in the development of insecticide resistance.

A Diet with Amikacin Changes the Bacteriobiome and the Physiological State of Galleria mellonella and Causes Its Resistance to Bacillus thuringiensis

Environmental pollution with antibiotics can cause antibiotic resistance in microorganisms, including the intestinal microbiota of various insects. The effects of low-dose aminoglycoside antibiotic (amikacin) on the resident gut microbiota of Galleria mellonella, its digestion, its physiological parameters, and the resistance of this species to bacteria Bacillus thuringiensis were investigated. Here, 16S rDNA analysis revealed that the number of non-dominant Enterococcus mundtii bacteria in the eighteenth generation of the wax moth treated with amikacin was increased 73 fold compared to E. faecalis, the dominant bacteria in the native line of the wax moth. These changes were accompanied by increased activity of acidic protease and glutathione-S-transferase in the midgut tissues of larvae. Ultra-thin section electron microscopy detected no changes in the structure of the midgut tissues. In addition, reduced pupa weight and resistance of larvae to B. thuringiensis were observed in the eighteenth generation of the wax moth reared on a diet with amikacin. We suggest that long-term cultivation of wax moth larvae on an artificial diet with an antibiotic leads to its adaptation due to changes in both the gut microbiota community and the physiological state of the insect organism.

Comparative metaproteomics reveal co-contribution of onion maggot and its gut microbiota to phoxim resistance

Pesticide resistance inflicts significant economic losses on a global scale each year. To address this pressing issue, substantial efforts have been dedicated to unraveling the resistance mechanisms, particularly the newly discovered microbiota-derived pesticide resistance in recent decades. Previous research has predominantly focused on investigating microbiota-derived pesticide resistance from the perspective of the pest host, associated microbes, and their interactions. However, a gap remains in the quantification of the contribution by the pest host and associated microbes to this resistance. In this study, we investigated the toxicity of phoxim by examining one resistant and one sensitive Delia antiqua strain. We also explored the critical role of associated microbiota and host in conferring phoxim resistance. In addition, we used metaproteomics to compare the proteomic profile of the two D. antiqua strains. Lastly, we investigated the activity of detoxification enzymes in D. antiqua larvae and phoxim-degrading gut microbes, and assessed their respective contributions to phoxim resistance in D. antiqua. The results revealed contributions by D. antiqua and its gut bacteria to phoxim resistance. Metaproteomics showed that the two D. antiqua strains expressed different protein profiles. Detoxifying enzymes including Glutathione S-transferases, carboxylesterases, Superoxide Dismutase, Glutathione Peroxidase, and esterase B1 were overexpressed in the resistant strain and dominated in differentially expressed insect proteins. In addition, organophosphorus hydrolases combined with a group of ABC type transporters were overexpressed in the gut microbiota of resistant D. antiqua compared to the sensitive strain. 85.2% variation of the larval mortality resulting from phoxim treatment could be attributed to the combined effects of proteins from both from gut bacteria and D. antiqua, while the individual contribution of proteins from gut bacteria or D. antiqua alone accounted for less than 10% of the variation in larval mortality caused by phoxim. The activity of the overexpressed insect enzymes and the phoxim-degrading activity of gut bacteria in resistant D. antiqua larvae were further confirmed. This work enhances our understanding of microbiota-derived pesticide resistance and illuminates new strategies for controlling pesticide resistance in the context of insect-microbe mutualism.

Comparative analysis of gut bacteria of silkworm Bombyx mori L. on exposure to temperature through 16S rRNA high throughput metagenomic sequencing

Global warming is one of the serious threats that adversely affects the development and reproduction of silkworms. The ideal temperature for silkworms to carryout normal life activities is 20-30 °C. Certain bivoltine silkworms that are raised in tropical regions are thermotolerant. But, prolonged exposure to high temperatures may be fatal. In the present study, fifth instar larvae of bivoltine silkworm were exposed to heat shock at 40 ± 2 °C for a short period of one hour per day to examine the changes in the gut microflora. The study used high throughput sequencing to evaluate the impact of intestinal microbes of silkworms in response to high temperature. The findings demonstrated that elevated temperature has a negative impact on the intestinal microbes of silkworm compared to the control which were reared under the optimum temperature (25 ± 3° C). Four hundred and fifty eight (458) species of microbes were reported in the control group whereas only 434 species were reported in the temperature exposed group. The digestive process of silkworms may also be impaired by heat shock due to their effect on digestive enzymes. So, the results indicated that heat shock has an impact on the intestinal microflora of silkworms that control the activity of associated digestive enzymes which affects the digestion and nutritional intake, eventually impacting the growth and development of silkworm larvae and cocoons produced. The morphometric parameters of silkworm larvae and cocoons also showed a considerable drop when exposed to heat shock.

Feeding Spodoptera exigua larvae with gut-derived Escherichia sp. increases larval juvenile hormone levels inhibiting cannibalism

Feed quality influences insect cannibalistic behavior and gut microbial communities. In the present study, Spodoptera exigua larvae were fed six different artificial diets, and one of these diets (Diet 3) delayed larval cannibalistic behavior and reduced the cannibalism ratio after ingestion. Diet 3-fed larvae had the highest gut bacterial load (1.396 ± 0.556 × 1014 bacteria/mg gut), whereas Diet 2-fed larvae had the lowest gut bacterial load (3.076 ± 1.368 × 1012 bacteria/mg gut). The gut bacterial composition and diversity of different diet-fed S. exigua larvae varied according to the 16S rRNA gene sequence analysis. Enterobacteriaceae was specific to the Diet 3-fed larval gut. Fifteen culturable bacterial isolates were obtained from the midgut of Diet 3-fed larvae. Of these, ten belonged to Escherichia sp. After administration with Diet 1- or 2-fed S. exigua larvae, two bacterial isolates (SePC-12 and -37) delayed cannibalistic behavior in both tested larval groups. Diet 2-fed larvae had the lowest Juvenile hormone (JH) concentration and were more aggressive against intraspecific predation. However, SePC-12 loading increased the JH hormone levels in Diet 2-fed larvae and inhibited their cannibalism. Bacteria in the larval midgut are involved in the stabilization of JH levels, thereby regulating host larval cannibalistic behavior.

Function of Cytochrome P450s and Gut Microbiome in Biopesticide Adaptation of Grapholita molesta on Different Host Diets

Insects that feed on various host plants possess diverse xenobiotic adaptations; however, the underlying mechanisms are poorly understood. In the present study, we used Grapholita molesta, which shifts feeding sites from peach shoots to apple fruits, as a model to explore the effects of shifts in host plant diet on the profiles of cytochrome P450s and the gut bacteria microbiome, as well as their effects on biopesticide adaptation. We found that the sensitivity of the fruit-feeding G. molesta to emamectin benzoate biopesticide was significantly lower than that of the shoot-feeding larvae. We also found that the P450 enzyme activity and the expression of nine cytochrome P450s were enhanced in G. molesta fed on Fuji apples compared to those fed on peach shoots. The survival rates of G. molesta exposed to emamectin benzoate significantly decreased as each of three of four emamectin benzoate-inducted cytochrome P450 genes were silenced. Furthermore, we discovered the gut bacteria dynamics of G. molesta changed with the host shift and the structure of the gut bacteria microbiome was determined by the final diet ingested; additionally, the dysbiosis of the gut microbiota induced by antibiotics could significantly increase the sensitivity to emamectin benzoate. Taken together, our results suggest that the expression of P450s and the composition of the gut bacteria microbiome promote adaptation to emamectin benzoate in G. molesta, providing new insights into the molecular mechanisms underlying xenobiotic adaptation in this notorious pest.

Rapid response of midgut bacteria in Bactrocera tau (Walker) (Diptera: Tephritidae) to lambda-cyhalothrin- and spinosad-induced stress

In recent decades, the increasingly widespread application of chemical pesticides has exacerbated the emergence of insecticide resistance among insect pests. In this study, we examined the rapid response of bacteria in the midgut of the fruit fly Bactrocera tau (Walker) (Diptera: Tephritidae) to stress induced by the insecticides lambda-cyhalothrin and spinosad by analyzing the bacterial community structure and diversity in the midguts of 4-day-old B. tau. The results revealed that 4-day-old B. tau females were more resistant to lambda-cyhalothrin and spinosad than their 4-day-old male counterparts. Alpha- and beta-diversity analyses revealed no significant differences between male and female B. tau with respect to the diversity and richness of gut bacteria in response to the same treatments. In response to treatment with lambda-cyhalothrin and spinosad at lethal concentration 50 (LC50), we detected significant changes in the structure and diversity of the bacterial community in the midguts of both male and female B. tau. Particularly among the dominant bacterial genera, there were decreases in the relative abundances of Citrobacter, Enterobacter, Klebsiella, and Pectobacterium. Increases were observed in the relative abundances of Dysgonomonas, Erwinia, and Providencia. Our findings provide a theoretical basis for gaining a better understanding of the relationships between midgut bacteria and the insecticide resistance of B. tau.

Impact of gut microbiota composition on black cutworm, Agrotis ipsilon (hufnagel) metabolic indices and pesticide degradation

Endosymbionts are known to have significant effects on their insect hosts, including nutrition, reproduction, and immunity. Insects gut microbiota is a critical component that affects their physiological and behavioral characteristics. The black cutworm (BCW), Agrotis ipsilon, is an economically important lepidopteran pest that has a diverse gut microbiome composed of nine species belonging to three phyla: Proteobacteria, Actinobacteria, and Firmicutes. This study was conducted to investigate the diversity of gut bacteria isolated from BCW larvae and moths and their effects on metabolism and pesticide degradation. The bacterial isolates were identified using the 16 S rRNA gene. The study showed that the gut microbiome composition significantly affected the metabolism of BCW larvae. Based on the screening results of synthesis of digestive enzymes and pesticide degradation, Brachybacterium conglomeratum and Glutamicibacter sp were selected to perform the remaining experiments as single isolates and consortium. The consortium-fed larvae showed high metabolic indices compared to antibiotic-fed larvae and the control. The gut bacteria were also shown to degrade three pesticide groups. Concerns regarding the health risk of chlorpyrifos have been raised due to its extensive use in agriculture. The isolated B. conglomeratum was more effective in chlorpyrifos degradation than the consortium. Furthermore, the study also examined the presence of sex related endosymbionts (Wolbachia, Spiroplasma, and Rickettsia) in the reproductive tissues of adults. The outcomes demonstrated that none of the examined endosymbionts existed. In conclusion, the study highlights the importance of the gut microbiome in insect physiology and behavior and its potential applications in biotechnology. It provides insights into developing eco-friendly pest control and bioremediation strategies using gut bacteria.

Short-term triphenyltin exposure alters microbial homeostasis in the silkworm (Bombyx mori) midgut

Triphenyltin (TPT) is a widespread synthetic chemical used in many fields and its potential risk to organisms has been comprehensively investigated using different animal models and species. Currently, little is known about the effects of TPT exposure on microbial midgut diversity, therefore we explored these effects in the lepidopterous silkworm model using 16S rDNA sequencing. In total, 5273 and 5065 operational taxonomic units (OTUs) were identified in control and TPT-exposure group samples, ranging from 424 to 728 OTUs/sample. Alpha-diversity analyses revealed that TPT exposure induced the fluctuations of gut microbial diversity and abundance while beta-diversity analyses identified a distinct impact on major gut microbiota components. In our microbiome analyses, 23 phyla and 353 genera were recognized in the control group, while 20 phyla and 358 genera were recognized in the TPT exposure group. At the genus level, midgut microbiota were composed of several predominant bacterial genera, including Muribaculaceae, Lactobacillus, and UCG-010. In the TPT exposure group, o__Bacillales, f__Bacillaceae, and f__Caldicoprobacteraceae abundance was relatively high, while f__Oscillospiraceae, f__Fusobacteriaceae, and f__SC_I_84 abundance was relatively high in the control group. Gene function analyses in silkworm microbiota after TPT exposure showed that biosynthesis of ansamycins, fructose and mannose metabolism, glycerolipid metabolism, type II diabetes mellitus, glycolysis/gluconeogenesis, lipid metabolism, translation proteins, atrazine degradation, DNA repair and recombination proteins, nicotinate and nicotinamide metabolism were significantly increased. Collectively, our silkworm model identified gut microbial diversity risks and the adverse effects from TPT exposure, which were similar to other aquatic animals. Therefore, TPT levels in environmental samples must be monitored to prevent ecological harm.

Transcriptomic analysis of the fat body of resistant and susceptible silkworm strains, Bombyx mori (Lepidoptera), after oral treatment with fenpropathrin

The widespread use of pyrethroid pesticides has brought serious economic losses in sericulture, but there is still no viable solution. The key to solving the problem is to improve silkworm resistance to pesticides, which depends on understanding the resistance mechanism of silkworms to pesticides. This study aimed to use transcriptomes to understand the underlying mechanism of silkworm resistance to fenpropathrin, which will provide a theoretical molecular reference for breeding pesticide-resistant silkworm varieties. In this study, the fat bodies of two strains with differential resistance after 12 h of fenpropathrin feeding were analyzed using RNA-Seq. After feeding fenpropathrin, 760 differentially expressed genes (DEGs) were obtained in the p50(r) strain and 671 DEGs in the 8y strain. The DEGs involved in resistance to fenpropathrin were further identified by comparing the two strains, including 207 upregulated DEGs in p50(r) and 175 downregulated DEGs in 8y. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis showed that these fenpropathrin-related DEGs are mainly enriched in the metabolism and transporter pathways. Moreover, 28 DEGs involved in the metabolic pathway and 18 in the transporter pathway were identified. Furthermore, organic cation transporter protein 6 (BmOCT6), a transporter pathway member, was crucial in enhancing the tolerance of BmN cells to fenpropathrin. Finally, the knockdown of the expression of the homologs of BmOCT6 in Glyphodes pyloalis (G. pyloalis) significantly decreased the resistant level of larvae to fenpropathrin. The findings showed that the metabolism and transporter pathways are associated with resistance to fenpropathrin in silkworm, and OCT6 is an effective and potential target not only for silkworm breeding but also for pest biocontrol.

The comparison of gut gene expression and bacterial community in Diaphorina citri (Hemiptera: Liviidae) adults fed on Murraya exotica and 'Shatangju' mandarin (Citrus reticulate cv. Shatangju)

BACKGROUND

Diaphorina citri Kuwayama is an important citrus pest. It serves as the vector for the transmission of Candidatus Liberibacter asiaticus (CLas), which induced a destructive disease, Huanglongbing, and caused huge economic losses. During the interaction between insects and plants, insects have evolved a series of mechanisms to adapt to various host plants. Murraya exotica and 'Shatangju' mandarin (Citrus reticulate cv. Shatangju) are the Rutaceae species from different genera that have been discovered as suitable hosts for D. citri adults. While the adaptation mechanism of this pest to these two host plants is unclear.

RESULTS

In this study, RNA-seq and 16 S rDNA amplification sequencing were performed on the gut of D. citri adults reared on M. exotica and 'Shatangju' mandarin. RNA-seq results showed that a total of 964 differentially expressed genes were found in different gut groups with two host plant treatments. The impacted genes include those that encode ribosomal proteins, cathepsins, and mitochondrial respiratory chain complexes. According to 16 S rDNA sequencing, the compositions of the gut bacterial communities were altered by different treatments. The α and β diversity analyses confirmed that the host plant changes influenced the gut microbial diversity. The functional classification analysis by Tax4Fun revealed that 27 KEGG pathways, mostly those related to metabolism, including those for nucleotide metabolism, energy metabolism, metabolism of cofactors and vitamins, amino acid metabolism, carbohydrate metabolism, xenbiotics biodegradation and metabolism, lipid metabolism, and biosynthesis of other secondary metabolites, were significantly altered.

CONCLUSION

Our preliminary findings shed light on the connection between D. citri and host plants by showing that host plants alter the gene expression profiles and bacterial community composition of D. citri adults.

Research Progresses on the Function and Detection Methods of Insect Gut Microbes

The insect gut is home to an extensive array of microbes that play a crucial role in the digestion and absorption of nutrients, as well as in the protection against pathogenic microorganisms. The variety of these gut microbes is impacted by factors such as age, diet, pesticides, antibiotics, sex, and caste. Increasing evidence indicates that disturbances in the gut microbiota can lead to compromised insect health, and that its diversity has a far-reaching impact on the host's health. In recent years, the use of molecular biology techniques to conduct rapid, qualitative, and quantitative research on the host intestinal microbial diversity has become a major focus, thanks to the advancement of metagenomics and bioinformatics technologies. This paper reviews the main functions, influencing factors, and detection methods of insect gut microbes, in order to provide a reference and theoretical basis for better research utilization of gut microbes and management of harmful insects.

The effects of short-term dietary exposure to SiO2 nanoparticle on the domesticated lepidopteran insect model silkworm (Bombyx mori): Evidence from the perspective of multi-omics

Silicon dioxide nanoparticles (nSiO₂) are one of the widely utilized nanoparticle (NPSs) materials, and exposure to nSiO₂ is ubiquitous. With the increasing commercialization of nSiO₂, the potential risk of nSiO₂ release to the health and the ecological environment have been attracted more attention. In this study, the domesticated lepidopteran insect model silkworm (Bombyx mori) was utilized to evaluate the biological effects of dietary exposure to nSiO₂. Histological investigations showed that nSiO₂ exposure resulted in midgut tissue injury in a dose-dependent manner. Larval body mass and cocoon production were reduced by nSiO₂ exposure. ROS burst was not triggered, and the activities of antioxidant enzymes were induced in the midgut of silkworm exposure to nSiO₂. RNA-sequencing revealed that the differentially expressed genes induced by nSiO₂ exposure were predominantly enriched into xenobiotics biodegradation and metabolism, lipid, and amino acid metabolism pathways. 16 S rDNA sequencing revealed that nSiO₂ exposure altered the microbial diversity in the gut of the silkworm. Metabolomics analysis showed that the combined uni- and multivariate analysis identified 28 significant differential metabolites from the OPLS-DA model. These significant differential metabolites were predominantly enriched into the metabolic pathways, including purine metabolism and tyrosine metabolism and so. Spearman correlation analysis and the Sankey diagram established the relationship between microbe and metabolites, and some genera may play crucial and pleiotropic functions in the interaction between microbiome and host. These findings indicated that nSiO₂ exposure could impact the dysregulation of genes related to xenobiotics metabolism, gut dysbiosis, and metabolic pathways and provided a valuable reference for assessing nSiO₂ toxicity from a multi-dimensional perspective.

Host-Adapted Strains of Spodoptera frugiperda Hold and Share a Core Microbial Community Across the Western Hemisphere

The fall armyworm Spodoptera frugiperda is an important polyphagous agricultural pest in the Western Hemisphere and currently invasive to countries of the Eastern Hemisphere. This species has two host-adapted strains named "rice" and "corn" strains. Our goal was to identify the occurrence of core members in the gut bacterial community of fall armyworm larvae from distinct geographical distribution and/or host strain. We used next-generation sequencing to identify the microbial communities of S. frugiperda from corn fields in Brazil, Colombia, Mexico, Panama, Paraguay, and Peru, and rice fields from Panama. The larval gut microbiota of S. frugiperda larvae did not differ between the host strains nor was it affected by the geographical distribution of the populations investigated. Our findings provide additional support for Enterococcus and Pseudomonas as core members of the bacterial community associated with the larval gut of S. frugiperda, regardless of the site of collection or strain. Further investigations are required for a deeper understanding of the nature of this relationship.

Axenic and gnotobiotic insect technologies in research on host-microbiota interactions

Insects are one of the most important animal life forms on earth. Symbiotic microbes are closely related to the growth and development of the host insects and can affect pathogen transmission. For decades, various axenic insect-rearing systems have been developed, allowing further manipulation of symbiotic microbiota composition. Here we review the historical development of axenic rearing systems and the latest progress in using axenic and gnotobiotic approaches to study insect-microbe interactions. We also discuss the challenges of these emerging technologies, possible solutions to address these challenges, and future research directions that can contribute to a more comprehensive understanding of insect-microbe interactions.

Comparative analysis of gut microbiota and immune genes linked with the immune system of wild and captive Spodoptera frugiperda (Lepidoptera: Noctuidae)

The fall armyworm (FAW), Spodoptera frugiperda (J.E. Smith), is one of the most highly polyphagous invasive pests causing serious damage to maize crops in China. However, little is known about the gut immune responses to the environment, particularly along the migration routes in Jianghuai, China, throughout the autumn and winter. In this study, high-throughput sequencing and real-time quantitative PCR (RT-qPCR) were employed to examine the variations in immune genes and gut microbiome communities between captive and wild fall armyworm populations. Results showed that the diversity and community of the gut's microbes were higher in wild populations, and the average weighted UniFrac distance between bacterial taxa varied. A wide variety of immune genes were more abundant in the wild populations than in others. Results indicated that diets and different survival conditions impacted the gut microbiota and immune system of S. frugiperda, which was crucial for environmental adaptation. These differences in gut microbiota and immune responses between wild and captive Fall armyworms are critical for comprehending the symbiotic relationship between microbes, immune genes, and hosts. They also highlight the need for increased focus on developing more effective and environmentally friendly pest control methods.

Effects of tolfenpyrad exposure on development and response mechanism in the silkworm, Bombyx mori

Tolfenpyrad is a broad spectrum of insecticide that can effectively kill different types of pests, including Lepidoptera. However, due to improper use, the adverse effects of tolfenpyrad on beneficial or economic insects have not been well studied. In this study, we systematically investigated the toxic effect of sublethal tolfenpyrad on silkworms. Sublethal tolfenpyrad exposure can affect the body weight, developments days, cocooning rate, eclosion rate and pupation rate. To further study the response mechanism of silkworms to tolfenpyrad stimulation, we compared the different expression genes by transcriptome sequencing and verified them by qRT-PCR. We found that significant changes in the genes expression was involved in xenobiotics biodegradation and metabolism, immune system and digestive system after tolfenpyrad treatment. To further investigate the possible mechanisms by which intestinal microbia in the response to tolfenpyrad, we analysed the microbia changes in the midgut of silkworms by 16S rRNA gene sequencing. The results showed that the relative abundances of Enterobacter and Staphylococcus were increased whereas the Tyzzerella and Methylobacterium-Methylorubrum were decreased after tolfenpyrad stimulation. Taken together, these results indicated that low concentration of tolfenpyrad affect the growth and development of silkworms. Silkworms respond to the toxicity of tolfenpyrad by inducing immune and detoxification-related gene expression or altering microbial composition in the midgut.

Effects of Microbial Transfer during Food-Gut-Feces Circulation on the Health of Bombyx mori

Change in habitual diet may negatively affect health. The domestic silkworm (Bombyx mori) is an economically important oligophagous insect that feeds on mulberry leaves. The growth, development, and immune-disease resistance of silkworms have declined under artificial dietary conditions. In this study, we used B. mori as a model insect to explore the relationship between changes in diet and balance of intestinal microbes due to its simpler guts compared with those of mammals. We found that artificial diets reduced the intestinal bacterial diversity in silkworms and resulted in a simple intestinal microbial structure. By analyzing the correlations among food, gut, and fecal microbial diversity, we found that an artificial diet was more easily fermented and enriched the lactic acid bacteria in the gut of the silkworms. This diet caused intestinal acidification and microbial imbalance (dysbiosis). When combined with the artificial diet, Enterococcus mundtii, a colonizing opportunistic pathogen, caused dysbiosis and allowed the frequent outbreak of bacterial diseases in the silkworms. This study provides further systematic indicators and technical references for future investigations of the relationship between diet-based environmental changes and intestinal microbial balance. IMPORTANCE The body often appears unwell after habitual dietary changes. The domestic silkworm (Bombyx mori) raised on artificial diets is a good model to explore the relationship between dietary changes and the balance of intestinal microbes. In this study, the food-gut-feces microbial model was established, and some potential key genera that could regulate the balance of intestinal microbiota were screened out. Our findings will provide a reference for future research to further our understanding of healthy silkworm development and may even be useful for similar research on other animals.

Gut bacterial communities and their assembly processing in Cnaphalocrocis medinalis from different geographic sources

Introduction

The insect gut harbors numerous microorganisms that may have functions in development and reproduction, digestion, immunity and protection, and detoxification. Recently, the influence factors on gut microbiota were evaluated in the rice leaffolder Cnaphalocrocis medinalis, a widespread insect pest in paddy fields. However, the relationship between gut microbiota composition and geography is poorly understood in C. medinalis.

Methods

To reveal the patterns of C. medinalis gut bacterial communities across geographic sources and the ecological processes driving the patterns, C. medinalis were sampled from six geographic sources in China, Thailand, and Vietnam in 2016, followed by gut bacterial 16S ribosomal RNA gene sequencing.

Results

A total of 22 bacterial phyla, 56 classes, 84 orders, 138 families, 228 genera, and 299 species were generated in C. medinalis from six geographic sources. All alpha diversity indices differed among the samples from different geographic sources. Analysis of similarity (ANOSIM) and permutational multivariate analysis of variance (PERMANOVA) both revealed significant differences in the gut microbiota of C. medinalis from six geographic sources. A total of 94 different taxa were screened as indicators for the gut microbiota of C. medinalis from six geographic sources by linear discriminant analysis effect size (LEfSe). The gene ontology (GO) pathways of the gut microbiota in C. medinalis differed among geographic sources. In total, the bacterial communities within geographic sources were mainly determined by stochastic processes, and those between geographic sources were mainly determined by deterministic processes.

Discussion

This study elucidates that geography plays a crucial role in shaping the gut microbiota of C. medinalis. Thus, it enriches our knowledge of gut bacteria in C. medinalis and sheds light on the mechanisms underlying C. medinalis gut microbial shifts across geography.

Intestinal Microflora Characteristics of Antheraea pernyi (Lepidoptera: Saturniidae) Larvae With Vomit Disease

Antheraea pernyi Guérin-Méneville (Lepidoptera: Saturniidae) is of high economic value as a source of silk, food, and bioactive substances with medicinal properties. A. pernyi larvae are prone to A. pernyi vomit disease (AVD), which results in substantial economic losses during cultivation; however, the relationship between AVD and A. pernyi gut microbiota remains unclear. Here, we investigated the bacterial community in the midgut and feces of A. pernyi larvae with and without AVD using 16S rRNA gene sequencing with Illumina MiSeq technology. Compared with healthy larvae, intestinal bacterial diversity and community richness increased and decreased in larvae with mild and severe AVD, respectively. In addition, the proportion of gut Enterobacter Hormaeche and Edwards(Enterobacteriales: Enterobacteriaceae) and Enterococcus Thiercelin and Jouhaud (Lactobacillales: Enterococcaceae) was higher and lower, respectively, in larvae with mild AVD than those in healthy larvae. A. pernyi vomit disease infection significantly increased the genera with abundance <1%. In the gut of larvae with severe AVD, the proportion of Turicibacter Bosshard et al. (Erysipelotrichales: Turicibacteraceae) increased significantly to 81.53-99.92%, whereas that of Enterobacter decreased compared with healthy larvae. However, the diversity of fecal bacteria was similar between healthy larvae and those with mild AVD. Overall, the findings demonstrate that intestinal microflora in A. pernyi larvae are altered by AVD infection and may cause secondary bacterial infection. This is the first report of the presence of Turicibacter in the intestinal tract of lepidopterans.

Implications of environmentally shaped microbial communities for insecticide resistance in Sitobion miscanthi

Insect-associated bacteria play an important role in the resistance to pesticides, yet bacterial community compositions in wild insect host populations and the environmental factors that shape them are mostly elusive. In this study, Sitobion miscanthi (Takahashi) populations were collected from major wheat growing regions in China. Following high-throughput sequencing of 16S rRNA gene fragments, association analyses were performed within the bacterial community associated with S. miscanthi, as well as with population resistance levels to four commonly used pesticides and different environmental factors. We found that bacterial community structures differed in various regions, and that the abundances of dominant bacteria such as Buchnera, Candidatus Regiella, Candidatus Hamiltonella showed high variations. The resistance of S. miscanthi to avermectin and bifenthrin was shown to decline with increasing bacterial diversity. Meanwhile, with the increase of bacterial network modularity, the resistance of S. miscanthi populations to imidacloprid, avermectin and bifenthrin also increased correspondingly. In addition, correlation analysis indicated that altitude and air pressure had the strongest impact on bacterial community diversity and relative abundance, followed by humidity, rainfall and temperature. Overall, insights into such complex interactions between bacteria and their insect hosts offer new directions for biological pest control.

Toxic effects of triphenyltin on the silkworm Bombyx mori as a lepidopterous insect model

Triphenyltin (TPT) is a widely used reagent in various industries and agriculture, but is also known to accumulate in natural ecosystems and animal tissues. Hence, the aim of this study was to comprehensively assess the toxicity of TPT in the silkworm Bombyx mori as a model insect. The results showed that TPT exposure for the entire 5th instar larval stage significantly reduced the weight of silkworm pupa and inhibited development of the silkworm midgut. Following exposure to 2 μg/kg of TPT for 4 days, differentially expressed genes in midgut were associated with enriched pathways involved in the metabolism of carbohydrates, lipids, and amino acids, as determined by RNA sequencing. Furthermore, the metabolic profiles of the intestinal content of silkworms exposed to 2 μg/kg of TPT for 4 days were markedly altered and differential metabolites produced by metabolism of carbohydrates, lipids, and amino acids were enriched as determined by non-targeted GC-MS/MS metabolomics. This study provides novel insights into the mechanisms underlying the toxicity of TPT and emphasizes the risks posed by such pollutants released into the environment.

Effect of Diet on the Midgut Microbial Composition and Host Immunity of the Fall Armyworm, Spodoptera frugiperda

The fall armyworm (Spodoptera frugiperda, J.E. Smith) is one of the most important agricultural pests in the world and causes serious damage to many significant crops. Insect gut microbiota plays a vital role in host immunity, digestion, and development, helping the higher organism colonize in a new environment. However, the effects of different diets on midgut microbial composition and host immunity in S. frugiperda remain unclear. So far, no reports have compared the gut microbiota of fall armyworm reared using an artificial diet compared to corn leaf in Guangzhou, China. High-throughput 16S rRNA sequencing technology was applied to gain insight into the composition of the gut microbiota of S. frugiperda feeding on corn leaf (field diet) and on a starch-rich artificial diet (lab diet). The fall armyworm gut microbiota was dominated by the bacterial phyla Firmicutes and Proteobacteria. Despite the difference in diet, the core bacterial community was represented by the genus Enterococcus. However, the bacterial community is dominated by a few phylotypes, namely operational taxonomical units 1 (OTU1) (Enterococcus casseliflavus), OTU3 (Enterobacteriaceae), OTU2 (Weissella), and OTU4 (Clostridium), accounting for 97.43% of the total OTUs in the complete dataset. A significant difference was identified in the bacterial communities between the "lab diet" and the "field diet" groups. OTU1 and OTU2 were significantly higher in the "field diet" group, whereas OTU3 and OTU4 were higher in the "lab diet" group. A phylogenetic investigation of the communities by reconstruction of unobserved states (PICRUSt) predicted functional analysis indicates the presence of several genes associated with plant biomass degradation. Importantly, antibiotic-mediated perturbation of the midgut microbial community significantly impacts the expression profile of the important immune genes of the host. Furthermore, the oral reintroduction of gut bacterial isolates (E. mundtii and E. gallinarum) significantly enhances host resistance to AcMNPV infection. Taken together, our results indicate that diet composition is an important driver in shaping insect gut microbiome and immune gene expression, ultimately playing an important role in the pest defense system.

Smartphones as an Ecological Niche of Microorganisms: Microbial Activities, Assembly, and Opportunistic Pathogens

Smartphone usage and contact frequency are unprecedentedly high in this era, and they affect humans mentally and physically. However, the characteristics of the microorganisms associated with smartphones and smartphone hygiene habits remain unclear. In this study, using various culture-independent techniques, including high-throughput sequencing, real-time quantitative PCR (RT-qPCR), the ATP bioluminescence system, and electron microscopy, we investigated the structure, assembly, quantity, and dynamic metabolic activity of the bacterial community on smartphone surfaces and the user's dominant and nondominant hands. We found that smartphone microbiotas are more similar to the nondominant hand microbiotas than the dominant hand microbiotas and show significantly decreased phylogenetic diversity and stronger deterministic processes than the hand microbiota. Significant interindividual microbiota differences were observed, contributing to an average owner identification accuracy of 70.6% using smartphone microbiota. Furthermore, it is estimated that approximately 1.75 × 106 bacteria (2.24 × 104/cm2) exist on the touchscreen of a single smartphone, and microbial activities remain stable for at least 48 h. Scanning electron microscopy detected large fragments harboring microorganisms, suggesting that smartphone microbiotas live on the secreta or other substances, e.g., human cell debris and food debris. Fortunately, simple smartphone cleaning/hygiene could significantly reduce the bacterial load. Taken together, our results demonstrate that smartphone surfaces not only are a reservoir of microbes but also provide an ecological niche in which microbiotas, particularly opportunistic pathogens, can survive, be active, and even grow. IMPORTANCE Currently, people spend an average of 4.2 h per day on their smartphones. Due to the COVID-19 pandemic, this figure may still be increasing. The high frequency of smartphone usage may allow microbes, particularly pathogens, to attach to-and even survive on-phone surfaces, potentially causing adverse effects on humans. We employed various culture-independent techniques in this study to evaluate the microbiological features and hygiene of smartphones, including community assembly, bacterial load, and activity. Our data showed that deterministic processes drive smartphone microbiota assembly and that approximately 1.75 × 106 bacteria exist on a single smartphone touchscreen, with activities being stable for at least 48 h. Fortunately, simple smartphone cleaning/hygiene could significantly reduce the bacterial load. This work expands our understanding of the microbial ecology of smartphone surfaces and might facilitate the development of electronic device cleaning/hygiene guidelines to support public health.

Antibiotic Treatment Reduced the Gut Microbiota Diversity, Prolonged the Larval Development Period and Lessened Adult Fecundity of Grapholita molesta (Lepidoptera: Tortricidae)

Grapholita molesta, the oriental fruit moth, is a serious pest of fruit trees with host transfer characteristics worldwide. The gut microbiota, which plays a crucial part in insect physiology and ecology, can be influenced by many elements, such as antibiotics, temperature, diet, and species. However, the effects of antibiotics on G. molesta gut microbiota are still unclear. In this study, we selected five common antibiotic agents to test the inhibition of G. molesta gut microbiota, and found ciprofloxacin shown the best antibacterial activity. After feeding 1 μg/mL of ciprofloxacin, the relative abundance of Actinobacteria and Cyanobacteria decreased significantly, while that of Firmicutes and Bacteroidetes increased. PICRUSt2 analysis indicated that most functional prediction categories were enriched in the G. molesta gut, including amino acid transport and metabolism, translation, ribosomal structure and biogenesis, carbohydrate transport and metabolism, transcription, cell wall/membrane/envelope biogenesis, and energy production and conversion. Finally, ciprofloxacin feeding significantly affected larval growth, development, and reproduction, resulting in prolonged larval development duration, shortened adult longevity, and significantly decreased single female oviposition and egg hatchability. In addition, we isolated and purified some culturable bacteria belonging to Proteobacteria, Firmicutes, Actinobacteria, and cellulase-producing bacteria from the G. molesta midgut. In brief, our results demonstrate that antibiotics can have an impact on G. molesta gut bacterial communities, which is beneficial for host growth and development, as well as helping female adults produce more fertile eggs. These results will thus provide a theoretical reference for developing new green control technology for G. molesta.

Glutamicibacter halophytocola-mediated host fitness of potato tuber moth on Solanaceae crops

BACKGROUND

The potato tuber moth (PTM), Phthorimaea operculella (Zeller) (Lepidoptera: Gelechiidae), is a destructive pest of Solanaceae crops worldwide. α-solanine and α-chaconine are toxic steroidal glycoalkaloids (SGAs) in Solanaceae crops and are most abundant in potatoes (Solanum tuberosum L.), accounting for more than 95% of the total SGAs. PTM grows on potatoes with a higher concentration of SGAs. Gut bacteria play an important role in the physiology and behavior of insects. To understand the role of gut bacteria of PTM in host adaptability, we isolated and identified major SGA (α-chaconine and α-solanine)-degrading gut bacteria in the gut of PTM by a selective medium and analyzed their degradability and degradation mechanism.

RESULTS

The gut Glutamicibacter halophytocola S2 of PTM with high degradation capacity to α-solanine and α-chaconine were detected by liquid chromatography mass spectrometry (LC-MS) and identified by morphological and 16S rRNA gene sequence analysis. A gene cluster involving α-rhamnosidases, β-glucosidases, and β-galactosidases was identified by whole-genome sequencing of G. halophytocola S2. These genes had higher expression on the α-solanine medium. PTM inoculated with the isolated G. halophytocola S2 obtained higher fitness than antibiotic-treated PTM.

CONCLUSION

The G. halophytocola S2 in the gut of PTM could degrade the major toxic α-solanine and α-chaconine in potatoes. This enhances the fitness of PTM feeding on potatoes with high SGA contents. The results provide a theoretical foundation for the integrated pest management of PTM and provide an effective strain for the treatment of α-solanine and α-chaconine in potato food. © 2022 Society of Chemical Industry.

Fall Armyworm Gut Bacterial Diversity Associated with Different Developmental Stages, Environmental Habitats, and Diets

The fall armyworm, Spodoptera frugiperda (Lepidoptera: Noctuidae), is a major invasive pest that seriously threatens world agricultural production and food security. Microorganisms play a crucial role in the growth and development of insects. However, the diversity and dynamics of gut microbes with different developmental stages, environmental habitats, and diets in S. frugiperda remain unclear. In this study, we found the changes of the microbiome of S. frugiperda across their life stages, and the bacteria were dominated by Firmicutes and Proteobacteria. The community composition of the egg stage was quite different from other developmental stages, which had the highest community diversity and community richness, and was dominated by Proteobacteria. The bacterial community compositions of male and female adults were similar to those of early larvae stage (L1-L2), and operational taxonomic units (OTUs) with abundant content were Enterococcus and Enterobacteriaceae bacteria, including Enterobacteria, Klebsiella, Pantoea, and Escherichia. The third instar larvae (L3) mainly consist of Enterococcus. The late stage larvae (L4-L6) harbored high proportions of Enterococcus, Rhodococcus, and Ralstonia. There was no significant difference in gut microbial composition between field populations and laboratory populations in a short period of rearing time. However, after long-term laboratory feeding, the gut microbial diversity of S. frugiperda was significantly reduced. Enterococcus and Rhodococccus of S. frugiperda feeding on maize showed higher relative proportion, while the microbial community of S. frugiperda feeding on artificial diet was composed mainly of Enterococcus, with a total of 98% of the gut microbiota. The gene functions such as metabolism, cell growth and death, transport and catabolism, and environmental adaptation were more active in S. frugiperda feeding on corn than those feeding on artificial diet. In short, these results indicate that developmental stage, habitat, and diet can alter the gut bacteria of S. frugiperda, and suggest a vertical transmission route of bacteria in S. frugiperda. A comprehensive understanding of gut microbiome of S. frugiperda will help develop novel pest control strategies to manage this pest.