Bacterial and fungal gut communities of Agrilus mali at different developmental stages and fed different diets

Unearthing Lactococcus lactis and Scheffersomyeces symbionts from edible wood-boring beetle larvae as a bio-resource for industrial applications

BACKGROUND

Gut microbiota have several advantages in influencing the host nutrition, metabolism, immunity and growth. However, the understanding of the gut microbiota in key edible wood-boring beetle larvae remain largely undefined. In the present study, the characteristics of the gut microbiota of two edible wood-boring species (Titocerus jaspideus and Passalus punctiger) from two indigenous forested areas were investigated.

RESULTS

Over 50% of Amplicon Sequence Variants (ASVs) constituted of Firmicutes in T. jaspideus. The dominant phyla in both beetle species were Bacteroidota (4.20-19.79%) and Proteobacteria (15.10-23.90%). Lactococcus lactis was the most abundant and core prokaryote in the guts of T. jaspideus. The fungi identified in the gut of both insects belong to the phylum Obazoa (66%) and Ascomycota (> 15%). Scheffersomyeces sp. was the core eukaryote recorded. The diversity of gut microbiota in both insect species did not vary significantly. Most of the prokaryotic genes expressed were predominantly associated with biosynthesis and metabolism.

CONCLUSION

Our findings demonstrated that Lactococcus lactis and Scheffersomyeces are core gut microbes of wood boring beetle larvae with desirable probiotic properties and promising use in food product fermentation for improved growth performance, gut barrier health, intestinal flora balance and immune protection for human and animals. Further studies to highlight the latest medical-based applications of L. lactis as live-delivery vector for the administration of therapeutics against both communicable and non-communicable diseases are warranted.

First Data on the Investigation of Gut Yeasts in Hermit Beetle (Osmoderma barnabita Motschulsky, 1845) Larvae in Lithuania

In this study, yeasts from the gut of O. barnabita larvae were isolated and molecularly identified. It is worth noting that this research provides the first analysis of the gut yeast community in O. barnabita larvae in Lithuania, which is a significant contribution to the field. Two hermit-like L3-praepupa instars were collected from a decaying oak log in Lithuania. The isolation, morphology, biochemistry, and physiology of the yeast isolates were characterized using standards commonly employed in yeast taxonomy studies. The isolates were identified by sequencing the large subunit (26S) rDNA (D1/D2 domain of the LSU). All gut compartments were colonized by the yeast. A total of 45 yeast strains were obtained from the gut of both O. barnabita larvae, with 23 strains originating from Larva 1, 16 strains from Larva 2, and 6 strains from the galleries. According to our identification results of the 45 yeast strains, most of the species were related to Ascomycota, with most of them belonging to the Saccharomycetales order. Yeasts of the genera Candida, Debaryomyces, Meyerozyma, Priceomyces, Schwanniomyces, Spencermartinsiella, Trichomonascus, and Blastobotrys were present in gut of O. barnabita larvae. Species of the Trichosporonales order represented the Basidiomycota phylum.

Analysis of differential effects of host plants on the gut microbes of Rhoptroceros cyatheae

As an indispensable part of insects, intestinal symbiotic bacteria play a vital role in the growth and development of insects and their adaptability. Rhoptroceros cyatheae, the main pest of the relict plant Alsophila spinulosa, poses a serious threat to the development of the A. spinulosa population. In the present study, 16S rDNA and internal transcribed spacer high-throughput sequencing techniques were used to analyze the structure of intestinal microbes and the diversity of the insect feeding on two different plants, as well as the similarities between the intestinal microorganisms of R. cyatheae. The dominant bacteria of leaf endophytes were also compared based on the sequencing data. The results showed that Proteobacteria, Firmicutes, and Actinobacteria were the dominant phyla of intestinal bacteria, and Ascomycota was the dominant phylum of intestinal fungi. Allorhizobium-Neorhizobium-Pararhizobium-Rhizobium, Methylobacterium-Methylorubrum, and Enterococcus were the dominant genera in the intestine of R. cyatheae feeding on two plants, and the relative abundance was significantly different between the two groups. Candida was the common dominant genus of intestinal fungi in the two groups, and no significant difference was observed in its abundance between the two groups. This showed that compared with the intestinal fungi of R. cyatheae, the abundance of the intestinal bacteria was greatly affected by food. The common core microbiota between the microorganisms in A. spinulosa leaves and the insect gut indicated the presence of a microbial exchange between the two. The network correlation diagram showed that the gut microbes of R. cyatheae feeding on Gymnosphaera metteniana were more closely related to each other, which could help the host to better cope with the adverse external environment. This study provides a theoretical basis for the adaptation mechanism of R. cyatheae and a new direction for the effective prevention and control of R. cyatheae.

Gut yeast diversity of Helicoverpa armigera (Lepidoptera: Noctuidae) under different dietary conditions

Yeast is one of the important symbiotic flora in the insect gut. However, little is known about the gut yeast in Helicoverpa armigera (Lepidoptera: Noctuidae) under various dietary conditions. The composition and function of the intestinal yeast community also remain unclear. In this research, we explored the composition of yeast microorganisms in H. armigera larvae under different feeding environments, including apple, pear, tomato, artificial diet (laboratory feeding), Urtica fissa, Helianthus annuus, and Zinnia elegans (wild environment) using high-throughput sequencing. Results showed that a total of 43 yeast OTU readings were obtained, comprising 33 yeast genera and 42 yeast species. The yeast genera with a total content of more than 5% were Hanseniaspora (36.27%), Moesziomyces (21.47%), Trichosporon (16.20%), Wickerhamomyces (12.96%) and Pichia (6.38%). Hanseniaspora was predominant when fed indoors with fruits, whereas Moesziomyces was only detected in the wild group (Urtica fissa, Helianthus annuus, Zinnia elegans) and the artificial diet group. After transferring the larvae from artificial diet to apple, pear and tomato, the composition of intestinal yeast community changed, mainly reflected in the increased relative abundance of Hanseniaspora and the decreased abundance of Trichosporon. Simultaneously, the results of α diversity index indicated that the intestinal yeast microbial diversity of H. armigera fed on wild plants was higher than that of indoor artificial feeding. PCoA and PERMANOVA analysis concluded that there were significant differences in the gut yeast composition of H. armigera larvae on different diets. Our results confirmed that gut yeast communities of H. armigera can be influenced by host diets and may play an important role in host adaptation.

Pecan secondary metabolites influenced the population of Zeuzera coffeae by affecting the structure and function of the larval gut microbiota

Background

The plant secondary metabolites (PSMs), as important plant resistance indicators, are important targets for screening plant insect resistance breeding. In this study, we aimed to investigate whether the population of Zeuzera coffeae (ZC) is affected by different varieties of Carya illinoinensis PSMs content. At the same time, the structure and function of the gut microbiome of ZC were also analyzed in relation to different pecan varieties.

Methods

We counted the populations of ZC larvae in four pecan varieties and determined the content of four types of PSMs. The structure and function of the larval gut microbiota were studied in connection to the number of larvae and the content of PSMs. The relationships were investigated between larval number, larval gut microbiota, and PSM content.

Results

We found that the tannins, total phenolics, and total saponins of 4 various pecans PSMs stifled the development of the ZC larval population. The PSMs can significantly affect the diversity and abundance of the larval gut microbiota. Enrichment of ASV46 (Pararhizobium sp.), ASV994 (Olivibacter sp.), ASV743 (Rhizobium sp.), ASV709 (Rhizobium sp.), ASV671 (Luteolibacter sp.), ASV599 (Agrobacterium sp.), ASV575 (Microbacterium sp.), and ASV27 (Rhizobium sp.) in the gut of larvae fed on high-resistance cultivars was positively associated with their tannin, total saponin, and total phenolic content. The results of the gut microbiome functional prediction for larvae fed highly resistant pecan varieties showed that the enriched pathways in the gut were related to the breakdown of hazardous chemicals.

Conclusion

Our findings provide further evidence that pecan PSMs influence the structure and function of the gut microbiota, which in turn affects the population stability of ZC. The study's findings can serve as a theoretical foundation for further work on selecting ZC-resistant cultivars and developing green management technology for ZC.

Uncovering the antifungal activities of wild apple-associated bacteria against two canker-causing fungi, Cytospora mali and C. parasitica

Cytospora canker has become a devastating disease of apple species worldwide, and in severe cases, it may cause dieback of entire trees. The aim of this study was to characterize the diversity of cultivable bacteria from the wild apple microbiota and to determine their antifungal ability against the canker-causing pathogenic fungi Cytospora mali and C. parasitica. Five bacterial strains belonging to the species Bacillus amyloliquefaciens, B. atrophaeus, B. methylotrophicus, B. mojavensis, and Pseudomonas synxantha showed strong antagonistic effects against pathogenic fungi. Therefore, since the abovementioned Bacillus species produce known antifungal compounds, we characterized the antifungal compounds produced by Ps. synxantha. Bacteria grown on nutritional liquid medium were dehydrated, and the active compound from the crude extract was isolated and analysed via a range of chromatographic processes. High-performance liquid chromatography, mass spectrometry, and nuclear magnetic resonance analyses revealed a bioactive antifungal compound, phenazine-1-carboxylic acid (PCA). The minimum inhibitory concentration (MIC) demonstrated that PCA inhibited mycelial growth, with a MIC of 10 mg mL-1. The results suggested that PCA could be used as a potential compound to control C. mali and C. malicola, and it is a potential alternative for postharvest control of canker disease.

Cladosporium-Insect Relationships

The range of interactions between Cladosporium, a ubiquitous fungal genus, and insects, a class including about 60% of the animal species, is extremely diverse. The broad case history of antagonism and mutualism connecting Cladosporium and insects is reviewed in this paper based on the examination of the available literature. Certain strains establish direct interactions with pests or beneficial insects or indirectly influence them through their endophytic development in plants. Entomopathogenicity is often connected to the production of toxic secondary metabolites, although there is a case where these compounds have been reported to favor pollinator attraction, suggesting an important role in angiosperm reproduction. Other relationships include mycophagy, which, on the other hand, may reflect an ecological advantage for these extremely adaptable fungi using insects as carriers for spreading in the environment. Several Cladosporium species colonize insect structures, such as galleries of ambrosia beetles, leaf rolls of attelabid weevils and galls formed by cecidomyid midges, playing a still uncertain symbiotic role. Finally, the occurrence of Cladosporium in the gut of several insect species has intriguing implications for pest management, also considering that some strains have proven to be able to degrade insecticides. These interactions especially deserve further investigation to understand the impact of these fungi on pest control measures and strategies to preserve beneficial insects.

Marked variations in diversity and functions of gut microbiota between wild and domestic stag beetle Dorcus Hopei Hopei

BACKGROUND

Although stag beetles are a popular saprophytic insect, their gut microbiome has been poorly studied. Here, 16 S rRNA gene sequencing was employed to reveal the gut microbiota composition and functional variations between wild and domestic Dorcus hopei hopei (Dhh) larval individuals.

RESULTS

The results indicated a significant difference between the wild and domestic Dhh gut microbiota., the domestic Dhh individuals contained more gut microbial taxa (e.g. genera Ralstonia and Methyloversatilis) with xenobiotic degrading functions. The wild Dhh possesses gut microbiota compositions (e.g. Turicibacter and Tyzzerella ) more appropriate for energy metabolism and potential growth. This study furthermore assigned all Dhh individuals by size into groups for data analysis; which indicated limited disparities between the gut microbiota of different-sized D. hopei hopei larvae.

CONCLUSION

The outcome of this study illustrated that there exists a significant discrepancy in gut microbiota composition between wild and domestic Dhh larvae. In addition, the assemblage of gut microbiome in Dhh was primarily attributed to environmental influences instead of individual differences such as developmental potential or size. These findings will provide a valuable theoretical foundation for the protection of wild saprophytic insects and the potential utilization of the insect-associated intestinal microbiome in the future.

Crosstalk between the microbiota and insect postembryonic development

Insect sequential development evolves from a simple molt towards complete metamorphosis. Like any multicellular host, insects interact with a complex microbiota. In this review, factors driving the microbiota dynamics were pointed out along their development. Special focus was put on tissue renewal, shift in insect ecology, and microbial interactions. Conversely, how the microbiota modulates its host development through nutrient acquisition, hormonal control, and cellular or tissue differentiation was exemplified. Such modifications might have long-term carry-over effects on insect physiology. Finally, remarkable microbe-driven control of insect behaviors along their life cycle was highlighted. Increasing knowledge of those interactions might offer new insights on how insects respond to their environment as well as perspectives on pest- or vector-control strategies.

Dynamics of gut microflora across the life cycle of Spodoptera frugiperda and its effects on the feeding and growth of larvae

BACKGROUND

Spodoptera frugiperda is an important invasive agricultural pest that causes huge economic losses worldwide. Gut microorganisms play a vital role in host feeding, digestion, nutrition, immunity, growth and insecticide resistance. Illumina high-throughput sequencing was used to study the gut microbial community dynamics across the life cycle (egg, 1st to 6th instar larvae, pupae, and male and female adults) of S. frugiperda fed on maize leaves. Furthermore, the gut microbial community and food intake of the 5th instar S. frugiperda larvae were studied after feeding them antibiotics.

RESULTS

Enterobacteriaceae and Enterococcaceae dominated the gut during growth and feeding of the larvae. The relative abundance of Enterobacteriaceae was higher in the 4th and 6th instar larvae. With the increase in larval feeding, the relative abundance of Enterococcaceae gradually increased. In addition, principal coordinate analysis and linear discriminant effect size analysis confirmed differences in the structure of gut microbiota at different developmental stages. After antibiotic treatment, the relative abundance of Firmicutes, Proteobacteria and Fusobacteriota decreased. The relative abundance of Enterococcus and Klebsiella decreased significantly. Antibiotic treatment inhibited the gut flora of S. frugiperda, which decreased larval food intake and body weight gain, and prolonged the larval stage.

CONCLUSION

The composition of the gut bacterial community plays an important role in the growth, development, and feeding of S. frugiperda. The results have a certain theoretical value for the development of bio-pesticides targeting intestinal flora. © 2022 Society of Chemical Industry.

Characterization of cultivable intestinal microbiota in Rhynchophorus palmarum Linnaeus (Coleoptera: Curculionidae) and determination of its cellulolytic activity

Rhynchophorus palmarum Linnaeus is an agricultural pest that affects various palm crops, including coconut (Cocos nucifera) plantations which are prominent in the economy of Northeastern Brazil. Characterization of the intestinal microbiota of R. palmarum, as well as elucidation of aspects related to the biochemistry and physiology of the insect's digestion, is essential for intervention in specific metabolic processes as a form of pest control. Thus, this study aimed to characterize the intestinal microbiota of R. palmarum and investigate its ability to degrade cellulosic substrates, to explore new biological control measures. Intestinal dissection of eight adult R. palmarum insects was performed in a laminar flow chamber, and the intestines were homogenized in sterile phosphate-buffered saline solution. Subsequently, serial dilution aliquots of these solutions were spread on nutritive agar plates for the isolation of bacteria and fungi. The microorganisms were identified by matrix-assisted laser desorption/ionization with a time-of-flight mass spectrometry and evaluated for their ability to degrade cellulose. Fourteen bacterial genera (Acinetobacter, Alcaligenes, Arthrobacter, Bacillus, Citrobacter, Enterococcus, Kerstersia, Lactococcus, Micrococcus, Proteus, Providencia, Pseudomonas, Serratia, and Staphylococcus) and two fungal genera (Candida and Saccharomyces)-assigned to the Firmicutes, Actinobacteria, Proteobacteria, and Ascomycota phyla-were identified. The cellulolytic activity was exhibited by six bacterial and one fungal species; of these, Bacillus cereus demonstrated the highest enzyme synthesis (enzymatic index = 4.6). This is the first study characterizing the R. palmarum intestinal microbiota, opening new perspectives for the development of strategies for the biological control of this insect.

Dynamics of Microbial Communities across the Life Stages of Nilaparvata lugens (Stål)

Understanding the composition of microorganismal communities hosted by insect pests is an important prerequisite for revealing their functions and developing new pest control strategies. Although studies of the structure of the microbiome of Nilaparvata lugens have been published, little is known about the dynamic changes in this microbiome across different developmental stages, and an understanding of the core microbiota is still lacking. In this study, we investigated the dynamic changes in bacteria and fungi in different developmental stages of N. lugens using high-throughput sequencing technology. We observed that the microbial diversity in eggs and mated adults was higher than that in nymphs and unmated adults. We also observed a notable strong correlation between fungal and bacterial α-diversity, which suggests that fungi and bacteria are closely linked and may perform functions collaboratively during the whole developmental period. Arsenophonus and Hirsutella were the predominant bacterial and fungal taxa, respectively. Bacteria were more conserved than fungi during the transmission of the microbiota between developmental stages. Compared with that in the nymph and unmated adult stages of N. lugens, the correlation between bacterial and fungal communities in the mated adult and egg stages was stronger. Moreover, the core microbiota across all developmental stages in N. lugens was identified, and there were more bacterial genera than fungal genera; notably, the core microbiota of eggs, nymphs, and mated and unmated adults showed distinctive functional enrichment. These findings highlight the potential value of further exploring microbial functions during different developmental stages and developing new pest management strategies.

Bugs in Bugs: The Role of Probiotics and Prebiotics in Maintenance of Health in Mass-Reared Insects

Simple Summary

The importance of insect farming is increasing in the livestock market by evolving into a form of intensive production that is often characterized by a high density of individuals kept in closed environments. These conditions can cause a higher risk of occurrence of insect diseases and the lowering of reproductive and growth performances. The role of microbiota composition in insect behaviour and health maintenance could be further studied for selecting microorganisms that act as probiotics for the main mass reared insect species. These probiotics could enhance host performances and reduce the incidence of risks related to insect diseases.

Abstract

Interactions between insects and their microbiota affect insect behaviour and evolution. When specific microorganisms are provided as a dietary supplement, insect reproduction, food conversion and growth are enhanced and health is improved in cases of nutritional deficiency or pathogen infection. The purpose of this review is to provide an overview of insect–microbiota interactions, to review the role of probiotics, their general use in insects reared for food and feed, and their interactions with the host microbiota. We review how bacterial strains have been selected for insect species reared for food and feed and discuss methods used to isolate and measure the effectiveness of a probiotic. We outline future perspectives on probiotic applications in mass-reared insects.

Bacterial Communities in the Feces of Laboratory Reared Gampsocleis gratiosa (Orthoptera: Tettigoniidae) across Different Developmental Stages and Sexes

Simple Summary

Many insects host a diverse gut microbial community, ranging from pathogenic to obligate mutualistic organisms. Little is known about the bacteria associated with katydids. Gampsocleis gratiosa (Orthoptera, Tettigoniidae) is an economically important singing pet in China. In the present study, the bacterial communities of the laboratory-reared G. gratiosa feces were characterized using Illumina sequencing of the 16S rDNA V3-V4 region.

Abstract

We used Illumina sequencing of the 16S rDNA V3-V4 region to identify the bacterial community in laboratory-reared G. gratiosa feces across different developmental stages (1st–7th instar nymph day 0, and 0-, 7-, 14-, and 21-day adult) and sexes. In total, 14,480,559 high-quality reads were clustered into 2982 species-level operational taxonomic units (OTUs), with an average of 481.197 (±137.366) OTUs per sample. These OTUs were assigned into 25 phyla, 42 classes, 60 orders, 116 families, 241 genera, and some unclassified groups. Only 21 core OTUs were shared by all samples. The most representative phylum was Proteobacteria, followed by Firmicutes, Bacteroidetes, and Acidobacteria. At the genus level, Kluyvera (387 OTUs), Obesumbacterium (339 OTUs), Buttiauxella (296 OTUs), Lactobacillus (286 OTUs), and Hafnia (152 OTUs) were dominant bacteria. The early-instar nymphs harbored a similar bacterial community with other developmental stages, which contain higher species diversity. Both principal coordinate analysis (PCoA) and non-metric multidimensional scaling analysis (NMDS) failed to provide a clear clustering based on the developmental stages and sexes. Overall, we assume that G. gratiosa transmits bacteria vertically by eating contaminated eggshells, and both developmental stages and sexes had no significant effect on the fecal bacterial community.

Stage correlation of symbiotic bacterial community and function in the development of litchi bugs (Hemiptera: Tessaratomidae)

Bacterial symbionts of insects have been shown to play important roles in host fitness. However, little is known about the bacterial community of Tessaratoma papillosa which is one of the most destructive pests of the well-known fruits Litchi chinensis Sonn and Dimocarpus longan Lour in Oriental Region, especially in South-east Asia and adjacent areas. In this study, we surveyed the bacterial community diversity and dynamics of T. papillosa in all developmental stages with both culture-dependent and culture-independent methods by the third-generation sequencing technology. Five bacterial phyla were identified in seven developmental stages of T. papillosa. Proteobacteria was the dominant phylum and Pantoea was the dominant genus of T. papillosa. The results of alpha and beta diversity analyses showed that egg stage had the most complex bacterial community. Some of different developmental stages showed similarities, which were clustered into three phases: (1) egg stage, (2) early nymph stages (instars 1-3), and (3) late nymph stages (instars 4-5) and adult stage. Functional prediction indicated that the bacterial community played different roles in these three phases. Furthermore, 109 different bacterial strains were isolated and identified from various developmental stages. This study revealed the relationship between the symbiotic bacteria and the development of T. papillosa, and may thus contribute to the biological control techniques of T. papillosa in the future.

Wild Apple-Associated Fungi and Bacteria Compete to Colonize the Larval Gut of an Invasive Wood-Borer Agrilus mali in Tianshan Forests

The gut microflora of insects plays important roles throughout their lives. Different foods and geographic locations change gut bacterial communities. The invasive wood-borer Agrilus mali causes extensive mortality of wild apple, Malus sieversii, which is considered a progenitor of all cultivated apples, in Tianshan forests. Recent analysis showed that the gut microbiota of larvae collected from Tianshan forests showed rich bacterial diversity but the absence of fungal species. In this study, we explored the antagonistic ability of the gut bacteria to address this absence of fungi in the larval gut. The results demonstrated that the gut bacteria were able to selectively inhibit wild apple tree-associated fungi. Among them, Pseudomonas synxantha showed strong antagonistic ability, producing antifungal compounds. Using different analytical methods, such as column chromatography, mass spectrometry, HPLC, and NMR, an antifungal compound, phenazine-1-carboxylic acid (PCA), was identified. Activity of the compound was determined by the minimum inhibitory concentration method and electron microscopy. Moreover, our study showed that the gut bacteria could originate from noninfested apple microflora during infestation. Overall, the results showed that in newly invaded locations, A. mali larvae changed their gut microbiota and adopted new gut bacteria that prevented fungal colonization in the gut.

Biological risk assessment in the History and Historical Documentation Library of the University of Milan

There are billions of books that in recent and in ancient times have been produced by the human race containing evidence of its intellectual and cultural efforts. Even when stored in libraries, not all these books survive over time undamaged, because in the biosphere their materials are potential nutrients. This is the unfortunate case of the History and Historical Documentation Library of the University of Milan, where biological agents have badly affected rare and valuable old books. An entomological monitoring was carried out using sticky traps and collecting insects during inspections. The beetle Gastrallus pubens Fairmaire, rarely identified in European libraries so far, was the main biological agent responsible for the book damage, since several tunnels due to larval activity and holes made by adults were observed. Using the Illumina MiSeq sequencing technology, Proteobacteria, Firmicutes and Actinobacteria were found to be the most abundant phyla. Ascomycota was the dominant phylum among three fungal phyla. As bacteria and fungi spread by the insects are primary indications of the insect presence in the library, in this paper a potential biomarker able to detect the G. pubens presence before visible infestation was searched for among the bacterial and fungal community peculiar in the insect frass and gut, but also found on books and the surfaces of shelves. Symbiotaphrina, an ascomycete fungus described as one of the symbiotic levuliform fungi, present in the anobiid beetles' gut, was the only one found in all samples analyzed and has therefore been proposed as a putative biomarker.

The phyllosphere microbiome of host trees contributes more than leaf phytochemicals to variation in the Agrilus planipennis Fairmaire gut microbiome structure

The microbiome composition of living organisms is closely linked to essential functions determining the fitness of the host for thriving and adapting to a particular ecosystem. Although multiple factors, including the developmental stage, the diet, and host-microbe coevolution have been reported to drive compositional changes in the microbiome structures, very few attempts have been made to disentangle their various contributions in a global approach. Here, we focus on the emerald ash borer (EAB), an herbivorous pest and a real threat to North American ash tree species, to explore the responses of the adult EAB gut microbiome to ash leaf properties, and to identify potential predictors of EAB microbial variations. The relative contributions of specific host plant properties, namely bacterial and fungal communities on leaves, phytochemical composition, and the geographical coordinates of the sampling sites, to the EAB gut microbial community was examined by canonical analyses. The composition of the phyllosphere microbiome appeared to be a strong predictor of the microbial community structure in EAB guts, explaining 53 and 48% of the variation in fungi and bacteria, respectively. This study suggests a potential covariation of the microorganisms associated with food sources and the insect gut microbiome.

Comparison of Gut Bacterial Communities of Grapholita molesta (Lepidoptera: Tortricidae) Reared on Different Host Plants

Intestinal symbiotic bacteria have played an important role in the digestion, immunity detoxification, mating, and reproduction of insects during long-term coevolution. The oriental fruit moth, Grapholita molesta, is an important fruit tree pest worldwide. However, the composition of the G. molesta microbial community, especially of the gut microbiome, remains unclear. To explore the differences of gut microbiota of G. molesta when reared on different host plants, we determined the gut bacterial structure when G. molesta was transferred from an artificial diet to different host plants (apples, peaches, nectarines, crisp pears, plums, peach shoots) by amplicon sequencing technology. The results showed that Proteobacteria and Firmicutes are dominant in the gut microbiota of G. molesta. Plum-feeding G. molesta had the highest richness and diversity of gut microbiota, while apple-feeding G. molesta had the lowest. PCoA and PERMANOVA analysis revealed that there were significant differences in the gut microbiota structure of G. molesta on different diets. PICRUSt2 analysis indicated that most of the functional prediction pathways were concentrated in metabolic and cellular processes. Our results confirmed that gut bacterial communities of G. molesta can be influenced by host diets and may play an important role in host adaptation.

Interkingdom Gut Microbiome and Resistome of the Cockroach Blattella germanica

Cockroaches are intriguing animals with two coexisting symbiotic systems, an endosymbiont in the fat body, involved in nitrogen metabolism, and a gut microbiome whose diversity, complexity, role, and developmental dynamics have not been fully elucidated. In this work, we present a metagenomic approach to study Blattella germanica populations not treated, treated with kanamycin, and recovered after treatment, both naturally and by adding feces to the diet, with the aim of better understanding the structure and function of its gut microbiome along the development as well as the characterization of its resistome.IMPORTANCE For the first time, we analyze the interkingdom hindgut microbiome of this species, including bacteria, fungi, archaea, and viruses. Network analysis reveals putative cooperation between core bacteria that could be key for ecosystem equilibrium. We also show how antibiotic treatments alter microbiota diversity and function, while both features are restored after one untreated generation. Combining data from B. germanica treated with three antibiotics, we have characterized this species' resistome. It includes genes involved in resistance to several broad-spectrum antibiotics frequently used in the clinic. The presence of genetic elements involved in DNA mobilization indicates that they can be transferred among microbiota partners. Therefore, cockroaches can be considered reservoirs of antibiotic resistance genes (ARGs) and potential transmission vectors.

Gut bacterial communities across 12 Ensifera (Orthoptera) at different feeding habits and its prediction for the insect with contrasting feeding habits

Insect microbial symbioses play a critical role in insect lifecycle, and insect gut microbiome could be influenced by many factors. Studies have shown that host diet and taxonomy have a strong influence on insect gut microbial community. In this study, we performed sequencing of V3-V4 region of 16S rRNA gene to compare the composition and diversity of 12 Ensifera from 6 provinces of China. Moreover, the influences of feeding habits and taxonomic status of insects on their gut bacterial community were evaluated, which might provide reference for further application research. The results showed that Proteobacteria (45.66%), Firmicutes (34.25%) and Cyanobacteria (7.7%) were the predominant bacterial phyla in Ensifera. Moreover, the gut bacterial community composition of samples with different feeding habits was significantly different, which was irrespective of their taxa. The highest diversity of gut bacteria was found in the omnivorous Ensifera. Furthermore, common and unique bacteria with biomarkers were found based on the dietary characteristics of the samples. However, the bacterial community structure of the Ensifera samples was significantly different from that of Caelifera. Therefore, we concluded that feeding habits and taxonomic status jointly affect the gut bacterial community composition of the samples from Orthoptera. However, the influence of feeding habit dominates when taxonomy category below the suborder level. In addition, the dominant, common and unique bacterial community structure could be used to predict the contrastic feeding habits of insects belonging to Ensifera.

Diversity structure of the microbial communities in the guts of four neotropical termite species

The termite gut microbiome is dominated by lignocellulose degrading microorganisms. This study describes the intestinal microbiota of four Argentinian higher termite species with different feeding habits: Microcerotermes strunckii (hardwood), Nasutitermes corniger (softwood), Termes riograndensis (soil organic matter/grass) and Cornitermes cumulans (grass) by deep sequencing of amplified 16S rRNA and ITS genes. In addition, we have performed a taxonomic and gut community structure comparison incorporating into the analysis the previously reported microbiomes of additional termite species with varied diets. The bacterial phylum Spirochaetes was dominant in the guts of M. strunckii, N. corniger and C. cumulans, whereas Firmicutes predominated in the T. riograndensis gut microbiome. A single bacterial genus, Treponema (Spirochaetes), was dominant in all termite species, except for T. riograndensis. Both in our own sequenced samples and in the broader comparison, prokaryotic α-diversity was higher in the soil/grass feeders than in the wood feeders. Meanwhile, the β-diversity of prokaryotes and fungi was highly dissimilar among strict wood-feeders, whereas that of soil- and grass-feeders grouped more closely. Ascomycota and Basidiomycota were the only fungal phyla that could be identified in all gut samples, because of the lack of reference sequences in public databases. In summary, higher microbial diversity was recorded in termites with more versatile feeding sources, providing further evidence that diet, along with other factors (e.g., host taxonomy), influences the microbial community assembly in the termite gut.

Gut microbiome of the emerald ash borer, Agrilus planipennis Fairmaire, and its relationship with insect population density

The gut microbial communities of beetles play crucial roles in their adaptive capacities. Environmental factors such as temperature or nutrition naturally affect the insect microbiome, but a shift in local conditions like the population density on a host tree could also lead to changes in the microbiota. The emerald ash borer (EAB), Agrilus planipennis Fairmaire, is an exotic wood borer that causes environmental and economic damage to ash trees in North America. This study aimed to describe the taxonomic structure of the EAB gut microbiome and explore its potential relationship with borer population size. The number of EAB adults collected per tree through a 75 km transect from an epicenter allowed the creation of distinct classes of population density. The Gammaproteobacteria and Ascomycota predominated in bacterial and fungal communities respectively, as determined by sequencing of the bacterial 16S rRNA gene and the fungal internal transcribed spacer ITS2. Species richness and diversity of the bacterial community showed significant dependence on population density. Moreover, α-diversity and β-diversity analysis revealed some indicator amplicon sequence variants suggesting that the plasticity of the gut microbiome could be related to the EAB population density in host trees.

Divergence in Gut Bacterial Community Among Life Stages of the Rainbow Stag Beetle Phalacrognathus muelleri (Coleoptera: Lucanidae)

Although stag beetles are popular saprophytic insects, there are few studies about their gut bacterial community. This study focused on the gut bacterial community structure of the rainbow stag beetle (i.e., Phalacrognathus muelleri) in its larvae (three instars) and adult stages, using high throughput sequencing (Illumina Miseq). Our aim was to compare the gut bacterial community structure among different life stages. The results revealed that bacterial alpha diversity increased from the 1st instar to the 3rd instar larvae. Adults showed the lowest gut bacterial alpha diversity. Bacterial community composition was significantly different between larvae and adults (p = 0.001), and 1st instar larvae (early instar) had significant differences with the 2nd (p= 0.007) and 3rd (p = 0.001) instar larvae (final instar). However, there was little difference in the bacterial community composition between the 2nd and 3rd instar larvae (p = 0.059). Our study demonstrated dramatic shifts in gut bacterial community structure between larvae and adults. Larvae fed on decaying wood and adults fed on beetle jelly, suggesting that diet is a crucial factor shaping the gut bacterial community structure. There were significant differences in bacterial community structure between early instar and final instars larvae, suggesting that certain life stages are associated with a defined gut bacterial community.

Fruit host-dependent fungal communities in the microbiome of wild Queensland fruit fly larvae

Bactrocera tryoni (Froggatt), the Queensland fruit fly (Qfly), is a highly polyphagous tephritid fly that is widespread in Eastern Australia. Qfly physiology is closely linked with its fungal associates, with particular relationship between Qfly nutrition and yeast or yeast-like fungi. Despite animal-associated fungi typically occurring in multi-species communities, Qfly studies have predominately involved the culture and characterisation of single fungal isolates. Further, only two studies have investigated the fungal communities associated with Qfly, and both have used culture-dependant techniques that overlook non-culturable fungi and hence under-represent, and provide a biased interpretation of, the overall fungal community. In order to explore a potentially hidden fungal diversity and complexity within the Qfly mycobiome, we used culture-independent, high-throughput Illumina sequencing techniques to comprehensively, and holistically characterized the fungal community of Qfly larvae and overcome the culture bias. We collected larvae from a range of fruit hosts along the east coast of Australia, and all had a mycobiome dominated by ascomycetes. The most abundant fungal taxa belonged to the genera Pichia (43%), Candida (20%), Hanseniaspora (10%), Zygosaccharomyces (11%) and Penicillium (7%). We also characterized the fungal communities of fruit hosts, and found a strong degree of overlap between larvae and fruit host communities, suggesting that these communities are intimately inter-connected. Our data suggests that larval fungal communities are acquired from surrounding fruit flesh. It is likely that the physiological benefits of Qfly exposure to fungal communities is primarily due to consumption of these fungi, not through syntrophy/symbiosis between fungi and insect ‘host’.

Diversity and dynamics of microbial communities in brown planthopper at different developmental stages revealed by high-throughput amplicon sequencing

The microbiome associated with brown planthopper (BPH) plays an important role in mediating host health and fitness. Characterization of the microbial community and its structure is prerequisite for understanding the intricate symbiotic relationships between microbes and host insect. Here, we investigated the bacterial and fungal communities of BPH at different developmental stages using high-throughput amplicon sequencing. Our results revealed that both the bacterial and fungal communities were diverse and dynamic during BPH development. The bacterial communities were generally richer than fungi in each developmental stage. At 97% similarly, 19 phyla and 278 genera of bacteria were annotated, while five fungal phyla comprising 80 genera were assigned. The highest species richness for the bacterial communities was detected in the nymphal stage. The taxonomic diversity of the fungal communities in female adults was generally at a relatively higher level when compared to other developmental stages. The most dominant phylum of bacteria and fungi at each developmental stage all belonged to Proteobacteria and Ascomycota, respectively. A significantly lower abundance of bacterial genus Acinetobacter was recorded in the egg stage when compared to other developmental stages, while the dominant fungal genus Wallemia was more abundant in the nymph and adult stages than in the egg stage. Additionally, the microbial composition differed between male and female adults, suggesting that the microbial communities in BPH were gender-dependent. Overall, our study enriches our knowledge on the microbial communities associated with BPH and will provide clues to develop potential biocontrol techniques against this rice pest.

Integrative developmental ecology: a review of density-dependent effects on life-history traits and host-microbe interactions in non-social holometabolous insects

Population density modulates a wide range of eco-evolutionary processes including inter- and intra-specific competition, fitness and population dynamics. In holometabolous insects, the larval stage is particularly susceptible to density-dependent effects because the larva is the resource-acquiring stage. Larval density-dependent effects can modulate the expression of life-history traits not only in the larval and adult stages but also downstream for population dynamics and evolution. Better understanding the scope and generality of density-dependent effects on life-history traits of current and future generations can provide useful knowledge for both theory and experiments in developmental ecology. Here, we review the literature on larval density-dependent effects on fitness of non-social holometabolous insects. First, we provide a functional definition of density to navigate the terminology in the literature. We then classify the biological levels upon which larval density-dependent effects can be observed followed by a review of the literature produced over the past decades across major non-social holometabolous groups. Next, we argue that host-microbe interactions are yet an overlooked biological level susceptible to density-dependent effects and propose a conceptual model to explain how density-dependent effects on host-microbe interactions can modulate density-dependent fitness curves. In summary, this review provides an integrative framework of density-dependent effects across biological levels which can be used to guide future research in the field of ecology and evolution.

Gut Bacteria in the Holometabola: A Review of Obligate and Facultative Symbionts

The diversity and ecological variety of Holometabola foregrounds a wide array of dynamic symbiotic relationships with gut-dwelling bacteria. A review of the literature highlights that holometabolous insects rely on both obligate bacteria and facultative bacteria living in their guts to satisfy a number of physiological needs. The driving forces behind these differing relationships can be hypothesized through the scrutiny of bacterial associations with host gut morphology, and transmission of bacteria within a given host taxon. Our knowledge of the evolution of facultative or obligate symbiotic bacteria in holometabolan systems is further enhanced by an assessment of the various services the bacteria provide, including nutrition, immune system health, and development. The diversity of Holometabola can thus be examined through an assessment of known bacterial partnerships within the orders of Holometabola.

Microbiome of the Queensland Fruit Fly through Metamorphosis

Bactrocera tryoni (Froggatt) (Queensland fruit fly, or “Qfly”) is a highly polyphagous tephritid fruit fly and a serious economic pest in Australia. Qfly biology is intimately linked to the bacteria and fungi of its microbiome. While there are numerous studies of the microbiome in larvae and adults, the transition of the microbiome through the pupal stage remains unknown. To address this knowledge gap, we used high-throughput Next-Generation Sequencing (NGS) to examine microbial communities at each developmental stage in the Qfly life cycle, targeting the bacterial 16S rRNA and fungal ITS regions. We found that microbial communities were similar at the larval and pupal stage and were also similar between adult males and females, yet there were marked differences between the larval and adult stages. Specific bacterial and fungal taxa are present in the larvae and adults (fed hydrolyzed yeast with sugar) which is likely related to differences in nutritional biology of these life stages. We observed a significant abundance of the Acetobacteraceae at the family level, both in the larval and pupal stages. Conversely, Enterobacteriaceae was highly abundant (>80%) only in the adults. The majority of fungal taxa present in Qfly were yeasts or yeast-like fungi. In addition to elucidating changes in the microbiome through developmental stages, this study characterizes the Qfly microbiome present at the establishment of laboratory colonies as they enter the domestication process.

Comparison of gut bacterial communities and their associations with host diets in four fruit borers

BACKGROUND

Microbiota that live in the gut of insects have a wide range of effects on host nutrition, physiology, and behavior. They may shape the adaptation of their hosts to different habitats and lifestyles. To characterize the gut microbiota of fruit borers comprehensively, we compared bacterial communities among Grapholita molesta, Conogethes punctiferalis, Carposina sasakii, and Cydia pomonella, which are serious lepidopteran pests. We selected G. molesta as a representative pest to more explicitly test the influence of host dietary niche on the insect gut microbiome, and compared the bacterial microbial communities of G. molesta fed different diets (peach shoots and apple) using Illumina high-throughput sequencing technology.

RESULTS

The results show that Proteobacteria and Firmicutes are dominant in their gut microbiota. The C. sasakii had the highest richness values and G. molesta (shoot-feeding) had the highest diversity, whereas C. pomonella and G. molesta (fruit-feeding) had the lowest bacterial richness and diversity, respectively. The ANOSIM analysis revealed significant differences in the structure of gut microbiota among different insects. In addition, G. molesta with a different feeding diet had significant differences in gut microbiota composition. PICRUSt analysis indicated that most functional prediction categories were related to metabolism.

CONCLUSION

Our results show that gut microbiota composition is affected significantly not only by host species but also host diets. An enhanced understanding of these herbivore-associated microbial symbionts is essential for understanding the biology and ecology of the host insect, and may offer new possibilities to improve integrated pest-management strategies for efficient control of fruit borers. © 2019 Society of Chemical Industry.

Characterization of the gut microbiota of invasive Agrilus mali Matsumara (Coleoptera: Buprestidae) using high-throughput sequencing: uncovering plant cell-wall degrading bacteria

The genus Agrilus comprises diverse exotic and agriculturally important wood-boring insects that have evolved efficient digestive systems. Agrilus mali Matsumara, an invasive insect, is causing extensive mortality to endangered wild apple trees in Tianshan. In this study, we present an in-depth characterization of the gut microbiota of A. mali based on high-throughput sequencing of the 16S rRNA gene and report the presence of lignocellulose-degrading bacteria. Thirty-nine operational taxonomic units (OTUs) were characterized from the larval gut. OTUs represented 6 phyla, 10 classes, 16 orders, 20 families, and 20 genera. The majority of bacterial OTUs belonged to the order Enterobacteriales which was the most abundant taxa in the larval gut. Cultivable bacteria revealed 9 OTUs that all belonged to Gammaproteobacteria. Subsequently, we examined the breakdown of plant cell-wall compounds by bacterial isolates. Among the isolates, the highest efficiency was observed in Pantoea sp., which was able to synthesize four out of the six enzymes (cellulase, cellobiase, β-xylanase, and β-gluconase) responsible for plant-cell wall degradation. One isolate identified as Pseudomonas orientalis exhibited lignin peroxidase activity. Our study provides the first characterization of the gut microbial diversity of A. mali larvae and shows that some cultivable bacteria play a significant role in the digestive tracts of larvae by providing nutritional needs.