The gut microbiota of the pine weevil is similar across Europe and resembles that of other conifer-feeding beetles

Gut microorganisms of Locusta migratoria in various life stages and its possible influence on cellulose digestibility

Locusta migratoria is an important phytophagous pest, and its gut microbial communities play an important role in cellulose degradation. In this study, the gut microbial and cellulose digestibility dynamics of Locusta migratoria were jointly analyzed using high-throughput sequencing and anthrone colorimetry. The results showed that the gut microbial diversity and cellulose digestibility across life stages were dynamically changing. The species richness of gut bacteria was significantly higher in eggs than in larvae and imago, the species richness and cellulose digestibility of gut bacteria were significantly higher in early larvae (first and second instars) than in late larvae (third to fifth instars), and the diversity of gut bacteria and cellulose digestibility were significantly higher in imago than in late larvae. There is a correlation between the dynamics of gut bacterial communities and cellulose digestibility. Enterobacter, Lactococcus, and Pseudomonas are the most abundant genera throughout all life stages. Six strains of highly efficient cellulolytic bacteria were screened, which were dominant gut bacteria. Carboxymethyl cellulase activity (CMCA) and filter paper activity (FPA) experiments revealed that Pseudomonas had the highest cellulase enzyme activity. This study provides a new way for the screening of cellulolytic bacteria and lays the foundation for developing insects with significant biomass into cellulose-degrading bioreactors.

IMPORTANCE

Cellulose is the most abundant and cheapest renewable resource in nature, but its degradation is difficult, so finding efficient cellulose degradation methods is an urgent challenge. Locusta migratoria is a large group of agricultural pests, and the large number of microorganisms that inhabit their intestinal tracts play an important role in cellulose degradation. We analyzed the dynamics of Locusta migratoria gut microbial communities and cellulose digestibility using a combination of high-throughput sequencing technology and anthrone colorimetry. The results revealed that the gut microbial diversity and cellulose digestibility were dynamically changed at different life stages. In addition, we explored the intestinal bacterial community of Locusta migratoria across life stages and its correlation with cellulose digestibility. The dominant bacterial genera at different life stages of Locusta migratoria were uncovered and their carboxymethyl cellulase activity (CMCA) and filter paper activity (FPA) were determined. This study provides a new avenue for screening cellulolytic bacteria and lays the foundation for developing insects with significant biomass into cellulose-degrading bioreactors.

Microbiomes, diet flexibility, and the spread of a beetle parasite of honey bees

Invasive pests may disturb and destructively reformat the local ecosystem. The small hive beetle (SHB), Aethina tumida, originated in Africa and has expanded to America, Australia, Europe, and Asia. A key factor facilitating its fast global expansion is its ability to subsist on diverse food inside and outside honey bee colonies. SHBs feed on various plant fruits and exudates in the environment while searching for bee hives. After sneaking into a bee hive, they switch their diet to honey, pollen, and bee larvae. How SHBs survive on such a broad range of food remains unclear. In this study, we simulated the outside and within hive stages by providing banana and hive resources and quantified the SHB associated microbes adjusted by the diet. We found that SHBs fed on bananas were colonized by microbes coding more carbohydrate-active enzymes and a higher alpha diversity than communities from SHBs feeding on hive products or those collected directly from bee hives. SHBs fed on bananas and those collected from the hive showed high symbiont variance, indicated by the beta diversity. Surprisingly, we found the honey bee core symbiont Snodgrassella alvi in the guts of SHBs collected in bee hives. To determine the role of S. alvi in SHB biology, we inoculated SHBs with a genetically tagged culture of S. alvi, showing that this symbiont is a likely transient of SHBs. In contrast, the fungus Kodamaea ohmeri is the primary commensal of SHBs. Diet-based microbiome shifts are likely to play a key role in the spread and success of SHBs.

Co-habiting ants and silverfish display a converging feeding ecology

BACKGROUND

Various animal taxa have specialized to living with social hosts. Depending on their level of specialization, these symbiotic animals are characterized by distinct behavioural, chemical, and morphological traits that enable close heterospecific interactions. Despite its functional importance, our understanding of the feeding ecology of animals living with social hosts remains limited. We examined how host specialization of silverfish co-habiting with ants affects several components of their feeding ecology. We combined stable isotope profiling, feeding assays, phylogenetic reconstruction, and microbial community characterization of the Neoasterolepisma silverfish genus and a wider nicoletiid and lepismatid silverfish panel where divergent myrmecophilous lifestyles are observed.

RESULTS

Stable isotope profiling (δ13C and δ15N) showed that the isotopic niches of granivorous Messor ants and Messor-specialized Neoasterolepisma exhibit a remarkable overlap within an ant nest. Trophic experiments and gut dissections further supported that these specialized Neoasterolepisma silverfish transitioned to a diet that includes plant seeds. In contrast, the isotopic niches of generalist Neoasterolepisma silverfish and generalist nicoletiid silverfish were clearly different from their ant hosts within the shared nest environment. The impact of the myrmecophilous lifestyle on feeding ecology was also evident in the internal silverfish microbiome. Compared to generalists, Messor-specialists exhibited a higher bacterial density and a higher proportion of heterofermentative lactic acid bacteria. Moreover, the nest environment explained the infection profile (or the 16S rRNA genotypes) of Weissella bacteria in Messor-specialized silverfish and the ant hosts.

CONCLUSIONS

Together, we show that social hosts are important determinants for the feeding ecology of symbiotic animals and can induce diet convergence.

Functional and Compositional Changes in Sirex noctilio Gut Microbiome in Different Habitats: Unraveling the Complexity of Invasive Adaptation

The mutualistic symbiosis relationship between the gut microbiome and their insect hosts has attracted much scientific attention. The native woodwasp, Sirex nitobei, and the invasive European woodwasp, Sirex noctilio, are two pests that infest pines in northeastern China. Following its encounter with the native species, however, there is a lack of research on whether the gut microbiome of S. noctilio changed, what causes contributed to these alterations, and whether these changes were more conducive to invasive colonization. We used high-throughput and metatranscriptomic sequencing to investigate S. noctilio larval gut and frass from four sites where only S. noctilio and both two Sirex species and investigated the effects of environmental factors, biological interactions, and ecological processes on S. noctilio gut microbial community assembly. Amplicon sequencing of two Sirex species revealed differential patterns of bacterial and fungal composition and functional prediction. S. noctilio larval gut bacterial and fungal diversity was essentially higher in coexistence sites than in separate existence sites, and most of the larval gut bacterial and fungal community functional predictions were significantly different as well. Moreover, temperature and precipitation positively correlate with most of the highly abundant bacterial and fungal genera. Source-tracking analysis showed that S. noctilio larvae at coexistence sites remain dependent on adult gut transmission (vertical transmission) or recruitment to frass (horizontal transmission). Meanwhile, stochastic processes of drift and dispersal limitation also have important impacts on the assembly of S. noctilio larval gut microbiome, especially at coexistence sites. In summary, our results reveal the potential role of changes in S. noctilio larval gut microbiome in the successful colonization and better adaptation of the environment.

The Eurasian spruce bark beetle Ips typographus shapes the microbial communities of its offspring and the gallery environment

The Eurasian spruce bark beetle (Ips typographus) is currently the most economically relevant pest of Norway spruce (Picea abies). Ips typographus associates with filamentous fungi that may help it overcome the tree's chemical defenses. However, the involvement of other microbial partners in this pest's ecological success is unclear. To understand the dynamics of the bark beetle-associated microbiota, we characterized the bacterial and fungal communities of wild-collected and lab-reared beetles throughout their development by culture-dependent approaches, meta-barcoding, and quantitative PCR. Gammaproteobacteria dominated the bacterial communities, while the fungal communities were mainly composed of yeasts of the Saccharomycetales order. A stable core of microbes is shared by all life stages, and is distinct from those associated with the surrounding bark, indicating that Ips typographus influences the microbial communities of its environment and offspring. These findings coupled with our observations of maternal behavior, suggest that Ips typographus transfers part of its microbiota to eggs via deposition of an egg plug treated with maternal secretions, and by inducing an increase in abundance of a subset of taxa from the adjacent bark.

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.

Microbial degradation of plant toxins

Plants produce a variety of secondary metabolites in response to biotic and abiotic stresses. Although they have many functions, a subclass of toxic secondary metabolites mainly serve plants as deterring agents against herbivores, insects, or pathogens. Microorganisms present in divergent ecological niches, such as soil, water, or insect and rumen gut systems have been found capable of detoxifying these metabolites. As a result of detoxification, microbes gain growth nutrients and benefit their herbivory host via detoxifying symbiosis. Here, we review current knowledge on microbial degradation of toxic alkaloids, glucosinolates, terpenes, and polyphenols with an emphasis on the genes and enzymes involved in breakdown pathways. We highlight that the insect-associated microbes might find application in biotechnology and become targets for an alternative microbial pest control strategy.

Gut microbiomes of cycad-feeding insects tolerant to β-methylamino-L-alanine (BMAA) are rich in siderophore biosynthesis

Ingestion of the cycad toxins β-methylamino-L-alanine (BMAA) and azoxyglycosides is harmful to diverse organisms. However, some insects are specialized to feed on toxin-rich cycads with apparent immunity. Some cycad-feeding insects possess a common set of gut bacteria, which might play a role in detoxifying cycad toxins. Here, we investigated the composition of gut microbiota from a worldwide sample of cycadivorous insects and characterized the biosynthetic potential of selected bacteria. Cycadivorous insects shared a core gut microbiome consisting of six bacterial taxa, mainly belonging to the Proteobacteria, which we were able to isolate. To further investigate selected taxa from diverging lineages, we performed shotgun metagenomic sequencing of co-cultured bacterial sub-communities. We characterized the biosynthetic potential of four bacteria from Serratia, Pantoea, and two different Stenotrophomonas lineages, and discovered a suite of biosynthetic gene clusters notably rich in siderophores. Siderophore semi-untargeted metabolomics revealed a broad range of chemically related yet diverse iron-chelating metabolites, including desferrioxamine B, suggesting the occurrence of an unprecedented desferrioxamine-like biosynthetic pathway that remains to be identified. These results provide a foundation for future investigations into how cycadivorous insects tolerate diets rich in azoxyglycosides, BMAA, and other cycad toxins, including a possible role for bacterial siderophores.

Erwiniaceae bacteria play defensive and nutritional roles in two widespread ambrosia beetles

Ambrosia beetles are fungal-growing insects excavating galleries deep inside the wood. Their success as invaders increased scientific interest towards them. However, most studies on their microbiota targeted their fungal associates whereas the role of bacterial associates is understudied. To explore the role of abundant microbial associates, we isolated bacteria from active galleries of two widespread ambrosia beetles, Xylosandrus crassiusculus and X. germanus. These isolates were classified within the Erwiniaceae family and through a phylogenetic analysis including isolates from other insects we showed that they clustered with isolates obtained from ambrosia and bark beetles, including Erwinia typographi. The whole genome analysis of the isolate from active galleries of X. crassiusculus suggested that this bacterium plays both a nutritional role, by providing essential amino acids and enzymes for the hydrolysis of plant biomass, and a defensive role, by producing antibiotics. This defensive role was also tested in vitro against fungi, including mutualists, common associates, and parasites. The bacteria inhibited the growth of some of the common associates and parasites but did not affect mutualists. Our study supported the hypothesis of a mutualist role of Erwiniaceae bacteria in ambrosia beetles and highlighed the importance of bacteria in maintaining the symbiosis of their host with nutritional fungi.

The pivotal roles of gut microbiota in insect plant interactions for sustainable pest management

The gut microbiota serves as a critical "organ" in the life cycle of animals, particularly in the intricate interplay between herbivorous pests and plants. This review summarizes the pivotal functions of the gut microbiota in mediating the insect-plant interactions, encompassing their influence on host insects, modulation of plant physiology, and regulation of the third trophic level species within the ecological network. Given these significant functions, it is plausible to harness these interactions and their underlying mechanisms to develop novel eco-friendly pest control strategies. In this context, we also outline some emerging pest control methods based on the intestinal microbiota or bacteria-mediated interactions, such as symbiont-mediated RNAi and paratransgenesis, albeit these are still in their nascent stages and confront numerous challenges. Overall, both opportunities and challenges coexist in the exploration of the intestinal microbiota-mediated interactions between insect pests and plants, which will not only enrich the fundamental knowledge of plant-insect interactions but also facilitate the development of sustainable pest control strategies.

Unraveling the Role of Antimicrobial Peptides in Insects

Antimicrobial peptides (AMPs) are short, mainly positively charged, amphipathic molecules. AMPs are important effectors of the immune response in insects with a broad spectrum of antibacterial, antifungal, and antiparasitic activity. In addition to these well-known roles, AMPs exhibit many other, often unobvious, functions in the host. They support insects in the elimination of viral infections. AMPs participate in the regulation of brain-controlled processes, e.g., sleep and non-associative learning. By influencing neuronal health, communication, and activity, they can affect the functioning of the insect nervous system. Expansion of the AMP repertoire and loss of their specificity is connected with the aging process and lifespan of insects. Moreover, AMPs take part in maintaining gut homeostasis, regulating the number of endosymbionts as well as reducing the number of foreign microbiota. In turn, the presence of AMPs in insect venom prevents the spread of infection in social insects, where the prey may be a source of pathogens.

Isolation and characterization of gut bacteria associated with the degradation of host-specific terpenoids in Pagiophloeus tsushimanus (Coleoptera: Curculionidae) larvae

Insect intestinal bacteria play an important role in resisting defensive substances of host plants. Pagiophloeus tsushimanus (Coleoptera: Curculionidae) feeds exclusively on camphor trees (Cinnamomum camphora, Laurales: Lauraceae) in China, causing substantial economic and ecological losses. It is unclear how the larvae of P. tsushimanus outcome the main secondary metabolites of C. camphora such as D-camphor, eucalyptol, and linalool. In this study, we isolated terpenoid-degrading bacteria from the gut of P. tsushimanus larvae by using selective culture medium. Maximum likelihood phylogenetic analyses were performed with 16S rDNA sequences to identify the bacteria, and results showed ten strains belonged to four genera, including Pseudomonas, Enterobacter, Serratia, and Corynebacterium. Then, gas chromatography was employed to determine the degradability of D-camphor, eucalyptol, and linalool by the isolated strains, results showed that Z5 strain (i.e., Corynebacterium variabile, Actinomycetales: Corynebacteriaceae), F1 strain (i.e., Pseudomonas aeruginosa, Pseudomonadales: Pseudomonaceae), and A3 strain (i.e., Serratia marcescens, Enterobacterales: Enterobacteriaceae) had the highest degradation rates of D-camphor, linalool, and eucalyptol, respectively. The intestinal bacteria were capable of terpenoid degradation in vitro, which suggested that these gut bacteria associated with P. tsushimanus play an important role in overcoming host plant secondary metabolite defense, thereby facilitating the host specialization of this pest.

Demonstrating the role of symbionts in mediating detoxification in herbivores

Plant toxins constitute an effective defense against herbivorous animals. However, many herbivores have evolved adaptations to cope with dietary toxins through detoxification, excretion, sequestration, target site insensitivity and/or via behavioral avoidance. While these adaptations are often directly encoded in herbivore genomes, evidence is accumulating that microbial symbionts can reduce the dose of plant toxins by metabolizing or sequestering them prior to absorption by the herbivore. Here, we describe a few well-studied examples to assess such symbiont-mediated detoxification and showcase different approaches that have been used for their analyses. These include: (i) a host phenotypic route in which the symbiotic association is manipulated to reveal host fitness costs upon toxin exposure in the presence/absence of detoxifying symbionts, including function restoration after symbiont re-infection, (ii) a molecular microbiological approach that focuses on the identification and characterization of microbial genes involved in plant toxin metabolism, and (iii) an analytical chemical route that aims to characterize the conversion of the toxin to less harmful metabolites in vivo and link conversion to the activities of a detoxifying symbiont. The advantages and challenges of each approach are discussed, and it is argued that a multi-pronged strategy combining phenotypic, molecular, and chemical evidence is needed to unambiguously demonstrate microbial contributions to plant toxin reduction and the importance of these processes for host fitness. Given the interdisciplinary nature of the topic, we aim to provide a guideline to researchers interested in symbiont-mediated detoxification and hope to encourage future studies that contribute to a more comprehensive and mechanistic understanding of detoxification in herbivores and their symbionts.

Seasonal variation of microbiota composition in Anopheles gambiae and Anopheles coluzzii in two different eco-geographical localities in Cameroon

Understanding the environmental factors affecting the microbiota in malaria vectors may help in the development of novel vector control interventions, similar to paratransgenesis. This study evaluated seasonal and geographical variations in the microbial community of the two major malaria vectors. Adult Anopheles mosquitoes were collected across two different eco-geographical settings in Cameroon, during the dry and wet seasons. DNA was extracted from the whole individual mosquitoes from each group and processed for microbial analysis using Illumina Miseq sequencing of the V3-V4 region of the 16S rRNA gene. Data analysis was performed using QIIME2 and R software programs. A total of 1985 mosquitoes were collected and among them, 120 were selected randomly corresponding to 30 mosquitoes per season and locality. Overall, 97 bacterial taxa were detected across all mosquito samples, with 86 of these shared between dry and wet seasons in both localities and species. There were significant differences in bacterial composition between both seasons, with a clear separation observed between the dry and wet seasons (PERMANOVA comparisons of beta diversity, Pseudo-F = 10.45; q-value = 0.01). This study highlights the influence of seasonal variation on microbial communities and this variation's impact on mosquito biology and vectorial capacity should be further investigated.

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.

Parallel meta-transcriptome analysis reveals degradation of plant secondary metabolites by beetles and their gut symbionts

Switching to a new host plant is a driving force for divergence and speciation in herbivorous insects. This process of incorporating a novel host plant into the diet may require a number of adaptations in the insect herbivores that allow them to consume host plant tissue that may contain toxic secondary chemicals. As a result, herbivorous insects are predicted to have evolved efficient ways to detoxify major plant defenses and increase fitness by either relying on their own genomes or by recruiting other organisms such as microbial gut symbionts. In the present study we used parallel meta-transcriptomic analyses of Altica flea beetles and their gut symbionts to explore the contributions of beetle detoxification mechanisms versus detoxification by their gut consortium. We compared the gut meta-transcriptomes of two sympatric Altica species that feed exclusively on different host plant species as well as their F₁ hybrids that were fed one of the two host plant species. These comparisons revealed that gene expression patterns of Altica are dependent on both beetle species identity and diet. The community structure of gut symbionts was also dependent on the identity of the beetle species, and the gene expression patterns of the gut symbionts were significantly correlated with beetle species and plant diet. Some of the enriched genes identified in the beetles and gut symbionts are involved in the degradation of secondary metabolites produced by plants, suggesting that Altica flea beetles may use their gut microbiota to help them feed on and adapt to their host plants.

Beetle-Bacterial Symbioses: Endless Forms Most Functional

Beetles are hosts to a remarkable diversity of bacterial symbionts. In this article, we review the role of these partnerships in promoting beetle fitness following a surge of recent studies characterizing symbiont localization and function across the Coleoptera. Symbiont contributions range from the supplementation of essential nutrients and digestive or detoxifying enzymes to the production of bioactive compounds providing defense against natural enemies. Insights on this functional diversity highlight how symbiosis can expand the host's ecological niche, but also constrain its evolutionary potential by promoting specialization. As bacterial localization can differ within and between beetle clades, we discuss how it corresponds to the microbe's beneficial role and outline the molecular and behavioral mechanisms underlying symbiont translocation and transmission by its holometabolous host. In reviewing this literature, we emphasize how the study of symbiosis can inform our understanding of the phenotypic innovations behind the evolutionary success of beetles.

Host species identity shapes the diversity and structure of insect microbiota

As for most of the life that inhabits our planet, microorganisms play an essential role in insect nutrition, reproduction, defence, and support their host in many other functions. More recently, we assisted to an exponential growth of studies describing the taxonomical composition of bacterial communities across insects' phylogeny. However, there is still an outstanding question that needs to be answered: Which factors contribute most to shape insects' microbiomes? This study tries to find an answer to this question by taking advantage of publicly available sequencing data and reanalysing over 4000 samples of insect-associated bacterial communities under a common framework. Results suggest that insect taxonomy has a wider impact on the structure and diversity of their associated microbial communities than the other factors considered (diet, sex, life stage, sample origin and treatment). However, when specifically testing for signatures of codiversification of insect species and their microbiota, analyses found weak support for this, suggesting that while insect species strongly drive the structure and diversity of insect microbiota, the diversification of those microbial communities did not follow their host's phylogeny. Furthermore, a parallel survey of the literature highlights several methodological limitations that need to be considered in the future research endeavours.

The microbiome extends host evolutionary potential

The microbiome shapes many host traits, yet the biology of microbiomes challenges traditional evolutionary models. Here, we illustrate how integrating the microbiome into quantitative genetics can help untangle complexities of host-microbiome evolution. We describe two general ways in which the microbiome may affect host evolutionary potential: by shifting the mean host phenotype and by changing the variance in host phenotype in the population. We synthesize the literature across diverse taxa and discuss how these scenarios could shape the host response to selection. We conclude by outlining key avenues of research to improve our understanding of the complex interplay between hosts and microbiomes.

The Influence of Gut Microbiota on the Fecundity of Henosepilachna vigintioctopunctata (Coleoptera: Coccinellidae)

The gut microbiota of insects usually plays an important role in the development and reproduction of their hosts. The fecundity of Henosepilachna vigintioctopunctata (Fabricius) varies greatly when they develop on different host plants. Whether and how the gut microbiota regulates the fecundity of H. vigintioctopunctata was unknown. To address this question, we used 16S rRNA sequencing to analyze the gut microbiomes of H. vigintioctopunctata adults fed on two host plant species (Solanum nigrum and Solanum melongena) and one artificial diet. The development of the ovaries and testes was also examined. Our results revealed that the diversity and abundance of gut microorganisms varied significantly in insects reared on different diets. The gut microbiota of H. vigintioctopunctata raised on the two host plants was similar, with Proteobacteria being the dominant phylum in both groups, whereas Firmicutes was the dominant phylum in the group reared on the artificial diet. The predominant microbiota in the S. nigrum group were Acinetobacter soli and Acinetobacter ursingii (Acinetobacter, Moraxellaceae); Moraxella osloensis (Enhydrobacter, Moraxellaceae); and Empedobacter brevis (Empedobacter, Weeksellaceae). The microbiota in this group are associated with high lipid metabolism. In addition, the beetles' ovaries and testes were more highly developed in the S. nigrum group than in the other two groups. These findings provide valuable information for elucidating the complex roles the gut microbiota play in the fecundity of H. vigintioctopunctata, and may also contribute to developing future novel control strategies involving this economically important pest.

Inter-trophic Interaction of Gut Microbiota in a Tripartite System

Gut microbiota can be transmitted either environmentally or socially and vertically at intraspecific level; however, whether gut microbiota interact along trophic levels has been largely overlooked. Here, we characterized the gut bacterial communities of weevil larvae of Curculio arakawai that infest acorns of Mongolian oak (Quercus mongolica) as well as acorn-eating mammals, Siberian chipmunk (Tamias sibiricus), to test whether consumption of seed-borne larvae remodels the gut bacterial communities of T. sibiricus. Ingestion of weevil larvae of C. arakawai significantly altered the gut bacterial communities of T. sibiricus. Consequently, T. sibiricus fed larvae of C. arakawai showed higher capability to counter the negative effects of tannins, in terms of body weight maintenance, acorn consumption, N content in feces, urine pH, and blood ALT activity. Our results may first show that seed-borne insects as hidden players have a potential to alter the gut microbiota of seed predators in the tripartite system.

Reduced insecticide susceptibility of the wheat aphid Sitobion miscanthi after infection by the secondary bacterial symbiont Hamiltonella defensa

BACKGROUND

Bacterial symbionts in insects, especially aphids, have a major influence on host adaptation. We previously showed that infection with the secondary symbiont Hamiltonella defensa increases the fitness of the wheat aphid Sitobion miscanthi, yielding increases in fitness parameters such as adult weight and offspring number. However, whether H. defensa affects the sensitivity of host aphids to insecticides remains unknown.

RESULTS

We tested the effects of H. defensa on host aphid susceptibility to the insecticides chlorpyrifos methyl, imidacloprid, cyantraniliprole and acetamiprid. Our results showed that compared with Hamiltonella-free aphid clones, Hamiltonella-infected aphid clones exhibited lower sensitivity to most of the tested insecticides at low concentrations. Quantitative polymerase chain reaction showed that the density of H. defensa in the infected clones was slightly decreased at 24 h but then sharply increased until the late stage after treatment with the different insecticides. H. defensa in the host aphids was detected by fluorescence in situ hybridization and was localized to the aphid hindgut. Levels of the detoxification enzymes acetylcholinesterase, glutathione transferase and carboxylesterase were significantly higher in Hamiltonella-infected clones than in Hamiltonella-free clones.

CONCLUSIONS

The findings indicated that infection with H. defensa reduced aphid susceptibility to the investigated insecticides at low concentrations, potentially by increasing detoxification enzyme activity in the host. Therefore, symbiont-mediated insecticide resistance should be taken into account when performing resistance-monitoring studies. Studies of symbiont-mediated insecticide resistance may enhance our understanding of the emergence of insecticide resistance in agricultural systems. © 2020 Society of Chemical Industry.

Comparison of Microbial Communities in Colorado Potato Beetles (Leptinotarsa decemlineata Say) Collected From Different Sources in China

Microbial communities in insects are related to their geographical sources and contribute to adaptation to the local habitat. The Colorado potato beetle (Leptinotarsa decemlineata) (CPB) is a potato pest that causes serious economic losses in Xinjiang Uygur Autonomous Region (XJ) and Heilongjiang Province (HL), China. The influence of microorganisms in the invasion and dispersal of CPB is unclear. We studied microbial communities of CPB collected from nine geographic sources in China using high throughput sequencing technology. Bacteroidetes, Firmicutes, and Proteobacteria were the most dominant phyla, Clostridia, Bacteroidetes, and γ-Proteobacteria were the most dominant classes, Enterobacterales, Lactobacillales, Clostridiales, and Bacteroidales were the most dominant orders, and Enterobacteriaceae, Streptococcidae, Verrucomicrobiaceae, and Rikenellaceae were the most dominant families. There were significant differences, among sources, in the relative abundance of taxa at the genus level. A total of 383 genera were identified, and the dominant bacteria at the genus level were compared between XJ and HL. Pseudomonas was the unique dominant microorganism in the HL area, and the other four microorganisms (Lelliottia, Enterococcus, Enterobacter, and Lactococcus) were common within the 2 regions. Bacterial community diversity in CPB from Urumqi, Jimunai, and Wenquan was higher than diversity in other regions. T-Distributed Stochastic Neighbor Embedding (tSNE) analysis indicated that order and genus were appropriate taxonomic levels to distinguish geographical sources of CPB. These findings provide insight into the diversity of microorganisms of CPB in the differences among geographically isolated populations.

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.

Comparative Analysis of the Gut Microbiota of Adult Mosquitoes From Eight Locations in Hainan, China

The midgut microbial community composition, structure, and function of field-collected mosquitoes may provide a way to exploit microbial function for mosquito-borne disease control. However, it is unclear how adult mosquitoes acquire their microbiome, how the microbiome affects life history traits and how the microbiome influences community structure. We analyzed the composition of 501 midgut bacterial communities from field-collected adult female mosquitoes, including Aedes albopictus, Aedes galloisi, Culex pallidothorax, Culex pipiens, Culex gelidus, and Armigeres subalbatus, across eight habitats using the HiSeq 4000 system and the V3-V4 hyper-variable region of 16S rRNA gene. After quality filtering and rarefaction, a total of 1421 operational taxonomic units, belonging to 29 phyla, 44 families, and 43 genera were identified. Proteobacteria (75.67%) were the most common phylum, followed by Firmicutes (10.38%), Bacteroidetes (6.87%), Thermi (4.60%), and Actinobacteria (1.58%). The genera Rickettsiaceae (33.00%), Enterobacteriaceae (20.27%), Enterococcaceae (7.49%), Aeromonadaceae (7.00%), Thermaceae (4.52%), and Moraxellaceae (4.31%) were dominant in the samples analyzed and accounted for 76.59% of the total genera. We characterized the midgut bacterial communities of six mosquito species in Hainan province, China. The gut bacterial communities were different in composition and abundance, among locations, for all mosquito species. There were significant differences in the gut microbial composition between some species and substantial variation in the gut microbiota between individuals of the same mosquito species. There was a marked variation in different mosquito gut microbiota within the same location. These results might be useful in the identification of microbial communities that could be exploited for disease control.

Liparus (Liparus) glabrirostris Küst. and Hylobius (Callirus) abietis (L.) (Coleoptera: Curculionidae) first records for Serbia

This paper presents a survey of data on two weevil species not recorded for the fauna of Serbia till now. Despite their large size, Liparus (Liparus) glabrirostris Küster, 1849 and Hylobius (Callirus) abietis (Linnaeus, 1758) have not been recorded for Serbia in the newest Palaearctic weevil catalogue (Alonso-Zarazaga et al., 2017) or in the Fauna Europaea (Alonso-Zarazaga et al., 2013, https://fauna-eu.org/). In this paper L. glabrirostris, found in a single locality on Mt Goč, is registered as the third representative of the genus Liparus Olivier, 1807 in Serbia. Hylobius abietis is a serious, widely distributed conifer pest, but was not faunistically registered for Serbia till now. Some ecological data and distribution maps with Serbian locations are given for both species.

Gut bacterial communities and their contribution to performance of specialist Altica flea beetles

Host plant shifts are a common mode of speciation in herbivorous insects. Although insects can evolve adaptations to successfully incorporate a new host plant, it is becoming increasingly recognized that the gut bacterial community may play a significant role in allowing insects to detoxify novel plant chemical defenses. Here, we examined differences in gut bacterial communities between Altica flea beetle species that feed on phylogenetically unrelated host plants in sympatry. We surveyed the gut bacterial communities of three closely related flea beetles from multiple locations using 16S rRNA amplicon sequencing. The results showed that the beetle species shared a high proportion (80.7%) of operational taxonomic units. Alpha-diversity indicators suggested that gut bacterial diversity did not differ among host species, whereas geography had a significant effect on bacterial diversity. In contrast, analyses of beta-diversity showed significant differences in gut bacterial composition among beetle species when we used species composition and relative abundance metrics, but there was no difference in composition when species presence/absence and phylogenetic distance indices were used. Within host beetle species, gut bacterial composition varied significantly among sites. A metagenomic functionality analysis predicted that the gut microbes had functions involved in xenobiotic biodegradation and metabolism as well as metabolism of terpenoids and polyketides. These predictions, however, did not differ among beetle host species. Antibiotic curing experiments showed that development time was significantly prolonged, and there was a significant decline in body weight of newly emerged adults in beetles lacking gut bacteria, suggesting the beetles may receive a potential benefit from the gut microbe-insect interaction. On the whole, our results suggest that although the gut bacterial community did not show clear host-specific patterns among Altica species, spatiotemporal variability is an important determinant of gut bacterial communities. Furthermore, the similarity of communities among these beetle species suggests that microbial facilitation may not be a determinant of host plant shifts in Altica.

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.

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.

High Diversity and Functional Complementation of Alimentary Canal Microbiota Ensure Small Brown Planthopper to Adapt Different Biogeographic Environments

Almost all insects harbor commensal bacteria in the alimentary canal lumen or within cells and often play a pivotal role in their host’s development, evolution, and environmental adaptation. However, little is known about the alimentary canal microbiota and their functions in sap-sucking insect pests of crops, which can damage plants by removing plant sap and by transmitting various plant viruses, especially in the small brown planthopper, Laodelphax striatellus. In this study, we characterized the alimentary canal microbiota of L. striatellus collected from seven regions in China by sequencing 16S rDNA. The insects harbored a rich diversity of microbes, mainly consisted of bacteria from phyla Proteobacteria, Actinobacteria, Firmicutes, Bacteroidetes, and Tenericutes. The composition and abundance of microbiota were more similar as the geographic distance decreased between the populations and clustered by geographic location into three groups: temperate, subtropical, and tropical populations. Although the abundance and species of microbes differed among the populations, the various major microbes for each population performed similar functions based on a clusters of orthologous group analysis. Greater diversity in ecological factors in different regions might lead to higher microbial diversity, thus enabling L. striatellus to adapt or tolerate various extreme environments to avoid the cost of long-distance migration. Moreover, the abundance of various metabolic functions in the Kaifeng populations might contribute to higher fecundity in L. striatellus.

Gut bacteria of weevils developing on plant roots under extreme desert conditions

BACKGROUND

Many phytophagous insects, whose diet is generally nitrogen-poor, rely on gut bacteria to compensate for nutritional deficits. Accordingly, we hypothesized that insects in desert environments may evolve associations with gut bacteria to adapt to the extremely low nutrient availability. For this, we conducted a systematic survey of bacterial communities in the guts of weevils developing inside mud chambers affixed to plant roots in the Negev Desert of Israel, based on 16S rRNA gene amplicon sequencing.

RESULTS

Our analyses revealed that gut bacterial communities in weevil larvae were similar across a wide geographical range, but differed significantly from those of the mud chambers and of the surrounding soils. Nevertheless, a high proportion of bacteria (including all of the core bacteria) found in the weevils were also detected in the mud chambers and soils at low relative abundances. The genus Citrobacter (of the Enterobacteriaceae family) was the predominant group in the guts of all individual weevils. The relative abundance of Citrobacter significantly decreased at the pupal and adult stages, while bacterial diversity increased. A mini literature survey revealed that members of the genus Citrobacter are associated with nitrogen fixation, recycling of uric acid nitrogen, and cellulose degradation in different insects.

CONCLUSIONS

The results suggest that although weevils could potentially acquire their gut bacteria from the soil, weevil host internal factors, rather than external environmental factors, were more important in shaping their gut bacterial communities, and suggest a major role for Citrobacter in weevil nutrition in this challenging environment. This study highlights the potential involvement of gut bacteria in the adaptation of insects to nutritional deficiencies under extreme desert conditions.

How Hosts Taxonomy, Trophy, and Endosymbionts Shape Microbiome Diversity in Beetles

Bacterial communities play a crucial role in the biology, ecology, and evolution of multicellular organisms. In this research, the microbiome of 24 selected beetle species representing five families (Carabidae, Staphylinidae, Curculionidae, Chrysomelidae, Scarabaeidae) and three trophic guilds (carnivorous, herbivorous, detrivorous) was examined using 16S rDNA sequencing on the Illumina platform. The aim of the study was to compare diversity within and among species on various levels of organization, including evaluation of the impact of endosymbiotic bacteria. Collected data showed that beetles possess various bacterial communities and that microbiota of individuals of particular species hosts are intermixed. The most diverse microbiota were found in Carabidae and Scarabaeidae; the least diverse, in Staphylinidae. On higher organization levels, the diversity of bacteria was more dissimilar between families, while the most distinct with respect to their microbiomes were trophic guilds. Moreover, eight taxa of endosymbiotic bacteria were detected including common genera such as Wolbachia, Rickettsia, and Spiroplasma, as well as the rarely detected Cardinium, Arsenophonus, Buchnera, Sulcia, Regiella, and Serratia. There were no correlations among the abundance of the most common Wolbachia and Rickettsia; a finding that does not support the hypothesis that these bacteria occur interchangeably. The abundance of endosymbionts only weakly and negatively correlates with diversity of the whole microbiome in beetles. Overall, microbiome diversity was found to be more dependent on host phylogeny than on the abundance of endosymbionts. This is the first study in which bacteria diversity is compared between numerous species of beetles in a standardized manner.

Anti-plant Defense Response Strategies Mediated by the Secondary Symbiont Hamiltonella defensa in the Wheat Aphid Sitobion miscanthi

Bacterial symbionts are omnipresent in insects, particularly aphids, and often exert important effects on the host ecology; however, examples of symbionts that mediate herbivore-plant interactions remain limited. Here, three clones with identical genetic backgrounds were established: a Hamiltonella defensa-free clone, H. defensa-infected clone and H. defensa-cured clone. H. defensa infection was found to increase the fitness of Sitobion miscanthi by increasing the total number of offspring and decreasing the age of first reproduction. Furthermore, gene expression studies and phytohormone measurement showed that feeding by the Hamiltonella-infected clone suppressed the salicylic acid (SA)- and jasmonic acid (JA)-related defense pathways and SA/JA accumulation in wheat plants relative to feeding by the other two clones. Additionally, after feeding by the Hamiltonella-infected clone, the activity levels of the defense-related enzymes polyphenol oxidase (PPO) and peroxidase (POD) in wheat plants were significantly decreased compared with the levels observed after feeding by the other two clones. Taken together, these data reveal for the first time the potential role of H. defensa of S. miscanthi in mediating the anti-plant defense responses of aphids.

A molecular and genomic reference system for conifer defence against insects

Insect pests are part of natural forest ecosystems contributing to forest rejuvenation but can also cause ecological disturbance and economic losses that are expected to increase with climate change. The white pine or spruce weevil (Pissodes strobi) is a pest of conifer forests in North America. Weevil-host interactions with various spruce (Picea) species have been explored as a genomic and molecular reference system for conifer defence against insects. Interactions occur in two major phases of the insect life cycle. In the exophase, adult weevils are free-moving and display behaviour of host selection for oviposition that is affected by host traits. In the endophase, insects live within the host where mobility and development from eggs to young adults are affected by a complex system of host defences. Genetic resistance exists in several spruce species and involves synergism of constitutive and induced chemical and physical defences that comprise the conifer defence syndrome. Here, we review conifer defences that disrupt the weevil life cycle and mechanisms by which trees resist weevil attack. We highlight molecular and genomic aspects and a possible role for the weevil microbiome. Knowledge of this conifer defence system is supporting forest health strategies and tree breeding for insect resistance.

Gut Microbiomics-A Solution to Unloose the Gordian Knot of Biological Effects of Ionizing Radiation

The Chernobyl and Fukushima nuclear accidents have called forth a growing body of research on their biological aftermaths. A variety of wild organisms, including primates, birds, fish, insects, and worms are being studied in the affected areas, with emerging morphological, physiological, and genetic aberrations ascribed to ionizing radiation. Despite the effort in surveying Chernobyl and Fukushima wildlife, little is known about the microorganisms associated with these radiation-contaminated animals. The microbiota, especially the gut commensal, plays an important role in shaping the metabolic reservoir and immune system of the host, and is sensitive to a wide array of environmental factors, including ionizing radiation. Humans and limited numbers of laboratory species have been the main subjects of microbiome studies, however, a more practical insight on host-gut microbiota dynamics under environmental impact should be explored in natural habitats. In this analysis, we introduced a working model explaining possible mechanisms of ionizing radiation on the gut microbiota, with an evaluation of the gut microbiota as a potential biomarker for exposure to ionizing radiation.

Functions of stone cells and oleoresin terpenes in the conifer defense syndrome

Conifers depend on complex defense systems against herbivores. Stone cells (SC) and oleoresin are physical and chemical defenses of Sitka spruce that have been separately studied in previous work. Weevil oviposit at the tip of the previous year's apical shoot (PYAS). We investigated interactions between weevil larvae and trees in controlled oviposition experiments with resistant (R) and susceptible (S) Sitka spruce. R trees have an abundance of SC in the PYAS cortex. SC are mostly absent in S trees. R trees and S trees also differ in the composition of oleoresin terpenes. Transcriptomes of R and S trees revealed differences in long-term weevil-induced responses. Performance of larvae was significantly reduced on R trees compared with S trees under experimental conditions that mimicked natural oviposition behavior at apical shoot tips and may be attributed to the effects of SC. In oviposition experiments designed for larvae to feed below the area of highest SC abundance, larvae showed an unusual feeding behavior and oleoresin appeared to function as the major defense. The results support a role for both SC and oleoresin terpenes and possible synergies between these traits in the defense syndrome of weevil-resistant Sitka spruce.

Bacterial and Fungal Midgut Community Dynamics and Transfer Between Mother and Brood in the Asian Longhorned Beetle (Anoplophora glabripennis), an Invasive Xylophage

Microbial symbionts play pivotal roles in the ecology and physiology of insects feeding in woody plants. Both eukaryotic and bacterial members occur in these systems where they facilitate digestive and nutrient provisioning. The larval gut of the Asian longhorned beetle (Anoplophora glabripennis) is associated with a microbial consortium that fulfills these metabolic roles. While members of the community vary in presence and abundance among individuals from different hosts, A. glabripennis is consistently associated with a fungus in the Fusarium solani species complex (FSSC). We used amplicon sequencing, taxon-specific PCR, culturing, and imaging to determine how bacterial and fungal communities differ between life stages and possible modes of symbiont transfer. The bacterial and fungal communities of adult guts were more diverse than those from larvae and eggs. The communities of larvae and eggs were more similar to those from oviposition sites than from adult female guts. FSSC isolates were not detected in the reproductive tissues of adult females, but were consistently detected on egg surfaces after oviposition and in frass. These results demonstrate that frass can serve as a vehicle of transmission of a subset for the beetle gut microbiota. Vertically transmitted symbionts are often beneficial to their host, warranting subsequent functional studies.

Gut Bacterial Communities of Dendroctonus valens and D. mexicanus (Curculionidae: Scolytinae): A Metagenomic Analysis across Different Geographical Locations in Mexico

Dendroctonus bark beetles are a worldwide significant pest of conifers. This genus comprises 20 species found in North and Central America, and Eurasia. Several studies have documented the microbiota associated with these bark beetles, but little is known regarding how the gut bacterial communities change across host range distribution. We use pyrosequencing to characterize the gut bacterial communities associated with six populations of Dendroctonus valens and D. mexicanus each across Mexico, determine the core bacteriome of both insects and infer the metabolic pathways of these communities with Phylogenetic Investigation of Communities by Reconstruction of Unobserved States (PICRUSt) to evaluate whether these routes are conserved across geographical locations. Our results show that the β-diversity with UniFrac unweighted varies among locations of both bark beetles mainly due to absence/presence of some rare taxa. No association is found between the pairwise phylogenetic distance of bacterial communities and geographic distance. A strict intraspecific core bacteriome is determined for each bark beetle species, but these cores are different in composition and abundance. However, both bark beetles share the interspecific core bacteriome recorded previously for the Dendroctonus genus consisting of Enterobacter, Pantoea, Providencia, Pseudomonas, Rahnella, and Serratia. The predictions of metabolic pathways are the same in the different localities, suggesting that they are conserved through the geographical locations.

Current state of knowledge on Wolbachia infection among Coleoptera: a systematic review

Background

Despite great progress in studies on Wolbachia infection in insects, the knowledge about its relations with beetle species, populations and individuals, and the effects of bacteria on these hosts, is still unsatisfactory. In this review we summarize the current state of knowledge about Wolbachia occurrence and interactions with Coleopteran hosts.

Methods

An intensive search of the available literature resulted in the selection of 86 publications that describe the relevant details about Wolbachia presence among beetles. These publications were then examined with respect to the distribution and taxonomy of infected hosts and diversity of Wolbachia found in beetles. Sequences of Wolbachia genes (16S rDNA, ftsZ) were used for the phylogenetic analyses.

Results

The collected publications revealed that Wolbachia has been confirmed in 204 beetle species and that the estimated average prevalence of this bacteria across beetle species is 38.3% and varies greatly across families and genera (0–88% infected members) and is much lower (c. 13%) in geographic studies. The majority of the examined and infected beetles were from Europe and East Asia. The most intensively studied have been two groups of herbivorous beetles: Curculionidae and Chrysomelidae. Coleoptera harbor Wolbachia belonging to three supergroups: F found in only three species, and A and B found in similar numbers of beetles (including some doubly infected); however the latter two were most prevalent in different families. A total of 59% of species with precise data were found to be totally infected. Single infections were found in 69% of species and others were doubly- or multiply-infected. Wolbachia caused numerous effects on its beetle hosts, including selective sweep with host mtDNA (found in 3% of species), cytoplasmic incompatibility (detected in c. 6% of beetles) and other effects related to reproduction or development (like male-killing, possible parthenogenesis or haplodiploidy induction, and egg development). Phylogenetic reconstructions for Wolbachia genes rejected cospeciation between these bacteria and Coleoptera, with minor exceptions found in some Hydraenidae, Curculionidae and Chrysomelidae. In contrast, horizontal transmission of bacteria has been suspected or proven in numerous cases (e.g., among beetles sharing habitats and/or host plants).

Discussion

The present knowledge about Wolbachia infection across beetle species and populations is very uneven. Even the basic data about infection status in species and frequency of infected species across genera and families is very superficial, as only c. 0.15% of all beetle species have been tested so far. Future studies on Wolbachia diversity in Coleoptera should still be based on the Multi-locus Sequence Typing system, and next-generation sequencing technologies will be important for uncovering Wolbachia relations with host evolution and ecology, as well as with other, co-occurring endosymbiotic bacteria.

Influence of Host Plant on Thaumetopoea pityocampa Gut Bacterial Community

Microbial communities associated to the gut of insects are attracting an increasing interest, mainly because of their role in influencing several host life-traits. The characterization of the gut microbial community is pivotal for understanding insect ecology and, thus, to develop novel pest management strategies. The pine processionary moth, Thaumetopoea pytiocampa (Denis & Schiff.) (Lepidoptera: Thaumetopoeidae), is a severe defoliator of pine forests, able to feed on several pine species. In this work, we performed a metabarcoding analysis to investigate, for the first time, the diversity of the gut bacterial community of pine processionary larvae associated with three different host pine species (Pinus halepensis, Pinus nigra subsp. laricio, and Pinus pinaster). We found that the gut microbial community of T. pityocampa larvae collected on P. halapensis was different from that associated with larvae collected from P. nigra and P. pinaster. Moreover, the high presence of bacteria belonging to the genera Modestobacter, Delftia, and unidentified Methylobacteriaceae retrieved in larvae feeding on P. halapensis suggested that specific interactions can occur. Our results provide the evidence that different host plant differently impact on the microbiota diversity of T. pityocampa larvae, contributing to the general knowledge of this pest with information that could be useful in shaping the next generation of pest control strategies.

Bacteriome from Pinus arizonica and P. durangensis: Diversity, Comparison of Assemblages, and Overlapping Degree with the Gut Bacterial Community of a Bark Beetle That Kills Pines

Symbioses between plants and microorganims have been fundamental in the evolution of both groups. The endophytic bacteria associated with conifers have been poorly studied in terms of diversity, ecology, and function. Coniferous trees of the genera Larix, Pseudotsugae, Picea and mainly Pinus, are hosts of many insects, including bark beetles and especially the Dendroctonus species. These insects colonize and kill these trees during their life cycle. Several bacteria detected in the gut and cuticle of these insects have been identified as endophytes in conifers. In this study, we characterized and compared the endophytic bacterial diversity in roots, phloem and bark of non-attacked saplings of Pinus arizonica and P. durangensis using 16S rRNA gene pyrosequencing. In addition, we evaluated the degree of taxonomic relatedness, and the association of metabolic function profiles of communities of endophytic bacteria and previously reported gut bacterial communities of D. rhizophagus; a specialized bark beetle that colonizes and kills saplings of these pine species. Our results showed that both pine species share a similar endophytic community. A total of seven bacterial phyla, 14 classes, 26 orders, 43 families, and 51 genera were identified. Enterobacteriaceae was the most abundant family across all samples, followed by Acetobacteraceae and Acidobacteriaceae, which agree with previous studies performed in other pines and conifers. Endophytic communities and that of the insect gut were significantly different, however, the taxonomic relatedness of certain bacterial genera of pines and insect assemblages suggested that some bacteria from pine tissues might be the same as those in the insect gut. Lastly, the metabolic profile using PICRUSt showed there to be a positive association between communities of both pines and insect gut. This study represents the baseline into the knowledge of the endophytic bacterial communities of two of the major hosts affected by D. rhizophagus.

Detoxifying symbiosis: microbe-mediated detoxification of phytotoxins and pesticides in insects

Symbiotic microorganisms degrade natural and artificial toxic compounds, and confer toxin resistance on insect hosts.

Drastic Genome Reduction in an Herbivore's Pectinolytic Symbiont

Pectin, an integral component of the plant cell wall, is a recalcitrant substrate against enzymatic challenges by most animals. In characterizing the source of a leaf beetle's (Cassida rubiginosa) pectin-degrading phenotype, we demonstrate its dependency on an extracellular bacterium housed in specialized organs connected to the foregut. Despite possessing the smallest genome (0.27 Mb) of any organism not subsisting within a host cell, the symbiont nonetheless retained a functional pectinolytic metabolism targeting the polysaccharide's two most abundant classes: homogalacturonan and rhamnogalacturonan I. Comparative transcriptomics revealed pectinase expression to be enriched in the symbiotic organs, consistent with enzymatic buildup in these structures following immunostaining with pectinase-targeting antibodies. Symbiont elimination results in a drastically reduced host survivorship and a diminished capacity to degrade pectin. Collectively, our findings highlight symbiosis as a strategy for an herbivore to metabolize one of nature's most complex polysaccharides and a universal component of plant tissues.

Revealing the gut bacteriome of Dendroctonus bark beetles (Curculionidae: Scolytinae): diversity, core members and co-evolutionary patterns

Dendroctonus bark beetles comprise 20 taxonomically recognized species, which are one of the most destructive pine forest pests in North and Central America, and Eurasia. The aims of this study were to characterize the gut bacterial diversity, to determine the core bacteriome and to explore the ecological association between these bacteria and bark beetles. A total of five bacterial phyla were identified in the gut of 13 Dendroctonus species; Proteobacteria was the most abundant, followed by Firmicutes, Fusobacteria, Actinobacteria and Deinococcus-Thermus. The α-diversity was low as demonstrated in previous studies and significant differences in β-diversity were observed. The core bacteriome was composed of Enterobacter, Pantoea, Pseudomonas, Rahnella, Raoultella, and Serratia. The tanglegram between bacteria and bark beetles suggests that members of bacterial community are acquired from the environment, possibly from the host tree. These findings improve the knowledge about the bacterial community composition, and provide the bases to study the metabolic functions of these bacteria, as well as their interaction with these bark beetles.

Symbiont dynamics and strain diversity in the defensive mutualism between Lagria beetles and Burkholderia

Defensive mutualisms are often facultative in nature, and their evolutionary dynamics can be shaped by changes in local antagonist communities or arms races with coevolving antagonists. Under these conditions, selection may favour hosts that flexibly acquire symbionts producing compounds with bioactivity against current antagonists. Here, we study the prevalence, dynamics and strain diversity of Burkholderia gladioli bacteria in Lagria beetles, a recently described protective symbiosis involving vertical transmission and antifungal defense for the host eggs. In Lagria hirta, we investigate the fate of the bacteria during the host life cycle. Despite a transmission route relying solely on the females, the bacteria are present in both sexes during the larval stage, suggesting a potentially multifaceted defensive role. In L. hirta and L. villosa adults, culture-dependent and -independent techniques revealed that individual beetles harbour diverse Burkholderia strains from at least two different phylogenetic clades, yet all closely related to free-living B. gladioli. Interestingly, rearing the beetles in the laboratory strongly impacted symbiont strain profiles in both beetle species. Our findings highlight the dynamic nature of the B. gladioli-Lagria symbiosis and present this as a valuable system for studying multiple strain coinfections, as well as the evolutionary and ecological factors regulating defensive symbiosis.

Detoxifying symbionts in agriculturally important pest insects

Pest insects lead to excessive agricultural and therefore economical losses on crops worldwide. These insects have to withstand toxic molecules that are inherent to plant defences, as well as those that are produced and introduced by humans in the form of insecticides. In recent years, research on insect–microbe symbioses has recognized that microbial symbionts may play a role protecting against these toxins, leading to a form of defensive symbiosis between the pest insect and different types of microorganisms that we term detoxifying symbioses. In this minireview, we will highlight well‐characterized and emerging insect model systems of detoxifying symbioses and assess how the microorganisms influence the host's success.

Evidence of a bacterial core in the stored products pest Plodia interpunctella: the influence of different diets

The potential influence of insects' feeding behaviour on their associated bacterial communities is currently a matter of debate. Using the major pest of commodities, Plodia interpunctella, as a model and adopting a culture-independent approach, the impact of different diets on the host-associated microbiota was evaluated. An analysis of similarity showed differences among the microbiotas of moths fed with five substrates and provided evidence that diet represents the only tested factor that explains this dissimilarity. Bacteria shared between food and insects provide evidence for a limited conveyance to the host of the bacteria derived from the diet; more likely, the content of carbohydrates and proteins in the diets promotes changes in the insect's microbiota. Moth microbiotas were characterized by two robust entomotypes, respectively, associated with a carbohydrate-rich diet and a protein-rich diet. These results were also confirmed by the predicted metagenome functional potential. A core microbiota, composed of six taxa, was shared between eggs and adults, regardless of the origin of the population. Finally, the identification of possible human and animal pathogens on chili and associated with the moths that feed on it highlights the possibility that these bacteria may be conveyed by moth frass.