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

Evaluation of Bacterial Communities of Listronotus maculicollis Kirby Reared on Primary and Secondary Host Plants

The annual bluegrass weevil (Listronotus maculicollis Kirby) is a devastating insect pest of annual bluegrass (Poa annua L.) and, to a lesser extent, creeping bentgrass (Agrostis stolonifera L.) on golf courses. Listronotus maculicollis-reared A. stolonifera, a comparatively tolerant host, incurs fitness costs, including longer developmental periods and reduced larval survivorship. This study sought to characterize microbiota diversity in L. maculicollis adults and larvae reared on P. annua and A. stolonifera cultivars (Penncross & A4) to explore whether intrinsic factors, such as microbial community composition, vary across host plants and developmental stages, potentially influencing host suitability. Alpha diversity analyses showed adults feeding on A4 exhibited higher bacterial species richness than their offspring reared on the same cultivar. Beta diversity analysis revealed significant dissimilarities between L. maculicollis adults and offspring regardless of host. Pseudomonas sp. was consistently abundant in larvae across all turfgrasses, indicating a potential association with larval development. Elevated levels of Wolbachia sp., known for insect reproductive manipulation, were observed in adults, but appear to be unrelated to host plant effects. The most prevalent bacterium detected was Candidatus Nardonella, a conserved endosymbiont essential for cuticular hardening in weevils. Given the role of cuticular integrity in insecticide resistance, further investigations into insect-microbe-plant interactions could guide the development of targeted pest management strategies, reducing resistance and improving control measures for L. maculicollis.

Incidence of endosymbiont bacteria Wolbachia in cowpea weevil Callosobruchus maculatus Fabricius (Coleoptera, Chrysomelidae)

This study focuses on the cowpea weevil, Callosobruchus maculatus, a globally distributed grain pest that affects cereals and pulses. Using chemicals to store grains can harm pest control and pose risks to consumers and the environment. The facultative intracellular symbiont bacteria Wolbachia can affect host's reproductive capacities in a variety of ways, which makes it useful in the management of pests such as C. maculatus. The main goal of the study was to identify Wolbachia diversity in the C. maculatus population. Phylogenetic analysis utilized mitochondrial COI and 12S rRNA genes to identify the host C. maculatus, while screening for Wolbachia was conducted using genes (wsp, coxA, and ftsZ) genes. Molecular phylogenetic analysis of the Wolbachia genes resulted in one new Wolbachia strain (wCmac1) in C. maculatus populations and contrasting already published data of other Callosobruchus strains. The study discussed the detection of Wolbachia and its phylogenetic comparison with other C. maculatus and Coleopteran populations. It is important to take these findings into account when considering host-pathogen interactions.

How host species and body part determine the microbial communities of five ambrosia beetle species

The ambrosia beetles are farming insects that feed mainly on their cultivated fungi, which in some occasions are pathogens from forest and fruit trees. We used a culture-independent approach based on 16S and 18S rRNA gene metabarcoding analysis to investigate the diversity and composition of the bacterial and fungal communities associated with five ambrosia beetle species: four species native to America (Monarthrum dimidiatum, Dryocoetoides capucinus, Euwallacea discretus, Corthylus consimilis) and an introduced species (Xylosandrus morigerus). For the bacterial community, the beetle species hosted a broad diversity with 1,579 amplicon sequence variants (ASVs) and 66 genera, while for the fungal community they hosted 288 ASVs and 39 genera. Some microbial groups dominated the community within a host species or a body part (Wolbachia in the head-thorax of E. discretus; Ambrosiella in the head-thorax and abdomen of X. morigerus). The taxonomic composition and structure of the microbial communities appeared to differ between beetle species; this was supported by beta-diversity analysis, which indicated that bacterial and fungal communities were clustered mainly by host species. This study characterizes for the first time the microbial communities associated with unexplored ambrosia beetle species, as well as the factors that affect the composition and taxonomic diversity per se, contributing to the knowledge of the ambrosia beetle system.

A survey of Wolbachia infection in brachyceran flies from Iran

Wolbachia is a maternally inherited intracellular bacterium that is considered to be the most plentiful endosymbiont found in arthropods. It reproductively manipulates its host to increase the chances of being transmitted to the insect progeny; and it is currently used as a means of suppressing disease vector populations or controlling vector-borne diseases. Studies of the dissemination and prevalence of Wolbachia among its arthropod hosts are important for its possible use as a biological control agent. The molecular identification of Wolbachia relies on different primers sets due to Wolbachia strain variation. Here, we screened for the presence of Wolbachia in a broad range of Brachycera fly species (Diptera), collected from different regions of Iran, using nine genetic markers (wsp, ftsZ, fbpA, gatB, CoxA, gltA, GroEL dnaA, and 16s rRNA), for detecting, assessing the sensitivity of primers for detection, and phylogeny of this bacterium. The overall incidence of Wolbachia among 22 species from six families was 27.3%. The most commonly positive fly species were Pollenia sp. and Hydrotaea armipes. However, the bacterium was not found in the most medically important flies or in potential human disease vectors, including Musca domestica, Sarcophaga spp., Calliphora vicinia, Lucilia sericata, and Chrysomya albiceps. The primer sets of 16s rRNA with 53.0% and gatB with 52.0% were the most sensitive primers for detecting Wolbachia. Blast search, phylogenetic, and MLST analysis of the different locus sequences of Wolbachia show that all the six distantly related fly species likely belonging to supergroup A. Our study showed some primer sets generated false negatives in many of the samples, emphasizing the importance of using different loci in detecting Wolbachia. The study provides the groundwork for future studies of a Wolbachia-based program for control of flies.

Assigning new supergroups V and W to the Wolbachia diversity

Wolbachia are endosymbiotic and alphaproteobacteria that belong to the order Rickettsiales. They are known to infect half of the insect population and cause host manipulation, and have been categorized into 19 monophyletic lineages called supergroups. Recently, two strains, wCfeJ and wCfeT were isolated from cat fleas (Ctenocephalides felis), but their supergroup relationships were not assigned. In this article, we have attempted to classify these two novel strains and establish their evolutionary lineage (i.e., supergroup designation). For this we performed 16S rRNA similarity analysis and reconstructed 16S rRNA phylogeny of 52 Wolbachia strains (including two novel strains) belong to 19 supergroups. We also performed average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) studies to measure genomic similarity between the two novel genomes. The results revealed that 16S rRNA similarity between the two novel strains is 97.94%, which is below the threshold value of 98.6% and phylogeny shows that they are placed at the two different positions (i.e., showing distinct evolutionary lineages). Further, genomic similarity analysis revealed that the novel genomes have ANI and dDDH values 79% and 22.4% respectively, which were below the threshold value of ANI (95%) and dDDH (70%). These results suggested that the novel strains neither shared a species boundary between them nor with any other previously identified supergroups, which designate them as two new supergroups, namely supergroup V (strain wCfeJ) and supergroup W (strain wCfeT).

Bias in sex ratios and polyandry rate in reproduction of Leptinotarsa decemlineata

The Colorado potato beetle (CPB, Leptinotarsa decemlineata Slechtd.) is an invasive pest with economic importance worldwide. Sex ratios during egg-hatching and a frequency of polyandry in single-female families were analysed to clarify the reproduction strategy of CPB, which was still known only in fragments. 1296 just hatching 1st instar CPB larvae were collected from 19 single-female families, of which 13 were random families collected from potato fields and 6 were families produced by laboratory farming of naturally fertilised females. All larvae were analysed to detect a sex using a qPCR-based method and to detect polymorphisms in genotypes of 9 microsatellite (SSR) markers. The bias in sex ratio in favour of females was confirmed using linear mixed-effects model in both experimental groups of families: field collections (F = 36.39; P = 0.0001) and laboratory farming (F = 13.74; P = 0.0139). The analysis of diversity in microsatellites proved the polyandry in all progenies as 73% of analysed segregation patterns did not match with the patterns expected for full-sib progenies; on average per locus, 46% of allelic and 49.7% of genotype ratios showed irregular segregation. Both findings contribute toward understanding CPB success rate as an invasive species, as the preferential bearing of females with polyandry has a great potential to keep fitness of progenies, to maintain and operate population diversity, and to accelerate the reproduction of the pest.

Symbiotic Wolbachia bacteria in coccinellid parasitoids: genetic diversity, horizontal transfer, and recombination

Parasitoids, which constitute about 25% of all insects and attack arthropods of virtually all taxa, are considered the most suitable vectors for horizontal transmission of the symbiotic bacterium Wolbachia among insects. The parasitoids studied in this article develop in the larvae and pupae of ladybirds. For the first time, Wolbachia was found in parasitic wasp species of the genus Homalotylus (Hymenoptera: Encyrtidae) and from the subfamily Tetrastichinae (Hymenoptera: Eulophidae). To characterize the Wolbachia strains, six bacterial housekeeping genes were examined and compared with previously published Wolbachia gene sequences. The same bacterial strains were found in all individuals of each species of parasitic wasps collected in different places and at different times, which indicates the absence of contamination and testifies to the heritability of the symbionts in the studied chalcids. No evidence was found that the parasitic wasps were infected with Wolbachia, identical to the symbionts of their ladybirds hosts. We found one Wolbachia strain, wHom-2, which is a product of bacterial recombination from unrelated insects, including ladybirds. The lack of correspondence between the molecular phylogenies of Wolbachia strains and mitochondrial DNA of their hosts indicates horizontal transfers of Wolbachia among parasitic wasps of the genus Homalotylus and from the subfamily Tetrastichinae.

Tardigrade Community Microbiomes in North American Orchards Include Putative Endosymbionts and Plant Pathogens

The microbiome of tardigrades, a phylum of microscopic animals best known for their ability to survive extreme conditions, is poorly studied worldwide and completely unknown in North America. An improved understanding of tardigrade-associated bacteria is particularly important because tardigrades have been shown to act as vectors of the plant pathogen Xanthomonas campestris in the laboratory. However, the potential role of tardigrades as reservoirs and vectors of phytopathogens has not been investigated further. This study analyzed the microbiota of tardigrades from six apple orchards in central Iowa, United States, and is the first analysis of the microbiota of North American tardigrades. It is also the first ever study of the tardigrade microbiome in an agricultural setting. We utilized 16S rRNA gene amplicon sequencing to characterize the tardigrade community microbiome across four contrasts: location, substrate type (moss or lichen), collection year, and tardigrades vs. their substrate. Alpha diversity of the tardigrade community microbiome differed significantly by location and year of collection but not by substrate type. Our work also corroborated earlier findings, demonstrating that tardigrades harbor a distinct microbiota from their environment. We also identified tardigrade-associated taxa that belong to genera known to contain phytopathogens (Pseudomonas, Ralstonia, and the Pantoea/Erwinia complex). Finally, we observed members of the genera Rickettsia and Wolbachia in the tardigrade microbiome; because these are obligate intracellular genera, we consider these taxa to be putative endosymbionts of tardigrades. These results suggest the presence of putative endosymbionts and phytopathogens in the microbiota of wild tardigrades in North America.

Cytoplasmic incompatibility in the semivoltine longicorn beetle Acalolepta fraudatrix (Coleoptera: Cerambycidae) double infected with Wolbachia

Wolbachia are obligatory endosymbiotic α-proteobacteria found in many arthropods. They are maternally inherited, and can induce reproductive alterations in the hosts. Despite considerable recent progress in studies on the associations between Wolbachia and various taxonomic groups of insects, none of the researches have revealed the effects of Wolbachia on longicorn beetles as the host insect. Acalolepta fraudatrix is a forest longicorn beetle that is distributed in East Asia. In this study, the relationship between Wolbachia and A. fraudatrix was investigated. Out of two populations of A. fraudatrix screened for Wolbachia using the genes ftsZ, wsp, and 16S rRNA, only one of the populations showed detection of all three genes indicating the presence of Wolbachia. Electron microscopy and fluorescent in situ hybridization also confirmed that the A. fraudatrix population was infected with Wolbachia. Sequencing the wsp genes derived from single insects revealed that two strains of Wolbachia coexisted in the insects based on the detection of two different sequences of the wsp gene. We designated these strains as wFra1 and wFra2. The bacterial titers of wFra1 were nearly 2-fold and 3-fold higher than wFra2 in the testes and ovaries, respectively. The two strains of Wolbachia in the insects were completely eliminated by rearing the insects on artificial diets containing 1% concentration of tetracycline for 1 generation. Reciprocal crosses between Wolbachia-infected and Wolbachia-uninfected A. fraudatrix demonstrated that only eggs produced by the crosses between Wolbachia-infected males and Wolbachia-uninfected females did not hatch, indicating that Wolbachia infecting A. fraudatrix causes cytoplasmic incompatibility in the host insect. This is the first report showing the effect of Wolbachia on reproductive function in a longicorn beetle, A. fraudatrix.

Does diet breadth affect the complexity of the phytophagous insect microbiota? The case study of Chrysomelidae

Chrysomelidae is a family of phytophagous insects with a highly variable degree of trophic specialization. The aim of this study is to test whether species feeding on different plants (generalists) harbour more complex microbiotas than those feeding on a few or a single plant species (specialists). The microbiota of representative leaf beetle species was characterized with a metabarcoding approach targeting V1–V2 and V4 regions of the bacterial 16S rRNA. Almost all the analysed species harbour at least one reproductive manipulator bacteria (e.g., Wolbachia, Rickettsia). Two putative primary symbionts, previously isolated only from a single species (Bromius obscurus), have been detected in two species of the same subfamily, suggesting a widespread symbiosis in Eumolpinae. Surprisingly, the well‐known aphid symbiont Buchnera is well represented in the microbiota of Orsodacne humeralis. Moreover, in this study, using Hill numbers to dissect the components of the microbiota diversity (abundant and rare bacteria), it has been demonstrated that generalist insect species harbour a more diversified microbiota than specialists. The higher microbiota diversity associated with a wider host‐plant spectrum could be seen as an adaptive trait, conferring new metabolic potential useful to expand the diet breath, or as a result of environmental stochastic acquisition conveyed by diet.

Food Resource Sharing of Alder Leaf Beetle Specialists (Coleoptera: Chrysomelidae) as Potential Insect-Plant Interface for Horizontal Transmission of Endosymbionts

Recent studies suggest that endosymbionts of herbivore insects can be horizontally transferred to other herbivores feeding on the same host plants, whereby the plant acts as an intermediate stage in the chain of transmission. If this mechanism operates, it is also expected that insect communities sharing the same host plant will have higher chances to share their endosymbionts. In this study, we use a high-throughput 16S rRNA metabarcoding approach to investigate the presence, diversity, and potential sharing of endosymbionts in several species of leaf beetles (Coleoptera: Chrysomelidae) of a local community specialized on an alder diet in North America. Rickettsia and Wolbachia were predominant in the sample, with strong evidence for each species having their own dominant infection, of either or both types of bacteria. However, all species shared a much lower proportion of a particular Wolbachia type, compatible with the same strain dominant in one of the species of leaf beetles. Crucially, the same 16S rRNA haplotype of Wolbachia was found on alder leaf extracts. The combined evidence and the absence of this strain in a syntopic species of leaf beetle feeding on a different host plant support the hypothesis that at least the initial stages of the mechanism that would allow horizontal transmission of endosymbionts across species feeding on the same plant is possible. The accessibility and characteristics of endosymbiont associations of this system make it suitable for deeper analyses of their diversity and transmission in natural conditions.

Wolbachia infection in wild mosquitoes (Diptera: Culicidae): implications for transmission modes and host-endosymbiont associations in Singapore

Background

Wolbachia are intracellular bacterial endosymbionts found in most insect lineages. In mosquitoes, the influence of these endosymbionts on host reproduction and arboviral transmission has spurred numerous studies aimed at using Wolbachia infection as a vector control technique. However, there are several knowledge gaps in the literature and little is known about natural Wolbachia infection across species, their transmission modes, or associations between various Wolbachia lineages and their hosts. This study aims to address these gaps by exploring mosquito-Wolbachia associations and their evolutionary implications.

Methods

We conducted tissue-specific polymerase chain reaction screening for Wolbachia infection in the leg, gut and reproductive tissues of wild mosquitoes from Singapore using the Wolbachia surface protein gene (wsp) molecular marker. Mosquito-Wolbachia associations were explored using three methods—tanglegram, distance-based, and event-based methods—and by inferred instances of vertical transmission and host shifts.

Results

Adult mosquitoes (271 specimens) representing 14 genera and 40 species were screened for Wolbachia. Overall, 21 species (51.2%) were found positive for Wolbachia, including five in the genus Aedes and five in the genus Culex. To our knowledge, Wolbachia infections have not been previously reported in seven of these 21 species: Aedes nr. fumidus, Aedes annandalei, Uranotaenia obscura, Uranotaenia trilineata, Verrallina butleri, Verrallina sp. and Zeugnomyia gracilis. Wolbachia were predominantly detected in the reproductive tissues, which is an indication of vertical transmission. However, Wolbachia infection rates varied widely within a mosquito host species. There was no clear signal of cophylogeny between the mosquito hosts and the 12 putative Wolbachia strains observed in this study. Host shift events were also observed.

Conclusions

Our results suggest that the mosquito-Wolbachia relationship is complex and that combinations of transmission modes and multiple evolutionary events likely explain the observed distribution of Wolbachia diversity across mosquito hosts. These findings have implications for a better understanding of the diversity and ecology of Wolbachia and for their utility as biocontrol agents.

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.

Antibiotic exposure perturbs the bacterial community in the small brown planthopper Laodelphax striatellus

Bacteria symbionts in herbivores play an important role in host biology and ecology, and are affected by environmental factors such as temperature, diet, habitat, antibiotics and so on. However, the effects of antibiotics on the microbiome of the small brown planthopper Laodelphax striatellus (SBPH) remain unclear. Here, we studied the effects of tetracycline on the diversity and composition of bacterial colonies in different tissues of SBPH using high throughput sequencing of 16S ribosomal RNA amplicons. Our results show that Proteobacteria, Firmicutes, Bacteroidetes, Actinobacteria were most abundant in SBPH, and the genera Asaia and Wolbachia were most abundant in all body parts of SBPH. Antibiotic treatment had persistent effects on the composition of the SBPH microbiome. Tetracycline depleted the population of Firmicutes, Bacteroidetes, Tenericutes and Fusobacteria, and nearly 100% eliminated Wolbachia, Bacteroides and Abiotrophia in SBPH. Together, these results suggest that antibiotic exposure affects the bacteria symbionts of different body parts in SBPH and will facilitate future studies of the bacterial symbionts of arthropod hosts.

Symbiont-mediated cytoplasmic incompatibility: what have we learned in 50 years?

Cytoplasmic incompatibility (CI) is the most common symbiont-induced reproductive manipulation. Specifically, symbiont-induced sperm modifications cause catastrophic mitotic defects in the fertilized embryo and ensuing lethality in crosses between symbiotic males and either aposymbiotic females or females harboring a different symbiont strain. However, if the female carries the same symbiont strain, then embryos develop properly, thereby imparting a relative fitness benefit to symbiont-transmitting mothers. Thus, CI drives maternally-transmitted bacteria to high frequencies in arthropods worldwide. In the past two decades, CI experienced a boom in interest due to its (i) deployment in worldwide efforts to curb mosquito-borne diseases, (ii) causation by bacteriophage genes, cifA and cifB, that modify sexual reproduction, and (iii) important impacts on arthropod speciation. This review serves as a gateway to experimental, conceptual, and quantitative themes of CI and outlines significant gaps in understanding CI’s mechanism that are ripe for investigation from diverse subdisciplines in the life sciences.

Phylogeny and Density Dynamics of Wolbachia Infection of the Health Pest Paederus fuscipes Curtis (Coleoptera: Staphylinidae)

The maternally inherited obligate intracellular bacteria Wolbachia infects the reproductive tissues of a wide range of arthropods and affects host reproduction. Wolbachia is a credible biocontrol agent for reducing the impact of diseases associated with arthropod vectors. Paederus fuscipes is a small staphylinid beetle that causes dermatitis linearis and conjunctivitis in humans when they come into contact with skin. Wolbachia occur in this beetle, but their relatedness to other Wolbachia, their infection dynamics, and their potential host effects remain unknown. In this study, we report the phylogenetic position and density dynamics of Wolbachia in P. fuscipes. The phylogeny of Wolbachia based on an analysis of MLST genotyping showed that the bacteria from P. fuscipes belong to supergroup B. Quantitative PCR indicated that the infection density in adults was higher than in any other life stage (egg, larva or pupa), and that reproductive tissue in adults had the highest infection densities, with similar densities in the sexes. These findings provide a starting point for understanding the Wolbachia infection dynamics in P. fuscipes, and interactions with other components of the microbiota.

First Insight into Microbiome Profiles of Myrmecophilous Beetles and Their Host, Red Wood Ant Formica polyctena (Hymenoptera: Formicidae)-A Case Study

Formica polyctena belongs to the red wood ant species group. Its nests provide a stable, food rich, and temperature and humidity controlled environment, utilized by a wide range of species, called myrmecophiles. Here, we used the high-throughput sequencing of the 16S rRNA gene on the Illumina platform for identification of the microbiome profiles of six selected myrmecophilous beetles (Dendrophilus pygmaeus, Leptacinus formicetorum, Monotoma angusticollis, Myrmechixenus subterraneus, Ptenidium formicetorum and Thiasophila angulata) and their host F. polyctena. Analyzed bacterial communities consisted of a total of 23 phyla, among which Proteobacteria, Actinobacteria, and Firmicutes were the most abundant. Two known endosymbionts-Wolbachia and Rickettsia-were found in the analyzed microbiome profiles and Wolbachia was dominant in bacterial communities associated with F. polyctena, M. subterraneus, L. formicetorum and P. formicetorum (>90% of reads). In turn, M. angusticollis was co-infected with both Wolbachia and Rickettsia, while in the microbiome of T. angulata, the dominance of Rickettsia has been observed. The relationships among the microbiome profiles were complex, and no relative abundance pattern common to all myrmecophilous beetles tested was observed. However, some subtle, species-specific patterns have been observed for bacterial communities associated with D. pygmaeus, M. angusticollis, and T. angulata.

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.

Global genetic diversity, lineage distribution, and Wolbachia infection of the alfalfa weevil Hypera postica (Coleoptera: Curculionidae)

The alfalfa weevil (Hypera postica) is a well-known example of a worldwide-distributed pest with high genetic variation. Based on the mitochondrial genes, the alfalfa weevil clusters into two main mitochondrial lineages. However, there is no clear picture of the global diversity and distribution of these lineages; neither the drivers of its diversification are known. However, it appears likely that historic demographic events including founder effects played a role. In addition, Wolbachia, a widespread intracellular parasite/symbiont, likely played an important role in the evolution of the species. Wolbachia infection so far was only detected in the Western lineage of H. postica with no information on the infecting strain, its frequency, and its consequences on the genetic diversity of the host. We here used a combination of mitochondrial and nuclear sequences of the host and sequence information on Wolbachia to document the distribution of strains and the degree of infection. The Eastern lineage has a higher genetic diversity and is found in the Mediterranean, the Middle East, Eastern Europe, and eastern America, whereas the less diverse Western lineage is found in Central Europe and the western America. Both lineages are infected with the same common strain of Wolbachia belonging to Supergroup B. Based on neutrality tests, selection tests, and the current distribution and diversification of Wolbachia in H. postica, we suggested the Wolbachia infection did not shape genetic diversity of the host. The introduced populations in the United States are generally genetically less diverse, which is in line with founder effects.

Co-occurrence of pederin-producing and Wolbachia endobacteria in Paederus fuscipes Curtis, 1840 (Coleoptera: Staphilinidae) and its evolutionary consequences

The dual occurrence of Pseudomonas-like and Wolbachia endobacteria has not been investigated in the Pederus beetles yet. We investigated pederin-producing bacteria (PPB) infection in Paederus fuscipes specimens from the southern margins of the Caspian Sea by designed genus-specific (OprF) and species-specific (16S rRNA) primers. Wolbachia infection was studied through a nested-PCR assay of Wolbachia surface protein (wsp) gene. Of the 125 analyzed beetles, 42 females (82.35%) and 15 males (20.27%) were positive to PPB infection; this is the first study reporting male P. fuscipes infection to PPB. Wolbachia infection was found in 45 female (88.23%) and 50 male (67.57%) analyzed beetles. Surprisingly, a number of 36 females (70.59%) and 13 males (17.57%) were found to be infected with both PPB and Wolbachia endosymbionts. In general, population infection rates to PPB and Wolbachia were determined to be 45.6% and 76%, respectively. The infection rates of female beetles to PPB and PPB-Wolbachia were significantly higher than males. In Paederus species, only female beetles shelter PPB and the discovery of this bacterium in adult males may reflect their cannibalistic behavior on the contaminated stages. Phylogenetic analysis showed that the sequences of OprF gene were unique among Pseudomonas spp.; however, sequences of 16S rRNA gene were related to the PPB of Pederus species. The co-occurrence and random distribution of these endobacteria may imply putative tripartite interactions among PPB, Wolbachia, and Paederus. In order to elucidate these possible tripartite interactions, further studies are required even at gender level.

Detection of a new bacterium of the family Holosporaceae (Alphaproteobacteria: Holosporales) associated with the oribatid mite Achipteria coleoptrata

We detected an unknown bacterium in Achipteria coleoptrata (Acari: Oribatida). Its 16S rDNA gene sequence showed 89% identity to the endosymbiont “Candidatus Nucleicultrix amoebiphila” from amoebae and “Candidatus Gortzia sp.” from ciliates. Phylogenetic analysis revealed that the microorganism is a member of the family Holosporaceae, order Holosporales of Alphaproteobacteria. Its occurrence in Oribatida is enigmatic. It cannot be excluded that it is a symbiont of Oribatida as well as it is an endosymbiont of a smaller, even unicellular, organisms living inside the mite. The issue of the occurrence of this microorganism is interesting and further research is needed to gain the knowledge of its role and the nature of bacterium-host interaction.

Bacterial Endosymbionts Are Common Among, but not Necessarily Within, Insect Species

Bacterial endosymbionts, particularly Wolbachia (Rickettsiales: Rickettsiaceae), Rickettsia (Rickettsiales: Rickettsiaceae), and Cardinium (Bacteroidales: Bacteroidaceae), are commonly found in several arthropod groups, including insects. Most estimates of the global infection rate of Wolbachia (52% [95% credible intervals: 44-60]) show that these bacteria infect more than half of all insect species. Other endosymbionts, such as Rickettsia (24% [confidence intervals [CIs] 20-42]) and Cardinium (13% [CIs 13-55]), infect a smaller but still substantial proportion of insect species. In spite of these observations, it is unclear what proportion of individuals within those species are infected. Here, we used published databases to estimate the proportion of individuals that are infected with either Wolbachia, Rickettsia, or Cardinium. We found that the majority (69%) of Wolbachia-infected species have less than half of their individuals infected with Wolbachia, indicating that although the bacterium may be common among species, it is not common within species. The same was true for Rickettsia (81%) and Cardinium (87%). This discrepancy was consistent across orders, in which less than 10% of individuals were typically infected, even though more than 50% of species within orders were infected. For example, according to our model, nearly 50% of beetle (Coleoptera) species are infected with Wolbachia (i.e., contain at least one individual that has tested positive for Wolbachia), but less than 5% of all individuals are infected. These results add to the growing knowledge base about endosymbionts in insects and should guide future sampling efforts and investigations on the role that these bacteria play in populations.

Phylogenetic analysis based on the 16S rDNA, gltA, gatB, and hcpA gene sequences of Wolbachia from the novel host Ceratozetes thienemanni (Acari: Oribatida)

We determined the occurrence of intracellular endosymbionts (Wolbachia, Cardinium, Arsenophonus, Rickettsia, Spiroplasma, Hamiltonella, flavobacteria, and microsporidia) in oribatid mites (Acari: Oribatida) with the use of PCR technique. For the first time we looked for and detected Wolbachia in parthenogenetic oribatid mite Ceratozetes thienemanni Willmann, 1943. The 16S rDNA, gatB, hcpA, and gltA sequences of Wolbachia in C. thienemanni showed the highest similarity (≥ 90%) to the genes of Wolbachia from springtails (Collembola) and oribatid mite Gustavia microcephala. We found the unique sequence 5'-GGGGTAATGGCC-3' in 16S rDNA of Wolbachia from C. thienemanni and collembolan representing group E. The phylogeny of Wolbachia based on the analysis of single genes as well as concatenated alignments of four bacterial loci showed that the bacteria from C. thienemanni belonged to Wolbachia group E, like the endosymbionts from springtail hosts and G. microcephala. Considering coexisting of representatives of Oribatida and Collembola in the same soil habitat and similar food, it is possible that the source of Wolbachia infection was the same. Residues of dead invertebrates could be in organic matter of their soil food, so the scenario of infection transferred by eating of remains of soil cohabitates is also possible. It could explain the similarity and relationship of the Wolbachia in these two arthropod groups. Oribatid mite C. thienemanni is a parthenogenetic mite which is a unique feature in the genus Ceratozetes. Moreover, this species, within the entire genus Ceratozetes, is characterized by the most northerly distribution. It is difficult to determine either it is parthenogenesis or the presence of endosymbionts that are in some way responsible for this kind of evolutionary success. Maybe we are dealing here with a kind of synergy of both factors?

Using host species traits to understand the Wolbachia infection distribution across terrestrial beetles

Knowledge of Wolbachia prevalence with respect to its hosts is restricted mainly to taxonomic/phylogenetic context. In contrast, relations between infection and most host’s ecological and biological traits are poorly understood. This study aimed to elaborate on relations between bacteria and its beetle hosts in taxonomic and the ecological contexts. In particular, the goal is to verify which ecological and biological traits of beetles could cause them to be prone to be infected. Verification of Wolbachia infection status across 297 beetle taxa showed that approximately 27% of taxa are infected by supergroups A and B. Only minor support for coevolution between bacteria and its beetle hosts was observed in some genera of beetles, but in general coevolution between beetles and Wolbachia was rejected. Some traits of beetles were found to be unrelated to Wolbachia prevalence (type of range and thermal preferences); some traits were related with ambiguous effects (habitats, distribution, mobility and body size); some were substantially related (reproduction mode and trophy). The aforementioned summary does not show obvious patterns of Wolbachia prevalence and diversity in relation to host taxonomy, biology, and ecology. As both Wolbachia and Coleoptera are diverse groups, this lack of clear patterns is probably a reflection of nature, which is characterised by highly diversified and probably unstable relations.