Evidence for horizontal transfer of Wolbachia by a Drosophila mite

Wolbachia supergroup A in Enoplognatha latimana (Araneae: Theridiidae) in Poland as an example of possible horizontal transfer of bacteria

Wolbachia (phylum Pseudomonadota, class Alfaproteobacteria, order Rickettsiales, family Ehrlichiaceae) is a maternally inherited bacterial symbiont infecting more than half of arthropod species worldwide and constituting an important force in the evolution, biology, and ecology of invertebrate hosts. Our study contributes to the limited knowledge regarding the presence of intracellular symbiotic bacteria in spiders. Specifically, we investigated the occurrence of Wolbachia infection in the spider species Enoplognatha latimana Hippa and Oksala, 1982 (Araneae: Theridiidae) using a sample collected in north-western Poland. To the best of our knowledge, this is the first report of Wolbachia infection in E. latimana. A phylogeny based on the sequence analysis of multiple genes, including 16S rRNA, coxA, fbpA, ftsZ, gatB, gltA, groEL, hcpA, and wsp revealed that Wolbachia from the spider represented supergroup A and was related to bacterial endosymbionts discovered in other spider hosts, as well as insects of the orders Diptera and Hymenoptera. A sequence unique for Wolbachia supergroup A was detected for the ftsZ gene. The sequences of Wolbachia housekeeping genes have been deposited in publicly available databases and are an important source of molecular data for comparative studies. The etiology of Wolbachia infection in E. latimana is discussed.

Metatranscriptomic Sequencing of Medically Important Mosquitoes Reveals Extensive Diversity of RNA Viruses and Other Microbial Communities in Western Australia

Mosquitoes harbor a wide diversity of microorganisms, including viruses that are human pathogens, or that are insect specific. We used metatranscriptomics, an unbiased high-throughput molecular approach, to describe the composition of viral and other microbial communities in six medically important mosquito species from across Western Australia: Aedes vigilax, Culex annulirostris, Cx. australicus, Cx. globocoxitus, Cx. pipiens biotype molestus, and Cx. quinquefasciatus. We identified 42 viral species, including 13 novel viruses, from 19 families. Culex mosquitoes exhibited a significantly higher diversity of viruses than Aedes mosquitoes, and no virus was shared between the two genera. Comparison of mosquito populations revealed a heterogenous distribution of viruses between geographical regions and between closely related species, suggesting that geography and host species may play a role in shaping virome composition. We also detected bacterial and parasitic microorganisms, among which Wolbachia bacteria were detected in three members of the Cx. pipiens complex, Cx. australicus, Cx. pipiens biotype molestus, and Cx. quinquefasciatus. In summary, our unbiased metatranscriptomics approach provides important insights into viral and other microbial diversity in Western Australian mosquitoes that vector medically important viruses.

Disentangling detrimental sand fly-mite interactions in a closed laboratory sand fly colony: implications for vector-borne disease studies and guidelines for overcoming severe mite infestations

BACKGROUND

Vector sand fly colonies are a critical component of studies aimed at improving the understanding of the neglected tropical disease leishmaniasis and alleviating its global impact. However, among laboratory-colonized arthropod vectors of infectious diseases, the labor-intensive nature of sand fly rearing coupled with the low number of colonies worldwide has generally discouraged the widespread use of sand flies in laboratory settings. Among the different factors associated with the low productivity of sand fly colonies, mite infestations are a significant factor. Sand fly colonies are prone to infestation by mites, and the physical interactions between sand flies and mites and metabolites have a negative impact on sand fly larval development.

METHODS

Mites were collected from sand fly larval rearing pots and morphologically identified using taxonomic keys. Upon identification, they were photographed with a scanning electron microscope. Several mite control measures were adopted in two different laboratories, one at the Laboratory of Malaria and Vector Research, National Institute of Allergy and Infectious Diseases-National Institutes of Health (Rockville, MD, USA), and the other at the University of Calgary (Calgary, AB, Canada).

RESULTS

The mite species associated with sand fly colonies in the two laboratories were morphologically identified as Tyrophagus sp. and Stratiolaelaps scimitus. While complete eradication of mites in sand fly colonies is considered unrealistic, drastically reducing their population has been associated with higher sand fly productivity.

CONCLUSIONS

We report a case of detrimental interaction between sand flies and Tyrophagus sp. and S. scimitus in a closed laboratory sand fly colony, discuss their impact on sand fly production and provide guidelines for limiting the mite population size in a closed laboratory colony leading to improved sand fly yields.

Wolbachia populations across organs of individual Culex pipiens: highly conserved intra-individual core pangenome with inter-individual polymorphisms

Wolbachia is a maternally inherited intracellular bacterium that infects a wide range of arthropods including mosquitoes. The endosymbiont is widely used in biocontrol strategies due to its capacity to modulate arthropod reproduction and limit pathogen transmission. Wolbachia infections in Culex spp. are generally assumed to be monoclonal but the potential presence of genetically distinct Wolbachia subpopulations within and between individual organs has not been investigated using whole genome sequencing. Here we reconstructed Wolbachia genomes from ovary and midgut metagenomes of single naturally infected Culex pipiens mosquitoes from Southern France to investigate patterns of intra- and inter-individual differences across mosquito organs. Our analyses revealed a remarkable degree of intra-individual conservancy among Wolbachia genomes from distinct organs of the same mosquito both at the level of gene presence-absence signal and single-nucleotide polymorphisms (SNPs). Yet, we identified several synonymous and non-synonymous substitutions between individuals, demonstrating the presence of some level of genomic heterogeneity among Wolbachia that infect the same C. pipiens field population. Overall, the absence of genetic heterogeneity within Wolbachia populations in a single individual confirms the presence of a dominant Wolbachia that is maintained under strong purifying forces of evolution.

Discovery of a novel circulation route of free-living Serratiasymbiotica mediated by predatory ladybird beetles

Horizontal transmission of bacteria to varied hosts can maintain and even expand microbial niches. We previously found that the aphid gut bacterium Serratia symbiotica strain SsMj can be transmitted to ladybird beetles via predation, but whether the predator is a new host, a reservoir or a dead end of this bacterium is unknown. This study aims to provide a clear picture of SsMj circulation from aphids to plants and predators. We first found that SsMj in aphids and ladybirds was abundantly distributed not only in digestive tracts but also in droppings. We found no evidence for vertical transmission of SsMj to aphid offspring. Instead, we showed that it could be transmitted to conspecific aphids by sharing the same plant or contacting honeydews. The key finding of this study is that SsMj was transmitted from aphids to ladybirds through predation, while ladybirds could also transfer SsMj back to aphids, possibly through feces. Together, this evidence suggests that SsMj is able to survive in the digestive tracts and droppings of insects and to expand its host range with plants and predators as reservoirs.

Using Wolbachia to control rice planthopper populations: progress and challenges

Wolbachia have been developed as a tool for protecting humans from mosquito populations and mosquito-borne diseases. The success of using Wolbachia relies on the facts that Wolbachia are maternally transmitted and that Wolbachia-induced cytoplasmic incompatibility provides a selective advantage to infected over uninfected females, ensuring that Wolbachia rapidly spread through the target pest population. Most transinfected Wolbachia exhibit a strong antiviral response in novel hosts, thus making it an extremely efficient technique. Although Wolbachia has only been used to control mosquitoes so far, great progress has been made in developing Wolbachia-based approaches to protect plants from rice pests and their associated diseases. Here, we synthesize the current knowledge about the important phenotypic effects of Wolbachia used to control mosquito populations and the literature on the interactions between Wolbachia and rice pest planthoppers. Our aim is to link findings from Wolbachia-mediated mosquito control programs to possible applications in planthoppers.

Ecology-relevant bacteria drive the evolution of host antimicrobial peptides in Drosophila

Antimicrobial peptides are host-encoded immune effectors that combat pathogens and shape the microbiome in plants and animals. However, little is known about how the host antimicrobial peptide repertoire is adapted to its microbiome. Here, we characterized the function and evolution of the Diptericin antimicrobial peptide family of Diptera. Using mutations affecting the two Diptericins (Dpt) of Drosophila melanogaster, we reveal the specific role of DptA for the pathogen Providencia rettgeri and DptB for the gut mutualist Acetobacter. The presence of DptA- or DptB-like genes across Diptera correlates with the presence of Providencia and Acetobacter in their environment. Moreover, DptA- and DptB-like sequences predict host resistance against infection by these bacteria across the genus Drosophila. Our study explains the evolutionary logic behind the bursts of rapid evolution of an antimicrobial peptide family and reveals how the host immune repertoire adapts to changing microbial environments.

Metagenomics of culture isolates and insect tissue illuminate the evolution of Wolbachia, Rickettsia and Bartonella symbionts in Ctenocephalides spp. fleas

While fleas are often perceived simply as a biting nuisance and a cause of allergic dermatitis, they represent important disease vectors worldwide, especially for bacterial zoonoses such as plague (transmitted by rodent fleas) and some of the rickettsioses and bartonelloses. The cosmopolitan cat (Ctenocephalides felis ) and dog (Ctenocephalides canis ) fleas, as well as Ctenocephalides orientis (restricted to tropical and subtropical Asia), breed in human dwellings and are vectors of cat-scratch fever (caused by Bartonella spp.) and Rickettsia spp., including Rickettsia felis (agent of flea-borne spotted fever) and Rickettsia asembonensis , a suspected pathogen. These Rickettsia spp. are members of a phylogenetic clade known as the ‘transitional group’, which includes both human pathogens and arthropod-specific endosymbionts. The relatively depauperate flea microbiome can also contain other endosymbionts, including a diverse range of Wolbachia strains. Here, we present circularized genome assemblies for two C. orientis -derived pathogens (Bartonella clarridgeiae and R. asembonensis ) from Malaysia, a novel Wolbachia strain (w Cori), and the C. orientis mitochondrion; all were obtained by direct metagenomic sequencing of flea tissues. Moreover, we isolated two Wolbachia strains from Malaysian C. felis into tick cell culture and recovered circularized genome assemblies for both, one of which (w CfeF) is newly sequenced. We demonstrate that the three Wolbachia strains are representatives of different major clades (‘supergroups’), two of which appear to be flea-specific. These Wolbachia genomes exhibit unique combinations of features associated with reproductive parasitism or mutualism, including prophage WO, cytoplasmic incompatibility factors and the biotin operon of obligate intracellular microbes. The first circularized assembly for R. asembonensis includes a plasmid with a markedly different structure and gene content compared to the published plasmid; moreover, this novel plasmid was also detected in cat flea metagenomes from the USA. Analysis of loci under positive selection in the transitional group revealed genes involved in host–pathogen interactions that may facilitate host switching. Finally, the first B. clarridgeiae genome from Asia exhibited large-scale genome stability compared to isolates from other continents, except for SNPs in regions predicted to mediate interactions with the vertebrate host. These findings highlight the paucity of data on the genomic diversity of Ctenocephalides -associated bacteria and raise questions regarding how interactions between members of the flea microbiome might influence vector competence.

Wolbachia springs eternal: symbiosis in Collembola is associated with host ecology

Wolbachia are endosymbiotic alpha-proteobacteria infecting a wide range of arthropods and nematode hosts with diverse interactions, from reproductive parasites to obligate mutualists. Their taxonomy is defined by lineages called supergroups (labelled by letters of the alphabet), while their evolutionary history is complex, with multiple horizontal transfers and secondary losses. One of the least recently derived, supergroup E, infects springtails (Collembola), widely distributed hexapods, with sexual and/or parthenogenetic populations depending on species. To better characterize the diversity of Wolbachia infecting springtails, the presence of Wolbachia was screened in 58 species. Eleven (20%) species were found to be positive, with three Wolbachia genotypes identified for the first time in supergroup A. The novel genotypes infect springtails ecologically and biologically different from those infected by supergroup E. To root the Wolbachia phylogeny, rather than distant other Rickettsiales, supergroup L infecting plant-parasitic nematodes was used here. We hypothesize that the ancestor of Wolbachia was consumed by soil-dwelling nematodes, and was transferred horizontally via plants into aphids, which then infected edaphic arthropods (e.g. springtails and oribatid mites) before expanding into most clades of terrestrial arthropods and filarial nematodes.

Facultative symbionts are potential agents of symbiont-mediated RNAi in aphids

Aphids are major crop pests, and they can be controlled through the application of the promising RNA interference (RNAi) techniques. However, chemical synthesis yield of dsRNA for RNAi is low and costly. Another sustainable aphid pest control strategy takes advantage of symbiont-mediated RNAi (SMR), which can generate dsRNA by engineered microbes. Aphid host the obligate endosymbiont Buchnera aphidicola and various facultative symbionts that not only have a wide host range but are also vertically and horizontally transmitted. Thus, we described the potential of facultative symbionts in aphid pest control by SMR. We summarized the community and host range of these facultative symbionts, and then reviewed their probable horizontal transmitted routes and ecological functions. Moreover, recent advances in the cultivation and genetic engineering of aphid facultative symbionts were discussed. In addition, current legislation of dsRNA-based pest control strategies and their safety assessments were reviewed.

Multiple long-range host shifts of major Wolbachia supergroups infecting arthropods

Wolbachia is a genus of intracellular bacterial endosymbionts found in 20–66% of all insect species and a range of other invertebrates. It is classified as a single species, Wolbachia pipientis, divided into supergroups A to U, with supergroups A and B infecting arthropods exclusively. Wolbachia is transmitted mainly via vertical transmission through female oocytes, but can also be transmitted across different taxa by host shift (HS): the direct transmission of Wolbachia cells between organisms without involving vertically transmitted gametic cells. To assess the HS contribution, we recovered 50 orthologous genes from over 1000 Wolbachia genomes, reconstructed their phylogeny and calculated gene similarity. Of 15 supergroup A Wolbachia lineages, 10 have similarities ranging from 95 to 99.9%, while their hosts’ similarities are around 60 to 80%. For supergroup B, four out of eight lineages, which infect diverse and distantly-related organisms such as Acari, Hemiptera and Diptera, showed similarities from 93 to 97%. These results show that Wolbachia genomes have a much higher similarity when compared to their hosts’ genes, which is a major indicator of HS. Our comparative genomic analysis suggests that, at least for supergroups A and B, HS is more frequent than expected, occurring even between distantly-related species.

Positive Selection and Horizontal Gene Transfer in the Genome of a Male-Killing Wolbachia

Wolbachia are a genus of widespread bacterial endosymbionts in which some strains can hijack or manipulate arthropod host reproduction. Male killing is one such manipulation in which these maternally transmitted bacteria benefit surviving daughters in part by removing competition with the sons for scarce resources. Despite previous findings of interesting genome features of microbial sex ratio distorters, the population genomics of male-killers remain largely uncharacterized. Here, we uncover several unique features of the genome and population genomics of four Arizonan populations of a male-killing Wolbachia strain, wInn, that infects mushroom-feeding Drosophila innubila. We first compared the wInn genome with other closely related Wolbachia genomes of Drosophila hosts in terms of genome content and confirm that the wInn genome is largely similar in overall gene content to the wMel strain infecting D. melanogaster. However, it also contains many unique genes and repetitive genetic elements that indicate lateral gene transfers between wInn and non-Drosophila eukaryotes. We also find that, in line with literature precedent, genes in the Wolbachia prophage and Octomom regions are under positive selection. Of all the genes under positive selection, many also show evidence of recent horizontal transfer among Wolbachia symbiont genomes. These dynamics of selection and horizontal gene transfer across the genomes of several Wolbachia strains and diverse host species may be important underlying factors in Wolbachia's success as a male-killer of divergent host species.

Wolbachia in scale insects: a distinct pattern of infection frequencies and potential transfer routes via ant associates

Wolbachia is one of the most successful endosymbiotic bacteria of arthropods. Known as the 'master of manipulation', Wolbachia can induce a wide range of phenotypes in its host that can have far-reaching ecological and evolutionary consequences and may be exploited for disease and pest control. However, our knowledge of Wolbachia's distribution and the infection rate is unevenly distributed across arthropod groups such as scale insects. We fitted a distribution of within-species prevalence of Wolbachia to our data and compared it to distributions fitted to an up-to-date dataset compiled from surveys across all arthropods. The estimated distribution parameters indicate a Wolbachia infection frequency of 43.6% (at a 10% prevalence threshold) in scale insects. Prevalence of Wolbachia in scale insects follows a distribution similar to exponential decline (most species are predicted to have low prevalence infections), in contrast to the U-shaped distribution estimated for other taxa (most species have a very low or very high prevalence). We observed no significant associations between Wolbachia infection and scale insect traits. Finally, we screened for Wolbachia in scale insect's ecological associates. We found a positive correlation between Wolbachia infection in scale insects and their ant associates, pointing to a possible route of horizontal transfer of Wolbachia.

Are ecological communities the seat of endosymbiont horizontal transfer and diversification? A case study with soil arthropod community

Maternally inherited endosymbionts of arthropods are one of the most abundant and diverse group of bacteria. These bacterial endosymbionts also show extensive horizontal transfer to taxonomically unrelated hosts and widespread recombination in their genomes. Such horizontal transfers can be enhanced when different arthropod hosts come in contact like in an ecological community. Higher rates of horizontal transfer can also increase the probability of recombination between endosymbionts, as they now share the same host cytoplasm. However, reports of community-wide endosymbiont data are rare as most studies choose few host taxa and specific ecological interactions among the hosts. To better understand endosymbiont spread within host populations, we investigated the incidence, diversity, extent of horizontal transfer, and recombination of three endosymbionts (Wolbachia, Cardinium, and Arsenophonus) in a specific soil arthropod community. Wolbachia strains were characterized with MLST genes whereas 16S rRNA gene was used for Cardinium and Arsenophonus. Among 3,509 individual host arthropods, belonging to 390 morphospecies, 12.05% were infected with Wolbachia, 2.82% with Cardinium and 2.05% with Arsenophonus. Phylogenetic incongruence between host and endosymbiont indicated extensive horizontal transfer of endosymbionts within this community. Three cases of recombination between Wolbachia supergroups and eight incidences of within-supergroup recombination were also found. Statistical tests of similarity indicated supergroup A Wolbachia and Cardinium show a pattern consistent with extensive horizontal transfer within the community but not for supergroup B Wolbachia and Arsenophonus. We highlight the importance of extensive community-wide studies for a better understanding of the spread of endosymbionts across global arthropod communities.

Wolbachia-driven selective sweep in a range expanding insect species

Background

Evolutionary processes can cause strong spatial genetic signatures, such as local loss of genetic diversity, or conflicting histories from mitochondrial versus nuclear markers. Investigating these genetic patterns is important, as they may reveal obscured processes and players. The maternally inherited bacterium Wolbachia is among the most widespread symbionts in insects. Wolbachia typically spreads within host species by conferring direct fitness benefits, and/or by manipulating its host reproduction to favour infected over uninfected females. Under sufficient selective advantage, the mitochondrial haplotype associated with the favoured maternally-inherited symbiotic strains will spread (i.e. hitchhike), resulting in low mitochondrial genetic variation across the host species range.

Method

The common bluetail damselfly (Ischnura elegans: van der Linden, 1820) has recently emerged as a model organism for genetics and genomic signatures of range expansion during climate change. Although there is accumulating data on the consequences of such expansion on the genetics of I. elegans, no study has screened for Wolbachia in the damselfly genus Ischnura. Here, we present the biogeographic variation in Wolbachia prevalence and penetrance across Europe and Japan (including samples from 17 populations), and from close relatives in the Mediterranean area (i.e. I. genei: Rambur, 1842; and I. saharensis: Aguesse, 1958).

Results

Our data reveal (a) multiple Wolbachia-strains, (b) potential transfer of the symbiont through hybridization, (c) higher infection rates at higher latitudes, and (d) reduced mitochondrial diversity in the north-west populations, indicative of hitchhiking associated with the selective sweep of the most common strain. We found low mitochondrial haplotype diversity in the Wolbachia-infected north-western European populations (Sweden, Scotland, the Netherlands, Belgium, France and Italy) of I. elegans, and, conversely, higher mitochondrial diversity in populations with low penetrance of Wolbachia (Ukraine, Greece, Montenegro and Cyprus). The timing of the selective sweep associated with infected lineages was estimated between 20,000 and 44,000 years before present, which is consistent with the end of the last glacial period about 20,000 years.

Conclusions

Our findings provide an example of how endosymbiont infections can shape spatial variation in their host evolutionary genetics during postglacial expansion. These results also challenge population genetic studies that do not consider the prevalence of symbionts in many insects, which we show can impact geographic patterns of mitochondrial genetic diversity.

Wolbachia prevalence in the vector species Culex pipiens and Culex torrentium in a Sindbis virus-endemic region of Sweden

Background

Wolbachia pipientis are endosymbiotic bacteria present in a large proportion of terrestrial arthropods. The species is known to sometimes affect the ability of its host to transmit vector-borne pathogens. Central Sweden is endemic for Sindbis virus (SINV), where it is mainly transmitted by the vector species Culex pipiens and Culex torrentium, with the latter established as the main vector. In this study we investigated the Wolbachia prevalence in these two vector species in a region highly endemic for SINV.

Methods

Culex mosquitoes were collected using CDC light traps baited with carbon dioxide over 9 years at 50 collection sites across the River Dalälven floodplains in central Sweden. Mosquito genus was determined morphologically, while a molecular method was used for reliable species determination. The presence of Wolbachia was determined through PCR using general primers targeting the wsp gene and sequencing of selected samples.

Results

In total, 676 Cx. pipiens and 293 Cx. torrentium were tested for Wolbachia. The prevalence of Wolbachia in Cx. pipiens was 97% (95% CI 94.8–97.6%), while only 0.7% (95% CI 0.19–2.45%) in Cx. torrentium. The two Cx. torrentium mosquitoes that were infected with Wolbachia carried different types of the bacteria.

Conclusions

The main vector of SINV in the investigated endemic region, Cx. torrentium, was seldom infected with Wolbachia, while it was highly prevalent in the secondary vector, Cx. pipiens. The presence of Wolbachia could potentially have an impact on the vector competence of these two species. Furthermore, the detection of Wolbachia in Cx. torrentium could indicate horizontal transmission of the endosymbiont between arthropods of different species.

Graphical abstract

Host-endoparasitoid-endosymbiont relationships: concealed Strepsiptera provide new twist to Wolbachia in Australian tephritid fruit flies

Wolbachia are widespread endosymbionts that affect arthropod reproduction and fitness. Mostly maternally inherited, Wolbachia are occasionally transferred horizontally. Previously, two Wolbachia strains were reported at low prevalence and titres across seven Australian tephritid species, possibly indicative of frequent horizontal transfer. Here, we performed whole-genome sequencing of field-caught Wolbachia-positive flies. Unexpectedly, we found complete mitogenomes of an endoparasitic strepsipteran, Dipterophagus daci, suggesting that Wolbachia in the flies are linked to concealed parasitization. We performed the first genetic characterization of D. daci and detected D. daci in Wolbachia-positive flies not visibly parasitized, and most but not all Wolbachia-negative flies were D. daci-negative, presumably reflecting polymorphism for the Wolbachia infections in D. daci. We dissected D. daci from stylopized flies and confirmed that Wolbachia infects D. daci, but also found Wolbachia in stylopized fly tissues, likely somatic, horizontally transferred, non-heritable infections. Furthermore, no Wolbachia cif and wmk genes were detected and very low mitogenomic variation in D. daci across its distribution. Therefore, Wolbachia may influence host fitness without reproductive manipulation. Our study of 13 tephritid species highlights that concealed early stages of strepsipteran parasitization led to the previous incorrect assignment of Wolbachia co-infections to tephritid species, obscuring ecological studies of this common endosymbiont and its horizontal transmission by parasitoids.

Characteristic and expression of Hsp70 and Hsp90 genes from Tyrophagus putrescentiae and their response to thermal stress

The development of insects is critically affected by temperature, which therefore plays an important role in the control of stored grain pests. Extreme temperature stress conditions lead to biological responses in mites, such as the synthesis of heat shock proteins. Tyrophagus putrescentiae (Tp) is a pest mite in stored grain that has negative effects on both economy and health. Since T. putrescentiae population dynamics are strongly influenced by temperature, in the present study we have cloned the cDNA of HSP70 and HSP90 (referred to as TpHSP70-1, TpHSP70-2 and TpHSP90) and determined their expression by fluorescence real time quantitative PCR. TpHSP70 and TpHSP90 showed high homology with similar genes in other species and the open reading frames of TpHSP70-1, TpHSP70-2 and TpHSP90 encoded proteins of 665, 661 and 718 amino acid residues, respectively. Under thermal stress, expression of TpHsp70-1 and TpHsp90 was up-regulated at higher temperatures, suggesting their role in the defense against thermal stress.

Comparative genome sequencing reveals insights into the dynamics of Wolbachia in native and invasive cherry fruit flies

Wolbachia is a maternally inherited obligate endosymbiont that can induce a wide spectrum of effects in its host, ranging from mutualism to reproductive parasitism. At the genomic level, recombination within and between strains, transposable elements, and horizontal transfer of strains between host species make Wolbachia an evolutionarily dynamic bacterial system. The invasive cherry fruit fly Rhagoletis cingulata arrived in Europe from North America ~40 years ago, where it now co‐occurs with the native cherry pest R. cerasi. This shared distribution has been proposed to have led to the horizontal transfer of different Wolbachia strains between the two species. To better understand transmission dynamics, we performed a comparative genome study of the strain wCin2 in its native United States and invasive European populations of R. cingulata with wCer2 in European R. cerasi. Previous multilocus sequence genotyping (MLST) of six genes implied that the source of wCer2 in R. cerasi was wCin2 from R. cingulata. However, we report genomic evidence discounting the recent horizontal transfer hypothesis for the origin of wCer2. Despite near identical sequences for the MLST markers, substantial sequence differences for other loci were found between wCer2 and wCin2, as well as structural rearrangements, and differences in prophage, repetitive element, gene content, and cytoplasmic incompatibility inducing genes. Our study highlights the need for whole‐genome sequencing rather than relying on MLST markers for resolving Wolbachia strains and assessing their evolutionary dynamics.

Supergroup F Wolbachia in terrestrial isopods: Horizontal transmission from termites?

Horizontal transmission between distantly related species has been used to explain how Wolbachia infect multiple species at astonishing rates despite the selection for resistance. Recently, a terrestrial isopod species was found to be infected by an unusual strain of supergroup F Wolbachia. However, only Wolbachia of supergroup B is typically found in isopods. One possibility is that these isopods acquired the infection because of their recurrent contact with termites—a group with strong evidence of infection by supergroup F Wolbachia. Thus, our goals were: (1) check if the infection was an isolated case in isopods, or if it revealed a broader pattern; (2) search for Wolbachia infection in the termites within Brazil; and (3) look for evidence consistent with horizontal transmission between isopods and termites. We collected Neotroponiscus terrestrial isopods and termites along the Brazilian coastal Atlantic forest. We sequenced and identified the Wolbachia strains found in these groups using coxA, dnaA, and fpbA genes. We constructed phylogenies for both bacteria and host taxa and tested for coevolution. We found the supergroup F Wolbachia in other species and populations of Neotroponiscus, and also in Nasutitermes and Procornitermes termites. The phylogenies showed that, despite the phylogenetic distance between isopods and termites, the Wolbachia strains clustered together. Furthermore, cophylogenetic analyses showed significant jumps of Wolbachia between terrestrial isopods and termites. Thus, our study suggests that the horizontal transmission of supergroup F Wolbachia between termites and terrestrial isopods is likely. Our study also helps understanding the success and worldwide distribution of this symbiont.

Systematic Review of Wolbachia Symbiont Detection in Mosquitoes: An Entangled Topic about Methodological Power and True Symbiosis

Wolbachia is an endosymbiotic bacterium that naturally infects several arthropods and nematode species. Wolbachia gained particular attention due to its impact on their host fitness and the capacity of specific Wolbachia strains in reducing pathogen vector and agricultural pest populations and pathogens transmission. Despite the success of mosquito/pathogen control programs using Wolbachia-infected mosquito release, little is known about the abundance and distribution of Wolbachia in most mosquito species, a crucial knowledge for planning and deployment of mosquito control programs and that can further improve our basic biology understanding of Wolbachia and host relationships. In this systematic review, Wolbachia was detected in only 30% of the mosquito species investigated. Fourteen percent of the species were considered positive by some studies and negative by others in different geographical regions, suggesting a variable infection rate and/or limitations of the Wolbachia detection methods employed. Eighty-three percent of the studies screened Wolbachia with only one technique. Our findings highlight that the assessment of Wolbachia using a single approach limited the inference of true Wolbachia infection in most of the studied species and that researchers should carefully choose complementary methodologies and consider different Wolbachia-mosquito population dynamics that may be a source of bias to ascertain the correct infectious status of the host species.

Wolbachia successfully replicate in a newly established horn fly, Haematobia irritans irritans (L.) (Diptera: Muscidae) cell line

BACKGROUND

Haematobia spp., horn flies (HF) and buffalo flies (BF), are economically important ectoparasites of dairy and beef cattle. Control of these flies relies mainly on treating cattle with chemical insecticides. However, the development of resistance to commonly used compounds is compromising the effectiveness of these treatments and alternative methods of control are required. Wolbachia are maternally transmitted endosymbiotic bacteria of arthropods that cause various reproductive distortions and fitness effects, making them a potential candidate for use in the biological control of pests. The first step towards this is the establishment and adaptation of xenobiotic infections of Wolbachia in target host cell lines.

RESULTS

Here, we report the successful establishment of a continuous HF cell line (HIE-18) from embryonic cells and its stable transinfection with Wolbachia strains wAlbB native to mosquitoes, and wMel and wMelPop native to Drosophila melanogaster. HIE-18 cells were typically round and diploid with ten chromosomes (2n = 10) or tetraploid with 20 chromosomes (4n = 20), with a doubling time of 67.2 h. Wolbachia density decreased significantly in HIE-18 cells in the first 48 h of infection, possibly due to overexpression of antimicrobial peptides through the Imd immune signalling pathway. However, density recovered after this time and HIE-18 cell lines stably infected with the three strains of Wolbachia have now each been subcultured more than 50 times as persistently infected lines.

CONCLUSION

The amenability of HF cells to infection with different strains of Wolbachia and the establishment of stable sustaining infections suggest the potential for use of Wolbachia in novel approaches for the control of Haematobia spp. Further, the availability of the HIE-18 cell line will provide an important resource for the study of genetics, host-parasite interactions and chemical resistance in Haematobia populations. © 2020 Society of Chemical Industry.

First report of Wolbachia in Damaeus onustus (Acari: Oribatida)

Purpose

Little is known about the distribution and phylogeny of bacterial endosymbionts in oribatid mites (Acari: Oribatida). Thus, we undertook the issue of occurrence of these microbial symbionts in this arthropod group.

Methods

We used PCR technique for detection of Wolbachia in Damaeus onustus. Phylogenetic analysis of the bacterium was conducted based on the 16S rDNA sequence.

Results

To the best of our knowledge, we present a novel finding of Wolbachia infection in the sexually reproducing oribatid mite, D. onustus. The presence of uninfected individuals (ca. 93%) suggests that the bacteria do not function as primary symbionts. A comparison of the bacterial 710-bp 16S rDNA sequence detected in the oribatid mite with the sequences deposited in GenBank revealed its 92–93% similarity to the 16S rDNA sequences of Wolbachia identified in some springtails (Collembola) and Bryobia sp. mite. Bacteria from D. onustus showed phylogenetic relationships with Wolbachia from springtails, Megalothorax minimus and Neelus murinus, which were included by other authors into a separate Wolbachia clade.

Conclusion

Our finding suggests that the strains of Wolbachia from D. onustus may form a new Wolbachia supergroup.

Titer regulation in arthropod-Wolbachia symbioses

Symbiosis between intracellular bacteria (endosymbionts) and animals are widespread. The alphaproteobacterium Wolbachia pipientis is known to maintain a variety of symbiotic associations, ranging from mutualism to parasitism, with a wide range of invertebrates. Wolbachia infection might deeply affect host fitness (e.g. reproductive manipulation and antiviral protection), which is thought to explain its high prevalence in nature. Bacterial loads significantly influence both the infection dynamics and the extent of bacteria-induced host phenotypes. Hence, fine regulation of bacterial titers is considered as a milestone in host-endosymbiont interplay. Here, we review both environmental and biological factors modulating Wolbachia titers in arthropods.

An elusive endosymbiont: Does Wolbachia occur naturally in Aedes aegypti?

Wolbachia are maternally inherited endosymbiotic bacteria found within many insect species. Aedes mosquitoes experimentally infected with Wolbachia are being released into the field for Aedes-borne disease control. These Wolbachia infections induce cytoplasmic incompatibility which is used to suppress populations through incompatible matings or replace populations through the reproductive advantage provided by this mechanism. However, the presence of naturally occurring Wolbachia in target populations could interfere with both population replacement and suppression programs depending on the compatibility patterns between strains. Aedes aegypti were thought to not harbor Wolbachia naturally but several recent studies have detected Wolbachia in natural populations of this mosquito. We therefore review the evidence for natural Wolbachia infections in A. aegypti to date and discuss limitations of these studies. We draw on research from other mosquito species to outline the potential implications of natural Wolbachia infections in A. aegypti for disease control. To validate previous reports, we obtained a laboratory population of A. aegypti from New Mexico, USA, that harbors a natural Wolbachia infection, and we conducted field surveys in Kuala Lumpur, Malaysia, where a natural Wolbachia infection has also been reported. However, we were unable to detect Wolbachia in both the laboratory and field populations. Because the presence of naturally occurring Wolbachia in A. aegypti could have profound implications for Wolbachia-based disease control programs, it is important to continue to accurately assess the Wolbachia status of target Aedes populations.

The Jekyll and Hyde Symbiont: Could Wolbachia Be a Nutritional Mutualist?

The most common intracellular symbiont on the planet-Wolbachia pipientis-is infamous largely for the reproductive manipulations induced in its host. However, more recent evidence suggests that this bacterium may also serve as a nutritional mutualist in certain host backgrounds and for certain metabolites. We performed a large-scale analysis of conserved gene content across all sequenced Wolbachia genomes to infer potential nutrients made by these symbionts. We review and critically evaluate the prior research supporting a beneficial role for Wolbachia and suggest future experiments to test hypotheses of metabolic provisioning.

Detection of diverse Wolbachia 16S rRNA sequences at low titers from malaria vectors in Kayin state, Myanmar

Background: Natural Wolbachia infections in malaria mosquitoes were recently reported in Africa, and negatively correlated with the development of Plasmodium falciparum in the vectors. The occurrence and effects of Wolbachia infections outside Africa have not been described and may have been underestimated.

Methods: Mosquitoes were collected by human-landing catch during May and June 2017 in ten villages in Kayin state, Myanmar. Closely related species of malaria vectors were identified with molecular assays. 16S rRNA Wolbachia DNA sequences were detected with quantitative real-time PCR.

Results: Low titer of Wolbachia DNA was detected in 13/370 samples in six malaria vector species. Sequences were diverse and different from those described in the African malaria mosquitoes.

Conclusion: The detection of Wolbachia DNA in malaria mosquitoes from Kayin state warrants further investigations to understand better the ecology and biology of Anopheles- Wolbachia interactions in Southeast Asia.

Low-density genetically diverse natural Wolbachia infections in malaria vectors in Kayin state, Myanmar

Background: Natural Wolbachia infections in malaria mosquitoes were recently reported in Africa, and negatively correlated with the development of Plasmodium falciparum in the vectors. The occurrence and effects of Wolbachia infections outside Africa have not been described and may have been underestimated. Methods: Mosquitoes were collected by human-landing catch during May and June 2017 in ten villages in Kayin state, Myanmar. Closely related species of malaria vectors were identified with molecular assays. Wolbachia infection rates were assessed with quantitative real-time PCR. Results: Low titer of Wolbachia DNA was detected in 13/370 samples in six malaria vector species. Phylogenetic analysis based on 16S rRNA sequences revealed a high diversity of Wolbachia strains and identified lineages different from those described in the African malaria mosquitoes. Conclusion: These low-density genetically diverse natural Wolbachia infections question the ecology and biology of Wolbachia-Anopheles interactions in Southeast Asia. Their effects on malaria transmission and mosquito vectors are yet to be determined.

Genetic Diversity and Wolbachia Infection Patterns in a Globally Distributed Invasive Ant

Understanding the phylogeographic history of an invasive species may facilitate reconstructing the history and routes of its invasion. The longhorn crazy ant, Paratrechina longicornis, is a ubiquitous agricultural and household pest throughout much of the tropics and subtropics, but little is known about the history of its spread. Here, we examine worldwide genetic variation in P. longicornis and its associated Wolbachia bacterial symbionts. Analyses of mtDNA sequences of 248 P. longicornis workers (one per colony) from 13 geographic regions reveal two highly diverged mtDNA clades that co-occur in most of the geographic regions. These two mtDNA clades are associated with different Wolbachia infection patterns, but are not congruent with patterns of nDNA (microsatellite) variation. Multilocus sequence typing reveals two distinct Wolbachia strains in P. longicornis, namely, wLonA and wLonF. The evolutionary histories of these two strains differ; wLonA appears to be primarily transmitted maternally, and patterns of mtDNA and nDNA variation and wLonA infection status are consistent with a relatively recent Wolbachia-induced selective sweep. In contrast, the observed patterns of mtDNA variation and wLonF infections suggest frequent horizontal transfer and losses of wLonF infections. The lack of nDNA structure among sampled geographic regions coupled with the finding that numerous mtDNA haplotypes are shared among regions implies that inadvertent long-distance movement through human commerce is common in P. longicornis and has shaped the genetic structure of this invasive ant worldwide.

Widespread Wolbachia infection in an insular radiation of damselflies (Odonata, Coenagrionidae)

Wolbachia is one of the most common endosymbionts found infecting arthropods. Theory predicts symbionts like Wolbachia will be more common in species radiations, as host shift events occur with greatest frequency between closely related species. Further, the presence of Wolbachia itself may engender reproductive isolation, and promote speciation of their hosts. Here we screened 178 individuals belonging to 30 species of the damselfly genera Nesobasis and Melanesobasis - species radiations endemic to the Fiji archipelago in the South Pacific - for Wolbachia, using multilocus sequence typing to characterize bacterial strains. Incidence of Wolbachia was 71% in Nesobasis and 40% in Melanesobasis, and prevalence was also high, with an average of 88% in the Nesobasis species screened. We identified a total of 25 Wolbachia strains, belonging to supergroups A, B and F, with some epidemic strains present in multiple species. The occurrence of Wolbachia in both males and females, and the similar global prevalence found in both sexes rules out any strong effect of Wolbachia on the primary sex-ratio, but are compatible with the phenotype of cytoplasmic incompatibility. Nesobasis has higher species richness than most endemic island damselfly genera, and we discuss the potential for endosymbiont-mediated speciation within this group.

Wolbachia Acquisition by Drosophila yakuba-Clade Hosts and Transfer of Incompatibility Loci Between Distantly Related Wolbachia

Maternally transmitted Wolbachia infect about half of insect species, yet the predominant mode(s) of Wolbachia acquisition remains uncertain. Species-specific associations could be old, with Wolbachia and hosts codiversifying (i.e., cladogenic acquisition), or relatively young and acquired by horizontal transfer or introgression. The three Drosophila yakuba-clade hosts [(D. santomea, D. yakuba) D. teissieri] diverged ∼3 MYA and currently hybridize on the West African islands Bioko and São Tomé. Each species is polymorphic for nearly identical Wolbachia that cause weak cytoplasmic incompatibility (CI)-reduced egg hatch when uninfected females mate with infected males. D. yakuba-clade Wolbachia are closely related to wMel, globally polymorphic in D. melanogaster We use draft Wolbachia and mitochondrial genomes to demonstrate that D. yakuba-clade phylogenies for Wolbachia and mitochondria tend to follow host nuclear phylogenies. However, roughly half of D. santomea individuals, sampled both inside and outside of the São Tomé hybrid zone, have introgressed D. yakuba mitochondria. Both mitochondria and Wolbachia possess far more recent common ancestors than the bulk of the host nuclear genomes, precluding cladogenic Wolbachia acquisition. General concordance of Wolbachia and mitochondrial phylogenies suggests that horizontal transmission is rare, but varying relative rates of molecular divergence complicate chronogram-based statistical tests. Loci that cause CI in wMel are disrupted in D. yakuba-clade Wolbachia; but a second set of loci predicted to cause CI are located in the same WO prophage region. These alternative CI loci seem to have been acquired horizontally from distantly related Wolbachia, with transfer mediated by flanking Wolbachia-specific ISWpi1 transposons.

Low-density genetically diverse natural Wolbachia infections in malaria vectors in Kayin state, Myanmar

Background: Natural Wolbachia infections in malaria mosquitoes were recently reported in Africa, and negatively correlated with the development of Plasmodium falciparum in the vectors. The occurrence and effects of Wolbachia infections outside Africa have not been described and may have been underestimated. Methods: Mosquitoes were collected by human-landing catch during May and June 2017 in ten villages in Kayin state, Myanmar. Closely related species of malaria vectors were identified with molecular assays. Wolbachia infection rates were assessed with quantitative real-time PCR. Results: Low titer of Wolbachia DNA was detected in 13/370 samples in six malaria vector species. Phylogenetic analysis based on 16S rRNA sequences revealed a high diversity of Wolbachia strains and identified lineages different from those described in the African malaria mosquitoes. Conclusion: These low-density genetically diverse natural Wolbachia infections question the ecology and biology of Wolbachia-Anopheles interactions in Southeast Asia. Their effects on malaria transmission and mosquito vectors are yet to be determined.

Endosymbiont diversity and prevalence in herbivorous spider mite populations in South-Western Europe

Bacterial endosymbionts are known as important players of the evolutionary ecology of their hosts. However, their distribution, prevalence and diversity are still largely unexplored. To this aim, we investigated infections by the most common bacterial reproductive manipulators in herbivorous spider mites of South-Western Europe. Across 16 populations belonging to three Tetranychus species, Wolbachia was the most prevalent (ca. 61%), followed by Cardinium (12%-15%), while only few individuals were infected by Rickettsia (0.9%-3%), and none carried Arsenophonus or Spiroplasma. These endosymbionts are here reported for the first time in Tetranychus evansi and Tetranychus ludeni, and showed variable infection frequencies between and within species, with several cases of coinfections. Moreover, Cardinium was more prevalent in Wolbachia-infected individuals, which suggests facilitation between these symbionts. Finally, sequence comparisons revealed no variation of the Wolbachia wsp and Rickettsia gtlA genes, but some diversity of the Cardinium 16S rRNA, both between and within populations of the three mite species. Some of the Cardinium sequences identified belonged to distantly-related clades, and the lack of association between these sequences and spider mite mitotypes suggests repeated host switching of Cardinium. Overall, our results reveal a complex community of symbionts in this system, opening the path for future studies.

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?

Wolbachia symbionts in mosquitoes: Intra- and intersupergroup recombinations, horizontal transmission and evolution

Many mosquitoes harbour Wolbachia symbionts that could affect the biology of their host in different ways. Evolutionary relationships of mosquitoes' Wolbachia infection, geographical distribution and symbiont prevalence in many mosquito species are not yet clear. Here, we present the results of Wolbachia screening of 17 mosquito species of four genera-Aedes, Anopheles, Coquillettidia and Culex collected from five regions of Eastern Europe and the Caucasus in 2012-2016. Based on multilocus sequence typing (MLST) data previously published and generated in this study, we try to reveal genetic links between mosquitoes' and other hosts' Wolbachia. The Wolbachia symbionts are found in Culex pipiens, Aedes albopictus and Coquillettidia richiardii and for the first time in Aedes cinereus and Aedes cantans, which are important vectors of human pathogens. Phylogenetic analysis demonstrated multiple origins of infection in mosquitoes although the one-allele-criterion approach revealed links among B-supergroup mosquito Wolbachia with allele content of lepidopteran hosts. The MLST gene content of strain wAlbA from the A-supergroup is linked with different ant species. Several cases of intersupergroup recombinations were found. One of them occurred in the wAlbaB strain of Aedes albopictus, which contains the coxA allele of the A-supergroup, whereas other loci, including wsp, belong to supergroup B. Other cases are revealed for non-mosquito symbionts and they exemplified genetic exchanges of A, B and F supergroups. We conclude that modern Wolbachia diversity in mosquitoes and in many other insect taxa is a recent product of strain recombination and symbiont transfers.

A new Cardinium group of bacteria found in Achipteria coleoptrata (Acari: Oribatida)

The understanding of the biology of arthropods requires an understanding of their bacterial associates. We determined the distribution of bacteria Wolbachia sp., Rickettsia sp., Cardinium sp., Spiroplasma sp., Arsenophonus sp., Hamiltonella sp., and Flavobacterium in oribatid mites (Acari: Oribatida). We identified Cardinium sp. in Achipteria coleoptrata. This is the first report of this bacterium in A. coleoptrata. Approximately 30% of the mite population was infected by Cardinium sp. The Cardinium 16S rDNA was examined for the presence of two sequences unique for this microorganism. One of them was noted in Cardinium sp. of A. coleoptrata. In the second sequence, we found nucleotide substitution in the 7th position: A instead of T. In our opinion, this demonstrated the unique nature of Cardinium sp. of A. coleoptrata. We also determined phylogenetic relationship between Cardinium sp., including the strain found in A. coleoptrata by studying the 16S rRNA and gyrB gene sequences. It revealed that Cardinium from A. coleoptrata did not cluster together with strains from groups A, B, C or D, and constituted a separate clade E. These observations make A. coleoptrata a unique Cardinium host in terms of the distinction of the strain.

Decision-making in a bisexual line and a thelytokous Wolbachia-infected line of Trichogramma dendrolimi Matsumura (Hymenoptera: Trichogrammatidae) regarding behavior toward their hosts

BACKGROUND

The use of thelytokous Wolbachia-infected Trichogramma (parasitic wasps) has long been considered as a way to enhance the efficacy of biocontrol. However, Wolbachia can affect the host physiology. We compared decision-making between bisexual and thelytokous Wolbachia-infected lines of Trichogramma dendrolimi Matsumura regarding behavior toward fresh and old eggs of Corcyra cephalonica at 25 ± 1 °C and 70 ± 5% relative humidity.

RESULTS

The behavioral patterns and sequences of the two lines were basically the same. The durations of various behavioral patterns and values of fitness indicators of the bisexual line on fresh eggs were generally significantly shorter and better, respectively, than on old eggs, whereas the thelytokous line behaved similarly toward the two types of eggs, and differences in most fitness indicators between fresh and old eggs were not significant. On fresh eggs, the durations of various behaviors in the bisexual line were generally significantly shorter than in the thelytokous line and the fitness indicators were generally significantly better.

CONCLUSION

Wolbachia affected the fitness of T. dendrolimi negatively. The potential of the thelytokous line as a biocontrol agent would not be as good as that of the bisexual line when decision-making only is considered. Therefore, further evaluations need to be carried out before the thelytokous line can be used in practical biocontrol. © 2018 Society of Chemical Industry.

Rapid Global Spread of wRi-like Wolbachia across Multiple Drosophila

Maternally transmitted Wolbachia, Spiroplasma, and Cardinium bacteria are common in insects [1], but their interspecific spread is poorly understood. Endosymbionts can spread rapidly within host species by manipulating host reproduction, as typified by the global spread of wRi Wolbachia observed in Drosophila simulans [2, 3]. However, because Wolbachia cannot survive outside host cells, spread between distantly related host species requires horizontal transfers that are presumably rare [4-7]. Here, we document spread of wRi-like Wolbachia among eight highly diverged Drosophila hosts (10-50 million years) over only about 14,000 years (5,000-27,000). Comparing 110 wRi-like genomes, we find ≤0.02% divergence from the wRi variant that spread rapidly through California populations of D. simulans. The hosts include both globally invasive species (D. simulans, D. suzukii, and D. ananassae) and narrowly distributed Australian endemics (D. anomalata and D. pandora) [8]. Phylogenetic analyses that include mtDNA genomes indicate introgressive transfer of wRi-like Wolbachia between closely related species D. ananassae, D. anomalata, and D. pandora but no horizontal transmission within species. Our analyses suggest D. ananassae as the Wolbachia source for the recent wRi invasion of D. simulans and D. suzukii as the source of Wolbachia in its sister species D. subpulchrella. Although six of these wRi-like variants cause strong cytoplasmic incompatibility, two cause no detectable reproductive effects, indicating that pervasive mutualistic effects [9, 10] complement the reproductive manipulations for which Wolbachia are best known. "Super spreader" variants like wRi may be particularly useful for controlling insect pests and vector-borne diseases with Wolbachia transinfections [11].

New Insights into the Microbiota of Moth Pests

In recent years, next generation sequencing (NGS) technologies have helped to improve our understanding of the bacterial communities associated with insects, shedding light on their wide taxonomic and functional diversity. To date, little is known about the microbiota of lepidopterans, which includes some of the most damaging agricultural and forest pests worldwide. Studying their microbiota could help us better understand their ecology and offer insights into developing new pest control strategies. In this paper, we review the literature pertaining to the microbiota of lepidopterans with a focus on pests, and highlight potential recurrent patterns regarding microbiota structure and composition.

Experimental Manipulation Shows a Greater Influence of Population than Dietary Perturbation on the Microbiome of Tyrophagus putrescentiae

Tyrophagus putrescentiae is inhabited by bacteria that differ among mite populations (strains) and diets. Here, we investigated how the microbiome and fitness of Tputrescentiae are altered by dietary perturbations and mite populations. Four T. putrescentiae populations, referred to as dog, Koppert, laboratory, and Phillips, underwent a perturbation, i.e., a dietary switch from a rearing diet to two experimental diets. The microbiome was investigated by sequencing the V1-V3 portion of the 16S rRNA gene, and selected bacterial taxa were quantified by quantitative PCR (qPCR) using group/taxon-specific primers. The parameters observed were the changes in mite population growth and nutritional status, i.e., the total glycogen, lipid, saccharide, and protein contents in mites. The effect of diet perturbation on the variability of the microbiome composition and population growth was lower than the effect induced by mite population. In contrast, the diet perturbation showed a greater effect on nutritional status of mites than the mite population. The endosymbionts exhibited high variations among T. putrescentiae populations, including Cardinium in the laboratory population, Blattabacterium-like bacteria in the dog population, and Wolbachia in the dog and Phillips populations. Solitalea-like and Bartonella-like bacteria were present in the dog, Koppert, and Phillips populations in different proportions. The T. putrescentiae microbiome is dynamic and varies based on both the mite population and perturbation; however, the mites remain characterized by robust bacterial communities. Bacterial endosymbionts were found in all populations but represented a dominant portion of the microbiome in only some populations.IMPORTANCE We addressed the question of whether population origin or perturbation exerts a more significant influence on the bacterial community of the stored product mite Tyrophagus putrescentiae The microbiomes of four populations of T. putrescentiae insects subjected to diet perturbation were compared. Based on our results, the bacterial community was more affected by the mite population than by diet perturbation. This result can be interpreted as indicating high stability of the putative intracellular symbionts in response to dietary perturbation. The changes in the absolute and relative numbers of Wolbachia, Blattabacterium-like, Solitalea-like, and Cardinium bacteria in the T. putrescentiae populations can also be caused by neutral processes other than perturbation. When nutritional status is considered, the effect of population appeared less important than the perturbation. We hypothesize that differences in the proportions of the endosymbiotic bacteria result in changes in mite population growth.

Plantmediated horizontal transmission of Wolbachia between whiteflies

Maternal transmission is the main transmission pathway of facultative bacterial endosymbionts, but phylogenetically distant insect hosts harbor closely related endosymbionts, suggesting that horizontal transmission occurs in nature. Here we report the first case of plant-mediated horizontal transmission of Wolbachia between infected and uninfected Bemisia tabaci AsiaII7 whiteflies. After infected whiteflies fed on cotton leaves, Wolbachia was visualized, both in the phloem vessels and in some novel 'reservoir' spherules along the phloem by fluorescence in situ hybridization using Wolbachia-specific 16S rRNA probes and transmission electron microscopy. Wolbachia persisted in the plant leaves for at least 50 days. When the Wolbachia-free whiteflies fed on the infected plant leaves, the majority of them became infected with the symbiont and vertically transmitted it to their progeny. Multilocus sequence typing and sequencing of the wsp (Wolbachia surface protein) gene confirmed that the sequence type of Wolbachia in the donor whiteflies, cotton phloem and the recipient whiteflies are all identical (sequence type 388). These results were replicated using cowpea and cucumber plants, suggesting that horizontal transmission is also possible through other plant species. Our findings may help explain why Wolbachia bacteria are so abundant in arthropods, and suggest that in some species, Wolbachia may be maintained in populations by horizontal transmission.

Comparison of bacterial microbiota of the predatory mite Neoseiulus cucumeris (Acari: Phytoseiidae) and its factitious prey Tyrophagus putrescentiae (Acari: Acaridae)

Neoseiulus cucumeris is a predatory mite used for biological control of arthropod pests. Mass-reared predators are fed with factitious prey mites such as Tyrophagus putrescentiae. Although some information on certain endosymbionts of N. cucumeris and T. putrescentiae exists, it is unclear whether both species share bacterial communities. The bacterial communities in populations of predator and prey mites, as well as the occurence of potential acaropathogenic bacteria were analyzed. The comparisons were based on the following groups: (i) N. cucumeris mass-production; (ii) N. cucumeris laboratory population with disease symptoms; (iii) T. putrescentiae pure populations and; (iv) T. putrescentiae from rearing units of N. cucumeris. Only 15% of OTUs were present in all samples from predatory and prey mite populations (core OTUs): the intracellular symbionts Wolbachia, Cardinium, plus other Blattabacterium-like, Solitalea-like, and Bartonella-like symbionts. Environmental bacteria were more abundant in predatory mites, while symbiotic bacteria prevailed in prey mites. Relative numbers of certain bacterial taxa were significantly different between the microbiota of prey mites reared with and without N. cucumeris. No significant differences were found in the bacterial communities of healthy N. cucumeris compared to N. cucumeris showing disease symptoms. We did not identify any confirmed acaropathogenic bacteria among microbiota.

Wolbachia from Drosophila incompta: just a hitchhiker shared by Drosophila in the New and Old World?

Wolbachia are intracellular endosymbionts that infect arthropods and filarial nematodes, occasionally causing a wide variety of modifications in host biology, such as male-killing and cytoplasmic incompatibility (CI), amongst others. This study assembled draft genomes for Wolbachia infecting Drosophila incompta, a species that uses flowers as exclusive breeding and feeding sites, in two distinct Brazilian populations. The absence of four genes involved in CI from this genome, together with literature reports of low frequencies of infected flies in wild populations that contain high mitogenome polymorphism, suggests that this bacterium does not induce CI in D. incompta. Phylogenomic analysis placed Wolbachia infecting D. incompta as closely related to the wMel strain which received such name since it was originally detected in Drosophila melanogaster. In addition, phylogenetic analysis using the Wolbachia surface protein gene and five genes used for multilocus sequence typing of Wolbachia found infecting Drosophila and other arthropod species of Old and New World displayed a complex evolutionary scenario involving recent horizontal transfer bursts in all major clades of Wolbachia pipens belonging to the supergroup A in both geographical regions.

The rich somatic life of Wolbachia

Wolbachia is an intracellular endosymbiont infecting most arthropod and some filarial nematode species that is vertically transmitted through the maternal lineage. Due to this primary mechanism of transmission, most studies have focused on Wolbachia interactions with the host germline. However, over the last decade many studies have emerged highlighting the prominence of Wolbachia in somatic tissues, implicating somatic tissue tropism as an important aspect of the life history of this endosymbiont. Here, we review our current understanding of Wolbachia-host interactions at both the cellular and organismal level, with a focus on Wolbachia in somatic tissues.