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RNA interference (RNAi) is an extremely conserved defence mechanism. The antiviral role of the RNAi pathway in insects is well documented; however, the relevance of this pathway in other aspects of insect immunity is largely unknown. In this study, we questioned whether RNAi has any function during insect–bacteria interactions. For this, we assessed induction of the RNAi pathway in response to bacterial infections by monitoring the expression of dicer1/argonaute1 and dicer2/argonaute2, which are important genes in the microRNA and short interfering RNA sub‐pathways respectively. Bacterial cells of Bacillus thuringiensis and Serratia marcescens were injected into the haemocoel of fifth‐instar larvae of Helicoverpa armigera, whereas double‐distilled water was injected into control insects. Expression levels of the RNAi‐related genes increased in the bacteria‐injected larvae compared with controls. Transcript knockdown of dicer1 reduced the replication of B. thuringiensis; as a consequence, larval mortality decreased compared with the control. However, replication of S. marcescens increased following dicer1 silencing, which led to higher rates of larval mortality when compared with the control. RNAi of dicer2 promoted replication of both bacteria in the larvae and also enhanced larval mortality. Therefore, dicer1 and dicer2 affected larval survival and the replication rates of the pathogenic bacteria, suggesting their roles in the interactions. [ABSTRACT FROM AUTHOR]

Extensive use of chemical pesticides poses a great threat to the environment and food safety. The discovery of Bacillus thuringiensis (Bt) toxins with effective insecticidal activity against pests and the development of transgenic technology of plants opened a new era of pest control. Transgenic Bt crops, including maize, cotton and soya bean, have now been produced and commercialized to protect against about 30 major coleopteran and lepidopteran pests, greatly benefiting the environment and the economy. However, with the long-term cultivation of Bt crops, some target pests have gradually developed resistance. Numerous studies have indicated that mutations in genes for toxins activation, toxin-binding and insect immunization are important sources in Bt resistance. An in-depth exploration of the corresponding Bt-resistance mechanisms will aid in the design of new strategies to prevent and control pests. Future research will focus on Bt crops expressing new genes and multiple genes to control a broader range of pests as part of an integrated pest management programme. [ABSTRACT FROM AUTHOR]

Wolbachia bacteria inhabit the cells of about half of all arthropod species, an unparalleled success stemming in large part from selfish invasive strategies. Cytoplasmic incompatibility (CI), whereby the symbiont makes itself essential to embryo viability, is the most common of these and constitutes a promising weapon against vector-borne diseases. After decades of theoretical and experimental struggle, major recent advances have been made toward a molecular understanding of this phenomenon. As pieces of the puzzle come together, from yeast and Drosophila fly transgenesis to CI diversity patterns in natural mosquito populations, it becomes clearer than ever that the CI induction and rescue stem from a toxin–antidote (TA) system. Further, the tight association of the CI genes with prophages provides clues to the possible evolutionary origin of this phenomenon and the levels of selection at play. Highlights Wolbachia are maternally inherited intracellular bacteria of many Arthropod species. They can invade populations through various strategies including CI, whereby the symbionts protect eggs from the lethal effect of the sperm of infected males. It has long been proposed that this phenomenon may rely on a toxin deposited by the bacterium before its elimination from maturing sperm, and on an antidote that is provided in an infected egg by the maternal symbiont. Recent research toward the molecular basis of CI has turned the spotlight on two syntenic loci in a prophage region which recapitulate the CI phenotype and are organized in a typical TA fashion. This genetic architecture, that is archetypal of TA systems that promote the spread of selfish mobile elements in free-living bacteria, provides clues to the possible evolutionary origin of CI. [ABSTRACT FROM AUTHOR]

Ticks are exclusive blood-feeding parasites that are of medical and veterinary importance. Ticks are also host for several maternally inherited symbiotic bacteria that are non-pathogenic bacteria and have potential roles in tick biology and the transmission of co-infecting pathogens. In order to gain a comprehensive view of these symbionts in ticks, we overviewed their incidence and biological importance within ticks based on available data. The symbionts in ticks are diverse, and their incidence and frequency vary across different tick species and different geographical populations of the same species. In some cases, symbionts of Coxiella, Francisella and Rickettsia genera may provide tick hosts essential nutrients absent from the exclusive food source of ticks and exhibit mutualistic relationships with their hosts. However, most symbionts are facultative and affect the biological phenotypes of their tick hosts through various ways. For some strains of Coxiella and Francisella, advanced genomic data and phylogenetic investigations have revealed their interactions with hosts and their evolutionary transitions of pathogenic and mutualistic forms. These findings are valuable for understanding tick-symbiont associations, and may help to develop new strategies to control ticks and tick-borne diseases. [ABSTRACT FROM AUTHOR]

Microbial interactions are an underappreciated force in shaping insect microbiome communities. Although pairwise patterns of symbiont interactions have been identified, we have a poor understanding regarding the scale and the nature of co-occurrence and co-exclusion interactions within the microbiome. To characterize these patterns in mosquitoes, we sequenced the bacterial microbiome of Aedes aegypti , Ae. albopictus , and Culex quinquefasciatus caught in the field or reared in the laboratory and used these data to generate interaction networks. For collections, we used traps that attracted host-seeking or ovipositing female mosquitoes to determine how physiological state affects the microbiome under field conditions. Interestingly, we saw few differences in species richness or microbiome community structure in mosquitoes caught in either trap. Co-occurrence and co-exclusion analysis identified 116 pairwise interactions substantially increasing the list of bacterial interactions observed in mosquitoes. Networks generated from the microbiome of Ae. aegypti often included highly interconnected hub bacteria. There were several instances where co-occurring bacteria co-excluded a third taxa, suggesting the existence of tripartite relationships. Several associations were observed in multiple species or in field and laboratory-reared mosquitoes indicating these associations are robust and not influenced by environmental or host factors. To demonstrate that microbial interactions can influence colonization of the host, we administered symbionts to Ae. aegypti larvae that either possessed or lacked their resident microbiota. We found that the presence of resident microbiota can inhibit colonization of particular bacterial taxa. Our results highlight that microbial interactions in mosquitoes are complex and influence microbiome composition. [ABSTRACT FROM AUTHOR]

BACKGROUND: Steinernema carpocapsae is a nematocomplex widely used as an alternative to chemicals for the biological control of insect pests; this nematode is symbiotically associated with the bacterium Xenorhabdus nematophila and both contribute to host death. The architecture and functions of structures and molecular components of the surface of nematodes and their symbiont bacteria are integral to early interactions with their hosts; thus, we assessed the role of protein pools isolated from the surface of S. carpocapsae and from phase I X. nematophila against Galleria mellonella. RESULTS: Using high‐salt treatments, we isolated the surface proteins and assayed them on G. mellonella haemocytes; haemocyte viability and phagocytic activity were investigated in the presence of surface proteins from nematodes or bacteria. Proteins from live S. carpocapsae possessed mild cytotoxicity on the haemocytes, whereas those from live X. nematophila markedly affected the host cells' viability. Bacterial proteins inhibited phagocytic activity, although they strongly triggered the host proPO (prophenoloxidase‐phenoloxidase) system. CONCLUSION: Nematocomplex surface compounds play a key role in immunoevasion/depression of insect hosts, causing a severe physiological disorder. Natural compounds newly identified as active against pests could improve the pest management of species potentially harmful to plants in urban green spaces and agriculture. © 2018 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

In the past years, the fruit fly Drosophila melanogaster has been extensively used to study the relationship between animals and their associated microbes. Compared to the one of wild populations, the microbiota of laboratory-reared flies is less diverse, and comprises fewer bacterial taxa; nevertheless, the main commensal bacteria found in fly microbiota always belong to the Acetobacteraceae and Lactobacillaceae families. The bacterial communities associated with the fly are environmentally acquired, and the partners engage in a perpetual re-association process. Adult flies constantly ingest and excrete microbes from and onto their feeding substrate, which are then transmitted to the next generation developing within this shared habitat. We wanted to analyze the potential changes in the bacterial community during its reciprocal transfer between the two compartments of the niche (i.e. the fly and the diet). To address this question, we used a diverse, wild-derived microbial community and analyzed its relationship with the fly population and the nutritive substrate in a given habitat. Here we show that the community was overall well maintained upon transmission to a new niche, to a new fly population and to their progeny, illustrating the stable association of a Drosophila -derived microbiota with its fly partner and the nutritional environment. These results highlight the preponderant role of the nutritional substrate in the dynamics of Drosophila /microbiota interactions, and the need to fully integrate this variable when performing such studies. [ABSTRACT FROM AUTHOR]

Many insects host facultative, bacterial symbionts that confer conditional fitness benefits to their hosts. Hamiltonella defensa is a common facultative symbiont of aphids that provides protection against parasitoid wasps. Protection levels vary among strains of H. defensa that are also differentially infected by bacteriophages named APSEs. However, little is known about trait variation among strains because only one isolate has been fully sequenced. Generating complete genomes for facultative symbionts is hindered by relatively large genome sizes but low abundances in hosts like aphids that are very small. Here, we took advantage of methods for culturing H. defensa outside of aphids to generate complete genomes and transcriptome data for four strains of H. defensa from the pea aphid Acyrthosiphon pisum. Chosen strains also spanned the breadth of the H. defensa phylogeny and differed in strength of protection conferred against parasitoids. Results indicated that strains shared most genes with roles in nutrient acquisition, metabolism, and essential housekeeping functions. In contrast, the inventory of mobile genetic elements varied substantially, which generated strain specific differences in gene content and genome architecture. In some cases, specific traits correlated with differences in protection against parasitoids, but in others high variation between strains obscured identification of traits with likely roles in defense. Transcriptome data generated continuous distributions to genome assemblies with some genes that were highly expressed and others that were not. Single molecule real-time sequencing further identified differences in DNA methylation patterns and restriction modification systems that provide defense against phage infection. [ABSTRACT FROM AUTHOR]

The increasing resistance of human pathogens severely limits the efficacy of antibiotics in medicine, yet many animals, including solitary beewolf wasps, successfully engage in defensive alliances with antibiotic-producing bacteria for millions of years. Here, we report on the in situ production of 49 derivatives belonging to three antibiotic compound classes (45 piericidin derivatives, 3 streptochlorin derivatives, and nigericin) by the symbionts of 25 beewolf host species and subspecies, spanning 68 million years of evolution. Despite a high degree of qualitative stability in the antibiotic mixture, we found consistent quantitative differences between species and across geographic localities, presumably reflecting adaptations to combat local pathogen communities. Antimicrobial bioassays with the three main components and in silico predictions based on the structure and specificity in polyketide synthase domains of the piericidin biosynthesis gene cluster yield insights into the mechanistic basis and ecoevolutionary implications of producing a complex mixture of antimicrobial compounds in a natural setting. [ABSTRACT FROM AUTHOR]

Gut bacteria engage in various symbiotic interactions with their host and impact gut immunity and homeostasis in different ways. In honey bees, the gut microbiota is composed of a relatively simple, but highly specialized bacterial community. One of its members, the gammaproteobacterium Frischella perrara induces the so-called scab phenotype, a dark-coloured band that develops on the epithelial surface of the pylorus. To understand the underlying host response, we analysed transcriptome changes in the pylorus in response to bacterial colonization. We find that, in contrast to the gut bacterium Snodgrassella alvi, F. perrara causes strong activation of the host immune system. Besides pattern recognition receptors, antimicrobial peptides and transporter genes, the melanization cascade was upregulated by F. perrara, suggesting that the scab phenotype corresponds to a melanization response of the host. In addition, transcriptome analysis of hive bees with and without the scab phenotype showed that F. perrara also stimulates the immune system under in-hive conditions in the presence of other gut bacterial species. Collectively, our study demonstrates that the presence of F. perrara influences gut immunity and homeostasis in the pylorus. This may have implications for bee health, because F. perrara prevalence differs between colonies and increased abundance of this bacterium has been shown to correlate with dietary alteration and impaired host development. Our transcriptome analysis sets the groundwork for investigating the interplay of bee gut symbionts with the host immune system. [ABSTRACT FROM AUTHOR]

Biological invasions are a threat to global biodiversity and provide unique opportunities to study ecological processes. Population bottlenecks are a common feature of biological invasions and the severity of these bottlenecks is likely to be compounded as an invasive species spreads from initial invasion sites to additional locations. Despite extensive work on the genetic consequences of bottlenecks, we know little about how they influence microbial communities of the invaders themselves. Due to serial bottlenecks, invasive species may lose microbial symbionts including pathogenic taxa (the enemy release hypothesis) and/or may accumulate natural enemies with increasing time after invasion (the pathogen accumulation and invasive decline hypothesis). We tested these alternate hypotheses by surveying bacterial communities of Argentine ants ( Linepithema humile). We found evidence for serial symbiont bottlenecks: the bacterial community richness declined over the invasion pathway from Argentina to New Zealand. The abundance of some genera, such as Lactobacillus, also significantly declined over the invasion pathway. Argentine ants from populations in the United States shared the most genera with ants from their native range in Argentina, while New Zealand shared the least (120 vs. 57, respectively). Nine genera were present in all sites around the globe possibly indicating a core group of obligate microbes. In accordance with the pathogen accumulation and invasive decline hypothesis, Argentine ants acquired genera unique to each specific invaded country. The United States had the most unique genera, though even within New Zealand these ants acquired symbionts. In addition to our biogeographic sampling, we administered antibiotics to Argentine ants to determine if changes in the micro-symbiont community could influence behavior and survival in interspecific interactions. Treatment with the antibiotics spectinomycin and kanamycin only slightly increased Argentine ant interspecific aggression, but this increase significantly decreased survival in interspecific interactions. The survival of the native ant species also decreased when the symbiotic microbial community within Argentine ants was modified by antibiotics. Our work offers support for both the enemy release hypothesis and that invasive species accumulate novel microbial taxa within their invaded range. These changes appear likely to influence invader behavior and survival. [ABSTRACT FROM AUTHOR]

Xenorhabdus is a bacterial symbiont of entomopathogenic Steinernema nematodes and is pathogenic for insects. Its life cycle involves a stage inside the insect cadaver, in which it competes for environmental resources with microorganisms from soil and the insect gut. Xenorhabdus is, thus, a useful model for identifying new interbacterial competition systems. For the first time, in an entomopathogenic bacterium, Xenorhabdus doucetiae strain FRM16, we identified a cdi-like locus. The cdi loci encode contact-dependent inhibition (CDI) systems composed of proteins from the two–partner secretion (TPS) family. CdiB is the outer membrane protein and CdiA is the toxic exoprotein. An immunity protein, CdiI, protects bacteria against inhibition. We describe here the growth inhibition effect of the toxic C-terminus of CdiA from X. doucetiae FRM16, CdiA-CTFRM16, following its production in closely and distantly related enterobacterial species. CdiA-CTFRM16 displayed Mg2+-dependent DNase activity, in vitro. CdiA-CTFRM16-mediated growth inhibition was specifically neutralized by CdiIFRM16. Moreover, the cdi FRM16 locus encodes an ortholog of toxin-activating proteins C that we named CdiCFRM16. In addition to E. coli, the cdiBCAI-type locus was found to be widespread in environmental bacteria interacting with insects, plants, rhizospheres and soils. Phylogenetic tree comparisons for CdiB, CdiA and CdiC suggested that the genes encoding these proteins had co-evolved. By contrast, the considerable variability of CdiI protein sequences suggests that the cdiI gene is an independent evolutionary unit. These findings further characterize the sparsely described cdiBCAI-type locus. [ABSTRACT FROM AUTHOR]

Eukaryotes commonly host communities of heritable symbiotic bacteria, many of which are not essential for their hosts' survival and reproduction. There is laboratory evidence that these facultative symbionts can provide useful adaptations, such as increased resistance to natural enemies. However, we do not know how symbionts affect host fitness when the latter are subject to attack by a natural suite of parasites and pathogens. Here, we test whether two protective symbionts, Regiella insecticola and Hamiltonella defensa, increase the fitness of their host, the pea aphid (Acyrthosiphon pisum), under natural conditions. We placed experimental populations of two pea aphid lines, each with and without symbionts, in five wet meadow sites to expose them to a natural assembly of enemy species. The aphids were then retrieved and mortality from parasitoids, fungal pathogens and other causes assessed. We found that both Regiella and Hamiltonella reduce the proportion of aphids killed by the specific natural enemies against which they have been shown to protect in laboratory and cage experiments. However, this advantage was nullified (Hamiltonella) or reversed (Regiella) by an increase in mortality from other natural enemies and by the cost of carrying the symbiont. Symbionts therefore affect community structure by altering the relative success of different natural enemies. Our results show that protective symbionts are not necessarily advantageous to their hosts, and may even behave more like parasites than mutualists. Nevertheless, bacterial symbionts may play an important role in determining food web structure and dynamics. [ABSTRACT FROM AUTHOR]

Colonisation times and development rates of specific blow fly species are used to estimate the minimum Post Mortem Interval (mPMI). The presence or absence of bacteria on a corpse can potentially affect the development and survival of blow fly larvae. Therefore an understanding of microbial-insect interactions is important for improving the interpretation of mPMI estimations. In this study, the effect of two bacteria (Escherichia coli and Staphylococcus aureus) on the growth rate and survival of three forensically important blow fly species (Lucilia sericata, Calliphora vicina and Calliphora vomitoria) was investigated. Sterile larvae were raised in a controlled environment (16:8h day: night light cycle, 23:21°C day: night temperature cycle and a constant 35% relative humidity) on four artificial diets prepared with 100μl of 10(5) CFU bacterial solutions as follows: (1) E. coli, (2) S. aureus, (3) a 50:50 E. coli:S. aureus mix and (4) a sterile bacteria-free control diet. Daily measurements (length, width and weight) were taken from first instar larvae through to the emergence of adult flies. Survival rates were also determined at pupation and adult emergence. Results indicate that bacteria were not essential for the development of any of the blow fly species. However, larval growth rates were affected by bacterial diet, with effects differing between blow fly species. Peak larval weights also varied according to species-diet combination; C. vomitoria had the largest weight on E. coli and mixed diets, C. vicina had the largest weight on S. aureus diets, and treatment had no significant effect on the peak larval weight of L. sericata. These results indicate the potential for the bacteria that larvae are exposed to during development on a corpse to alter both developmental rates and larval weight in some blow fly species. [ABSTRACT FROM AUTHOR]

It has become increasingly clear that microbes form close associations with the vast majority of animal species, especially insects. In fact, an array of diverse microbes is known to form shared metabolic pathways with their insect hosts. A growing area of research in insect-microbe interactions, notably for hemipteran insects and their mutualistic symbionts, is to elucidate the regulation of this inter-domain metabolism. This review examines two new emerging mechanisms of gene regulation and their importance in host-microbe interactions. Specifically, we highlight how the incipient areas of research on regulatory "dark matter" such as epigenomics and small RNAs, can play a pivotal role in the evolution of both insect and microbe gene regulation. We then propose specific models of how these dynamic forms of gene regulation can influence insect-symbiont-plant interactions. Future studies in this area of research will give us a systematic understanding of how these symbiotic microbes and animals reciprocally respond to and regulate their shared metabolic processes. [ABSTRACT FROM AUTHOR]

1. Many insects host secondary bacterial symbionts that are known to have wide-ranging effects on their hosts, from host-plant use to resistance against natural enemies. This has been most widely studied in aphids, which have become a model system to study insect--bacteria interactions. 2. While there is an increasing understanding of the role of symbionts in aphids from controlled laboratory studies, we are only beginning to explore the impact of hosting these symbionts on eco-evolutionary dynamics in natural systems. To date, many research groups have identified bacterial symbionts from various aphid species, providing us with a bank of literature on aphid--symbiont associations in natural populations. 3. The role of secondary symbionts in aphids is discussed, and the taxonomic and geographical distribution of symbionts among aphids are summarised, and the potential reasons for the patterns observed. The need to test for multiple symbiont species (and co-infections) across many individuals and the whole distribution range of an aphid is highlighted, including sampling on all known host-plant species. 4. It is further important also to consider variation within the symbiont, the aphid-host and the surrounding community, e.g. host-plants or the natural enemies, to understand how these have the potential to mediate aphid--symbiont interactions. 5. Finally, the knowledge gained from experimental work should now be used to understand the role of aphid secondary symbionts in field systems, to fully understand the potentially far-reaching consequences of aphid endosymbionts on community and ecosystem processes. [ABSTRACT FROM AUTHOR]

Bacterial endosymbionts that associate facultatively with insect herbivores can influence insect fitness and trophic interactions. The pea aphid, Acyrthosiphon pisum, can be protected from parasitism by the braconid wasp Aphidius ervi when harbouring particular symbiotic bacteria, with specific endosymbiont coinfections providing almost complete protection. However, studies often quantify aphid mummification with no control over parasitoid oviposition per aphid; thus, if mummy production fails or is low, the causes are often unclear. Here, we show that the high level of protection associated with the coinfecting endosymbionts Hamiltonella defensa and X-type is maintained even when pea aphids are superparasitised. This contrasts strongly with the protection provided by H. defensa alone, which has been shown by others to be overcome by superparasitism. By dissecting aphids exposed to two parasitoid attacks, we reveal that A. ervi deposits eggs equally freely in endosymbiont-infected and uninfected nymphs, and lack of mummification in endosymbiont-protected nymphs arises from failure of the wasp eggs to hatch or emerging larvae to develop. [ABSTRACT FROM AUTHOR]

Fungus-growing termites (subfamily Macrotermitinae) mix plant forage with asexual spores of their plant-degrading fungal symbiont Termitomyces in their guts and deposit this blend in fungus comb structures, within which the plant matter is degraded. As Termitomyces grows, it produces nodules with asexual spores, which the termites feed on. Since all comb material passes through termite guts, it is inevitable that gut bacteria are also deposited in the comb, but it has remained unknown which bacteria are deposited and whether distinct comb bacterial communities are sustained. Using high-throughput sequencing of the 16S rRNA gene, we explored the bacterial community compositions of 33 fungus comb samples from four termite species (three genera) collected at four South African geographic locations in 2011 and 2013. We identified 33 bacterial phyla, with Firmicutes, Bacteroidetes, Proteobacteria, Actinobacteria, and Candidate division TM7 jointly accounting for 92 % of the reads. Analyses of gut microbiotas from 25 of the 33 colonies showed that dominant fungus comb taxa originate from the termite gut. While gut communities were consistent between 2011 and 2013, comb community compositions shifted over time. These shifts did not appear to be due to changes in the taxa present, but rather due to differences in the relative abundances of primarily gut-derived bacteria within fungus combs. This indicates that fungus comb microbiotas are largely termite species-specific due to major contributions from gut deposits and also that environment affects which gut bacteria dominate comb communities at a given point in time. [ABSTRACT FROM AUTHOR]

Bacteria associated with varroa mites were cultivated and genotyped by 16S RNA. Under our experimental conditions, the cultivable bacteria were few in number, and most of them proved to be fastidious to grow. Cultivation with seven different media under O2/ CO2 conditions and selection for colony morphology yielded a panel of species belonging to 13 different genera grouped in two different phyla, proteobacteria and actinobacteria. This study identified one species of actinobacteria that is a known commensal of the honey bee. Some isolates are oxalotrophic, a finding that may carry ramifications into the use of oxalic acid to control the number of phoretic mites in the managed colonies of honey bees. Significance and Impact of the Study Oxalic acid, legally or brevi manu, is widely used to control phoretic Varroa destructor mites, a major drive of current honey bees' colony losses. Unsubstantiated by sanctioned research are rumours that in certain instances oxalic acid is losing efficacy, forcing beekeepers to increase the frequency of treatments. This investigation fathoms the hypothesis that V. destructor associates with bacteria capable of degrading oxalic acid. The data show that indeed oxalotrophy, a rare trait among bacteria, is common in bacteria that we isolated from V. destructor mites. This finding may have ramifications in the use of oxalic acid as a control agent. [ABSTRACT FROM AUTHOR]

Wolbachia are intracellular bacteria that infect a vast range of arthropod species, making them one of the most prevalent endosymbionts in the world. Wolbachia's stunning evolutionary success is mostly due to their reproductive parasitism but also to mutualistic effects such as increased host fecundity or protection against pathogens. However, the mechanisms underlying Wolbachia phenotypes, both parasitic and mutualistic, are only poorly understood. Moreover, it is unclear how the insect immune system is involved in these phenotypes and why it is not more successful in eliminating the bacteria. Here we argue that reactive oxygen species (ROS) are likely to be key in elucidating these issues. ROS are essential players in the insect immune system, and Wolbachia infection can affect ROS levels in the host. Based on recent findings, we elaborate a hypothesis that considers the different effects of Wolbachia on the oxidative environment in novel vs. native hosts. We propose that newly introduced Wolbachia trigger an immune response and cause oxidative stress, whereas in coevolved symbioses, infection is not associated with oxidative stress, but rather with restored redox homeostasis. Redox homeostasis can be restored in different ways, depending on whether Wolbachia or the host is in charge. This hypothesis offers a mechanistic explanation for several of the observed Wolbachia phenotypes. [ABSTRACT FROM AUTHOR]

Summary Gamete compatibility is fundamental to sexual reproduction. Wolbachia are maternally inherited endosymbiotic bacteria that manipulate gamete compatibility in many arthropod species. In Drosophila , the fertilization of uninfected eggs by sperm from Wolbachia -infected males often results in early developmental arrest. This gamete incompatibility is called cytoplasmic incompatibility (CI). CI is highest in young males, suggesting that Wolbachia affect sperm properties during male development. Here, we show that Wolbachia modulate testis development. Unexpectedly, this effect was associated with Wolbachia infection in females, not males. This raised the possibility that females influenced testis development by communicating with males prior to adulthood. Using a combinatorial rearing protocol, we provide evidence for such a female-to-male communication during metamorphosis. This communication involves the perception of female pheromones by male olfactory receptors. We found that this communication determines the compatibility range of sperm. Wolbachia interfere with this female-to-male communication through changes in female pheromone production. Strikingly, restoring this communication partially suppressed CI in Wolbachia -infected males. We further identified a reciprocal male-to-female communication at metamorphosis that restricts the compatibility range of female gametes. Wolbachia also perturb this communication by feminizing male pheromone production. Thus, Wolbachia broaden the compatibility range of eggs, promoting thereby the reproductive success of Wolbachia -infected females. We conclude that pheromone communication between pupae regulates gamete compatibility and is sensitive to Wolbachia in Drosophila . [ABSTRACT FROM AUTHOR]

The guts of beetle larvae constitute a complex system where relationships among fungi, bacteria, and the insect host occur. In this study, we collected larvae of five families of wood-feeding Coleoptera in tropical forests of Costa Rica, isolated fungi and bacteria from their intestinal tracts, and determined the presence of five different pathways for lignocellulolytic activity. The fungal isolates were assigned to three phyla, 16 orders, 24 families, and 40 genera; Trichoderma was the most abundant genus, detected in all insect families and at all sites. The bacterial isolates were assigned to five phyla, 13 orders, 22 families, and 35 genera; Bacillus, Serratia, and Pseudomonas were the dominant genera, present in all the Coleopteran families. Positive results for activities related to degradation of wood components were determined in 65% and 48% of the fungal and bacterial genera, respectively. Our results showed that both the fungal and bacterial populations were highly diverse in terms of number of species and their phylogenetic composition, although the structure of the microbial communities varied with insect host family and the surrounding environment. The recurrent identification of some lignocellulolytic-positive inhabitants suggests that particular microbial groups play important roles in providing nutritional needs for the Coleopteran host. [ABSTRACT FROM AUTHOR]

Nitric oxide (NO) produced by the nitric oxide synthase (NOS) enzyme is a reactive oxygen molecule widely considered as important participant in the immune system of different organisms to confront microbial infections. In insects the NO molecule has also been implicated in immune response against microbial pathogens. Bacillus thuringiensis (Bt) is an insect-pathogenic bacterium that produces insecticidal proteins such as Cry toxins. These proteins kill insects because they form pores in the larval-midgut cells. Here we show that intoxication of Manduca sexta larvae with Cry1Ab activates expression of NOS with a corresponding increase in NO. This effect is not observed with a non-toxic mutant toxin Cry1Ab-E129K that is affected in pore formation. The increased production of NO triggered by intoxication with LC 50 dose of Cry1Ab toxin is not associated with higher expression of antimicrobial peptides. NO participates in Cry1Ab toxicity since inhibition of NOS by selective l -NAME inhibitor prevented NO production and resulted in reduced mortality of the larvae. The fact that mortality was not completely abolished by L-NAME indicates that other processes participate in toxin action and induction of NO production upon Cry1Ab toxin administration accounts only for a part of the toxicity of this protein to M. sexta larvae. [ABSTRACT FROM AUTHOR]

The endemic New Zealand weta is an enigmatic insect. Although the insect is well known by its distinctive name, considerable size, and morphology, many basic aspects of weta biology remain unknown. Here, we employed cultivation-independent enumeration techniques and rRNA gene sequencing to investigate the gut microbiota of the Auckland tree weta ( Hemideina thoracica). Fluorescence in situ hybridisation performed on different sections of the gut revealed a bacterial community of fluctuating density, while rRNA gene-targeted amplicon pyrosequencing revealed the presence of a microbial community containing high bacterial diversity, but an apparent absence of archaea. Bacteria were further studied using full-length 16S rRNA gene sequences, with statistical testing of bacterial community membership against publicly available termite- and cockroach-derived sequences, revealing that the weta gut microbiota is similar to that of cockroaches. These data represent the first analysis of the weta microbiota and provide initial insights into the potential function of these microorganisms. [ABSTRACT FROM AUTHOR]

The microbiome can significantly impact host phenotypes and serve as an additional source of heritable genetic variation. While patterns across eukaryotes are consistent with a role for symbiotic microbes in host macroevolution, few studies have examined symbiont-driven host evolution or the ecological implications of a dynamic microbiome across temporal, spatial or ecological scales. The pea aphid, Acyrthosiphon pisum, and its eight heritable bacterial endosymbionts have served as a model for studies on symbiosis and its potential contributions to host ecology and evolution. But we know little about the natural dynamics or ecological impacts of the heritable microbiome of this cosmopolitan insect pest. Here we report seasonal shifts in the frequencies of heritable defensive bacteria from natural pea aphid populations across two host races and geographic regions. Microbiome dynamics were consistent with symbiont responses to host-level selection and findings from one population suggested symbiont-driven adaptation to seasonally changing parasitoid pressures. Conversely, symbiont levels were negatively correlated with enemy-driven mortality when measured across host races, suggesting important ecological impacts of host race microbiome divergence. Rapid drops in symbiont frequencies following seasonal peaks suggest microbiome instability in several populations, with potentially large costs of 'superinfection' under certain environmental conditions. In summary, the realization of several laboratory-derived, a priori expectations suggests important natural impacts of defensive symbionts in host-enemy eco-evolutionary feedbacks. Yet negative findings and unanticipated correlations suggest complexities within this system may limit or obscure symbiont-driven contemporary evolution, a finding of broad significance given the widespread nature of defensive microbes across plants and animals. [ABSTRACT FROM AUTHOR]

While a number of studies have identified host factors that influence endosymbiont titer, little is known concerning environmental influences on titer. Here we examined nutrient impact on maternally transmitted Wolbachia endosymbionts in Drosophila. We demonstrate that Drosophila reared on sucrose- and yeast-enriched diets exhibit increased and reduced Wolbachia titers in oogenesis, respectively. The yeast-induced Wolbachia depletion is mediated in large part by the somatic TOR and insulin signaling pathways. Disrupting TORC1 with the small molecule rapamycin dramatically increases oocyte Wolbachia titer, whereas hyper-activating somatic TORC1 suppresses oocyte titer. Furthermore, genetic ablation of insulin-producing cells located in the Drosophila brain abolished the yeast impact on oocyte titer. Exposure to yeast-enriched diets altered Wolbachia nucleoid morphology in oogenesis. Furthermore, dietary yeast increased somatic Wolbachia titer overall, though not in the central nervous system. These findings highlight the interactions between Wolbachia and germline cells as strongly nutrient-sensitive, and implicate conserved host signaling pathways by which nutrients influence Wolbachia titer. [ABSTRACT FROM AUTHOR]

Mealybugs are sap-feeding insect pests that pose a serious threat to horticulture. The citrus mealybug, Planococcus citri (Risso) (Hemiptera: Pseudococcidae), like most other mealybug species, harbours two obligate maternally transmitted bacterial endosymbionts, which are essential for nutrient acquisition and host survival. These are 'Candidatus Tremblaya princeps', a member of the β-Proteobacteria, and 'Candidatus Moranella endobia', a member of the γ-Proteobacteria. The density of symbionts in the hosts is now understood to be dynamic, being influenced by the age and gender of the host and by environmental conditions during development. Here, we examine the impact of short-term heat stress treatment on the obligate symbionts and life-history parameters of P. citri, using qPCR to measure changes in symbiont density. Heat stress killed juveniles and adult males, and significantly reduced levels of 'Ca. Moranella endobia' and 'Ca. Tremblaya princeps' in adult females. However, adult females were resilient to this and it did not affect their fecundity or brood survival, although the sex ratio of their brood was slightly, but significantly, more female biased. Our results suggest that 'Ca. Tremblaya princeps' and 'Ca. Moranella endobia' are not as essential to the survival of adult mealybugs as they are to the survival of immature mealybugs and that sub-lethal heat treatment alone is unlikely to be effective as a disinfestation tactic. [ABSTRACT FROM AUTHOR]

Insects are associated with a diversity of bacteria that colonize their midguts. The extent to which these communities reflect maternal transmission, environmental acquisition, and subsequent structuring by the extreme conditions within the insect gut are poorly understood in many species. We used gypsy moth ( Lymantria dispar L.) as a model to investigate interactions between egg mass and environmental sources of bacteria on larval midgut communities. Egg masses were collected from several wild and laboratory populations, and the effects of diet, initial egg mass community, and internal host environment were evaluated using 454 16S-rRNA gene pyrosequencing. Wild populations were highly diverse, while laboratory-maintained egg masses were associated with few operational taxonomic units. As larvae developed, their midgut bacterial communities became more similar to each other and the consumed diet despite initial differences in egg mass-associated bacteria. Subsequent experiments revealed that while midgut membership was more similar to bacteria associated with diet than with egg mass-associated bacteria, we were unable to detect distinct, persistent differences attributable to specific host plants. The differences between foliar communities and midgut communities of larvae that ingested them were owing to relative changes in populations of several bacteria phylotypes. We conclude that gypsy moth has a relatively characteristic midgut bacterial community that is reflective of, but ultimately distinct from, its foliar diet. This work demonstrates that environmental acquisition of diverse microbes can lead to similar midgut bacterial assemblages, underscoring the importance of host physiological environment in structuring bacterial communities. [ABSTRACT FROM AUTHOR]

The entomopathogen Bacillus thuringiensis is used to control various pest species of scarab beetle but is not particularly effective. Gut bacteria have diverse ecological and evolutionary effects on their hosts, but whether gut bacteria can protect scarabs from B. thuringiensis infection remains poorly understood. To investigate this, we isolated 32 cultivable gut bacteria from Holotrichia oblita Faldermann, Holotrichia parallela Motschulsky, and Anomala corpulenta Motschulsky, and analyzed their effect on B. thuringiensis multiplication and Cry toxin stability. 16S rDNA analysis indicated that these gut bacteria belong to the Proteobacteria, Actinobacteria, Firmicutes, and Bacteroidetes phyla. A confrontation culture analyses of the 32 isolates against three scarab-specific B. thuringiensis strains showed that the majority of the scarab gut bacteria had antibacterial activity against the B. thuringiensis strains. The Cry toxin stability analysis results showed that while several strains produced proteases capable of processing the scarab-specific toxin Cry8Ea, none were able to completely degrade it. These results suggest that gut bacteria can potentially affect the susceptibility of scarabs to B. thuringiensis and that this should be considered when considering future control measures. [ABSTRACT FROM AUTHOR]

Aphids are a group of insects frequently associated with bacterial symbionts. Although Chinese aphids harbor a high level of species diversity, the associations between Chinese aphids and bacterial symbionts are less known. In this study, we uncovered the diversity of bacterial symbionts in a Chinese widespread aphid, Sitobion miscanthi (Takahashi). In this study, we detected the aphid obligate symbiont Buchnera aphidicola, and two secondary symbionts, Hamiltonella defensa and Regiella insecticola, with the diagnostic polymerase chain reaction method in S. miscanthi samples. In addition, symbiotic species of Acinetobacter, Aeromonas, Enterobacter, Pantoea, and Pseudomonas, and the family Enterobacteriaceae were also found. Geographically, sporadic occurrences were detected for H. defensa and R. insecticola. Moreover, the infection rates of them vary widely among the infected populations: H. defensa (5.26-95.2%) and R. insecticola (5.26-46.7%). Phylogenetic analyses indicated that the strain of B. aphidicola mirrored the history and divergence of S. miscanthi; however, the H. defensa and R. insecticola strains were probably experienced horizontal transmission among S. miscanthi and its distantly related species. [ABSTRACT FROM AUTHOR]

A recent invader of North America, the brown marmorated stink bug ( Halyomorpha halys Stål) is a polyphagous pentatomid that harbors a gammaproteobacterial mutualist in the crypts of specialized midgut gastric caeca (region V4). Histological analyses revealed a single rod-shaped morphology abundant in distal V4 midgut caecal crypts. A strong fluorescence signal was detected when thin sections of these tissues were hybridized with a fluorescently-labeled, Enterobacteriaceae-specific oligonucleotide probe. A single operational taxonomic unit (OTU) assigned to the Pantoea genus represented >99% of 3,454 16S rDNA amplicons obtained from midgut V4 tissues and egg samples. Detection of H. halys primary symbiont in DNA extracted from eggs suggested vertical maternal inheritance as the mode of intergenerational transmission. Consistent detection of the bacterial symbiont in geographically distinct H. halys populations strongly supports an intimate association between these two organisms. An inferred phylogeny of gammaproteobacterial symbionts of pentatomids placed the Pantoea-assigned OTU from H. halys within a clade distinct from primary bacterial symbionts of related stink bugs, Nezara viridula (L.) and Eurydema rugosa Motschulsky. Given these data, Candidatus 'Pantoea carbekii' is proposed as the name of the primary bacterial symbiont of H. halys. [ABSTRACT FROM AUTHOR]

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The γ-proteobacterium Arsenophonus and its close relatives ( Arsenophonus and like organisms, ALOs) are emerging as a novel clade of endosymbionts, which are exceptionally widespread in insects. The biology of ALOs is, however, in most cases entirely unknown, and it is unclear how these endosymbionts spread across insect populations. Here, we investigate this aspect through the examination of the presence, the diversity and the evolutionary history of ALOs in 25 related species of blood-feeding flies: tsetse flies (Glossinidae), louse flies (Hippoboscidae) and bat flies (Nycteribiidae and Streblidae). While these endosymbionts were not found in tsetse flies, we identify louse flies and bat flies as harbouring the highest diversity of ALO strains reported to date, including a novel ALO clade, as well as Arsenophonus and the recently described Candidatus Aschnera chinzeii. We further show that the origin of ALO endosymbioses extends deep into the evolutionary past of louse flies and bat flies, and that it probably played a major role in the ecological specialization of their hosts. The evolutionary history of ALOs is notably complex and was shaped by both vertical transmission and horizontal transfers with frequent host turnover and apparent symbiont replacement in host lineages. In particular, ALOs have evolved repeatedly and independently close relationships with diverse groups of louse flies and bat flies, as well as phylogenetically more distant insect families, suggesting that ALO endosymbioses are exceptionally dynamic systems. [ABSTRACT FROM AUTHOR]

Invasive species often depend on microbial symbionts, but few studies have examined the evolutionary dynamics of symbionts during the early stages of an invasion. The insect Megacopta cribraria and its bacterial nutritional symbiont Candidatus Ishikawaella capsulata invaded the southeastern US in 2009. While M. cribraria was initially discovered on wild kudzu plants, it was found as a pest on soybeans within 1 year of infestation. Because prior research suggests Ishikawaella confers the pest status-that is, the ability to thrive on soybeans-in some Megacopta species, we performed a genomic study on Ishikawaella from US. Megacopta cribraria populations to understand the role of the symbiont in driving host plant preferences. We included Ishikawaella samples collected in the first days of the invasion in 2009 and from 23 locations across the insect's 2011 US range. The 0.75 Mb symbiont genome revealed only 47 fixed differences from the pest-conferring Ishikawaella in Japan, with only one amino acid change in a nutrition-provisioning gene. This similarity, along with a lack of fixed substitutions in the US symbiont population, indicates that Ishikawella likely arrived in the US capable of being a soybean pest. Analyses of allele frequency changes between 2009 and 2011 uncover signatures of both positive and negative selection and suggest that symbionts on soybeans and kudzu experience differential selection for genes related to nutrient provisioning. Our data reveal the evolutionary trajectory of an important insect-bacteria symbiosis in the early stages of an invasion, highlighting the role microbial symbionts may play in the spread of invasive species. [ABSTRACT FROM AUTHOR]

Symbiotic microbes have become increasingly recognized to mediate interactions between natural enemies and their hosts. The ecologies of these symbioses, however, are poorly understood in many systems, and a predictive framework is needed to guide future studies. To achieve this, we focus on heritable, defensive microbes of insects. Our review of laboratory-based studies identifies diverse bacterial species that have independently evolved to protect a range of insects against parasitoids, parasites, predators and pathogens. Although defensive mechanisms are typically unknown, some involve toxins or the upregulation of host immunity., Despite substantial benefits of infection in the presence of natural enemies, the protective symbionts of insects are often found at intermediate levels in natural populations. Using a host-centred population genetics approach made possible by the host restriction and cytoplasmic inheritance of these microbes, we propose that balancing selection plays a major role in symbiont maintenance, with protective benefits in the presence of enemies and infection costs in their absence. Other mediating factors are likely to be important, including temperature, superinfections and transmission dynamics., While few studies have provided evidence for defence in the field, several studies have shown symbiont infection frequencies to be dynamic, varying across temporal and spatial gradients and food-plant associations. Newly presented data from our pea aphid research reveal that temporal shifts in defensive symbiont prevalence can be quite rapid, with Hamiltonella defensa showing 10-20% shifts around a seasonal average of c. 50%. Such findings contrast with more unidirectional changes seen in laboratory population cages, suggesting temporal changes in the costs and benefits of symbionts in the field., To frame future research on defensive symbiont ecology, we briefly consider a range of studies needed to test laboratory- and field-derived predictions on defensive symbiosis. Included are investigations of defensive mechanisms, symbiont-driven co-evolution and community-level effects. We also consider the need for more thorough and highly resolved molecular diagnostics of natural infections, laboratory studies on functional differences between symbiont strains and species and studies on the relative costs and benefits of defenders in nature., The emerging theme of symbiont-mediated defence across eukaryotes suggests that knowledge of the functional mechanisms behind protection and natural symbiont dynamics could be key to understanding many of the world's antagonistic species interactions. Thus, the development of insects as a model for such studies holds promise for these organisms and beyond. [ABSTRACT FROM AUTHOR]

The bacterial endosymbiont Wolbachia manipulates arthropod host biology in numerous ways, including sex ratio distortion and differential offspring survival. These bacteria infect a vast array of arthropods, some of which pose serious agricultural and human health threats. Wolbachia-mediated phenotypes such as cytoplasmic incompatibility and/or pathogen interference can be used for vector and disease control; however, many medically important vectors and important agricultural species are uninfected or are infected with strains of Wolbachia that do not elicit phenotypes desirable for disease or pest control. The ability to transfer strains of Wolbachia into new hosts (transinfection) can create novel Wolbachia-host associations. Transinfection has two primary benefits. First, Wolbachia-host interactions can be examined to tease apart the influence of the host and bacteria on phenotypes. Second, desirable phenotypes induced by Wolbachia in a particular insect can be transferred to another recipient host. This can allow the manipulation of insect populations that transmit pathogens or detrimentally affect agriculture. As such, transinfection is a valuable tool to explore Wolbachia biology and control arthropod-borne disease. The present review summarizes what is currently known about Wolbachia transinfection methods and applications. We also provide a comprehensive list of published successful and unsuccessful Wolbachia transinfection attempts. [ABSTRACT FROM AUTHOR]

Many hemipterans are associated with symbiotic bacteria, which are usually found intracellularly in specific bacteriomes. In this study, we provide the first molecular identification of the bacteriome-associated, obligate endosymbiont in a Gondwanan relict insect taxon, the moss bugs ( Hemiptera: Coleorrhyncha: Peloridiidae), which represents one of the oldest lineages within the Hemiptera. Endosymbiotic associations of fifteen species of the family were analysed, covering representatives from South America, Australia/ Tasmania and New Zealand. Phylogenetic analysis based on four kilobases of 16 S-23 S r RNA gene fragments showed that the obligate endosymbiont of Peloridiidae constitute a so far unknown group of Gammaproteobacteria which is named here ' Candidatus Evansia muelleri'. They are related to the sternorrhynchous endosymbionts Candidatus Portiera and Candidatus Carsonella. Comparison of the primary-endosymbiont and host ( COI + 28 S rRNA) trees showed overall congruence indicating co-speciation the hosts and their symbionts. The distribution of the endosymbiont within the insect body and its transmission was studied using FISH. The endosymbionts were detected endocellularly in a pair of bacteriomes as well as in the 'symbiont ball' of the posterior pole of each developing oocyte. Furthermore, ultrastructural analysis of the Malpighian tubules revealed that most host nuclei are infected by an endosymbiotic, intranuclear bacterium that was determined as an Alphaproteobacterium of the genus Rickettsia. [ABSTRACT FROM AUTHOR]

While there is increasing concern that pesticide stress can interact with stress imposed by antagonistic species including pathogens, it is unknown whether this also holds for non-pathogenic bacteria. We exposed Enallagma cyathigerum damselfly larvae to the pesticide chlorpyrifos and a non-pathogenic Escherichia coli strain. Both exposure to chlorpyrifos and E. coli reduced growth rate and fat storage, probably due to the observed energetically costly increases in physiological defence (glutathione-S-transferase and Hsp70) and, for E. coli, immune defence (phenoloxidase). Moreover, these stressors interacted for both fitness-related traits. Most importantly, another fitness-related trait, bacterial load, increased drastically with chlorpyrifos concentration. A possible explanation is that the upregulation of phenoloxidase in the presence of E. coli changed into a downregulation when combined with chlorpyrifos. We argue that the observed interactive, partly synergistic effects between pesticides and widespread non-pathogenic bacteria may be common and deserves further attention to improve ecological risk assessment of pesticides. [Copyright &y& Elsevier]

Wolbachia is a maternally transmitted symbiotic bacterium of insects that has been proposed as a potential agent for the control of insect-transmitted diseases. One of the major limitations preventing the development of Wolbachia for malaria control has been the inability to establish inherited infections of Wolbachia in anopheline mosquitoes. Here, we report the establishment of a stable Wolbachia infection in an important malaria vector, Anopheles stephensi. In A. stephensi, Wolbachia strain wAlbB displays both perfect maternal transmission and the ability to induce high levels of cytoplasmic incompatibility. Seeding of naturally uninfected A. stephensi populations with infected females repeatedly resulted in Wolbachia invasion of laboratory mosquito populations. Furthermore, wAlbB conferred resistance in the mosquito to the human malaria parasite Plasmodium falciparum. [ABSTRACT FROM AUTHOR]

The bean bug Riptortus pedestris possesses a specialized symbiotic organ in a posterior region of the midgut, where numerous crypts harbor extracellular betaproteobacterial symbionts of the genus Burkholderia. Second instar nymphs orally acquire the symbiont from the environment, and the symbiont infection benefits the host by facilitating growth and by occasionally conferring insecticide resistance. Here we performed comparative transcriptomic analyses of insect genes expressed in symbiotic and non-symbiotic regions of the midgut dissected from Burkholderia-infected and uninfected R. pedestris. Expression sequence tag analysis of cDNA libraries and quantitative reverse transcription PCR identified a number of insect genes expressed in symbiosis- or aposymbiosis-associated patterns. For example, genes up-regulated in symbiotic relative to aposymbiotic individuals, including many cysteine-rich secreted protein genes and many cathepsin protease genes, are likely to play a role in regulating the symbiosis. Conversely, genes up-regulated in aposymbiotic relative to symbiotic individuals, including a chicken-type lysozyme gene and a defensin-like protein gene, are possibly involved in regulation of non-symbiotic bacterial infections. Our study presents the first transcriptomic data on gut symbiotic organ of a stinkbug, which provides initial clues to understanding of molecular mechanisms underlying the insect-bacterium gut symbiosis and sheds light on several intriguing commonalities between endocellular and extracellular symbiotic associations. [ABSTRACT FROM AUTHOR]

In Australia, galls develop on Melaleuca quinquenervia (Cav.) S.T. Blake (Myrtaceae) as a result of the mutualistic association between the fly Fergusonina turneri Taylor (Diptera: Fergusoninidae) and its obligate nematode Fergusobia quinquenerviae Davies & Giblin-Davis (Tylenchida: Sphaerulariidae). The nematode induces gall formation, whereas the fly promotes gall maturation. Together they exploit M. quinquenervia buds and may inhibit stem elongation and flower formation. We delimited the physiological host range of this pair to determine their suitability as biological control agents of invasive M. quinquenervia populations in Florida, USA. Host use was assessed for eight species of Myrtaceae native to Florida, eight phylogenetically related ornamental species and oviposition alone on five non-myrtaceous species. Although oviposition was less specific, galls developed and matured only on M. quinquenervia. After establishment, galls are predicted to prevent flower and seed production, thereby reducing the regenerative potential of M. quinquenervia. This is the first example of an insect/nematode mutualism released as biological control agents of an invasive plant. [ABSTRACT FROM AUTHOR]

Despite extensive study, little is known about the origins of the mutualistic bacterial endosymbionts that inhabit approximately 10% of the world's insects. In this study, we characterized a novel opportunistic human pathogen, designated "strain HS," and found that it is a close relative of the insect endosymbiont Sodalis glossinidius. Our results indicate that ancestral relatives of strain HS have served as progenitors for the independent descent of Sodalis-allied endosymbionts found in several insect hosts. Comparative analyses indicate that the gene inventories of the insect endosymbionts were independently derived from a common ancestral template through a combination of irreversible degenerative changes. Our results provide compelling support for the notion that mutualists evolve from pathogenic progenitors. They also elucidate the role of degenerative evolutionary processes in shaping the gene inventories of symbiotic bacteria at a very early stage in these mutualistic associations. [ABSTRACT FROM AUTHOR]

Rickettsia typhi and Rickettsia felis (Rickettsiales: Rickettsiaceae) are two rickettsiae principally transmitted by fleas, but the detection of either pathogen has rarely been attempted in Taiwan. Of 2048 small mammals trapped in eastern Taiwan, Apodemus agrarius Pallas (24.5%) and Mus caroli Bonhote (24.4%) (both: Rodentia: Muridae) were the most abundant, and M. caroli hosted the highest proportion of fleas (63.9% of 330 fleas). Two flea species were identified: Stivalius aporus Jordan and Rothschild (Siphonaptera: Stivaliidae), and Acropsylla episema Rothschild (Siphonaptera: Leptopsyllidae). Nested polymerase chain reaction targeting parts of the ompB and gltA genes showed six fleas to be positive for Rickettsia spp. (3.8% of 160 samples), which showed the greatest similarity to R. felis, Rickettsia japonica, Rickettsia conorii or Rickettsia sp. TwKM01. Rickettsia typhi was not detected in the fleas and Rickettsia co-infection did not occur. Both flea species were more abundant during months with lower temperatures and less rainfall, and flea abundance on M. caroli was not related to soil hardness, vegetative height, ground cover by litter or by understory layer, or the abundance of M. caroli. Our study reveals the potential circulation of R. felis and other rickettsiae in eastern Taiwan, necessitating further surveillance of rickettsial diseases in this region. This is especially important because many novel rickettsioses are emerging worldwide. [ABSTRACT FROM AUTHOR]

Although the gut microbiome influences numerous aspects of organismal fitness, its role in animal evolution and the origin of new species is largely unknown. Here we present evidence that beneficial bacterial communities in the guts of closely related species of the genus Nasonia form species-specific phylosymbiotic assemblages that cause lethality in interspecific hybrids. Bacterial constituents and abundance are irregular in hybrids relative to parental controls, and antibiotic curing of the gut bacteria significantly rescues hybrid survival. Moreover, feeding bacteria to germ-free hybrids reinstates lethality and recapitulates the expression of innate immune genes observed in conventionally reared hybrids. We conclude that in this animal complex, the gut microbiome and host genome represent a coadapted "hologenome" that breaks down during hybridization, promoting hybrid lethality and assisting speciation. [ABSTRACT FROM AUTHOR]

The brown marmorated stink bug Halyomorpha halys (Stål) is a globally invasive species that harbours the primary bacterial symbiont 'Candidatus Pantoea carbekii'. In this work, P. carbekii was used as another genetic marker to investigate the biodiversity and biogeographical patterns of this important pest, in native and newly invaded areas, especially in Italy. The correlation between the genetic structure of the symbiont and that of its host was studied through the analyses of one bacterial and one host marker, the putative pseudogene ΔybgF and the mitochondrial gene COI, respectively. As a result, five new P. carbekii haplotypes were identified, and an association pattern between host-symbiont haplotypes was observed. Host species showed higher haplotype diversity than symbiont, which can be expected in a long term host-symbiont association. Populations from the north-eastern Italy showed the highest values of genetic diversity for both markers, highlighting that this particular Italian area could be the result of multiple ongoing introductions. Moreover, some of the symbiont-host haplotypes observed were shared only by populations from north-eastern Italy and native areas, especially Japan, suggesting further introductions from this native country to Italy. Overall, our findings improve the understanding of the potential origin of multiple accidental introductions of H. halys in Italy. [ABSTRACT FROM AUTHOR]

The article discusses the study titled "Collapse of insect-microbe symbiosis under simulated climate change," by Yoshitomo Kikuchi and colleagues. Topics include the significant impacts of climate change on biodiversity, symbiosis between the southern green stink bug (Nezara viridula) and its gut bacteria, and reduced population of symbiotic bacteria in the bug's gut due to higher temperature.

The article discusses the article "Attenuation of the sensing capabilities of PhoQ in transition to obligate insect-bacterial association," by M. H. Pontes and colleagues. It demonstrates how one such virulence determinant has been adapted for the symbiotic lifestyle. The researchers speculate that the sensory ability of PhoQ has been attenuated in Sodalis glossinidius, so PhoP has become locked in a constitutively active state.

Many insects harbour facultative symbiotic bacteria, some of which have been shown to provide resistance against natural enemies. One of the best-known protective symbionts is Hamiltonella defensa, which in pea aphid (Acyrthosiphon pisum) confers resistance against attack by parasitoid wasps in the genus Aphidius (Braconidae). We asked (i) whether this symbiont also confers protection against a phylogenetically distant group of parasitoids (Aphelinidae) and (ii) whether there are consistent differences in the effects of bacteria found in pea aphid biotypes adapted to different host plants. We found that some H. defensa strains do provide protection against an aphelinid parasitoid Aphelinus abdominalis. Hamiltonella defensa from the Lotus biotype provided high resistance to A. abdominalis and moderate to low resistance to Aphidius ervi, while the reverse was seen from Medicago biotype isolates. Aphids from Ononis showed no evidence of symbiont-mediated protection against either wasp species and were relatively vulnerable to both. Our results may reflect the different selection pressures exerted by the parasitoid community on aphids feeding on different host plants, and could help explain the maintenance of genetic diversity in bacterial symbionts. [ABSTRACT FROM AUTHOR]