Symbiotic bacteria motivate the foraging decision and promote fecundity and survival of Bactrocera dorsalis (Diptera: Tephritidae)

The fall armyworm converts maize endophytes into its own probiotics to detoxify benzoxazinoids and promote caterpillar growth

BACKGROUND

The fall armyworm (FAW, Spodoptera frugiperda) threatens maize production worldwide, and benzoxazinoids (Bxs) are known as the main secondary metabolites produced by maize to defend against FAW. However, we do not yet know whether and in what ways certain endophytes in the digestive system of FAW can metabolize Bxs, thus enhancing the fitness of FAW when feeding on maize.

RESULTS

Using Bxs as the sole carbon and nitrogen source, we isolated Pantoea dispersa from the guts of FAW. P. dispersa can colonize maize roots and leaves as indicated by GFP-labeling and further successfully established itself as an endophyte in the Malpighian tubules and the gut of FAW after FAW feeding activities. Once established, it can be vertically transmitted through FAW eggs, suggesting the potential that FAW can convert maize-derived endophytes into symbiotic bacteria for intergenerational transmission. The prevalence of P. dispersa in FAW guts and maize leaves was also confirmed over large geographic regions, indicating its evolutionary adaptation in fields. Bxs determination in the gut and frass of FAW combined with bioassays performance on maize bx2 mutants revealed that the colonization of P. dispersa can promote FAW growth by metabolizing Bxs rather than other metabolites. Additionally, genome and transcriptome analyses identified plasmid-borne genes, rather than chromosomes of this species, were crucial for Bxs metabolism. This was further validated through in vitro prokaryotic expression assays by expressing two candidate genes form the plasmid.

CONCLUSIONS

FAW can convert maize endophytes into its own probiotics to detoxify Bxs and thus enhance caterpillar growth. This represents a novel strategy for lepidopteran pests-transforming allies of the host into its own-thereby shedding light on the rapid spread of FAW and enhancing our understanding of ecological and evolutionary mechanisms underlying the pest-microbe-plant interactions. Video Abstract.

Succeed to culture a novel lineage symbiotic bacterium of Mollicutes which widely found in arthropods intestine uncovers the potential double-edged sword ecological function

Symbiotic gut bacteria play crucial role in host health. Symbionts are widely distributed in arthropod intestines, but their ecological functions are poorly understood due to the inability to cultivate them. Members of Candidatus Bacilliplasma (CB) are widely distributed in crustacean intestine and maybe commensals with hosts, but the paucity of pure cultures has limited further insights into their physiologies and functions. Here, four strains of representative CB bacteria in shrimp intestine were successfully isolated and identified as members of a novel Order in the Phylum Mycoplasmatota. Through genome assembly, the circular genome maps of the four strains were obtained, and the number of coding genes ranged from 1,886 to 1,980. Genomic analysis suggested that the bacteria were missing genes for many critical pathways including the TCA cycle and biosynthesis pathways for amino acids and coenzyme factors. The analysis of 16S amplification data showed that Shewanella, Pseudomonas and CB were the dominant at the genera level in the intestine of Penaeus vannamei. Ecological functional experiments revealed that the strains were symbionts and colonized shrimp intestines. Our valued findings can greatly enhance our understanding and provides new insights into the potentially significant role of uncultured symbiotic bacteria in modulating host health.

Honeybee gut bacterial strain improved survival and gut microbiota homeostasis in Apis mellifera exposed in vivo to clothianidin

Pesticides are causing honeybee mortality worldwide. Research carried out on honeybees indicates that application of pesticides has a significant impact on the core gut community, which ultimately leads to an increase in the growth of harmful pathogens. Disturbances caused by pesticides also affect the way bacterial members interact, which results in gut microbial dysbiosis. Administration of beneficial microbes has been previously demonstrated to be effective in treating or preventing disease in honeybees. The objective of this study was to measure under in vivo conditions the ability of two bacterial strains (the Enterobacter sp. and Pantoea sp.) isolated from honeybee gut to improve survival and mitigate gut microbiota dysbiosis in honeybees exposed to a sublethal clothianidin dose (0.1 ppb). Both gut bacterial strains were selected for their ability to degrade clothianidin in vitro regardless of their host-microbe interaction characteristics (e.g., beneficial, neutral, or harmful). To this end, we conducted cage trials on 4- to 6-day-old newly emerging honeybees. During microbial administration, we jointly monitored the taxonomic distribution and activity level of bacterial symbionts quantifying 16S rRNA transcripts. First, curative administration of the Pantoea sp. strain significantly improved the survival of clothianidin-exposed honeybees compared to sugar control bees (i.e., supplemented with sugar [1:1]). Second, curative administration of the Enterobacter sp. strain significantly mitigated the clothianidin-induced dysbiosis observed in the midgut structural network, but without improving survival.

IMPORTANCE

The present work suggests that administration of bacterial strains isolated from honeybee gut may promote recovery of gut microbiota homeostasis after prolonged clothianidin exposure, while improving survival. This study highlights that gut bacterial strains hold promise for developing efficient microbial formulations to mitigate environmental pesticide exposure in honeybee colonies.

The Food Source and Gut Bacteria Show Effects on the Invasion of Alien Pests-A Case of Bactrocera dorsalis (Hendel) (Diptera: Tephritidae)

How alien pests invade new areas has always been a hot topic in invasion biology. The spread of the Bactrocera dorsalis from southern to northern China involved changes in food sources. In this paper, in controlled conditions, we take Bactrocera dorsalis as an example to study how plant host transformation affects gut bacteria by feeding it its favorite host oranges in the south, its favorite host peaches and apples in the north, and feeding it cucumbers as a non-favorite host plant, thereby further affecting their fitness during invasion. The result showed that, after three generations of feeding on cucumbers, Bactrocera dorsalis took longer to develop as a larva while its longevity and fecundity decreased and pre-adult mortality increased. Feeding it cucumbers significantly reduced the overall diversity of gut microbiota of Bactrocera dorsalis. The relative abundance of Enterobacter necessary for survival decreased, while the Empedobacter and Enterococcus increased, resulting in decreased carbohydrate transport and metabolism and increased lipid transport and metabolism. Feeding Bactrocera dorsalis Empedobacter brevis and Enterococcus faecalis resulted in a 26% increase in pre-adult mortality and a 2-3 d increase in adult preoviposition period (APOP). Additionally, Enterococcus faecalis decreased the longevity of female and male adults by 17 and 12 d, respectively, and decreased fecundity by 11%. We inferred that the shifted plant hosts played an important role in posing serious harm to Bactrocera dorsalis invading from the south to the north. Therefore, after an invasion of Bactrocera dorsalis into northern China, it is difficult to colonize cucumbers for a long time, but there is still a risk of short-term harm. The findings of this study have established that the interactions between an insect's food source and gut bacteria may have an important effect on insect invasions.

The Global Epidemic of Bactrocera Pests: Mixed-Species Invasions and Risk Assessment

Throughout the past century, the global spread of Bactrocera pests has continued to pose a significant threat to the commercial fruit and vegetable industry, resulting in substantial costs associated with both control measures and quarantine restrictions. The increasing volume of transcontinental trade has contributed to an escalating rate of Bactrocera pest introductions to new regions. To address the worldwide threat posed by this group of pests, we first provide an overview of Bactrocera. We then describe the global epidemic, including border interceptions, species diagnosis, population genetics, geographical expansion, and invasion tracing of Bactrocera pests. We further consider the literature concerning the invasion co-occurrences, life-history flexibility, risk assessment, bridgehead effects, and ongoing implications of invasion recurrences, as well as a case study of Bactrocera invasions of California. Finally, we call for global collaboration to effectively monitor, prevent, and control the ongoing spread of Bactrocera pests and to share experience and knowledge to combat it.

Probiotic consortium modulating the gut microbiota composition and function of sterile Mediterranean fruit flies

The sterile insect technique (SIT) remains a successful approach in managing pest insects. However, the long-term mass rearing and sterilizing radiation associated with SIT have been observed to induce physiological and ecological fitness decline in target insects. This decline may be attributed to various factors, including commensal microbiota dysbiosis, selection procedures, loss of heterozygosity, and other complex interactions.. There is evidence that the bacterial symbiont of insects may play critical roles in digestion, development, reproduction, and behavior. Probiotics are an increasingly common approach for restoring the intestinal microbiota structure and fitness parameters of sterile insects, particularly in the Vienna 8 genetic sexing strain (V8-GSS) of the Mediterranean fruit fly (medfly), Ceratitis capitata. Here, we explore the influence of the previously isolated bacterial strain, Lactococcus lactis, Enterobacter sp., and Klebsiella oxytoca, administration as probiotic consortia (LEK-PC) to the larvae and/or adult diet over the course of 20 rearing generations on fitness parameters. The experiment was carried out in four colonies: a control colony (C), one to which probiotics were not added, one to which probiotics were added to the larval medium (L+), one to which probiotics were added to the adult medium (A+), and one to which probiotics were added to both the larval and adult mediums (AL+). Emergence, flight ability, survival under stress conditions, and mating competitiveness, were all significantly improved by the LEK-PC treatment independently of the administration stage. The intestinal microbiota structure of various medfly V8-GSS colonies also underwent a significant shift, despite the fact that the core microbial community was unaffected by the LEK-PC administration stage, according to 16S metagenomics sequencing. Comparison of the metabolic function prediction and associated carbohydrate enzymes among colonies treated with "LEK-PC" showed an enrichment of metabolic functions related to carbohydrates, amino acids, cofactors, and vitamins metabolism, as well as, glycoside hydrolase enzymes in the AL+ colony compared to the control. This study enriches the knowledge regarding the benefits of probiotic treatment to modulate and restore the intestinal microbiota of C. capitata sterile males for a better effectiveness of the SIT.

Analysis of gut microbiota of ladybug beetle (Harmonia axyridis) after feeding on different artificial diets

BACKGROUND

Harmonia axyridis is an effective natural enemy insect to a variety of phloem-sucking pests and Lepidopteran larvae, such as aphids, scabies, and phylloxera, while its industrial production is limited due to unmature artificial diet. Insect intestinal microbiota affect host development and reproduction. The aim of this study is to understand intestinal microbiota composition of H. axyridis and screen effective probiotics on artificial diet. Considering the role of the components and composition of the diet on the structure and composition of the intestinal microbiome, four kinds of diets were set up: (1) aphid; (2) basic diet; (3) basic diet + glucose; (4) basic diet + trehalose. The gut microbiota of H. axyridis was detected after feeding on different diets.

RESULTS

Results showed that the gut microbiota between artificial diet group and aphid groups were far apart, while the basic and glucose groups were clearly clustered. Besides, the glucose group and trehalose group had one unique phylum, Cryptophyta and Candidatus Saccharibacteria, respectively. The highest abundance of Proteobacteria was found in the aphid diet. The highest abundance of Firmicutes was found in the basic diet. However, the addition of glucose or trehalose alleviated the change. In addition, the relative abundance of Enterobacter, Klebsiella, Enterobacteriaceae_unclassified, Enterobacteriales_unclassified and Serratia in the aphid group was higher than other groups. Moreover, the function of gut genes in each group also showed clear differences.

CONCLUSION

These results have offered a strong link between artificial diets and gut microbes, and also have provided a theoretical basis for the screening of synergistic probiotics in artificial diet.

Glyphosate decreases survival, increases fecundity, and alters the microbiome of the natural predator Harmonia axyridis (ladybird beetle)

Glyphosate is a widely-used herbicide that shows toxicity to non-target organisms. The predatory natural enemy Harmonia axyridis may ingest glyphosate present in pollen and aphid prey. The present study characterized the responses of adult H. axyridis to environmentally relevant concentrations of glyphosate (5, 10, and 20 mg/L) for one or five days. There were no obvious effects on adult H. axyridis survival rates or fecundity in response to 5 or 10 mg/L glyphosate. However, exposure to 20 mg/L glyphosate significantly reduced the survival rate and increased fecundity. Analysis of the adult H. axyridis microbiota with 16S rRNA sequencing demonstrated changes in the relative and/or total abundance of specific taxa, including Serratia, Enterobacter, Staphylococcus, and Hafnia-Obesumbacterium. These changes in symbiotic bacterial abundance may have led to changes in survival rates or fecundity of this beetle. This is the first report of herbicide-induced stimulation of fecundity in a non-target predatory natural enemy, reflecting potentially unexpected risks of glyphosate exposure in adult H. axyridis. Although glyphosate resistant crops have been widely planted, the results of this study indicate a need to strengthen glyphosate management to prevent over-use, which could cause glyphosate toxicity and threaten environmental and human health.

Composition and diversity of gut microbiota across developmental stages of Spodoptera frugiperda and its effect on the reproduction

Introduction

Spodoptera frugiperda is a serious world-wide agricultural pest. Gut microorganisms play crucial roles in growth, development, immunity and behavior of host insects.

Methods

Here, we reported the composition of gut microbiota in a laboratory-reared strain of S. frugiperda using 16S rDNA sequencing and the effects of gut microbiota on the reproduction.

Results

Proteobacteria and Firmicutes were the predominant bacteria and the taxonomic composition varied during the life cycle. Alpha diversity indices indicated that the eggs had higher bacterial diversity than larvae, pupae and adults. Furthermore, eggs harbored a higher abundance of Ralstonia, Sediminibacterium and microbes of unclassified taxonomy. The dynamics changes in bacterial communities resulted in differences in the metabolic functions of the gut microbiota during development. Interestingly, the laid eggs in antibiotic treatment groups did not hatch much due to the gut dysbacteriosis, the results showed gut microbiota had a significant impact on the male reproduction.

Discussion

Our findings provide new perspectives to understand the intricate associations between microbiota and host, and have value for the development of S. frugiperda management strategies focusing on the pest gut microbiota.

Establishment of a Rapid Detection Method for Yeast-like Symbionts in Brown Planthopper Based on Droplet Digital PCR Technology

The brown planthopper Nilaparvata lugens (Stål) (BPH) is a typical monophagous sucking rice pest. Over the course of their evolution, BPH and its symbionts have established an interdependent and mutually beneficial relationship, with the symbionts being important to the growth, development, reproduction, and variation in virulence of BPH. Yeast-like symbionts (YLS), harbored in the abdomen fat body cells of BPH, are vital to the growth and reproduction of the host. In recent research, the symbionts in BPH have mainly been detected using blood cell counting, PCR, real-time quantitative PCR, and other methods. These methods are vulnerable to external interference, cumbersome, time consuming and laborious. Droplet digital PCR (ddPCR) does not need a standard curve, can achieve absolute quantification, does not rely on Cq values, and is more useful for analyzing copy number variation, gene mutations, and relative gene expression. A rapid detection method for the YLS of BPH based on ddPCR was established and optimized in this study. The results showed that the method's limits of detection for the two species of YLS (Ascomycetes symbionts and Pichia guilliermondii) were 1.3 copies/μL and 1.2 copies/μL, respectively. The coefficient of variation of the sample repetition was less than 5%; therefore, the ddPCR method established in this study had good sensitivity, specificity, and repeatability. It can be used to detect the YLS of BPH rapidly and accurately.

Selection on female reproductive schedules in the marula fly, Ceratitis cosyra (Diptera: Tephritidae) affects dietary optima for female reproductive traits but not lifespan

Introduction

A changing environment can select on life-history traits and trade-offs in a myriad of ways. For example, global warming may shift phenology and thus the availability of host-plants. This may alter selection on survival and fertility schedules in herbivorous insects. If selection on life-histories changes, this may in turn select for altered nutrient intake, because the blend of nutrients organisms consume helps determine the expression of life-history traits. However, we lack empirical work testing whether shifts in the timing of oviposition alter nutrient intake and life-history strategies.

Methods

We tested in the marula fruit fly, Ceratitis cosyra, how upward-selection on the age of female oviposition, in comparison with laboratory adapted control flies, affects the sex-specific relationship between protein and carbohydrate intake and life-history traits including lifespan, female lifetime egg production and daily egg production. We then determined the macronutrient ratio consumed when flies from each selection line and sex were allowed to self-regulate their intake.

Results

Lifespan, lifetime egg production and daily egg production were optimised at similar protein to carbohydrate (P:C) ratios in flies from both selection lines. Likewise, females and males of both lines actively defended similar nutrient intake ratios (control =1:3.6 P:C; upward-selected = 1:3.2 P:C).

Discussion

Our results are comparable to those in non-selected C. cosyra, where the optima for each trait and the self-selected protein to carbohydrate ratio observed were nearly identical. The nutrient blend that needs to be ingested for optimal expression of a given trait appeared to be well conserved across laboratory adapted and experimentally selected populations. These results suggest that in C. cosyra, nutritional requirements do not respond to a temporal change in oviposition substrate availability.

Friend or Foe: Symbiotic Bacteria in Bactrocera dorsalis-Parasitoid Associations

Parasitoids are promising biocontrol agents of the devastating fruit fly, Bactrocera dorsalis. However, parasitoid performance is a function of several factors, including host-associated symbiotic bacteria. Providencia alcalifaciens, Citrobacter freundii, and Lactococcus lactis are among the symbiotic bacteria commonly associated with B. dorsalis, and they influence the eco-physiological functioning of this pest. However, whether these bacteria influence the interaction between this pest and its parasitoids is unknown. This study sought to elucidate the nature of the interaction of the parasitoids, Fopius arisanus, Diachasmimorpha longicaudata, and Psyttlia cosyrae with B. dorsalis as mediated by symbiotic bacteria. Three types of fly lines were used: axenic, symbiotic, and bacteria-mono-associated (Lactococcus lactis, Providencia alcalifaciens, and Citrobacter freundii). The suitable stages of each fly line were exposed to the respective parasitoid species and reared until the emergence of adult flies/parasitoids. Thereafter, data on the emergence and parasitoid fitness traits were recorded. No wasps emerged from the fly lines exposed to P. cosyrae. The highest emergence of F. arisanus and D. longicaudata was recorded in the L. lactis fly lines. The parasitoid progeny from the L. lactis and P. alcalifaciens fly lines had the longest developmental time and the largest body size. Conversely, parasitoid fecundity was significantly lower in the L. lactis lines, whereas the P. alcalifaciens lines significantly improved fecundity. These results elucidate some effects of bacterial symbionts on host-parasitoid interactions and their potential in enhancing parasitoid-oriented management strategies against B. dorsalis.

Burkholderia gut symbiont induces insect host fecundity by modulating Kr-h1 gene expression

Full-length cDNAs of the Broad-Complex (BR-C) from Riptortus pedestris were cloned. Moreover, Kr-h1 and BR-C expression levels in apo-symbiotic and symbiotic host insects were compared to verify whether they are modulated by Burkholderia gut symbionts. Interestingly, Kr-h1 expression level was significantly increased in symbiotic females. To determine how Kr-h1 affects fecundity in insects, the biosynthesis of two reproduction-associated proteins, hexamerin-α and vitellogenin, was investigated in R. pedestris females. Hexamerin-α and vitellogenin expression at the transcriptional and translational levels decreased in Kr-h1-suppressed symbiotic females, subsequently reduced egg production. These results suggest that Burkholderia gut symbiont modulates Kr-h1 expression to enhance ovarian development and egg production of R. pedestris by increasing the biosynthesis of the two proteins.

Diversity of endosymbionts in camellia spiny whitefly, Aleurocanthus camelliae (Hemiptera: Aleyrodidae), estimated by 16S rRNA analysis and their biological implications

Camellia spiny whitefly, Aleurocanthus camelliae (Hemiptera: Aleyrodidae), is a major pest in tea, which poses a serious threat to tea production. Similar to many insects, various bacterial symbioses inside A. camelliae may participate in the reproduction, metabolism, and detoxification of the host. However, few reports included research on the microbial composition and influence on A. camelliae growth. We first applied high-throughput sequencing of the V4 region in the 16S rRNA of symbiotic bacteria to study its component and effect on the biological trait of A. camelliae by comparing it with the antibiotic treatment group. The population parameters, survival rate, and fecundity rate of A. camelliae were also analyzed using the age-stage two-sex life table. Our results demonstrated that phylum Proteobacteria (higher than 96.15%) dominated the whole life cycle of A. camelliae. It unveiled the presence of Candidatus Portiera (primary endosymbiont) (67.15-73.33%), Arsenophonus (5.58-22.89%), Wolbachia (4.53-11.58%), Rickettsia (0.75-2.59%), and Pseudomonas (0.99-1.88%) genus. Antibiotic treatment caused a significant decrease in the endosymbiont, which negatively affected the host's biological properties and life process. For example, 1.5% rifampicin treatment caused a longer preadult stage in the offspring generation (55.92 d) compared to the control (49.75d) and a lower survival rate (0.36) than the control (0.60). The decreased intrinsic rate of increase (r), net reproductive rate (R ₀), and prolonged mean generation time (T) were signs of all disadvantageous effects associated with symbiotic reduction. Our findings confirmed the composition and richness of symbiotic bacteria in larva and adult of A. camelliae by an Illumina NovaSeq 6000 analysis and their influence on the development of the host by demographic research. Together, the results suggested that symbiotic bacteria play an important role in manipulating the biological development of their hosts, which might help us for developing new pest control agents and technologies for better management of A. camelliae.

Lactobacillus spp. in the reproductive system of female moths and mating induced changes and possible transmission

BACKGROUND

The microbiome in the insect reproductive tract is poorly understood. Our previous study demonstrated the presence of Lactobacillus spp. in female moths, but their distribution and function remain unclear. Lactobacillus spp. are known as the 'healthy' vaginal microbiome in humans.

RESULTS

Here, we studied the microbiome in the reproductive system (RS) and gut of Spodoptera frugiperda using 16S rDNA sequences. The obtained 4315 bacterial OTUs were classified into 61 phyla and 642 genera, with Proteobacteria, Firmicutes and Bacteroidota being the top three dominant phyla and Enterococcus and Asaia being dominant genera in most samples. Mating dramatically increased the abundance of pathogens or pathogenic functions in the gut, while in the RS, the change range was trivial. Taxonomy assignment identified thirteen Lactobacillus spp. in S. frugiperda, with Lactobacillus crustorum and Lactobacillus murinus showing high abundance. Three species found in S. frugiperda, namely L. reuteri, L. plantarum and L. brevis, have also been identified as human 'healthy' vaginal bacterial species. Lactobacillus spp. showed higher abundance in the RS of virgin females and lower abundance in the RS of virgin males and the gut of virgin females. Mating reduced their abundance in the RS of females but increased their abundance in the RS of males, especially in males mated with multiple females. The RS of virgin females and of multiple mated males were very similar in terms of composition and abundance of Lactobacillus species, with Lactobacillus crustorum showing much higher abundance in both tissues, potentially due to sexual transmission.

CONCLUSIONS

Lactobacillus spp. showed high abundance and diversity in the RS of female moths. The higher abundance of Lactobacillus spp. in the RS of female moths and the similarity of Lactobacillus species in female moths with human 'healthy' vaginal Lactobacillus spp. suggest that these bacterial strains are also an important microbiome in the RS of female moths.

Dietary restriction and ageing: Recent evolutionary perspectives

Dietary restriction (DR) represents one of the most robust interventions for extending lifespan. It is not known how DR increases lifespan. The prevailing evolutionary hypothesis suggests the DR response redirects metabolic resources towards somatic maintenance at the expense of investment in reproduction. Consequently, DR acts as a proximate mechanism which promotes a pro-longevity phenotype. This idea is known as resource reallocation. However, growing findings suggest this paradigm could be incomplete. It has been argued that during DR it is not always possible to identify a trade-off between reproduction and lifespan. It is also suggested the relationship between reproduction and somatic maintenance can be uncoupled by the removal or inclusion of specific nutrients. These findings have created an imperative to re-explore the nexus between DR and evolutionary theory. In this review I will address this evolutionary conundrum. My overarching objectives are fourfold: (1) to outline some of the evidence for and against resource reallocation; (2) to examine recent findings which have necessitated a theoretical re-evaluation of the link between life history theory and DR; (3) to present alternatives to the resource reallocation model; (4) to present emerging variables which potentially influence how DR effects evolutionary trade-offs.

Versatile Roles of Microbes and Small RNAs in Rice and Planthopper Interactions

Planthopper infestation in rice causes direct and indirect damage through feeding and viral transmission. Host microbes and small RNAs (sRNAs) play essential roles in regulating biological processes, such as metabolism, development, immunity, and stress responses in eukaryotic organisms, including plants and insects. Recently, advanced metagenomic approaches have facilitated investigations on microbial diversity and its function in insects and plants, highlighting the significance of microbiota in sustaining host life and regulating their interactions with the environment. Recent research has also suggested significant roles for sRNA-regulated genes during rice-planthopper interactions. The response and behavior of the rice plant to planthopper feeding are determined by changes in the host transcriptome, which might be regulated by sRNAs. In addition, the roles of microbial symbionts and sRNAs in the host response to viral infection are complex and involve defense-related changes in the host transcriptomic profile. This review reviews the structure and potential functions of microbes and sRNAs in rice and the associated planthopper species. In addition, the involvement of the microbiota and sRNAs in the rice-planthopper-virus interactions during planthopper infestation and viral infection are discussed.

Antibiotic Treatment Reduced the Gut Microbiota Diversity, Prolonged the Larval Development Period and Lessened Adult Fecundity of Grapholita molesta (Lepidoptera: Tortricidae)

Grapholita molesta, the oriental fruit moth, is a serious pest of fruit trees with host transfer characteristics worldwide. The gut microbiota, which plays a crucial part in insect physiology and ecology, can be influenced by many elements, such as antibiotics, temperature, diet, and species. However, the effects of antibiotics on G. molesta gut microbiota are still unclear. In this study, we selected five common antibiotic agents to test the inhibition of G. molesta gut microbiota, and found ciprofloxacin shown the best antibacterial activity. After feeding 1 μg/mL of ciprofloxacin, the relative abundance of Actinobacteria and Cyanobacteria decreased significantly, while that of Firmicutes and Bacteroidetes increased. PICRUSt2 analysis indicated that most functional prediction categories were enriched in the G. molesta gut, including amino acid transport and metabolism, translation, ribosomal structure and biogenesis, carbohydrate transport and metabolism, transcription, cell wall/membrane/envelope biogenesis, and energy production and conversion. Finally, ciprofloxacin feeding significantly affected larval growth, development, and reproduction, resulting in prolonged larval development duration, shortened adult longevity, and significantly decreased single female oviposition and egg hatchability. In addition, we isolated and purified some culturable bacteria belonging to Proteobacteria, Firmicutes, Actinobacteria, and cellulase-producing bacteria from the G. molesta midgut. In brief, our results demonstrate that antibiotics can have an impact on G. molesta gut bacterial communities, which is beneficial for host growth and development, as well as helping female adults produce more fertile eggs. These results will thus provide a theoretical reference for developing new green control technology for G. molesta.

Bacterial Symbionts in Ceratitis capitata

Ceratitis capitata (Diptera: Tephritidae) is responsible for extensive damage in agriculture with important economic losses. Several strategies have been proposed to control this insect pest including insecticides and the Sterile Insect Technique. Traditional control methods should be implemented by innovative tools, among which those based on insect symbionts seem very promising. Our study aimed to investigate, through the 16S Miseq analysis, the microbial communities associated with selected organs in three different medfly populations to identify possible candidates to develop symbiont-based control approaches. Our results confirm that Klebsiella and Providencia are the dominant bacteria in guts, while a more diversified microbial community has been detected in reproductive organs. Concertedly, we revealed for the first time the presence of Chroococcidiopsis and Propionibacterium as stable components of the medfly’s microbiota. Additionally, in the reproductive organs, we detected Asaia, a bacterium already proposed as a tool in the Symbiotic Control of Vector-Borne Diseases. A strain of Asaia, genetically modified to produce a green fluorescent protein, was used to ascertain the ability of Asaia to colonize specific organs of C. capitata. Our study lays the foundation for the development of control methods for C. capitata based on the use of symbiont bacteria.

Mating Leads to a Decline in the Diversity of Symbiotic Microbiomes and Promiscuity Increased Pathogen Abundance in a Moth

Mating may promote microbial diversity through sexual transmission, while mating-induced immune responses may decrease it. Therefore, the study of mating-induced microbiomes changes under different mating systems is informative to unravel its biological relevance and evolutionary significance. Here, we studied the microbiomes in a community context within the abdomen of Spodoptera frugiperda females using 16S rDNA sequences by setting virgin females, and females mated once, twice, or thrice with the same or different males. Alpha and beta diversities revealed that mating significantly affected the composition of microbiomes in S. frugiperda females, wherein virgin females have the highest diversity, followed by one-time mated females and females mated with multiple males, while females mated repeatedly with the same male showed the lowest diversity. The low diversity in females mated repeatedly with the same male may be due to lower sexual transmission as only mated with one mate and higher immune response from repeated matings. Functional prediction by FAPROTAX and literature searching found 17 possible pathogens and 12 beneficial microbiomes. Multiple mating turned over the abundance of pathogens and beneficial microbes, for example, Enterococcus and Lactobacillus spp. (beneficial) showed higher abundance in virgin females while Morganella and Serratia spp. (pathogens) showed higher abundance in females mated with multiple males. These results suggest that mating causes a decline in the diversity of symbiotic microbiomes and promiscuity incurs a higher pathogen abundance in S. frugiperda females, which may be the result of sexual transmission of bacterial strains and immune responses targeting members of the microbiomes. To our knowledge, we demonstrate microbiomes changes in female insects under virgin and different mating regimes for the first time.

Dynamics of the Queensland Fruit Fly Microbiome through the Transition from Nature to an Established Laboratory Colony

The transition from nature to laboratory or mass rearing can impose significant physiological and evolutionary impact on insects. The Queensland fruit fly (also known as ‘Qfly’), Bactrocera tryoni (Froggatt) (Diptera: Tephritidae), is a serious economic pest that presents major challenges for horticulture industries in Australia. The sterile insect technique (SIT) is being developed to manage outbreaks in regions that remain free of Qfly and to suppress populations in regions where this species is endemic. The biology of Qfly is intimately connected to its microbiome. Therefore, changes in the microbiome that occur through domestication have implications for SIT. There are numerous studies of the microbiome in Qfly larvae and adults, but there is little information on how the microbiome changes as Qfly laboratory colonies are established. In this study, high-throughput Illumina sequencing was used to assess the Qfly microbiome in colonies reared from wild larvae, collected from fruit, for five generations, on a gel-based larval diet. Beta diversity analysis showed that the bacterial communities from Generation 5 (G5) clustered separately from earlier generations. At the genus level, bacterial communities were significantly different between the generations and mostly altered at G5. However, communities were found similar at phyla to family taxonomic levels. We observed high abundance of Morganella and Burkholderia at the genus level in the larval and pupal stages respectively at G5, but these were not detected in earlier generations. Overall, our findings demonstrate that the domestication process strongly affects the Qfly microbiome and prompts questions about the functional relationship between the Qfly and its microbiome, as well as implications for the performance of insects that have been domesticated and mass-reared for SIT programs.

High-resolution Microbiome Analyses of Nine Psyllid Species of the Family Triozidae Identified Previously Unrecognized but Major Bacterial Populations, including Liberibacter and Wolbachia of Supergroup O

Psyllids (Hemiptera: Sternorrhyncha: Psylloidea) are plant sap-sucking insects that include important agricultural pests. To obtain insights into the ecological and evolutionary behaviors of microbes, including plant pathogens, in Psylloidea, high-resolution ana-lyses of the microbiomes of nine psyllid species belonging to the family Triozidae were performed using high-throughput amplicon sequencing of the 16S rRNA gene. Analyses identified various bacterial populations, showing that all nine psyllids have at least one secondary symbiont, along with the primary symbiont "Candidatus Carsonella ruddii" (Gammaproteobacteria: Oceanospirillales: Halomonadaceae). The majority of the secondary symbionts were gammaproteobacteria, particularly those of the order Enterobacterales, which included Arsenophonus and Serratia symbiotica, a bacterium formerly recognized only as a secondary symbiont of aphids (Hemiptera: Sternorrhyncha: Aphidoidea). The non-Enterobacterales gammaproteobacteria identified in the present study were Diplorickettsia (Diplorickettsiales: Diplorickettsiaceae), a potential human pathogen, and Carnimonas (Oceanospirillales: Halomonadaceae), a lineage detected for the first time in Psylloidea. Regarding alphaproteobacteria, the potential plant pathogen "Ca. Liberibacter europaeus" (Rhizobiales: Rhizobiaceae) was detected for the first time in Epitrioza yasumatsui, which feeds on the Japanese silverberry Elaeagnus umbellata (Elaeagnaceae), an aggressive invasive plant in the United States and Europe. Besides the detection of Wolbachia (Rickettsiales: Anaplasmataceae) of supergroup B in three psyllid species, a lineage belonging to supergroup O was identified for the first time in Psylloidea. These results suggest the rampant transfer of bacterial symbionts among animals and plants, thereby providing deeper insights into the evolution of interkingdom interactions among multicellular organisms and bacteria, which will facilitate the control of pest psyllids.

Effects of symbiotic population impairment on microbiome composition and longevity of Bactrocera dorsalis

In order to understand the role of symbionts for their insect hosts, it is customary to treat them with antibiotics or to sterilize eggs (treatments), resulting in aposymbiotic and axenic insects, respectively. Such axenic insects can then be compared with untreated controls. Fruit flies often bear complex communities which are greatly reduced by such treatments. However, the bacterial community is not completely eliminated. Here, we examine the effect of these procedures on the structure of the remaining bacterial communities in Bactrocera dorsalis (Diptera: Tephritidae) and on the insect longevity. The antibiotics (Norfloxacin and Ceftazedime) were administered to 1-day-old adult flies through sugar meal for 7 days, and eggs were surface sterilized and dechorionated to produce axenic lines. The flies were starved of protein before they were offered full diets or diets containing non-essential amino acids only. Antibiotic and egg disinfection treatments resulted in a significant reduction of the vast majority of gut bacterial populations, especially Proteobacteria, Firmicutes and Bacteroidetes. On the other hand, antibiotic allowed the persistence of Actinobacteria, Cyanobacteria and Acidobacteria populations. In untreated control flies, longevity was extended irrespective of diet quality in comparison to treated flies. Conversely, when gut bacteria were largely reduced (aposymbiotic and axenic flies), longevity was reduced in the non-essential amino acids diet treatment versus slightly improved in the presence of a protein diet. We discuss these results in an ecological-life-history perspective.

Diversity and Functions of Yeast Communities Associated with Insects

Following the concept of the holobiont, insect-microbiota interactions play an important role in insect biology. Many examples of host-associated microorganisms have been reported to drastically influence insect biological processes such as development, physiology, nutrition, survival, immunity, or even vector competence. While a huge number of studies on insect-associated microbiota have focused on bacteria, other microbial partners including fungi have been comparatively neglected. Yeasts, which establish mostly commensal or symbiotic relationships with their host, can dominate the mycobiota of certain insects. This review presents key advances and progress in the research field highlighting the diversity of yeast communities associated with insects, as well as their impact on insect life-history traits, immunity, and behavior.

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

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

Diversity of bacteria in different life stages and their impact on the development and reproduction of Zeugodacus tau (Diptera: Tephritidae)

Fruit flies usually harbor diverse communities of bacteria in their digestive systems, which are known to play a significant role in their fitness. However, little information is available on Zeugodacus tau, a polyphagous pest worldwide. This study reports the first extensive analysis of bacterial communities in different life stages and their effect on the development and reproduction of laboratory-reared Z. tau. Cultured bacteria were identified using the conventional method, and all bacteria were identified by high-throughput technologies (16S ribosomal RNA gene sequencing of V3-V4 region). A total of six bacterial phyla were identified in larvae, pupae, and male and female adult flies, which were distributed into 14 classes, 32 orders, 58 families and 96 genera. Proteobacteria was the most represented phylum in all the stages except larvae. Enterobacter, Klebsiella, Providencia, and Pseudomonas were identified by conventional and next-generation sequencing analysis in both male and female adult flies, and Enterobacter was found to be the main genus. After being fed with antibiotics from the first instar larvae, bacterial diversity changed markedly in the adult stage. Untreated flies laid eggs and needed 20 days before oviposition while the treated flies showed ovary development inhibited and were not able to lay eggs, probably due to the alteration of the microbiota. These findings provide the cornerstone for unexplored research on bacterial function in Z. tau, which will help to develop an environmentally friendly management technique for this kind of harmful insect.

Mechanisms underlying gut microbiota-host interactions in insects

Insects are the most diverse group of animals and colonize almost all environments on our planet. This diversity is reflected in the structure and function of the microbial communities inhabiting the insect digestive system. As in mammals, the gut microbiota of insects can have important symbiotic functions, complementing host nutrition, facilitating dietary breakdown or providing protection against pathogens. There is an increasing number of insect models that are experimentally tractable, facilitating mechanistic studies of gut microbiota-host interactions. In this Review, we will summarize recent findings that have advanced our understanding of the molecular mechanisms underlying the symbiosis between insects and their gut microbiota. We will open the article with a general introduction to the insect gut microbiota and then turn towards the discussion of particular mechanisms and molecular processes governing the colonization of the insect gut environment as well as the diverse beneficial roles mediated by the gut microbiota. The Review highlights that, although the gut microbiota of insects is an active field of research with implications for fundamental and applied science, we are still in an early stage of understanding molecular mechanisms. However, the expanding capability to culture microbiomes and to manipulate microbe-host interactions in insects promises new molecular insights from diverse symbioses.

Dysbacteriosis of the Intestinal Flora Is an Important Reason for the Death of Adult House Flies Caused by Beauveria bassiana

Beauveria bassiana is one of the most widespread insect pathogens and can be used in the biological control of agricultural, forestry and medical pests. The mechanisms by which B. bassiana leads to mortality in different host insects are also different. For house flies, B. bassiana has strong virulence, but its microecological mechanism is not clear. In this paper, the virulence of three strains of B. bassiana (TB, CB and BB) isolated from different hosts to house flies was studied. The results showed that the three strains of B. bassiana had strong pathogenicity to house fly adults. Specifically, TB was the strongest, CB was the second strongest, and BB was the weakest, with maximum lethal effects on house fly populations 5, 6, and 7 days after infection, respectively. Further study showed that the intestinal flora of house flies was disordered 3, 4, and 5 days after B. bassiana TB, CB and BB strain infection, respectively. Intestinal flora dysbacteriosis may be an important reason for the death of house flies caused by B. bassiana. After infection, the negative interaction ratio of bacteria in the house fly intestine decreased, and the stronger the virulence was, the lower the negative interaction ratio was. The time from B. bassiana infection to intestinal flora dysbacteriosis was not fixed. We named this period the “spring stage”. The stronger the virulence of the B. bassiana strain was, the shorter the “spring stage” was. Therefore, the “spring stage” can be used as a virulence marker for evaluating the pathogenicity of different B. bassiana strains.

Recent Advancements in Studies on Chemosensory Mechanisms Underlying Detection of Semiochemicals in Dacini Fruit Flies of Economic Importance (Diptera: Tephritidae)

Dacini fruit flies mainly contain two genera, Bactrocera and Zeugodacus, and include many important pests of fruits and vegetables. Their life cycle is affected by various environmental cues. Among them, multiple characteristic semiochemicals have remarkable effects on their reproductive and host-finding behaviors. Notably, floral fragrances released from so-called fruit fly orchids strongly attract males of several Dacini fruit fly species. Focusing on the strong attraction of male flies to particular chemicals, natural and synthetic lures have been used for pest management. Thus, the perception of semiochemicals is important to understand environmental adaptation in Dacini fruit flies. Since next-generation sequencers are available, a large number of chemosensory-related genes have been identified in Dacini fruit flies, as well as other insects. Furthermore, recent studies have succeeded in the functional analyses of olfactory receptors in response to semiochemicals. Thus, characterization of molecular components required for chemoreception is under way. However, the mechanisms underlying chemoreception remain largely unknown. This paper reviews recent findings on peripheral mechanisms in the perception of odors in Dacini fruit flies, describing related studies in other dipteran species, mainly the model insect Drosophilamelanogaster. Based on the review, important themes for future research have also been discussed.

Comparative genomics of Klebsiella michiganensis BD177 and related members of Klebsiella sp. reveal the symbiotic relationship with Bactrocera dorsalis

Background

Bactrocera dorsalis is a destructive polyphagous and highly invasive insect pest of tropical and subtropical species of fruit and vegetable crops. The sterile insect technique (SIT) has been used for decades to control insect pests of agricultural, veterinary, and human health importance. Irradiation of pupae in SIT can reduce the ecological fitness of the sterile insects. Our previous study has shown that a gut bacterial strain BD177 that could restore ecological fitness by promoting host food intake and metabolic activities.

Results

Using long-read sequence technologies, we assembled the complete genome of K. michiganensis BD177 strain. The complete genome of K. michiganensis BD177 comprises one circular chromosome and four plasmids with a GC content of 55.03%. The pan-genome analysis was performed on 119 genomes (strain BD177 genome and 118 out of 128 published Klebsiella sp. genomes since ten were discarded). The pan-genome includes a total of 49305 gene clusters, a small number of 858 core genes, and a high number of accessory (10566) genes. Pan-genome and average nucleotide identity (ANI) analysis showed that BD177 is more similar to the type strain K. michiganensis DSM2544, while away from the type strain K. oxytoca ATCC13182. Comparative genome analysis with 21 K. oxytoca and 12 K. michiganensis strains, identified 213 unique genes, several of them related to amino acid metabolism, metabolism of cofactors and vitamins, and xenobiotics biodegradation and metabolism in BD177 genome.

Conclusions

Phylogenomics analysis reclassified strain BD177 as a member of the species K. michiganensis. Comparative genome analysis suggested that K. michiganensis BD177 has the strain-specific ability to provide three essential amino acids (phenylalanine, tryptophan and methionine) and two vitamins B (folate and riboflavin) to B. dorsalis. The clear classification status of BD177 strain and identification of unique genetic characteristics may contribute to expanding our understanding of the symbiotic relationship of gut microbiota and B. dorsalis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12863-020-00945-0.

Artificial Larval Diet Mediates the Microbiome of Queensland Fruit Fly

Larval diets used for artificial rearing can have a significant effect on insect biology. The Queensland fruit fly (aka "Qfly"), Bactrocera tryoni (Froggatt) (Diptera: Tephritidae), is one of the greatest challenges for fruit growers in Australia. The sterile insect technique (SIT) is being developed to manage outbreaks in regions that remain free of Qfly and to reduce populations in regions where this species is endemic. Factory scale rearing is essential for SIT; however, artificial larval diets are known to affect the microbiome of Qfly, which may then affect fly performance. In this study, high-throughput Illumina sequencing was used to assess the Qfly microbiome in colonies reared, for five generations from nature, on two common artificial diets (carrot and gel). At generation five (G5), the microbiome was assessed in larvae, pupae, adult males and adult females and standard fly quality control parameters were assessed together with additional performance measures of mating propensity and survival under nutritional stress. At the genus level, bacterial communities were significantly different between the colonies reared on the two larval diets. However, communities converged at Phyla to family taxonomic levels. Bacterial genera of Morganella, Citrobacter, Providencia, and Burkholderia were highly abundant in all developmental stages of Qfly reared on the gel diet, when compared to the carrot diet. Despite abundance of these genera, a greater percentage of egg hatching, heavier pupal weight and a higher percentage of fliers were found in the Qfly reared on the gel diet. Mating propensity and survival under nutritional stress was similar for adult Qfly that had been reared on the two larval diets. Overall, our findings demonstrate that the artificial larval diet strongly influences the microbiome and quality control measures of Qfly, with likely downstream effects on performance of flies released in SIT programs.