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Background Endosymbiotic bacteria have been reported to mediate interactions between parasitoids and their insect hosts. How parasitic wasps influence changes in host microbial communities and the relationship between them are of great importance to the study of host-parasitoid co-evolutionary and ecological interactions. However, these interactions remain largely unreported for interactions between in Aphis gossypii and Lysiphlebia japonica. Results In this study, we characterize the bacterial microbiota of L. japonica wasps at different developmental stages and monitor changes over time in the bacterial microbiota of their parasitized and non-parasitized aphid hosts, using metagenomic analysis of 16S rDNA sequencing data. Proteobacteria, Firmicutes, and Actinobacteria were the three most abundant bacterial phyla identified in L. japonica. We found that parasitism was associated with an increased abundance of Buchnera nutritional endosymbionts, but decreased abundance of Acinetobacter, Arsenophonus, Candidatus_Hamiltonella, and Pseudomonas facultative symbionts in aphid hosts. Functional analysis of enriched pathways of parasitized aphids showed significant differences in the 'transport and metabolism of carbohydrates' and 'amino acid, lipid, and coenzyme biosynthesis' pathways. Notably, the composition of symbiotic bacteria in wasp larvae was highly similar to that of their aphid hosts, especially the high abundance of Buchnera. Conclusion The results provide a conceptual framework for L. japonica interactions with A. gossypii in which the exchange of symbiotic microbes provides a means by which microbiota can potentially serve as evolutionary drivers of complex, multilevel interactions underlying the ecology and co-evolution of these hosts and parasites. This article is protected by copyright. All rights reserved.

Additional file 5: Table S1. Primers used in RT-qPCR.

Additional file 7: Table S3. Fold changes of selected DEGs validated by using RT-qPCR.

Understanding of neonicotinoid insecticides toxicity on non-target organisms, such as bees, has indirectly promoted their soil treatment use. However, their effect on soil ecosystems haven’t fully understood. Here, based on 16S rRNA high-throughput sequencing and metagenomics, the effects of neonicotinoid insecticide thiamethoxam on bacterial communities and metabolic functions in two types of soils were studied. Thiamethoxam treatment significantly affected soil bacterial abundance, reduced microbial diversity, and changed the bacterial community structure in the short term, and the structure soon returned to a stable state. Soil type and time were important factors affecting bacterial community structure. Some plant growth-promoting rhizosphere bacteria (PGPR) including Actinobacteria were found, and their populations were reduced, while pollutant-degrading bacteria including Firmicutes were also found, and their populations were increased. Based on metagenomics analysis, thiamethoxam treatment insignificantly promoted or inhibited multiple metabolic processes, but gene abundance of some key processes significantly changed. Subtypes of 18 biodegradation genes (BDGs) and 5 pesticide degradation genes (PDGs) were identified. Thiamethoxam treatment significantly increased the abundance of BDGs and PDGs, including cytochrome P450. Potential hosts of P450 degradation genes, including the genus Rhodococcus, were discovered. Conclusions of this study will promote safety evaluation and degradation-related research on neonicotinoid insecticides in soil.

The relationship of host and symbionts is complex and dynamic. Symbionts can significantly impact host phenotypes and parasite epidemics may be influenced by interactions among symbionts. Aphids are well known for their symbiotic associations with bacteria. However, few studies have examined the offsprings of parasitized host and the ecological implications of a dynamic microbiome longitudinaly. In the present study, we surveyed the microbiota in non-parasitized aphids and parasitized aphids its offspring for over four consecutive generations by using high-throughput 16S rRNA sequencing. Across hosts, parasite strongly altered symbiont composition of parasitized aphids offspring, especially in the fourth generation. Moreover, parasitism reduced weight and reproductive capacity of the parasitized offspring and influenced parasite epidemics. Taken together, these results indicate that parasitoids can influence host-microbiome interactions by altering the symbionts composition in the host offspring. Our findings further supports the importance host-parasite-microbiome tirad interactions, which can create intense reciprocal selection resulting in coevolution between species.

Lysiphlebia japonica Ashmead (Hymenoptera, Braconidae) is an endophagous parasitoid and Aphis gossypii Glover (Hemiptera, Aphididae) is a major pest in cotton. The relationship between insect host-parasitoids and their hosts involves complex physiological, biochemical and genetic interactions. This study examines changes in the development and physiological metabolism of A. gossypii regulated by L. japonica. Our results demonstrated that both the body length and width increased compared to non-parasitized aphids. We detected significantly increases in the developmental period as well as severe reproductive castration following parasitization by L. japonica. We then used proteomics to characterize these biological changes, and when combined with transcriptomes, this analysis demonstrated that the differential expression of mRNA (up or downregulation) captured a maximum of 48.7% of the variations of protein expression. We assigned these proteins to functional categories that included immunity, energy metabolism and transport, lipid metabolism, and reproduction. We then verified the contents of glycogen and 6-phosphate glucose, which demonstrated that these important energy sources were significantly altered following parasitization. These results uncover the effects on A. gossypii following parasitization by L. japonica, additional insight into the mechanisms behind insect-insect parasitism, and a better understanding of host-parasite interactions.

Background: Three wing morphs exists in the life cycle of the worldwide pest Aphis gossypii, i.e., wing parthenogenetic female (WPF), gynopara (GP) and male, which were produced mostly by crowding and host quality, photoperiod, loss of X chromosome, respectively. However, the shared molecular mechanism underlying their wing differentiation remains an enigma. Here we firstly induced gynoparae and males indoors and compared the characters of these wing morphs in body, internal genitals and fecundity. Then we identified the shared and separate differentially expressed genes (DEGs) and signaling pathways potentially involved in the wing morphs regulation in WPF, GP and male compared to wingless parthenogenetic female (WLPF). Results: Newly-born nymphs reared in short photoperiod condition exclusively produce gynoparae and males in adulthood successively, in which the sex ratio is gynoparae biased. Compared with WLPF, three wing morphs have similar morphology in bodies but is obviously discriminated in the reproductive system and fecundity. Built upon our previous study, 37 090 annotated unigenes were obtained from libraries constructed by the four morphs above through RNA-sequencing, in which 10 867, 19 334 DEGs were identified in pairwise comparison of GP vs. WLPF, Male vs. WLPF, respectively. Furthermore, 2 335 shared DEGs including 1 658 up- and 677 downregulated were obtained in these wing morphs compared to WLPF. The 1 658 shared up-regulated DEGs were enriched in multiple signaling pathways including insulin, FoxO, MAPK, strarch and sucrose metabolism, fatty acid biosynthesis and degradation which hint their key roles in the regulation of wing plasticity in cotton aphid. Gene expression levels were validated by using Pearson’s correlation (r) and potential roles of 15 DEGs related to the insulin signaling pathway in cotton wing dimorphism were discussed. Conclusions: The results of this study establish a solid foundation for deciphering molecular mechanisms underlying the switch between wingless and wing morphs in the cotton aphid and provide valuable resources for future research on the host-alternating aphid species.

Odorant-binding proteins (OBPs) play a significant role in the olfactory signal transduction of insects and help them locate hosts, oviposition sites, and mating partners. The sap-sucking insect, Aphis gossypii Glover (Homoptera: Aphididae), is a destructive cosmopolitan pest and yet the molecular mechanisms by which A. gossypii perceives pheromones and host volatiles remain unknown. In this study, we identified and characterized 6 OBPs, using the A. gossypii RNA-seq transcriptome dataset previously constructed in our laboratory. Real-time PCR indicated specific expression patterns of the 6 genes, which had different levels of expression based on development stage, tissue, morph, and life cycle. In addition, binding specificities of the 6 proteins investigated using the ligand-binding assays showed that all 6 OBPs exhibited high binding affinities towards Phlorizin dehydrate while AgosOBP3 and AgosOBP4 had strong affinity to beta-ionone and AgosOBP8 displayed higher binding affinities for Nerolidol and Cis-3-hexenyl acetate compared to other OBPs.

Lipids play an important role in energy storage, membrane structure stabilization and signaling. Parasitoids are excellent models to study lipidomics because a majority of them do not accumulate during their free-living life-stage. Studies on parasitoids have mostly focused on the changes in the lipids and gene transcripts in hosts and little attention has been devoted to lipidomics and transcriptomics changes in parasitoids. In this study, a relative quantitative analysis of lipids and their gene transcripts in 3-days-old Lysiphlebia japonica larva (3 days after spawning) and pupae were performed using liquid chromatography, mass spectrometry and RNA-seq. Thirty-three glycerolipids and 250 glycerophospholipids were identified in this study; all triglycerides and the vast majority of phospholipids accumulated in the pupal stage. This was accompanied by differentially regulated lipid uptake and remolding. Furthermore, our data showed that gene transcription was up-regulated in key nutrient metabolic pathways involved in lipid synthesis in 3-days-old larvae. Finally, our data suggests that larva and pupa of L. japonica may lack the ability for fatty acids synthesis. A comprehensive, quantitative, and expandable resource was provided for further studies of metabolic regulation and molecular mechanisms underlying parasitic response to hosts defense.

Lysiphlebia japonica (Ashmead) is a predominant parasitoid of cotton-melon aphids in the fields of northern China with a proven ability to effectively control cotton aphid populations in early summer. For accurate normalization of gene expression in L. japonica using quantitative reverse transcriptase-polymerase chain reaction (RT-qPCR), reference genes with stable gene expression patterns are essential. However, no appropriate reference genes is L. japonica have been investigated to date. In the present study, 12 selected housekeeping genes from L. japonica were cloned. We evaluated the stability of these genes under various experimental treatments by RT-qPCR using four independent (geNorm, NormFinder, BestKeeper and Delta Ct) and one comparative (RefFinder) algorithm. We identified genes showing the most stable levels of expression: DIMT, 18S rRNA, and RPL13 during different stages; AK, RPL13, and TBP among sexes; EF1A, PPI, and RPL27 in different tissues, and EF1A, RPL13, and PPI in adults fed on different diets. Moreover, the expression profile of a target gene (odorant receptor 1, OR1) studied during the developmental stages confirms the reliability of the chosen selected reference genes. This study provides for the first time a comprehensive list of suitable reference genes for gene expression studies in L. japonica and will benefit subsequent genomics and functional genomics research on this natural enemy.

Gut microbiota has been suggested as an important component of host defense. However, microbiota in other parts of the body have rarely been characterized. In our present work, we give a detailed view of the body of Spodoptera exigua larvae, the midgut with intestinal contents (MG), midgut excluding intestinal contents (PM), intestinal contents (IC) and remaining parts excluding the MG (RM), with the objective of revealing the complexity of microorganisms and comparing the biodiversity of the S. exigua larvae-associated microbiota. Our results provide the first evidence that third and fifth larvae samples of S. exigua were dominated by members of the phyla Firmicutes and Proteobacteria. In addition, there were no obvious differences in relative abundances of microbiota among MG, PM and RM at the phylum level. MG3 and MG5 (nearly RM5) harbored the richest microbial community, with much higher abundance of Halomonas, Pseudomonas and Methylobacterium, respectively. Intestinal contents contained the lowest diversity and highest abundance of Enterococcus. Knowledge of the bacteria in a major herbivorous insect, such as S. exigua, can facilitate the acquisition of special biological resources for agricultural pest control.

An amendment to this paper has been published and can be accessed via the original article.

Common varieties of genetically modified (GM) cotton increasingly display insect-resistant properties via expression of bacterial-derived toxins from Bacillus thuringiensis (Bt). This necessitates a deeper understanding of the possible effects of these crops on non-target insects. The mirid bug Apolygus lucorum is a major pest in cotton production in China, however, the effect of GM cotton on this non-target species is currently virtually unknown. This insect is exposed to these transgenic plants by consuming genetically modified (GM) leaves. In this study, laboratory experiments were conducted to assess the toxicity of CCRI41 and CCRI45, (genetically modified cotton varieties which express the toxins Cry1Ac and CpTI (Cowpea Trypsin Inhibitor)) on nymphs and adults of A. lucorum. There was no detectable increase in mortality after A. lucorum fed on GM cotton leaves for 20 days. While we detected trace amounts of Cry1Ac proteins in both A. lucorum nymphs and adults (10 ng/g fresh weight), the expression of genes related to detoxification did not detectably differ from those feeding on non-GM cotton. Our binding assays did not show Cry1Ac binding to receptors on the midgut brush border membrane from either A. lucorum nymphs or adults. Our findings collectively indicate that feeding on leaves of the GM cotton varieties CCRI41 and CCRI45 have few toxic effects on A. lucorum.

Cotton (Gossypium hirsutum Linn.) is widely cultivated in China. The polyphagous insect Adelphocoris suturalis (Jakovlev) is a serious insect pest in cotton growing regions. Plants have evolved sophisticated systems to cope with herbivore attacks. However, the cotton defense mechanisms induced by A. suturalis feeding have lagged behind. We carried out untargeted proteomic analysis using the iTARQ technique and metabolomics based on LC-MS/MS analysis of cotton leaves fed upon by A. suturalis. Proteomic analysis identified 775 upregulated proteins and 477 downregulated proteins in plants that were infested by A. sututralis compared to the controls. Metabolomic analysis identified 50 differentially expressed metabolites in the positive ion mode and 14 in the negative ion mode compared to the controls. The tryptophan metabolism pathway was significantly changed in both the positive and negative ion mode in the metabolomics analysis. The alpha-linolenic acid pathway was significantly changed in both the proteomic and metabolomics analyses. Furthermore, the result was validated by RT-qPCR analysis of 5 related genes involved in alpha-linolenic acid pathway. These results indicate that tryptophan metabolism and the alpha-linolenic acid pathway may be important in cotton defense against herbivores and would enhance our understanding of plant defenses induced by A. sututrali feeding.

Reference genes have been utilized in estimating gene expression levels using quantitative reverse transcriptase-quantitative polymerase chain reaction (qRT-PCR) analysis. Aphidius gifuensis Ashmaed is one of the most widely used biological control agents for aphids. The biological properties of this species have been studied in detail, and current investigations are focused on elucidating the regulatory mechanisms in its host However, the appropriate reference genes for target gene expression studies have not been identified. In this study, the expression profiles of 12 candidate reference genes were evaluated under different experimental conditions(development stage, sex, tissue type, diet) by using dedicated algorithms, including geNorm, Normfinder, BestKeeper, and ΔCt. In addition, RefFinder was used to rank the overall stability of the candidate genes. Finally, we recommend three optimal reference genes for the normalization of qRT-PCR data in the presence of specific variables, which include ACTB, RPL13, and PPI for different developmental stages; RPS18, ACTB, and RPL13 for sexes; RPL13, PRII3, and RPS18 in different tissue types; and RPL13, RPL27, and ACTB in diverse diets. The present study has identified optimal reference genes that could be used in estimating the expression levels of specific genes under these conditions following the Minimum Information for publication of Quantitative real-time PCR Experiments (MIQE) guidelines, which would facilitate in advancements in functional genomics research on A. gifuensis.