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.

RNAi-mediated CrebA silencing inhibits reproduction and immunity in Locusta migratoria manilensis.

Locusta migratoria manilensis is a major agricultural pest that causes severe direct and indirect damage to several crops. Thus, to provide a theoretical foundation for pest control, the role of CrebA in the reproduction and immune regulation of L. migratoria was investigated. CrebA is a bZIP transcription factor that critically regulates intracellular protein secretion. In this study, CrebA was widely expressed in the brain, fat body, integument, midgut, and reproductive tissues of different maturity stages of adult locusts, especially in the female fat body. RNA interfering (RNAi)-mediated silencing of CrebA inhibited locusts ovarian development, and key reproduction gene expressions, Vgs, VgRs, Chico, and JHAMT were downregulated. After the locusts were injected with Micrococcus luteus or Escherichia coli, M. luteus activated lysozyme expression, while the E. coli activated both phenol oxidase cascade and lysozyme expression. Furthermore, both bacteria stimulated the upregulation of the antimicrobial peptide genes DEF3 and DEF4. However, CrebA silencing is fatal to locusts infection with E. coli, with a mortality rate of up to 96.3%, and resulted in a significant decrease in the expression of DEF3 and DEF4 and changes in the activities of phenol oxidase and lysozyme of locusts infected by bacteria. Collectively, CrebA may be involved in diverse biological processes, including reproduction and immunity. CrebA inhibited locusts reproduction by regulating JH signaling pathway and inhibits the expression of immune genes TLR6, IMD, and AMPs. These results demonstrate CrebA seems to play a crucial role in reproduction and innate immunity.

Suppression of yolk formation, oviposition and egg quality of locust (Locusta migratoria manilensis) infected by Paranosema locustae.

Locusta migratoria manilensis is one of the most important agricultural pests in China. The locust has high fecundity and consumes large quantities of food, causing severe damage to diverse crops such as corn, sorghum, and rice. Immunity against pathogens and reproductive success are two important components of individual fitness, and many insects have a trade-off between reproduction and immunity when resources are limited, which may be an important target for pest control. In this study, adult females L. migratoria manilensis were treated with different concentrations (5 × 106 spores/mL or 2 × 107 spores/mL) of the entomopathogenic fungus Paranosema locustae. Effects of input to immunity on reproduction were studied by measuring feeding amount, enzyme activity, vitellogenin (Vg) and vitellogenin receptor (VgR) production, ovary development, and oviposition amount. When infected by P. locustae, feeding rate and phenol oxidase and lysozyme activities increased, mRNA expression of Vg and VgR genes decreased, and yolk deposition was blocked. Weight of ovaries decreased, with significant decreases in egg, length and weight.Thus, locusts used nutritive input required for reproduction to resist invasion by microsporidia. This leads to a decrease in expression of Vg and VgR genes inhibited ovarian development, and greatly decreased total fecundity. P. locustae at 2 × 107 spores/mL had a more obvious inhibitory effect on the ovarian development in migratory locusts. This study provides a detailed trade-off between reproduction and immune input of the female, which provides a reliable basis to find pest targets for biological control from those trade-off processes.

Involvement of glucose transporter 4 in ovarian development and reproductive maturation of Harmonia axyridis (Coleoptera: Coccinellidae).

Glucose is vital to embryogenesis, as are glucose transporters. Glucose transporter 4 (Glut4) is one of the glucose transporters, which is involved in rapid uptake of glucose by various cells and promotes glucose homeostasis. Although energy metabolism in insect reproduction is well known, the molecular mechanism of Glut4 in insect reproduction is poorly understood. We suspect that Glut4 is involved in maintaining glucose concentrations in the ovaries and affecting vitellogenesis, which is critical for subsequent oocyte maturation and insect fertility. Harmonia axyridis (Pallas) is a model organism for genetic research and a natural enemy of insect pests. We studied the influence of the Glut4 gene on the reproduction and development of H. axyridis using RNA interference technology. Reverse transcription quantitative polymerase chain reaction analysis revealed that HaGlut4 was most highly expressed in adults. Knockdown of the HaGlut4 gene reduced the transcript levels of HaGlut4, and the weight and number of eggs produced significantly decreased. In addition, the transcript levels of vitellogenin receptor and vitellogenin in the fat bodies and the ovaries of H. axyridis decreased after the interference of Glut4, and decreased the triglyceride, fatty acid, total amino acid and adenosine triphosphate content of H. axyridis. This resulted in severe blockage of ovary development and reduction of yolk formation; there was no development of ovarioles in the developing oocytes. These changes indicate that a lack of HaGlut4 can impair ovarian development and oocyte maturation and result in decreased fecundity.

GFAT and PFK genes show contrasting regulation of chitin metabolism in Nilaparvata lugens.

Glutamine:fructose-6-phosphate aminotransferase (GFAT) and phosphofructokinase (PFK) are enzymes related to chitin metabolism. RNA interference (RNAi) technology was used to explore the role of these two enzyme genes in chitin metabolism. In this study, we found that GFAT and PFK were highly expressed in the wing bud of Nilaparvata lugens and were increased significantly during molting. RNAi of GFAT and PFK both caused severe malformation rates and mortality rates in N. lugens. GFAT inhibition also downregulated GFAT, GNPNA, PGM1, PGM2, UAP, CHS1, CHS1a, CHS1b, Cht1-10, and ENGase. PFK inhibition significantly downregulated GFAT; upregulated GNPNA, PGM2, UAP, Cht2-4, Cht6-7 at 48 h and then downregulated them at 72 h; upregulated Cht5, Cht8, Cht10, and ENGase; downregulated Cht9 at 48 h and then upregulated it at 72 h; and upregulated CHS1, CHS1a, and CHS1b. In conclusion, GFAT and PFK regulated chitin degradation and remodeling by regulating the expression of genes related to the chitin metabolism and exert opposite effects on these genes. These results may be beneficial to develop new chitin synthesis inhibitors for pest control.

Regulatory Functions of Nilaparvata lugens GSK-3 in Energy and Chitin Metabolism.

Glucose metabolism is a biologically important metabolic process. Glycogen synthase kinase (GSK-3) is a key enzyme located in the middle of the sugar metabolism pathway that can regulate the energy metabolism process in the body through insulin signaling. This paper mainly explores the regulatory effect of glycogen synthase kinase on the metabolism of glycogen and trehalose in the brown planthopper (Nilaparvata lugens) by RNA interference. In this paper, microinjection of the target double-stranded GSK-3 (dsGSK-3) effectively inhibited the expression of target genes in N. lugens. GSK-3 gene silencing can effectively inhibit the expression of target genes (glycogen phosphorylase gene, glycogen synthase gene, trehalose-6-phosphate synthase 1 gene, and trehalose-6-phosphate synthase 2 gene) in N. lugens and trehalase activity, thereby reducing glycogen and glucose content, increasing trehalose content, and regulating insect trehalose balance. GSK-3 can regulate the genes chitin synthase gene and glucose-6-phosphate isomerase gene involved in the chitin biosynthetic pathway of N. lugens. GSK-3 gene silencing can inhibit the synthesis of chitin N. lugens, resulting in abnormal phenotypes and increased mortality. These results indicated that a low expression of GSK-3 in N. lugens can regulate the metabolism of glycogen and trehalose through the insulin signal pathway and energy metabolism pathway, and can regulate the biosynthesis of chitin, which affects molting and wing formation. The relevant research results will help us to more comprehensively explore the molecular mechanism of the regulation of energy and chitin metabolism of insect glycogen synthase kinases in species such as N. lugens.

Role of phosphoglucomutase in regulating trehalose metabolism in Nilaparvata lugens.

Phosphoglucomutase (PGM) is a key enzyme in glycolysis and gluconeogenesis, regulating both glycogen and trehalose metabolism in insects. In this study, we explored the potential function of phosphoglucomutase (PGM) using RNA interference technology in Nilaparvata lugens, the brown planthopper. PGM1 and PGM2 were found highly expressed in the midgut of brown planthoppers, with different expression levels in different instar nymphs. The glycogen, glucose, and trehalose levels were also significantly increased after brown planthoppers were injected with dsRNA targeting PGM1 (dsPGM1) or PGM2 (dsPGM2). In addition, injection of dsPGM1 or dsPGM2 resulted in increased membrane-bound trehalase activity but not soluble trehalase activity. Furthermore, the expression of genes related to trehalose and glycogen metabolism decreased significantly after injection with dsPGM1 and dsPGM2. The expression levels of genes involved in chitin metabolism in the brown planthopper were also significantly decreased and the insects showed wing deformities and difficulty molting following RNAi. We suggest that silencing of PGM1 and PGM2 expression directly inhibits trehalose metabolism, leading to impaired chitin synthesis.

Evaluation of the Expression and Function of the TRE2-like and TRE2 Genes in Ecdysis of Harmonia axyridis.

Harmonia axyridis is an important predatory insect and widely used in biological control of agricultural and forestry pests. Trehalose is directly involved in the energy storage of the H. axyridis and in the oxidative function of various physiological activities thereby providing an energy source for its growth and development. The aim of this study was to explore the potential function of membrane-bound-like trehalase (TRE2-like) and membrane-bound trehalase (TRE2) genes in H. axyridis by RNAi. In addition, the activity of soluble and membrane-bound trehalase and the expression of genes related to trehalose and glycogen metabolism were determined in the larvae injected with dsTRE2-like or dsTRE2. The results showed that wing abnormality and mortality appeared in adults, as well as the activity of soluble trehalase and glycogen contents increased when interfering with TRE2-like gene. However, the activity of membrane-bound trehalase, trehalose and glucose contents in the larvae decreased. The expression of glycogen synthase (GS) and glycogen phosphorylase (GP) genes were decreased after RNAi in the ecdysis stage. The expression of chitin synthase gene A (CHSA), chitin synthase gene B (CHSB), and trehalose-6-phosphate synthase genes (TPS) were decreased significantly after RNAi, especially in the ecdysis stage. These results indicated that RNA interference is capable of knocking down gene expression of TRE2-like and TRE2, thereby disrupting trehalose metabolism which affects the chitin synthesis pathway in turn and also leads to developmental defects, such as wing deformities. This study could provide some theoretical guidance for the function of TRE2 gene in other insects.

Three novel trehalase genes from Harmonia axyridis (Coleoptera: Coccinellidae): cloning and regulation in response to rapid cold and re-warming.

Trehalose is the main blood sugar in insects. To study the function of trehalase during exposure to low temperatures, three other novel cDNAs of trehalase were cloned from Harmonia axyridis by transcriptome sequencing and rapid amplification of cDNA ends. One of the cloned cDNAs encoded a soluble trehalase, the second trehalase cDNA encoded a transmembrane-like domain, and the third cDNA encoded a membrane-bound protein. Therefore, these cDNAs were, respectively, named HaTreh1-5, HaTreh2-like, and HaTreh2. HaTreh1-5, HaTreh2-like, and HaTreh2 cDNAs encoded proteins containing 586, 553, and 633 amino acids with predicted masses of approximately 69.47, 63.46, and 73.66 kDa, and pIs of 9.20, 5.52, and 6.31, respectively. All three novel trehalases contained signal motifs "PGGINKESYYLDSY", "QWDYPNAWPP", and a highly conserved glycine-rich (GGGGEY) region. The expression levels of HaTreh1-5 and HaTreh2 mRNAs were high during adult stages, whereas HaTreh2-like was expressed in low amounts in the fourth larval stage. The results showed that the activity of membrane-bound trehalases decreased from 25 to 10 °C and from 5 to - 5 °C during cooling. The results also revealed a decreasing trend in expression of the three HaTreh mRNAs during the cooling treatment, and an initial decrease followed by an increase during the process of re-warming.

Invertebrate Trehalose-6-Phosphate Synthase Gene: Genetic Architecture, Biochemistry, Physiological Function, and Potential Applications.

The non-reducing disaccharide trehalose is widely distributed among various organisms. It plays a crucial role as an instant source of energy, being the major blood sugar in insects. In addition, it helps countering abiotic stresses. Trehalose synthesis in insects and other invertebrates is thought to occur via the trehalose-6-phosphate synthase (TPS) and trehalose-6-phosphate phosphatase (TPP) pathways. In many insects, the TPP gene has not been identified, whereas multiple TPS genes that encode proteins harboring TPS/OtsA and TPP/OtsB conserved domains have been found and cloned in the same species. The function of the TPS gene in insects and other invertebrates has not been reviewed in depth, and the available information is quite fragmented. The present review discusses the current understanding of the trehalose synthesis pathway, TPS genetic architecture, biochemistry, physiological function, and potential sensitivity to insecticides. We note the variability in the number of TPS genes in different invertebrate species, consider whether trehalose synthesis may rely only on the TPS gene, and discuss the results of in vitro TPS overexpression experiment. Tissue expression profile and developmental characteristics of the TPS gene indicate that it is important in energy production, growth and development, metamorphosis, stress recovery, chitin synthesis, insect flight, and other biological processes. We highlight the molecular and biochemical properties of insect TPS that make it a suitable target of potential pest control inhibitors. The application of trehalose synthesis inhibitors is a promising direction in insect pest control because vertebrates do not synthesize trehalose; therefore, TPS inhibitors would be relatively safe for humans and higher animals, making them ideal insecticidal agents without off-target effects.

Study on the Effect of Wing Bud Chitin Metabolism and Its Developmental Network Genes in the Brown Planthopper, Nilaparvata lugens, by Knockdown of TRE Gene.

The brown planthopper, Nilaparvata lugens is one of the most serious pests of rice, and there is so far no effective way to manage this pest. However, RNA interference not only can be used to study gene function, but also provide potential opportunities for novel pest management. The development of wing plays a key role in insect physiological activities and mainly involves chitin. Hence, the regulating role of trehalase (TRE) genes on wing bud formation has been studied by RNAi. In this paper, the activity levels of TRE and the contents of the two sugars trehalose and glucose were negatively correlated indicating the potential role of TRE in the molting process. In addition, NlTRE1-1 and NlTRE2 were expressed at higher levels in wing bud tissue than in other tissues, and abnormal molting and wing deformity or curling were noted 48 h after the insect was injected with any double-stranded TRE (dsTRE), even though different TREs have compensatory functions. The expression levels of NlCHS1b, NlCht1, NlCht2, NlCht6, NlCht7, NlCht8, NlCht10, NlIDGF, and NlENGase decreased significantly 48 h after the insect was injected with a mixture of three kinds of dsTREs. Similarly, the TRE inhibitor validamycin can inhibit NlCHS1 and NlCht gene expression. However, the wing deformity was the result of the NlIDGF, NlENGase, NlAP, and NlTSH genes being inhibited when a single dsTRE was injected. These results demonstrate that silencing of TRE gene expression can lead to wing deformities due to the down-regulation of the AP and TSH genes involved in wing development and that the TRE inhibitor validamycin can co-regulate chitin metabolism and the expression of wing development-related genes in wing bud tissue. The results provide a new approach for the prevention and management of N. lugens.

Effects of starvation on the carbohydrate metabolism in Harmonia axyridis (Pallas).

Trehalose plays an important role in energy storage, metabolism, and protection from extreme environmental conditions in insects. Trehalose is the main blood sugar in insects, and it can be rapidly used as an energy source in times of need. To elucidate the mechanisms of the starvation response, we observed the effects of starvation on trehalose and glycogen, trehalase activity, and the relative gene expression of genes in the trehalose and glycogen metabolic pathways in the invasive beetle Harmonia axyridis Our results show that trehalose levels and the activities of two types of trehalases decreased significantly in the first 8 h of starvation, while the relative expression of HaTreh1-1 increased. While trehalose remained nearly constant at a relatively high level from 8 to 24 h, glycogen levels decreased significantly from 8 h to 24 h of starvation. Likewise, glycogen phosphorylase (HaGP) expression was significantly higher at 12 to 24 h starvation than the first 8 h, while the expression of glycogen synthase (HaGS) was relatively stable. Furthermore, trehalose decreased significantly from 24 h starvation to 72 h starvation, while trehalase activities and the relative expression of some HaTreh genes generally increased toward the end of the starvation period. The expression of trehalose-6-phosphate synthase (HaTPS) increased significantly, supporting the increase in trehalose synthesis. These results show that trehalose plays a key role in the energy provided during the starvation process through the molecular and biochemical regulation of trehalose and glycogen metabolism.

Molecular Cloning and Induced Expression of Six Small Heat Shock Proteins Mediating Cold-Hardiness in Harmonia axyridis (Coleoptera: Coccinellidae).

The main function of small heat shock proteins (sHSPs) as molecular chaperones is to protect proteins from denaturation under adverse conditions. Molecular and physiological data were used to examine the sHSPs underlying cold-hardiness in Harmonia axyridis. Complementary DNA sequences were obtained for six H. axyridis sHSPs based on its transcriptome, and the expression of the genes coding for these sHSPs was evaluated by quantitative real-time PCR (qRT-PCR) in several developmental stages, under short-term cooling or heating conditions, and in black and yellow females of experimental and overwintering populations under low-temperature storage. In addition, we measured water content and the super cooling and freezing points (SCP and FP, respectively) of H. axyridis individuals from experimental and overwintering populations. The average water content was not significantly different between adults of both populations, but the SCP and FP of the overwintering population were significantly lower than that of the experimental population. Overall, the six sHSPs genes showed different expression patterns among developmental stages. In the short-term cooling treatment, Hsp16.25 and Hsp21.00 expressions first increased and then decreased, while Hsp10.87 and Hsp21.56 expressions increased during the entire process. Under short-term heating, the expressions of Hsp21.00, Hsp21.62, Hsp10.87, and Hsp16.25 showed an increasing trend, whereas Hsp36.77 first decreased and then increased. Under low-temperature storage conditions, the expression of Hsp36.77 decreased, while the expressions of Hsp21.00 and Hsp21.62 were higher than that of the control group in the experimental population. The expression of Hsp36.77 first increased and then decreased, whereas Hsp21.56 expression was always higher than that of the control group in the overwintering population. Thus, differences in sHSPs gene expression were correlated with the H. axyridis forms, suggesting that the mechanism of cold resistance might differ among them. Although, Hsp36.77, Hsp16.25, Hsp21.00, and Hsp21.62 regulated cold- hardiness, the only significant differences between overwintering and experimental populations were found for Hsp16.25 and Hsp21.00.

Transcriptome analysis and identification of induced genes in the response of Harmonia axyridis to cold hardiness.

Harmonia axyridis is an important predatory lady beetle that is a natural enemy of agricultural and forestry pests. In this research, the cold hardiness induced genes and their expression changes in H. axyridis were screened and detected by the way of the transcriptome and qualitative real-time PCR under normal and low temperatures, using high-throughput transcriptome and digital gene-expression-tag technologies. We obtained a 10Gb transcriptome and an 8Mb gene expression tag pool using Illumina deep sequencing technology and RNA-Seq analysis (accession number SRX540102). Of the 46,980 non-redundant unigenes identified, 28,037 (59.7%) were matched to known genes in GenBank, 21,604 (46.0%) in Swiss-Prot, 19,482 (41.5%) in Kyoto Encyclopedia of Genes and Genomes and 13,193 (28.1%) in Gene Ontology databases. Seventy-five percent of the unigene sequences had top matches with gene sequences from Tribolium castaneum. Results indicated that 60 genes regulated the entire cold-acclimation response, and, of these, seven genes were always up-regulated and five genes always down-regulated. Further screening revealed that six cold-resistant genes, E3 ubiquitin-protein ligase, transketolase, trehalase, serine/arginine repetitive matrix protein 2, glycerol kinase and sugar transporter SWEET1-like, play key roles in the response. Expression from a number of the differentially expressed genes was confirmed with quantitative real-time PCR (HaCS_Trans). The paper attempted to identify cold-resistance response genes, and study the potential mechanism by which cold acclimation enhances the insect's cold endurance. Information on these cold-resistance response genes will improve the development of low-temperature storage technology of natural enemy insects for future use in biological control.

Elongation factor 1ß' gene from Spodoptera exigua: characterization and function identification through RNA interference.

Elongation factor (EF) is a key regulation factor for translation in many organisms, including plants, bacteria, fungi, animals and insects. To investigate the nature and function of elongation factor 1ß' from Spodoptera exigua (SeEF-1ß'), its cDNA was cloned. This contained an open reading frame of 672 nucleotides encoding a protein of 223 amino acids with a predicted molecular weight of 24.04 kDa and pI of 4.53. Northern blotting revealed that SeEF-1ß' mRNA is expressed in brain, epidermis, fat body, midgut, Malpighian tubules, ovary and tracheae. RT-PCR revealed that SeEF-1ß' mRNA is expressed at different levels in fat body and whole body during different developmental stages. In RNAi experiments, the survival rate of insects injected with SeEF-1ß' dsRNA was 58.7% at 36 h after injection, which was significantly lower than three control groups. Other elongation factors and transcription factors were also influenced when EF-1ß' was suppressed. The results demonstrate that SeEF-1ß' is a key gene in transcription in S. exigua.