Knockdown of a putative argininosuccinate lyase gene reduces arginine content and impairs nymphal development in Nilaparvata lugens

Nilaparvata lugens is a typical phloem feeder. Rice phloem is high in simple sugars and very low in essential amino acids. Nilaparvata lugens harbors an ascomycete Entomomyces delphacidicola that hypothetically biosynthesizes several amino acids to meet the nutrition requirement of the planthopper. Among these amino acids, here, we focused on arginine biosynthesis. A complete cDNA of an E. delphacidicola gene, arginine-succinate lyase, EdArg4, the last step in arginine biosynthesis, was obtained. RNAi-mediated suppression of EdArg4 reduced arginine content in the hemolymph, and decreased the expression of several arginine biosynthesis genes. Silencing of EdArg4 delayed nymphal development and led to nymphal lethality. About 20% of the EdArg4 RNAi surviving adults were deformed. The most obvious defect was wider and larger abdomen. The EdArg4 RNAi-treated planthoppers had thickened wings and enlarged antennae, legs, and anal tubes and a few adults did not normally emerge. Arginine deficiency in the EdArg4 RNAi planthoppers repressed nitric oxide signaling, determined at the transcriptional level. We infer that E. delphacidicola biosynthesizes essential arginine to compensate for nutrition deficiency in N. lugens.

Cryptic Species Identification and Composition of Bemisia tabaci (Hemiptera: Aleyrodidae) Complex in Henan Province, China

Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) is a cryptic species complex, causing significant crop losses in China during the last decade. Although knowledge of cryptic species composition and dynamics within B. tabaci complex is critical for developing sustainable pest management strategies, limited information is available on this pest in the Henan province of China. A systematic survey of the cryptic species composition and distribution of B. tabaci complex in different locations of Henan province was conducted in 2012. The results of RAPD-PCR and the gene for the mitochondrial cytochrome oxidase subunit-1 (mtCOI) based phylogenetic relationships established using Bayesian method indicated there were four known cryptic species MEAM1, MED, Asia II 3, Asia II 9 and a new cryptic species named China 6 in Henan province. In the survey, the invasive cryptic species MED and MEAM1 were found to be predominant with wide spread distribution across the surveyed regions. On the contrary, the indigenous B. tabaci cryptic species including Asia II 3, Asia II 9 and China 6 remained with low prevalence in some surveyed regions. Cryptic species MEAM1 and MED have not completely displaced the native B. tabaci in Henan province. This current study for the first time unifies our knowledge of the diversity and distribution of B. tabaci across Henan province of China.

Differential transcriptome analysis supports Rhodnius montenegrensis and Rhodnius robustus (Hemiptera, Reduviidae, Triatominae) as distinct species

Chagas disease is one of the main parasitic diseases found in Latin America and it is estimated that between six and seven million people are infected worldwide. Its etiologic agent, the protozoan Trypanosoma cruzi, is transmitted by triatomines, some of which from the genus Rhodnius. Twenty species are currently recognized in this genus, including some closely related species with low levels of morphological differentiation, such as Rhodnius montenegrensis and Rhodnius robustus. In order to investigate genetic differences between these two species, we generated large-scale RNA-sequencing data (consisting of four RNA-seq libraries) from the heads and salivary glands of males of R. montenegrensis and R. robustus. Transcriptome assemblies produced for each species resulted in 64,952 contigs for R. montenegrensis and 70,894 contigs for R. robustus, with N50 of approximately 2,100 for both species. SNP calling based on the more complete R. robustus assembly revealed 3,055 fixed interspecific differences and 216 transcripts with high levels of divergence which contained only fixed differences between the two species. A gene ontology enrichment analysis revealed that these highly differentiated transcripts were enriched for eight GO terms related to AP-2 adaptor complex, as well as other interesting genes that could be involved in their differentiation. The results show that R. montenegrensis and R. robustus have a substantial quantity of fixed interspecific polymorphisms, which suggests a high degree of genetic divergence between the two species and likely corroborates the species status of R. montenegrensis.

Phylogeny and historical biogeography of leafhopper subfamily Evacanthinae (Hemiptera: Cicadellidae) based on morphological and molecular data

Phylogenetic relationships among major lineages of the Evacanthinae, a highly diverse leafhopper subfamily distributed worldwide, were explored by analysing a dataset of 100 discrete morphological characters and DNA sequence data from five gene regions. Sixty-seven taxa representing all evacanthine tribes and all regional faunas, and fourteen putative outgroup taxa were included. Maximum-likelihood and Bayesian analyses yielded similar tree topologies that were well resolved with strong support for the monophyly of Evacanthinae and its four previously included tribes, but indicated that Draconirvana Dietrich, was incorrectly placed to tribe and that Sophonia Walker, Evacanthus Le Peletier &Serville, Bundera Distant, Paraonukia Ishihara and Onukia Matsumura are not monophyletic. Divergence time analysis suggests that the deepest divergences coincided with breakup of Gondwana but that more recent divergences occurred largely within a single biogeographic realm during the Paleogene, with a few long-distance dispersal events. Biogeographical analyses suggest that Evacanthinae originated in Neotropical region. A new tribe, Pentoffiini trib.n., is established to include Pentoffia Kramer and Evanirvana Hill, the genus Draconirvana Dietrich, placement n. is transferred to Evacanthini from Nirvanini, a key to tribes is also given and illustrations of representative genera are provided.

Effect of RNAi-mediated knockdown of NlTOR gene on fertility of male Nilaparvata lugens

The target gene of rapamycin (TOR) is conserved from invertebrates to vertebrates, and plays critical roles in cell growth, nutrient sensing, lifespan and reproduction. In this paper, we employed RNA interference (RNAi) to study the function of TOR in male brown planthoppers (BPH), Nilaparvata lugens. Here we discovered that no offspring was produced when wildtype females BPH mated with NlTOR RNAi males. To understand the influence of NlTOR on male BPH infertility, we dissected the reproductive system of a NlTOR RNAi male, and found that the testes were normal and the seminal vesicles were full of sperm, while the accessory gland was poorly developed after knocking down NlTOR expression. Furthermore, transmission electron microscopy data showed defective structure of epithelial cells of the accessory gland, and the deferent duct was collapsed. Also, behavioral data revealed that wildtype virgin females refused to mate with NlTOR RNAi males, and the acoustic signals of dsNlTOR males differed from controls. Our results indicate that NlTOR plays an essential role in the development of the male BPH reproductive system and regulates mating behavior.

Identification and expression analyses of vitellogenin in Bactericera cockerelli (Šulc)

The potato psyllid, Bactericera cockerelli (Šulc) (Hemiptera: Triozidae), is a phloem-feeding insect with preference for Solanaceae. This insect species is vector of the pathogenic bacteria 'Candidatus Liberibacter solanacearum' the causative agent of zebra chip, an important disease of commercial potatoes in several countries worldwide. The recent classification of psyllids among the most dangerous vectors has promoted their study, but still many biological processes such as reproduction and vitellogenesis need to be investigated. As a first step towards the elucidation of vitellogenesis in B. cockerelli, one candidate vitellogenin transcript (6622 bases long) was identified and the expression of the transcript and the protein were analyzed in virgin and mated females between 1 and 7days old. In virgin females, Vg expression increased up to 5days old; while mating significantly up-regulated Vg expression in 5- and 7-day-old females. To determine the role of juvenile hormone in B. cockerelli Vg expression, topical applications of juvenile hormone III were performed on virgin females, resulting in an up-regulation of Vg expression and an increase in the number of mature oocytes present in female reproductive organs. Overall, this study represents the first step to understand vitellogenesis of B. cockerelli and it highlights the role of JH III in the hormonal regulation of Vg expression and oocyte development.

Use of the synergist piperonyl butoxide can slow the development of alpha-cypermethrin resistance in the whitefly Bemisia tabaci

The development of insecticide resistance in insect pests of crops is a growing threat to sustainable food production, and strategies that slow the development of resistance are therefore urgently required. The insecticide synergist piperonyl butoxide (PBO) inhibits certain insect detoxification systems and so may delay the evolution of metabolic resistance. In the current study we characterized resistance development in the silverleaf whitefly, Bemisia tabaci, after selection with either a neonicotinoid (thiacloprid) or pyrethroid (alpha-cypermethrin) insecticide alone or in combination with PBO. Resistance development was significantly suppressed (> 60%) in the line selected with alpha-cypermethrin + PBO compared to the line selected with alpha-cypermethrin alone. RNA sequencing (RNAseq) analyses revealed an increase in frequency of a knock-down resistance mutation but no differentially expressed genes were identified that could explain the sensitivity shift. No significant difference was observed in the level of resistance between the thiacloprid and thiacloprid + PBO selected lines, and RNA sequencing (RNAseq) analyses revealed that the cytochrome P450 monooxygenase CYP6CM1, known to metabolize neonicotinoids, was significantly upregulated (>10-fold) in both lines. The findings of this study demonstrate that PBO used in combination with certain insecticides can suppress the development of resistance in a laboratory setting; however, the mechanism by which PBO supresses resistance development remains unclear.

Oral delivery of double-stranded RNAs induces mortality in nymphs and adults of the Asian citrus psyllid, Diaphorina citri

The Asian citrus psyllid (ACP), Diaphorina citri Kuwayama, is one of the most important citrus pests. ACP is the vector of the phloem-limited bacteria Candidatus Liberibacter americanus and Candidatus Liberibacter asiaticus, the causal agents of the devastating citrus disease huanglongbing (HLB). The management of HLB is based on the use of healthy young plants, eradication of infected plants and chemical control of the vector. RNA interference (RNAi) has proven to be a promising tool to control pests and explore gene functions. Recently, studies have reported that target mRNA knockdown in many insects can be induced through feeding with double-stranded RNA (dsRNA). In the current study, we targeted the cathepsin D, chitin synthase and inhibitor of apoptosis genes of adult and nymph ACP by feeding artificial diets mixed with dsRNAs and Murraya paniculata leaves placed in dsRNAs solutions, respectively. Adult ACP mortality was positively correlated with the amount of dsRNA used. Both nymphs and adult ACP fed dsRNAs exhibited significantly increased mortality over time compared with that of the controls. Moreover, qRT-PCR analysis confirmed the dsRNA-mediated RNAi effects on target mRNAs. These results showed that RNAi can be a powerful tool for gene function studies in ACP and perhaps for HLB control.

Expression pattern and pharmacological characterisation of two novel alternative splice variants of the glutamate-gated chloride channel in the small brown planthopper Laodelphax striatellus

BACKGROUND

Glutamate-gated chloride channels (GluCl) mediate fast inhibitory neurotransmission in invertebrate nervous systems. Although only one GluCl gene was presented in insects, it showed diverse alternative splicing that was speculated could affect channel function and pharmacology.

RESULTS

In this study, we isolated GluCl cDNAs from adults of the small brown planthopper (SBPH) Laodelphax striatellus and showed that six L. striatellus GluCl variants (LsGluCl-AS, LsGluCl-BS, LsGluCl-CS, LsGluCl-AL, LsGluCl-BL, LsGluCl-CL) were present in the SBPH. The expression patterns of six variants differed among developmental stages (egg, first- to fifth-instar nymphs, male and female adults) and among the body parts (head, thorax, abdomen, leg) of the female adult SBPH. All the transcripts were abundant in the head of the adult. When expressed in African clawed frog, Xenopus laevis, oocytes, the two functional variants (LsGluCl-AS, LsGluCl-AL) had similar EC₅₀ and IC₅₀ values for L-glutamate and channel blockers picrotoxinin and fipronil.

CONCLUSION

This study represents a comprehensive molecular, expression and pharmacological characterisation of GluCl in the SBPH. These findings should be useful in providing more opportunities to discover novel insect control chemicals. © 2016 Society of Chemical Industry.

Lack of cross-resistance between neonicotinoids and sulfoxaflor in field strains of Q-biotype of whitefly, Bemisia tabaci, from eastern China

Control of Bemisia tabaci has depended primarily and heavily on insecticides, especially neonicotinoids. The novel sulfoximine insecticide sulfoxaflor exhibits high potency against a broad range of sap-feeding insect species, including those resistant to neonicotinoids. The resistance levels of Q-biotype B. tabaci field strains collected from 8 locations in eastern China to neonicotinoids and sulfoxaflor were investigated, and single nucleotide polymorphisms (SNPs) of nicotinic acetylcholine receptor β1 subunit gene (Btβ1) were detected. Compared with the reference strain, the field strains had developed low to moderate levels of resistance to imidacloprid and nitenpyram with the resistance ratios (RR) ranging between 4.07 and 21.75-fold and 3.37 and 16.14-fold, respectively. While YZ strain exhibited high resistance (RF 40.38) to thiamethoxam, only low levels of resistance to thiamethoxam (RF 3.50-8.58) was observed in other strains. All strains were relatively susceptible to both dinotefuran (RF 0.50-2.55) and sulfoxaflor (RF 0.40-3.07). Sequence analysis of Btβ1 cDNA fragments revealed 23 SNPs representing 19 amino acid replacements in these strains. Notably, a 45bp fragment deletion was detected in JY strain, which encodes 15 amino acid residues (positions 66-80) containing arginine at position 79 (R79) corresponding to the R81T mutation in Loop D of nAChR β1 subunit in Myzus persicae resistant to neonicotinoids. The lack of cross-resistance indicates that both dinotefuran and sulfoxaflor could play an important role in the control of B. tabaci already resistant to the first and second generation neonicotinoids.

Effects of high temperature on life history traits and heat shock protein expression in chlorpyrifos-resistant Laodelphax striatella

The resistance of the small brown planthopper (SBPH), Laodelphax striatella, to insecticides has been widely found in China, and has posed serious problems to efforts to control the pest. To determine the costs and benefits of resistance, the life tables of chlorpyrifos-resistant and -susceptible strains were constructed at 24 and 30°C. The results showed the resistant SBPH (YN-CPF) had lower fitness at 24°C, but slightly higher fitness at 30°C compared to the susceptible SBPH. Transcriptomic analysis showed there are five heat shock protein genes changed their expression, and the up-regulated genes are LsHsc70-1 and LsHsc70-2. The deduced amino acid sequences of LsHsc70-1 and LsHsc70-2 include three heat shock protein 70 (HSP70) family signatures, but LsHSC70-1 has the conserved HSP70 carboxyl terminal region of the "EEVD" motif, while LsHSC70-2 has the endoplasmic reticulum (ER) retention signal of the "KDEL" motif. The phylogenetic tree further identified LsHsc70-1 has closer evolutionary distances to cytoplasmic/nuclear HSP70s from human and Drosophila melanogaster, while LsHsc70-2 has closer evolutionary distances to HSP70s localized to ER. After treatment at 30-44°C, the expression of LsHsc70-1 and LsHsc70-2 was slightly increased in YN-CPF. These results suggested that LsHsc70-1 and LsHsc70-2 are members of Hsc70 family, localized to the cytosol/nucleus and ER, respectively. The up-regulated expression of these genes may protect the chlorpyrifos-resistant pest against damage under high temperatures, increasing its relative fitness, but the lower relative fitness of this population under optimal temperature may be the trade-off.

A Salivary Endo-β-1,4-Glucanase Acts as an Effector That Enables the Brown Planthopper to Feed on Rice

The brown planthopper (BPH) Nilaparvata lugens is one of the most destructive insect pests on rice (Oryza sativa) in Asia. After landing on plants, BPH rapidly accesses plant phloem and sucks the phloem sap through unknown mechanisms. We discovered a salivary endo-β-1,4-glucanase (NlEG1) that has endoglucanase activity with a maximal activity at pH 6 at 37°C and is secreted into rice plants by BPH NlEG1 is highly expressed in the salivary glands and midgut. Silencing NlEG1 decreases the capacity of BPH to reach the phloem and reduces its food intake, mass, survival, and fecundity on rice plants. By contrast, NlEG1 silencing had only a small effect on the survival rate of BPH raised on artificial diet. Moreover, NlEG1 secreted by BPH did not elicit the production of the defense-related signal molecules salicylic acid, jasmonic acid, and jasmonoyl-isoleucine in rice, although wounding plus the application of the recombination protein NlEG1 did slightly enhance the levels of jasmonic acid and jasmonoyl-isoleucine in plants compared with the corresponding controls. These data suggest that NlEG1 enables the BPH's stylet to reach the phloem by degrading celluloses in plant cell walls, thereby functioning as an effector that overcomes the plant cell wall defense in rice.

Molecular characterization and expression pattern of three GABA receptor-like subunits in the small brown planthopper Laodelphax striatellus (Hemiptera: Delphacidae)

Ionotropic γ-aminobutyric acid (GABA)-gated chloride channel receptors mediate rapid inhibitory neurotransmission in vertebrates and invertebrates. GABA receptors are well known to be the molecular targets of synthetic insecticides or parasiticides. Three GABA receptor-like subunits, LsLCCH3, LsGRD and LS8916, of the small brown planthopper, Laodelphax striatellus (Fallén), a major insect pest of crop systems in East Asia, had been identified and characterized in this study. All three genes were cloned using the reverse transcriptase polymerase chain reaction (RT-PCR) and rapid amplification of cDNA ends (RACE). They shared common structural features with known Cys-loop ligand-gated ion channels (LGICs): the well-conserved dicysteine-loop structures, an extracellular N-terminal domain containing six distinct regions (loops A-F) that form the ligand binding sites and four transmembrane regions (TM1-4). Additionally, temporal and spatial transcriptional profiling analysis indicated that Lslcch3 was significantly higher than the other two genes. All of them were expressed at higher levels in fifth-instar nymph and adults than in eggs and from first- to fourth-instar nymph. They were predominantly expressed in the heads of 2-d old female adults. These findings enhanced our understanding of cys-loop LGIC functional characterization in Hemiptera and provided a useful basis for the development of improved insecticides that targeting this important agricultural pest.

RNA interference of carboxyesterases causes nymph mortality in the Asian citrus psyllid, Diaphorina citri

Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Liviidae), is an important pest of citrus. In addition, D. citri is the vector of Huanglongbing, a destructive disease in citrus, also known as citrus greening disease caused by Candidatus Liberibacter asiaticus. Huanglongbing causes huge losses for citrus industries. Insecticide application for D. citri is the major strategy to prevent disease spread. The heavy use of insecticides causes development of insecticide resistance. We used RNA interference (RNAi) to silence genes implicated in pesticide resistance in order to increase the susceptibility. The activity of dsRNA to reduce the expression of carboxyesterases including esterases FE4 (EstFE4) and acetylcholinesterases (AChe) in D. citri was investigated. The dsRNA was applied topically to the fourth and fifth instars of nymphs. We targeted several EstFE4 and AChe genes using dsRNA against a consensus sequence for each of them. Five concentrations (25, 50, 75, 100, 125 ng/μl) from both dsRNAs were used. The treatments with the dsRNA caused concentration dependent nymph mortality. The highest gene expression levels of both AChe and EstFE4 were found in the fourth and fifth nymphal instars. Gene expression analysis showed that AChe genes were downregulated in emerged adults from dsRNA-AChe-treated nymphs compared to controls. However, EstFE4 genes were not affected. In the same manner, treatment with dsRNA-EstFE4 reduced expression level of EstFE4 genes in emerged adults from treated nymphs, but did not affect the expression of AChe genes. In the era of environmentally friendly control strategies, RNAi is a new promising venue to reduce pesticide applications.

Metabolic resistance in Nilaparvata lugens to etofenprox, a non-ester pyrethroid insecticide

Etofenprox, a non-ester pyrethroid insecticide, will be registered to control rice pests such as the brown planthopper (BPH, Nilaparvata lugens Stål) in mainland China. Insecticide resistance is always a problem to the effective control of N. lugens by chemical insecticides. An etofenprox resistance selection of N. lugens was performed in order to understand the related mechanisms. Through successive selection by etofenprox for 16 generations in the laboratory, an etofenprox-resistant strain (G16) with the resistance ratio (RR) of 422.3-fold was obtained. The resistance was partly synergised (2.68-fold) with the metabolic inhibitor PBO, suggesting a role for P450 monooxygenases. In this study, 11 P450 genes were significantly up-regulated in G16, among which eight genes was above 2.0-fold higher than that in US16, a population with the same origin of G16 but without contacting any insecticide in the laboratory. The expression level of four genes (CYP6AY1, CYP6FU1 and CYP408A1 from Clade 3, and CYP425A1 from Clade 4) were above 4.0-fold when compared to US16. RNA interference (RNAi) was performed to evaluate the importance of the selected P450s in etofenprox resistance. When CYP6FU1, CYP425A1 or CYP6AY1 was interfered, the susceptibility was significantly recovered in both G16 and US16, while the knockdown of CYP408A1 or CYP353D1 did not cause significant changes in etofenprox susceptibility. We supposed that CYP6FU1 was the most important P450 member for etofenprox resistance because of the highest expression level and the most noticeable effects on resistance ratios following RNAi.

Ras-like family small GTPases genes in Nilaparvata lugens: Identification, phylogenetic analysis, gene expression and function in nymphal development

Twenty-nine cDNAs encoding Ras-like family small GTPases (RSGs) were cloned and sequenced from Nilaparvata lugens. Twenty-eight proteins are described here: 3 from Rho, 2 from Ras, 9 from Arf and 14 from Rabs. These RSGs from N.lugens have five conserved G-loop motifs and displayed a higher degree of sequence conservation with orthologues from insects. RT-qPCR analysis revealed NlRSGs expressed at all life stages and the highest expression was observed in hemolymph, gut or wing for most of NlRSGs. RNAi demonstrated that eighteen NlRSGs play a crucial role in nymphal development. Nymphs with silenced NlRSGs failed to molt, eclosion or development arrest. The qRT-PCR analysis verified the correlation between mortality and the down-regulation of the target genes. The expression level of nuclear receptors, Kr-h1, Hr3, FTZ-F1 and E93 involved in 20E and JH signal pathway was impacted in nymphs with silenced twelve NlRSGs individually. The expression of two halloween genes, Cyp314a1 and Cyp315a1 involved in ecdysone synthesis, decreased in nymphs with silenced NlSar1 or NlArf1. Cyp307a1 increased in nymphs with silenced NlArf6. In N.lugens with silenced NlSRβ, NlSar1 and NlRab2 at 9^th day individually, 0.0% eclosion rate and almost 100.0% mortality was demonstrated. Further analysis showed NlSRβ could be served as a candidate target for dsRNA-based pesticides for N.lugens control.

Identification and expression profile analysis of odorant binding protein and chemosensory protein genes in Bemisia tabaci MED by head transcriptome

Odorant binding proteins (OBPs) and chemosensory proteins (CSPs) of arthropods are thought to be involved in chemical recognition which regulates pivotal behaviors including host choice, copulation and reproduction. In insects, OBPs and CSPs located mainly in the antenna but they have not been systematically characterized yet in Bemisia tabaci which is a cryptic species complex and could damage more than 600 plant species. In this study, among the 106,893 transcripts in the head assembly, 8 OBPs and 13 CSPs were identified in B. tabaci MED based on head transcriptomes of adults. Phylogenetic analyses were conducted to investigate the relationships of B. tabaci OBPs and CSPs with those from several other important Hemipteran species, and the motif-patterns between Hemiptera OBPs and CSPs were also compared by MEME. The expression profiles of the OBP and CSP genes in different tissues of B. tabaci MED adults were analyzed by real-time qPCR. Seven out of the 8 OBPs found in B. tabaci MED were highly expressed in the head. Conversely, only 4 CSPs were enriched in the head, while the other nine CSPs were specifically expressed in other tissues. Our findings pave the way for future research on chemical recognition of B. tabaci at the molecular level.

Characterization of the voltage-gated sodium channel of the Asian citrus psyllid, Diaphorina citri

The Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Liviidae), is an important insect pest of citrus. It is the vector of 'Candidatus' Liberibacter asiaticus, a phloem-limited bacterium that infects citrus, resulting in the disease Huanglongbing (HLB). Disease management relies heavily on suppression of D. citri populations with insecticides, including pyrethroids. In recent annual surveys to monitor insecticide resistance, reduced susceptibility to fenpropathrin was identified in several field populations of D. citri. The primary target of pyrethroids is the voltage-gated sodium channel (VGSC). The VGSC is prone to target-site insensitivity because of mutations that either reduce pyrethroid binding and/or alter gating kinetics. These mutations, known as knockdown resistance or kdr, have been reported in a wide diversity of arthropod species. Alternative splicing, in combination with kdr mutations, has been also associated with reduced pyrethroid efficacy. Here we report the molecular characterization of the VGSC in D. citri along with a survey of alternative splicing across developmental stages of this species. Previous studies demonstrated that D. citri has an exquisite enzymatic arsenal to detoxify insecticides resulting in reduced efficacy. The results from the current investigation demonstrate that target-site insensitivity is also a potential basis for insecticide resistance to pyrethroids in D. citri. The VGSC sequence and its molecular characterization should facilitate early elucidation of the underlying cause of an established case of resistance to pyrethroids. This is the first characterization of a VGSC from a hemipteran to this level of detail, with the majority of the previous studies on dipterans and lepidopterans.

Genomics of interaction between the brown planthopper and rice

Rice (Oryza sativa L.) and the brown planthopper (Nilaparvata lugens (Stål)) form a model system for dissection of the mechanism of interaction between insect pest and crop. In this review, we focus on the genomics of BPH-rice interaction. On the side of rice, a number of BPH-resistance genes have been identified genetically. Thirteen of these genes have been cloned which shed a light on the molecular basis of the interaction. On the aspect of BPH, a lot of salivary proteins have been identified using transcriptome and proteome techniques. The genetic loci of virulence were mapped in BPH genome based on the linkage map. The understanding of interaction between BPH and rice will provide novel insights into efficient control of this pest.

Knock down of Whitefly Gut Gene Expression and Mortality by Orally Delivered Gut Gene-Specific dsRNAs

Control of the whitefly Bemisia tabaci (Genn.) agricultural pest and plant virus vector relies on the use of chemical insecticides. RNA-interference (RNAi) is a homology-dependent innate immune response in eukaryotes, including insects, which results in degradation of the corresponding transcript following its recognition by a double-stranded RNA (dsRNA) that shares 100% sequence homology. In this study, six whitefly 'gut' genes were selected from an in silico-annotated transcriptome library constructed from the whitefly alimentary canal or 'gut' of the B biotype of B. tabaci, and tested for knock down efficacy, post-ingestion of dsRNAs that share 100% sequence homology to each respective gene target. Candidate genes were: Acetylcholine receptor subunit α, Alpha glucosidase 1, Aquaporin 1, Heat shock protein 70, Trehalase1, and Trehalose transporter1. The efficacy of RNAi knock down was further tested in a gene-specific functional bioassay, and mortality was recorded in 24 hr intervals, six days, post-treatment. Based on qPCR analysis, all six genes tested showed significantly reduced gene expression. Moderate-to-high whitefly mortality was associated with the down-regulation of osmoregulation, sugar metabolism and sugar transport-associated genes, demonstrating that whitefly survivability was linked with RNAi results. Silenced Acetylcholine receptor subunit α and Heat shock protein 70 genes showed an initial low whitefly mortality, however, following insecticide or high temperature treatments, respectively, significantly increased knockdown efficacy and death was observed, indicating enhanced post-knockdown sensitivity perhaps related to systemic silencing. The oral delivery of gut-specific dsRNAs, when combined with qPCR analysis of gene expression and a corresponding gene-specific bioassay that relates knockdown and mortality, offers a viable approach for functional genomics analysis and the discovery of prospective dsRNA biopesticide targets. The approach can be applied to functional genomics analyses to facilitate, species-specific dsRNA-mediated control of other non-model hemipterans.

Improved annotation of the insect vector of citrus greening disease: biocuration by a diverse genomics community

Database URL

https://citrusgreening.org/.

Knockdown of two trehalose-6-phosphate synthases severely affects chitin metabolism gene expression in the brown planthopper Nilaparvata lugens

BACKGROUND

RNA interference combined with digital gene expression (DGE) analysis can be used to study gene function. Trehalose-6-phosphate synthase (TPS) plays a key role in the synthesis of trehalose and insect development.

RESULTS

DGE analysis revealed that the expression of nine or four chitinase genes was reduced significantly 48 h after NlTPS1 and NlTPS2 knockdown by RNAi, respectively. Additionally, abnormal phenotypes were noted, and approximately 30% of insects died. HK and G6PI2 expression decreased significantly whereas GFAT, GNPNA and UAP expression increased significantly 72 h after NlTPS1 and NlTPS2 knockdown. PGM1 expression decreased significantly after TPS2 knockdown, whereas PGM2 expression increased significantly and the expression of three CHS genes decreased 48 h after TPS1 knockdown. The mRNA expression of all 12 chitin degradation genes decreased 48 h after NlTPS1 and NlTPS2 treatment, and Cht2, Cht3, Cht6, Cht7, Cht10 and ENGase levels remained significantly decreased up to 72 h after NlTPS1 and NlTPS2 knockdown.

CONCLUSIONS

These results demonstrate that silencing of TPS genes can lead to increased moulting deformities and mortality rates owing to the misregulation of genes involved in chitin metabolism, and TPS genes are potential pest control targets in the future. © 2016 Society of Chemical Industry.

Rice Stripe Virus Infection Alters mRNA Levels of Sphingolipid-Metabolizing Enzymes and Sphingolipids Content in Laodelphax striatellus

Sphingolipids and their metabolites have been implicated in viral infection and replication in mammal cells but how their metabolizing enzymes in the host are regulated by viruses remains largely unknown. Here we report the identification of 12 sphingolipid genes and their regulation by Rice stripe virus in the small brown planthopper (Laodelphax striatellus Fallén), a serious pest of rice throughout eastern Asia. According to protein sequence similarity, we identified 12 sphingolipid enzyme genes in L. striatellus. By comparing their mRNA levels in viruliferous versus nonviruliferous L. striatellus at different life stages by qPCR, we found that RSV infection upregulated six genes (LsCGT1, LsNAGA1, LsSGPP, LsSMPD4, LsSMS, and LsSPT) in most stages of L. striatellus Especially, four genes (LsCGT1, LsSMPD2, LsNAGA1, and LsSMS) and another three genes (LsNAGA1, LsSGPP, and LsSMS) were significantly upregulated in viruliferous third-instar and fourth-instar nymphs, respectively. HPLC-MS/MS results showed that RSV infection increased the levels of various ceramides, such as Cer18:0, Cer20:0, and Cer22:0 species, in third and fourth instar L. striatellus nymphs. Together, these results demonstrate that RSV infection alters the transcript levels of various sphingolipid enzymes and the contents of sphingolipids in L. striatellus, indicating that sphingolipids may be important for RSV infection or replication in L. striatellus.

Genome sequence of a rice pest, the white-backed planthopper (Sogatella furcifera)

Background

Sogatella furcifera is an important phloem sap-sucking and plant virus-transmitting migratory insect of rice. Because of its high reproductive potential, dispersal capability and transmission of plant viral diseases, S. furcifera causes considerable damage to rice grain production and has great economical and agricultural impacts. Comprehensive studies into ecological aspects and virus-host interactions of S. furcifera have been limited because of the lack of a well-assembled genome sequence.

Findings

A total of 241.3 Gb of raw reads from the whole genome of S. furcifera were generated by Illumina sequencing using different combinations of mate-pair and paired-end libraries from 17 insert libraries ranging between 180 bp and 40 kbp. The final genome assembly (0.72 Gb), with average N50 contig size of 70.7 kb and scaffold N50 of 1.18 Mb, covers 98.6 % of the estimated genome size of S. furcifera . Genome annotation, assisted by eight different developmental stages (embryos, 1 st -5 th instar nymphs, 5-day-old adults and 10-day-old adults), generated 21 254 protein-coding genes, which captured 99.59 % (247/248) of core CEGMA genes and 91.7 % (2453/2675) of BUSCO genes.

Conclusions

We report the first assembled and annotated whole genome sequence and transcriptome of S. furcifera . The assembled draft genome of S. furcifera will be a valuable resource for ecological and virus-host interaction studies of this pest.

Glycogen Phosphorylase and Glycogen Synthase: Gene Cloning and Expression Analysis Reveal Their Role in Trehalose Metabolism in the Brown Planthopper, Nilaparvata lugens Stål (Hemiptera: Delphacidae)

RNA interference has been used to study insects' gene function and regulation. Glycogen synthase (GS) and glycogen phosphorylase (GP) are two key enzymes in carbohydrates' conversion in insects. Glycogen content and GP and GS gene expression in several tissues and developmental stages of the Brown planthopper Nilaparvata lugens Stål (Hemiptera: Delphacidae) were analyzed in the present study, using quantitative reverse-transcription polymerase chain reaction to determine their response to double-stranded trehalases (dsTREs), trehalose-6-phosphate synthases (dsTPSs), and validamycin injection. The highest expression of both genes was detected in the wing bud, followed by leg and head tissues, and different expression patterns were shown across the developmental stages analyzed. Glycogen content significantly decreased 48 and 72 h after dsTPSs injection and 48 h after dsTREs injection. GP expression increased 48 h after dsTREs and dsTPSs injection and significantly decreased 72 h after dsTPSs, dsTRE1-1, and dsTRE1-2 injection. GS expression significantly decreased 48 h after dsTPS2 and dsTRE2 injection and 72 h after dsTRE1-1 and dsTRE1-2 injection. GP and GS expression and glycogen content significantly decreased 48 h after validamycin injection. The GP activity significantly decreased 48 h after validamycin injection, while GS activities of dsTPS1 and dsTRE2 injection groups were significantly higher than that of double-stranded GFP (dsGFP) 48 h after injection, respectively. Thus, glycogen is synthesized, released, and degraded across several insect tissues according to the need to maintain stable trehalose levels.