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Aphids are important agricultural pests, vectors of many plant viruses and have sophisticated relationships with symbiotic microorganisms. Abundant asymptomatic RNA viruses have been reported in aphids due to the application of RNA-seq, but aphid-virus interactions remain unclear. Bunyavirales is the most abundant RNA virus order, which can infect mammals, arthropods, and plants. However, many bunyaviruses have specific hosts, such as insects. Here, we discovered 18 viruses from 10 aphid species by RNA-seq. Importantly, a widespread presence bunyavirus, Aphid bunyavirus 1 (ABV-1), was determined to have a wide host range, infecting and replicating in all 10 tested aphid species. ABV-1 may be transmitted horizontally during feeding on plant leaves and vertically through reproduction. In a comparison of the physiological parameters of ABV-1

Pesticide resistance and resurgence are serious problems often occurring simultaneously in the field. In our long-term study of a fenpropathrin resistant strain of Tetranychus cinnabaribus, enhancement of detoxification and modified fecundity mechanisms were both observed. Here we investigate the network across these two mechanisms and find a key node between resistance and resurgence. We show that the ecdysone pathway is involved in regulating the fecundity of T. cinnabaribus. The concentration change of ecdysone is consistent with the fecundity curve, the concentration of ecdysone is higher in the fenpropathrin resistant strain which has stronger fecundity. The enhancement of ecdysone is due to over-expression of two P450 genes (CYP314A1 and CYP315A1) in the ecdysone synthesis pathway. Silencing expression of these CYP genes resulted in lower concentration of ecdysone, reduced expression of vitellogenin, and reduced fecundity of T. cinnabaribus. The expression of CYP315A1 is regulated by transcription factors Cap-n-collar isoform C (CncC) and Musculoaponeurotic fibrosarcoma protein (Maf), which are involved in regulating other P450 genes functioning in detoxification of fenpropathrin in T. cinnabaribus. A similar regulation is established in citrus pest mite Panonychus citri showing that the CncC pathway regulates expression of PcCYP315A1, which affects mite fecundity. Transcription factors are activated to up-regulate detoxification genes facilitating pesticide resistance, while the "one to multiple" regulation mode of transcription factors simultaneously increases expression of metabolic enzyme genes in hormone pathways and alters the physiology of pests. This is an important response of arthropods to pesticides which leads to resistance and population resurgence. This article is protected by copyright. All rights reserved.

SID1-like (SIL1) is considered as a core component in dsRNA uptake in some selected insect species. Investigation related to the potential function of SIL1 in dsRNA uptake can contribute to a further understanding of RNAi mechanism in insects and agricultural pest control. However, the role of SIL1 in dsRNA uptake in insects such as aphids remains controversial. Thus, we have thoroughly analyzed the role of SIL1 from the model aphid Acyrthosiphon pisum (ApSIL1) in cellular dsRNA to clarify its function. First, the induced expression of ApSIL1 upon dsRNA oral exposure provided a vital clue for the possible involvement of ApSIL1 in cellular dsRNA uptake. Subsequent in vivo experiments using the RNAi-of-RNAi approach for ApSIL1 supported our hypothesis that the silencing efficiencies of reporter genes were reduced after inhibition of ApSIL1 expression. The impaired biological phenotypes of aphids, including cumulative average offspring, deformities of the nymph, and mortality upon the pathogen infection were then observed in the treatment group. Thereafter, in vitro dual-luciferase reporter assay showed compelling evidence that the luciferin signal was significantly attenuated when dsluciferase or dsGFP was transferred into ApSIL1-transfected Drosophila S2 cells. These observations further confirmed that the signal of Cy3-labeled dsRNA was rapidly attenuated with time in ApSIL1-transfected Drosophila S2 cells. Overall, these findings conclusively establish that ApSIL1 is involved in dsRNA uptake in A. pisum. This article is protected by copyright. All rights reserved.

Spider mites (Tetranychidae) are destructive agricultural pests that have evolved strategies to overcome plant defenses, such as the ability to puncture the leaves of their hosts to feed. The expression of many genes with unknown functions is altered during feeding, but little is known about the role of these genes in plant-mite interactions. Here, we identified three novel gene families through analysis of genomic and transcriptomic data from three spider mite species. These GARP family genes encode glycine and alanine-rich proteins; they are present in mites (Acariformes) but absent in ticks (Parasitiformes) in the subclass Acari, indicating that these genes have undergone a significant expansion in spider mites and thus play important adaptive roles. Transcriptomic analysis revealed that the expression of GARP genes is strongly correlated with feeding and the transfer to new hosts. We used RNA interference to silence GARP1d in the two-spotted spider mite Tetranychus urticae, which inhibited feeding and egg laying and significantly increased mortality when the mites were transferred to soybean shoots; a similar effect was observed after TuVATPase was silenced. However, no changes in mite mortality were observed after TuGARP1d-silenced mites were placed on an artificial diet, which was different from the effect of TuVATPase silencing. Our results indicate that GARP family members play important roles in mite-plant interactions. Additional studies are needed to clarify the mechanisms underlying these interactions. This article is protected by copyright. All rights reserved.

Carotenoids are involved in many essential physiological functions and are produced from geranylgeranyl pyrophosphate through synthase, desaturase, and cyclase activities. In the pea aphid (Acyrthosiphon pisum), the duplication of carotenoid biosynthetic genes, including carotenoid synthases/cyclases (ApCscA-C) and desaturases (ApCdeA-D), through horizontal gene transfer from fungi has been detected, and ApCdeB has known dehydrogenation functions. However, whether other genes contribute to aphid carotenoid biosynthesis, and its specific regulatory pathway, remains unclear. In the current study, functional analyses of seven genes were performed using heterologous complementation and RNA interference assays. The bifunctional enzymes ApCscA-C were responsible for the synthase of phytoene, and ApCscC may also have a cyclase activity. ApCdeA, ApCdeC, and ApCdeD had diverse dehydrogenation functions. ApCdeA catalyzed the enzymatic conversion of phytoene to neurosporene (three-step product), ApCdeC catalyzed the enzymatic conversion of phytoene to ζ-carotene (two-step product), and ApCdeD catalyzed the enzymatic conversion of phytoene to lycopene (four-step product). Silencing of ApCscs reduced the expression levels of ApCdes, and silencing these carotenoid biosynthetic genes reduced the α-, β-, and γ-carotene levels, as well as the total carotenoid level. The results suggest that these genes were activated and led to carotenoid biosynthesis in the pea aphid.

Thiacloprid is a new chlorinated nicotinoid insecticide against stinging-oral pests, such as aphids. It is less toxic to bees but more toxic to earthworms. In this study, a pH- and amylase-responsive MOF (ZIF-8) was constructed for site-specific delivery of thiacloprid to control pea aphids and more safety for earthworms. Thiacloprid from α-cyclodextrin@Thiacloprid@ZIF-8 (α-CD@T@ZIF-8) could be released quickly in pea aphids, which was ascribed to disintegration of ZIF-8 at low pH values in pea aphid intestines and degradation of α-CD under the action of α-amylase. The release results showed a significant pH dependence of α-CD@T@ZIF-8, with an approximately 65 % release amount at pH = 7 and a 95 % release amount at pH = 5 for 7 d. The results of the pot experiment and biosafety showed that for α-CD@T@ZIF-8, 88 % pea aphids could be killed compared with 32 % aphids for commercially available formulation on the 7th day after application. Meanwhile the LC

Gram-negative binding proteins (GNBPs) are important in the innate immune system of insects in recognition of fungi pathogen, such as Beauveria bassiana. However, this information in aphids is not clear, which might be exploited to develop a novel aphid control strategy based on integrating RNAi and B. bassiana. Here, we firstly identified two GNBPs, ApGNBP1 and ApGNBP2, using the model aphid Acyrthosiphon pisum, and observed that two ApGNBPs were highly expressed in hemolymph and fat body as well as upon the injection of β-1,3-glucan and heat-killed B. bassiana. Intriguingly, RNAi-based silencing of ApGNBP1 but not ApGNBP2 decreased the activity of immune-related phenoloxidase. This led to the increased virulence of B. bassiana in A. pisum upon silencing of ApGNBP1, and the synergetic effects were also observed in other two aphids: Myzus persicae and Aphis citricidus. Importantly, no negative effects were detected in aphid predator Propylaea japonica under the co-application of the RNAi in targeting ApGNBP1 and B. bassiana. Taking together, we conclude that GNBP1 could be an optimal target in aphid control by combining RNAi, entomopathogenic fungi and ladybeetle predator.

Aphids feed on plant phloem sap that contains massive amounts of sucrose; this not only provides vital nutrition for the aphids but also produces high osmotic pressure. To utilize this carbon source and overcome the osmotic pressure, sucrose is hydrolyzed into the monosaccharides, glucose and fructose. In the green peach aphid (Myzus persicae), we show that this process is facilitated by a key α-glucosidase (MpAgC2-2), which is abundant in the aphid salivary gland and is secreted into leaves during feeding. MpAgC2-2 has a pH optimum of 8.0 in vitro, suggesting it has adapted to the environment of plant cells. Silencing MpAgC2-2 (but not the gut-specific MpAgC3-4) significantly increased the amount of sucrose ingested and hindered aphid feeding on the phloem of tobacco seedlings, resulting in a smaller body size, as well as lower α-glucosidase activity and glucose levels. These effects could be rescued by feeding aphids on tobacco plants transiently expressing MpAgC2-2. The transient expression of MpAgC2-2 also led to the hydrolysis of sucrose in tobacco leaves. Taken together, these results demonstrate that MpAgC2-2 is a salivary protein that facilitates extra-intestinal feeding via sucrose hydrolysis. Our findings provide insight into the ability of aphids to digest the high concentration of sucrose in phloem, and the underlying mechanism of extra-intestinal digestion.

The innate immune system of insects is the front line of self-defense against pathogen invasion. Peptidoglycan recognition proteins (PGRPs) are important components and play key roles in insect immune systems by recognizing peptidoglycan (PGN) in bacterial cell walls. We characterized two isoforms of the PGRP-LC gene, BdPGRP-LCa and BdPGRP-LCb, from Bactrocera dorsalis (Hendel), an important fruit and vegetable pest worldwide. These two isoforms contain an open reading frames of 1 668 bp and 1 731 bp, encoding a protein of 555 and 576 amino acids, respectively. Quantitative real-time PCR results showed that both transcripts were prominently expressed in midgut and fat body of B. dorsalis adult. Inoculation of pathogens showed that both isoforms actively responded to Escherichia coli PGN. We also observed a light response to Staphylococcus aureus PGN. Upon Beauveria bassiana inoculation, the expression of BdPGRP-LCa was enhanced, but the expression of BdPGRP-LCb was suppressed. Suppression of both transcripts by RNA interference led to increased mortality of flies challenged by E. coli, indicating that the two isoforms are involved in sensing Gram-negative bacterial infections.

Wing dimorphism is a phenomenon of phenotypic plasticity in aphid dispersal. However, the signal transduction for perceiving environmental cues (e.g., crowding) and the regulation mechanism remain elusive. Here, we found that aci-miR-9b was the only down-regulated microRNA (miRNA) in both crowding-induced wing dimorphism and during wing development in the brown citrus aphid Aphis citricidus . We determined a targeted regulatory relationship between aci-miR-9b and an ABC transporter ( AcABCG4 ). Inhibition of aci-miR-9b increased the proportion of winged offspring under normal conditions. Overexpression of aci-miR-9b resulted in decline of the proportion of winged offspring under crowding conditions. In addition, overexpression of aci-miR-9b also resulted in malformed wings during wing development. This role of aci-miR-9b mediating wing dimorphism and development was also confirmed in the pea aphid Acyrthosiphon pisum . The downstream action of aci-miR-9b- AcABCG4 was based on the interaction with the insulin and insulin-like signaling pathway. A model for aphid wing dimorphism and development was demonstrated as the following: maternal aphids experience crowding, which results in the decrease of aci-miR-9b. This is followed by the increase of ABCG4 , which then activates the insulin and insulin-like signaling pathway, thereby causing a high proportion of winged offspring. Later, the same cascade, “ miR-9b-ABCG4-insulin signaling ,” is again involved in wing development. Taken together, our results reveal that a signal transduction cascade mediates both wing dimorphism and development in aphids via miRNA. These findings would be useful in developing potential strategies for blocking the aphid dispersal and reducing viral transmission.

Wing polyphenism (alate and apterous morphs) in aphids is a trade-off between dispersal and reproduction. How bacterial communities are associated with wing polyphenism in aphids is still not clearly understood. This study used 16S rRNA sequencing to examine the differences in diversity of the bacterial community between alate and apterous morphs in Aphis citricidus, the main vector of the Citrus tristeza virus. Eighty-one operational taxonomic units (OTUs) belonging to 37 orders, 34 classes, and 13 phyla were identified from all samples. Among these OTUs, Wolbachia (79.17%), Buchnera (17.64%), and Pseudomonas (2.99%) were the dominant bacterial genera. The diversity of symbionts varied between the two morphs; apterous morphs had more bacterial diversity (69 OTUs belonging to 45 families, 21 classes, and 12 phyla) than alate morphs (45 OTUs belonging to 36 families, 15 classes, and 10 phyla). In addition, the abundance of five OTUs was significantly different between two morphs. Among these OTUs, two Pseudomonas species (Pseudomonas_brenneri [OTU21] and unclassified_Pseudomonas [OTU13]) represented a high proportion (3.93% and 2.06%) in alate morphs but were present in low abundance (0.006% and 0.002%) in apterous morphs. RT-qPCR showed consistent results with high-throughput DNA sequencing. The preliminary survey showed the difference in composition and frequency of bacteria between alate and apterous morphs. Thus, the results contribute to anew insight of microorganisms that may be involved in wing dimorphism and helpful for controlling the dispersal of this pest through artificial elimination or reinfection of bacterial symbionts or targeting symbiosis-related host genes by RNA interference in future.

Background RNA interference (RNAi) has potential as a pest insect control technique. One possible RNAi target is the cuticle protein, which is important in insect molting and development. As an example, here we evaluate the possibility of designing double-stranded RNA (RNA) that is effective for silencing the cuticle protein 19 gene (CP19) in aphids but is harmless to non-target predator insects. Results The sequences of CP19s were similar (86.6-94.4%) among the tested aphid species (Aphis citricidus, Acyrthosiphon pisum, and Myzus persicae) but different in the predator Propylaea japonica. Ingestion of species-specific dsRNAs of CP19 by the three aphids produced 39.3-64.2% gene silencing and 45.8-55.8% mortality. Ingestion of non-species-specific dsRNA (dsAcCP19) by Ac. pisum and M. persicae gave gene silencing levels ranging from 40.4% to 50.3% and 43.3-50.8% mortality. The dsApCP19 did not affect PjCP19 expression or developmental duration in P. japonica. Conclusion The results demonstrate that CP19 is a promising RNAi target for aphid control via one dsRNA design. The targeting of genes that are conserved in insect pests but not present in beneficial insects is a useful RNAi-based pest control strategy. © 2019 Society of Chemical Industry.

In insects, the ecdysteroid 20-hydroxyecdysone coordinates with juvenile hormone (JH) to regulate the process of molting, development and metamorphosis; however, this interaction is still unclear in the mites. In this study, we investigated the gene related to ecdysteroid and JH biosynthesis pathways, including four ecdysteroid and 11 JH biosynthesis genes. We examined their expression patterns during molting of different developmental stages of the two-spotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae), an important agricultural pest that feeds on more than 1100 plant species. The expression of ecdysteroid biosynthesis Halloween genes exhibited a positive zigzag-like pattern, with a peak after 8 h of molting and a drop 8 h after entering each quiescent stage. In contrast, JH biosynthesis genes expression displayed a negative zigzag-like pattern, with a peak at 8 h after entering each quiescent stage and a drop after 8 h of each molting. These opposite patterns imply that ecdysteroid and JH expression is coordinated during the developmental transition. Our data provide an initial perspective on the co-expression of ecdysteroid and JH biosynthesis genes to regulate this important developmental process in the two-spotted spider mite.

BACKGROUND With the growing number of available aphid genomes and transcriptomes, an efficient and easy-to-adapt tool for gene function study is urgently required. RNA interference (RNAi), as a post-transcriptional gene silencing mechanism, is important as a research tool for determining gene functions and has potential as a novel insect control strategy. However, these applications have been hampered by the lack of effective dsRNA delivery approaches in aphids. RESULTS Here, we developed a convenient and efficient dsRNA delivery method, topical RNAi, in aphids. An investigation of its dose and time-dependent RNAi efficiencies revealed that with as little as 60 ng dsRNA per adult pea aphid (Acyrthosiphon pisum), the indicator gene, Aphunchback, could be significantly silenced within 2 h of exposure. The method was further validated by successfully silencing other different genes, and it was also efficient toward two other aphid species, Aphis citricidus and Myzus persicae. Furthermore, a noticeable mortality was also observed in pea aphids using topical RNAi-mediated gene silencing, within 4 days post-dsRNA application for four out of seven tested genes. CONCLUSION Compared with the currently used dsRNA delivery methods in aphids, microinjection and ingestion, topical RNAi is time- and cost-effective, which could greatly influence RNAi-based gene functional studies and potential candidate gene selection for developing RNAi-based aphid control strategies in the future. © 2019 Society of Chemical Industry.

Although the PbCl2 has been exploited to improve the performance of perovskite solar cells, the mechanism of enhancement by the introducing PbCl2 is not fully understudied. In present work, we used the PbCl2 as a dopant to improve the perovskite film quality, we found the crystalline and grain size of perovskite film both increased with 10% molar ratio of PbCl2. The in situ time-resolved grazing incidence wide-angle X-ray scattering measurements revealed that more pre-nucleated suspended in the solution when employed the PbCl2 dopant, leading to high crystalline for perovskite film. An incorporation of the space charge limit current, photoluminescence, time-resolved photoluminescence measurements, we uncover the function of PbCl2 in reduced trap density, decreased charge recombination and enhanced carrier lifetime. As a result, the efficiency of planar-structure perovskite solar cells based on PbCl2 enhanced to as high as 19.79% with reduced hysteresis, increased by ∼23% compared to the device without PbCl2 (16.05%). We believe that this work would provide a fundamental prospective for mixed perovskite and promote its application in perovskite photovoltaics.

Euproctis pseudoconspersa is a major pest of tea plants, and also causes a skin rash on workers in tea plantations. Research on virus could provide fundamental insights for classification, genetic diversity, evolution, and host–virus interaction mechanisms. Here, we identified a novel RNA virus, Euproctis pseudoconspersa bunyavirus (Phenuiviridae), and found that it is widely distributed in field populations of E. pseudoconspersa. The replication of virus in E. pseudoconspersa was indicated by Tag-PCR. These results contribute to the classification of bunyaviruses and provide insight into the diversity of commensal E. pseudoconspersa bunyavirus and the host.

Spider mites have one ecdysone receptor (EcR) and multiple retinoid X receptors (RXRs). However, the function of these RXRs in spider mite development is unknown. Here, we screened the expression dynamics of two PcRXR isoforms at 4 h intervals in the deutonymphal stage of Panonychus citri. The results showed that PcEcR had an expression pattern similar to that of PcRXR2. For PcRXR1, its expression remained at a certain high level, when there was a decrease of both PcEcR and PcRXR2. In situ hybridization showed that PcRXR2 was detected in the central nervous mass, while the ecdysteroid biosynthesis gene PcSpo was mainly expressed at the edge of the central nervous mass. RNAi-based silencing of PcRXR1 or PcRXR2 showed the same phenotype as in mites with that of silencing PcEcR. Furthermore, RNA-seq was used to mine the genes associated with the expression dynamics of PcRXR1 or PcRXR2, which revealed that the heterodimer of EcR-RXR2 in spider mites might be linked with the cell autophagy and tissue remodeling during apolysis, and RXR1 might be linked with new epicuticle and exocuticle secretion during ecdysis. Taken together, these results increase our understanding of the regulation mechanism of ecdysteroid signal pathway in spider mite development.

The CD@Fe

RNAi is an essential technology for studying gene function in eukaryotes, and is also considered to be a potential strategy for pest control. However, the mechanism behind the cellular uptake of dsRNA in aphids, a group of important agricultural sucking pests, remains unknown. Here, using the pea aphid Acyrthosiphon pisum as model for aphids, we identified two core genes of clathrin-dependent endocytosis (CDE), Apchc and Apvha16. We confirmed that expression of Apchc, Apvha16 and RNAi core component genes (ApAgo2, ApDcr2 and ApR2d2) were simultaneously induced at 12 h after feeding dsRNA. By using an RNAi-of-RNAi approach, we demonstrated that suppression of Apchc and Apvha16 transcripts by RNAi significantly impaired RNAi efficiency of selected reporter genes (RGs), including ApGNBP1, Apmts and Aphb, suggesting the involvement of CDE in cellular dsRNA uptake in aphids. Further confirmation was also provided using two inhibitors, chlorpromazine (CPZ) and bafilomycin A1 (BafA1). Administration of CPZ and of BafA1 both led to an impaired silencing efficiency of the RGs in the pea aphid. Finally, these RNAi-of-RNAi results were reconfirmed in the peach aphid Myzus persicae. Taking these findings together, we conclude that CDE is involved in cellular dsRNA uptake in aphids.

The tea aphid, Aphis aurantii, has become one of the destructive pests in tea plantations in the tropics and subtropics. Very few functional studies have so far focused on the developmental and reproductive biology at a molecular level, because of the lack of comprehensive genetic information. Full-length transcriptomes represent a very highly efficient approach to obtain reference gene sequences in non-model insects. In the present study, the transcriptome of A. aurantii was comprehensively sequenced using PacBio Iso-Seq technology. A total of 46.8 Gb nucleotides and 15,938 non-redundant full-length transcripts were obtained, 13,498 (84.69%) of which were annotated into seven databases. Of these transcripts, 2,029 alternative splicing events and 15,223 simple sequence repeats were detected. Among these transcripts, 4,571 (28.68%) and 11,367 (71.32%) were long non-coding RNAs (lncRNAs) and protein-coding genes, respectively. Five hundred and ninety transcription factors were detected. The first full-length transcriptome represents a significant increase in the known genetic information of A. aurantii. It will assist the future functional study of genes involved in its development and reproduction.

Eotetranychus kankitus is an important mite pest in citrus, but molecular data on the developmental processes of E. kankitus are lacking. The different development stages mix of E. kankitus was used to sequence for transcriptome and small RNAs to identify genes and predict miRNAs associated with sesquiterpenoid and ecdysteroid biosynthesis and signaling pathways. More than 36 million clean reads were assembled and 67,927 unigenes were generated. Of the unigenes, 19,300 were successfully annotated through annotation databases NR, SwissProt, COG, GO, KEGG, PFAM, and KOG. The transcripts were involved in sesquiterpenoid biosynthesis (11 genes) and ecdysteroid biosynthesis and signaling pathway (13 genes). Another, small RNA library was obtained and 31 conserved miRNAs were identified. Five most abundant miRNAs were Ek-miR-5735, Ek-miR-1, Ek-miR-263a, Ek-miR-184, and Ek-miR-8. The target genes related to sesquiterpenoid and ecdysteroid showed that 10 of the conserved miRNAs could potentially target the sesquiterpenoid and ecdysteroid pathway according to four-prediction software, sRNAT, miRanda, RNAhybrid, and Risearch2. Thus, the results of this study will provide bioinformatics information for further molecular studies of E. kankitus which may facilitate improved pest control strategies.

We report a new positive-sense single-stranded RNA (ss RNA+) virus from the brown citrus aphid Aphis citricidus. The 20,300 nucleotide (nt)-long viral genome contains five open-reading frames and encodes six conserved domains (TM2, 3CLpro, TM3, RdRp, Zm, and HEL1). Phylogenetic analysis and amino acid sequence analysis revealed this virus might belong to an unassigned genus in the family Mesoniviridae. The presence of the virus was also confirmed in the field population. Importantly, analysis of the virus-derived small RNAs showed a 22-nt peak, implying that viral infection triggers the small interfering RNA pathway as antiviral immunity in aphids. This is the first report of a mesonivirus in invertebrates other than mosquitoes.

The pea aphid is an important pest of vegetables and causes serious losses worldwide. RNA interference (RNAi) is an effective pest control tool, and three sub-pathways have been described: The miRNA pathway, siRNA pathway, and piRNA pathway. A large number of genes in miRNA pathway and piRNA pathway are found to be expanded. To study the roles of these genes, the expression of 25 core RNAi genes was screened in spatiotemporal samples, artificially synthesized dsRNA and miRNA treated samples. The 25 genes were all expressed during different development stages and in different tissues. In dsRNA-treated samples and miRNA-treated samples, the expressions of genes in these three pathways were induced, especially the expanded genes. This suggests a complex network of RNAi core genes in the three sub-pathways. Treatment of miRNA seems to induce gene expression in a dosage-dependent manner. These results increase our knowledge of the siRNA pathway and related factors from RNAi pathway in aphids and promote the use of RNAi for the control of aphid pests.

One of the main functions of the piwi-interacting RNA pathway is the post-transcriptional silencing of transposable elements in the germline of many species. In insects, proteins belonging to the Tudor superfamily proteins belonging to the Tudor superfamily play an important role in to play an important role in this mechanism. In this study, we identified the tudor gene in the oriental fruit fly, Bactrocera dorsalis, investigated the spatiotemporal expressional profile of the gene, and performed a functional analysis using RNA interference. We identified one transcript for a tudor homologue in the B. dorsalis transcriptome, which encodes a protein containing the typical 10 Tudor domains and an Adenosine triphosphate (ATP) synthase delta subunit signature. Phylogenetic analysis confirmed the identity of this transcript as a tudor homologue in this species. The expression profile indicated a much higher expression in the adult and pupal stages compared to the larval stages (up to a 60-fold increase), and that the gene was mostly expressed in the ovaries, Malpighian tubules and fat body. Finally, gene knockdown of tudor in B. dorsalis led to clearly underdeveloped ovaries in the female adult and reductions in copulation rate and amount of oviposition, indicating its important role in reproduction. The results of this study shed more light on the role of tudor in ovary development and reproduction.

The oriental fruit fly, Bactrocera dorsalis (Hendel), is an important invasive agricultural insect pest with a wide host range, and has spread around the world over the last century. This evolutionary trait may have arisen primarily from interactions between B. dorsalis and other invertebrates that share the same ecological niches. The invasive behavior of B. dorsalis also frequently exposes them to diverse species of viruses. Thereby, RNA viromes may be useful microbial markers to understand the ecological evolution of B. dorsalis as well as to investigate virus-host interactions. Here, we reported eight novel RNA viruses in B. dorsalis of a lab colony, including four positive-strand RNA viruses, two negative-strand RNA viruses, and two double-stranded RNA viruses using high-throughput sequencing technology. Analysis of the virus-derived small RNAs suggested that most of these viruses may be active and trigger the host antiviral RNAi responses. The viruses were also detected in various geographical populations of B. dorsalis, implying that there is a strong association between the viromes and host. In addition, these viruses infected specific fly tissues, predominately the central nervous system and gut. Furthermore, we explored the dynamics of the viruses when hosts were exposed to short- or long-term stressors, which showed that titers of some viruses were responsively altered in the stressed B. dorsalis. The discovery of these viruses may enrich our understanding of the species diversity of RNA viruses and also provide information on viruses in association with host adaptation in insects.

Ecdysteroids regulate molting in arthropods by binding to heterodimers of the ecdysone receptor and retinoid-X-receptor, homologous to the ultraspiracle protein, to induce the expression of downstream signal response genes including the nuclear receptor HR3. However, the detailed expression dynamics of HR3 during molting in spider mites are not yet clear. In this study, the full length of PcHR3 was retrieved based on the genome of citrus red mite, Panonychus citri. The open reading frame is 1707 bp encoding 568 amino acids, which contains a DNA binding domain and a ligand binding domain. Then, the expression pattern of PcHR3 was analyzed throughout the development of the deutonymph by RT-qPCR. The result showed that PcHR3 was mainly transcribed in the late deutonymph stage, when the deutonymph was at least 24 h old and motionless, the critical point at which the mites started molting. Transcription reached the highest level in 32-h-old deutonymphs and decreased by 36 h, where the mites remained in a quiescent state. Further silencing of PcHR3 by leaf-disc-based delivery of dsRNA to 8-h-old deutonymph mites, resulted in retarded development and death of 58% of deutonymphs. In summary, we suggest that PcHR3 regulates the latter stages of molting in P. citri.

Carotenoids play many crucial roles in organisms. Recently, the de novo synthesis of carotenoids has been reported in pea aphid (Acyrthosiphon pisum) through horizontally transferred genes. However, their upstream pathway in the pea aphid is poorly understood. Geranylgeranyl diphosphate synthase (GGPPS) is the functional enzyme in the synthesis of geranylgeranyl diphosphate (GGPP) which is a precursor for the biosynthesis of many biological metabolites, including carotenoid synthesis. In this study, we performed a series of experiments to characterize GGPPS gene and its association with carotenoid biosynthesis. (1) determining the transcript abundance and carotenoid content in two geographical strain with red and green morphs, and (2) examining the abundance of carotenoid related genes and carotenoid levels after silencing of GGPPS in both red and green morphs. We observed that GGPPS was more highly expressed in the green morph than in the red morph of two strains of the pea aphid. The total level of carotenoids was also higher in green morphs than in red morphs in both strains. In addition to the total carotenoid difference, the carotenoids found in the two morphs also differed. There were α-carotene, β-carotene, and γ-carotene in the green morphs, but three additional carotenoids, including cis-torulene∗, trans-torulene∗, and 3,4-didehydrolycopene∗, were present in the red morphs. Silencing the GGPPS by RNAi in both the red and green morphs decreased the expression of some carotenoid biosynthesis-related genes, including carotenoid synthase/cyclase genes and carotenoid desaturase genes in green morphs. Carotenoid levels were decreased in both green and red morphs. However, the specific carotenoids present were not changed after silencing GGPPS. These results demonstrated that GGPPS may act as the upstream enzyme to influence the synthesis of the total amount of carotenoids. The present study provided important molecular evidence for the conserved roles of GGPPS associated with carotenoids biosynthesis and will enhance further investigation on the mechanisms of carotenoid biosynthesis in pea aphid.

Mites comprise a group of key agricultural pests on a wide range of crops. They cause harm through feeding on the plant and transferring dangerous pathogens, and the rapid evolution of pesticide resistance in mites highlights the need for novel control methods. Currently, RNA interference (RNAi) shows great potential for insect pest control. Here, we review the literature regarding RNAi in mite pests. We discuss different target genes and RNAi efficiency in various mite species, a promising Varroa control program using RNAi, the synergy of RNAi with plant defense mechanisms and microorganisms, and current understanding of systemic movement of double-stranded RNA (dsRNA). On the basis of this evidence, we can conclude that there is clear potential for application of RNAi-based mite control, but further research on several aspects of RNAi in mites is needed, including: (i) the factors influencing RNAi efficiency, (ii) the mechanism of environmental RNAi and cross-kingdom dsRNA trafficking, (iii) the mechanism of possible systemic and parental RNAi, and (iv) non-target effects, specifically in predatory mites, which should be considered during RNAi target selection. © 2018 Society of Chemical Industry.

Molting is essential for arthropods to grow. As one of the important arthropod pests in agriculture, key spider mite species (Tetranychus and Panonychus) can normally molt three times from the larva to adult stage within a week. This physiological strategy results in the short lifecycle of spider mites and difficulties in their control in the field. Long non-coding RNAs (lncRNAs) regulate transcriptional editing, cellular function, and biological processes. Thus, analysis of the lncRNAs in the spider mite molting process may provide new insights into their roles in the molting mechanism. For this purpose, we used high-throughput RNA-seq to examine the expression dynamics of lncRNAs and mRNAs in the molting process of different development stages in Panonychus citri. We identified 9199 lncRNAs from 18 transcriptomes. Analysis of the lncRNAs suggested that they were shorter and had fewer exons and transcripts than mRNAs. Among these, 356 lncRNAs were differentially expressed during three molting processes: late larva to early protonymph, late protonymph to early deutonymph, and late deutonymph to early adult. A time series profile analysis of differentially expressed lncRNAs showed that 77 lncRNAs were clustered into two dynamic expression profiles (Pattern a and Pattern c), implying that lncRNAs were involved in the molting process of spider mites. Furthermore, the lncRNA–mRNA co-expression networks showed that several differentially expressed hub lncRNAs were predicted to be functionally associated with typical molting-related proteins, such as cuticle protein and chitin biosynthesis. These data reveal the potential regulatory function of lncRNAs in the molting process and provide datasets for further analysis of lncRNAs and mRNAs in spider mites.

Perovskite solar cells (PSCs) have received great attention because of their excellent photovoltaic properties especially for the comparable efficiency to silicon solar cells. The electron transport layer (ETL) is regarded as a crucial medium in transporting electrons and blocking holes for PSCs. In this study, CO2 plasma generated by plasma-enhanced chemical vapor deposition (PECVD) was introduced to modify the TiO2 ETL. The results indicated that the CO2 plasma-treated compact TiO2 layer exhibited better surface hydrophilicity, higher conductivity, and lower bulk defect state density in comparison with the pristine TiO2 film. The quality of the stoichiometric TiO2 structure was improved, and the concentration of oxygen-deficiency-induced defect sites was reduced significantly after CO2 plasma treatment for 90 s. The PSCs with the TiO2 film treated by CO2 plasma for 90 s exhibited simultaneously improved short-circuit current (JSC) and fill factor. As a result, the PSC-based TiO2 ETL with CO2 plasma treatment affords a power conversion efficiency of 15.39%, outperforming that based on pristine TiO2 (13.54%). These results indicate that the plasma treatment by the PECVD method is an effective approach to modify the ETL for high-performance planar PSCs.

Inverted perovskite solar cells have attracted a great deal of attention due to its high power conversion efficiency, simple configuration, and low-cost processing. The hole transport material (HTM) is a crucial factor in high performance inverted perovskite solar cell. However, the hole mobility for most common of HTM is too low to matching perovskite materials. Herein, we report a superior HTM with high hole mobility to significantly improve solar cell efficiency. Upon doing the commonly used PEDOT:PSS HTM by graphene oxide (GO), its hole mobility is increased from 5.55 × 10 −5 to 1.57 × 10 −4 cm 2 V −1 s −1 , leading to efficient hole extraction and low current leakage, therefore 20% higher power conversion efficiency comparing to the control device without the GO doping. The development open the opportunities for efficient HTMs based on the two-dimensional materials in the perovskite solar cells.

The oriental fruit fly, Bactrocera dorsalis (Hendel) (Diptera: Tephritidae), is one of the most important economic pests in tropical and subtropical areas of the world, where it causes serious damage to fruit production. This study aimed to investigate the criteria for dividing the instars of B. dorsalis, which will be fundamental for the control and forecasting of development rates, as well as the development of efficient control measures for B. dorsalis. Five morphological variables, including the body length, the length and width of mouth hooks, and the length and width of the pharyngeal sclerite of the larvae, were measured. The Crosby growth rule was used in determining that B. dorsalis has 3 instars. The length of the pharyngeal sclerite is the best morphological variable for distinguishing the instars of B. dorsalis, whereas the length and the width of mouth hooks and the width of the pharyngeal sclerite can be used as additional characteristics. There was an overlap in the body length bet...

Electron transport layer (ETL), facilitating charge carrier separation and electron extraction, is a key component in planar perovskite solar cells (PSCs). We developed an effective ETL using low-temperature solution-processed Nb-doped SnO2 (Nb:SnO2). Compared to the pristine SnO2, the power conversion efficiency of PSCs based on Nb:SnO2 ETL is raised to 17.57% from 15.13%. The splendid performance is attributed to the excellent optical and electronic properties of the Nb:SnO2 material, such as smooth surface, high electron mobility, appropriate electrical conductivity, therefore making a better growth platform for a high quality perovskite absorber layer. Experimental analyses reveal that the Nb:SnO2 ETL significantly enhances the electron extraction and effectively suppresses charge recombination, leading to improved solar cell performance.

Chemical composition and film quality are two key figures of merit for large-area high-efficiency perovskite solar cells. To date, all studies on mixed perovskites have used solution-processing, which results in imperfect surface coverage and pin-holes generated during solvent evaporation, execrably influencing the stability and efficiency of perovskite solar cells. Herein, we report our development using a vacuum co-evaporation deposition method to fabricate pin-hole-free cesium (Cs)-substituted perovskite films with complete surface coverage. Apart from the simplified procedure, the present method also promises tunable band gap, reduced trap-state density and longer carrier lifetime, leading to solar cell efficiency as high as 20.13%, which is among the highest reported for planar perovskite solar cells. The splendid performance is attributed to superior merits of the Cs-substituted perovskite film including tunable band gap, reduced trap-state density and longer carrier lifetime. Moreover, the Cs-substituted perovskite device without encapsulation exhibits significantly higher stability in ambient air compared with the single-component counterpart. When the Cs-substituted perovskite solar cells are stored in dark for one year, the PCE remains at 19.25%, degrading only 4.37% of the initial efficiency. The excellent stability originates from reduced lattice constant and relaxed strain in perovskite lattice by incorporating Cs cations into the crystal lattice, as demonstrated by the positive peak shifts and reduced peak width in X-ray diffraction analysis.

BACKGROUND: Aphids obtained carotenoid biosynthesis genes via horizontal gene transfers from fungi. However, the roles of these genes in the contributions of in aphids'adaptation and whether these genes could be used as RNAi-based pest control targets are not yet clear. Thus, in this study we used parental RNAi to analyze the potential function of a carotenoid desaturase gene (CdeB) by combined molecular and chemical approaches in the pea aphid (Acyrthosiphon pisum). RESULTS: Transcriptional analyses showed that CdeB was significantly more highly expressed in the red morphs compared to the green ones and was associated with the production of red carotenoid. Co-transferring of pET28a-CdeB (the CdeB gene was cloned into pET28a) and pACCRT-EIB (produced lycopene) showed a deep red color in the bacterial precipitate and produced more of a red pigment, lycopene, in vitro. Parental gene-silencing of CdeB resulted in a lower body color intensity in the treated aphids and following generations in vivo. Interestingly, the dsCdeB treatment also reduced aphid performance as reflected by a delay in nymphal developmental duration, lower weight, smaller number, and altered age structure of the population. CONCLUSION: Our results demonstrate that CdeB is involved in red color formation and the silencing of this gene by parental RNAi reduced fitness in the pea aphid. The results enhance our understanding of the biosynthesis of carotenoid in aphids and provide insights into the potential ecological significance of carotenoids in the adaptation of the aphid's biology to the environment and developing environmentally friendly control strategies for this pest.

As a polyphagous herbivore, the two-spotted spider mite Tetranychus urticae is engaged with various plant hosts and interacts with diverse organisms that share the same ecological niche. Thus, T. urticae faces frequent challenges from viral infections. However, the RNA viruses of T. urticae are still unknown. Here, we constructed two libraries (~8 Gb for RNA and ~10 Mb for small RNA) from a strain of T. urticae using deep sequencing, and identified three novel RNA viruses from the families Kitaviridae, Dicistroviridae, and Chuviridae. Among them, the Kitaviridae and Dicistroviridae viruses presented a possible interaction pattern with the host RNA interference pathway.

The citrus leaf beetle, Clitea metallica, is a specialized citrus pest through feeding on fresh leaves by larva and adults, and causes nicks and holes into leaves, leaving only a waxy surface layer. Insect cuticle is a complex exoskeleton that is not only involved in development but also protects the insect from environmental contaminations. Due to these key roles of the cuticle, cuticle-related genes are currently investigated in understanding the insect physiology in adaptation. Therefore, in this study, we built two libraries, transcriptomic (43 million clean reads) and small RNA (17 million clean reads), of C. metallica to identify cuticle-related genes and possibly associated miRNAs, being as an example to explore these data sets. Our results showed that a total of 47 cuticular protein genes were identified and most of these genes harbored a conserved motif (the Rebers and Riddiford motif) and belonged to the CPR family. Unigenes encoding proteins involved in chitin synthesis and degradation were also identified, including chitin synthase (2 unigenes), chitinase (14 unigenes), chitinase-like protein (2 unigenes), and chitin deacetylase (5 unigenes). Based on the small RNA library, we identified 30 miRNAs conserved across insect species. Among these miRNAs, 14 were predicted to be target genes associated with cuticle synthesis and degradation. In summary, 70 cuticle-related genes and 14 cuticle-related miRNAs were identified based on the transcriptome and small RNA library of C. metallica. These data sets will promote the understanding of cuticle molecular regulation in C. metallica as well as provide new potential targets for pest control.

Tomato yellow leaf curl virus (TYLCV) and Tomato chlorosis virus (ToCV) are two of the most devastating cultivated tomato viruses, causing significant crop losses worldwide. As the vector of both TYLCV and ToCV, the whitefly Bemisia tabaci Mediterranean (MED) is mainly responsible for the rapid spread and mixed infection of TYLCV and ToCV in China. However, little is known concerning B. tabaci MED's molecular response to TYLCV and ToCV infection or their co-infection. We determined the transcriptional responses of the whitefly MED to TYLCV infection, ToCV infection, and TYLCV&ToCV co-infection using Illumina sequencing. In all, 78, 221, and 60 differentially expressed genes (DEGs) were identified in TYLCV-infected, ToCV-infected, and TYLCV&ToCV co-infected whiteflies, respectively, compared with non-viruliferous whiteflies. Differentially regulated genes were sorted according to their roles in detoxification, stress response, immune response, transport, primary metabolism, cell function, and total fitness in whiteflies after feeding on virus-infected tomato plants. Alterations in the transcription profiles of genes involved in transport and energy metabolism occurred between TYLCV&ToCV co-infection and single infection with TYLCV or ToCV; this may be associated with the adaptation of the insect vector upon co-infection of the two viruses. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses demonstrated that the single infection with TYLCV or ToCV and the TYLCV&ToCV co-infection could perturb metabolic processes and metabolic pathways. Taken together, our results provide basis for further exploration of the molecular mechanisms of the response to TYLCV, ToCV single infection, and TYLCV&ToCV co-infection in B. tabaci MED, which will add to our knowledge of the interactions between plant viruses and insect vectors.

The pea aphid, Acyrthosiphon pisum, is an important agricultural pest and an ideal model organism for various studies. Chitin synthase (CHS) catalyses chitin synthesis, a critical structural component of insect exoskeletons. Here, we identified a CHS gene from A. pisum, ApisCHS. The ApisCHS expression profiles showed that ApisCHS was expressed in various developmental stages and in all tested tissues of A. pisum, including the epidermis, embryo, gut and haemolymph. Notably, ApisCHS exhibited peak expression in the middle of each nymphal period and was extremely highly expressed in the epidermis and embryo. RNA interference (RNAi) showed that ~600 ng of dsRNA is an effective dose for gene silencing by injection for dsRNA delivery; moreover, 1200 ng·μL−1 dsRNA induced CHS gene silencing by a plant-mediated feeding approach. A 44.7% mortality rate and a 51.3% moulting rate were observed 72 h after injection of dsApisCHS into fourth-instar nymphs, compared with the levels in the control (injected with dsGFP). Moreover, a longer period was required for nymph development and a 44.2% deformity rate among newborn nymphs was obtained upon ingestion of dsApisCHS. These results suggest that ApisCHS plays a critical role in nymphal growth and embryonic development in pea aphids, and is a potential target for RNAi-based aphid pest control.

High-throughput sequencing is widely used for virus discovery, and many RNA viruses have been discovered and identified. A new negative-sense single-stranded RNA virus was identified in the brown citrus aphid and named Aphis citricidus bunyavirus. The genome consists of large (7037 nt), medium (3462 nt), and small (1163 nt) segments. Phylogenetic analysis and amino acid sequences identities of this virus with other bunyaviruses suggest that it is a new species belonging to the family Phenuiviridae. The small interfering RNA pathway could be involved against the infection of this virus in brown citrus aphid as supported by the viral derived small RNAs. The discovery of this virus illustrates the diversity of RNA viruses and contributes to the classification of bunyaviruses.

The pea aphid, Acyrthosiphon pisum, is an important agricultural pest and biological model organism, and RNA interference (RNAi) is an important tool for functional genomics and for insect pest management. However, the efficiency of RNAi in pea aphids is variable, limiting its application in aphids. In this study, we present optimized conditions for inducing and increasing the gene silencing efficiency of RNAi in pea aphids. The optimal gene silencing of the target Aphunchback gene was achieved by injecting 600 ng double-stranded (ds) RNA, and the highest mRNA depletion rate (74%) was detected at 36 h after injection. Moreover, the same gene silencing conditions were used to achieve transcript silencing for nine different genes in the pea aphid, although the silencing efficiencies for the different genes varied. Furthermore, the pre-exposure of aphids to dsRNA (600 ng dsGFP) led to significant hunchback silencing following a secondary exposure to 60 ng of dshunchback, a dose which did not lead to gene silencing when independently injected. The information presented here can be exploited to develop more efficient RNAi bioassays for pea aphids, both as gene functional study tools and an insect pest control strategy.

The citrus leaf beetle, Clitea metallica, is a specialized citrus pest through feeding on fresh leaves by larva and adults, and causes nicks and holes into leaves, leaving only a waxy surface layer. Insect cuticle is a complex exoskeleton that is not only involved in development but also protects the insect from environmental contaminations. Due to these key roles of the cuticle, cuticle-related genes are currently investigated in understanding the insect physiology in adaptation. Therefore, in this study, we built two libraries, transcriptomic (43 million clean reads) and small RNA (17 million clean reads), of C. metallica to identify cuticle-related genes and possibly associated miRNAs, being as an example to explore these data sets. Our results showed that a total of 47 cuticular protein genes were identified and most of these genes harbored a conserved motif (the Rebers and Riddiford motif) and belonged to the CPR family. Unigenes encoding proteins involved in chitin synthesis and degradation were also identified, including chitin synthase (2 unigenes), chitinase (14 unigenes), chitinase-like protein (2 unigenes), and chitin deacetylase (5 unigenes). Based on the small RNA library, we identified 30 miRNAs conserved across insect species. Among these miRNAs, 14 were predicted to be target genes associated with cuticle synthesis and degradation. In summary, 70 cuticle-related genes and 14 cuticle-related miRNAs were identified based on the transcriptome and small RNA library of C. metallica. These data sets will promote the understanding of cuticle molecular regulation in C. metallica as well as provide new potential targets for pest control.

The CD@Fe3O4 photocatalysts were synthesized via hydrothermal synthesis method. The CD@Fe3O4 particles were synthesized using Fe3O4 as the core and using citric acid and ethylenediamine as a raw material, which were heated to 200 °C for 4 h. The synthesized fluorescent CD@Fe3O4 was characterized by HR-TEM, IR and fluorescence spectrophotometer. The HR-TEM results showed CD and Fe3O4 nanoparticles were uniform, mono-dispersed sphere or hemisphere particles with an average size of approximately 3 nm, and particle size of CD@Fe3O4 were mainly in range of 20–30 nm. XRD results showed the nanoparticles mainly belonged to Fe3O4 and CD@Fe3O4, which made recycling our photocatalysts possible due to the magnetic performance. On daylight lamp, the half-life of hexaconazole in CD@Fe3O4 photocatalysts was about 4 days, and it is lower than half-life (over 100 days) of hexaconazole without CD@Fe3O4 photocatalysts.

Chitinases are hydrolytic enzymes that are required for chitin degradation and reconstruction in arthropods. In this study, we report a cDNA sequence encoding a putative chitinase (PcCht1) from the citrus red mite, Panonychus citri. The PcCht1 (564 aa) possessed a signal peptide, a conserver domain, and a chitin-binding domain. Structural and phylogenetic analyses found that PcCht1 had high sequence similarity to chitinases in Tetranychus urticae. Real-time quantitative PCR analyses showed that the transcript levels of PcCht1 peaked periodically in larval and nymph stages. Moreover, significant increase of PcCht1 transcript level in the larvae was observed upon the exposure of diflubenzuron. In contrast, exposures of the larvae to diflubenzuron resulted in the decreased chitin content. Furthermore, through a feeding-based RNA interference approach, we were able to reduce the PcCht1 transcript level by 59.7 % in the larvae, and consequently the treated larvae showed a very low molting rate compared with the control. Our results expanded the understanding of the important role of PcCht1 in the growth and development of P. citri.

RNA interference (RNAi)-based technology has emerged as a potential tool for controlling insect pests, however, previous studies found that the efficiency of RNAi in Bactrocera dorsalis was variable. In nature, insects often meet various challenges, such as pathogen infections, extreme temperatures, lack of nutrition and heavy metals. To better understand the association of the stressors with efficiency of RNAi, in the current study we tested the expression of three core genes, dicer2 (Bddcr2), r2d2 (Bdr2d2) and argonaute2 (Bdago2), of the small interfering RNA (siRNA) pathway of B. dorsalis upon various stressors. Our results showed that all three genes were upregulated by the infection of invertebrate iridescent virus 6, which suggested a function of the siRNA pathway against viral infection. The loading of FeCl3 could also increase the expression of Bddcr2. The treatments of Escherichia coli, extremely high (40°C) and low (0°C) temperatures, as well as starvation, could negatively influence the expression of Bddcr2 and/or Bdago2. In total, our results showed that various stressors could influence the expression of core components of B. dorsalis siRNA pathway. This highlights further speculation on the RNAi efficiency upon these stressors. Considering the complexity and variation of RNAi efficiency in different conditions, these results provide initial aspects in possible environmental stressors to influence the activity of the siRNA pathway, but the real impact of RNAi efficiency posed by these stressors requires further studies.

In this editorial for the Special Issue on ‘RNAi in insect pest control’, three important applications of RNA interference (RNAi) in insects are briefly discussed and linked to the different studies published in this Special Issue. The discovery of the RNAi mechanism revolutionized entomological research, as it presented researchers with a tool to knock down genes, which is easily applicable in a wide range of insect species. Furthermore, RNAi also provides crop protection with a novel and promising pest control mode-of-action. The sequence-dependent nature allows RNAi-based control strategies to be highly species selective and the active molecule, a natural biological molecule known as double-stranded RNA (dsRNA), has a short environmental persistence. However, more research is needed to investigate different cellular and physiological barriers, such as cellular uptake and dsRNA degradation in the digestive system in insects, in order to provide efficient control methods against a wide range of insect pest species. Finally, the RNAi pathway is an important part of the innate antiviral immune defence of insects, and could even lead to applications targeting viruses in beneficial insects such as honeybees in the future.