Delivery of dsRNA for RNAi in insects: an overview and future directions

Successful oral RNA interference efficiency in the silkworm Bombyx mori through nanoparticle-shielded dsRNA delivery

Double-stranded RNA (dsRNA) mediated RNA interference (RNAi) is a tool in functional gene study and pest control. However, RNAi efficiency in Lepidoptera is low compared to the RNAi sensitive Coleoptera. Previous studies on RNAi in the silkworm Bombyx mori, the lepidopteran model insect, were performed by injection only. Successful oral RNAi in the silkworm has never been reported yet. This study aims to develop a successful oral dsRNA delivery method to the silkworm larvae. Chitosan is an economical and biodegradable polymer. Chitosan/dsRNA nanoparticles were prepared by self-assembly. These nanoparticles were found to be stable when incubated in the midgut juice of the silkworm larvae, whereas naked dsRNA underwent complete degradation. Chitosan/dsRNA nanoparticles targeting various immune genes in oral administration to the silkworm larvae mediated significant knockdown of gene transcript. This silencing effect resulted in smaller larvae and cocoons when the silkworms were fed with Chitosan/dsRNA nanoparticles targeting BmToll9-2 gene, indicating that immune genes might be used as targets in pest control. Optimization of the chitosan/dsRNA nanoparticles maintained an RNAi effect from 3-5 days. The efficient RNAi was due to the persistence of nanoparticle-shielded dsRNA in the larvae. The above findings contribute to the first oral RNAi report in the silkworm, which facilitates the application of RNAi in insects and oral RNAi in pest control.

Unlocking the small RNAs: local and systemic modulators for advancing agronomic enhancement

Small regulatory RNAs (sRNAs) are essential regulators of gene expression across a wide range of organisms to precisely modulate gene activity based on sequence-specific recognition. In model plants like Arabidopsis thaliana, extensive research has primarily concentrated on 21 to 24-nucleotide (nt) sRNAs, particularly microRNAs (miRNAs). Recent advancements in cell and tissue isolation techniques, coupled with advanced sequencing technologies, are revealing a diverse array of preciously uncharacterized sRNA species. These include previously novel structural RNA fragments as well as numerous cell- and tissue-specific sRNAs that are active during distinct developmental stages, thereby enhancing our understanding of the precise and dynamic regulatory roles of sRNAs in plant development regulation. Additionally, a notable feature of sRNAs is their capacity for amplification and movement between cells and tissues, which facilitates long-distance communication-an adaptation critical to plants due to their sessile nature. In this review, we will discuss the classification and mechanisms of action of sRNAs, using legumes as a primary example due to their essential engagement for the unique organ establishment of root nodules and long-distance signaling, and further illustrating the potential applications of sRNAs in modern agricultural breeding and environmentally sustainable plant protection strategies.

Gene Silencing via Ingestion of Double-Stranded RNA in Wireworm of Agriotes Species

Wireworms are the most destructive soil insect pests affecting horticultural crops. The damage often renders them unsuitable for commercial purposes, resulting in substantial economic losses. RNA interference (RNAi) has been broadly used to inhibit gene functions to control insect populations. It employs double-stranded RNA (dsRNA) to knockdown essential genes in target organisms, rendering them incapable of development or survival. Although it is a robust approach, the primary challenges are identifying effective target genes and delivering their dsRNA into wireworms. Thus, the present study established a liquid ingestion methodology that efficiently delivers dsRNA into wireworms. We then investigated the effects of four target genes on wireworm mortality. The highest mortality rate reached 50% when the gene encoding vacuolar ATPase subunit A was targeted. Its transcript content in the fed wireworms was also significantly reduced. The mortality rates of the other three target genes of vacuolar ATPase subunit E, beta-actin, and chitin synthase 1 were 28%, 33%, and 35%, respectively. This is the first report demonstrating an efficient feeding methodology and the silencing of target genes in wireworms. Our findings indicate that RNAi is an effective alternative method for controlling the wireworm pest, and can be used to develop field treatment strategies.

Development of a controlled-release mosquito RNAi yeast larvicide suitable for the sustained control of large water storage containers

Large household water storage containers are among the most productive habitats for Aedes aegypti (Linnaeus, 1762), the primary mosquito vector for dengue and other arboviral pathogens. Increasing concerns for insecticide resistance and larvicide safety are limiting the successful treatment of large household water storage containers, which are among the most productive habitats for Aedes juveniles. The recent development of species-specific RNAi-based yeast larvicides could help overcome these problems, particularly if shelf stable ready-to-use formulations with significant residual activity in water can be developed. Here we examine the hypothesis that development of a shelf-stable controlled-release RNAi yeast formulation can facilitate lasting control of A. aegypti juveniles in large water storage containers. In this study, a dried inactivated yeast was incorporated into a biodegradable matrix containing a mixture of polylactic acid, a preservative, and UV protectants. The formulation was prepared using food-grade level components to prevent toxicity to humans or other organisms. Both floating and sinking versions of the tablets were prepared for treatment of various sized water containers, including household water storage tank-sized containers. The tablets passed accelerated storage tests of shelf life stability and demonstrated up to six months residual activity in water. The yeast performed well in both small and large containers, including water barrels containing 20-1000 larvae each, and in outdoor barrel trials. Future studies will include the evaluation of the yeast larvicide in larger operational field trials that will further assess the potential for incorporating this new technology into integrated mosquito control programs worldwide.

Knockdown of the ZcVgR Gene Alters the Expression of Genes Related to Reproduction and Lifespan in Zeugodacus cucurbitae (Coquillett) Under Extreme Heat Conditions

Zeugodacus cucurbitae (Coquillett) is an important migratory vegetable pest. Previous research has demonstrated that short-term high temperatures induce differential expression of the vitellogenin receptor (ZcVgR) gene, reducing the number of eggs laid and the lifespan of female Z. cucurbitae. In this paper, we used Tandem Mass Tags (TMT) quantitative proteomics and Illumina high-throughput sequencing to determine the proteomic and transcriptomic information of female Z. cucurbitae after siRNA-mediated silencing of the target gene (ZcVgR) to gain a comprehensive understanding of the molecular mechanism of this gene in the regulation of reproduction and lifespan. The findings demonstrated that following the target gene's silencing, the ZcVgR gene's transcriptional expression was significantly downregulated, and there was no significant difference in protein level. The transcriptome and proteome had a low correlation; when the ZcVgR gene was silenced, vitellogenin-1 (ZcVg1), juvenile hormone epoxide hydrolase (JHEH), troponin C (TnC), heat shock protein 70 (HSP70), and other related genes were downregulated at the transcriptional level. By silencing the ZcVgR gene, transcriptionally level immune-related pathways were activated and energy metabolism-related pathways were inhibited; protein-level glycometabolism and phagosome pathways were activated, while phototransduction-fly and autophagy-animal pathways were inhibited. The findings of this study might offer a theoretical foundation for integrated management of Z. cucurbitae in the summertime.

Microinjection-enabled gene silencing in first instar larvae of western flower thrips, Frankliniella occidentalis, reveals vital genes for larval survival

The western flower thrips (Frankliniella occidentalis) is a significant agricultural pest, causing severe global yield losses due to extensive feeding damage and the transmission of plant pathogenic viruses. Despite recent advancements in RNA interference (RNAi) in thrips species, its application has been mostly limited to the adult stage. Given the crucial role of first instar larval thrips in acquiring and transmitting orthotospoviruses, achieving gene silencing in these larvae is critical for studying virus entry and acquisition. While thoracic and abdominal injections have proven effective in adult thrips, the low post-injection survival rate hinders their use in larval thrips. This study addresses this challenge by presenting a microinjection methodology to deliver dsRNA into the hemolymph of first instar larval thrips through the coxa, the first proximal segment of the foreleg. This method significantly improved larval survival rate by preventing detrimental damage to the internal tissues. Significant knockdown of V-ATPase-B, cytochrome P450 (CYP3653A2), and apolipophorin-II/I (ApoLp-II/I) transcripts was confirmed after 48 and/or 72 h post injection (hpi), corresponding to the first and second instar larval stages, respectively. Silencing CYP3653A2 or ApoLp-II/I significantly increased larval mortality. These findings demonstrate proof-of-principle of gene silencing and associated silencing phenotype (mortality) for first instar larval thrips and highlight the essential role of CYP3653A2 and ApoLp-II/I in larval vitality. Our RNAi-based tool offers an opportunity to investigate the molecular mechanisms of thrips-orthotospovirus interactions, as the virus must be acquired by young larval thrips for successful transmission to plants, thus presenting potential targets for thrips pest management.

Development and evaluation of RNA microsphere-based RNAi approaches for managing the striped flea beetle (Phyllotreta striolata), a globally destructive pest of Cruciferae crops

BACKGROUND

RNA interference (RNAi) technology has emerged as a promising strategy for species-specific management of agricultural pests. However, the application of this technology has been significantly hindered by the instability of the interfering RNA molecules in the insect body after ingestion leading to variations in the susceptibility to the RNA triggers across different taxonomic groups of insects. Therefore, it is necessary to develop new approaches that will overcome these challenges associated with the use of RNAi-based insect pest management strategies. This study explored the use of RNA microspheres (RMS) synthesized via rolling-circle transcription (RCT) technology as a potential method for managing striped flea beetle (Phyllotreta striolata), a globally destructive pest of Cruciferae crops.

RESULTS

The synthesized RMS against the genes encoding reticulocalbin (RMS-PsRCN) and ribosomal RNA (RMS-PsrRNA) were highly effective in both silencing their target genes and causing increased P. striolata adult mortality. Relative expression levels of the target genes RMS-PsRCN and RMS-PsrRNA were decreased by 74.9% and 68.92%, respectively, in RMS fed adults, compared with the control adults fed RMS-EGFP. Consequently, the adult mortalities were 81.7% and 73.3% when fed RMS-PsRCN and RMS-PsrRNA, respectively, compared with 8.3% in the control adults. Furthermore, movements of adults fed RMS-PsRCN and RMS-PsrRNA were decreased by 70.2% and 55.7%, respectively, compared with the control adults.

CONCLUSIONS

This study shows the potential of using RMS to suppress the expression of target genes and subsequently produce significant mortality rates and behavioral changes in RMS-fed adult P. striolata. These findings underscore the promises and viability of using RMS as an effective strategy for gene function studies and species-specific management of agricultural important insect pests. © 2024 Society of Chemical Industry.

Functions and applications of RNA interference and small regulatory RNAs

Small regulatory RNAs play a variety of crucial roles in eukaryotes, influencing gene regulation, developmental timing, antiviral defense, and genome integrity via a process termed RNA interference (RNAi). This process involves Argonaute/small RNA (AGO/sRNA) complexes that target transcripts via sequence complementarity and modulate gene expression and epigenetic modifications. RNAi is a highly conserved gene regulatory phenomenon that recognizes self- and non-self nucleic acids, thereby defending against invasive sequences. Since its discovery, RNAi has been widely applied in functional genomic studies and a range of practical applications. In this review, we focus on the current understanding of the biological roles of the RNAi pathway in transposon silencing, fertility, developmental regulation, immunity, stress responses, and acquired transgenerational inheritance. Additionally, we provide an overview of the applications of RNAi technology in biomedical research, agriculture, and therapeutics.

Knock down to level up: Reframing RNAi for invertebrate ecophysiology

Comparative ecophysiologists strive to understand physiological problems in non-model organisms, but molecular tools such as RNA interference (RNAi) are under-used in our field. Here, we provide a framework for invertebrate ecophysiologists to use RNAi to answer questions focused on physiological processes, rather than as a tool to investigate gene function. We specifically focus on non-model invertebrates, in which the use of other genetic tools (e.g., genetic knockout lines) is less likely. We argue that because RNAi elicits a temporary manipulation of gene expression, and resources to carry out RNAi are technically and financially accessible, it is an effective tool for invertebrate ecophysiologists. We cover the terminology and basic mechanisms of RNA interference as an accessible introduction for "non-molecular" physiologists, include a suggested workflow for identifying RNAi gene targets and validating biologically relevant gene knockdowns, and present a hypothesis-testing framework for using RNAi to answer common questions in the realm of invertebrate ecophysiology. This review encourages invertebrate ecophysiologists to use these tools and workflows to explore physiological processes and bridge genotypes to phenotypes in their animal(s) of interest.

Citrus-mediated gene silencing of cytochrome P450 suppresses insecticide resistance and increases mortality in Diaphorina citri

BACKGROUND

Asian citrus psyllid, Diaphorina citri, is a hemipteran that vectors the causal pathogen of citrus greening disease, or huanglongbing (HLB). HLB is a tree killing disease that has severely limited citrus production globally. Unfortunately, there is no cure for this disease, and mitigation depends on multiple insecticide applications to reduce vector populations. Silencing of cytochrome P450 expression associated with detoxification enzymes by RNA interference is known to increase susceptibility of D. citri to insecticides. However, dsRNA was previously introduced into psyllids by topical applications. The possible application of this technology for pest management will require effective field delivery of the dsRNA. Therefore, we evaluated a virus vector (Citrus tristeza virus; 'mild strain' T36) to deliver gene silencing directly to this sap-sucking insect via plant phloem. Citrus macrophylla plants inoculated with CTV expressing a truncated consensus sequence of CYP450 (CTV-tCYP450) constantly produced small interfering RNA in the plant phloem that targeted five cytochrome p540 (CYP450) genes in D. citri.

RESULTS

Insecticide susceptible D. citri reared on citrus infected with CTV-tCYP450 were subsequently more susceptible to imidacloprid, fenpropathrin, carbaryl, and chlorpyrifos than those reared on citrus infected with wildtype CTV or non-infected negative controls. Additionally, nymph survival and adult lifespan were significantly reduced when psyllids were reared on CTV-tCYP450 citrus plants compared with controls. Interestingly, similar results were obtained after one and two generations of rearing. Finally, field-collected psyllids from areas with known broad-spectrum insecticide resistance were rendered more susceptible to imidacloprid and fenpropathrin after feeding on CTV-tCYP450 citrus trees as compared with those reared on controls.

CONCLUSION

The integration of citrus-mediated RNA inference targeting psyllid detoxification enzymes could function as a resistance management tool and reduce insecticide input in an integrated pest management program for HLB. © 2024 Society of Chemical Industry.

Fem-1 Gene of Chinese White Pine Beetle (Dendroctonus armandi): Function and Response to Environmental Treatments

Dendroctonus armandi (Tsai and Li) (Coleoptera: Curculionidae: Scolytinae) is regarded as the most destructive forest pest in the Qinling and Bashan Mountains of China. The sex determination of Dendroctonus armandi plays a significant role in the reproduction of its population. In recent years, the role of the fem-1 gene in sex determination in other insects has been reported. However, the function and expression of the fem-1 gene in Dendroctonus armandi remain uncertain. In this study, three fem-1 genes were cloned and characterized. These were named Dafem-1A, Dafem-1B, and Dafem-1C, respectively. The expression levels of these three Dafem-1 genes vary at different stages of development and between the sexes. In response to different environmental treatments, including temperature, nutrients, terpenoids, and feeding duration, significant differences were observed between the three Dafem-1 genes at different developmental stages and between males and females. Furthermore, injection of double-stranded RNA (dsRNA) targeting the expressions of the Dafem-1A, Dafem-1B, and Dafem-1C genes resulted in increased mortality, deformity, and decreased emergence rates, as well as an imbalance in the sex ratio. Following the interference with Dafem-1A and Dafem-1C, no notable difference was observed in the expression of the Dafem-1B gene. Similarly, after the interference with the Dafem-1B gene, no significant difference was evident in the expression levels of the Dafem-1A and Dafem-1C genes. However, the interference of either the Dafem-1A or Dafem-1C gene results in the downregulation of the other gene. The aforementioned results demonstrate that the Dafem-1A, Dafem-1B, and Dafem-1C genes play a pivotal role in the regulation of life development and sex determination. Furthermore, it can be concluded that external factors such as temperature, nutrition, terpenoids, and feeding have a significant impact on the expression levels of the Dafem-1A, Dafem-1B, and Dafem-1C genes. This provides a crucial theoretical foundation for further elucidating the sex determination mechanism of Dendroctonus armandi.

The Fat Body-Specific GST Gene SlGSTe11 Enhances the Tolerance of Spodoptera litura to Cyantraniliprole and Nicotine

Spodoptera litura is a significant agricultural pest, and its glutathione S-transferase (GST) plays a crucial role in insecticide resistance. This study aimed to investigate the relationship between the SlGSTe11 gene of S. litura and resistance to cyantraniliprole and nicotine. Transcriptome analysis revealed that SlGSTe11 is highly expressed mainly in fat bodies, with a significant increase in SlGSTe11 gene expression under induction by cyantraniliprole and nicotine. The ectopic expression of the SlGSTe11 gene in transgenic fruit flies resulted in a 5.22-fold increase in the tolerance to cyantraniliprole. Moreover, compared to the UAS-SlGSTe11 line, the Act5C-UAS>SlGSTe11 line laid more eggs and had a lower mortality after nicotine exposure. RNAi-mediated inhibition of SlGSTe11 gene expression led to a significant increase in the mortality of S. litura under cyantraniliprole exposure. In vitro metabolism experiments demonstrated that the recombinant SlGSTe11 protein efficiently metabolizes cyantraniliprole. Molecular docking results indicated that SlGSTe11 has a strong affinity for both cyantraniliprole and nicotine. These findings suggest that SlGSTe11 is involved in the development of resistance to cyantraniliprole and nicotine in S. litura.

Linc20486 promotes BmCPV replication through inhibiting the transcription of AGO2 and Dicers

The silkworm holds pivotal economic importance, serving not only as a primary source of silk but also as a prominent model organism in scientific research. Nonetheless, silkworm farming remains vulnerable to diverse factors, with viral infections posing the gravest threat to the sericulture industry. Among these, the Bombyx mori cytoplasmic polyhedrosis virus (BmCPV), a member of the Reoviridae family and the cytoplasmic polyhedrosis virus genus, emerges as a significant pathogen in silkworm production. BmCPV infection primarily induces midgut sepsis in silkworms, spreads rapidly, and can inflict substantial economic losses on sericulture production. Presently, effective strategies for preventing and treating BmCPV infections are lacking. Long non-coding RNA (lncRNA) constitutes a class of RNA molecules with transcripts exceeding 200 nt, playing a crucial role in mediating the interplay between pathogens and host cells. Investigation through high-throughput technology has unveiled that BmCPV infection markedly upregulates the expression of Linc20486. This observation suggests potential involvement of Linc20486 in regulating virus replication. Indeed, as anticipated, knockdown of Linc20486 in cells profoundly impedes BmCPV replication, whereas overexpression significantly enhances virus propagation. To probe into the mechanism underlying Linc20486's impact on virus replication, its effects on autophagy, innate immunity, and RNAi-related pathways were scrutinized. The findings revealed that Linc20486 exerts significant influence on the expression of RNAi pathway-related genes, such as Dicer1, Dicer2 and AGO2. This discovery holds promise for unveiling novel avenues to comprehend and combat BmCPV infections in silkworms.

The use of cell and larval assays to identify target genes for RNA interference-meditated control of the Australian sheep blowfly (Lucilia cuprina)

BACKGROUND

Flystrike, primarily caused by Lucilia cuprina, is a major health and welfare issue for sheep wool industries. Current chemical-based controls can have limited effectiveness due to the emergence of resistance in the parasite. RNA interference (RNAi), which uses double-stranded RNA (dsRNA) as a trigger molecule, has been successfully investigated for the development of innovative pest control strategies. Although RNAi offers great potential, the efficient identification, selection of target genes and delivery of dsRNA represent challenges to be overcome for the successful application of RNAi for control of L. cuprina.

RESULTS

A primary L. cuprina (blowfly) embryo cell line (BFEC) was established and confirmed as being derived from L. cuprina eggs by PCR and amplicon sequencing. The BFECs were successfully transfected with plasmids and messenger RNA (mRNA) expressing fluorescent reporter proteins and dsRNA using lipid-based transfection reagents. The transfection of dsRNA into BEFC in this study suggested decreased mRNA levels of target gene expression, which suggested RNAi-mediated knockdown. Three of the dsRNAs identified in this study resulted in reductions of in target gene mRNA levels in BFEC and loss of biological fitness by L. cuprina larvae in a feeding bioassay.

CONCLUSION

This study confirms that the novel BFEC cell line can be used to improve the efficacy of dsRNA-mediated screening to accelerate the identification of potential target genes in the development of RNAi mediated control approaches for L. cuprina. The research models established in this study are encouraging with respect to the use of RNAi as a blowfly control method, however further improvement and validation are required for field applicationsnot prefect, and could be ongoing developing. © 2024 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Development of an agroinfiltration-based transient hairpin RNA expression system in pak choi leaves (Brassica rapa ssp. chinensis) for RNA interference against Liriomyza sativae

The vegetable leafminer (Liriomyza sativae) is a devastating invasive pest of many vegetable crops and horticultural plants worldwide, causing serious economic loss. Conventional control strategy against this pest mainly relies on the synthetic chemical pesticides, but widespread use of insecticides easily causes insecticide resistance development and is harmful to beneficial organisms and environment. In this context, a more environmentally friendly pest management strategy based on RNA interference (RNAi) has emerged as a powerful tool to control of insect pests. Here we report a successful oral RNAi in L. sativae after feeding on pak choi (Brassica rapa ssp. chinensis) that transiently express hairpin RNAs targeting vital genes in this pest. First, potentially lethal genes are identified by searching an L. sativae transcriptome for orthologs of the widely used V-ATPase A and actin genes, then expression levels are assessed during different life stages and in different adult tissues. Interestingly, the highest expression levels for V-ATPase A are observed in the adult heads (males and females) and for actin in the abdomens of adult females. We also assessed expression patterns of the target hairpin RNAs in pak choi leaves and found that they reach peak levels 72 h post agroinfiltration. RNAi-mediated knockdown of each target was then assessed by letting adult L. sativae feed on agroinfiltrated pak choi leaves. Relative transcript levels of each target gene exhibit significant reductions over the feeding time, and adversely affect survival of adult L. sativae at 24 h post infestation in genetically unmodified pak choi plants. These results demonstrate that the agroinfiltration-mediated RNAi system has potential for advancing innovative environmentally safe pest management strategies for the control of leaf-mining species.

A review on RNA interference studies in Anophelines to reveal candidate genes for malaria transmission blocking vaccine

Malaria is a major public health concern. The development of parasite-based vaccine RTS/AS01 has some therapeutic value but its lower efficacy is one of the major limitations. Mosquito-based transmission-blocking vaccines could have a higher potential for parasite inhibition within the mosquitoes. Several genes of mosquito midgut, salivary gland, hemolymph, etc. get activate in response to the Plasmodium-infected blood and helps in parasite invasion directly or indirectly inside the mosquito. The studies of such genes provided a new insight into developing the more efficient vaccines. In the field of malaria genetics research, RNAi has become an innovative strategy used to identify mosquito candidate genes for transmission-blocking vaccines. This review targeted the gene studies that have been conducted in the period 2000-2023 in different malaria vectors against different malarial parasites using the RNAi approach to reveal mosquito novel gene candidates for vaccine development.

Transgenic poplar (Populus davidiana×P. bolleana Loucne) expressing dsRNA of insect chitinase gene: lines identification and resistance assay

Poplar is a valuable tree species that is distributed all over the world. However, many insect pests infest poplar trees and have caused significant damage. To control poplar pests, we transformed a poplar species, Populus davidiana × P. bolleana Loucne, with the dsRNA of the chitinase gene of a poplar defoliator, Clostera anastomosis (Linnaeus) (Lepidoptera: Notodontidae), employing an Agrobaterium-mediated approach. The transgenic plant has been identified by cloning the T-DNA flanking sequences using TAIL-PCR and quantifying the expression of the dsRNA using qPCR. The toxicity assay of the transgenic poplar lines was carried out by feeding the target insect species (C. anastomosis). The results showed that, in C. anastomosis, the activity of chitinase was significantly decreased, consistent with the expression on mRNA levels, and the larval mortality was significantly increased. These results suggested that the transgenic poplar of dsRNA could be used for pest control.

The development of an egg-soaking method for delivering dsRNAs into spider mites

Recently, the first sprayable RNAi biopesticide, Ledprona, against the Colorado potato beetle, Leptinotarsa decemlineata, has been registered at the United States Environmental Protection Agency. Spider mites (Acari: Tetranychidae), a group of destructive agricultural and horticultural pests, are notorious for rapid development of insecticide/acaricide resistance. The management options, on the other hand, are extremely limited. RNAi-based biopesticides offer a promising control alternative to address this emerging issue. In this study, we i) developed an egg-soaking dsRNA delivery method; ii) evaluated the factors influencing RNAi efficiency, and finally iii) investigated the potential mode of entry of this newly developed egg-soaking RNAi method. In comparison to other dsRNA delivery methods, egg-soaking method was the most efficient, convenient/practical, and cost-effective method for delivering dsRNAs into spider mites. RNAi efficiency of this RNAi method was affected by target genes, dsRNA concentration, developmental stages, and mite species. In general, the hawthorn spider mite, Amphitetranychus viennensis, is more sensitive to RNAi than the two-spotted spider mite, Tetranychus urticae, and both of them have dose-dependent RNAi effect. For different life stages, egg and larvae are the most sensitive life stages to dsRNAs. For different target genes, there is no apparent association between the suppression level and the resultant phenotype. Finally, we demonstrated that this egg-soaking RNAi method acts as both stomach and contact toxicity. Our combined results demonstrate the effectiveness of a topically applied dsRNA delivery method, and the potential of a spray induced gene silencing (SIGS) method as a control alternative for spider mites.

The small heat shock protein Hsp20.8 imparts tolerance to high temperatures in the leafminer fly, Liriomyza trifolii (Diptera: Agtomyzidae)

As an environmental factor, temperature impacts the distribution of species and influences interspecific competition. The molecular chaperones encoded by small heat shock proteins (sHsps) are essential for rapid, appropriate responses to environmental stress. This study focuses on Hsp20.8, which encodes a temperature-responsive sHsp in Liriomyza trifolii, an insect pest that infests both agricultural and ornamental crops. Hsp20.8 expression was highest at 39℃ in L. trifolii pupae and adults, and expression levels were greater in pupae than in adults. Recombinant Hsp20.8 was expressed in Escherichia coli and conferred a higher survival rate than the empty vector to bacterial cells exposed to heat stress. RNA interference experiments were conducted using L. trifolii adults and prepupae and the knockdown of Hsp20.8 expression increased mortality in L. trifolii during heat stress. The results expand our understanding of sHsp function in Liriomyza spp. and the ongoing adaptation of this pest to climate change. In addition, this study is also important for predicting the distribution of invasive species and proposing new prevention and control strategies based on temperature adaptation.

Direct dsRNA preparation by promoter-free RCT and RNase H cleavage using one circular dsDNA template with a mismatched bubble

Double-stranded RNA (dsRNA) has aroused widespread interest due to its effects on immunity and applications based on RNAi. However, the in vitro preparation of dsRNA is costly and laborious. In this study, we have developed a novel and interesting method designated as pfRCT (promoter-free rolling-circle transcription) for direct, facile, and efficient dsRNA preparation. This method generates equal amounts of sense and antisense strands simultaneously from a single circular dsDNA template. To initiate transcription by T7 RNA polymerase without directional preference, a 9-15-bp bubble (mismatched duplex with strong sequence symmetry) is introduced into the template. During RCT, all the necessary reagents, including the template, NTPs, RNA polymerase, RNase H, and Helpers, are present in one pot; and the just-transcribed RNA is immediately truncated by RNase H to monomers with the desired size. The ends of the dsRNA product can also be simply sealed by T4 RNA ligase 1 after pfRCT. This new approach is expected to promote the applications of dsRNA.

Knockdown of double-stranded RNases (dsRNases) enhances oral RNA interference (RNAi) in the corn leafhopper, Dalbulus maidis

The leafhopper Dalbulus maidis is a harmful pest that causes severe damage to corn crops. Conventional chemical pesticides have negative environmental impacts, emphasizing the need for alternative solutions. RNA interference (RNAi) is a more specific and environmentally friendly method for controlling pests and reducing the negative impacts of current pest management practices. Previous studies have shown that orally administered double-stranded RNA (dsRNA) is less effective than injection protocols in silencing genes. This study focuses on identifying and understanding the role of double-stranded ribonucleases (dsRNases) in limiting the efficiency of oral RNAi in D. maidis. Three dsRNases were identified and characterized, with Dmai-dsRNase-2 being highly expressed in the midgut and salivary glands. An ex vivo degradation assay revealed significant nuclease activity, resulting in high instability of dsRNA when exposed to tissue homogenates. Silencing Dmai-dsRNase-2 improved the insects' response to the dsRNA targeting the gene of interest, providing evidence of dsRNases involvement in oral RNAi efficiency. Therefore, administering both dsRNase-specific and target gene-specific-dsRNAs simultaneously is a promising approach to increase the efficiency of oral RNAi and should be considered in future control strategies.

A gut commensal bacterium promotes black soldier fly larval growth and development partly via modulation of intestinal protein metabolism

IMPORTANCE

Black solider fly larvae and the gut microbiota can recycle nutrients from various organic wastes into valuable insect biomass. We found that Citrobacter amalonaticus, a gut commensal bacterium of the insect, exerts beneficial effects on larval growth and development and that the expression of many metabolic larval genes was significantly impacted by the symbiont. To identify the larval genes involved in the host-symbiont interaction, we engineered the symbiont to produce double-strand RNA and enabled the strain to silence host genes in the larval gut environment where the interaction takes place. With this approach, we confirmed that two intestinal protease families are involved in the interaction and provided further evidence that intestinal protein metabolism plays a role in the interaction. This work expands the genetic toolkits available to study the insect functional genomics and host-symbiont interaction and provide the prospective for the future application of gut microbiota on the large-scale bioconversion.

Effect of silencing Thrips palmi Btk29A and COL3A1 on fitness and virus acquisition

Thrips palmi (Thysanoptera: Thripidae) is a major agricultural pest infesting over 200 plant species. Along with direct injury caused by feeding, T. palmi spreads several orthotospoviruses. Groundnut bud necrosis orthotospovirus (GBNV, family Tospoviridae, genus Orthotospovirus) is the predominant orthotospovirus in Asia, vectored by T. palmi. It is responsible for almost 89 million USD losses in Asia annually. Several transcripts of T. palmi related to innate immune response, receptor binding, cell signaling, cellular trafficking, viral replication, and apoptosis are responsive to the infection of orthotospoviruses in thrips. Expression of T. palmi tyrosine kinase Btk29A isoform X1 (Btk29A) and collagen alpha-1(III) chain-like (COL3A1) are significantly regulated post-GBNV and capsicum chlorosis orthotospovirus infection. In the present study, T. palmi Btk29A and COL3A1 were silenced and the effect on virus titer and fitness was assessed. The expression of Btk29A and COL3A1 was significantly reduced by 3.62 and 3.15-fold, respectively, 24 h post-dsRNA exposure. Oral administration of Btk29A and COL3A1 dsRNAs induced 60 and 50.9% mortality in T. palmi. The GBNV concentration in T. palmi significantly dropped post-silencing Btk29A. In contrast, the silencing of COL3A1 led to an increase in GBNV concentration in T. palmi compared to the untreated control. To the best of our knowledge, this is the first report on the effect of silencing Btk29A and COL3A1 on the fitness and GBNV titer in T. palmi.

RNA Interference Past and Future Applications in Plants

Antisense RNA was observed to elicit plant disease resistance and post-translational gene silencing (PTGS). The universal mechanism of RNA interference (RNAi) was shown to be induced by double-stranded RNA (dsRNA), an intermediate produced during virus replication. Plant viruses with a single-stranded positive-sense RNA genome have been instrumental in the discovery and characterization of systemic RNA silencing and suppression. An increasing number of applications for RNA silencing have emerged involving the exogenous application of dsRNA through spray-induced gene silencing (SIGS) that provides specificity and environmentally friendly options for crop protection and improvement.

RNA interference to combat the Asian tiger mosquito in Europe: A pathway from design of an innovative vector control tool to its application

The Asian tiger mosquito Aedes albopictus is currently spreading across Europe, facilitated by climate change and global transportation. It is a vector of arboviruses causing human diseases such as chikungunya, dengue hemorrhagic fever and Zika fever. For the majority of these diseases, no vaccines or therapeutics are available. Options for the control of Ae. albopictus are limited by European regulations introduced to protect biodiversity by restricting or phasing out the use of pesticides, genetically modified organisms (GMOs) or products of genome editing. Alternative solutions are thus urgently needed to avoid a future scenario in which Europe faces a choice between prioritizing human health or biodiversity when it comes to Aedes-vectored pathogens. To ensure regulatory compliance and public acceptance, these solutions should preferably not be based on chemicals or GMOs and must be cost-efficient and specific. The present review aims to synthesize available evidence on RNAi-based mosquito vector control and its potential for application in the European Union. The recent literature has identified some potential target sites in Ae. albopictus and formulations for delivery. However, we found little information concerning non-target effects on the environment or human health, on social aspects, regulatory frameworks, or on management perspectives. We propose optimal designs for RNAi-based vector control tools against Ae. albopictus (target product profiles), discuss their efficacy and reflect on potential risks to environmental health and the importance of societal aspects. The roadmap from design to application will provide readers with a comprehensive perspective on the application of emerging RNAi-based vector control tools for the suppression of Ae. albopictus populations with special focus on Europe.

Fox transcription factor AccGRF1 in response to glyphosate stress in Apis cerana cerana

Glyphosate is an herbicide commonly used in agriculture, and its widespread use has adversely affected the survival of nontarget organisms. Among these organisms, bees in particular are important pollinators, and declining bee populations have severely affected crop yields around the world. However, the molecular mechanism by which glyphosate harms bees remains unclear. In our experiment, we screened and cloned a glyphosate-induced gene in Apis cerana cerana (A. c. cerana) and named glyphosate response factor 1 (AccGRF1). Sequence analysis showed that AccGRF1 contains a winged-helix DNA binding domain, which suggests that it belongs to the Forkhead box (Fox) protein family. qRT-PCR and heterologous expression in Escherichia coli and yeast showed that AccGRF1 can respond to glyphosate and oxidative stress. After AccGRF1 knockdown by means of RNA interference (RNAi), the resistance of A. c. cerana to glyphosate stress improved. The results suggested that AccGRF1 is involved in A. c. cerana glyphosate stress tolerance. This study reveals the functions of Fox transcription factors in response to glyphosate stress and provides molecular insights into the regulation of glyphosate responses in honeybees.

Eco-friendly deacetylated chitosan base siRNA biological-nanopesticide loading cyromazine for efficiently controlling Spodoptera frugiperda

Spodoptera frugiperda is a serious threat to various crops, such as corn and rice, and results in severe economic losses. Herein, a chitin synthase sfCHS highly expressed in the epidermis of S. frugiperda was screened, and when interfered by an sfCHS-siRNA nanocomplex, most individuals could not ecdysis (mortality rate 53.3 %) or pupate (abnormal pupation 80.6 %). Based on the results of structure-based virtual screening, cyromazine (CYR, binding free energy -57.285 kcal/mol) could inhibit ecdysis (LC₅₀, 19.599 μg/g). CYR-CS/siRNA nanoparticles encapsulating CYR and SfCHS-siRNA with chitosan (CS) were successfully prepared, as confirmed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and 74.9 mg/g CYR was characterized in the core of CYR-CS/siRNA by high-performance liquid chromatography and Fourier transform infrared spectroscopy. Small amounts of prepared CYR-CS/siRNA containing only 1.5 μg/g CYR could better inhibit chitin synthesis in the cuticle and peritrophic membrane (mortality rate 84.4 %). Therefore, chitosan/siRNA nanoparticle-loaded pesticides were useful for pesticide reduction and comprehensive control of S. frugiperda.

Bacteria-mediated RNAi for managing fall webworm, Hyphantria cunea: screening target genes and analyzing lethal effect

BACKGROUND

The fall webworm, Hyphantria cunea, an invasive forest pest found worldwide, causes serious ecological and economic damage. Currently, the application of chemical pesticides is the most widely used strategy for H. cunea management. However, long-term pesticide use leads to pest resistance, phytotoxicity, human poisoning, and environmental deterioration. RNA interference (RNAi) technology may provide an environmentally friendly and cost-effective option for H. cunea control. However, effective RNAi targets and application methods for H. cunea are lacking.

RESULTS

We screened and obtained two highly effective RNAi targets, vATPase A (V-type proton ATPase catalytic subunit A) and Rop (Ras opposite), from 23 candidate genes, using initial and repeat screening tests with the double-stranded RNA (dsRNA) injection method. RNAi against these two genes was effective in suppressing each target messenger RNA level and interfering with larval growth, leading to significant larval mortality and pupal abnormality. For massive production of dsRNA and practical application of RNAi technology in H. cunea, transformed bacteria expressing dsRNAs of these two genes were prepared using the L4440 expression vector and HT115 strain of Escherichia coli. Oral administration of bacterially expressed dsRNA targeting vATPase A and Rop genes showed high mortality and the same malformed phenotype as the injection treatment. To further investigate the lethal effects of targeting these two genes on larval development, transcriptome sequencing (RNA-seq) was performed on RNAi samples. The results demonstrated disorders in multiple metabolic pathways, and the expression levels of most genes related to insect cuticle metabolism were significantly different, which may directly threaten insect survival. In addition, some new findings were obtained via RNA-seq analysis; for example, the progesterone-mediated oocyte maturation and oocyte meiosis processes were significantly different after silencing vATPase A, and the insect olfactory protein-related genes were significantly downregulated after dsHcRop treatment.

CONCLUSION

vATPase A and Rop are two highly effective RNAi-mediated lethal genes in H. cunea that regulate insect growth via multiple metabolic pathways. Oral delivery of bacterially expressed dsRNA specific to vATPase A and Rop can potentially be used for RNAi-based H. cunea management. This is the first study to apply bacteria-mediated RNAi for the control of this invasive pest, which is a major step forward in the application of the RNAi technology in H. cunea. © 2022 Society of Chemical Industry.

RNA interference in cytochrome P450 monooxygenase (CYP) gene results in reduced insecticide resistance in Megalurothrips usitatus Bagnall

Genes of the cytochrome P450 (CYP450) superfamily are known to be involved in the evolution of insecticide resistance. In this study, the transcriptomes of two Megalurothrips usitatus Bagnall (Thysanoptera: Thripidae) strains (resistant and susceptible) were screened for detoxification genes. MusiDN2722 encodes a protein composed of 504 amino acid residues with a relative molecular mass of 57.3 kDa. Multiple sequence alignment and phylogenetic analysis showed that MusiDN2722 is a member of the CYP450 family and has characteristics of the conserved CYP6 domain shared by typical CYP450 family members. RT-qPCR (real-time quantitative polymerase chain reaction) analysis showed that MusiDN2722 was upregulated in the acetamiprid-resistant strain compared with the susceptible strain (p < 0.05), and the relative expression level was significantly higher at 48 h after exposure than at 24 h after exposure. The interference efficiency of the injection method was higher than that of the membrane-feeding method. Silencing of MusiDN2722 through RNA interference significantly increased the sensitivity of M. usitatus to acetamiprid. Overall, this study revealed that MusiDN2722 plays a crucial role in the resistance of M. usitatus to acetamiprid. The findings will not only advance our understanding of the role of P450s in insecticide resistance but also provide a potential target for the sustainable control of destructive pests such as thrips.

Functional characterization of five developmental signaling network genes in the white-backed planthopper: Potential application for pest management

BACKGROUND

The white-backed planthopper (WBPH, Sogatella furcifera) is a major rice pest that exhibits condition dependent wing dimorphisms - a macropterous (long wing) form and a brachypterous (short wing) form. Although, the gene cascade that regulates wing development and dimorphic differentiation has been largely defined, the utility of these genes as targets for pest control has yet to be fully explored.

RESULTS

Five genes typically associated with the developmental signaling network, armadillo (arm), apterous A (apA), scalloped (sd), dachs (d), and yorkie (yki) were identified from the WBPH genome and their roles in wing development assessed following RNA interference (RNAi)-mediated knockdown. At 5 days-post injection, transcript levels for all five targets were substantially decreased compared with the dsGFP control group. Among the treatment groups, those injected with dsSfarm had the most pronounced effects on transcript reduction, mortality (95 ± 3%), and incidence (45 ± 3%) of wing deformities, whereas those injected with dsSfyki had the lowest incidence (6.7 ± 4%). To assess the utility of topical RNAi for Sfarm, we used a spray-based approach that complexed a large-scale, bacteria-based double-stranded RNA (dsRNA) expression pipeline with star polycation (SPc) nanoparticles. Rice seedlings infested with third and fourth instar nymphs were sprayed with SPc-dsRNA formulations and RNAi phenotypic effects were assessed over time. At 2 days post-spray, Sfarm transcript levels decreased by 86 ± 9.5% compared with dsGFP groups, and the subsequent incidences of mortality and wing defects were elevated in the treatment group.

CONCLUSIONS

This study characterized five genes in the WBPH developmental signaling cascade, assessed their impact on survival and wing development via RNAi, and developed a nanoparticle-dsRNA spray approach for potential field control of WBPH. © 2023 Society of Chemical Industry.

Functional characterization of tyrosine melanin genes in the white-backed planthopper and utilization of a spray-based nanoparticle-wrapped dsRNA technique for pest control

As a significant pest of rice the white-backed planthopper (WBPH) Sogatella furcifera is a focus of pest management. However, traditional chemical-based control methods risk the development of pesticide resistance as well as severe ecological repercussions. Although nanoparticle-encapsulated dsRNAs provide a promising alternative method for sustainable pest management, gene targets specific to WBPH have yet to be optimized. Genes in the tyrosine-melanin pathway impact epidermal melanization and sclerotization, two processes essential for insect development and metabolism, have been proposed as good candidate targets for pest management. Seven genes (aaNAT, black, DDC, ebony, tan, TH, and yellow-y) in this group were identified from WBPH genome and functionally characterized by using RNAi for their impact on WBPH body color, development, and mortality. Knockdown of SfDDC, Sfblack, SfaaNAT, and Sftan caused cuticles to turn black, whereas Sfyellow-y and Sfebony knockdown resulted in yellow coloration. SfTH knockdown resulted in pale-colored bodies and high mortality. Additionally, an Escherichia coli expression system for large-scale dsRNA production was coupled with star polycation nanoparticles to develop a sprayable RNAi method targeting SfTH that induced high WBPH mortality rates on rice seedlings. These findings lay the groundwork for the development of large-scale dsRNA nanoparticle sprays as a WBPH control method.

Functional characterization of developmentally critical genes in the white-backed planthopper: Efficacy of nanoparticle-based dsRNA sprays for pest control

BACKGROUND

Epidermal growth factor receptor (EGFR), zinc finger homeodomain-2 (zfh-2), Abdominal-A (Abd-A), and Abdominal-B (Abd-B) regulate the growth and development of the insect abdomen. However, their potential roles in pest control have not been fully assessed. The development of insecticide resistance to multiple chemistries in the white-backed planthopper (WBPH), a major pest of rice, has prompted interest in novel pest control approaches that are ecologically friendly. Although pest management approaches based on double-stranded RNA (dsRNA)-mediated RNA interference (RNAi) have potential, their susceptibility to degradation limits large-scale field applications. These limitations, however, can be overcome with nanoparticle-dsRNA complexes that have greater environmental stability and improved cellular uptake.

RESULTS

In this study, at 5 days post-injection, transcripts for the four gene targets were reduced relative to controls and all of the experimental groups exhibited significant phenotypic defects and increased mortality. To evaluate the potential of these gene targets for field applications, a nanocarrier-dsRNA spray delivery system was assessed for RNAi efficacy. At 11 days post-spray, significant phenotypic defects and increased mortality were observed in all experimental groups.

CONCLUSION

Taken together, the results confirm the suitability of the target genes (SfEGFR, Sfzfh-2, SfAbd-A, and SfAbd-B) for pest management and demonstrate the efficacy of the nanocarrier spray system for inducing RNAi-mediated knockdown. As such, the study lays the foundation for the further development and optimization of this technology for large-scale field applications. © 2022 Society of Chemical Industry.

Host-pathogen interaction in arthropod vectors: Lessons from viral infections

Haematophagous arthropods can harbor various pathogens including viruses, bacteria, protozoa, and nematodes. Insects possess an innate immune system comprising of both cellular and humoral components to fight against various infections. Haemocytes, the cellular components of haemolymph, are central to the insect immune system as their primary functions include phagocytosis, encapsulation, coagulation, detoxification, and storage and distribution of nutritive materials. Plasmatocytes and granulocytes are also involved in cellular defense responses. Blood-feeding arthropods, such as mosquitoes and ticks, can harbour a variety of viral pathogens that can cause infectious diseases in both human and animal hosts. Therefore, it is imperative to study the virus-vector-host relationships since arthropod vectors are important constituents of the ecosystem. Regardless of the complex immune response of these arthropod vectors, the viruses usually manage to survive and are transmitted to the eventual host. A multidisciplinary approach utilizing novel and strategic interventions is required to control ectoparasite infestations and block vector-borne transmission of viral pathogens to humans and animals. In this review, we discuss the arthropod immune response to viral infections with a primary focus on the innate immune responses of ticks and mosquitoes. We aim to summarize critically the vector immune system and their infection transmission strategies to mammalian hosts to foster debate that could help in developing new therapeutic strategies to protect human and animal hosts against arthropod-borne viral infections.

Fluorescent Nanoparticle-RNAi-Mediated Silencing of Sterol Carrier Protein-2 Gene Expression Suppresses the Growth, Development, and Reproduction of Helicoverpa armigera

Helicoverpa armigera is a polyphagous destructive lepidopteran pest with strong Bacillus thuringiensis (Bt) resistance. Cholesterol, a vital component for insect growth, can only be obtained from food, and its transfer and metabolism are regulated by sterol carrier protein-2 (SCP-2). This study examined whether H. armigera SCP-2 (HaSCP-2) gene expression, involved in cholesterol absorption, can be silenced by nanocarrier fluorescent nanoparticle-RNA interference (FNP-RNAi) by larval feeding and whether the silencing affected H. armigera development. Fluorescence microscopy showed that nanoparticle-siRNA was distributed in Ha cells and the larval midgut. FNP-HaSCP-2 siRNA suppressed HaSCP-2 expression by 52.5% in H.armigera Ha cells. FNP can effectively help deliver siRNA into cells, protect siRNA, and is not affected by serum. FNP-siRNA in vivo biological assays showed that HaSCP-2 transcript levels were inhibited by 70.19%, 68.16%, and 67.66% in 3rd, 4th, and 5th instar larvae, leading to a decrease in the cholesterol level in the larval and prepupal fatbodies. The pupation rate and adult emergence were reduced to 26.0% and 56.52%, respectively. This study demonstrated that FNP could deliver siRNA to cells and improve siRNA knockdown efficiency. HaSCP-2 knockdown by FNP-siRNA in vivo hindered H. armigera growth and development. FNP could enhance RNAi efficiency to achieve pest control by SCP-2-targeted FNP-RNAi.

Functional validation of CYP304A1 associated with haedoxan A detoxification in Aedes albopictus by RNAi and transgenic drosophila

BACKGROUND

Insect cytochrome P450 monooxygenases play important roles in the detoxification metabolism of endogenous and exogenous compounds. Haedoxan A (HA) from Phryma leptostachya L. is a highly efficient natural pesticide used to control houseflies and mosquitos. CYP4C21 and CYP304A1 were previously demonstrated to be transcriptionally increased in Aedes albopictus in response to HA exposure, but their involvement in HA metabolism is unknown.

RESULTS

Our data showed that CYP304A1 expression levels in A. albopictus were highest in third-instar larvae, and the expression level of CYP4C21 decreased significantly with the growth of instars, with the lowest occurring in the pupal stage. Compared with the control, the silencing of CYP304A1 and CYP4C21 genes by chitosan nanoparticle-mediated RNA interference could deplete 58.2% and 54.0% of the expression of corresponding genes, respectively. The bioassay data showed that knocking down the expression of CYP304A1 increased the mortality of A. albopictus when exposed to HA at LC₃₀ and LC₅₀ doses, but did not significantly increase mortality after silencing CYP4C21. Our data demonstrated that CYP304A1, but not CYP4C21, may be involved in HA detoxification. Moreover, the resistance ratio of CYP304A1 overexpressing flies was approximately 2-fold higher than that of the control line. The metabolized product of HA by CYP304A1 needs to be further confirmed by in vitro expression.

CONCLUSION

This finding showed that inducibility was not always linked to detoxifying capabilities, and enhanced our understanding of the molecular basis of HA metabolic detoxification in A. albopictus. © 2022 Society of Chemical Industry.

Insight into aphid mediated Potato Virus Y transmission: A molecular to bioinformatics prospective

Potato, the world's most popular crop is reported to provide a food source for nearly a billion people. It is prone to a number of biotic stressors that affect yield and quality, out of which Potato Virus Y (PVY) occupies the top position. PVY can be transmitted mechanically and by sap-feeding aphid vectors. The application of insecticide causes an increase in the resistant vector population along with detrimental effects on the environment; genetic resistance and vector-virus control are the two core components for controlling the deadly PVY. Using transcriptomic tools together with differential gene expression and gene discovery, several loci and genes associated with PVY resistance have been widely identified. To combat this virus we must increase our understanding on the molecular response of the PVY-potato plant-aphid interaction and knowledge of genome organization, as well as the function of PVY encoded proteins, genetic diversity, the molecular aspects of PVY transmission by aphids, and transcriptome profiling of PVY infected potato cultivars. Techniques such as molecular and bioinformatics tools can identify and monitor virus transmission. Several studies have been conducted to understand the molecular basis of PVY resistance/susceptibility interactions and their impact on PVY epidemiology by studying the interrelationship between the virus, its vector, and the host plant. This review presents current knowledge of PVY transmission, epidemiology, genome organization, molecular to bioinformatics responses, and its effective management.

Silencing of V-ATPase-E gene causes midgut apoptosis of Diaphorina citri and affects its acquisition of Huanglongbing pathogen

The Asian citrus psyllid, Diaphorina citri Kuwayama, is among the most important pests of citrus. It is the main vector of the Huanglongbing (HLB) pathogen Candidatus Liberibacter asiaticus (CLas), which causes severe losses in citrus crops. Control of D. citri is therefore of paramount importance to reduce the spread of HLB. In this regard, using RNA interference (RNAi) to silence target genes is a useful strategy to control psyllids. In this study, using RNAi, we examined the biological functions of the V-ATPase subunit E (V-ATP-E) gene of D. citri, including its effect on acquisition of CLas. The amino acid sequence of V-ATP-E from D. citri had high homology with proteins from other insects. V-ATP-E was expressed at all D. citri life stages analyzed, and the expression level in mature adults was higher than that of teneral adults. Silencing of V-ATP-E resulted in a significant increase in mortality, reduced body weight, and induced cell apoptosis of the D. citri midgut. The reduced expression of V-ATP-E was indicated to inhibit CLas passing through the midgut and into the hemolymph, leading to a majority of CLas being confined to the midgut. In addition, double-stranded RNA of D. citri V-ATP-E was safe to non-target parasitic wasps. These results suggest that V-ATP-E is an effective RNAi target that can be used in D. citri control to block CLas infection.

Three Heat Shock Protein Genes and Antioxidant Enzymes Protect Pardosa pseudoannulata (Araneae: Lycosidae) from High Temperature Stress

Pardosa pseudoannulata (P. pseudoannulata) is an essential natural predatory enemy in rice ecosystems. The fluctuating climate may cause them to experience heat stress, whereas heat shock proteins (HSPs) and antioxidant enzymes help resist heat damage. Herein, we cloned and characterized the full-length genes PpHSP27, PpHSP60, and PpHSC70 from P. pseudoannulata. Changes in gene expression levels and superoxide dismutase (SOD), catalase (CAT), and glutathione transferase (GST) activities in adult male and female P. pseudoannulata were measured at different stress exposure times and temperatures. We found that the abovementioned HSP genes belong to the sHSP, HSP60, and HSP70 families. The expression of the three HSP genes and the activities of SOD, CAT, and GST were significantly upregulated with the increasing stress temperature and time. The knockdown of the three HSP genes via RNA interference significantly decreased the survival rate of male and female P. pseudoannulata during high temperature stress. Thus, PpHSP27, PpHSP60, and PpHSC70 play an important role in the heat tolerance of P. pseudoannulata, and SOD, CAT, and GST enable recovery heat stress-induced oxidative damage. Their changes and regulation during high temperature stress can improve spiders' adaptability in the field and enhance the biological control of environmental pests.

Characteristics of environmental RNAi in potato psyllid, Bactericera cockerelli (Sulc) (Hemiptera: Psylloidea: Triozidae)

RNA interference (RNAi) has potential to become a major tool for integrated management of insect pests of agricultural crops based on sequence-specificity and low doses of rapidly biodegradable dsRNA. Deploying ‘environmental RNAi’ for control of insect vectors of plant pathogens is of increasing interest for combatting emerging plant diseases. Hemipteran insect vectors, including psyllids, are vascular feeders, making their development difficult to control specifically by targeting with pesticidal chemistries. Psyllids transmit “Candidatus Liberibacter solanacearum” the causal organism of potato zebra chip and tomato vein greening diseases, transmitted, respectively, by the potato or tomato psyllid (PoP). Until now, the optimal effective concentration(s) of double-stranded RNA (dsRNA) required for significant gene knockdown and RNAi persistence in PoP have not been determined. The objective of this study was to optimize RNAi in young PoP adults and 3rd instars for screening by oral delivery of dsRNAs. The minimal effective dsRNA concentrations required for robust knockdown and persistence were evaluated by delivering seven concentrations spanning 0.1 ng/μL to 500 ng/μL over post ingestion-access periods (IAP) ranging from 48 h to 12 days. The PoP gene candidates evaluated as targets were vacuolar ATPase subunit A, clathrin heavy chain, and non-fermenting protein 7, which were evaluated for knockdown by qPCR amplification. The minimum and/or the second most effective dsRNA concentration resulting in effective levels of gene knockdown was 100 ng/μL for all three targets. Higher concentrations did not yield further knockdown, indicating potential RISC saturation at the higher doses. Gene silencing post-IAP of 100 ng/μL dsRNA persisted for 3–5 days in adults and nymphs, with the PoP 3rd instar, followed by teneral and mature adults, respectively, exhibiting the most robust RNAi-response.

A Comparison of RNA Interference via Injection and Feeding in Honey Bees

RNA interference (RNAi) has been used successfully to reduce target gene expression and induce specific phenotypes in several species. It has proved useful as a tool to investigate gene function and has the potential to manage pest populations and reduce disease pathogens. However, it is not known whether different administration methods are equally effective at interfering with genes in bees. Therefore, we compared the effects of feeding and injection of small interfering RNA (siRNA) on the messenger RNA (mRNA) levels of alpha-aminoadipic semialdehyde dehydrogenase (ALDH7A1), 4-coumarate-CoA ligase (4CL), and heat shock protein 70 (HSP70). Both feeding and injection of siRNA successfully knocked down the gene but feeding required more siRNA than the injection. Our results suggest that both feeding and injection of siRNA effectively interfere with brain genes in bees. The appropriateness of each method would depend on the situation.

Strategies for the production of dsRNA biocontrols as alternatives to chemical pesticides

Current crop pest control strategies rely on insecticidal and fungicidal sprays, plant genetic resistance, transgenes and agricultural practices. However, many insects, plant viruses, and fungi have no current means of control or have developed resistance against traditional pesticides. dsRNA is emerging as a novel sustainable method of plant protection as an alternative to traditional chemical pesticides. The successful commercialisation of dsRNA based biocontrols for effective pest management strategies requires the economical production of large quantities of dsRNA combined with suitable delivery methods to ensure RNAi efficacy against the target pest. A number of methods exist for the production and delivery of dsRNA based biocontrols and here we review alternative methods currently employed and emerging new approaches for their production. Additionally, we highlight potential challenges that will need to be addressed prior to widespread adoption of dsRNA biocontrols as novel sustainable alternatives to traditional chemical pesticides.

Nanoparticle facilitated stacked-dsRNA improves suppression of the Lepidoperan pest Chilo suppresallis

In recent years, gene knockdown technology using double-stranded RNA (dsRNA) has been widely used as an environment-friendly pest control strategy, but its instability and limited cellular uptake have limited its overall effect. Studies have shown that the efficiency of single dsRNA can be improved by using various nanomaterials. However, the effect of stacked-dsRNA wrapped by nanomaterial on pests remains unclear. In the present study, both CYP15C1 and C-factor genes were cloned from the midgut of C. suppressalis, and the transcript of C-factor is most highly expressed in heads. Feeding a dsCYP15C1 or dsC-factor - nanomaterial mixture can downregulate the gene expression and significantly increase larval mortality. More importantly, feeding the stacked-dsRNA wrapped by nanomaterial can significantly increase the mortality of C. suppressalis, compared with feeding dsCYP15C1 or dsC-factor - nanomaterial mixture alone. These results showed that CYP15C1 and C-factor could be potential targets for an effective management of C. suppressalis, and we developed a nanoparticle-facilitated stacked-dsRNA strategy in the control of C. suppresallis. Our research provides a theoretical basis for gene function analysis and field pest control, and will promote the application of RNAi technology in the stacked style of pest control.

A species-specific lncRNA modulates the reproductive ability of the asian tiger mosquito

Long non-coding RNA (lncRNA) research has emerged as an independent scientific field in recent years. Despite their association with critical cellular and metabolic processes in plenty of organisms, lncRNAs are still a largely unexplored area in mosquito research. We propose that they could serve as exceptional tools for pest management due to unique features they possess. These include low inter-species sequence conservation and high tissue specificity. In the present study, we investigated the role of ovary-specific lncRNAs in the reproductive ability of the Asian tiger mosquito, Aedes albopictus. Through the analysis of transcriptomic data, we identified several lncRNAs that were differentially expressed upon blood feeding; we called these genes Norma (NOn-coding RNA in Mosquito ovAries). We observed that silencing some of these Normas resulted in significant impact on mosquito fecundity and fertility. We further focused on Norma3 whose silencing resulted in 43% oviposition reduction, in smaller ovaries and 53% hatching reduction of the laid eggs, compared to anti-GFP controls. Moreover, a significant downregulation of 2 mucins withing a neighboring (∼100 Kb) mucin cluster was observed in smaller anti-Norma3 ovaries, indicating a potential mechanism of in-cis regulation between Norma3 and the mucins. Our work constitutes the first experimental proof-of-evidence connecting lncRNAs with mosquito reproduction and opens a novel path for pest management.

Why is oral-induced RNAi inefficient in Diatraea saccharalis? A possible role for DsREase and other nucleases

The efficiency of RNAi technology in insects varies considerably, particularly in lepidopterans. An important limiting factor of RNAi-mediated gene silencing is the degradation of dsRNA by insect nucleases before cellular uptake. To date, few studies have reported effective gene knockdown in the sugarcane borer Diatraea saccharalis. However, yielding contradictory results when using oral delivery. Further, the RNAi efficiency in D. saccharalis and presumed activity of gut nucleases remain poorly understood. Therefore, we investigated whether gene silencing was feasible via dsRNA feeding in D. saccharalis. Two different genes were tested, juvenile hormone esterase (DsJHE) and chitin synthase 1 (DsCHS1). Discrete knockdown was verified only for DsCHS1 with high dsRNA dosages and long exposure times. Neither mortality nor abnormal phenotypes were observed after treatment with any tested dsRNA. It was also verified that dsRNAs were quickly degraded when incubated with gut juice. Furthermore, we identified four possible nucleases that could reduce the knockdown efficiency in D. saccharalis. Three of them had the endonuclease_NS domain (DsNucleases), and one had the PIN domain (DsREase), with REase-like genes being scarcely represented in databanks. We further remark that DsNuclease1 and DsREase are highly expressed in the larval gut, and DsREase was upregulated as insects were fed with artificial diet (without dsRNA), and also when injected with dsRNA. Conversely, no nuclease was triggered when insects were fed with a sucrose droplet containing dsRNA. Thus, our findings suggest that nuclease activity within the gut is one of the possible reasons for the inefficiency of RNAi in D. saccharalis. Our data may shed light on the challenges to overcome when introducing RNAi as a strategy for controlling lepidopteran pests.

Development of efficient RNAi methods in the corn leafhopper Dalbulus maidis, a promising application for pest control

BACKGROUND

The corn leafhopper Dalbulus maidis is the main vector of important stunting pathogens that affect maize production. Currently, there are no effective methods available to manage this pest without adverse impact on the environment. In this context, genomic-based technologies such as RNA interference (RNAi) provide a more environmentally friendly pest control strategy. Therefore, we aimed to assess the application of RNAi in D. maidis and determine the function of a candidate gene related to insect reproduction and propagation.

RESULTS

We have characterized the core RNAi genes and evaluated the functionality of the RNAi machinery. We assessed the potential of RNAi technology in D. maidis via injection or ingestion of double-stranded RNA (dsRNA) to adult females. We chose Bicaudal C (BicC) as a target gene due to its important role during insect oogenesis. Administration of dsRNA^BicC caused significant reductions in the transcript levels (fold changes up to 170 times) and ovipositions. Phenotypic analysis of the ovaries revealed alterations in oocyte development, providing additional confirmation for our results and supporting the idea that Dmai-BicC is a key player of D. maidis oogenesis.

CONCLUSION

This is, to our knowledge, the first report of efficient RNAi in D. maidis. We believe our findings provide a starting point for future control strategies against one of the most important maize pests in the Americas. © 2022 Society of Chemical Industry.

Silencing of multiple target genes via ingestion of dsRNA and PMRi affects development and survival in Helicoverpa armigera

RNA interference (RNAi) triggered by exogenous double-stranded RNA (dsRNA) is a powerful tool to knockdown genetic targets crucial for the growth and development of agriculturally important insect pests. Helicoverpa armigera is a pest feeding on more than 30 economically important crops worldwide and a major threat. Resistance to insecticides and Bt toxins has been gradually increasing in the field. RNAi-mediated knockdown of H. armigera genes by producing dsRNAs homologous to genetic targets in bacteria and plants has a high potential for insect management to decrease agricultural loss. The acetylcholinesterase (AChE), ecdysone receptor (EcR) and v-ATPase-A (vAA) genes were selected as genetic targets. Fragments comprising a coding sequence of < 500 bp were cloned into the L4440 vector for dsRNA production in bacteria and in a TRV-VIGS vector in antisense orientation for transient expression of dsRNA in Solanum tuberosum leaves. After ingesting bacterial-expressed dsRNA, the mRNA levels of the target genes were significantly reduced, leading to mortality and abnormal development in larva of H. armigera. Furthermore, the S. tuberosum plants transformed with TRV-VIGS expressing AChE exhibited higher mortality > 68% than the control plants 17%, recorded ten days post-feeding and significant resistance in transgenic (transient) plants was observed. Moreover, larval lethality and molting defects were observed in larva fed on potato plants expressing dsRNA specific to EcR. Analysis of transcript levels by quantitative RT–PCR revealed that larval mortality was attributable to the knockdown of genetic targets by RNAi. The results demonstrated that down-regulation of H. armigera genes involved in ATP hydrolysis, transcriptional stimulation of development genes and neural conduction has aptitude as a bioinsecticide to control H. armigera population sizes and therefore decreases crop loss.

Nanocarrier-delivered dsRNA suppresses wing development of green peach aphids

RNA interference (RNAi) has developed rapidly as a potential "green" pest management strategy. At present, most studies have focused on the screening of aphid lethal genes, whereas only a few studies have been conducted on wing development, which is crucial for aphid migration and plant-virus dissemination. Here, the Myzus persicae genes vestigial (vg) and Ultrabithorax (Ubx) related to wing development, were cloned. These two genes were expressed in various tissues of 3rd-instar winged aphids. The mRNA level of vg was high in 3rd-instar nymphs, whereas the expression level of Ubx was high in adults. The nanocarrier-mediated delivery system delivered double-stranded RNAs for aphid RNAi using topical and root applications. The expression levels of vg and Ubx were downregulated by 44.0% and 36.5%, respectively, using the topical application. The simultaneous RNAi of the two target genes caused 63.3% and 32.2% wing aberration rates using topical and root applications, respectively. The current study provided a promising method for controlling aphid migration to alleviate the spread of insect transmitted plant diseases.

Targeting coat protein II complex genes via RNA interference inhibits female adult feeding and reproductive development in the cabbage beetle Colaphellus bowringi

BACKGROUND

The cabbage beetle Colaphellus bowringi is a highly destructive cruciferous vegetable pest in Asia. This beetle is predominantly controlled by synthetic chemical pesticides, which leave pesticide residues on food and constitute a major hidden danger to human health. Based on preliminary research, we hypothesized that the coat protein II (COPII) complex, a primary coated vesicle that exports cargo molecules from the endoplasmic reticulum, is a promising novel target for the control of Colaphellus bowringi.

RESULTS

This study investigated whether disrupting COPII using RNA interference (RNAi) affects the growth and development of Colaphellus bowringi adults. The results showed that five COPII assembly genes, Sar1, Sec23, Sec24, Sec13, and Sec31, were uniformly expressed in multiple tissues of adult female Colaphellus bowringi. Injecting double-stranded RNA (dsRNA) against each gene induced a high RNAi efficiency by approximately 55-99%, and considerably inhibited yolk deposition and ovarian growth. Moreover, knockdown of Sar1, Sec23 and Sec24 suppressed feeding and increased mortality to 26.67%, 46.67%, and 42.22%, respectively. This was partially due to the down-regulation of insulin/mTOR-associated nutritional pathways. The results indicate that silencing any of the five genes responsible for COPII complex assembly represses Juvenile hormone and ecdysone signaling pathways, suggesting that vesicle transport plays a vital role in the endocrine regulation of Colaphellus bowringi females.

CONCLUSION

This study suggests that the COPII complex could be a promising RNAi target for the management of Colaphellus bowringi, which would reduce our dependence on chemical pesticides for pest control. © 2022 Society of Chemical Industry.

Advances in the Immune Regulatory Role of Non-Coding RNAs (miRNAs and lncRNAs) in Insect-Pathogen Interactions

Insects are by far the most abundant and diverse living organisms on earth and are frequently prone to microbial attacks. In other to counteract and overcome microbial invasions, insects have in an evolutionary way conserved and developed immune defense mechanisms such as Toll, immune deficiency (Imd), and JAK/STAT signaling pathways leading to the expression of antimicrobial peptides. These pathways have accessory immune effector mechanisms, such as phagocytosis, encapsulation, melanization, nodulation, RNA interference (RNAi), lysis, autophagy, and apoptosis. However, pathogens evolved strategies that circumvent host immune response following infections, which may have helped insects further sophisticate their immune response mechanisms. The involvement of ncRNAs in insect immunity is undeniable, and several excellent studies or reviews have investigated and described their roles in various insects. However, the functional analyses of ncRNAs in insects upon pathogen attacks are not exhaustive as novel ncRNAs are being increasingly discovered in those organisms. This article gives an overview of the main insect signaling pathways and effector mechanisms activated by pathogen invaders and summarizes the latest findings of the immune modulation role of both insect- and pathogen-encoded ncRNAs, especially miRNAs and lncRNAs during insect–pathogen crosstalk.