Ingested double-stranded RNAs can act as species-specific insecticides

The role of OR5, which is highly expressed in the winged grain aphid Sitobion miscanthi, in specific recognition of EBF

Winged parthenogenetic aphids are mainly responsible for migration and dispersal. Aphid alarm pheromone (E)-β-Farnesene (EBF) has dual effects on repelling and stimulating wing differentiation in aphids. Previous studies have shown that the odorant coreceptor SmisOrco is involved in the perception of EBF by S. miscanthi; however, its EBF-specific odorant receptor (OR) and the difference between winged and wingless aphids remain unclear. In this study, the Xenopus oocyte expression system and RNAi technology were used to detect the transmission of EBF signals, and it was found that the olfactory receptor SmisOR5 is an EBF-specific OR in S. miscanthi and is specifically highly expressed in the antennae of winged aphids. Furthermore, when OR5 was silenced with dsRNA, the repellent effect of EBF was weakened, and aphids showed more active aimless movements. Therefore, as a specific OR for EBF, the high expression level of SmisOR5 in winged aphids suggests a molecular basis for its high sensitivity to EBF. This study advances our understanding of the molecular mechanisms of aphid EBF perception and provides novel ideas for effective management and prevention of the migration of winged aphids.

Bioactive peptides inhibit feeding activity in the grey garden slug, Deroceras reticulatum

BACKGROUND

The grey garden slug (Deroceras reticulatum) is considered the most damaging slug pest in global agriculture. Control methods primarily rely on chemical pesticides, which pose environmental risks and potential hazards to human health. There is a need for sustainable management alternatives such as biologically-based slug control options. However, the efficacy of nonchemical measures for controlling pest slug populations remains limited, particularly in the context of variable outdoor conditions. Neuropeptides and their corresponding receptors have been proposed as promising biological targets for the development of new pest management strategies.

RESULTS

A total of 23 bioactive peptides belonging to the PRX family, previously identified from the grey garden slug, D. reticulatum, were injected into or fed to this species. The detrimental effects of these peptides, including a reduction in body weight and an inhibition of feeding activity, were evaluated in feeding choice tests with D. reticulatum. Furthermore, the bioactive peptide formulated with a lipid particle demonstrated a feeding deterrent effect. One of the myomodulin (MM) peptides, APPLPRY, demonstrated a significant reduction in feeding activity, resulting in a reduction in slug weight or mortality in just 30 min.

CONCLUSION

The results represent the first evidence of a bioactive peptide having detrimental effects on D. reticulatum including causing feeding deterrent for this slug pest. The in vivo results provide insights into the potential development of active ingredients for managing slugs in the field. © 2024 Society of Chemical Industry.

Trophic microRNA: Post-transcriptional regulation of target genes and larval development impairment in Plutella xylostella upon precursor and mature microRNA ingestion

MicroRNAs (miRNAs) are post-transcriptional gene regulators. In the miRNA pathway's cytoplasmic part, the miRNA is processed from a hairpin-structured precursor to a double-stranded (ds) mature RNA and ultimately to a single-stranded mature miRNA. In insects, ingesting these two ds forms can regulate the target gene expression; this inspired the trophic miRNA's use as a functional genomics and pest management tool. However, systematic studies enabling comparisons of pre- and mature forms, dosages, administration times and instar-wise effects on target transcripts and phenotypes, which can help develop a miRNA administration method, are unavailable due to the different focuses of the previous investigations. We investigated the impact of trophically delivered Px-let-7 miRNA on the lepidopteran pest Plutella xylostella, to compare the efficacies of its pre- and ds-mature forms. Continuous feeding on the miRNA-supplemented diet suppressed expressions of FTZ-F1 and E74, the target ecdysone pathway genes. Both the pre-let-7 and mature let-7 miRNA forms similarly downregulated the target transcripts in all four larval instars. Pre-let-7 and let-7 ingestions decreased larval mass and instar duration and increased mortality in all instars, exhibiting adverse effects on larval growth and development. miRNA processing Dicer-1 and AGO-1's upregulations upon miRNA ingestion denoted the systemic miRNA spread in larval tissues. The scrambled sequence controls did not affect the target transcripts, suggesting the sequence-specific targeting by the mature miRNA and hairpin cassette's non-involvement in the target downregulation. This work provides a framework for miRNA and target gene function analyses and potentiates the trophic miRNA's utility in pest management.

Beekeepers Support the Use of RNA Interference (RNAi) to Control Varroa destructor

Current Varroa mite management strategies rely heavily on the use of pesticides, adversely affecting honey bee health and leaving toxic residues in hive products. To explore the likelihood of RNAi technology being utilised as an alternative control method for pests like Varroa, the opinions of beekeepers on the use of this new biotechnology were obtained using a mixed-methodology approach. In-person surveys and focus groups using the Q method were conducted to discover the willingness of beekeepers to utilise Varroa-targeting RNAi treatments in their hives, and to gain feedback to inform decisions before the implementation of this new technology. Overall, the beekeepers saw potential in RNAi being used to control Varroa in their hives and were eager to have access to an alternative to pesticide treatments. Participants raised concerns about unknown long-term effects on bees and other non-target species, and the potential of an uninformed public preventing them from accessing a new Varroa treatment. While further research and discussion is needed before RNAi treatments for Varroa become commercially available, RNAi technology presents a promising, species-specific and non-toxic solution for Varroa management.

Chromosome-Scale Genome Assembly of the Sheep-Biting Louse Bovicola ovis Using Nanopore Sequencing Data and Pore-C Analysis

Bovicola ovis, commonly known as the sheep-biting louse, is an ectoparasite that adversely affects the sheep industry. Sheep louse infestation lowers the quality of products, including wool and leather, causing a loss of approximately AUD 123M per annum in Australia alone. The lack of a high-quality genome assembly for the sheep-biting louse, as well as any closely related livestock lice, has hindered the development of louse research and management control tools. In this study, we present the assembly of B. ovis with a genome size of ~123 Mbp based on a nanopore long-read sequencing library and Illumina RNA sequencing, complemented with a chromosome-level scaffolding using the Pore-C multiway chromatin contact dataset. Combining multiple alignment and gene prediction tools, a comprehensive annotation on the assembled B. ovis genome was conducted and recalled 11,810 genes as well as other genomic features including orf, ssr, rRNA and tRNA. A manual curation using alignment with the available closely related louse species, Pediculus humanus, increased the number of annotated genes to 16,024. Overall, this study reported critical genetic resources and biological insights for the advancement of sheep louse research and the development of sustainable control strategies in the sheep industry.

Exogenous Application of dsRNA in Plant Protection: Efficiency, Safety Concerns and Risk Assessment

The use of double-stranded RNA (dsRNA) for plant protection shows great potential as a sustainable alternative to traditional pesticides. This review summarizes the current state of knowledge on using exogenous dsRNA in plant protection and includes the latest findings on the safety and efficiency of this strategy. The review also emphasizes the need for a cautious and comprehensive approach, considering safety considerations such as off-target effects and formulation challenges. The regulatory landscape in different regions is also discussed, underscoring the need for specific guidelines tailored to dsRNA-based pesticides. The review provides a crucial resource for researchers, regulators, and industry stakeholders, promoting a balanced approach incorporating innovation with thorough safety assessments. The continuous dialog emphasized in this review is essential for shaping the future of dsRNA-based plant protection. As the field advances, collaboration among scientists, regulators, and industry partners will play a vital role in establishing guidelines and ensuring the responsible, effective, and sustainable use of dsRNA in agriculture.

RNAi-mediated pest control targeting the Troponin I (wupA) gene in sweet potato weevil, Cylas formicarius

The sweet potato weevil (Cylas formicarius) is a critical pest producing enormous global losses in sweet potato crops. Traditional pest management approaches for sweet potato weevil, primarily using chemical pesticides, causes pollution, food safety issues, and harming natural enemies. While RNA interference (RNAi) is a promising environmentally friendly approach to pest control, its efficacy in controlling the sweet potato weevil has not been extensively studied. In this study, we selected a potential target for controlling C. formicarius, the Troponin I gene (wupA), which is essential for musculature composition and crucial for fundamental life activities. We determined that wupA is abundantly expressed throughout all developmental stages of the sweet potato weevil. We evaluated the efficiency of double-stranded RNAs in silencing the wupA gene via microinjection and oral feeding of sweet potato weevil larvae at different ages. Our findings demonstrate that both approaches significantly reduced the expression of wupA and produced high mortality. Moreover, the 1st instar larvae administered dswupA exhibited significant growth inhibition. We assessed the toxicity of dswupA on the no-target insect silkworm and assessed its safety. Our study indicates that wupA knockdown can inhibit the growth and development of C. formicarius and offer a potential target gene for environmentally friendly 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.

Lethal and sublethal effects of orally delivered double-stranded RNA on the cabbage stem flea beetle, Psylliodes chrysocephala

BACKGROUND

The cabbage stem flea beetle (Psylliodes chrysocephala) is one of the most important insect pests of oilseed rape (Brassica napus) in northern Europe. The emergence of insecticide-resistant populations and the ban on neonicotinoid seed treatments have made the management of this pest challenging and research is needed to develop alternative strategies such as RNA interference (RNAi). We investigated lethal and sublethal effects of orally delivered double-stranded (ds)RNAs targeting P. chrysocephala orthologs of Sec23 and vacuolar adenosine triphosphatase subunit G (VatpG), which are involved in endoplasmic reticulum-Golgi transport and organelle acidification, respectively.

RESULTS

Feeding bioassays on P. chrysocephala adults showed that the highest concentration (200 ng/leaf disk) of dsSec23 caused mortalities of 76% and 56% in pre-aestivating and post-aestivating beetles, respectively, while the same concentration of dsVatpG led to mortality rates of ~34% in both stages. Moreover, sublethal effects, such as decreased feeding rates and attenuated locomotion were observed. Small RNA sequencing and gene expression measurements following the delivery of dsRNAs demonstrated the generation of ~21 nucleotide-long small interfering RNAs and a systemic RNAi response in P. chrysocephala.

CONCLUSION

We demonstrate that P. chrysocephala is a promising candidate for developing RNAi-based pest management strategies. Further research is necessary to identify more effective target genes and to assess potential non-target effects. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Nanomaterial-encapsulated dsRNA of ecdysone-induced early gene E75, a potential RNAi-based SIT strategy for pest control against Bactrocera dorsalis

Bactrocera dorsalis is a notorious pest widely distributed across most Asian countries. With the rapid development of pesticide resistance, new pest control methods are urgently needed. RNAi-based sterile insect technique (SIT) is a species-specific pest management strategy for B. dorsalis control. It is of great significance to identify more target genes from B. dorsalis, and improve the RNAi efficiency. In this study, microinjection-based RNAi results showed that six 20E response genes were necessary for male fertility of B. dorsalis, of which E75 was identified as the key target according to the lowest egg-laying number and hatching rate after E75 knockdown. Three nanoparticles chitosan (CS), chitosan‑sodium tripolyphosphate (CS-TPP), and star polycation (SPc) were used to encapsulate dsE75 expressed by HT115 strain. Properties analysis of nanoparticle-dsRNA complexes showed that both CS-TPP-dsRNA and SPc-dsRNA exhibited better properties (smaller size and polydispersity index) than CS-dsRNA. Moreover, oral administration of CS-TPP-dsE75 and SPc-dsE75 by males resulted in more abnormal testis and significantly lower fertility than feeding naked dsE75. Semi-field trials further confirmed that the number of hatched larvae was dramatically reduced in these two groups. Our study not only provides more valuable targets for RNAi-based SIT, but also promotes the application of environment-friendly management against B. dorsalis in the field.

RNAi-mediated silencing of Mediterranean fruit fly (Ceratitis capitata) endogenous genes using orally-supplied double-stranded RNAs produced in Escherichia coli

BACKGROUND

The Mediterranean fruit fly (medfly), Ceratitis capitata Wiedemann, is a major pest affecting fruit and vegetable production worldwide, whose control is mainly based on insecticides. Double-stranded RNA (dsRNA) able to down-regulate endogenous genes, thus affecting essential vital functions via RNA interference (RNAi) in pests and pathogens, is envisioned as a more specific and environmentally-friendly alternative to traditional insecticides. However, this strategy has not been explored in medfly yet.

RESULTS

Here, we screened seven candidate target genes by injecting in adult medflies gene-specific dsRNA hairpins transcribed in vitro. Several genes were significantly down-regulated, resulting in increased insect mortality compared to flies treated with a control dsRNA targeting the green fluorescent protein (GFP) complementary DNA (cDNA). Three of the dsRNAs, homologous to the beta subunit of adenosine triphosphate (ATP) synthase (ATPsynbeta), a vacuolar ATPase (V-ATPase), and the ribosomal protein S13 (RPS13), were able to halve the probability of survival in only 48 h after injection. We then produced new versions of these three dsRNAs and that of the GFP control as circular molecules in Escherichia coli using a two-self-splicing-intron-based expression system and tested them as orally-delivered insecticidal compounds against medfly adults. We observed a significant down-regulation of V-ATPase and RPS13 messenger RNAs (mRNAs) (approximately 30% and 90%, respectively) compared with the control medflies after 3 days of treatment. No significant mortality was recorded in medflies, but egg laying and hatching reduction was achieved by silencing V-ATPase and RPS13.

CONCLUSION

In sum, we report the potential of dsRNA molecules as oral insecticide in medfly. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

DsRNA-based pesticides: Considerations for efficiency and risk assessment

In view of the ongoing climate change and the ever-growing world population, novel agricultural solutions are required to ensure sustainable food supply. Microbials, natural substances, semiochemicals and double stranded RNAs (dsRNAs) are all considered potential low risk pesticides. DsRNAs function at the molecular level, targeting specific regions of specific genes of specific organisms, provided that they share a minimal sequence complementarity of approximately 20 nucleotides. Thus, dsRNAs may offer a great alternative to conventional chemicals in environmentally friendly pest control strategies. Any low-risk pesticide needs to be efficient and exhibit low toxicological potential and low environmental persistence. Having said that, in the current review, the mode of dsRNA action is explored and the parameters that need to be taken into consideration for the development of efficient dsRNA-based pesticides are highlighted. Moreover, since dsRNAs mode of action differs from those of synthetic pesticides, custom-made risk assessment schemes may be required and thus, critical issues related to the risk assessment of dsRNA pesticides are discussed here.

RNA Interference in Insects: From a Natural Mechanism of Gene Expression Regulation to a Biotechnological Crop Protection Promise

Insect pests rank among the major limiting factors in agricultural production worldwide. In addition to direct effect on crops, some phytophagous insects are efficient vectors for plant disease transmission. Large amounts of conventional insecticides are required to secure food production worldwide, with a high impact on the economy and environment, particularly when beneficial insects are also affected by chemicals that frequently lack the desired specificity. RNA interference (RNAi) is a natural mechanism gene expression regulation and protection against exogenous and endogenous genetic elements present in most eukaryotes, including insects. Molecules of double-stranded RNA (dsRNA) or highly structured RNA are the substrates of cellular enzymes to produce several types of small RNAs (sRNAs), which play a crucial role in targeting sequences for transcriptional or post-transcriptional gene silencing. The relatively simple rules that underlie RNAi regulation, mainly based in Watson-Crick complementarity, have facilitated biotechnological applications based on these cellular mechanisms. This includes the promise of using engineered dsRNA molecules, either endogenously produced in crop plants or exogenously synthesized and applied onto crops, as a new generation of highly specific, sustainable, and environmentally friendly insecticides. Fueled on this expectation, this article reviews current knowledge about the RNAi pathways in insects, and some other applied questions such as production and delivery of recombinant RNA, which are critical to establish RNAi as a reliable technology for insect control in crop plants.

Effective delivery and selective insecticidal activity of double-stranded RNA via complexation with diblock copolymer varies with polymer block composition

BACKGROUND

Chemical insecticides are an important tool to control damaging pest infestations. However, lack of species specificity, the rise of resistance and the demand for biological alternatives with improved ecotoxicity profiles means that chemicals with new modes of action are required. RNA interference (RNAi)-based strategies using double-stranded RNA (dsRNA) as a species-specific bio-insecticide offer an exquisite solution that addresses these issues. Many species, such as the fruit pest Drosophila suzukii, do not exhibit RNAi when dsRNA is orally administered due to degradation by gut nucleases and slow cellular uptake pathways. Thus, delivery vehicles that protect and deliver dsRNA are highly desirable.

RESULTS

In this work, we demonstrate the complexation of D. suzukii-specific dsRNA for degradation of vha26 mRNA with bespoke diblock copolymers. We study the ex vivo protection of dsRNA against enzymatic degradation by gut enzymes, which demonstrates the efficiency of this system. Flow cytometry then investigates the cellular uptake of Cy3-labelled dsRNA, showing a 10-fold increase in the mean fluorescence intensity of cells treated with polyplexes. The polymer/dsRNA polyplexes induced a significant 87% decrease in the odds of survival of D. suzukii larvae following oral feeding only when formed with a diblock copolymer containing a long neutral block length (1:2 cationic block/neutral block). However, there was no toxicity when fed to the closely related Drosophila melanogaster.

CONCLUSION

We provide evidence that dsRNA complexation with diblock copolymers is a promising strategy for RNAi-based species-specific pest control, but optimisation of polymer composition is essential for RNAi success. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Transcript Level and Sequence Matching Are Key Determinants of Off-Target Effects in RNAi

Double-stranded RNA (dsRNA) pesticides, those based on RNA interference (RNAi) technology utilizing dsRNA, have shown potential for pest control. However, the off-target effects of dsRNA pose limitations to the widespread application of RNAi and raise concerns regarding potential side effects on other beneficial organisms. The precise impact and underlying factors of these off-target effects are still not well understood. Here, we found that the transcript level and sequence matching jointly regulate off-target effects of dsRNA. The much lower expressed target genes were knocked down to a lesser extent than genes with higher expression levels, and the critical sequence identity of off-target effects is approximately 80%. Moreover, off-target effects could be triggered by a contiguous matching sequence length exceeding 15 nt as well as nearly perfectly matching sequences with one or two base mismatches exceeding 19 nt. Increasing the dosage of dsRNA leads to more severe off-target effects. However, the length of mismatched dsRNA, the choice of different RNAi targets, and the location of target sites within the same gene do not affect the severity of off-target effects. These parameters can be used to guide the design of possibly selective sequences for RNAi, optimize the specificity and efficiency of dsRNA, and facilitate practical applications of RNAi for pest control.

Comparative Analyses of Reproductive Caste Types Reveal Vitellogenin Genes Involved in Queen Fertility in Solenopsis invicta

The red imported fire ant (Solenopsis invicta Buren) is a social pest species with a robust reproductive ability that causes extensive damage. Identification of the genes involved in queen fertility is critical in order to better understand the reproductive biology and screening for the potential molecular targets in S. invicta. Here, we used the mRNA deep sequencing (RNA-seq) approach to identify differentially expressed genes (DEGs) in the transcriptomes of three reproductive caste types of S. invicta, including queen (QA) and winged female (FA) and male (MA) ants. The genes that were specific to and highly expressed in the queens were then screened, and the Vg2 and Vg3 genes were chosen as targets to explore their functions in oogenesis and fertility. A minimum of 6.08 giga bases (Gb) of clean reads was obtained from all samples, with a mapping rate > 89.78%. There were 7524, 7133, and 977 DEGs identified in the MA vs. QA, MA vs. FA, and FA vs. QA comparisons, respectively. qRT-PCR was used to validate 10 randomly selected DEGs, including vitellogenin 2 (Vg2) and 3 (Vg3), and their expression patterns were mostly consistent with the RNA-seq data. The S. invicta Vgs included conserved domains and motifs that are commonly found in most insect Vgs. SiVg2 and SiVg3 were highly expressed in queens and winged females and were most highly expressed in the thorax, followed by the fat body, head, and epidermis. Evaluation based on a loss-of-function-based knockdown analysis showed that the downregulation of either or both of these genes resulted in smaller ovaries, less oogenesis, and less egg production. The results of transcriptional sequencing provide a foundation for clarifying the regulators of queen fertility in S. invicta. The functions of SiVg2 and SiVg3 as regulators of oogenesis highlight their importance in queen fecundity and their potential as targets of reproductive disruption in S. invicta control.

The use of RNA interference for the management of arthropod pests in livestock farms

Pest management in farm animals is an important action to contain economic damage to livestock production and prevent transmission of severe diseases to the stock. The use of chemical insecticides is still the most common approach followed by farmers; however, avoiding possible toxic effects on animals is a fundamental task for pest control measures compatible with animal well-being. Moreover, legal constraints and insurgence of resistance by target species to the available insecticidal compounds are increasingly complicating farmers' operations. Alternatives to chemical pesticides have been explored with some promising results in the area of biological control or the use of natural products as sprays. The application of RNA interference techniques has enabled the production of new means of pest control in agriculture, and it is opening a promising avenue for controlling arthropod pests of livestock. Transcript depletion of specific target genes of the recipient organisms is based on the action of double-strand RNAs (dsRNA) capable of impairing the production of fundamental proteins. Their mode of action, based on the specific recognition of short genomic sequences, is expected to be highly selective towards non-target organisms potentially exposed; in addition, there are physical and chemical barriers to dsRNA uptake by mammalian cells that render these products practically innocuous for higher animals. Summarising existing literature on gene silencing for main taxa of arthropod pests of livestock (Acarina, Diptera, Blattoidea), this review explores the perspectives of practical applications of dsRNA-based pesticides against the main pests of farm animals. Knowledge gaps are summarised to stimulate additional research in this area.

Gene silencing of cathepsins B and L using CTV-based, plant-mediated RNAi interferes with ovarial development in Asian citrus psyllid (ACP), Diaphorina citri

Diaphorina citri Kuwayama (Hemiptera: Liviidae) is a vector of the bacteria Candidatus Liberibacter americanus (CLam) and Candidatus Liberibacter asiaticus (CLas), which are phloem-restricted and associated with the most important and destructive worldwide citrus disease, Huanglongbing (HLB). Currently, no cure for HLB has been described. Therefore, measures have focused on reducing D. citri populations. In these insects, cathepsin B (DCcathB) and L (DCcathL) enzymes play an important role in digestion, and are involved in embryogenesis, immune defense, and ecdysis. In this study, we used a CTV-based vector to deliver dsRNA (CTV-dsRNA) into Citrus macrophylla plants targeting DCcathB and DCcathL genes in D. citri that fed on the phloem of these CTV-RNAi infected plants. Subsequently, we evaluated expression of DCcathB and DCcathL genes as well as the Vitellogenin (Vg) gene by RT-qPCR in D. citri fed on CTV-dsRNA occurring in plant phloem. It was found that a defective phenotype in D. citri females as a result of knockdown of DCcathB and DCcathL genes mediated by CTV dsRNA. These results showed that Psyllids fed on plants treated with the CTV-dsRNA exhibited downregulation of the Vg gene, one of the most important genes associated with embryogenic and female development, which was associated with dsRNA-mediated silencing of the two cathepsin genes. Based on our findings, a CTV-based strategy for delivering RNAi via plants that targets DCcathB and DCcathL genes may represent a suitable avenue for development of dsRNA-based tools to manage D. citri that limits the spread of HLB.

Double-stranded RNA mediated knockdown of sucrase gene induced mortality and reduced offspring production in Aphis gossypii

The importance of gut sucrase in maintaining osmotic equilibrium and utilizing phloem contents as a carbon source has been widely investigated and proven in sap-sucking insects. In the present study, silencing of Aphis gossypii sucrase1 (Agsuc1) was carried out by double-stranded RNA (dsRNA), which would be lethal to it due to disruption of osmotic balance. The dsRNA corresponding to Agsuc1 was synthesized by two methods, i.e., in vitro synthesis using T7/SP6 RNA polymerase and in vivo synthesis by bacterial expression, i.e., Escherichia coli strain HT115 transformed with the L4440 vector system. Oral delivery of double-stranded Agsuc1 synthesized in vitro (dsAgsuc1) and in vivo (HT115Agsuc1) induced around 50% mortality in nymphs of A. gossypii. Moreover, the number of offspring produced by the survived aphids decreased by 39-43%. Parthenogenetic reproduction of the aphids is the critical factor for their fast population build-up, leading to yield losses of economic significance. Thus, the present study demonstrated that the silencing of the Agsuc1 gene reduced the aphid population by killing it and inhibited the population buildup by reducing the number of offspring produced by the survived aphids, likely to result in a significant reduction in crop damage. The production of dsRNA by bacterial expression is a cost-effective method. It has the potential to be used as a biopesticide. The sucrase gene is an excellent putative target gene for RNAi against A. gossypii. It could be used to develop a transgenic plant that produces dsAgsuc1 to keep A. gossypii populations below the economic threshold level.

Plant and insect virus-like particles: emerging nanoparticles for agricultural pest management

Virus-like particles (VLPs) represent a biodegradable, biocompatible nanomaterial made from viral coat proteins that can improve the delivery of antigens, drugs, nucleic acids, and other substances, with most applications in human and veterinary medicine. Regarding agricultural viruses, many insect and plant virus coat proteins have been shown to assemble into VLPs accurately. In addition, some plant virus-based VLPs have been used in medical studies. However, to our knowledge, the potential application of plant/insect virus-based VLPs in agriculture remains largely underexplored. This review focuses on why and how to engineer coat proteins of plant/insect viruses as functionalized VLPs, and how to exploit VLPs in agricultural pest control. The first part of the review describes four different engineering strategies for loading cargo at the inner or the outer surface of VLPs depending on the type of cargo and purpose. Second, the literature on plant and insect viruses the coat proteins of which have been confirmed to self-assemble into VLPs is reviewed. These VLPs are good candidates for developing VLP-based agricultural pest control strategies. Lastly, the concepts of plant/insect virus-based VLPs for delivering insecticidal and antiviral components (e.g., double-stranded RNA, peptides, and chemicals) are discussed, which provides future prospects of VLP application in agricultural pest control. In addition, some concerns are raised about VLP production on a large scale and the short-term resistance of hosts to VLP uptake. Overall, this review is expected to stimulate interest and research exploring plant/insect virus-based VLP applications in agricultural pest management. © 2023 Society of Chemical Industry.

Transgenic East African Highland Banana Plants Are Protected against Radopholus similis through Host-Delivered RNAi

The burrowing nematode Radopholus similis is considered a major problem of intensive banana cultivation. It can cause extensive root damage resulting in the toppling disease of banana, which means that plants fall to the ground. Soaking R. similis in double-stranded (ds) RNA of the nematode genes Rps13, chitin synthase (Chs-2), Unc-87, Pat-10 or beta-1,4-endoglucanase (Eng1a) suppressed reproduction on carrot discs, from 2.8-fold (Chs-2) to 7-fold (Rps13). The East African Highland Banana cultivar Nakitembe was then transformed with constructs for expression of dsRNA against the same genes, and for each construct, 30 independent transformants were tested with nematode infection. Four months after transfer from in vitro culture to the greenhouse, the banana plants were transferred to a screenhouse and inoculated with 2000 nematodes per plant, and thirteen weeks later, they were analyzed for several parameters including plant growth, root necrosis and final nematode population. Plants with dsRNA constructs against the nematode genes were on average showing lower nematode multiplication and root damage than the nontransformed controls or the banana plants expressing dsRNA against the nonendogenous gene. In conclusion, RNAi seems to efficiently protect banana against damage caused by R. similis, opening perspectives to control this pest.

The Study of Cell-Penetrating Peptides to Deliver dsRNA and siRNA by Feeding in the Desert Locust, Schistocerca gregaria

RNA(i) interference is a gene silencing mechanism triggered by double-stranded (ds)RNA, which promises to contribute to species-specific insect pest control strategies. The first step toward the application of RNAi as an insecticide is to enable efficient gene silencing upon dsRNA oral delivery. The desert locust, Schistocerca gregaria is a devastating agricultural pest. While this species is responsive to dsRNA delivered by intra-hemocoelic injection, it is refractory to orally delivered dsRNA. In this study, we evaluated the capacity of five cell-penetrating peptides (CPPs) to bind long dsRNA and protect it from the locust midgut environment. We then selected the CPP EB1 for further in vivo studies. EB1:dsRNA complexes failed to induce RNAi by feeding. Interestingly, we observed that intra-hemocoelic injection of small-interfering (si)RNAs does not result in a silencing response, but that this response can be obtained by injecting EB1:siRNA complexes. EB1 also protected siRNAs from midgut degradation activity. However, EB1:siRNA complexes failed as well in triggering RNAi when fed. Our findings highlight the complexity of the dsRNA/siRNA-triggered RNAi in this species and emphasize the multifactorial nature of the RNAi response in insects. Our study also stresses the importance of in vivo studies when it comes to dsRNA/siRNA delivery systems.

Target gene selection for RNAi-based biopesticides against the hawthorn spider mite, Amphitetranychus viennensis (Acari: Tetranychidae)

BACKGROUND

Recently, RNA interference (RNAi)-based biopesticide, a species-specific pest control alternative, has been deregulated and commercialized in the US and Canada. The hawthorn spider mite, Amphitetranychus viennensis Zacher, is a major pest for rosaceous plants, which has been controlled primarily by synthetic pesticides. To address the emerging resistance issues in A. viennensis, we initiated a project to develop RNAi-based biopesticides.

RESULTS

In this study, we (i) developed a dietary RNAi system for A. viennensis using leaf disc, (ii) assessed the suitability of multiple control genes to distinguish sequence-specific silencing from non-specific effects within this RNAi system, and (iii) screened for the target gene candidates. As a result, β-Glucuronidase (GUS), an enzyme derived from E. coli and a broadly used reporter for plants is the appropriate control for A. viennensis RNAi, while green fluorescent protein (GFP), is not suitable due to its significantly higher mortality than the other controls. For target gene screening, suppression was confirmed for all the candidates, including two housekeeping genes (Vacuolar-type H + -ATPase subunit A (V-ATPase A) and Glyceraldehyde 3-phosphate dehydrogenase, (GAPDH)), and three genes associated with development (ATP-dependent RNA Helicase DDX3Y (Belle), CREB-binding protein (CBP), and Farnesoic acid O-methyltransferase (FaMet)). Knocking down of V-ATPase A resulted in the highest mortality (~ 90%) and reduced fecundity (over 90%) than other candidates. As for the genes associated with development, suppression of Belle and CBP, led to approximately 65% mortality, as well as 86% and 40% reduction in fecundity, respectively. Silencing of FaMet, however, had negligible biological impacts on A. viennensis.

CONCLUSION

The combined efforts not only establish an effective dsRNA delivery method, but also provide potential target genes for RNAi-based biopesticides against A. viennensis, a devastating invasive pest for fruit trees and woody ornamental plants throughout Asia and Europe. © 2023 Society of Chemical Industry.

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.

Gene Co-Expression Network Analysis Reveals Key Regulatory Genes in Metisa plana Hormone Pathways

Metisa plana Walker (Lepidoptera: Psychidae) is a major oil palm pest species distributed across Southeast Asia. M. plana outbreaks are regarded as serious ongoing threats to the oil palm industry due to their ability to significantly reduce fruit yield and subsequent productivity. Currently, conventional pesticide overuses may harm non-target organisms and severely pollute the environment. This study aims to identify key regulatory genes involved in hormone pathways during the third instar larvae stage of M. plana gene co-expression network analysis. A weighted gene co-expression network analysis (WGCNA) was conducted on the M. plana transcriptomes to construct a gene co-expression network. The transcriptome datasets were obtained from different development stages of M. plana, i.e., egg, third instar larvae, pupa, and adult. The network was clustered using the DPClusO algorithm and validated using Fisher's exact test and receiver operating characteristic (ROC) analysis. The clustering analysis was performed on the network and 20 potential regulatory genes (such as MTA1-like, Nub, Grn, and Usp) were identified from ten top-most significant clusters. Pathway enrichment analysis was performed to identify hormone signalling pathways and these pathways were identified, i.e., hormone-mediated signalling, steroid hormone-mediated signalling, and intracellular steroid hormone receptor signalling as well as six regulatory genes Hnf4, Hr4, MED14, Usp, Tai, and Trr. These key regulatory genes have a potential as important targets in future upstream applications and validation studies in the development of biorational pesticides against M. plana and the RNA interference (RNAi) gene silencing method.

Double-stranded RNA (dsRNA) technology to control forest insect pests and fungal pathogens: challenges and opportunities

Climate change alters the seasonal synchronization between plants and respective pests plus pathogens. The geographical infiltration helps to shift their hosts, resulting in novel outbreaks that damage forests and ecology. Traditional management schemes are unable to control such outbreaks, therefore unconventional and competitive governance is needed to manage forest pests and pathogens. RNA interference (RNAi) mediated double-stranded RNA (dsRNA) treatment method can be implemented to protect forest trees. Exogenous dsRNA triggers the RNAi-mediated gene silencing of a vital gene, and suspends protein production, resulting in the death of targeted pathogens and pests. The dsRNA treatment method is successful for many crop insects and fungi, however, studies of dsRNA against forest pests and pathogens are depleting. Pesticides and fungicides based on dsRNA could be used to combat pathogens that caused outbreaks in different parts of the world. Although the dsRNA has proved its potential, the crucial dilemma and risks including species-specific gene selection, and dsRNA delivery methods cannot be overlooked. Here, we summarized the major fungi pathogens and insect pests that have caused outbreaks, their genomic information, and studies on dsRNA fungi-and pesticides. Current challenges and opportunities in dsRNA target decision, delivery using nanoparticles, direct applications, and a new method using mycorrhiza for forest tree protection are discussed. The importance of affordable next-generation sequencing to minimize the impact on non-target species is discussed. We suggest that collaborative research among forest genomics and pathology institutes could develop necessary dsRNA strategies to protect forest tree species.

Nanoparticle-Shielded dsRNA Delivery for Enhancing RNAi Efficiency in Cotton Spotted Bollworm Earias vittella (Lepidoptera: Nolidae)

The spotted bollworm Earias vittella (Lepidoptera: Nolidae) is a polyphagous pest with enormous economic significance, primarily affecting cotton and okra. However, the lack of gene sequence information on this pest has a significant constraint on molecular investigations and the formulation of superior pest management strategies. An RNA-seq-based transcriptome study was conducted to alleviate such limitations, and de novo assembly was performed to obtain transcript sequences of this pest. Reference gene identification across E. vittella developmental stages and RNAi treatments were conducted using its sequence information, which resulted in identifying transcription elongation factor (TEF), V-type proton ATPase (V-ATPase), and Glyceraldehyde -3-phosphate dehydrogenase (GAPDH) as the most suitable reference genes for normalization in RT-qPCR-based gene expression studies. The present study also identified important developmental, RNAi pathway, and RNAi target genes and performed life-stage developmental expression analysis using RT-qPCR to select the optimal targets for RNAi. We found that naked dsRNA degradation in the E. vittella hemolymph is the primary reason for poor RNAi. A total of six genes including Juvenile hormone methyl transferase (JHAMT), Chitin synthase (CHS), Aminopeptidase (AMN), Cadherin (CAD), Alpha-amylase (AMY), and V-type proton ATPase (V-ATPase) were selected and knocked down significantly with three different nanoparticles encapsulated dsRNA conjugates, i.e., Chitosan-dsRNA, carbon quantum dots-dsRNA (CQD-dsRNA), and Lipofectamine-dsRNA conjugate. These results demonstrate that feeding nanoparticle-shielded dsRNA silences target genes and suggests that nanoparticle-based RNAi can efficiently manage this pest.

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.

Co-Expression Network Analysis: A Future Approach for Pest Control Target Discovery

The striped stem borer (SSB, Chilo suppressalis Walker) is a major pest of rice worldwide. Double-stranded RNAs (dsRNAs) targeting essential genes can trigger a lethal RNA interference (RNAi) response in insect pests. In this study, we applied a Weighted Gene Co-expression Network Analysis (WGCNA) to diet-based RNA-Seq data as a method to facilitate the discovery of novel target genes for pest control. Nieman-Pick type c 1 homolog b (NPC1b) was identified as the gene with the highest correlation values to hemolymph cholesterol levels and larval size. Functional characterization of the gene supported CsNPC1b expression with dietary cholesterol uptake and insect growth. This study revealed the critical role of NPC1b for intestinal cholesterol absorption in lepidopteran insects and highlights the utility of the WGCNA approach for identifying new pest management targets.

Clathrin-dependent endocytosis plays a critical role in larval and pupal development, and female oocyte production in the red flour beetle (Tribolium castaneum)

BACKGROUND

Clathrin-dependent endocytosis is a vesicular transport process by which cells take macromolecules from the extracellular space to the intracellular space. It plays important roles in various cellular functions, but its biological significance in insect development and reproduction has not been well studied.

RESULTS

We characterized and functionally analyzed four major clathrin-dependent endocytic pathway genes (TcChc, TcAP50, TcVhaSFD, TcRab7) in Tribolium castaneum. RNA interference (RNAi) by injecting double-stranded RNA (dsRNA) targeting each gene at three doses (50, 100, or 200 ng per insect) in 20-day-old larvae led to 100% larval mortality. When the expressions of TcChc, TcVhaSFD, and TcRab7 were suppressed by injecting their respective dsRNAs at each dose in 1-day-old pupae, the adults that emerged from the dsRNA-injected pupae were deformed, with the absence of wing development. The deformed adults died within 2 days after eclosion. When the expression of TcAP50 was suppressed by injecting its dsRNA into 1-day-old pupae, although no apparent deformed adults were observed, all the adults died within 35 days after eclosion. In addition, when the expressions of TcChc and TcVhaSFD were suppressed by injecting their respective dsRNAs at a reduced dose (10 ng per insect) in 5-day-old pupae, the ovarian development and oocyte production in the resultant females were completely inhibited.

CONCLUSION

Our results indicate that clathrin-dependent endocytosis is essential for insect development and reproduction. The results from this study can help researchers identify potential molecular targets for developing novel strategies for insect pest management. © 2023 Society of Chemical Industry.

Greenhouse test of spraying dsRNA to control the western flower thrips, Frankliniella occidentalis, infesting hot peppers

BACKGROUND

The western flower thrips Frankliniella occidentalis is an insect pest that damages various crops, including hot peppers. It is a vector of a plant pathogen, tomato spotted wilt virus. To control this pest, chemical insecticides have been used in the past, but the control efficacy is unsatisfactory owing to rapid resistance development by F. occidentalis.

METHODOLOGY

This study reports a novel control technology against this insect pest using RNA interference (RNAi) of the vacuolar-type ATPase (vATPase) expression. Eight subunit genes (vATPase-A ∼ vATPase-H) of vATPase were obtained from the F. occidentalis genome and confirmed for their expressions at all developmental stages.

RESULTS

Double-stranded RNAs (dsRNAs) specific to the eight subunit genes were fed to larvae and adults, which significantly suppressed the corresponding gene expressions after 24-h feeding treatment. These RNAi treatments resulted in significant mortalities, in which the dsRNA treatments at ∼2,000 ppm specific to vATPase-A or vATPase-B allowed complete control efficacy near 100% mortality in 7 days after treatment. To prevent dsRNA degradation by the digestive proteases during oral feeding, dsRNAs were formulated in a liposome and led to an enhanced mortality of the larvae and adults of F. occidentalis. The dsRNAs were then sprayed at 2,000 ppm on F. occidentalis infesting hot peppers in a greenhouse, which resulted in 53.5-55.9% control efficacy in 7 days after treatment. Even though the vATPases are conserved in different organisms, the dsRNA treatment was relatively safe for non-target insects owing to the presence of mismatch sequences compared to the dsRNA region of F. occidentalis.

CONCLUSION

These results demonstrate the practical feasibility of spraying dsRNA to control F. occidentalis infesting crops.

Potential effects of RNA interference of Asian longhorned beetle on its parasitoid

BACKGROUND

It is important to understand how non-target insects such as parasitoids may be impacted directly or indirectly by RNA interference with double-stranded RNA (dsRNA) that has emerged as a novel pest control tool. We examined the potential effects of a dsRNA targeting an inhibitor of apoptosis (IAP) of the Asian longhorned beetle Anoplophora glabripennis on its gregarious larval ectoparasitoid Ontsira mellipes, directly on adult wasp's survival via injection of 4 μg of dsIAP per wasp, and indirectly on the detectability and suitability of host larvae injected with 2, 4 or 8 μg of dsIAP per larva.

RESULTS

Compared with no injection or injection with a control dsGFP targeting a region of gene coding for a green fluorescence protein (GFP), dsIAP did not affect adult wasp's survival. Ontsira mellipes locates hosts in the wood by sensing their movement. Host larvae did not completely cease movement after the injection of dsIAP and were still detected and parasitized. Clutch size was reduced and only 3.8% of the parasitoid offspring developed into adults on host larvae treated at the highest dose. However, clutch size was not affected and 25.5% of the parasitoid offspring developed into adults on host larvae treated at the lowest dose. The fitness of developed wasps (development time, sex ratio, body size, and fecundity) was not affected when compared to the control treatments. No dsIAP was detected in parasitoid larvae.

CONCLUSION

The results show no direct effect of the dsRNA on its parasitoid, but the potential indirect effect of dsRNA-affected host on the parasitoid, which may be minimized through optimizing dsRNA dosage to promote compatible applications of both management options for this invasive forest pest. © 2022 Society of Chemical Industry. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.

Role of gut symbionts of insect pests: A novel target for insect-pest control

Insects possess beneficial and nuisance values in the context of the agricultural sector and human life around them. An ensemble of gut symbionts assists insects to adapt to diverse and extreme environments and to occupy every available niche on earth. Microbial symbiosis helps host insects by supplementing necessary diet elements, providing protection from predators and parasitoids through camouflage, modulation of signaling pathway to attain homeostasis and to trigger immunity against pathogens, hijacking plant pathways to circumvent plant defence, acquiring the capability to degrade chemical pesticides, and degradation of harmful pesticides. Therefore, a microbial protection strategy can lead to overpopulation of insect pests, which can drastically reduce crop yield. Some studies have demonstrated increased insect mortality via the destruction of insect gut symbionts; through the use of antibiotics. The review summarizes various roles played by the gut microbiota of insect pests and some studies that have been conducted on pest control by targeting the symbionts. Manipulation or exploitation of the gut symbionts alters the growth and population of the host insects and is consequently a potential target for the development of better pest control strategies. Methods such as modulation of gut symbionts via CRISPR/Cas9, RNAi and the combining of IIT and SIT to increase the insect mortality are further discussed. In the ongoing insect pest management scenario, gut symbionts are proving to be the reliable, eco-friendly and novel approach in the integrated pest management.

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.

RNAi-Based Biopesticides Against 28-Spotted Ladybeetle Henosepilachna vigintioctopunctata Does Not Harm the Insect Predator Propylea japonica

RNA interference (RNAi)-mediated control of the notorious pest Henosepilachna vigintioctopunctata is an emerging environment friendly research area. However, the characterization of key target genes in H. vigintioctopunctata is crucial for this. Additionally, assessing the risk of RNAi to nontarget organisms (NTOs) is necessary for environmental safety. In this study, the potential of RNAi technology in controlling H. vigintioctopunctata infestation has been investigated by the oral delivery of double-stranded RNA (dsRNA). The results revealed that the silencing of six genes, including HvABCH1, HvHel25E, HvProsbeta5, HvProsalpha6, HvProsbeta6, and HvSrp54k, was highly lethal to H. vigintioctopunctata. The LC50 values of the dsRNAs used to silence these six genes were found to be less than 13 ng/μL. Moreover, the use of the bacterially expressed dsRNAs caused high mortality in the lab and field populations of H. vigintioctopunctata. Further, administration of HvHel25E and HvSrp54k dsRNAs in the predatory lady beetle Propylea japonica confirmed no transcriptional or organismal levels effects. This risk-assessment result ensured no off-target RNAi effects on the NTOs. Overall, the findings of the study suggested that HvABCH1, HvHel25E, HvProsbeta5, HvProsalpha6, HvProsbeta6, and HvSrp54k can be novel promising molecular targets with high specificity for H. vigintioctopunctata management with negligible effects on the NTOs.

Selection and Comparative Gene Expression of Midgut-Specific Targets for Drosophila suzukii

Spotted-wing drosophila (SWD), Drosophila suzukii, is a destructive and invasive pest that attacks most small fruits and cherries. The current management for SWD involves the use of conventional insecticides. In an effort to develop a biologically based control option, the application of RNA interference (RNAi) has been investigated. To develop an RNAi approach, suitable targets must be identified, and an efficient delivery method must be developed for introducing the double-stranded RNA (dsRNA) in the midgut. In D. suzukii, we previously found that dsRNA nucleases actively degrade dsRNA molecules in the midgut. In this study, we focused on identifying biological targets focused on the midgut membrane. The profile of midgut-specific genes was analyzed and compared with the genes expressed in the whole-body using transcriptome analysis. Differential gene expression analysis revealed that 1921 contigs were upregulated and 1834 contigs were downregulated in the midgut when compared to genes from other body tissues. We chose ten midgut-specifically upregulated genes and empirically confirmed their expressions. We are particularly interested in the midgut membrane proteins, including G protein-coupled receptors (GPCRs) such as diuretic hormone 31 (DH31) receptor, neuropeptide F (NPF) recepror, toll-9, adhesion receptors, methuselah (mth), and gustatory receptor, because insect GPCRs have been offered great potential for next-generation pest management.

Gene silencing for invasive paper wasp management: Synthesized dsRNA can modify gene expression but did not affect mortality

Invasive paper wasps such as Polistes dominula are a major pest and problem for biodiversity around the globe. Safe and highly targeted methods for the control of these and other social wasp populations are needed. We attempted to identify potentially-lethal gene targets that could be used on adult paper wasps in a gene silencing or RNA interference (RNAi) approach. Double-stranded RNA (dsRNA) was designed to target genes for which silencing has proven lethal in other insects. dsRNA was provided either orally to foragers or directly injected into the wasps. We also provided the dsRNA unprotected or protected from degradation by gut nucleases in two different forms (lipofectamine and carbon quantum dots). The effects of oral delivery of 22 different gene targets to forager wasps was evaluated. The expression of five different genes was successfully reduced following dsRNA ingestion or injection. These gene targets included the FACT complex subunit spt16 (DRE4) and RNA-binding protein fusilli (FUSILLI), both of which have been previously shown to have potential as lethal targets for pest control in other insects. However, we found no evidence of significant increases in adult wasp mortality following ingestion or injection of dsRNA for these genes when compared with control treatments in our experiments. The methods we used to protect the dsRNA from digestive degradation altered gene expression but similarly did not influence wasp mortality. Our results indicate that while many of the same gene targets can be silenced and induce mortality in other insects, dsRNA and RNAi approaches may not be useful for paper wasp control.

Functional genomic tools for emerging model species

Most studies in the field of ecology and evolution aiming to connect genotype to phenotype rarely validate identified loci using functional tools. Recent developments in RNA interference (RNAi) and clustered regularly interspaced palindromic repeats (CRISPR)-Cas genome editing have dramatically increased the feasibility of functional validation. However, these methods come with specific challenges when applied to emerging model organisms, including limited spatial control of gene silencing, low knock-in efficiencies, and low throughput of functional validation. Moreover, many functional studies to date do not recapitulate ecologically relevant variation, and this limits their scope for deeper insights into evolutionary processes. We therefore argue that increased use of gene editing by allelic replacement through homology-directed repair (HDR) would greatly benefit the field of ecology and evolution.

FAR knockout significantly inhibits Chilo suppressalis survival and transgene expression of double-stranded FAR in rice exhibits strong pest resistance

Chilo suppressalis is one of the most prevalent and damaging rice pests, causing significant economic losses each year. Chemical control is currently the primary method of controlling C. suppressalis. However, the indiscriminate use of chemical insecticides increases pest resistance, pollutes the environment and poses a significant health threat to humans and livestock, highlighting the need to find safer, more pest-specific and more effective alternatives to pest control. Plant-mediated RNA interference (RNAi) is a promising agricultural pest control method that is highly pest-specific and has less of an impact on the environment. Using multi-sgRNAs/Cas9 technology to delete Fatty acyl-CoA reductase (FAR) of C. suppressalis in the G0 generation, we show that downregulating FAR transcription may significantly increase the mortality rate and darken the epidermis of C. suppressalis compared with the control. Subsequently, we developed dsFAR transgenic rice lines using Agrobacterium-mediated genetic transformation and then screened three strains expressing dsFAR at high levels using transcriptional level analysis. Using transgenic rice stems, a laboratory feeding bioassay indicated that at least one line (L#10) displayed a particularly high level of insect resistance, with an insect mortality rate of more than 80%. In the field trials, dsFAR transgenic rice displayed high levels of resistance to C. suppressalis damage. Collectively, these results suggest the potential of a new environment-friendly, species-specific strategy for rice pest management.

The role of polyplexes in developing a green sustainable approach in agriculture

Rise in global population has increased the food demands and thus the competition among farmers to produce more and more. In the race to obtain higher productivity, farmers have resorted to injudicious farming practices that include the reckless use of nitrogenous fertilizers and intensive cropping on farmlands. Such practices have paved the path for large scale infestations of crops and plants by pests thus affecting the plant productivity and crop vigour. There are several traditional techniques to control pest infestations in plants such as the use of chemical or bio-pesticides, and integrated pest management practices which face several drawbacks. Delivery of gene/nucleic acid in plants through genetic engineering approaches is a more sustainable and effective method of protection against pests. The technology of RNA interference (RNAi) provides a sustainable solution to counter pest control problems faced by other traditional techniques. The RNAi technique involves delivery of dsDNA/dsRNA or other forms of nucleic acids into target organisms thereby bringing about gene silencing. However, RNAi is also limited to its use because of their susceptibility to degradation wherein the use of cationic polymers can provide a tangible solution. Cationic polymers form stable complexes with the nucleic acids known as "polyplexes", which may be attributed to their high positive charge densities thus protecting the exogenous nucleic acids from extracellular degradation. The current paper focuses on the utility of nucleic acids as a sustainable tool for pest control in crops and the use of cationic polymers for the efficient delivery of nucleic acids in pests thus protecting the plant from infestations.

RNA interference of vATPase subunits A and E affects survival of larvae and adults in Plagiodera versicolora (Coleoptera: Chrysomelidae)

Vacuolar-type H⁺-ATPases (vATPases) are ATP-driven proton pumps and play essential roles in many physiological functions. Plagiodera versicolora (Coleoptera: Chrysomelidae) is a leaf-eating forest pest found in salicaceous trees worldwide. RNA interference (RNAi) is a powerful tool for functional identify and pest control. In this study, we used RNAi as an approach to knock down subunits A and E of the vATPase gene. The phylogenetic analysis showed that vATPase-A and vATPase-E from the same order were clustered together to form Coleoptera subclades, respectively. The expression levels of vATPase-A and vATPase-E were higher in gut, Malpighian tubules and 1st instar larvae. Ingest the dsvATPase-A and dsvATPase-E significantly inhibited the development of 1st to 3th instar larvae, incapacitated of mating and oviposition in adults. In addition, knockdown of vATPase subunit genes caused higher mortality in larvae and adults. The results demonstrate that RNAi efficiencies both vATPase-A and vATPase-E genes at various larvae stages and adults. Moreover, this research suggested that silencing of two vATPase subunits A and E offers a potential strategy to control P. versicolora.

Synthetic Nanoscale RNAi Constructs as Pesticides for the Control of Locust Migratoria

The low efficiency of RNA interference (RNAi) in insects via the oral administration of double-stranded RNA (dsRNA) is a considerable obstacle preventing its application in insect pest control. The instability of dsRNA and insufficient dsRNA uptake are known to limit the RNAi efficiency. To overcome these limitations, the block copolymer poly(ethylene glycol)-polylysine(thiol) [PEG-PLys(SH)] was designed in this study to form well-defined, core-shell nanoparticles to protect dsRNA from premature degradation and to facilitate its movement through various physiological barriers. The developed material had excellent structural stability and dsRNA-protecting capacity, thereby enabling the prolonged survival of dsRNA in the digestive tract for endocytosis into the midgut cells of the migratory locust, Locusta migratoria. After encapsulation of a dsLmCHS2 payload (a midgut gene), a 60% down-regulation of LmCHS2, accompanied with observations of amorphous and discontinuous linings of the peritrophic matrix and abnormal phenotypes, was observed. In addition, the elaborated nanoscale dsRNA condensates appeared to readily extravasate through the narrow fenestrations in the linings of midgut epithelial cells into the hemolymph and be distributed throughout the body. After encapsulation of a dsLmCHS1 payload (a cuticle gene), a distinctive lethal phenotype with molting failure was observed as a result of a 50% down-regulation in LmCHS1. The persistent leaf adherence of these dsRNA constructs was also capable of resisting continuous rinsing. Therefore, these dsRNA constructs represent a robust type of RNAi pesticide, which has potential as a versatile pesticide against a variety of molecular targets for the control of destructive insects and insects resistant to conventional pesticides.

Spatial Distribution and Retention in Loblolly Pine Seedlings of Exogenous dsRNAs Applied through Roots

Exogenously applied double-stranded RNA (dsRNA) can induce potent host specific gene knockdown and mortality in insects. The deployment of RNA-interference (RNAi) technologies for pest suppression is gaining traction in both agriculture and horticulture, but its implementation in forest systems is lagging. While numerous forest pests have demonstrated susceptibility to RNAi mediated gene silencing, including the southern pine beetle (SPB), Dendroctonus frontalis, multiple barriers stand between laboratory screening and real-world deployment. One such barrier is dsRNA delivery. One possible delivery method is through host plants, but an understanding of exogenous dsRNA movement through plant tissues is essential. Therefore, we sought to understand the translocation and persistence of dsRNAs designed for SPB throughout woody plant tissues after hydroponic exposure. Loblolly pine, Pinus taeda, seedlings were exposed to dsRNAs as a root soak, followed by destructive sampling. Total RNA was extracted from different tissue types including root, stem, crown, needle, and meristem, after which gel electrophoresis confirmed the recovery of the exogenous dsRNAs, which were further verified using Sanger sequencing. Both techniques confirmed the presence of the exogenously applied target dsRNAs in each tissue type after 1, 3, 5, and 7 d of dsRNA exposure. These findings suggest that root drench applications of exogenous dsRNAs could provide a viable delivery route for RNAi technology designed to combat tree feeding pests.

Knockdown of sphingomyelinase (NlSMase) causes ovarian malformation of brown planthopper, Nilaparvata lugens (Stål)

Sphingomyelinases (SMases) are a group of enzymes that catalyse the hydrolysis of sphingomyelins into ceramides and phosphorylcholine. They have been intensively investigated for their pathophysiological roles in mammals whereas much remains unclear about their counterparts in insects. Herein we report the cloning and functional characterization of four SMase homologue genes, designated NlSMase1-4, from brown planthopper (BPH). The phylogenetic analysis revealed that NlSMase1 and NlSMase2 were clustered into acid SMase family, and NlSMase3 and NlSMase4 with neutral SMase family. NlSMase1, NlSMase3 and NlSMase4 were highly expressed in BPH females, and NlSMaes2 in the 5th instar nymph. All four NlSMases had the lowest transcription in BPH males. NlSMase1 and NlSMase4 were highly expressed in BPH ovaries, while NlSMase2 and NlSMase3 in midgut and wings, respectively. Knocking-down of each NlSMase individual by RNA interference (RNAi) caused the ovarian malformation in BPH. The transcriptomic analysis revealed that NlSMase4 knockdown could strongly affect diacylglycerol (DAG)-related metabolisms and their downstream pathways. Further, qRT-PCR analysis of vitellogenin (Vg) genes indicates that the DAG metabolism disorder could interrupt the essential Vg accumulation for BPH oogenesis. Our study demonstrates the vital role of NlSMases in BPH reproductive development and provides new insights into the mediated mechanism of how SMases function.

Risk assessment of RNAi-based pesticides to non-target organisms: Evaluating the effects of sequence similarity in the parasitoid wasp Telenomus podisi

RNA interference (RNAi)-based pesticides are promising novel pest management products that might reduce environmental impacts compared to other pesticides. Their sequence-guided mode of action facilitates a high species-selectivity, preventing harm on non-target organisms. However, there is currently no consensus on the minimum needed sequence similarity for efficient RNAi in insects and studies have shown that adverse effects in non-targets cannot always be ruled out a priori. This study investigates the effects of exposing the parasitoid wasp Telenomus podisi to double-stranded RNA (dsRNA) which is lethal to its host, the Neotropical brown stink bug Euschistus heros. Feeding T. podisi with wasp-specific dsRNA targeting the vATPase A and actin-2 genes led to 76.4 ± 9.9% and 76.7 ± 8.8% mortality respectively, demonstrating that dietary RNAi is functional in T. podisi. When feeding T. podisi with E. heros-specific dsRNA targeting the same genes, no lethal or sublethal effects were observed. To link sequence similarity to potential gene silencing effects in the parasitoids, the expression of genes showing the highest degree of similarity (17-21 nucleotide matches) with these two target genes was monitored and was found unaffected by the E. heros-specific dsRNA. Our study confirms that RNAi was in this case highly specific and that for E. heros, RNAi-based pesticides can be used complementary to biological control in an integrated pest management context.

Trunk injection delivery of dsRNA for RNAi-based pest control in apple trees

BACKGROUND

RNA interference (RNAi) is a promising new approach for controlling insect pests without the use of synthetic pesticides. Trunk injection is a delivery system for woody plants that harnesses the vascular system of the tree to transport materials to the tree canopy. Full size apple trees were injected with double-stranded RNA (dsRNA), and season-long leaf samples were taken to measure the vascular mobility and temporal persistence of dsRNA, using quantitative reverse transcription polymerase chain reaction (qRT-PCR).

RESULTS

The qRT-PCR results revealed that the quantities of dsRNA in the apple leaves of treated trees were significantly greater than those in the leaves of untreated trees for both 2019 and 2020 studies. The peak dsRNA concentration in 2019 was 242 pg/30 mg of leaf tissue, and in 2020 was 16.4 pg/30 mg. The persistence of dsRNA in the apple tree canopy in 2019 was at least 84 days, and in 2020 was at least 141 days.

CONCLUSIONS

The highest mean measurement of dsRNA on a single date in 2019 was 242 pg, which is approximately equivalent to 8 ng/1 g leaf tissue. The projection using the highest replicate concentration from the same date is approximately equivalent to 27 ng/1 g leaf tissue, which may be sufficient to be considered biologically active. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Paninvasion severity assessment of a U.S. grape pest to disrupt the global wine market

Economic impacts from plant pests are often felt at the regional scale, yet some impacts expand to the global scale through the alignment of a pest's invasion potentials. Such globally invasive species (i.e., paninvasives) are like the human pathogens that cause pandemics. Like pandemics, assessing paninvasion risk for an emerging regional pest is key for stakeholders to take early actions that avoid market disruption. Here, we develop the paninvasion severity assessment framework and use it to assess a rapidly spreading regional U.S. grape pest, the spotted lanternfly planthopper (Lycorma delicatula; SLF), to spread and disrupt the global wine market. We found that SLF invasion potentials are aligned globally because important viticultural regions with suitable environments for SLF establishment also heavily trade with invaded U.S. states. If the U.S. acts as an invasive bridgehead, Italy, France, Spain, and other important wine exporters are likely to experience the next SLF introductions. Risk to the global wine market is high unless stakeholders work to reduce SLF invasion potentials in the U.S. and globally.

Notch is an alternative splicing gene in brown planthopper, Nilaparvata lugens

Much research has assumed that Notch codes one protein. Then the protein will be cleaved into two parts and regenerates a heterodimers receptor to construct Notch signal pathways to regulate development in the past three decades. Here, we show that Notch in brown planthopper is a complex alternatively spliced gene has at least three transcriptional start sites, four exon skips, and 21 transcriptional endpoints that uses these to form variants and codes a series of proteins. When used dsRNAs to suppression different regions of the full-length variant NlNF resulted in a similar phenotype. Insects were molting after treatment, sensation circles on antennas near to root decayed, bristles on wings shortened, thickened or disappeared, accompanied by thickening veins and blades of fore-wing apex regions thickened. These results suggested that Notch influenced developmental of sensation circles, bristles, veins, and blades in nymph late periods. This study has deepened our understanding of Notch.

Protection of Double-Stranded RNA via Complexation with Double Hydrophilic Block Copolymers: Influence of Neutral Block Length in Biologically Relevant Environments

Interaction between the anionic phosphodiester backbone of DNA/RNA and polycations can be exploited as a means of delivering genetic material for therapeutic and agrochemical applications. In this work, quaternized poly(2-(dimethylamino)ethyl methacrylate)-block-poly(N,N-dimethylacrylamide) (PQDMAEMA-b-PDMAm) double hydrophilic block copolymers (DHBCs) were synthesized via reversible addition-fragmentation chain-transfer (RAFT) polymerization as nonviral delivery vehicles for double-stranded RNA. The assembly of DHBCs and dsRNA forms distinct polyplexes that were thoroughly characterized to establish a relationship between the length of the uncharged poly(N,N-dimethylacrylamide) (PDMA) block and the polyplex size, complexation efficiency, and colloidal stability. Dynamic light scattering reveals the formation of smaller polyplexes with increasing PDMA lengths, while gel electrophoresis confirms that these polyplexes require higher N/P ratio for full complexation. DHBC polyplexes exhibit enhanced stability in low ionic strength environments in comparison to homopolymer-based polyplexes. In vitro enzymatic degradation assays demonstrate that both homopolymer and DHBC polymers efficiently protect dsRNA from degradation by RNase A enzyme.

Positional effects of double-stranded RNAs targeting β-Actin gene affect RNA interference efficiency in Colorado potato beetle

Pesticide resistance in pests drives the development of RNA interference (RNAi)-based technology as a novel approach for pest control. To investigate the effects of the positional dependency of double-stranded RNAs (dsRNAs), we newly designed four different 200 bp dsRNAs targeting Colorado potato beetle (CPB) β-Actin gene, termed as dsACT200-1 to dsACT200-4, to compare their insecticidal activity to CPB larvae together with our previously used 200 bp and 700 bp dsRNAs (dsACT200 and dsACT700), respectively (He et al., 2020a). Each of dsRNAs harbors different numbers of expected siRNAs predicted by sequence-based prediction platform, dsACT200 and dsACT200-2 have a relatively higher number of siRNA than other 200 bps dsRNAs. When CPB larvae were fed with in vitro synthesized dsRNA-painted potato leaves, all the tested dsRNAs showed significant effects to protect against CPB larvae. Combined with the survival rate of CPB larvae, β-Actin gene expression level and the surviving CPB larvae weight, various positional dsRNAs from the same allele showed different plant protection activity against CPB larvae and partially correlated with the predicted siRNA numbers and distribution on the target sequence. This study suggests the specific allelic locus for rational dsRNA design triggering RNAi efficiency for target gene silencing is an essential factor in enhancing the insecticidal activity.