The South American Fruit Fly: An Important Pest Insect With RNAi-Sensitive Larval Stages

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.

Broad anti-pathogen potential of DEAD box RNA helicase eIF4A-targeting rocaglates

Inhibition of eukaryotic initiation factor 4A has been proposed as a strategy to fight pathogens. Rocaglates exhibit the highest specificities among eIF4A inhibitors, but their anti-pathogenic potential has not been comprehensively assessed across eukaryotes. In silico analysis of the substitution patterns of six eIF4A1 aa residues critical to rocaglate binding, uncovered 35 variants. Molecular docking of eIF4A:RNA:rocaglate complexes, and in vitro thermal shift assays with select recombinantly expressed eIF4A variants, revealed that sensitivity correlated with low inferred binding energies and high melting temperature shifts. In vitro testing with silvestrol validated predicted resistance in Caenorhabditis elegans and Leishmania amazonensis and predicted sensitivity in Aedes sp., Schistosoma mansoni, Trypanosoma brucei, Plasmodium falciparum, and Toxoplasma gondii. Our analysis further revealed the possibility of targeting important insect, plant, animal, and human pathogens with rocaglates. Finally, our findings might help design novel synthetic rocaglate derivatives or alternative eIF4A inhibitors to fight pathogens.

Delivery of Methoprene-Tolerant dsRNA to Improve RNAi Efficiency by Modified Liposomes for Pest Control

The application of RNA interference (RNAi) technology for pest control is environmentally friendly and accurate. However, the efficiency of RNAi is often inconsistent and unreliable, and finding a suitable carrier element is considered critical to success in overcoming biotic and abiotic barriers to reach the target site. The fall armyworm, Spodoptera frugiperda (FAW), which is one of most important global agricultural pests, has recently spread rapidly to other parts of the world. In this study, a method to improve the stability and RNAi efficiency of the dsRNA carrier complex was reported. Methoprene-tolerant gene (Met) was selected as a target, a gene which is critical to the growth and development of FAW. Biomaterials nanoliposomes (LNPs) were modified with polyethylenimine (PEI) to deliver the dsRNA of Met. The synthesized Met3@PEI@LNPs reached a size of 385 nm and were found to load dsRNA effectively. Through stability and protection assays, it was found that LNPs provided reliable protection. In addition, the release curve also demonstrated that LNPs were able to prevent premature release under alkaline condition of the insect midgut but accelerate the release after entering the acidic environment of the target cells. The cell transfection efficiency of the prepared LNPs reached 96.4%. Toxicity tests showed that the use of LNPs could significantly improve the interference efficiency, with 91.7% interference efficiency achieved when the concentration of dsRNA in LNPs was only 25% of that of the control. Successful interference of Met demonstrated it could significantly shorten the larval period and make the larvae pupate earlier, thus achieving the purpose of control. In this study, we have demonstrated the use of nanotechnology to provide a novel RNAi delivery method for pest control.

Cascade-Responsive 2-DG Nanocapsules Encapsulate aV-siCPT1C Conjugates to Inhibit Glioblastoma through Multiple Inhibition of Energy Metabolism

Aerobic glycolysis is the primary energy supply mode for glioblastoma (GBM) cells to maintain growth and proliferation. However, due to the metabolic reprogramming of tumor cells, GBM can still produce energy through fatty acid oxidation (FAO) and amino acid metabolism after blocking this metabolic pathway. In addition, GBM can provide a steady stream of nutrients through high-density neovascularization, which puts the block energy metabolism therapy for glioma in the situation of "internal and external problems". Herein, based on the abundant reactive oxygen species (ROS) and glutathione (GSH) in the tumor microenvironment and cytoplasm, we successfully designed and developed a cascade-responsive 2-DG nanocapsule delivery system. This nanocapsule contains a conjugate of anti-VEGFR2 monoclonal antibody (aV) and CPT1C siRNA (siCPT1C) linked by a disulfide cross-linker (aV-siCPT1C). The surface of this nanocapsule (2-DG/aV-siCPT1C NC) is loaded with the glycolysis inhibitor 2-DG, and it utilizes GLUT1, which is highly expressed on the blood-brain barrier (BBB) and GBM cells, to effectively penetrate the BBB and target GBM. The nanocapsule realizes multidrug codelivery, jointly blocks glycolysis and FAO of GBM, and reduces angiogenesis. Meanwhile, it also solves the problems of low delivery efficiency of mAb in the central nervous system (CNS) and easy degradation of siRNA. In general, this drug joint delivery strategy could open up a new avenue for the treatment of GBM.

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.

Insights into the Use of Eco-Friendly Synergists in Resistance Management of Leptinotarsa decemlineata (Coleoptera: Chrysomelidae)

The Colorado potato beetle (CPB), Leptinotarsa decemlineata (Say), is the most notorious insect pest of potato globally. Injudicious use of insecticides for management of this pest has resulted in resistance to all major groups of insecticides along with many human, animal health, and environmental concerns. Additionally, the input cost of insecticide development/discovery is markedly increasing because each year thousands of chemicals are produced and tested for their insecticidal properties, requiring billions of dollars. For the management of resistance in insect pests, synergists can play a pivotal role by reducing the application dose of most insecticides. These eco-friendly synergists can be classified into two types: plant-based synergists and RNAi-based synergists. The use of plant-based and RNAi-based synergists in resistance management of insect pests can give promising results with lesser environmental side effects. This review summarizes the resistance status of CPB and discusses the potential advantage of plant-based and RNAi-based synergists for CPB resistance management. It will motivate researchers to further investigate the techniques of using plant- and RNAi-based synergists in combination with insecticides.

Role of Genes in Regulating Host Plants Expansion in Tephritid Fruit Flies (Diptera) and Potential for RNAi-Based Control

Host plant expansion is an important survival strategy for tephritids as they expand their range. Successful host expansion requires tephritids to adapt to the chemical and nonchemical properties of a novel host fruit, such as fruit color, phenology, and phytochemicals. These plant properties trigger a series of processes in tephritids, with each process having its own genetic basis, which means that various genes are involved in regulating host plant expansion by tephritids. This review summarizes current knowledge on the categories and roles of genes involved in host plant expansion in several important tephritid species, including genes related to chemoreception (olfactory and gustation), vision, digestion, detoxification, development, ribosomal and energy metabolism. Chemoreception- and detoxification- and digestion-related genes are stimulated by volatile chemicals and secondary chemicals of different hosts, respectively, which are involved in the regulation of nervous signal transduction that triggers behavioral, physical, and chemical responses to the novel host fruit. Vision-, nerve-, and development-related genes and metabolism-associated genes are activated in response to nonchemical stimuli from different hosts, such as color and phenology, to regulate a comprehensive adaptation of the extending host for tephritids. The chemical and nonchemical signals of hosts activate ribosomal and energy-related genes that result in the basic regulation of many processes of host expansion, including detoxification and development. These genes do not regulate novel host use individually, but multiple genes regulate multilevel adaptation to novel host fruits via multiple mechanisms. These genes may also be potential target genes for RNAi-based control of tephritid pests.

Argonaute1 and Gawky Are Required for the Development and Reproduction of Melon fly, Zeugodacus cucurbitae

Argonaute family genes encode a highly conserved group of proteins that have been associated with RNA silencing in both animals and plants. This study investigates the importance of microRNA biogenesis key regulators Argonaute1 (Ago1) and Gawky genes in the post-embryonic and ovarian development of the melon fly, Zeugodacus cucurbitae. The expression levels of these genes were mapped in all developmental stages and different adult tissues. Their roles in development were investigated using RNA interference (RNAi) via two different dsRNA delivery techniques. Embryo microinjection and oral feeding of third instar larvae successfully knocked down and greatly reduced the expression level of the target genes. Additionally, ex vivo essays revealed the stability of dsRNA in food was sufficient for gene silencing, although its integrity was affected in midgut. A wide range of phenotypes were observed on pupation, segmentation, pigmentation, and ovarian development. RNAi-mediated silencing of Gawky caused high mortality and loss of body segmentation, while Ago1 knockdown affected ovarian development and pigmentation. Developmental abnormalities and ovarian malformations caused by silencing these genes suggest that these genes are crucial for viability and reproductive capacity of Z. cucurbitae, and may be used as potential target genes in pest management.

Innate and adaptive resistance to RNAi: a major challenge and hurdle to the development of double stranded RNA-based pesticides

RNA interference (RNAi) is a post-transcriptional gene silencing process where short interfering RNAs degrade targeted mRNA. Exploration of gene function through reverse genetics is the major achievement of RNAi discovery. Besides, RNAi can be used as a potential strategy for the control of insect pests. This has led to the idea of developing RNAi-based pesticides. Differential RNAi efficiency in the different insect orders is the biggest biological obstacle in developing RNAi-based pesticides. dsRNA stability, the sensitivity of core RNAi machinery, uptake of dsRNA and amplification and spreading of the RNAi signal are the key factors responsible for RNAi efficiency in insects. This review discusses the physiological and adaptive factors responsible for reduced RNAi in insects that pose a major challenge in developing dsRNA- based pesticides.

Effect of RNAi targeting CYP6CY3 on the growth, development and insecticide susceptibility of Aphis gossypii by using nanocarrier-based transdermal dsRNA delivery system

RNA interference (RNAi) has been proved to be a viable method for agricultural pest control. Due to the limited uptake of dsRNA in hemiptera insects, this study used nanocarrier SPc (star polycation) transdermal delivery systems to deliver two truncated fragments (P1/P2) dsRNA of the CYP6CY3 for silencing this target gene in Aphis gossypii. After the cotton aphid was sprayed with the SPc + dsP1/P2 mixture, the expression level of target gene in SPc + dsP1 treatment group was not different from that in dsP1 group at 24 h, 48 h, and significantly lower than that in dsP1 group at 60 h, 72 h, respectively; and the expression level of target gene in SPc + dsP2 treatment group was not different from that in dsP2 group at 24 h, and significantly lower than that in dsP2 group from 48 h, 60 h, 72 h, respectively. In addition, the expression level was continuously silenced after spraying the SPc + dsP1/P2 mixture and significant reduced by 79.7% and 84.3% at 48 h compared with the H₂O control group, the mortality rate reached 48.09% and 43.18% at 84 h, respectively. And the cumulative reproduction number of cotton aphids also decreased, but the cumulative death number of newborn nymphs had an increase trend, compared with the control groups. Bioassays after RNAi showed that the silencing of CYP6CY3 increased the susceptibility of the 4^th instar aphid to imidacloprid, and increased mortality by 67.21% and 58.69% at 96 h, respectively. The life table parameters of the offspring from the 4^th instar cotton aphids from the SPc + dsP1/P2 treatment groups showed that the offspring had a longer pre-reproductive period and post-reproductive period. The intrinsic growth rate was 0.231 ± 0.005, 0.210 ± 0.013 and the finite growth rate was 1.260 ± 0.007 and 1.234 ± 0.016 in the SPc + dsP1/P2 treatment group, these two parameters of the two groups were lower than that of the corresponding control，the population doubling time of the two groups was prolonged and the developmental duration was delayed. These results indicate that CYP6CY3 plays a key role in the growth, development, reproduction and detoxification ability in cotton aphids, and may be as a potential RNAi target for controlling aphids, laying the foundation for the development of new environmentally-friendly RNA pesticides in this field.

dsRNA-Mediated Pest Management of Tuta absoluta Is Compatible with Its Biological Control Agent Nesidiocoris tenuis

Simple Summary

The zoophytophagous mirid bug Nesidiocoris tenuis is an efficient predator of the tomato leafminer, Tuta absoluta. RNA interference (RNAi) targeting the alphaCOP (αCOP) (Coatomer subunit alpha protein) gene of N. tenuis (Nt-αCOP) was proven to be functional in N. tenuis, causing downregulation of gene expression, mortality and sub-lethal effects. In contrast, when N. tenuis were fed with dsRNA (dsTa-αCOP) targeting the ortholog αCOP gene of T. absoluta, no lethal nor sub-lethal effects were observed. These results indicate the compatibility of this biocontrol agent along with RNAi-mediated management in order to suppress T. absoluta efficiently in tomato crop.

Abstract

RNAi-mediated insect pest management has recently shown promising results against the most serious pest of tomato, the tomato leafminer, Tuta absoluta. This study aimed to investigate whether dsRNA (dsTa-αCOP) designed to target the T. absoluta-αCOP gene could cause adverse effects to its biocontrol agent, the mirid predator, Nesidiocoris tenuis. Oral exposure of N. tenuis to dsRNA (dsNt-αCOP) designed to target N. tenuis-αCOP resulted in a 61%, 67% and 55% reduction in its transcript level in comparison to the sucrose, dsGFP and dsTa-αCOP treatments, respectively. In addition, significantly higher mortality of 57% was recorded in dsNt-αCOP-treated N. tenuis when compared to the sucrose (7%), dsGFP (10%) and dsTa-αCOP (10%) treatments. Moreover, the predation rate of ~33–39 Ephestia kuehniella eggs per N. tenuis adult dramatically reduced to almost half in the surviving dsNt-αCOP-treated N. tenuis. This worst-case exposure scenario confirmed for the first time that the RNAi machinery is functional in this species and that the risk of exposure through the oral route is possible. In contrast, dsTa-αCOP did not cause any sub-lethal effects to N. tenuis upon oral exposure. Oral exposure of T. absoluta to dsTa-αCOP resulted in 50% mortality. In the context of a biosafety risk assessment of RNAi-mediated insect management, investigating the effects on non-target organisms is essential in order to include this method as part of an integrated pest management strategy. Based on our laboratory assays, RNAi-mediated control is compatible with the biological control of T. absoluta by its natural enemy N. tenuis, adding the RNAi approach in the armoire of integrated pest management of T. absoluta.

Nanoparticle-mediated double-stranded RNA delivery system: A promising approach for sustainable pest management

RNA interference (RNAi) targeting lethal genes in insects has great potential for sustainable crop protection. Compared with traditional double-stranded (ds)RNA delivery systems, nanoparticles such as chitosan, liposomes, and cationic dendrimers offer advantages in delivering dsRNA/small interfering (si)RNA to improve RNAi efficiency, thus promoting the development and practice of RNAi-based pest management strategies. Here, we illustrate the limitations of traditional dsRNA delivery systems, reveal the mechanism of nanoparticle-mediated RNAi, summarize the recent progress and successful applications of nanoparticle-mediated RNAi in pest management, and finally address the prospects of nanoparticle-based RNA pesticides.

Characterization, expression patterns, and transcriptional responses of three core RNA interference pathway genes from Ostrinia nubilalis

RNA interference (RNAi) is commonly used in the laboratory to analyze gene function, and RNAi-based pest management strategies are now being employed. Unfortunately, RNAi is hindered by inefficient and highly-variable results when different insects are targeted, especially lepidopterans, such as the European corn borer (ECB), Ostrinia nubilalis (Lepidoptera: Crambidae). Previous efforts to achieve RNAi-mediated gene suppression in ECB revealed low RNAi efficiency with both double-stranded RNA (dsRNA) injection and ingestion. One mechanism that can affect RNAi efficiency in insects is the expression and function of core RNAi pathway genes, such as those encoding Argonaut 2 (Ago2), Dicer 2 (Dcr2), and a dsRNA binding protein (R2D2). To determine if deficiencies in these core RNAi pathway genes contribute to low RNAi efficiency in ECB, full-length complementary DNAs encoding OnAgo2, OnDcr2, and OnR2D2 were cloned, sequenced, and characterized. A comparison of domain architecture suggested that all three predicted proteins contained the necessary domains to function. However, a comparison of evolutionary distances revealed potentially important variations in the first RNase III domain of OnDcr2, the double-stranded RNA binding domains of OnR2D2, and both the PAZ and PIWI domains of OnAgo2, which may indicate functional differences in enzymatic activity between species. Expression analysis indicated that transcripts for all three genes were expressed in all developmental stages and tissues investigated. Interestingly, the introduction of non-target dsRNA into ECB second-instar larvae via microinjection did not affect OnAgo2, OnDcr2, or OnR2D2 expression. In contrast, ingestion of the same dsRNAs resulted in upregulation of OnDcr2 but downregulation of OnR2D2. The unexpected transcriptional responses of the core machinery and the divergence in amino-acid sequence between specific domains in each core RNAi protein may possibly contribute to low RNAi efficiency in ECB. Understanding the contributions of different RNAi pathway components is critical to adapting this technology for use in controlling lepidopteran pests that exhibit low RNAi efficiency.

Transcriptome analysis of Anastrepha fraterculus sp. 1 males, females, and embryos: insights into development, courtship, and reproduction

BACKGROUND

Anastrepha fraterculus sp. 1 is considered a quarantine pest in several American countries. Since chemical control applied in an integrated pest management program is the only strategy utilized against this pest, the development of pesticide-free methods, such as the Sterile Insect Technique, is being considered. The search for genes involved in sex-determination and differentiation, and in metabolic pathways associated with communication and mating behaviour, contributes with key information to the development of genetic control strategies. The aims of this work were to perform a comprehensive analysis of A. fraterculus sp. 1 transcriptome and to obtain an initial evaluation of genes associated with main metabolic pathways by the expression analysis of specific transcripts identified in embryos and adults.

RESULTS

Sexually mature adults of both sexes and 72 h embryos were considered for transcriptome analysis. The de novo transcriptome assembly was fairly complete (62.9% complete BUSCO orthologs detected) with a total of 86,925 transcripts assembled and 28,756 GO annotated sequences. Paired-comparisons between libraries showed 319 transcripts differently expressed between embryos and females, 1242 between embryos and males, and 464 between sexes. Using this information and genes searches based on published studies from other tephritid species, we evaluated a set of transcripts involved in development, courtship and metabolic pathways. The qPCR analysis evidenced that the early genes serendipity alpha and transformer-2 displayed similar expression levels in the analyzed stages, while heat shock protein 27 is over-expressed in embryos and females in comparison to males. The expression of genes associated with courtship (takeout-like, odorant-binding protein 50a1) differed between males and females, independently of their reproductive status (virgin vs mated individuals). Genes associated with metabolic pathways (maltase 2-like, androgen-induced gene 1) showed differential expression between embryos and adults. Furthermore, 14,262 microsatellite motifs were identified, with 11,208 transcripts containing at least one simple sequence repeat, including 48% of di/trinucleotide motifs.

CONCLUSION

Our results significantly expand the available gene space of A. fraterculus sp. 1, contributing with a fairly complete transcript database of embryos and adults. The expression analysis of the selected candidate genes, along with a set of microsatellite markers, provides a valuable resource for further genetic characterization of A. fraterculus sp. 1 and supports the development of specific genetic control strategies.

Insecticidal Gene Silencing by RNAi in the Neotropical Region

Insecticidal gene silencing by RNA interference (RNAi) involves a post-transcriptional mechanism with great potential for insect control. Here, we aim to summarize the progress on RNAi research toward control of insect pests in the Neotropical region and discuss factors determining its efficacy and prospects for pest management. We include an overview of the available RNAi information for Neotropical pests in the Lepidoptera, Coleoptera, Diptera, and Hemiptera orders. Emphasis is put on significant findings in the use of RNAi against relevant Neotropical pests, including diamondback moth (Plutella xylostella L.), Asian citrus psyllid (Diaphorina citri Kuwayama), and the cotton boll weevil (Anthonomus grandis Boheman). We also examine the main factors involved in insecticidal RNAi efficiency and major advances to improve screening of lethal genes, formulation, and delivery. Few studies detail resistance mechanisms to RNAi, demonstrating a need for more research. Advances in formulation, delivery, and resistance management tools for insecticidal RNAi in the Neotropics can provide a basis for efficient field application.