RNAi suppression of the ryanodine receptor gene results in decreased susceptibility to chlorantraniliprole in Colorado potato beetle Leptinotarsa decemlineata

Comparative transcriptome profiling of two pesticides, Acephate and Chlorantraniliprole in non-targeted insect model, Drosophila melanogaster

Acephate and chlorantraniliprole are two insecticides widely used in agricultural applications. Several studies were focused on the mode of action and related biological and cellular level expressions. However, the sub-lethal dose and related molecular expression level of acephate and chlorantraniliprole have not been evaluated or studied to the same degree. In this study, we investigated the sub-lethal toxicity of acephate and chlorantraniliprole in Drosophila melanogaster. The EC50 value was recorded with high difference, and is found to be 1.9 μg/ml and 0.029 μg/ml respectively for acephate and chlorantraniliprole, the difference is simply because of the different modes of action. The 1/5th EC50 concentration was selected for studying the pesticide induced transcriptomics in D. melanogaster. Both pesticides significantly altered the expression profile of several transcripts which are involved in proteolysis, detoxification, chromosome associated proteins and immune response genes and so on. The effect of both pesticides on D. melanogaster was further explored by screening the genes involved in toxicity, which were analyzed using, GO and KEGG pathways. The results revealed that the sub-lethal exposure of both pesticides caused significant changes in the global gene transcription profiles and each pesticide had their unique mode of alteration in the D. melanogaster.

Combined Analysis of Metabolomics and Biochemical Changes Reveals the Nutritional and Functional Characteristics of Red Palm Weevil Rhynchophus ferrugineus (Coleoptera: Curculionidae) Larvae at Different Developmental Stages

In this study, the changes in the conventional nutrient and mineral compositions as well as the metabolomics characteristics of the red palm weevil (RPW) Rhynchophus ferrugineus Olivier (Curculionidae: Coleoptera) larvae at early (EL), middle (ML) and old (OL) developmental stages were investigated. Results showed that the EL and ML had the highest content of protein (53.87 g/100 g dw) and fat (67.95 g/100 g), respectively, and three kinds of RPW larvae were all found to be rich in unsaturated fatty acids (52.17-53.12%), potassium (5707.12-15,865.04 mg/kg) and phosphorus (2123.87-7728.31 mg/kg). In addition, their protein contained 17 amino acids with the largest proportion of glutamate. A total of 424 metabolites mainly including lipids and lipid-like molecules, organic acids and their derivatives, organic heterocycle compounds, alkaloids and their derivatives, etc. were identified in the RPW larvae. There was a significant enrichment in the ABC transport, citrate cycle (TCA cycle), aminoacyl-tRNA biosynthesis, and mTOR signaling pathways as the larvae grow according to the analysis results of the metabolic pathways of differential metabolites. The water extract of EL exhibited relatively higher hydroxyl, 2,2-diphenyl-1-pyrroline hydrochloride (DPPH) and 2,2'-azobis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical-scavenging ability with the EC50 values of 1.12 mg/mL, 11.23 mg/mL, and 2.52 mg/mL, respectively. These results contribute to a better understanding of the compositional changes of the RPW larvae during its life cycle and provide a theoretical grounding for its deep processing and high-value utilization.

Development of Sustainable Insecticide Candidates for Protecting Pollinators: Insight into the Bioactivities, Selective Mechanism of Action and QSAR of Natural Coumarin Derivatives against Aphids

Plants employ abundant toxic secondary metabolites to withstand insect attack, while pollinators can tolerate some natural defensive compounds. Coumarins, as promising green alternatives to chemical insecticides, possess wide application prospects in the crop protection field. Herein, the bioactivities of 30 natural coumarin derivatives against Aphis gossypii were assessed and revealed that 6-methylcoumarin exhibited potent aphicidal activity against aphids but displayed no toxicity to honeybees. Additionally, using biochemical, bioinformatic, and molecular assays, we confirmed that the action mode of 6-methylcoumarin against aphids was by inhibiting acetylcholinesterase (AChE). Meanwhile, functional assays revealed that the difference in action site, which located in Lys585 in aphid AChE (equivalent to Val548 in honeybee AChE), was the principal reason for 6-methylcoumarin being toxic to aphids but safe to pollinators. This action site was further validated by mutagenesis data, which uncovered how 6-methylcoumarin was unique selective to the aphid over honeybee or mammalian AChE. Furthermore, a 2D-QSAR model was established, revealing that the central structural feature was H3m, which offers guidance for the future design of more potent coumarin compounds. This work provides a sustainable strategy to take advantage of coumarin analogues for pest management while protecting nontarget pollinators.

Functional Characterization of the Ryanodine Receptor Gene in Diaphorina citri

The Asian citrus psyllid Diaphorina citri (Hemiptera: Liviidae) is a major citrus pest spread around the world. It is also a vector of the bacterium 'Candidatus Liberibacter asiaticus', considered the cause of the fatal citrus disease huanglongbing (HLB). Insect ryanodine receptors (RyRs) are the primary target sites of diamide insecticides. In this study, full-length RyR cDNA from D. citri (named DcRyR) was isolated and identified. The 15,393 bp long open reading frame of DcRyR encoded a 5130 amino acid protein with a calculated molecular weight of 580,830 kDa. This protein had a high sequence identity (76-79%) with other insect homologs and a low sequence identity (43-46%) with mammals. An MIR domain, two RIH domains, three SPRY domains, four RyR repeat domains, an RIH-associated domain at the N-terminus, two consensus calcium-binding EF-hands, and six transmembrane domains were among the characteristics that DcRyR shared with insect and vertebrate RyRs. In expression analysis, the DcRyR gene displayed transcript abundance in all tissues and developmental stages as well as gene-differential and stage-specific patterns. In addition, diagnostic PCR experiments revealed that DcRyR had three potential alternative splice variants and that splicing events might have contributed to the various functions of DcRyR. However, diamide resistance-related amino acid residue mutations I4790M/K and G4946E were not found in DcRyR. These results can serve as the basis for further investigation into the target-based diamide pesticide resistance of D. citri.

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.

Characterization of Insecticide Response-Associated Transcripts in the Colorado Potato Beetle: Relevance of Selected Cytochrome P450s and Clothianidin

Simple Summary

The Colorado potato beetle is an insect pest that can significantly harm potato crops. Various approaches are available to mitigate its damages including the use of insecticides. Unfortunately, its ability to develop resistance towards these compounds is substantial, and understanding the basis of this process is of utmost importance to design strategies to limit the impact of this insect. This work thus aims at quantifying the expression of key transcripts coding for proteins associated with insecticide resistance in Colorado potato beetles exposed to four insecticides. Significant variations were observed, notably in insects exposed to the insecticide clothianidin. Interestingly, subsequent reduction of endogenous levels of selected targets modulated by clothianidin was associated with increased insect susceptibility to this neonicotinoid. These results further highlight molecular players with potential relevance for insecticide resistance, and introduce novel targets that underlie clothianidin resistance in the Colorado potato beetle.

Abstract

The Colorado potato beetle (Leptinotarsa decemlineata (Say)) is known for its capacity to cause significant damages to potato crops worldwide. Multiple approaches have been considered to limit its spread including the use of a diverse arsenal of insecticides. Unfortunately, this insect frequently develops resistance towards these compounds. Investigating the molecular bases underlying the response of L. decemlineata against insecticides is of strong interest to ultimately devise novel and targeted approaches aimed at this pest. This work aimed to characterize, via qRT-PCR, the expression status of targets with relevance to insecticide response, including ones coding for cytochrome P450s, glutathione s-transferases, and cuticular proteins, in L. decemlineata exposed to four insecticides; chlorantraniliprole, clothianidin, imidacloprid, and spinosad. Modulation of levels associated with transcripts coding for selected cytochrome P450s was reported in insects treated with three of the four insecticides studied. Clothianidin treatment yielded the most variations in transcript levels, leading to significant changes in transcripts coding for CYP4c1, CYP4g15, CYP6a13, CYP9e2, GST, and GST-1-Like. Injection of dsRNA targeting CYP4c1 and CYP9e2 was associated with a substantial decrease in expression levels and was, in the case of the latter target, linked to a greater susceptibility of L. decemlineata towards this neonicotinoid, supporting a potential role for this target in clothianidin response. Overall, this data further highlights the differential expression of transcripts with potential relevance in insecticide response, as well as generating specific targets that warrant investigation as novel dsRNA-based approaches are developed against this insect pest.

Characterization of the ryanodine receptor gene in Encarsia formosa (Gahan) and its expression profile in response to diamide insecticides

Ryanodine receptors (RyRs) are the targets of diamide insecticides, which have been identified and characterized in a dozen insect pests of Lepidoptera, Hemiptera, Diptera and Coleoptera, but limited attention has been paid to the RyR in parasitoid natural enemies. Without this knowledge, it will hinder our effective and efficient application using both parasitoid natural enemies and diamide insecticides simultaneously in the integrated pest management (IPM). In this study, the full-length cDNA of RyR was cloned from Encarsia formosa (EfRyR), a parasitic wasp used worldwide for the biological control of whitefly. Its expression profile was examined in various tissues of E. formosa adults. The toxicities of four diamide insecticides to E. formosa were measured, and then the expression profile of EfRyR after 12 h and 24 h exposure to the LC₅₀ dosages of diamide insecticides was investigated. The results showed that the full-length cDNA of EfRyR was 16, 778 bp including a 15, 345 bp open reading frame, and two alternative splice (AS) sites. Comparing to its expression in the abdomen, EfRyR was highly expressed in the head (11.9-fold) and the thorax (3.7-fold). The toxicities of four dimide insecticides against E. formosa from low to high were chlorantraniliprole (LC₅₀ = 367.84 mg L^-1), cyantraniliprole (221.72 mg L^-1), cyclaniliprole (51.77 mg L^-1), and tetrachlorantraniliprole (8.35 mg L^-1). The expressions of EfRyR and its variants with AS were significantly increased after E. formosa adults were exposed to different diamide insecticides. This study improves our understanding of the RyR in parasitoid wasps and provides useful information on IPM by using E. formosa.

Methods for Delivery of dsRNAs for Agricultural Pest Control: The Case of Lepidopteran Pests

RNA interference (RNAi) is a natural mechanism of gene regulation, highly conserved in eukaryotes. Since the elucidation of the gene silencing mechanism, RNAi became an important tool used in insect reverse genetics. The demonstration of effective target-gene silencing by ingestion of double-stranded RNA (dsRNA) produced by transgenic plants indicated the RNAi potential to be used in insect pest management, particularly in agriculture. However, the efficiency of gene silencing by RNAi in insects may vary according to the target taxa, and lepidopteran species have been shown to be quite recalcitrant to RNAi. Developing transgenic plants is a time-consuming and labor-intensive process, so alternative oral delivery systems are required to develop and optimize RNAi settings, such as selecting an efficient target gene, and dsRNA design, length, and stability, among other features. We have developed delivery systems to evaluate dsRNAs to silence genes from two important lepidopteran crop pests of tomato (Solanum lycopersicum) and sugarcane (Saccharum × officinarum): Tuta absoluta (Meyrick), the South American Tomato Pinworm, and Diatraea saccharalis (Fabricius), the Sugarcane Borer, respectively. The protocol described here can be used in similar species and includes (a) direct oral delivery by droplets containing dsRNA; (b) oral delivery by tomato leaflets that absorbed dsRNA solution; (c) delivery by Escherichia coli expressing dsRNA; and (d) delivery by transgenic plants expressing dsRNA.

A Comparative Perspective on Functionally-Related, Intracellular Calcium Channels: The Insect Ryanodine and Inositol 1,4,5-Trisphosphate Receptors

Calcium (Ca²⁺) homeostasis is vital for insect development and metabolism, and the endoplasmic reticulum (ER) is a major intracellular reservoir for Ca²⁺. The inositol 1,4,5- triphosphate receptor (IP₃R) and ryanodine receptor (RyR) are large homotetrameric channels associated with the ER and serve as two major actors in ER-derived Ca²⁺ supply. Most of the knowledge on these receptors derives from mammalian systems that possess three genes for each receptor. These studies have inspired work on synonymous receptors in insects, which encode a single IP₃R and RyR. In the current review, we focus on a fundamental, common question: “why do insect cells possess two Ca²⁺ channel receptors in the ER?”. Through a comparative approach, this review covers the discovery of RyRs and IP₃Rs, examines their structures/functions, the pathways that they interact with, and their potential as target sites in pest control. Although insects RyRs and IP₃Rs share structural similarities, they are phylogenetically distinct, have their own structural organization, regulatory mechanisms, and expression patterns, which explains their functional distinction. Nevertheless, both have great potential as target sites in pest control, with RyRs currently being targeted by commercial insecticide, the diamides.

Insecticidal action of the botanical insecticide wilforine on Mythimna separata (Walker) related with the changes of ryanodine receptor expression

The detailed molecular mechanism of wilforine, a novel botanical insecticidal component, remains unclear, except for the knowledge that it affects the calcium signaling pathway. The aim of the current study was to examine the underlying molecular mechanism of wilforine in Mythimna separata (Walker) by transcriptome and RNA interference (RNAi), with chlorantraniliprole as control. RNA sequencing showed that the relative expression of genes related to the calcium signaling pathway and muscle contraction in M. separata treated with wilforine significantly changed and was further validated by qRT-PCR. Interestingly, the expression level of the ryanodine receptor (MsRyR) gene was downregulated by wilforine at relatively high concentrations and long treatment time, contrary to that observed using chlorantraniliprole. Furthermore, a putative MsRyR was cloned using a 16,258-bp contiguous sequence containing a 308-bp 5'-untranslated region and 578-bp 3'-untranslated region by RT-PCR and RACE. The results of the RNAi experiment showed that injection of dsMsRyR significantly reduced MsRyR mRNA levels, and growth and development were inhibited. Importantly, silencing of the MsRyR gene resulted in decreased susceptibility to both wilforine and chlorantraniliprole. Together with the results of our previous studies on toxic symptoms and muscle tissue lesions between wilforine and chlorantraniliprole, we propose that RyR Ca²⁺ release channel dysfunction is closely related with significant lethal mechanisms of wilforine.

Target verification of allyl isothiocyanate on the core subunits of cytochrome c oxidase in Sitophilus zeamais by RNAi

BACKGROUND

Allyl isothiocyanate (AITC) is a volatile organic compound with a potent insecticidal activity to the stored-grain pest Sitophilus zeamais Motschulsky, which severely damages grain storage and container transport worldwide. Our previous study showed that mitochondrial complex IV was the primary target of AITC in adult Sitophilus zeamais. To further verify the targets of AITC, we employed RNA interference (RNAi) by using double-stranded RNA (dsRNA) to knockdown three core subunits of cytochrome c oxidase (COX)-I, -II and -III in 18-day-old larvae prior to their exposure to AITC to detect susceptibility changes.

RESULTS

The susceptibility of dsRNACOX-I and -II injection treatments to AITC significantly increased at 72 h while the mortality reached up to 85.56% and 67.78%, respectively, and dsRNACOX-I and dsRNACOX-II injection showed the same subcellular structural characteristics showing vacuolization and vague mitochondrial cristae and decrease of COX activity during AITC fumigation treatment, suggesting the potential of COX-I and COX-II as the targets of AITC. High mortality reached up to 75.55%, 71.88% and 82.22%, respectively, and the phenotype of larvae turning from milky white to dark brown in the thorax and death eventually was confirmed after dsRNACOX-I, -II and -III injection.

CONCLUSION

COX-I and -II were elucidated as the potential targets of AITC and dsRNACOX-I, -II and -III have the potential to be developed into nucleic acid pesticides for their robust lethal effects and are worth pursuing for improving AITC fumigation activity in Sitophilus zeamais control. © 2020 Society of Chemical Industry.

Functional analysis of an upregulated calmodulin gene related to the acaricidal activity of curcumin against Tetranychus cinnabarinus (Boisduval)

BACKGROUND

Curcumin is a promising botanical acaricidal compound with activity against Tetranychus cinnabarinus. Calmodulin (CaM) is a key calcium ion (Ca²⁺ ) sensor that plays a vital role in calcium signaling. Overexpression of the CaM gene with inducible character occurs in curcumin-treated mites, but its functional role remains to be further analyzed by RNA interference (RNAi) and protein expression.

RESULTS

A CaM gene was cloned from T. cinnabarinus (designated TcCaM). TcCaM was upregulated and the protein was activated in mites by curcumin. The susceptibility of mites to curcumin was decreased after inhibiting CaM function with anti-CaM drug trifluoperazine (TFP) and silencing CaM transcription with RNAi, suggesting that the CaM gene is involved in the acaricidal activity of curcumin against mites. Moreover, the TFP pre-treated Sf9 cells were resistant to curcumin-mediated increase in [Ca²⁺ ]i levels, indicating that CaM-mediated Ca²⁺ homeostasis was disturbed by curcumin. TcCaM was then re-engineered for heterologous expression in Escherichia coli. Strikingly, our results showed that the recombinant CaM protein was directly activated by curcumin via inducing its conformational changes, its half-maximal effective concentration (EC₅₀ ) value is 0.3 μmol L^-1 in vitro, which is similar to curcumin against CaM-expressing Sf9 cells (0.76 μmol L^-1 ) in vivo.

CONCLUSION

These results confirm that the overexpressed CaM gene is involved in the acaricidal activity of curcumin, and the mode of action of curcumin may be via activating CaM function, and thereby disrupting Ca²⁺ homeostasis in T. cinnabarinus. This study highlights the novel target mechanism of new acaricides, promoting our understanding of the molecular mechanism of CaM-mediated acaricide targets in mites.

Elevated rates of positive selection drive the evolution of pestiferousness in the Colorado potato beetle (Leptinotarsa decemlineata, Say)

Contextualizing evolutionary history and identifying genomic features of an insect that might contribute to its pest status is important in developing early detection and control tactics. In order to understand the evolution of pestiferousness, which we define as the accumulation of traits that contribute to an insect population's success in an agroecosystem, we tested the importance of known genomic properties associated with rapid adaptation in the Colorado potato beetle (CPB), Leptinotarsa decemlineata Say. Within the leaf beetle genus Leptinotarsa, only CPB, and a few populations therein, has risen to pest status on cultivated nightshades, Solanum. Using whole genomes from ten closely related Leptinotarsa species native to the United States, we reconstructed a high-quality species tree and used this phylogenetic framework to assess evolutionary patterns in four genomic features of rapid adaptation: standing genetic variation, gene family expansion and contraction, transposable element abundance and location, and positive selection at protein-coding genes. Throughout approximately 20 million years of history, Leptinotarsa species show little evidence of gene family turnover and transposable element variation. However, there is a clear pattern of CPB experiencing higher rates of positive selection on protein-coding genes. We determine that these rates are associated with greater standing genetic variation due to larger effective population size, which supports the theory that the demographic history contributes to rates of protein evolution. Furthermore, we identify a suite of coding genes under positive selection that are putatively associated with pestiferousness in the Colorado potato beetle lineage. They are involved in the biological processes of xenobiotic detoxification, chemosensation and hormone function.

Ryanodine receptor-targeting small molecule fluorescent probes enables non-isotopic labeling and efficient drug screening for green insecticides

Ryanodine receptors (RyRs) are calcium release channels located on endoplasmic reticulum (ER) membrane, which play important role in excitation-contraction coupling in muscular response. Flubendiamide represents a novel chemical family of green insecticides which selectively activate invertebrate RyR by interacting with the receptor distinct from the ryanodine binding site and has almost no effect on mammalian ryanodine receptors. Traditional methods to screen RyR modulators involve either radio-labeled RyR substrates or calcium signal-based indirect approaches. However, there is lack of RyR-directed non-isotope molecular tools for RyR agonists/antagonists screening and bioimaging. Here we developed a series of fluorescent probes based on the pharmacophore of flubendiamide with the aims to elucidate the mechanism of diamide insecticides and screen novel RyR-targeting insecticides. These probes revealed the specific RyR staining and in vivo RyR targeting properties in diamondback moth RyR transfected Sf9 cells (Sf9-RyR) and RyR enriched insect tissues. The designed fluorescent probes could induce an effective calcium release from ER membrane of Sf9-RyR cells and also showed competitive RyR binding effect with flubendiamide in cell-based fluorometric assay. Having the non-isotope RyR recognition probes will not only accelerate the screening process of new green agrochemicals but also enables deciphering molecular mechanisms of the high selectivity and the drug resistance associated with the diamides.

Differential expression of transcripts with potential relevance to chlorantraniliprole response in the Colorado potato beetle, Leptinotarsa decemlineata

The Colorado potato beetle (Leptinotarsa decemlineata [Say]) is an insect pest that can significantly harm potato plants worldwide. Control of this insect relies heavily on chemical insecticides such as chlorantraniliprole. Nevertheless, the complete molecular signature associated with response to this compound is lacking in L. decemlineata. In this study, amplification and quantification by qRT-PCR (quantitative reverse transcription-polymerase chain reaction) of targets relevant to chlorantraniliprole were undertaken in insects exposed to this chemical. This approach showed modulation of numerous cytochrome P450s, such as CYP350D1 and CYP4Q3, as well as upregulation of microRNAs (miRNAs), including miR-1-3p and miR-305-5p, in chlorantraniliprole-exposed insects. Functional assessment of transcript targets predicted to be regulated by these miRNAs was performed and revealed their likely impact on transcriptional regulation. RNAi-based targeting of CYP350D1 notably provided preliminary evidence of its underlying implication for chlorantraniliprole response in L. decemlineata. Overall, this study strengthens the current knowledge of the molecular changes linked to chlorantraniliprole response in L. decemlineata and provides novel targets with potential relevance to chlorantraniliprole susceptibility in this insect pest of global relevance.

Chlorantraniliprole resistance and its biochemical and new molecular target mechanisms in laboratory and field strains of Chilo suppressalis (Walker)

BACKGROUND

The rice striped stem borer (SSB), Chilo suppressalis (Walker), is one of the most economically important and destructive rice pests in China. To date, the efficiency of conventional insecticides has decreased greatly because of the development of high resistance. Since the introduction of chlorantraniliprole in 2008, SSB has presented resistance issues.

RESULTS

In this study, laboratory resistant strains R1 and R2 [resistance ratio (RR) of 38.8 and 110.4, respectively] were established and a field population HR (RR of 249.6) was collected. Synergist assessment and enzyme activity data suggested the potential involvement of P450s and esterases in the resistance mechanism. No target (ryanodine receptor, RyR) mutation was found in R1, but a novel mutation Y4667D was found in R2. At the same position of RyR in HR strain, Y4667D and Y4667C were observed at low frequencies. In addition, the conserved mutation I4758M was found with a frequency of 94.4%. RyR mRNA expression was significantly lower in R1, R2 and HR than in S. When treated with chlorantraniliprole, RyR mRNA expression in all four strains was downregulated to ∼ 50%.

CONCLUSIONS

A comprehensive analysis, including biochemical, target mutations and target mRNA expression, was conducted in an attempt to interpret the chlorantraniliprole resistance mechanism in both laboratory and field SSB strains. © 2017 Society of Chemical Industry.

Silence of ryanodine receptor gene decreases susceptibility to chlorantraniliprole in the oriental armyworm, Mythimna separata Walker

The ryanodine receptors of insects are the main target sites of diamide insecticides, which show highly selective insecticidal activity relative to toxicity in mammals and provide a novel option for managing lepidopteran pests. The oriental armyworm, Mythimna separata (Walker), is a destructive pest of agricultural crops, and great efforts have been undertaken to control this pest including repeated insecticide applications. In this study, full-length cDNA of a ryanodine receptor gene from M. separata (MsRyR) was cloned and characterized. The cDNA of MsRyR had a 15,372 bp open reading frame and encoded 5124 amino acids (GenBank ID: MG712298). MsRyR shares 78-97% identity with RyR isoforms of other insects, and <50% identities with Homo sapiens RyRs 1-3. Temporal and spatial expression analysis detected MsRyR at all developmental stages and in all tissues. The highest relative levels of MsRyR were detected in the second instar and head. Exposure to chlorantraniliprole after 24 h significantly increased the expression levels of whole body MsRyR mRNA. In addition, dietary ingestion of dsMsRyR significantly reduced the mRNA level of MsRyR and greatly decreased chlorantraniliprole-induced mortality. Our results revealed that the MsRyR could be the molecular target of chlorantraniliprole, and provided the basis for further understanding the resistance mechanism of chlorantraniliprole.

RNA interference of glutamate-gated chloride channel decreases abamectin susceptibility in Bemisia tabaci

The Bemisia tabaci (Gennadius) cryptic species complex comprises very destructive insect pests of agricultural crops worldwide and has been found to be resistant to various insecticides in China. Abamectin is one of the most widely used insecticides for insect pest control and the glutamate-gated chloride channel (GluCl) in insects was presumed to be the main target site of abamectin. In this study, a 1353bp full-length cDNA encoding GluCl (named BtGluCl, GenBank ID: MF673854) was cloned and characterized from B. tabaci. BtGluCl encodes 450 amino acids, which shares 71-81% identity with other insect GluCl isoforms. Spatial and temporal expression revealed BtGluCl was highly expressed in the 4th nymphal instar and adult head, and the least expressed in the 1st nymphal instar and adult leg. Dietary ingestion of dsBtGluCl significantly reduced the mRNA level of BtGluCl in the treated adults by 62.9% and greatly decreased abamectin-induced mortality. Thus, our results could be conducive to further understanding the mechanisms of resistance to abamectin in arthropods.

Systemic RNAi in western corn rootworm, Diabrotica virgifera virgifera, does not involve transitive pathways

Western corn rootworm (WCR, Diabrotica virgifera virgifera LeConte) is highly sensitive to orally delivered double-stranded RNA (dsRNA). RNAi in WCR is systemic and spreads throughout the insect body. This raises the question whether transitive RNAi is a mechanism that functions in WCR to amplify the RNAi response via production of secondary siRNA. Secondary siRNA production is achieved through RNA-dependent RNA polymerase (RdRP) activity in other eukaryotic organisms, but RdRP has not been identified in WCR and any other insects. This study visualized the spread of the RNAi-mediated knockdown of Dv v-ATPase C mRNA throughout the WCR gut and other tissues using high-sensitivity branched DNA in situ hybridization. Furthermore, we did not detect either secondary siRNA production or transitive RNAi in WCR through siRNA sequence profile analysis. Nucleotide mismatched sequences introduced into either the sense or antisense strand of v-ATPase C dsRNAs were maintained in siRNAs derived from WCR fed with the mismatched dsRNAs in a strand specific manner. The distribution of all siRNAs was restricted to within the original target sequence regions, which may indicate the lack of new dsRNA synthesis leading to production of secondary siRNA. Thus, the systemic spread of RNAi in WCR may be derived from the original dsRNA molecules taken up from the gut lumen. These results indicate that the initial dsRNA dose is important for a lethal systemic RNAi response in WCR and have implications in developing effective dsRNA traits to control WCR and in resistance management to prolong the durability of RNAi trait technology.

High Concentrations of Chlorantraniliprole Reduce Its Compatibility with a Key Predator, Hippodamia convergens (Coleoptera: Coccinellidae)

Diamides are a novel insecticide group that act by disrupting insect muscle contraction. Recommended field rates (FRs) vary greatly among target pests and cropping systems, leading to variable risks for non-target organisms. We evaluated the toxicity of chlorantraniliprole to the predator Hippodamia convergens Guérin-Méneville (Coleoptera: Coccinellidae) by exposure to residues, topical application, and consumption of contaminated food. We also estimated lethal concentrations (LCs) of chlorantraniliprole in two target pests, cotton leafworm, Alabama argillacea (Hübner) (Lepidoptera: Erebidae), and tobacco budworm, Chloridea virescens (F.) (Lepidoptera: Noctuidae), by exposing larvae to treated cotton, Gossypium hirsutum L., leaves and assessed residual activity at various intervals after application to cotton plants. Exposure to dried residues and ingestion of treated moth eggs resulted in similar toxicity to H. convergens, whereas topical application was a less toxic route of exposure. Regardless of exposure route, the LC50s and LC90s obtained for H. convergens were higher than those calculated for the pests. Residues at the upper limit of the LC90 for C. virescens remained effective against this pest for up to 16 d, while exhibiting minor impacts on H. convergens. In contrast, the FR concentration of C. virescens caused significant mortality in H. convergens. The results suggest that the current FR for C. virescens is too high to be safe for H. convergens, and given the LCs observed for this pest in the present study, trials to explore the potential efficacy of lower FRs are justified. Depending on the concentration and route of exposure, this insecticide has the potential to be compatible with H. convergens.

Molecular cloning, mRNA expression and alternative splicing of a ryanodine receptor gene from the citrus whitefly, Dialeurodes citri (Ashmead)

Insect ryanodine receptors are the main targets of diamide insecticides that have highly selective insecticidal activity but are less toxic to mammals. Therefore, these insecticides are ideal for pest control. Ryanodine receptors (RyRs) play a critical role in Ca²⁺ signaling in muscle and non-muscle cells. In this study, we cloned the complete cDNA (DcRyR) of the RyR from the citrus whitefly, Dialeurodes citri, a serious pest of citrus orchards in China. The open reading frame of RyR is 15,378bp long and encodes a protein with 5126 amino acids with a computed molecular weight of 579.523kDa. DcRyR shows a high amino acid sequence identity to RyRs from other insects (76%-95%) and low identity to those from nematodes and mammals (44%-52%). DcRyR shares many features of insect and vertebrate RyRs, including a MIR domain, two RIH domains, three SPRY domains, four copies of RyR repeat domain, RIH-associated domain at the N-terminus, two consensus calcium-binding EF-hands and six transmembrane domains at the C-terminus. The expression of DcRyR mRNA was the highest in the nymphs and lowest in eggs; DcRyR mRNA was 1.85-fold higher in the nymphs than in the eggs. Among the tissues, DcRyR mRNA expression was 4.18- and 4.02-fold higher in the adult head and thorax than in the abdomen. DcRyR had three alternative splice sites and the splice variants showed body part-specific expression and were developmentally regulated. These results may help investigate target-based resistance to diamide insecticides in D. citri.

Overexpression of a cytochrome P450 and a UDP-glycosyltransferase is associated with imidacloprid resistance in the Colorado potato beetle, Leptinotarsa decemlineata

Current control of insect pests relies on chemical insecticides, however, insecticide resistance development by pests is a growing concern in pest management. The main mechanisms for insecticide resistance typically involve elevated activity of detoxifying enzymes and xenobiotic transporters that break-down and excrete insecticide molecules. In this study, we investigated the molecular mechanisms of imidacloprid resistance in the Colorado potato beetle, Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae), an insect pest notorious for its capacity to develop insecticide resistance rapidly. We compared the transcriptome profiles of imidacloprid-resistant and sensitive beetle strains and identified 102 differentially expressed transcripts encoding detoxifying enzymes and xenobiotic transporters. Of these, 74 were up-regulated and 28 were down-regulated in the resistant strain. We then used RNA interference to knock down the transcript levels of seven up-regulated genes in the resistant beetles. Ingestion of double-stranded RNA successfully knocked down the expression of the genes for three cytochrome P450s (CYP6BQ15, CYP4Q3 and CYP4Q7), one ATP binding cassette (ABC) transporter (ABC-G), one esterase (EST1), and two UDP-glycosyltransferases (UGT1 and UGT2). Further, we demonstrated that silencing of CYP4Q3 and UGT2 significantly increased susceptibility of resistant beetles to imidacloprid, indicating that overexpression of these two genes contributes to imidacloprid resistance in this resistant strain.

A meta-analysis testing eusocial co-option theories in termite gut physiology and symbiosis

The termite gut accomplishes key physiologic functions that underlie termite symbiosis and sociality. However, potential candidate functions of the host-symbiont holobiome have not yet been explored across seemingly divergent processes such as digestion, immunity, caste differentiation, and xenobiotic tolerance. This study took a meta-analysis approach for concurrently studying host and symbiont gut metatranscriptome responses of the lower termite Reticulitermes flavipes, which has ancestral characteristics and hosts a diverse mix of eukaryotic and bacterial symbionts. Thirteen treatments were compared from 5 categories (dietary, social, hormonal, immunological, and xenobiotic), revealing 3 main insights. First, each of the 5 tested colonies had distinct magnitudes of transcriptome response, likely as a result of unique symbiont profiles, which highlights the uniqueness of individual termite colonies. Second, after normalization to standardize colony response magnitudes, unique treatment-linked metatranscriptome topologies became apparent. Third, despite colony and topology differences, 4 co-opted master genes emerged that were universally responsive across diverse treatments. These master genes encode host functions related to protein translation and symbiont functions related to protein degradation and pore formation in microbial cell walls. Three of the 4 master genes were from co-evolved protist symbionts, highlighting potentially co-evolved roles for gut symbiota in coordinating functional responses of the collective host-symbiont holobiome. Lastly, for host genes identified, these results provide annotations of recent termite genome sequences. By revealing conserved domain genes, as well as apparent roles for gut symbiota in holobiome regulation, this study provides new insights into co-opted eusocial genes and symbiont roles in termite sociobiology.

Ryanodine receptor genes of the rice stem borer, Chilo suppressalis: Molecular cloning, alternative splicing and expression profiling

The ryanodine receptor (RyR) of the calcium release channel is the main target of anthranilic and phthalic diamide insecticides which have high selective insecticidal activity relative to mammalian toxicity. In this study, the full-length cDNA of Chilo suppressalis RyR (CsRyR) was isolated and characterized. The CsRyR mRNA has an open reading frame (ORF) of 15,387bp nucleotides, which encodes 5128 amino acids with GenBank ID: KR088972. Comparison of protein sequences showed that CsRyR shared high identities with other insects of 77-96% and lower identity to mammals and nematodes with only 42-45%. One alternative splicing site (KENLG) unique to Lepidoptera was found and two exclusive exons of CsRyR (I /II) were revealed. Spatial and temporal expression of CsRyR mRNA was at the highest relative level in 3rd instar larvae and head (including brain and muscle), and at the lowest expression level in egg and fat body. The expression levels of whole body CsRyR mRNA were increased remarkably after injection of 4th instar larvae with chlorantraniliprole at 0.004 to 0.4μg/g. This structural and functional information on CsRyR provides the basis for further understanding the selective action of chlorantraniliprole and possibly other diamide insecticides.

RNA interference of three up-regulated transcripts associated with insecticide resistance in an imidacloprid resistant population of Leptinotarsa decemlineata

The Colorado potato beetle, Leptinotarsa decemlineata (Say), is a major agricultural pest of potatoes in the Central Sands production region of Wisconsin. Previous studies have shown that populations of L. decemlineata have become resistant to many classes of insecticides, including the neonicotinoid insecticide, imidacloprid. Furthermore, L. decemlineata has multiple mechanisms of resistance to deal with a pesticide insult, including enhanced metabolic detoxification by cytochrome p450s and glutathione S-transferases. With recent advances in the transcriptomic analysis of imidacloprid susceptible and resistant L. decemlineata populations, it is possible to investigate the role of candidate genes involved in imidacloprid resistance. A recently annotated transcriptome analysis of L. decemlineata was obtained from select populations of L. decemlineata collected in the Central Sands potato production region, which revealed a subset of mRNA transcripts constitutively up-regulated in resistant populations. We hypothesize that a portion of the up-regulated transcripts encoding for genes within the resistant populations also encode for pesticide resistance and can be suppressed to re-establish a susceptible phenotype. In this study, a discrete set of three up-regulated targets were selected for RNA interference experiments using a resistant L. decemlineata population. Following the successful suppression of transcripts encoding for a cytochrome p450, a cuticular protein, and a glutathione synthetase protein in a select L. decemlineata population, we observed reductions in measured resistance to imidacloprid that strongly suggest these genes control essential steps in imidacloprid metabolism in these field populations.

RNA interference of chitin synthase genes inhibits chitin biosynthesis and affects larval performance in Leptinotarsa decemlineata (Say)

Dietary introduction of bacterially expressed double-stranded RNA (dsRNA) has great potential for management of Leptinotarsa decemlineata. Identification of the most attractive candidate genes for RNA interference (RNAi) is the first step. In the present paper, three complete chitin synthase cDNA sequences (LdChSAa, LdChSAb and LdChSB) were cloned. LdChSAa and LdChSAb, two splicing variants of LdChSA gene, were highly expressed in ectodermally-derived epidermal cells forming epidermis, trachea, foregut and hindgut, whereas LdChSB was mainly transcribed in midgut cells. Feeding bacterially expressed dsChSA (derived from a common fragment of LdChSAa and LdChSAb), dsChSAa, dsChSAb and dsChSB in the second- and fourth-instar larvae specifically knocked down their target mRNAs. RNAi of LdChSAa+LdChSAb and LdChSAa lowered chitin contents in whole body and integument samples, and thinned tracheal taenidia. The resulting larvae failed to ecdyse, pupate, or emerge as adults. Comparably, knockdown of LdChSAb mainly affected pupal-adult molting. The LdChSAb RNAi pupae did not completely shed the old larval exuviae, which caused failure of adult emergence. In contrast, silencing of LdChSB significantly reduced foliage consumption, decreased chitin content in midgut sample, damaged midgut peritrophic matrix, and retarded larval growth. As a result, the development of the LdChSB RNAi hypomorphs was arrested. Our data reveal that these LdChSs are among the effective candidate genes for an RNAi-based control strategy against L. decemlineata.

Knockdown of juvenile hormone acid methyl transferase severely affects the performance of Leptinotarsa decemlineata (Say) larvae and adults

BACKGROUND

Juvenile hormone (JH) plays a critical role in the regulation of metamorphosis in Leptinotarsa decemlineata, a notorious defoliator of potato. JH acid methyltransferase (JHAMT) is involved in one of the final steps of JH biosynthesis.

RESULTS

A putative JHAMT cDNA (LdJHAMT) was cloned. Two double-stranded RNAs (dsRNAs) (dsJHAMT1 and dsJHAMT2) against LdJHAMT were constructed and bacterially expressed. Experiments were conducted to investigate the effectiveness of RNAi in both second- and fourth-instar larvae. Dietary introduction of dsJHAMT1 and dsJHAMT2 successfully knocked down the target gene, lowered JH titre in the haemolymph and reduced the transcript of Krüppel homologue 1 gene. Ingestion of dsJHAMT caused larval death and weight loss, shortened larval developmental period and impaired pupation. Moreover, the dsJHAMT-fed pupae exhibited lower adult emergence rates. The resulting adults weighed an average of 50 mg less than the control group, and the females did not deposit eggs. Application of pyriproxyfen to the dsJHAMT-fed insects rescued all the negative effects.

CONCLUSIONS

LdJHAMT expresses functional JHAMT enzyme. The RNAi targeting LdJHAMT could be used for control of L. decemlineata. © 2015 Society of Chemical Industry.

The subunit gene Ldα1 of nicotinic acetylcholine receptors plays important roles in the toxicity of imidacloprid and thiamethoxam against Leptinotarsa decemlineata

Nicotinic acetylcholine receptors (nAChRs) are pentameric ACh-gated ion channels. It is believed that nAChRs composed of different subunits may vary in their function and toxicological characteristics. Neonicotinoids are activators of nAChRs and important insecticides that are extensively used for crop protection and resistance has been developed by some pests. They are also major insecticides for the control of Leptinotarsa decemlineata, which is a destructive defoliator pest that invaded the Xinjiang region of China in the 1990s. However, little is known about the constitution or subunits of the target in this pest. In this study, the full-length cDNAs encoding four new nAChR subunits (named Ldα3, Ldα6, Ldα10, and Ldβ1) were cloned from L. decemlineata. These genes encode 822-, 753-, 672-, and 759-amino acid proteins, respectively, which share typical features of insect nAChRs subunits and closely resemble the corresponding subunits of the nAChRs from Tribolium castaneum. Temporal and spatial expression analyses showed that these genes, as well as the previously identified Ldα1, Ldα2, and Ldα8 genes, are widely expressed in all developmental stages, including eggs, larvae of various instars, pupae, and adults. All genes monitored were expressed at higher levels in the head than in the thorax and abdomen, except for Ldα10. Dietary ingestion of double-stranded RNA bacterially expressed for Ldα1 (dsLdα1) significantly reduced the mRNA level of Ldα1 in treated larvae and adults by 48.0% and 78.6%, respectively. Among the non-target genes, Ldα3, Ldα9, and Ldβ1 were significantly up-regulated in larvae. A toxicity bioassay showed that dsLdα1 treatment greatly decreased the sensitivity to imidacloprid and thiamethoxam in adults. The larval susceptibility to thiamethoxam but not to imidacloprid was also reduced because of the lower down-regulation of Ldα1. Thus, our results suggest that Ldα1 encodes a subunit of a functional nAChR that mediates the toxicity of imidacloprid and thiamethoxam against L. decemlineata and that the down-regulation of Ldα1 might be an important mechanism for resistance and/or tolerance of L. decemlineata to neonicotinoids.

Knocking down a putative Δ(1) -pyrroline-5-carboxylate dehydrogenase gene by RNA interference inhibits flight and causes adult lethality in the Colorado potato beetle Leptinotarsa decemlineata (Say)

BACKGROUND

Leptinotarsa decemlineata is an able disperser by flight. Novel control strategies must be explored to control the damage and inhibit the dispersal efficiently. Proline is a major energy substrate during flight. Δ-Pyrroline-5-carboxylate dehydrogenase (P5CDh) catalyses the second step of proline degradation for the production of ATP.

RESULTS

A full-length Ldp5cdh cDNA was cloned. Ldp5cdh was ubiquitously expressed in the eggs, the first through fourth larval instars, wandering larvae, pupae and adults. In the adults, Ldp5cdh mRNA was widely distributed in thorax muscles, midgut, foregut, hindgut, Malpighian tubules, ventral ganglion, fat body and epidermis, with the expression levels from the highest to the lowest. Two double-stranded RNAs (dsRNAs) (dsLdp5cdh1 and dsLdp5cdh2) targeting Ldp5cdh were constructed and bacterially expressed. Ingestion of dsLdp5cdh1 and dsLdp5cdh2 successfully silenced Ldp5cdh, significantly increased the contents of proline, arginine and alanine, but strongly decreased the contents of asparate, asparagine, glutamate and glutamine in the haemolymph. Moreover, knocking down Ldp5cdh significantly reduced ATP content, decreased flight speed, shortened flight distance and increased adult mortality.

CONCLUSIONS

It seems that identified Ldp5cdh encodes a functional P5CDh enzyme, and Ldp5cdh may serve as a potential target for dsRNA-based pesticide for controlling the damage and dispersal of L. decemlineata adults. © 2014 Society of Chemical Industry.

Instar-dependent systemic RNA interference response in Leptinotarsa decemlineata larvae

RNA interference (RNAi) is a promising approach to control Leptinotarsa decemlineata. In this study, RNAi efficiency by double-stranded RNA (dsRNA) targeting S-adenosyl-L-homocysteine hydrolase (LdSAHase) was compared among L. decemlineata first- to fourth-instar larvae. Ingesting dsLdSAHase successfully decreased the target gene expression, caused lethality, inhibited growth and impaired pupation in an instar- and concentration-dependent manner. To study the role of Dicer2 and Argonaute2 genes in RNAi efficiency, we identified LdDcr2a, LdDcr2b, LdAgo2a and LdAgo2b. Their expression levels were higher in young larvae than those in old ones. Exposure to dsegfp for 6 h significantly elevated LdDcr2a, LdDcr2b, LdAgo2a and LdAgo2b mRNA levels in the first-, second-, third- and fourth-instar larvae. When the exposure periods were extended, however, the expression levels were gradually reduced. Continuous exposure for 72 h significantly repressed the expression of LdAgo2a and LdAgo2b in the first, second and third larval instars, and the four genes in final instars. Moreover, we found that dsLdSAHase-caused LdSAHase suppressions and larval mortalities were influenced by previous dsegfp exposure: 12 h of previous exposure increased LdSAHase silencing and mortality of the final instar larvae, whereas 72 h of exposure reduced LdSAHase silencing and mortality. Thus, it seems the activities of core RNAi-machinery proteins affect RNAi efficiency in L. decemlineata.

Functions of nuclear receptor HR3 during larval-pupal molting in Leptinotarsa decemlineata (Say) revealed by in vivo RNA interference

Our previous results revealed that RNA interference-aided knockdown of Leptinotarsa decemlineata FTZ-F1 (LdFTZ-F1) reduced 20E titer, and impaired pupation. In this study, we characterized a putative LdHR3 gene, an early-late 20E-response gene upstream of LdFTZ-F1. Within the first, second and third larval instars, three expression peaks of LdHR3 occurred just before the molt. In the fourth (final) larval instar 80 h after ecdysis and prepupal stage 3 days after burying into soil, two LdHR3 peaks occurred. The LdHR3 expression peaks coincide with the peaks of circulating 20E level. In vitro midgut culture and in vivo bioassay revealed that 20E and an ecdysteroid agonist halofenozide (Hal) enhanced LdHR3 expression in the final larval instars. Conversely, a decrease in 20E by feeding a double-stranded RNA (dsRNA) against an ecdysteroidogenesis gene Ldshd repressed the expression. Moreover, Hal rescued the transcript levels in the Ldshd-silenced larvae. Thus, 20E peaks activate the expression of LdHR3. Furthermore, ingesting dsRNA against LdHR3 successfully knocked down the target gene, and impaired pupation. Finally, knockdown of LdHR3 upregulated the transcription of three ecdysteroidogenesis genes (Ldphm, Lddib and Ldshd), increased 20E titer, and activated the expression of two 20E-response genes (LdEcR and LdFTZ-F1). Thus, LdHR3 functions in regulation of pupation in the Colorado potato beetle.

Molecular Characterization, mRNA Expression and Alternative Splicing of Ryanodine Receptor Gene in the Brown Citrus Aphid, Toxoptera citricida (Kirkaldy)

Ryanodine receptors (RyRs) play a critical role in regulating the release of intracellular calcium, which enables them to be effectively targeted by the two novel classes of insecticides, phthalic acid diamides and anthranilic diamides. However, less information is available about this target site in insects, although the sequence and structure information of target molecules are essential for designing new control agents of high selectivity and efficiency, as well as low non-target toxicity. Here, we provided sufficient information about the coding sequence and molecular structures of RyR in T. citricida (TciRyR), an economically important pest. The full-length TciRyR cDNA was characterized with an open reading frame of 15,306 nucleotides, encoding 5101 amino acid residues. TciRyR was predicted to embrace all the hallmarks of ryanodine receptor, typically as the conserved C-terminal domain with consensus calcium-biding EF-hands (calcium-binding motif) and six transmembrane domains, as well as a large N-terminal domain. qPCR analysis revealed that the highest mRNA expression levels of TciRyR were observed in the adults, especially in the heads. Alternative splicing in TciRyR was evidenced by an alternatively spliced exon, resulting from intron retention, which was different from the case of RyR in Myzus persicae characterized with no alternative splicing events. Diagnostic PCR analysis indicated that the splicing of this exon was not only regulated in a body-specific manner but also in a stage-dependent manner. Taken together, these results provide useful information for new insecticide design and further insights into the molecular basis of insecticide action.

RNA interference: Applications and advances in insect toxicology and insect pest management

Since its discovery, RNA interference (RNAi) has revolutionized functional genomic studies due to its sequence-specific nature of post-transcriptional gene silencing. In this paper, we provide a comprehensive review of the recent literature and summarize the current knowledge and advances in the applications of RNAi technologies in the field of insect toxicology and insect pest management. Many recent studies have focused on identification and validation of the genes encoding insecticide target proteins, such as acetylcholinesterases, ion channels, Bacillus thuringiensis receptors, and other receptors in the nervous system. RNAi technologies have also been widely applied to reveal the role of genes encoding cytochrome P450 monooxygenases, carboxylesterases, and glutathione S-transferases in insecticide detoxification and resistance. More recently, studies have focused on understanding the mechanism of insecticide-mediated up-regulation of detoxification genes in insects. As RNAi has already shown great potentials for insect pest management, many recent studies have also focused on host-induced gene silencing, in which several RNAi-based transgenic plants have been developed and tested as proof of concept for insect pest management. These studies indicate that RNAi is a valuable tool to address various fundamental questions in insect toxicology and may soon become an effective strategy for insect pest management.

Co-silence of the coatomer β and v-ATPase A genes by siRNA feeding reduces larval survival rate and weight gain of cotton bollworm, Helicoverpa armigera

Coatomer and v-ATPase are two genes expressed in insect midgut epithelial cells and their knockdown is lethal to insect larvae. To investigate the RNAi response mediated by multiple siRNA duplexes, partial length cDNA of Helicoverpa armigera coatomer β and v-ATPase A was cloned and siRNA feeding-based RNAi was performed. Simultaneous ingestion of siRNAs specific to the H. armigera coatomer β and v-ATPase A led to co-silencing of the target genes and reduction in larval survival rate and weight gain. These results suggest that silencing two genes by feeding of multiple siRNAs is a good RNAi strategy.

RNA interference in Colorado potato beetle: steps toward development of dsRNA as a commercial insecticide

Colorado potato beetle (CPB) is a notorious pest on potatoes and has a remarkable ability to detoxify plant chemicals and develop resistance against insecticides. dsRNA targeting CPB genes could be expressed in potato plants to control this pest. However, previous attempts at introducing transgenic potato plants to control CPB were not highly successful. Recent studies showed that feeding dsRNA expressed in bacteria works very well to kill CPB. To realize the potential of RNAi to control this and other economically important pests, more efficient methods for production and delivery of dsRNA need to be developed. Extensive research to determine off-target and non-target effects, environmental fate and potential for resistance development is also essential.