RNA interference of ace1 and ace2 in Chilo suppressalis reveals their different contributions to motor ability and larval growth

JAK/STAT signaling regulated intestinal regeneration defends insect pests against pore-forming toxins produced by Bacillus thuringiensis

A variety of coordinated host-cell responses are activated as defense mechanisms against pore-forming toxins (PFTs). Bacillus thuringiensis (Bt) is a worldwide used biopesticide whose efficacy and precise application methods limits its use to replace synthetic pesticides in agricultural settings. Here, we analyzed the intestinal defense mechanisms of two lepidopteran insect pests after intoxication with sublethal dose of Bt PFTs to find out potential functional genes. We show that larval intestinal epithelium was initially damaged by the PFTs and that larval survival was observed after intestinal epithelium regeneration. Further analyses showed that the intestinal regeneration caused by Cry9A protein is regulated through c-Jun NH (2) terminal kinase (JNK) and Janus tyrosine kinase/signal transducer and activator of transcription (JAK/STAT) signaling pathways. JAK/STAT signaling regulates intestinal regeneration through proliferation and differentiation of intestinal stem cells to defend three different Bt proteins including Cry9A, Cry1F or Vip3A in both insect pests, Chilo suppressalis and Spodoptera frugiperda. Consequently, a nano-biopesticide was designed to improve pesticidal efficacy based on the combination of Stat double stranded RNA (dsRNA)-nanoparticles and Bt strain. This formulation controlled insect pests with better effect suggesting its potential use to reduce the use of synthetic pesticides in agricultural settings for pest control.

Cry9A and Vip3A protein-induced transcriptional changes correspond to their synergistic damage to the midgut of Chilo suppressalis

Cry and Vip3 proteins are both pore-forming toxins produced by Bacillus thuringiensis that show synergistic insecticidal activity against different insect pests. However, the synergistic effect of Cry and Vip3 proteins on the midgut in target insects is still unclear. In this study, faster and more serious damage was observed after treatment with both Cry9A and Vip3A proteins in the Chilo suppressalis midgut compared to single-protein treatment. Through RNA sequencing, midgut transcriptomic comparison was performed between dual- and single-protein treatments according to midgut injury. After 6 h, 609 differentially expressed genes were found with the combined Cry9A and Vip3A treatments, which was much more than that in the single treatment, corresponding to faster and more serious damage. These genes were mainly enriched in similar pathways, such as lipid metabolic, oxidation-reduction and carbohydrate metabolic process, peptide secretion and cell-cell adhesion; however, the number and expression level of differentially expressed genes are increased. For specific genes significantly regulated by induction of Cry9A and Vip3A, lipases, phospholipid scramblase, probable tape measure protein and arylsulfatase J were significantly downregulated after 6 h treatment. In addition, regular genes related to the activation and receptor binding of B. thuringiensis toxins were differentially regulated, such as ATP-binding cassette subfamily G member 1 and serine protease. Validation with RT-qPCR showed agreement with the sequencing results. Overall, our results support that stronger and faster midgut responses at the cellular and transcriptional levels are induced by the synergistic toxicity of Cry9A and Vip3A in C. suppressalis.

The cholinergic pathway transmits signals of neuropeptide F to regulate feeding of Ostrinia furnacalis larvae

BACKGROUND

Feeding is the basis of animal survival and reproduction. In insects, the neuropeptide F (NPF), a homologous polypeptide of NPY in vertebrates, plays an important role in regulation of feeding behavior. However, relatively little has been known about the molecular mechanism of feeding.

RESULTS

In this study, we show that the cholinergic pathway is very important in signaling transmission of NPF feeding regulation in Ostrinia furnacalis larvae, in which the choline acetyltransferase (ChAT), the vesicular acetylcholine transporter (vAChT) in presynaptic membrane and the nicotinic acetylcholine receptor (nAChR) in postsynaptic membrane are positively regulated by NPF, while the ace1 and ace2 encoding the acetylcholinesterase (AChE) are negatively regulated by NPF, leading to a balance of acetylcholine (ACh)-the excitatory transmitter. More, the cholinergic pathway further transmits signaling to the downstream pathways of the phosphoInositide-3 kinase (PI3K) and the cAMP responsive element binding protein (CREB), respectively.

CONCLUSION

The cholinergic transmission, positively regulated by NPF, is involved in feeding of O. furnacalis larvae via downstream PI3K and the CREB pathways, respectively. The deexcitation of cell cholinergic pathway or inhibition of PI3K and CREB lead to decreases of larval feeding amount. © 2023 Society of Chemical Industry.

Multiple acetylcholinesterases in Pardosa pseudoannulata brain worked collaboratively to provide protection from organophosphorus insecticides

Acetylcholinesterase (AChE) is an essential neurotransmitter hydrolase in nervous systems of animals and its number varies among species. So far, five AChEs have been identified in the natural enemy Pardosa pseudoannulata. Here we found that Ppace1, Ppace2 and Ppace5 were highly expressed in the spider brain, among which the mRNA level of Ppace5, but not Ppace1 and Ppace2, could be up-regulated by organophosphorus insecticides at their sublethal concentrations. In spider brain, the treatment by organophosphorus insecticides at the sublethal concentrations could increase total AChE activity, although high concentrations inhibited the activity. The activity that increased from the sublethal concentration pretreatment could compensate for the activity inhibition due to subsequent application of organophosphorus insecticides at lethal concentrations, and consequently reduce the mortality of spiders. PpAChE1 and PpAChE2 were highly sensitive to organophosphorus insecticides, and their activities would be strongly inhibited by the insecticides. In contrast, PpAChE5 displayed relative insensitivity towards organophosphorus insecticides, but with the highest catalytic efficiency for ACh. That meant the up-regulation of Ppace5 under insecticide exposure was important for maintaining AChE activity in spider brain, when PpAChE1 and PpAChE2 were inhibited by organophosphorus insecticides. The study demonstrated that multiple AChEs in the spider brain worked collaboratively, with part members for maintaining AChE activity and other members responding to organophosphorus inhibition, to provide protection from organophosphorus insecticides. In fields, high concentration insecticides are often applied when ineffective controls of insect pests occur due to relative-low concentration of insecticides in last round application. This application pattern of organophosphorus insecticides provides more chances for P. pseudoannulata to survive and controlling insect pests as a natural enemy.

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

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

Silencing a Myzus persicae Macrophage Inhibitory Factor by Plant-Mediated RNAi Induces Enhanced Aphid Mortality Coupled with Boosted RNAi Efficacy in Transgenic Potato Lines

Myzus persicae causes considerable losses to crops as a major pest. The damage is direct by feeding and also partly indirect because it vectors plant viruses. The currently available control strategies rely on unsafe and nonecofriendly chemical pesticide applications. Plant-mediated RNA interference (RNAi) has emerged as a powerful tool in crop protection from insect pests. Aphid salivary proteins are essential for phloem feeding and act as mediators of the complex interactions between aphids and their host plants. We documented the efficacy of dsRNA directed against macrophage inhibitory factor (MIF1) of M. persicae to induce aphid mortality and gene silencing through the generation of transgenic potato lines. A binary construct harbouring dsMIF1 driven by the CaMV35S promoter was introduced into the local potato variety 'AGB-white' by Agrobacterium-mediated transformation. PCR and Southern blotting validated the transgene presence and genomic integration in seven transgenic potato lines. An in vitro detached leaf assay revealed a significantly high aphid mortality of 65% in the transgenic potato line sDW-2, while the aphid mortality was 77% in the sDW-2 transgenic line during the in planta bioassay in comparison with 19% aphid mortality in the control nontransgenic potato line. A significantly high silencing effect was observed in the mRNA expression of MIF1, which was reduced to 21% in aphids fed on the transgenic potato line sDW-2. However, variable knockdown effects were found among six other transgenic potato lines, ranging from 30 to 62%. The study concluded that plant-mediated silencing of aphid RNA induces significant RNAi in M. persicae, along with enhanced aphid mortality.

Neurotoxic Zanthoxylum chalybeum root constituents invoke mosquito larval growth retardation through ecdysteroidogenic CYP450s transcriptional perturbations

Intracellular effects exerted by phytochemicals eliciting insect growth-retarding responses during vector control intervention remain largely underexplored. We studied the effects of Zanthoxylum chalybeum Engl. (Rutaceae) (ZCE) root derivatives against malaria (Anopheles gambiae) and arbovirus vector (Aedes aegypti) larvae to decipher possible molecular targets. We report dose-dependent biphasic effects on larval response, with transient exposure to ZCE and its bioactive fraction (ZCFr.5) inhibiting acetylcholinesterase (AChE) activity, inducing larval lethality and growth retardation at sublethal doses. Half-maximal lethal concentrations (LC₅₀) for ZCE against An. gambiae and Ae. aegypti larvae after 24-h exposure were 9.00 ppm and 12.26 ppm, respectively. The active fraction ZCFr.5 exerted LC₅₀ of 1.58 ppm and 3.21 ppm for An. gambiae and Ae. aegypti larvae, respectively. Inhibition of AChE was potentially linked to larval toxicity afforded by 2-tridecanone, palmitic acid (hexadecanoic acid), linoleic acid ((Z,Z)-9,12-octadecadienoic acid), sesamin, β-caryophyllene among other compounds identified in the bioactive fraction. In addition, the phenotypic larval retardation induced by ZCE root constituents was exerted through transcriptional modulation of ecdysteroidogenic CYP450 genes. Collectively, these findings provide an explorative avenue for developing potential mosquito control agents from Z. chalybeum root constituents.

Cloning and RNAi-mediated three lethal genes that can be potentially used for Chilo suppressalis (Lepidoptera: Crambidae) management

RNA interference (RNAi) has gained attention in recent years as a viable pest control strategy. Here, RNAi assays were performed to screen the potential functionality of genes in Chilo suppressalis, a serious pest of rice, and to determine their potential for developing a highly targeted molecular control approach. Potential homologs of NADH dehydrogenase (ND), glycerol 3-phosphate dehydrogenase (GPDH) and male specific lethal 3 (MSL3) were cloned from C. suppressalis, and their spatiotemporal gene expression evaluated. The expression of all three genes was higher in the pupal and adult stages than the larval stages and largely higher in the larval head compared to other tissues. Newly hatched larvae exhibited high mortalities and suppressed growth when fed bacteria producing double-stranded RNAs (dsRNAs) corresponding to the three target genes. This study provides insights into the function of ND, GPDH and MSL3 during C. suppressalis larval development and suggests that all may be candidate gene targets for C. suppressalis pest management.

Biomicroplastics versus conventional microplastics: An insight on the toxicity of these polymers in dragonfly larvae

The toxicological safety of products developed as alternative for conventional plastics (i.e., petroleum derivatives) inevitably demands conducting (eco)toxicological studies. Thus, the aim of the current study was to evaluate the biochemical toxicity of polyethylene microplastics (PE MPs) (representative of conventional MPs) and polylactic acid biomicroplastics (PLA BioMPs) in Aphylla williamsoni larvae used as experimental models. Animals subjected to short exposure to both pollutants (48 h), at environmentally relevant concentration (6 mg/L). At the end of the experiment, different toxicity biomarkers were evaluated. To assess the possible impact of pollutants on the nutritional status of the animals, the total protein, total soluble carbohydrate and triglyceride levels were determined. However, we did not observe differences between the groups, which suggests that PE MPs and PLA BioMPs did not affect the animals' energy metabolism, inducing them to a nutritional deficit. However, larvae exposed to PLA BioMPs have shown increased nitrite and lipid peroxidation levels, which supports the hypothesis that these pollutants increase oxidative stress processes in the animals evaluated, which can affect the animals' physiological homeostasis from different changes. In addition, the decrease in superoxide dismutase activity and of total thiols levels, in these same animals, is suggestive of the impact of PLA BioMPs on the antioxidant defenses, causing a REDOX imbalance, never before reported. On the other hand, decreased AChE activity was only observed in larvae exposed to PLA BioMPs, which demonstrates the anticholinergic activity of the tested polymers; the consequences of which include changes in different neurophysiological functions. Thus, the current study has helped improving the scientific knowledge about impacts caused by PLA BioMPs on freshwater ecosystems, as well as corroborated assertions about the risks posed by such biopolymers on these environments.

Carbon nanofibers are bioaccumulated in Aphylla williamsoni (Odonata) larvae and cause REDOX imbalance and changes of acetylcholinesterase activity

Carbon-based materials have been considered very promising for the technological industry due to their unique physical and chemical properties, namely: ability to reduce production costs and to improve the efficiency of several products. However, there is little information on what is the level of exposure that leads to adverse effects and what kind of effects is expected in aquatic biota. Thus, the aim of the present study was to evaluate the toxicity of carbon nanofibers (CNFs) in dragonfly larvae (Aphylla williamsoni) based on predictive oxidative-stress biomarkers, antioxidant activity reduction and neurotoxicity. After ephemeral models' exposure to CNFs (48 h; at 500 μg/L), data have shown that these pollutants did not change larvae's nutritional status given the concentration of total soluble carbohydrates, total proteins and triglycerides in them. However, the levels of both nitric oxide and substances reactive to thiobarbituric acid (lipid peroxidation indicators) have increased and the antioxidant activity based on total thiol levels and on 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity (%) has reduced, and it suggests REDOX imbalance induction by CNFs. In addition, larvae exposed to these pollutants showed significant acetylcholinesterase activity reduction in comparison to the control group. Thus, the present study has brought further knowledge about how carbon-based materials can affect benthic macroinvertebrates and emphasized their ecotoxicological potential in freshwater environments.

Toxicity of polystyrene nanoplastics in dragonfly larvae: An insight on how these pollutants can affect bentonic macroinvertebrates

Although nanoplastics (NPs) are known to be toxic to several groups of animals, the effects of such a toxicity on freshwater benthic macroinvertebrate communities remain unknown. Thus, the aim of the current study is to test the hypothesis that polystyrene nanoplastics (PS NPs) (34 μg/L - 48 h of exposure) lead to biochemical damage in Aphylla williamsoni larvae. Data have evidenced high bioaccumulation factor in the analyzed individuals; this finding indicates that, similar to sediments, water is also part of aquatic systems and favors PS NPs retention in dragonfly larvae. Despite the lack of evidence about the interference of these pollutants in the nutritional status of the analyzed animals, their bioaccumulation was associated with REDOX imbalance featured by concomitant increase in the number of evaluated oxidative stress biomarkers (nitric oxide and lipid peroxidation) and antioxidants (antioxidant activity against the DPPH radical and the superoxide dismutase enzyme). On the other hand, the reduced acetylcholinesterase activity observed in larvae exposed to PS NPs has suggested the neurotoxic effect of these pollutants, with potential impact on their nerve and neuromuscular functions. Therefore, the current study is pioneer in showing that PS NPs can affect the health of the investigated larvae, even at small concentrations, for short exposure-time; this outcome reinforces the ecotoxicological risk of these pollutants for freshwater benthic macroinvertebrates.

Assessment of the cytotoxic and mutagenic potential of dichlorvos (DDVP) using in silico classification model; a health hazard awareness in Nigeria

Dichlorvos (DDVP) has been abused in Nigeria for suicide attempts, topical applications to treat an ectoparasitic infestation, and indiscriminate use on farm produce. Exposure to this compound in subacute concentration can cause toxicity in different tissues by alteration of the cellular antioxidative defence mechanism. This analysis is aimed at the systematic profiling of DDVP to assess its cytotoxic and mutagenic potential for human vulnerability using an in silico classification model. DDVP was grouped into categories of analogue chemical compounds generated from inventories based on structural alerts that measure the biological effects on cell lines and animal models using the quantitative structure-activity relationship (QSAR) model. The cytotoxic and mutagenic potential of DDVP was assessed by analyzing target endpoints like skin sensitization, oral/inhalation toxicity, neurotoxicity and mutagenicity. DDVP shows moderate sensitization potential that can induce skin irritation during prolonged exposure because of the presence of dichlorovenyl side-chain that interacts with cellular proteins and causes degradation. 50% lethal dose (LD₅₀) of DDVP per body weight was determined to be 26.2 mg/kg in a rat model at 95% confidence range for acute oral toxicity, and 14.4 mmol/L was estimated as 50% lethal concentration (LC₅₀) in the atmosphere due to acute inhalation toxicity. DDVP can also inhibit acetylcholinesterase in the nervous system to produce nicotinic and muscarinic symptoms like nausea, vomiting, lacrimation, salivation, bradycardia, and respiratory failure may cause death. The widely used pesticide causes weak DNA methylation which can repress gene transcription on promoter sites. DDVP is volatile so it can cause oral and inhalation toxicity coupled with neurotoxicity during prolonged exposure. Serum cholinesterase blood tests should be encouraged in federal and state hospitals to investigate related health challenges as DDVP is still used in Nigeria.

Nanomaterial-wrapped dsCYP15C1, a potential RNAi-based strategy for pest control against Chilo suppressalis

BACKGROUND

Although the utility of double-stranded RNA (dsRNA)-mediated knockdown as an environmentally friendly pest management strategy has gained traction in recent years, its overall efficacy has been limited by poor stability and limited cellular uptake. Encapsulation of dsRNAs with various nanomaterials, however, has shown promise in overcoming these limitations. This study sought to investigate the biological efficacy of an oral dsRNA nanomaterial mixture targeting the CYP15C1 gene product in the economically important rice pest, Chilo suppressalis.

RESULTS

A putative CYP15C1 ortholog was cloned from C. suppressalis midguts. The transcript is downregulated in fifth-instar larvae and is most highly expressed in heads. RNA interference (RNAi)-mediated knockdown of CsCYP15C1 was associated with significantly increased mortality. More importantly, feeding a dsRNA-nanomaterial mixture significantly increased larval mortality compared with feeding dsRNA alone.

CONCLUSION

A critical role for CsCYP15C1 function in molting is supported by sequence similarity with known juvenile hormone epoxidases, its expression profile, and abnormal molting phenotypes associated with RNA-mediated knockdown. CsCYP15C1 is thus a prime target for controlling C. suppressalis. Furthermore, RNAi-mediated characterization of candidate gene function can be enhanced by incorporating an enveloping nanomaterial. © 2020 Society of Chemical Industry.

Involvement of Two Paralogous Methoprene-Tolerant Genes in the Regulation of Vitellogenin and Vitellogenin Receptor Expression in the Rice Stem Borer, Chilo suppressalis

Besides the function of preventing metamorphosis in insects, the juvenile hormone (JH) plays a role in female reproduction; however, the underlying mechanism is largely unknown. The methoprene-tolerant (Met) protein belongs to a family of basic helix-loop-helix–Per-Arnt-Sim (bHLH-PAS) transcription factors and functions as the JH intracellular receptor. In this study, two full length cDNAs encoding Met (CsMet1 and CsMet2) were isolated from the rice stem borer, Chilo suppressalis. Structural analysis revealed that both CsMet1 and CsMet2 exhibited typical bHLH, PAS-A, PAS-B, and PAC (PAS C terminal motif) domains. Comparative analysis of transcript level using reverse transcription-quantitative PCR (RT-qPCR) revealed that CsMet1 was predominant in almost all examined developmental stages and tissues. Treatment with methoprene in vivo induces the transcription of both CsMet1 and CsMet2. Notably, injection of dsCsMet1 and dsCsMet2 suppressed the expression levels of vitellogenin (CsVg) and Vg receptor (CsVgR). These findings revealed the potential JH signaling mechanism regulating C. suppressalis reproduction, and provided evidence that RNAi-mediated knockdown of Met holds great potential as a control strategy of C. suppressalis.

Comparison of efficacy of RNAi mediated by various nanoparticles in the rice striped stem borer (Chilo suppressalis)

RNA interference (RNAi) has proven to be a very promising prospect for insect pest control. However, low RNAi efficacy limits further development of this biotechnology for use on lepidopteran insects, including the rice striped stem borer (SSB) (Chilo suppressalis), one of the major destructive rice pests. In this work, the application of various nanoparticles (NPs) by which double-stranded RNA (dsRNA) could be encapsulated was evaluated as an alternative delivery strategy to potentially increase the bioactivity of dsRNA. Three NPs, chitosan, carbon quantum dot (CQD), and lipofectamine2000, complexed with dsRNA (to target the glyceraldehyde-3-phosphate dehydrogenase gene (G3PDH)) were tested to examine their use in controlling SSB. Relative mRNA expressions were quantified using qPCR to evaluate knockdown efficiency of NP-dsRNA treated larvae, and the correlated dsRNA-mediated SSB larval mortality was tested. Thereafter, the content dynamics of hemolymph dsRNA after ingesting different NP-dsRNA were monitored in vivo; the hemolymph dsRNA content was in ratios of 5.67, 9.43, and 1 with chitosan, CQD, and lipofectamine2000 induced samples, respectively. The results demonstrated that all three tested NPs led to efficient feeding delivery by improving both dsRNA stability and cellular uptake equally. Furthermore, there was a strong correlation (r= 0.9854) between the hemolymph dsRNA contents and the average RNAi depletions in the non-gut tissues of SSB. Overall, our results strongly suggest that due to its strong endosomal escaping ability, CQD was the most efficient carrier for inducing systemic RNAi, and thereby causing effective gene silencing and mortality in SSB.

Vaccination with Schistosoma mansoni Cholinesterases Reduces the Parasite Burden and Egg Viability in a Mouse Model of Schistosomiasis

Schistosomiasis is a neglected tropical disease caused by parasitic blood flukes of the genus Schistosoma, which kills 300,000 people every year in developing countries, and there is no vaccine. Recently, we have shown that cholinesterases (ChEs)-enzymes that regulate neurotransmission-from Schistosoma mansoni are expressed on the outer tegument surface and present in the excretory/secretory products of larval schistosomula and adult worms, and are essential for parasite survival in the definitive host, highlighting their utility as potential schistosomiasis vaccine targets. When treated in vitro with anti-schistosome cholinesterase (SmChE) IgG, both schistosomula and adult worms displayed significantly decreased ChE activity, which eventually resulted in parasite death. Vaccination with individual SmChEs, or a combination of all three SmChEs, significantly reduced worm burdens in two independent trials compared to controls. Average adult worm numbers and liver egg burdens were significantly decreased for all vaccinated mice across both trials, with values of 29-39% and 13-46%, respectively, except for those vaccinated with SmAChE1 in trial 1. Egg viability, as determined by egg hatching from liver homogenates, was significantly reduced in the groups vaccinated with the SmChE cocktail (40%) and SmAChE2 (46%). Furthermore, surviving worms from each vaccinated group were significantly stunted and depleted of glycogen stores, compared to controls. These results suggest that SmChEs could be incorporated into a vaccine against schistosomiasis to reduce the pathology and transmission of this debilitating disease.

Molecular characterization and functional analysis of the vitellogenin receptor in the rice stem borer, Chilo suppressalis

As a member of the low-density lipoprotein receptor (LDLR) superfamily, vitellogenin (Vg) receptor (VgR) is responsible for the uptake of Vg into developing oocytes and is a potential target for pest control. Here, a full-length VgR complementary DNA (named as CsVgR) was isolated and characterized in the rice stem borer, Chilo suppressalis. The composite CsVgR gene contained an open reading frame of 5,484 bp encoding a protein of 1,827 amino acid residues. Structural analysis revealed that CsVgR contained two ligand-binding domains (LBDs) with four Class A (LDLR_A ) repeats in LBD1 and seven in LBD2, which was structurally different from most non-Lepidopteran insect VgRs having five repeats in LBD1 and eight in LBD2. The developmental expression analysis showed that CsVgR messenger RNA expression was first detectable in 3-day-old pupae, sharply increased in newly emerged female adults, and reached a peak in 2-day-old female adults. Consistent with most other insects VgRs, CsVgR was exclusively expressed in the ovary. Notably, injection of dsCsVgR into late pupae resulted in fewer follicles in the ovarioles as well as reduced fecundity, suggesting a critical role of CsVgR in female reproduction. These results may contribute to the development of RNA interference-mediated disruption of reproduction as a control strategy of C. suppressalis.

Novel cholinesterase paralogs of Schistosoma mansoni have perceived roles in cholinergic signalling and drug detoxification and are essential for parasite survival

Cholinesterase (ChE) function in schistosomes is essential for orchestration of parasite neurotransmission but has been poorly defined with respect to the molecules responsible. Interrogation of the S. mansoni genome has revealed the presence of three ChE domain-containing genes (Smche)s, which we have shown to encode two functional acetylcholinesterases (AChE)s (Smache1 –smp_154600 and Smache2 –smp_136690) and a butyrylcholinesterase (BChE) (Smbche1 –smp_125350). Antibodies to recombinant forms of each SmChE localized the proteins to the tegument of adults and schistosomula and developmental expression profiling differed among the three molecules, suggestive of functions extending beyond traditional cholinergic signaling. For the first time in schistosomes, we identified ChE enzymatic activity in fluke excretory/secretory (ES) products and, using proteomic approaches, attributed this activity to the presence of SmAChE1 and SmBChE1. Parasite survival in vitro and in vivo was significantly impaired by silencing of each smche, either individually or in combination, attesting to the essential roles of these molecules. Lastly, in the first characterization study of a BChE from helminths, evidence is provided that SmBChE1 may act as a bio-scavenger of AChE inhibitors as the addition of recombinant SmBChE1 to parasite cultures mitigated the effect of the anti-schistosome AChE inhibitor 2,2- dichlorovinyl dimethyl phosphate—dichlorvos (DDVP), whereas smbche1-silenced parasites displayed increased sensitivity to DDVP.

Cholinesterases—aceytlcholinesterases (AChE)s and butyrylcholinesterases (BChE)s—are multi-functional enzymes that play a pivotal role in the nervous system of parasites by regulating neurotransmission through acetylcholine hydrolysis. Herein, we provide a detailed characterization of schistosome cholinesterases using molecular, enzymatic and gene-silencing approaches and show evidence for these molecules having roles in addition to their neuronal function. Further, we demonstrate the importance of these proteins to parasite development and survival through gene knockdown experiments in laboratory animals, providing evidence for the use of these proteins in the development of novel intervention strategies against schistosomiasis.

Molecular characterization of glutamate-gated chloride channel and its possible roles in development and abamectin susceptibility in the rice stem borer, Chilo suppressalis

Glutamate-gated chloride channels (GluCls) mediate fast inhibitory neurotransmission in invertebrate nervous systems, and are of considerable interest in insecticide discovery. The full length cDNA encoding CsGluCl was cloned from the rice stem borer Chilo suppressalis (Walker). Multiple cDNA sequence alignment revealed three variants of CsGluCl generated by alternative splicing of exon 3 and exon 9. While all the transcripts were predominantly expressed in both nerve cord and brain, the expression patterns of these three variants differed among other tissues and developmental stages. Specifically, the expression level of CsGluCl C in cuticle was similar to that in nerve cord and brain, and was the predominant variant in late pupae and early adult stages. Both injection and oral delivery of dsGluCl significantly reduced the mRNA level of CsGluCl. Increased susceptibility to abamectin and reduced larvae growth and pupation rate were observed in dsGluCl-treated larvae. Thus, our results provide the evidence that in addition to act as the target of abamectin, GluCls also play important physiological roles in the development of insects.

Potential of RNA interference in the study and management of the whitefly, Bemisia tabaci

Whiteflies cause considerable losses to crops, directly by feeding, and indirectly by transmission of viruses. The current control methods consist of a combination of different control tactics, mainly still relying on unsafe and non-ecofriendly chemical control. RNA interference (RNAi) is a post-transcriptional gene-silencing strategy in which double-stranded RNA (dsRNA), corresponding specifically to a target gene, is introduced in a target organism. Research on RNAi in the previous decade has shown its success as a potential insect control strategy, which can be highly species-specific and environment friendly. In whiteflies, the success of dsRNA delivery through the oral route opened possibilities for its management through plant-mediated RNAi. To date, several genes have been targeted in whiteflies through RNAi and these assays demonstrated its potential to manage whiteflies at lab level. However, further research and investments are needed to move toward an application at field level. In this review, for the first time, we collected the literature on genes targeted for silencing via RNAi in whiteflies and discuss the potential of RNAi in whitefly pest control. We also discuss likely delivery methods, including transgenic in planta delivery and symbiont-mediated delivery, and its potential for studying and interfering with insecticide resistance mechanisms and virus transmission by whiteflies.

Knockdown of the GABA receptor RDL genes decreases abamectin susceptibility in the rice stem borer, Chilo suppressalis

The γ-aminobutyric acid (GABA) receptor is a primary neurotransmitter receptor in both vertebrate and invertebrate nervous systems. Multiple RDL subunits have been found in insects including the rice stem borer, Chilo suppressalis, however, comparative characterization of duplicated RDL genes in insects is still limited. In this study, comparison of the genomic sequences and the cDNA sequences revealed that both CsRDL1 and CsRDL2 consisted of 10 exons and 9 introns, and their exon-intron boundaries occur in the same position with respect to the coding sequences. Expression profiling showed that both CsRDL1 and CsRDL2 were predominantly expressed in nervous system, and had low expression levels in the gut and integument. The transcript level of CsRDL2 dramatically increased from the prepupae to late pupae and were much higher than that of CsRDL1 in adult stages. Notably, dietary ingestion of dsRDL1 and dsRDL2 significantly decreased the larval susceptibility to abamectin. These results suggest that CsRDL1 and CsRDL2 might play both physiological roles in development and toxicological roles in action of abamectin in C. suppressalis.

Molecular Characterization and Expression Analysis of Two Acetylcholinesterase Genes From the Small White Butterfly Pieris rapae (Lepidoptera: Pieridae)

Acetylcholinesterases (AChEs) are essential for the hydrolysis of the neurotransmitter acetylcholine and play crucial roles in the termination of neurotransmission. AChEs are encoded by the ace genes. However, the ace genes from the small white butterfly, Pieris rapae (L.) (Lepidoptera: Pieridae), remained uncharacterized. In this study, two aces (Prace1 and Prace2) were identified from P. rapae. Prace1 encoded a PrAChE1 protein consisting of 694 amino acid residues, and Prace2 encoded the 638-amino-acid PrAChE2. The two identified PrAChEs both had features typical of AChEs, including the catalytic triad, choline-binding sites, an oxyanion hole, an acyl pocket, a peripheral anionic subsite, an FGESAG motif and 14 conserved aromatic amino acids. Phylogenetic analysis showed that Prace1 and Prace2 were clustered into two distinct groups: ace1 and ace2, respectively. The two Praces were distributed on different genomic scaffolds: Prace1 on scaffold 156 and Prace2 on scaffold 430. Additionally, Prace1 consisted of three exons and two introns, whereas Prace2 consisted of six exons and five introns. One amino acid mutation (Gly324Ala) in PrAChE1 and two (Ser291Gly and Ser431Phe) in PrAChE2 were consistent with mutations in other insect AChEs that are associated with insecticide insensitivity. Both Prace1 and Prace2 were highly expressed at the fifth-instar larval stage and in the larval head, and the transcriptional levels of Prace1 were significantly higher than those of Prace2 in all of the tested life stages and tissues. This is the first report characterizing two ace genes in P. rapae. The results pave the way for functional study of these genes.

Sublethal effects of chlorantraniliprole on juvenile hormone levels and mRNA expression of JHAMT and FPPS genes in the rice stem borer, Chilo suppressalis

BACKGROUND

Juvenile hormone (JH) regulates the development and reproduction of insects. The sublethal effects of chlorantraniliprole on JH levels and mRNA expression of JH acid methyltransferase gene (CsJHAMT) and farnesyl diphosphate synthase genes (CsFPPS1 and CsFPPS2) in Chilo suppressalis (Walker) were investigated.

RESULTS

Exposure of sublethal concentrations of chlorantraniliprole (LC₁₀ and LC₃₀ ) to the third instar larvae of C. suppressalis significantly increased the JH levels in all developmental stages investigated including larvae 72 h after treatment, the first, third and fifth day of female pupae, as well as newly emerged, 12-h-old and 24-h-old female adults. A general trend of increased mRNA expression levels of CsJHAMT, CsFPPS1and CsFPPS2 was also observed in LC₁₀ and LC₃₀ treatment groups. Notably, the mRNA expression level of CsJHAMT significantly increased by 7.46-fold in the larvae 72 h after LC₃₀ treatment. A significant increase of the mRNA expression levels of CsFPPS2 was also observed in the fifth day female pupae of LC₁₀ and LC₃₀ treatment groups (2.60-fold and 2.62-fold, respectively) as well as in 12-h-old female adults of the LC₃₀ treatment group (3.45-fold).

CONCLUSION

Sublethal concentrations of chlorantraniliprole might upregulate the expression of JH biosynthesis genes and in turn result in an increase of JH level in C. suppressalis. © 2017 Society of Chemical Industry.

The Role of p38 MAPK, JNK, and ERK in Antibacterial Responses of Chilo suppressalis (Lepidoptera: Crambidae)

The mitogen-activated protein kinases (MAPKs) are conserved signal transduction pathways and broadly responsible for bacterial infection from yeast to mammals, and virus, fungi, and bacteria, specifically Bacillus thuringiensis, to insects. But little is known about the MAPK pathways in antibacterial responses in Chilo suppressalis (Walker), an important lepidopteran pest of rice. In this study, we used the bacteria of Bacillus thuringiensis, Escherichia coli, and Staphyloccocus aureus to infect C. suppressalis larvae, and the responses of MAPK pathways were analyzed. The results showed that E. coli infection induced the up-regulated expression of Csp38 and CsERK1 at 24 h postinfection (pi). Meanwhile, injection of B. thuringiensis and S. aureus resulted in strong activation of CsJNK phosphorylation at 3 h pi. These results suggest that MAPK signaling pathways play important functional roles in antibacterial responses in C. suppressalis larvae.

Characterization of the Fifth Putative Acetylcholinesterase in the Wolf Spider, Pardosa pseudoannulata

Background: Acetylcholinesterase (AChE) is an important neurotransmitter hydrolase in invertebrate and vertebrate nervous systems. The number of AChEs is various among invertebrate species, with different functions including the 'classical' role in terminating synaptic transmission and other 'non-classical' roles. Methods: Using rapid amplification of cDNA ends (RACE) technology, a new putative AChE-encoding gene was cloned from Pardosa pseudoannulata, an important predatory natural enemy. Sequence analysis and in vitro expression were employed to determine the structural features and biochemical properties of this putative AChE. Results: The cloned AChE contained the most conserved motifs of AChEs family and was clearly clustered with Arachnida AChEs. Determination of biochemical properties revealed that the recombinant enzyme had the obvious preference for the substrate ATC (acetylthiocholine iodide) versus BTC (butyrylthiocholine iodide). The AChE was highly sensitive to AChE-specific inhibitor BW284C51, but not butyrylcholinesterase-specific inhibitor tetraisopropyl pyrophosphoramide (ISO-OMPA). Based on these results, we concluded that a new AChE was identified from P. pseudoannulata and denoted as PpAChE5. Conclusion: Here we report the identification of a new AChE from P. pseudoannulata and increased the AChE number to five in this species. Although PpAChE5 had the biggest Vmax value among five identified AChEs, it showed relatively low affinity with ATC. Similar sensitivity to test insecticides indicated that this AChE might serve as the target for both organophosphorus and carbamate insecticides.

Two Bombyx mori acetylcholinesterase genes influence motor control and development in different ways

Among its other biological roles, acetylcholinesterase (AChE, EC 3.1.1.7), encoded by two ace in most insects, catalyses the breakdown of acetylcholine, thereby terminating synaptic transmission. ace1 encodes the synaptic enzyme and ace2 has other essential actions in many insect species, such as Chilo suppressalis and Plutella xylostella. The silkworm, Bombyx mori, has been domesticated for more than two thousand years and its aces have no history of pesticide exposure. Here, we investigated the functional differences between two ace genes, BmAce1 and BmAce2, in the silkworm. qPCR analysis indicated that BmAce1 is highly expressed in muscle and BmAce2 is more ubiquitously expressed among tissues and enriched in the head. Both genes were separately suppressed using chemically synthesized siRNAs. The mRNA abundance of the two ace genes was significantly reduced to about 13% - 75% of the control levels after siRNA injection. The AChE activities were decreased to 32% to 85% of control levels. Silencing BmAce2 resulted in about 26% mortality, faster and higher than the 20% in the siBmAce1-treated group. Silencing BmAce1 impacted motor control and development to a greater extent than silencing BmAce2, although both treatment groups suffered motor disability, slowed development and reduced cocoons. Both genes have essential, differing biological significance.

Knockdown of the MAPK p38 pathway increases the susceptibility of Chilo suppressalis larvae to Bacillus thuringiensis Cry1Ca toxin

The bacterium Bacillus thuringiensis (Bt) produces a wide range of toxins that are effective against a number of insect pests. Identifying the mechanisms responsible for resistance to Bt toxin will improve both our ability to control important insect pests and our understanding of bacterial toxicology. In this study, we investigated the role of MAPK pathways in resistance against Cry1Ca toxin in Chilo suppressalis, an important lepidopteran pest of rice crops. We first cloned the full-length of C. suppressalis mitogen-activated protein kinase (MAPK) p38, ERK1, and ERK2, and a partial sequence of JNK (hereafter Csp38, CsERK1, CsERK2 and CsJNK). We could then measure the up-regulation of these MAPK genes in larvae at different times after ingestion of Cry1Ca toxin. Using RNA interference to knockdown Csp38, CsJNK, CsERK1 and CsERK2 showed that only knockdown of Csp38 significantly increased the mortality of larvae to Cry1Ca toxin ingested in either an artificial diet, or after feeding on transgenic rice expressed Cry1Ca. These results suggest that MAPK p38 is responsible for the resistance of C. suppressalis larvae to Bt Cry1Ca toxin.

Cloning, expression, and functional analysis of two acetylcholinesterase genes in Spodoptera litura (Lepidoptera: Noctuidae)

Two acetylcholinesterase genes (SlAce1 and SlAce2) were cloned from Spodoptera litura, which is an important pest that causes widespread economic damage to vegetables and ornamental plants. We analyzed their expression patterns and compared their biological functions by using RNA interference. Our results showed that SlAce1 and SlAce2 cDNA contains 2085bp and 1917bp nucleotides and encoding proteins of 694 and 638 amino acid residues, respectively. Phylogenic analysis indicated that the lineage of SlAce genes and SlAce1 was completely different from SlAce2. Although both genes were expressed in all developmental stages and majorly in the brain. The expression levels of the both genes were suppressed by inserting their related dsRNA in the 6th instar larvae, which led to 47.3% (SlAce1) and 37.9% (SlAce2) mortality. Interestingly, the suppression of the SlAce2 transcripts also led to significant reductions in the fecundity, hatching, and offspring in the parental generation of S. litura. It is concluded that SlAce2 is responsible for the hydrolysis of acetylcholine and also plays role in female breeding, embryo progress, and the development of progeny. Considerable larval mortality was observed after both AChE genes (i.e. Ace1 and Ace2) were silenced in S. litura confirms its insecticidal effectiveness, which provided a molecular basis in biological pest control approach.

MOLECULAR CHARACTERIZATION OF TWO ACETYLCHOLINESTERASE GENES FROM THE RICE LEAFFOLDER, Cnaphalocrocis medinalis (LEPIDOPTERA: PYRALIDAE)

In this study, two full-length cDNA sequences (Cmace1 and Cmace2) encoding putative acetylcholinesterases (AChEs) were cloned and characterized from the rice leaffolder, Cnaphalocrocis medinalis, an important lepidopteran rice pest in Asia. Cmace1 encodes a CmAChE1 consisting of 689 amino acid residues, while Cmace2 encodes a 639 amino acids CmAChE2. The two CmAChEs both have N-terminal signal peptides and conserved motifs including the catalytic triad, choline-binding sites, oxianion hole, acyl pocket, peripheral anionic subsite, and the characteristic FGESAG motif and conserved 14 aromatic amino acids. Phylogenetic analysis showed that Cmace1 and Cmace2 are clustered into distinct clusters that are completely diverged from each other. Reverse-transcription quantitative PCR analysis revealed that Cmace1 and Cmace2 were predominately expressed in the larval brain and at the fifth-instar larvae stage, and the transcription levels of Cmace1 were significantly higher than those of Cmace2 in all the tested samples. Recombinant CmAChE1 and CmAChE2 were heterologously expressed in baculovirus system. Using acetylthiocholine iodide (ATChI) as substrate, the Michaelis constant (K_m ) values of rCmAChE1 and rCmAChE2 were 39.81 ± 6.49 and 68.29 ± 6.72 μmol/l, respectively; and the maximum velocity (V_max ) values of the two rCmAChEs were 0.60 ± 0.02 and 0.31 ± 0.06 μmol/min/mg protein, respectively. Inhibition assay indicated that rCmAChE1 was more sensitive to the organophosphate insecticides chlorpyrifos and triazophos than rCmAChE2. This study is the first report of molecular cloning and biochemical characterization of two acetylcholinesterase genes/enzymes in C. medinalis.

Genome-wide analysis of chitinase genes and their varied functions in larval moult, pupation and eclosion in the rice striped stem borer, Chilo suppressalis

Some insect chitinases are required to degrade chitin and ensure successful metamorphosis. Although chitinase genes have been well characterized in several model insects, no reports exist for the rice striped stem borer, Chilo suppressalis, a highly destructive pest that causes huge yield losses in rice production. Here, we conducted a genome-level analysis of chitinase genes in C. suppressalis. After amplification of full-length transcripts with rapid amplification of cDNA ends, we identified 12 chitinase genes in C. suppressalis. All these genes had the conserved domains and motifs of glycoside hydrolase family 18 and grouped phylogenetically into five subgroups. C. suppressalis chitinase 1 (CsCht1) was highly expressed in late pupae, whereas CsCht3 was abundant in early pupae. Both CsCht2 and CsCht4 were highly expressed in larvae. CsCht2 was abundant specifically in the third-instar larvae and CsCht4 showed periodic high expression in 2- to 5-day-old larvae in each instar. Tissue specific expression analysis indicated that CsCht1 and CsCht3 were highly expressed in epidermis whereas CsCht2 and CsCht4 were specifically abundant in the midgut. Knockdown of CsCht1 resulted in adults with curled wings, indicating that CsCht1 might have an important role in wing expansion. Silencing of CsCht2 or CsCht4 arrested moulting, suggesting essential roles in larval development. When the expression of CsCht3 was interfered, defects in pupation occurred. Overall, we provide here the first catalogue of chitinase genes in the rice striped stem borer and have elucidated the functions of four chitinases in metamorphosis.

The effect of silencing 20E biosynthesis relative genes by feeding bacterially expressed dsRNA on the larval development of Chilo suppressalis

RNA interference (RNAi) is a robust tool to study gene functions as well as potential for insect pest control. Finding suitable target genes is the key step in the development of an efficient RNAi-mediated pest control technique. Based on the transcriptome of Chilo suppressalis, 24 unigenes which putatively associated with insect hormone biosynthesis were identified. Amongst these, four genes involved in ecdysteroidogenesis i.e., ptth, torso, spook and nm-g were evaluated as candidate targets for function study. The partial cDNA of these four genes were cloned and their bacterially expressed dsRNA were fed to the insects. Results revealed a significant reduction in mRNA abundance of target genes after 3 days. Furthermore, knocked down of these four genes resulted in abnormal phenotypes and high larval mortality. After 15 days, the survival rates of insects in dsspook, dsptth, dstorso, and dsnm-g groups were significantly reduced by 32%, 38%, 56%, and 67% respectively, compared with control. Moreover, about 80% of surviving larvae showed retarded development in dsRNA-treated groups. These results suggest that oral ingestion of bacterially expressed dsRNA in C. suppressalis could silence ptth, torso, spook and nm-g. Oral delivery of bacterially expressed dsRNA provides a simple and potential management scheme against C. suppressalis.

Silencing of CYP6 and APN Genes Affects the Growth and Development of Rice Yellow Stem Borer, Scirpophaga incertulas

RNAi is a powerful tool to target the insect genes involved in host-pest interactions. Key insect genes are the choice for silencing to achieve pest derived resistance where resistance genes are not available in gene pool of host plant. In this study, an attempt was made to determine the effect of dsRNA designed from two genes Cytochrome P450 derivative (CYP6) and Aminopeptidase N (APN) of rice yellow stem borer (YSB) on growth and development of insect. The bioassays involved injection of chemically synthesized 5' FAM labeled 21-nt dsRNA into rice cut stems and allowing the larvae to feed on these stems which resulted in increased mortality and observed growth and development changes in larval length and weight compared with its untreated control at 12-15 days after treatment. These results were further supported by observing the reduction in transcripts expression of these genes in treated larvae. Fluorescence detection in treated larvae also proved that dsRNA was readily taken by larvae when fed on dsRNA treated stems. These results from the present study clearly show that YSB larvae fed on dsRNA designed from Cytochrome P450 and Aminopeptidase N has detrimental effect on larval growth and development. These genes can be deployed to develop YSB resistance in rice using RNAi approach.

De novo assembly and characterization of central nervous system transcriptome reveals neurotransmitter signaling systems in the rice striped stem borer, Chilo suppressalis

Background

Neurotransmitter signaling systems play crucial roles in multiple physiological and behavioral processes in insects. Genome wide analyses of de novo transcriptome sequencing and gene specific expression profiling provide rich resources for studying neurotransmitter signaling pathways. The rice striped stem borer, Chilo suppressalis is a destructive rice pest in China and other Asian countries. The characterization of genes involved in neurotransmitter biosynthesis and transport could identify potential targets for disruption of the neurochemical communication and for crop protection.

Results

Here we report de novo sequencing of the C. suppressalis central nervous system transcriptome, identification and expression profiles of genes putatively involved in neurotransmitter biosynthesis, packaging, and recycling/degradation. A total of 54,411 unigenes were obtained from the transcriptome analysis. Among these unigenes, we have identified 32 unigenes (31 are full length genes), which encode 21 enzymes and 11 transporters putatively associated with biogenic aminergic signaling, acetylcholinergic signaling, glutamatergic signaling and GABAergic signaling. RT-PCR and qRT-PCR results indicated that 12 enzymes were highly expressed in the central nervous system and all the transporters were expressed at significantly high levels in the central nervous system. In addition, the transcript abundances of enzymes and transporters in the central nervous system were validated by qRT-PCR. The high expression levels of these genes suggest their important roles in the central nervous system.

Conclusions

Our study identified genes potentially involved in neurotransmitter biosynthesis and transport in C. suppressalis and these genes could serve as targets to interfere with neurotransmitter production. This study presents an opportunity for the development of specific and environmentally safe insecticides for pest control.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1742-7) contains supplementary material, which is available to authorized users.

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.

Gene silencing of two acetylcholinesterases reveals their cholinergic and non-cholinergic functions in Rhopalosiphum padi and Sitobion avenae

BACKGROUD

The function of acetylcholinesterase (AChE) is to terminate synaptic transmission by hydrolysing the neurotransmitter acetylcholine (ACh) in the synaptic cleft, and thus it is an effective target for organophosphate (OP) and carbamate (CB) insecticides.

RESULTS

The transcript levels of the four Ace genes were dramatically suppressed by injection of their respective dsRNA in Rhopalosiphum padi and Sitobion avenae. However, the AChE activity changes in the Ace1 knockdown aphids were consistent with the significant transcript level changes of Ace1 genes in these aphids, but not for Ace2. Bioassay results indicated that the suppression of RpAce1 increased its susceptibilities to pirimicarb and malathion, and SaAce1 silencing also increased susceptibility to pirimicarb in S. avenae, whereas the knockdowns of RpAce2 and SaAce2 had a slight effect on their susceptibilities. The knockdown of Ace1 genes also caused significant reductions in fecundity in the aphids of their parental generation.

CONCLUSIONS

These results suggest that AChE1 is a predominant cholinergic enzyme and is the target of anticholinesterase insecticides in both R. padi and S. avenae. It also plays a non-cholinergic role in fecundity of these aphids. AChE2 may also be important for the toxicological function, although its importance appeared to be lower than that of AChE1.

Testing insecticidal activity of novel chemically synthesized siRNA against Plutella xylostella under laboratory and field conditions

BACKGROUND

Over the last 60 years, synthetic chemical pesticides have served as a main tactic in the field of crop protection, but their availability is now declining as a result of the development of insect resistance. Therefore, alternative pest management agents are needed. However, the demonstration of RNAi gene silencing in insects and its successful usage in disrupting the expression of vital genes opened a door to the development of a variety of novel, environmentally sound approaches for insect pest management.

METHODOLOGY/PRINCIPAL FINDINGS

Six small interfering RNAs (siRNAs) were chemically synthesized and modified according to the cDNA sequence of P. xylostella acetylcholine esterase genes AChE1 and AChE2. All of them were formulated and used in insecticide activity screening against P. xylostella. Bioassay data suggested that Si-ace1_003 and Si-ace2_001 at a concentration of 3 µg cm(-2) displayed the best insecticidal activity with 73.7% and 89.0%, mortality, respectively. Additional bioassays were used to obtain the acute lethal concentrations of LC50 and LC90 for Si-ace2_001, which were 53.66 µg/ml and 759.71 µg/ml, respectively. Quantitative Real-time PCR was used to confirm silencing and detected that the transcript levels of P. xylostella AChE2 (PxAChE2) were reduced by 5.7-fold compared to the control group. Consequently, AChE activity was also reduced by 1.7-fold. Finally, effects of the siRNAs on treated plants of Brassica oleracea and Brassica alboglabra were investigated with different siRNA doses. Our results showed that Si-ace2_001 had no negative effects on plant morphology, color and growth of vein under our experimental conditions.

CONCLUSIONS

The most important finding of this study is the discovery that chemically synthesized and modified siRNA corresponding to P. xylostella AChE genes cause significant mortality of the insect both under laboratory and field conditions, which provides a novel strategy to control P. xylostella and to develop bio-pesticides based on the RNA interference technology.

Advances in the use of the RNA interference technique in Hemiptera

RNA interference (RNAi) suppresses the expression of target genes by post-transcriptional regulation. Because double-stranded RNA (dsRNA) mediated gene silencing is a conserved mechanism in many eukaryotes, RNAi has become a valuable tool for unveiling gene function in many model insects. Recent research has also shown that RNAi can also be effective in the downregulation of target genes in Hemiptera. In this review, we discuss the use of the RNAi technique in gene functional analysis in hemipterans, highlighting the methods of dsRNA uptake by these insects and discuss the knock-down efficiency of these techniques. Although the RNAi technique has disadvantages, our primary goal here is to determine whether it can be exploited further in the discovery of new gene functions, and as a pest control strategy, in some important Hemipteran pests.

Characterization of a β-adrenergic-like octopamine receptor from the rice stem borer (Chilo suppressalis)

Octopamine, the invertebrate counterpart of adrenaline and noradrenaline, plays a key role in regulation of many physiological and behavioral processes in insects. It modulates these functions through binding to specific octopamine receptors, which are typical rhodopsin-like G-protein coupled receptors. A cDNA encoding a seven-transmembrane receptor was cloned from the nerve cord of the rice stem borer, Chilo suppressalis, viz. CsOA2B2, which shares high sequence similarity to CG6989, a Drosophila β-adrenergic-like octopamine receptor (DmOctβ2R). We generated an HEK-293 cell line that stably expresses CsOA2B2 in order to examine the functional and pharmacological properties of this receptor. Activation of CsOA2B2 by octopamine increased the production of cAMP in a dose-dependent manner (EC(50)=2.33 nmol l(-1)), with a maximum response at 100 nmol l(-1). Tyramine also activated the receptor but with much less potency than octopamine. Dopamine and serotonin had marginal effects on cAMP production. Using a series of known agonists and antagonists for octopamine receptors, we observed a rather unique pharmacological profile for CsOA2B2 through measurements of cAMP. The rank order of potency of the agonists was naphazoline > clonidine. The activated effect of octopamine is abolished by co-incubation with phentolamine, mianserin or chlorpromazine. Using in vivo pharmacology, CsOA2B2 antagonists mianserin and phentolamine impaired the motor ability of individual rice stem borers. The results of the present study are important for a better functional understanding of this receptor as well as for practical applications in the development of environmentally sustainable pesticides.

Cholinergic and non-cholinergic functions of two acetylcholinesterase genes revealed by gene-silencing in Tribolium castaneum

We compared biological functions of two acetylcholinesterase genes (TcAce1 and TcAce2) in Tribolium castaneum, a globally distributed major pest of stored grain products and an emerging model organism, by using RNA interference. Although both genes expressed at all developmental stages and mainly in the brain, the transcript level of TcAce1 was 1.2- to 8.7-fold higher than that of TcAce2, depending on developmental stages. Silencing TcAce1 in 20-day larvae led to 100% mortality within two weeks after eclosion and increased larval susceptibilities to anticholinesterase insecticides. In contrast, silencing TcAce2 did not show insect mortality and significantly affect insecticide susceptibility, but delayed insect development and reduced female egg-laying and egg hatching. These results demonstrate for the first time that TcAce1 plays a major role in cholinergic functions and is the target of anticholinesterase insecticides, whereas TcAce2 plays an important, non-cholinergic role in female reproduction, embryo development, and growth of offspring.

RNA interference of two acetylcholinesterase genes in Plutella xylostella reveals their different functions

Acetylcholinesterase (AChE, EC 3.1.1.7) is an important enzyme with a typical function of degrading the neurotransmitter acetylcholine. Although two ace genes were reported in Plutella xylostella, their function differences remain largely unknown. The chemically synthesized siRNAs (si-Pxace1 and si-Pxace2) were injected into the second instar larvae to knock down Pxace1 and Pxace2, either respectively or simultaneously. The mRNA abundance of Pxace1 and Pxace2 was significantly reduced to 7-33.5% of the control levels at 72 h after siRNA injection. The AChE activities were significantly decreased at 96 h after treatment. Silencing of Pxace1 or Pxace2 resulted in mortality of 33.9 and 22.9%, respectively. The survivors in siRNA-treated groups had apparent growth inhibition such as reduction in larvae weights and lengths, malformation and motor retardation. Knockdown of Pxace1 apparently affected more on larvae growth than that of Pxace2, suggesting that Pxace1 had more important roles than Pxace2. Both Pxace1 and Pxace2 genes might have atypical functions in regulating larvae growth and motor ability.