Regulation of GSTu1-mediated insecticide resistance in Plutella xylostella by miRNA and lncRNA

Chlorantraniliprole Resistance in Spodoptera frugiperda: Resistance Monitoring, Resistance Risk, and Resistance Mechanisms

Spodoptera frugiperda is a significant global pest, and chlorantraniliprole (CAP) is extensively used in China for its control. Understanding CAP resistance in S. frugiperda is crucial for effective management of this pest. Field populations exhibited varying degrees of resistance to CAP (RR = 1.74-5.60-fold). After 10 generations of selection, the CAP-resistant strain developed over 10-fold resistance, with a realized heritability (h2) of 0.10. Genetic analysis reveals inheritance patterns as autosomal, incomplete recessive, and monofactorial. The CAP-resistant strain showed limited cross-resistance to lufenuron and tetrachlorantraniliprole, negative cross-resistance to spinetoram, and no observed cross-resistance to other insecticides. Biochemical analysis suggested that P450-mediated detoxification is the primary resistance mechanism, with 26 genes overexpressed in the CAP-resistant strain. Additionally, the knockdown of CYP4L13, CYP6B39, CYP6B40, and CYP4G74 significantly increased the sensitivity of the resistant larvae to CAP. These findings highlight the resistance risk of CAP in S. frugiperda and emphasize the crucial role of P450 enzymes in resistance.

Insights into the role of non-coding RNAs in the development of insecticide resistance in insects

Pest control heavily relies on chemical pesticides has been going on for decades. However, the indiscriminate use of chemical pesticides often results in the development of resistance in pests. Almost all pests have developed some degree of resistance to pesticides. Research showed that the mechanisms of insecticide resistance in insects encompass metabolic resistance, behavioral resistance, penetration resistance and target-site resistance. Research on the these mechanisms has been mainly focused on the cis-regulatory or trans-regulatory for the insecticide resistance-related genes, with less attention paid to non-coding RNAs (ncRNAs), such as microRNA (miRNA), long non-coding RNA (lncRNA), and circular RNA (circRNA). There has been increased studies focus on understanding how these ncRNAs are involved in post-transcriptional regulation of insecticide resistance-related genes. Besides, the formatted endogenous RNA (ceRNA) regulatory networks (lncRNA/circRNA-miRNA-mRNA) has been identified as a key player in governing insect resistance formation. This review delves into the functions and underlying mechanisms of miRNA, lncRNA, and circRNA in regulating insect resistance. ncRNAs orchestrate insect resistance by modulating the expression of detoxification enzyme genes, insecticide target genes, as well as receptor genes, effectively regulating both target-site, metabolic and penetration resistance in insects. It also explores the regulatory mechanisms of ceRNA networks in the development of resistance. By enhancing our understanding of the mechanisms of ncRNAs in insecticide resistance, it will not only provide valuable insights into the new mechanisms of insecticide resistance but also help to enrich new directions in ncRNAs gene regulation research.

New and emerging mechanisms of insecticide resistance

The continuous use of insecticides over the last eight decades has led to the development of resistance to these insecticides. Research in the last few decades showed that the mechanisms underlying resistance are diverse but can generally be classified under several modes of resistance such as target-site resistance, metabolic resistance, and penetration resistance. In this review, we highlight new discoveries in insecticide resistance research made over the past few years, including an emerging new mode of resistance, sequestration resistance, where the overexpression of olfactory proteins binds and sequesters insecticides in resistant strains, as well as recent research on how posttranscriptional regulation can impact resistance. Future research will determine the generality of these emerging mechanisms across insect species.

Identification and Functional Characterization of an Omega-Class Glutathione Gene PcGSTO1 Associated with Cyetpyrafen Resistance in Panonychus citri (McGregor)

Cyetpyrafen is a recently developed acaricide. The citrus red mite, Panonychus citri (McGregor), has developed significant resistance to cyetpyrafen. However, the molecular mechanism underlying the cyetpyrafen resistance in P. citri remains unclear. Glutathione S-transferases (GSTs) play a critical role in arthropod pesticide resistance. This study showed that GSTs were potentially related to the resistance of P. citri to cyetpyrafen through synergistic experiments and enzyme activity analysis. An omega-family GST gene, PcGSTO1, was significantly up-regulated in the egg, nymph, and adult stages of the cyetpyrafen-resistant strain. Additionally, silencing of PcGSTO1 significantly increased the mortality of P. citri to cyetpyrafen and recombinant PcGSTO1 demonstrated the ability to metabolize cyetpyrafen. Our results indicated that the overexpression of PcGSTO1 is associated with cyetpyrafen resistance in P. citri, and they also provided valuable information for managing resistance in P. citri.

miR-317-3p and miR-283-5p Play a Crucial Role in Regulating the Resistance to Indoxacarb in Spodoptera frugiperda by Targeting GSTs4

Spodoptera frugiperda is primarily controlled through chemical insecticides. Our RNA-seq data highlight the overexpression of GSTs4 in indoxacarb-resistant S. frugiperda. However, the exact role of GSTs4 in indoxacarb resistance and its regulatory mechanisms remains elusive. Therefore, we investigated the functional role of GSTs4 in S. frugiperda and explored the underlying post-transcriptional regulatory mechanisms. GSTs4 was highly overexpressed (27.6-fold) in the indoxacarb-resistant strain, and GSTs4 silencing significantly increases the susceptibility of S. frugiperda to indoxacarb, increasing mortality by 27.3%. miR-317-3p and miR-283-5p can bind to the 3'UTR of GSTs4, and the targeting relationship was confirmed by dual-luciferase reporter assays. Injecting miR-317-3p and miR-283-5p agomirs reduces GSTs4 levels by 64.8 and 42.3%, respectively, resulting in an increased susceptibility of S. frugiperda to indoxacarb. Conversely, the administration of miR-317-3p and miR-283-5pantagomirs increases GSTs4 expression and reduces larval susceptibility to indoxacarb. These findings demonstrate that miR-317-3p and miR-283-5p contribute to indoxacarb resistance in S. frugiperda by regulating the overexpression of GSTs4.

miRNA Dynamics for Pest Management: Implications in Insecticide Resistance

Utilizing chemical agents in pest management in modern agricultural practices has been the predominant approach since the advent of synthetic insecticides. However, insecticide resistance is an emerging issue, as pest populations evolve to survive exposure to chemicals that were once effective in controlling them, underlining the need for advanced and innovative approaches to managing pests. In insects, microRNAs (miRNAs) serve as key regulators of a wide range of biological functions, characterized by their dynamic expression patterns and the ability to target genes. Recent studies are increasingly attributed to the significance of miRNAs in contributing to the evolution of insecticide resistance in numerous insect species. Abundant miRNAs have been discovered in insects using RNA sequencing and transcriptome analysis and are known to play vital roles in regulation at both the transcriptional and post-transcriptional levels. Globally, there is growing research interest in the characterization and application of miRNAs, especially for their potential role in managing insecticide resistance. This review focuses on how miRNAs contribute to regulating insecticide resistance across various insect species. Furthermore, we discuss the gain and loss of functions of miRNAs and the techniques for delivering miRNAs into the insect system. The review emphasizes the application of miRNA-based strategies to studying their role in diminishing insecticide resistance, offering a more efficient and lasting approach to insect management.

N6-methyloxyadenine-mediated detoxification and ferroptosis confer a trade-off between multi-fungicide resistance and fitness

Multi-fungicide resistance (MFR) is a serious environmental problem, which results in the excessive use of fungicides. Fitness penalty, as a common phenomenon in MFR, can partially counteract the issue of resistance due to the weakened vigor of MFR pathogens. Their underlying mechanism and relationship remain unexplained. By Oxford Nanopore Technologies sequencing and dot blot, we found that N6-methyloxyadenine (6mA) modification, the dominate epigenetic marker in Phytophthora capsici, was significantly altered after MFR emerged. Among the differently methylated genes, PcGSTZ1 could efficiently detoxify SYP-14288, a novel uncoupler, through complexing the fungicide with glutathione and induce MFR. Interestingly, PcGSTZ1 overexpression was induced by elevated 6mA levels and chromatin accessibility to its genomic loci. Moreover, the overexpression led to reactive oxygen species burst and ferroptosis in SYP-14288-resistant mutants, which enhanced the resistance and induced fitness penalty in P. capsici through triggering low energy shock adaptive response. Furthermore, this study revealed that the 6mA-PcGSTZ1-ferroptosis axis could mediate intergenerational resistance memory transmission and enabled adaptive advantage to P. capsici. In conclusion, the findings provide new insights into the biological role of 6mA as well as the mechanisms underlying the trade-off between MFR and fitness. These could also benefit disease control through the blockade of the epigenetic axis to resensitize resistant isolates.IMPORTANCEN6-methyloxyadenine (6mA) modification on DNA is correlated with tolerance under different stress in prokaryotes. However, the role of 6mA in eukaryotes remains poorly understood. Our current study reveals that DNA adenine methyltransferase 1 (DAMT1)-mediated 6mA modification at the upstream region of GST zeta 1 (GSTZ1) is elevated in the resistant strain. This elevation promotes the detoxification uncoupler and induces multifungicide resistance (MFR). Moreover, the overexpression led to reactive oxygen species burst and ferroptosis in SYP-14288-resistant mutants, which enhanced the resistance and induced fitness penalty in Phytophthora capsici through triggering low energy shock adaptive response. Furthermore, this study revealed that the 6mA-PcGSTZ1-ferroptosis axis could mediate intergenerational resistance memory transmission and enabled adaptive advantage to P. capsici. Overall, our findings uncover an innovative mechanism underlying 6mA modification in regulating PcGSTZ1 transcription and the ferroptosis pathway in P. capsici.

Evidence of Nonrandom Patterns of Functional Chromosome Organization in Danaus plexippus

Our understanding on the interplay between gene functionality and gene arrangement at different chromosome scales relies on a few Diptera and the honeybee, species with quality reference genome assemblies, accurate gene annotations, and abundant transcriptome data. Using recently generated 'omic resources in the monarch butterfly Danaus plexippus, a species with many more and smaller chromosomes relative to Drosophila species and the honeybee, we examined the organization of genes preferentially expressed at broadly defined developmental stages (larva, pupa, adult males, and adult females) at both fine and whole-chromosome scales. We found that developmental stage-regulated genes do not form more clusters, but do form larger clusters, than expected by chance, a pattern consistent across the gene categories examined. Notably, out of the 30 chromosomes in the monarch genome, 12 of them, plus the fraction of the chromosome Z that corresponds to the ancestral Z in other Lepidoptera, were found enriched for developmental stage-regulated genes. These two levels of nonrandom gene organization are not independent as enriched chromosomes for developmental stage-regulated genes tend to harbor disproportionately large clusters of these genes. Further, although paralogous genes were overrepresented in gene clusters, their presence is not enough to explain two-thirds of the documented cases of whole-chromosome enrichment. The composition of the largest clusters often included paralogs from more than one multigene family as well as unrelated single-copy genes. Our results reveal intriguing patterns at the whole-chromosome scale in D. plexippus while shedding light on the interplay between gene expression and chromosome organization beyond Diptera and Hymenoptera.

Unclassified glutathione-S-transferase AiGSTu1 confers chlorantraniliprole tolerance in Agrotis ipsilon

BACKGROUND

Chlorantraniliprole (CAP) is a diamide insecticide with high efficacy against many pest insects, including the black cutworm, Agrotis ipsilon. Agrotis ipsilon is a serious pest causing significant yield losses in crops. Glutathione-S-transferases (GSTs) belong to a family of metabolic enzymes that can detoxify a wide range of pesticides. However, little is known about the functions of GSTs in CAP tolerance in A. ipsilon.

RESULTS

A cDNA sequence (designated AiGSTu1) encoding an unclassified GST was identified from A. ipsilon. AiGSTu1 is highly expressed during the 3rd -instar larval and the pupal stages. Most of the mRNA transcripts were found in larval Malpighian tubules. Exposure to CAP strongly enhanced AiGSTu1 expression, GST activity, hydrogen peroxide (H2 O2 ) and malondialdehyde levels in larvae. H2 O2 treatment upregulated the transcription level of AiGSTu1, suggesting that CAP-induced oxidative stress may activate AiGSTu1 expression. The activity of recombinant AiGSTu1 was inhibited by CAP in a dose-dependent manner. Metabolism assay results demonstrated that AiGSTu1 is capable of depleting CAP. Overexpression of AiGSTu1 enhanced the tolerance of Escherichia coli cells to H2 O2 and the oxidative stress inducer, cumene hydroperoxide. Silencing of AiGSTu1 by RNA interference increased the susceptibility of A. ipsilon larvae to CAP.

CONCLUSION

The findings of this study provide valuable insights into the potential role of AiGSTu1 in CAP detoxification and will improve our understanding of CAP tolerance in A. ipsilon. © 2023 Society of Chemical Industry.

Identification of differentially expressed miRNAs associated with diamide detoxification pathways in Spodoptera frugiperda

The fall armyworm (FAW) Spodoptera frugiperda is a severe economic pest of multiple crops globally. Control of this pest is often achieved using insecticides; however, over time, S. frugiperda has developed resistance to new mode of action compounds, including diamides. Previous studies have indicated diamide resistance is a complex developmental process involving multiple detoxification genes. Still, the mechanism underlying the possible involvement of microRNAs in post-transcriptional regulation of resistance has not yet been elucidated. In this study, a global screen of microRNAs (miRNAs) revealed 109 known and 63 novel miRNAs. Nine miRNAs (four known and five novel) were differentially expressed between insecticide-resistant and -susceptible strains. Gene Ontology analysis predicted putative target transcripts of the differentially expressed miRNAs encoding significant genes belonging to detoxification pathways. Additionally, miRNAs are involved in response to diamide exposure, indicating they are probably associated with the detoxification pathway. Thus, this study provides comprehensive evidence for the link between repressed miRNA expression and induced target transcripts that possibly mediate diamide resistance through post-transcriptional regulation. These findings highlight important clues for further research to unravel the roles and mechanisms of miRNAs in conferring diamide resistance.

Key Contributions of the Overexpressed Plutella xylostella Sigma Glutathione S-Transferase 1 Gene (PxGSTs1) in the Resistance Evolution to Multiple Insecticides

The overexpression of insect detoxification enzymes is a typical adaptive evolutionary strategy for insects to cope with insecticide pressure. In this study, we identified a glutathione S-transferase (GST) gene, PxGSTs1, that exhibited pronounced expression in the field-resistant population of Plutella xylostella. By using RNAi (RNA interference), the transgenic fly models, and quantitative real-time polymerase chain reaction (RT-qPCR) methods, we confirmed that the augmented expression of PxGSTs1 mediates the resistance of P. xylostella to various types of insecticides, including chlorantraniliprole, novaluron, λ-cyhalothrin, and abamectin. PxGSTs1 was found to bolster insecticide resistance in two ways: direct detoxification and enhancing antioxidative defenses. In addition, our findings demonstrated that pxy-miR-8528a exerts a pivotal influence on forming insecticide resistance in P. xylostella by downregulating PxGSTs1 expression. In summary, we elucidated the multifaceted molecular and biochemical underpinnings of PxGSTs1-driven insecticide resistance in P. xylostella. Our results provide a new perspective for understanding the insecticide resistance mechanism of P. xylostella.

MicroRNA Targets PAP1 to Mediate Melanization in Plutella xylostella (Linnaeus) Infected by Metarhizium anisopliae

MicroRNAs (miRNAs) play a pivotal role in important biological processes by regulating post-transcriptional gene expression and exhibit differential expression patterns during development, immune responses, and stress challenges. The diamondback moth causes significant economic damage to crops worldwide. Despite substantial advancements in understanding the molecular biology of this pest, our knowledge regarding the role of miRNAs in regulating key immunity-related genes remains limited. In this study, we leveraged whole transcriptome resequencing data from Plutella xylostella infected with Metarhizium anisopliae to identify specific miRNAs targeting the prophenoloxidase-activating protease1 (PAP1) gene and regulate phenoloxidase (PO) cascade during melanization. Seven miRNAs (pxy-miR-375-5p, pxy-miR-4448-3p, pxy-miR-279a-3p, pxy-miR-3286-3p, pxy-miR-965-5p, pxy-miR-8799-3p, and pxy-miR-14b-5p) were screened. Luciferase reporter assays confirmed that pxy-miR-279a-3p binds to the open reading frame (ORF) and pxy-miR-965-5p to the 3' untranslated region (3' UTR) of PAP1. Our experiments demonstrated that a pxy-miR-965-5p mimic significantly reduced PAP1 expression in P. xylostella larvae, suppressed PO activity, and increased larval mortality rate. Conversely, the injection of pxy-miR-965-5p inhibitor could increase PAP1 expression and PO activity while decreasing larval mortality rate. Furthermore, we identified four LncRNAs (MSTRG.32910.1, MSTRG.7100.1, MSTRG.6802.1, and MSTRG.22113.1) that potentially interact with pxy-miR-965-5p. Interference assays using antisense oligonucleotides (ASOs) revealed that silencing MSTRG.7100.1 and MSTRG.22113.1 increased the expression of pxy-miR-965-5p. These findings shed light on the potential role of pxy-miR-965-5p in the immune response of P. xylostella to M. anisopliae infection and provide a theoretical basis for biological control strategies targeting the immune system of this pest.

Novel Evodiamine-Based Sulfonamide Derivatives as Potent Insecticide Candidates Targeting Insect Ryanodine Receptors

Pests represent an important impediment to efficient agricultural production and pose a threat to global food security. On the basis of our prior research focused on identifying insecticidal leads targeting insect ryanodine receptors (RyRs), we aimed to identify evodiamine scaffold-based novel insecticides. Thus, a variety of evodiamine-based derivatives were designed, synthesized, and assessed for their insecticidal activity against the larvae of Mythimna separata (M. separata) and Plutella xylostella (P. xylostella). The preliminary bioassay results revealed that more than half of the target compounds exhibited superior activity compared to evodiamine, matrine, and rotenone against M. separata. Among these, compound 21m displayed the most potent larvicidal efficiency, with a remarkable mortality rate of 93.3% at 2.5 mg/L, a substantial improvement over evodiamine (10.0% at 10 mg/L), matrine (10.0% at 200 mg/L), and rotenone (30.0% at 200 mg/L). In the case of P. xylostella, compounds 21m and 21o displayed heightened larvicidal activity, boasting LC50 values of 9.37 × 10-2 and 0.13 mg/L, respectively, surpassing that of evodiamine (13.41 mg/L), matrine (291.78 mg/L), and rotenone (18.39 mg/L). A structure-activity relationship analysis unveiled that evodiamine-based derivatives featuring a cyclopropyl sulfonyl group at the nitrogen atom of the B ring and a fluorine atom in the E ring exhibited more potent larvicidal effects. This finding was substantiated by calcium imaging experiments and molecular docking, which suggested that 21m could target insect RyRs, including resistant mutant RyRs of P. xylostella (G4946E and I4790M), with higher affinity than chlorantraniliprole (CHL). Additionally, cytotoxicity assays highlighted that the potent compounds 21i, 21m, and 21o displayed favorable selectivity and low toxicity toward nontarget organisms. Consequently, compound 21m emerges as a promising candidate for further development as an insecticide targeting insect RyRs.

Genetic Modification of a Hox Locus Drives Mimetic Color Pattern Variation in a Highly Polymorphic Bumble Bee

Müllerian mimicry provides natural replicates ideal for exploring mechanisms underlying adaptive phenotypic divergence and convergence, yet the genetic mechanisms underlying mimetic variation remain largely unknown. The current study investigates the genetic basis of mimetic color pattern variation in a highly polymorphic bumble bee, Bombus breviceps (Hymenoptera, Apidae). In South Asia, this species and multiple comimetic species converge onto local Müllerian mimicry patterns by shifting the abdominal setal color from orange to black. Genetic crossing between the orange and black phenotypes suggested the color dimorphism being controlled by a single Mendelian locus, with the orange allele being dominant over black. Genome-wide association suggests that a locus at the intergenic region between 2 abdominal fate-determining Hox genes, abd-A and Abd-B, is associated with the color change. This locus is therefore in the same intergenic region but not the same exact locus as found to drive red black midabdominal variation in a distantly related bumble bee species, Bombus melanopygus. Gene expression analysis and RNA interferences suggest that differential expression of an intergenic long noncoding RNA between abd-A and Abd-B at the onset setal color differentiation may drive the orange black color variation by causing a homeotic shift late in development. Analysis of this same color locus in comimetic species reveals no sequence association with the same color shift, suggesting that mimetic convergence is achieved through distinct genetic routes. Our study establishes Hox regions as genomic hotspots for color pattern evolution in bumble bees and demonstrates how pleiotropic developmental loci can drive adaptive radiations in nature.

Transcriptional regulation and overexpression of GST cluster enhances pesticide resistance in the cotton bollworm, Helicoverpa armigera (Lepidoptera: Noctuidae)

The rapid evolution of resistance in agricultural pest poses a serious threat to global food security. However, the mechanisms of resistance through metabolic regulation are largely unknown. Here, we found that a GST gene cluster was strongly selected in North China (NTC) population, and it was significantly genetically-linked to lambda-cyhalothrin resistance. Knockout of the GST cluster using CRISPR/Cas9 significantly increased the sensitivity of the knockout strain to lambda-cyhalothrin. Haplotype analysis revealed no non-synonymous mutations or structural variations in the GST cluster, whereas GST_119 and GST_121 were significantly overexpressed in the NTC population. Silencing of GST_119 or co-silencing of GST_119 and GST_121 with RNAi significantly increased larval sensitivity to lambda-cyhalothrin. We also identified additional GATAe transcription factor binding sites in the promoter of NTC_GST_119. Transient expression of GATAe in Hi5 cells activated NTC_GST_119 and Xinjiang (XJ)_GST_119 transcription, but the transcriptional activity of NTC_GST_119 was significantly higher than that of XJ_GST_119. These results demonstrate that variations in the regulatory region result in complex expression changes in the GST cluster, which enhances lambda-cyhalothrin resistance in field-populations. This study deepens our knowledge of the evolutionary mechanism of pest adaptation under environmental stress and provides potential targets for monitoring pest resistance and integrated management.

Enthralling genetic regulatory mechanisms meddling insecticide resistance development in insects: role of transcriptional and post-transcriptional events

Insecticide resistance in insects severely threatens both human health and agriculture, making insecticides less compelling and valuable, leading to frequent pest management failures, rising input costs, lowering crop yields, and disastrous public health. Insecticide resistance results from multiple factors, mainly indiscriminate insecticide usage and mounted selection pressure on insect populations. Insects respond to insecticide stress at the cellular level by modest yet significant genetic propagations. Transcriptional, co-transcriptional, and post-transcriptional regulatory signals of cells in organisms regulate the intricate processes in gene expressions churning the genetic information in transcriptional units into proteins and non-coding transcripts. Upregulation of detoxification enzymes, notably cytochrome P450s (CYPs), glutathione S-transferases (GSTs), esterases [carboxyl choline esterase (CCE), carboxyl esterase (CarE)] and ATP Binding Cassettes (ABC) at the transcriptional level, modification of target sites, decreased penetration, or higher excretion of insecticides are the noted insect physiological responses. The transcriptional regulatory pathways such as AhR/ARNT, Nuclear receptors, CncC/Keap1, MAPK/CREB, and GPCR/cAMP/PKA were found to regulate the detoxification genes at the transcriptional level. Post-transcriptional changes of non-coding RNAs (ncRNAs) such as microRNAs (miRNA), long non-coding RNAs (lncRNA), and epitranscriptomics, including RNA methylation, are reported in resistant insects. Additionally, genetic modifications such as mutations in the target sites and copy number variations (CNV) are also influencing insecticide resistance. Therefore, these cellular intricacies may decrease insecticide sensitivity, altering the concentrations or activities of proteins involved in insecticide interactions or detoxification. The cellular episodes at the transcriptional and post-transcriptional levels pertinent to insecticide resistance responses in insects are extensively covered in this review. An overview of molecular mechanisms underlying these biological rhythms allows for developing alternative pest control methods to focus on insect vulnerabilities, employing reverse genetics approaches like RNA interference (RNAi) technology to silence particular resistance-related genes for sustained insect management.

Cuticular competing endogenous RNAs regulate insecticide penetration and resistance in a major agricultural pest

BACKGROUND

The continuously developing pesticide resistance is a great threat to agriculture and human health. Understanding the mechanisms of insecticide resistance is a key step in dealing with the phenomenon. Insect cuticle is recently documented to delay xenobiotic penetration which breaks the previous stereotype that cuticle is useless in insecticide resistance, while the underlying mechanism remains scarce.

RESULTS

Here, we find the integument contributes over 40.0% to insecticide resistance via different insecticide delivery strategies in oriental fruit fly. A negative relationship exists between cuticle thickening and insecticide penetration in resistant/susceptible, also in field strains of oriental fruit fly which is a reason for integument-mediated resistance. Our investigations uncover a regulator of insecticide penetration that miR-994 mimic treatment causes cuticle thinning and increases susceptibility to malathion, whereas miR-994 inhibitor results in opposite phenotypes. The target of miR-994 is a most abundant cuticle protein (CPCFC) in resistant/susceptible integument expression profile, which possesses capability of chitin-binding and influences the cuticle thickness-mediated insecticide penetration. Our analyses find an upstream transcriptional regulatory signal of miR-994 cascade, long noncoding RNA (lnc19419), that indirectly upregulates CPCFC in cuticle of the resistant strain by sponging miR-994. Thus, we elucidate the mechanism of cuticular competing endogenous RNAs for regulating insecticide penetration and demonstrate it also exists in field strain of oriental fruit fly.

CONCLUSIONS

We unveil a regulatory axis of lnc19419 ~ miR-994 ~ CPCFC on the cuticle thickness that leads to insecticide penetration resistance. These findings indicate that competing endogenous RNAs regulate insecticide resistance by modulating the cuticle thickness and provide insight into the resistance mechanism in insects.

Functional analysis of an overexpressed glutathione S-transferase BdGSTd5 involved in malathion and malaoxon detoxification in Bactrocera dorsalis

Glutathione S-transferases (GSTs) are one of the three detoxification enzyme families. The constitutive and inducible overexpression of GSTs genes plays an important role in insecticide resistance. Previous study showed that malathion resistance was polygenic, and elevated GSTs activity was one of the important factor participating in malathion resistance of Bactrocera dorsalis (Hendel), a serious economic pest worldwide. BdGSTd5 overexpression was inducible upon exposure to malathion. However, the involvement of BdGSTd5 in malathion resistance has not been clarified. In this study, we found that BdGSTd5 sequence harbored the conserved region of delta class GSTs, which were overexpressed in malathion resistant strain of B. dorsalis compared to malathion susceptible strain. The highest mRNA expression level of BdGSTd5 was found in 1-day-old adult, and the levels decreased with aging. The dsBdGSTd5 injection effectively silenced (73.4% reduction) the expression of BdGSTd5 and caused significant increase in susceptibility to malathion with a cumulative mortality increasing of 13.5% at 72 h post malathion treatment (p < 0.05). Cytotoxicity assay demonstrated that BdGSTd5 was capable of malathion detoxification. Molecular docking analysis further indicated the interactive potential of BdGSTd5 with malathion and its toxic oxide malaoxon. The recombinant BdGSTd5 exhibited glutathione-conjugating activity toward 1-chloro-2, 4-dinitrobenzene and malathion and malaoxon metabolic capacity with significant reduction (p < 0.05) of the peak areas by 90.0% and 73.1%, respectively. Taken together, the overexpressed BdGSTd5 contributes to malathion metabolism and resistance, which detoxify the malathion in B. dorsalis via directly depleting malathion and malaoxon.

Response patterns of lncRNAs of the Spodoptera frugiperda (Lepidoptera: Noctuidae) larvae under 23 pesticide treatments

The response of Spodoptera frugiperda genes toward insecticides is crucial for guiding insecticide use. The regulation of the S. frugiperda genes via long noncoding RNAs (lncRNAs) under insecticide treatment should be investigated. In this study, 452 differentially expressed lncRNAs were identified by analyzing RNA-sequencing data of S. frugiperda under 23 pesticide treatments. We found 59 and 43 differentially expressed lncRNAs that could regulate detoxification-related cytochrome P450 and UDP-glucuronosyltransferase genes, respectively. Furthermore, the target genes of differentially expressed lncRNAs were enriched in Pfam, including chitin bind 4 and gene ontology terms such as structural constituent of the cuticle, revealing their potential mechanism of action on the growth inhibition of S. frugiperda larvae. Insecticide-specific expression of lncRNAs highlights the properties and commonalities of different insecticide-induced lncRNA regulatory mechanisms. To conclude, the results of this study provide new insights and perspectives on the use of 23 insecticides via lncRNA regulation of mRNAs.

Identification and Characterization of Glutathione S-transferase Genes in Spodoptera frugiperda (Lepidoptera: Noctuidae) under Insecticides Stress

Insect glutathione S-transferases (GSTs) serve critical roles in insecticides and other forms of xenobiotic chemical detoxification. The fall armyworm, Spodoptera frugiperda (J. E. Smith), is a major agricultural pest in several countries, especially Egypt. This is the first study to identify and characterize GST genes in S. frugiperda under insecticidal stress. The present work evaluated the toxicity of emamectin benzoate (EBZ) and chlorantraniliprole (CHP) against the third-instar larvae of S. frugiperda using the leaf disk method. The LC₅₀ values of EBZ and CHP were 0.029 and 1.250 mg/L after 24 h of exposure. Moreover, we identified 31 GST genes, including 28 cytosolic and 3 microsomal SfGSTs from a transcriptome analysis and the genome data of S. frugiperda. Depending on the phylogenetic analysis, sfGSTs were divided into six classes (delta, epsilon, omega, sigma, theta, and microsomal). Furthermore, we investigated the mRNA levels of 28 GST genes using qRT-PCR under EBZ and CHP stress in the third-instar larvae of S. frugiperda. Interestingly, SfGSTe10 and SfGSTe13 stood out with the highest expression after the EBZ and CHP treatments. Finally, a molecular docking model was constructed between EBZ and CHP using the most upregulated genes (SfGSTe10 and SfGSTe13) and the least upregulated genes (SfGSTs1 and SfGSTe2) of S. frugiperda larvae. The molecular docking study showed EBZ and CHP have a high binding affinity with SfGSTe10, with docking energy values of -24.41 and -26.72 kcal/mol, respectively, and sfGSTe13, with docking energy values of -26.85 and -26.78 kcal/mol, respectively. Our findings are important for understanding the role of GSTs in S. frugiperda regarding detoxification processes for EBZ and CHP.

ATP Synthase Subunit α from Helicoverpa armigera Acts as a Receptor of Bacillus thuringiensis Cry1Ac and Synergizes Cry1Ac Toxicity

Insect resistance to Bacillus thuringiensis (Bt) toxins has led to an urgent need to explore the insecticidal mechanisms of Bt. Previous studies indicated that Helicoverpa armigera ATP synthase subunit α (HaATPs-α) is involved in Cry1Ac resistance. In this study, a real-time quantitative polymerase chain reaction (RT-PCR) confirmed that HaATPs-α expression was significantly reduced in the Cry1Ac-resistant strain (BtR). Cry1Ac feeding induced the downregulated expression of HaATPs-α in the susceptible strain, but not in the BtR strain. Furthermore, the interaction between HaATPs-α and Cry1Ac was verified by ligand blotting and homologous competition experiments. The in vitro gain and loss of function analyses showed HaATPs-α involved in Cry1Ac toxicity by expressing endogenous HaATPs-α and HaATPs-α double-stranded RNAs in Sf9 and midgut cells, respectively. Importantly, purified HaATPs-α synergized Cry1Ac toxicity to H. armigera larvae. These findings provide the first evidence that HaATPs-α is a potential receptor of Cry1Ac, it shows downregulated participation in Cry1Ac resistance, and it exhibits higher enhancement of Cry1Ac toxicity to H. armigera larvae.

Apoptosis-related long non-coding RNA LINC5438 of Bombyx mori promotes the proliferation of BmNPV

Apoptosis, as an important part of the immune response, is one of the core events in the host-virus interaction. Studies have shown that long non-coding RNAs (lncRNAs) play important roles in the process of cell apoptosis and pathophysiology. To investigate the apoptosis-related lncRNAs involved in Bombyx mori nucleopolyhedrovirus (BmNPV) infecting silkworms, transcriptome sequencing was conducted based on silkworm cells infected with BmNPV before and after B. mori inhibitor of apoptosis (Bmiap) gene knockout. A total of 23 differentially expressed lncRNAs were identified as being associated with the mitochondrial apoptosis pathway. Moreover, we demonstrated that B. mori LINC5438 has the function of inhibiting apoptosis in silkworm cells. Overexpression of LINC5438 promoted the proliferation of BmNPV, while interference with LINC5438 inhibited its proliferation, indicating that LINC5438 plays an important role in BmNPV infection. Our results also showed that LINC5438 can regulate the expression of Bmiap, BmDronc, BmICE, and its predicted target gene BmAIF, suggesting that LINC5438 may function through the mitochondrial pathway. These findings provide important insights into the mechanisms of virus-host interaction and the applications of baculoviruses as biological insecticides.

A novel V263I mutation in the glutamate-gated chloride channel of Plutella xylostella (L.) confers a high level of resistance to abamectin

The frequent and extensive use of insecticides leads to the evolution of insecticide resistance, which has become one of the constraints on global agricultural production. Avermectins are microbial-derived insecticides that target a wide number of insect pests, including the diamondback moth Plutella xylostella, an important global pest of brassicaceous vegetables. However, field populations of P. xylostella have evolved serious resistance to avermectins, including abamectin, thereby threatening the efficiency of these insecticides. In this study, a novel valine to isoleucine mutation (V263I) was identified in the glutamate-gated chloride channel (GluCl) of field P. xylostella populations, which showed different levels of resistance to abamectin. Electrophysiological analysis revealed that the V263I mutation significantly reduced the sensitivity of PxGluCl to abamectin by 6.9-fold. Genome-modified Drosophila melanogaster carrying the V263I mutation exhibited 27.1-fold resistance to abamectin. Then, a knockin strain (V263I-KI) of P. xylostella expressing the homozygous V263I mutation was successfully constructed using the CRISPR/Cas9. The V263I-KI had high resistance to abamectin (106.3-fold), but significantly reduced fecundity. In this study, the function of V263I mutation in PxGluCl was verified for the first time. These findings provide a more comprehensive understanding of abamectin resistance mechanisms and lay the foundation for providing a new molecular detection method for abamectin resistance monitoring.

CRISPR/Cas9-mediated D472N substitution in the Rdl1 of Plutella xylostella confers low resistance to abamectin

BACKGROUND

Abamectin is one of the main insecticides used for the control of Plutella xylostella, a destructive pest of cruciferous crops. Target-site mutation plays an important role in insecticide resistance. A point mutation (D472N) has been reported in the Rdl1 γ-aminobutyric acid receptor (GABAR) in P. xylostella, but its roles in insecticide resistance remain unknown.

RESULTS

In this study, the D472N mutation of the Rdl1 GABAR was detected in several field populations of P. xylostella and showed a positive correlation with abamectin resistance. A knock-in homozygous mutation strain (D472N-KI) of P. xylostella was successfully constructed using CRISPR/Cas9 coupled with homology-directed repair, and the bioassay results demonstrated that compared with the susceptible strain, the D472N-KI strain had 11.1- and 3.7-fold increased resistance to abamectin and endosulfan, respectively. There was no difference in resistance to fipronil, broflanilide or isocycloseram, which also target the GABAR. In addition, the total fecundity of the D472N-KI strain was significantly reduced by 50.0%.

CONCLUSION

Our results suggest that the homozygous D472N mutation in Rdl1 confers a low level of resistance to abamectin in P. xylostella but causes significant fecundity disadvantages, which may delay the development of resistance to some extent. These results lay a foundation for further understanding the mechanisms of abamectin resistance in insect pests. © 2022 Society of Chemical Industry.

Recent Advances and Future Potential of Long Non-Coding RNAs in Insects

Over the last decade, long non-coding RNAs (lncRNAs) have witnessed a steep rise in interest amongst the scientific community. Because of their functional significance in several biological processes, i.e., alternative splicing, epigenetics, cell cycle, dosage compensation, and gene expression regulation, lncRNAs have transformed our understanding of RNA's regulatory potential. However, most knowledge concerning lncRNAs comes from mammals, and our understanding of the potential role of lncRNAs amongst insects remains unclear. Technological advances such as RNA-seq have enabled entomologists to profile several hundred lncRNAs in insect species, although few are functionally studied. This article will review experimentally validated lncRNAs from different insects and the lncRNAs identified via bioinformatic tools. Lastly, we will discuss the existing research challenges and the future of lncRNAs in insects.

Whole-transcriptome profiling across different developmental stages of Aedes albopictus (Diptera: Culicidae) provides insights into chitin-related non-coding RNA and competing endogenous RNA networks

BACKGROUND

The Asian tiger mosquito, Aedes albopictus, is one of the most invasive species and a vector of numerous arboviruses. The deleterious effects of long-term and inappropriate use of chemical pesticides have stimulated the exploration of new, environmentally friendly control strategies. Non-coding RNAs (ncRNAs) have been proven to participate in almost all biological processes of insects.

METHODS

In this study, circular RNAs (circRNAs) and microRNAs (miRNAs) covering five developmental stages [egg, early larvae, late larvae, pupae, adult (female and male)] of A. albopictus were obtained using whole-transcriptome sequencing technology. Combined with long non-coding RNAs (lncRNAs) from previous research, circRNA/lncRNA‒miRNA‒mitochondrial RNA (mRNA) networks were constructed.

RESULTS

A total of 1434 circRNAs and 208 miRNAs were identified. More differentially expressed circRNAs (DE circRNAs) and miRNAs (DE miRNAs) were found in the egg versus early larvae comparison group. Functional enrichment analysis demonstrated that most of the circRNA/lncRNA‒miRNA‒mRNA networks were involved in chitin metabolism. Hub genes of each circRNA/lncRNA‒miRNA‒mRNA network were screened out, which can be used as novel targets to disturb the molting process of A. albopictus.

CONCLUSIONS

Regulatory relationships obtained from competing endogenous RNA (ceRNA) networks provide more information to manipulate the metamorphosis process and are helpful for developing effective and sustainable methods to control mosquitoes.

Genome-wide identification and functional analysis of long non-coding RNAs in Chilo suppressalis reveal their potential roles in chlorantraniliprole resistance

Long non-coding RNAs, referred to as lncRNAs, perform essential functions in some biological processes, including reproduction, metamorphosis, and other critical life functions. Yet, lncRNAs are poorly understood in pesticide resistance, and no reports to date have characterized which lncRNAs are associated with chlorantraniliprole resistance in Chilo suppressalis. Here, RNA-seq was performed on two strains of C. suppressalis exposed to chlorantraniliprole: one is a susceptible strain (S), and the other is a resistant strain (R). In total, 3,470 lncRNAs were identified from 40,573 merged transcripts in six libraries, including 1,879 lincRNAs, 245 intronic lncRNAs, 853 sense lncRNAs, and 493 antisense lncRNAs. Moreover, differential expression analysis revealed 297 and 335 lncRNAs upregulated in S and R strains, respectively. Differentially expressed (DE) lncRNAs are usually assumed to be involved in the chlorantraniliprole resistance in C. suppressalis. As potential targets, adjacent protein-coding genes (within <1000 kb range upstream or downstream of DE lncRNAs), especially detoxification enzyme genes (cytochrome P450s, carboxyl/cholinesterases/esterases, and ATP-binding cassette transporter), were analyzed. Furthermore, the strand-specific RT-PCR was conducted to confirm the transcript orientation of randomly selected 20 DE lincRNAs, and qRT-PCR was carried out to verify the expression status of 8 out of them. MSTRG.25315.3, MSTRG.25315.6, and MSTRG.7482.1 were upregulated in the R strain. Lastly, RNA interference and bioassay analyses indicated overexpressed lincRNA MSTRG.7482.1 was involved in chlorantraniliprole resistance. In conclusion, we represent, for the first time, the genome-wide identification of chlorantraniliprole-resistance-related lncRNAs in C. suppressalis. It elaborates the views underlying the mechanism conferring chlorantraniliprole resistance in lncRNAs.

Analysis of Long Non-Coding RNA-Mediated Regulatory Networks of Plutella xylostella in Response to Metarhizium anisopliae Infection

Long non-coding RNAs (lncRNAs) represent a diverse class of RNAs that are structurally similar to messenger RNAs (mRNAs) but do not encode proteins. Growing evidence suggests that in response to biotic and abiotic stresses, the lncRNAs play crucial regulatory roles in plants and animals. However, the potential role of lncRNAs during fungal infection has yet to be characterized in Plutella xylostella, a devastating pest of cruciferous crops. In the current study, we performed a strand-specific RNA sequencing of Metarhizium anisopliae-infected (Px36hT, Px72hT) and uninfected (Px36hCK, Px72hCK) P. xylostella fat body tissues. Comprehensive bioinformatic analysis revealed a total of 5665 and 4941 lncRNAs at 36 and 72-h post-infection (hpi), including 563 (Px36hT), 532 (Px72hT) known and 5102 (Px36hT), 4409 (Px72hT) novel lncRNA transcripts. These lncRNAs shared structural similarities with their counterparts in other species, including shorter exon and intron length, fewer exon numbers, and a lower expression profile than mRNAs. LncRNAs regulate the expression of neighboring protein-coding genes by acting in a cis and trans manner. Functional annotation and pathway analysis of cis-acting lncRNAs revealed their role in several immune-related genes, including Toll, serpin, transferrin, βGRP etc. Furthermore, we identified multiple lncRNAs acting as microRNA (miRNA) precursors. These miRNAs can potentially regulate the expression of mRNAs involved in immunity and development, suggesting a crucial lncRNA-miRNA-mRNA complex. Our findings will provide a genetic resource for future functional studies of lncRNAs involved in P. xylostella immune responses to M. anisopliae infection and shed light on understanding insect host-pathogen interactions.

Functional and Structural Diversity of Insect Glutathione S-transferases in Xenobiotic Adaptation

As a superfamily of multifunctional enzymes that is mainly associated with xenobiotic adaptation, glutathione S-transferases (GSTs) facilitate insects' survival under chemical stresses in their environment. GSTs confer xenobiotic adaptation through direct metabolism or sequestration of xenobiotics, and/or indirectly by providing protection against oxidative stress induced by xenobiotic exposure. In this article, a comprehensive overview of current understanding on the versatile functions of insect GSTs in detoxifying chemical compounds is presented. The diverse structures of different classes of insect GSTs, specifically the spatial localization and composition of their amino acid residues constituted in their active sites are also summarized. Recent availability of whole genome sequences of numerous insect species, accompanied by RNA interference, X-ray crystallography, enzyme kinetics and site-directed mutagenesis techniques have significantly enhanced our understanding of functional and structural diversity of insect GSTs.

Deciphering the Molecular Mechanisms of Insecticide Resistance From the Transcriptome Data of Field Evolved Spinosad Resistant and Susceptible Populations of Plutella xylostella (Lepidoptera: Plutellidae)

Diamondback moth, Plutella xylostella is a serious pest of cruciferous vegetables and causes substantial economic loss all over the world. This study was undertaken to decipher the molecular mechanisms involved in the field evolved insecticide resistance in P. xylostella upon exposure to spinosad. To do so, spinosad-resistant and susceptible larval populations were subjected to transcriptome analysis using Illumina paired-end sequencing. De novo assembly was generated from raw reads of both the samples which resulted in the identification of 41,205 unigenes. Functional annotation and digital gene expression analysis were carried out to determine the differentially expressed genes. 1,348 unigenes were found to have a significant differential expression in the resistant population. Several genes involved in insecticide resistance like CYP P450, GSTs, small heat shock protein, and UDP glycosyltransferase were found to be up-regulated while genes related to mitochondrial energy metabolism and cuticular processes were down-regulated. Further, gene mining and phylogenetic analysis of two important gene families namely, CYP and GSTs were performed and the results revealed that these genes could play a major role in the development of field evolved spinosad resistance in P. xylostella by gene duplication and differential gene expression.

Genome-wide identification of long non-coding (lncRNA) in Nilaparvata lugens's adaptability to resistant rice

Background

The brown planthopper (BPH), Nilaparvata lugens (Stål), is a very destructive pest that poses a major threat to rice plants worldwide. BPH and rice have developed complex feeding and defense strategies in the long-term co-evolution.

Methods

To explore the molecular mechanism of BPH's adaptation to resistant rice varieties, the lncRNA expression profiles of two virulent BPH populations were analyzed. The RNA-seq method was used to obtain the lncRNA expression data in TN1 and YHY15.

Results

In total, 3,112 highly reliable lncRNAs in TN1 and YHY15 were identified. Compared to the expression profiles between TN1 and YHY15, 157 differentially expressed lncRNAs, and 675 differentially expressed mRNAs were identified. Further analysis of the possible regulation relationships between differentially expressed lncRNAs and differentially expressed mRNAs, identified three pair antisense targets, nine pair cis-regulation targets, and 3,972 pair co-expressed targets. Function enriched found arginine and proline metabolism, glutathione metabolism, and carbon metabolism categories may significantly affect the adaptability in BPH when it is exposed to susceptible and resistant rice varieties. Altogether, it provided scientific data for the study of lncRNA regulation of brown planthopper resistance to rice. These results are helpful in the development of new control strategies for host defense against BPH and breeding rice for high yield.

Functional investigation of lncRNAs and target cytochrome P450 genes related to spirotetramat resistance in Aphis gossypii Glover

BACKGROUND

Spirotetramat is a tetramic acid derivative insecticide with novel modes of action for controlling Aphis gossypii Glover in the field. Previous studies have shown that long noncoding RNAs (lncRNAs) and cytochrome P450 monooxygenases (P450s) are involved in the detoxification process. However, the functions of lncRNAs in regulating P450 gene expression in spirotetramat resistance in A. gossypii are unknown.

RESULTS

In this study, we found CYP4CJ1, CYP6CY7 and CYP6CY21 expression levels to be significantly upregulated in a spirotetramat-resistant (SR) strain compared with a susceptible (SS) strain. Furthermore, knockdown of CYP4CJ1, CYP6CY7 and CYP6CY21 increased nymph and adult mortality in the SR strain following exposure to spirotetramat. Drosophila ectopically expressing CYP380C6, CYP4CJ1, CYP6DA2, CYP6CY7 and CYP6CY21 showed significantly decreased mortality after spirotetramat exposure, and CYP380C6, CYP4CJ1 and CYP6CY21 are putative targets of six lncRNAs. Silencing of lncRNAs MSTRG.36649.2/5 and MSTRG.71880.1 changed CYP6CY21 and CYP380C6 expression, altering the sensitivity of the SR strain to spirotetramat. Moreover, MSTRG.36649.2/5 did not compete for microRNA (miRNA) binding to regulate CYP6CY21 expression.

CONCLUSION

Our results confirm that CYP380C6, CYP4CJ1, CYP6DA2, CYP6CY7 and CYP6CY21 are potentially involved in the development of spirotetramat resistance in A. gossypii, and MSTRG.36649.2/5 and MSTRG.71880.1 probably regulate CYP6CY21 and CYP380C6 expression other than through the "sponge effect" of competing for miRNA binding. Our results provide a favorable molecular basis for studying cotton aphid P450 genes and lncRNA functions in spirotetramat resistance development.

Bioactivity-Guided Synthesis Accelerates the Discovery of Evodiamine Derivatives as Potent Insecticide Candidates

Pests threaten worldwide food security by decreasing crop yields and damaging their quality. Natural product-based molecular design and structural optimization have been one of the most effective ways to innovate pesticides for integrated insect management. To continue our previous studies on the discovery of insecticidal lead, a series of evodiamine derivatives were designed, synthesized, and evaluated for their insecticidal activities. The bioassay results demonstrated that compounds Ian and Iao exhibited 90 and 80% insecticidal activities against Mythimna separata at 2.5 mg/L, respectively, which were superior to evodiamine (10% at 10 mg/L), matrine (45% at 600 mg/L), and rotenone (30% at 200 mg/L). Compounds Ian-Iap showed 90% insecticidal activities against Plutella xylostella at 1.0 mg/L, far more potent than those of evodiamine, matrine, and rotenone. Compound Ian displayed 60% insecticidal activity against Helicoverpa armigera at 5.0 mg/L, while evodiamine, matrine, and rotenone showed very poor activities. The study on the insecticidal mechanism of action by a calcium imaging experiment indicated that the insect ryanodine receptors (RyRs) could be the potential target of Ian. Furthermore, the molecular docking indicated that Ian anchored in the binding site of the RyR of P. xylostella. The above results manifested the potential of evodiamine derivatives as potent insecticide candidates.