Four MicroRNAs, miR-13b-3p, miR-278-5p, miR-10483-5p, and miR-10485-5p, Mediate Insecticide Tolerance in Spodoptera frugiperda

Insecticide-induced sublethal effect in the fall armyworm is mediated by miR-9993/miR-2a-3p - FPPS/JHAMT - JH molecular module

The sublethal effect of insecticides can affect the population dynamics of pests by changing the physiological or behavioral changes, which poses a serious threat to the sustainable control of crop pests in the field. However, the molecular regulation mechanism that mediates the sublethal effect of insecticides on crop pests remains unsolved. Here, we show that the sublethal effect of spinetoram and cyantraniliprole on Spodoptera frugiperda is mediated by the molecular module of microRNA-9993/microRNA-2a-3p - farnesyl diphosphate synthase gene (FPPS)/juvenile hormone (JH) acid methyltransferase gene (JHAMT) - JH. Spinetoram prolonged the duration of larvae and pupae, decreased the weight of pupae, while cyantraniliprole prolonged the duration of larvae and decreased the emergence rate. Similarly, injection of the juvenile hormone analogue (JHA) methoprene significantly prolonged the developmental duration of larvae and pupae, decreased the pupal weight and emergence rate. This sublethal phenotypic change was due to the upregulation of key JH synthesis genes, including FPPS and JHAMT, mediated by spinetoram and cyantraniliprole, resulting in an increase in JH titer. Furthermore, it was confirmed by small RNA sequencing, dual luciferase analysis and agomir-miRNA injection, miR-9993 and miR-2a-3p that it could bind FPPS and JHAMT respectively, and regulated the expression level of FPPS and JHAMT to affect the titer of JH, thus changing the phenotype of S. frugiperda. Collectively, these results provide insights into the mechanism of insecticide regulation of sublethal effects of pests, expand our understanding of development-related miRNAs, and reveal key factors involved in JH signaling pathways that support sublethal effects of insecticides.

miRNA Expression Response of Aedes aegypti (Linnaeus 1762) (Diptera: Culicidae) to Imidacloprid Exposure

Aedes aegypti is a major vector of arboviruses, including dengue, Zika, chikungunya, yellow fever, and Mayaro. The extensive use of insecticides has led to resistance, complicating vector control efforts. MicroRNAs (miRNAs) are post-transcriptional regulators involved in detoxification and stress adaptation; however, their role in the insecticide response of Ae. aegypti remains unclear. This study analyzed miRNA expression in Ae. aegypti following imidacloprid exposure, comparing a field strain, Martinez de la Torre from Mexico (MT), and a susceptible reference strain, New Orleans (NO). Small RNA sequencing identified 96 miRNAs, with miR-1, miR-281-5p, miR-100, and miR-184 being consistently expressed across all conditions. In contrast, let-7, miR-124, and miR-13-3p were exclusively detected in wild mosquitoes exposed to imidacloprid, while miR-14 and miR-275-3p showed condition-specific expression. Distinct miRNA expression patterns were observed between the field and susceptible strains, with specific miRNAs showing condition-dependent expression. These findings suggest that certain miRNAs may serve as potential biomarkers for resistance monitoring, contributing to a better understanding of insecticide response mechanisms and informing novel vector control strategies.

Bioinsecticide control and enzymatic responses in Spodoptera frugiperda

Spodoptera frugiperda (Lepidoptera: Noctuidae) is a serious invasive pest, which has attracted concern regarding the effectiveness of environmental bioinsecticide as a substitution for synthetic insecticide in controlling its damage to numerous agricultural crops in recent years. Hence, laboratory and field experiments have investigated insecticidal toxicity in S. frugiperda by 5 insecticides and have determined the activity of acetylcholinesterase (AChE) and detoxifying enzymes, namely mixed function oxidase (MFO), carboxylesterase (CarE), and glutathione S-transferase (GST) on 3rd instar larvae at 25% lethal concentration (LC25) to explore detoxification mechanisms. The results showed that the most effective insecticides were 3.0% emamectin benzoate (0.024 mg/L), 60 g/L spinetoram (0.282 mg/L), and 1.3% matrine (0.380 mg/L) at 48 h depending on LC50 values. The field efficiencies of emamectin benzoate and spinetoram were over 80% at 24 h and 90% at 72 h, indicating that both insecticides had acute and long-lasting toxicity on S. frugiperda; matrine had extended-release toxicity with 90% field efficiency at 72 h. Emamectin benzoate and spinetoram activated the activities of AChE, MFO and GST, and spinetoram decreased in CarE activity; cyantraniliprole induced an increase of 4 detoxifying enzymes; spinosad increased the activities of AChE, MFO, and CarE but not GST. Furthermore, matrine had an inhibiting effect on AChE and acceleration on CarE and GST. Overall results obviously depicted that semi-synthetic insecticide spinetoram and bioinsecticide matrine were recommended to control S. frugiperda with effective and long-lasting toxicity. Moreover, this study will provide basic information for sustainable control of S. frugiperda under field conditions in China.

miR-92a-3p regulates egg fertilization through ribogenesis in the invasive fall armyworm Spodoptera frugiperda

Understanding the epigenetic molecular mechanisms (EMMs) of reproduction is crucial for developing advanced and targeted control strategies for Spodoptera frugiperda. Differential expression analysis revealed 11 known miRNAs with varying expression levels, including nine upregulated and two downregulated miRNAs, in virgin females compared with males. The predictive analysis identified 426 target genes for these miRNAs, with ribogenesis highlighted as a key process in oogenesis and egg fertilization. This study also investigated the expression of miRNAs in both virgin and mated male and female S. frugiperda, with a focus on their roles in reproduction. A strong negative correlation was observed between miRNA expression levels and their target hub genes, confirming the transcriptional regulation by miRNAs. Additionally, protein-protein interaction (PPI) network identified the gene CG5033 (BOP1), as a central hub, was also predicted to be the target of miR-92a-3p in S. frugiperda, is involved in the maturation of large ribosomal RNA subunits. This study further provided experimental evidence that either the depletion of miR-92a-3p in virgin females or the knockdown of BOP1 in virgin males led to the production of infertile eggs post-mating. These findings validate the regulatory role of the miR-92a-3p - BOP1 interaction and underscore its importance in oogenesis and fertilization.

miR-9a and miR-10482-5p regulate the expression of chitin synthase and chitinase genes, enhancing lufenuron tolerance in Spodoptera frugiperda

Spodoptera frugiperda is a significant agricultural pest, severely impacting the yield and quality of grain. Chitin is the momentous component of exoskeletons, which has a significant impact on the growth and development of insects. Our previous study found that exposure to lufenuron can reduce the expression of chitinase gene (SfCHT5) and increase the expression of chitin synthase gene (SfCHSB), two key genes for chitin synthesis in S. frugiperda. However, the post-transcriptional regulatory mechanisms of these key genes in S. frugiperda remain unclear. With miRNA as the entry point, target site prediction, dual luciferase reporter assays, and mimics/inhibitors injection were used to explore the post-transcriptional regulatory mechanism of SfCHSB and SfCHT5. The combined results confirm that miR-10482-5p targets SfCHT5 and regulates its expression, while miR-9a targets and regulates the expression of both SfCHT5 and SfCHSB. Additionally, injection of miR-10482-5p and miR-9a mimic significantly reduced the mortality rates of S. frugiperda treated with lufenuron, increased pupation rate, and emergence rate. These findings underscore the critical regulatory role of miR-10482-5p and miR-9a in modulating the expression of key genes involved in chitin synthesis, thereby enhancing the tolerance of S. frugiperda to lufenuron and influencing its growth and development. In summary, this study preliminarily elucidates the post-transcriptional regulatory mechanisms of miRNA-mediated SfCHSB and SfCHT5 expression.

Isolation and Evaluation of Indigenous Isolates of Beauveria bassiana and Synergistic Control of Spodoptera frugiperda with the Parasitoid Microplitis prodeniae

Entomopathogenic fungi (EPFs) are capable of infecting a variety of insect pests and are widely used as biopesticides worldwide. This study intended to isolate indigenous EPFs from cadavers of Protaetia brevitarsis and investigate their effects on the fall armyworm Spodoptera frugiperda (FAW), a globally widespread invasive pest. Morphological and molecular analyses confirmed four native EPF strains all belong to Beauveria bassiana. Pathogenicity tests showed they were virulent toward FAW 1st instar larvae. The application of EPFs either by dipping or spraying significantly increased the larval mortalities compared to the control group, with corrected mortalities ranging from 92% to 73% after dipping in a fungal suspension of 108 conidia/mL, and those ranging from 76% to 35% after spraying with a fungal suspension of 107 conidia/mL. Our findings revealed the infectivity of four strains to FAW larvae significantly changed in a dose- and time-dependent manner. In addition, the combination use of the local B. bassiana strain and parasitoid Microplitis prodeniae resulted in a significantly enhanced S. frugiperda 3rd instar larval mortality compared to a single inoculation with one of them, suggesting an apparent synergistic effect for the joint application of these two biological control agents. The mortality inflicted by B. bassiana was probably promoted by the release of parasitoids, since the parasitoids' movements and attacks could strengthen the fungal distribution and infection processes. This study underscores the potential of the combination use of EPFs and parasitoids against S. frugiperda early-instar larvae, and provides insights into the consequences of integrating these EPFs into integrated pest management systems.

Identification and Prediction of Differentially Expressed MicroRNAs Associated with Detoxification Pathways in Larvae of Spodoptera frugiperda

Spodoptera frugiperda poses a severe threat to crops, causing substantial economic losses. The increased use of chemical pesticides has led to resistance in S. frugiperda populations. Micro ribonucleic acids (MicroRNAs or miRNAs) are pivotal in insect growth and development. This study aims to identify miRNAs across different developmental stages of S. frugiperda to explore differential expression and predict target gene functions. High-throughput sequencing of miRNAs was conducted on eggs, 3rd instar larvae, pupae, and adults. Bioinformatics analyses identified differentially expressed miRNAs specifically in larvae, with candidate miRNAs screened to predict target genes, particularly those involved in detoxification pathways. A total of 184 known miRNAs and 209 novel miRNAs were identified across stages. Comparative analysis revealed 54, 15, and 18 miRNAs differentially expressed in larvae, compared to egg, pupa, and adult stages, respectively. Eight miRNAs showed significant differential expression across stages, validated by quantitative reverse transcription PCR (qRT-PCR). Gene Ontology and Kyoto Encyclopedia of Genes and Genomes enrichment analyses predicted target genes' functions, identifying eight differentially expressed miRNAs targeting 10 gene families associated with detoxification metabolism, including P450s, glutathione S-transferase (GSTs), ATP-binding cassette (ABC) transporters, and sodium channels. These findings elucidate the species-specific miRNA profiles and regulatory mechanisms of detoxification-related genes in S. frugiperda larvae, offering insights and strategies for effectively managing this pest.

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.

Molecular mechanisms of cytochrome P450-mediated detoxification of tetraniliprole, spinetoram, and emamectin benzoate in the fall armyworm, Spodoptera frugiperda (J.E. Smith)

The fall armyworm (FAW) Spodoptera frugiperda (J.E. Smith) is a highly damaging invasive omnivorous pest that has developed varying degrees of resistance to commonly used insecticides. To investigate the molecular mechanisms of tolerance to tetraniliprole, spinetoram, and emamectin benzoate, the enzyme activity, synergistic effect, and RNA interference were implemented in S. frugiperda. The functions of cytochrome P450 monooxygenase (P450) in the tolerance to tetraniliprole, spinetoram, and emamectin benzoate in S. frugiperda was determined by analysing changes in detoxification metabolic enzyme activity and the effects of enzyme inhibitors on susceptibility to the three insecticides. 102 P450 genes were screened via transcriptome and genome, of which 67 P450 genes were differentially expressed in response to tetraniliprole, spinetoram, and emamectin benzoate and validated by quantitative real-time PCR. The expression patterns of CYP9A75, CYP340AA4, CYP340AX8v2, CYP340L16, CYP341B15v2, and CYP341B17v2 were analysed in different tissues and at different developmental stages in S. frugiperda. Silencing CYP340L16 significantly increased the susceptibility of S. frugiperda to tetraniliprole, spinetoram, and emamectin benzoate. Furthermore, knockdown of CYP340AX8v2, CYP9A75, and CYP341B17v2 significantly increased the sensitivity of S. frugiperda to tetraniliprole. Knockdown of CYP340AX8v2 and CYP340AA4 significantly increased mortality of S. frugiperda to spinetoram. Knockdown of CYP9A75 and CYP341B15v2 significantly increased the susceptibility of S. frugiperda to emamectin benzoate. These results may help to elucidate the mechanisms of tolerance to tetraniliprole, spinetoram and emamectin benzoate in S. frugiperda.

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.

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.

Exposure to sublethal concentrations of thiacloprid insecticide modulated the expression of microRNAs in honeybees (Apis mellifera L.)

This study aimed to investigate the sublethal effects of thiacloprid on microRNA (miRNA) expression in honeybees (Apis mellifera L.) and the role of a specific miRNA, ame-miR-283-5p, in thiacloprid resistance. The high-throughput small RNA-sequencing was used to analyze global miRNA expression profile changes in honeybees orally exposed to sublethal concentrations of thiacloprid (20 mg/L and 4 mg/L) for 72 h. Thiacloprid at 20 mg/L had no observed adverse effects. In addition, bees were fed with miRNA mimics or inhibitors to increase or decrease ame-miR-283-5p expression, and its effects on P450 gene expression (CYP9Q2 and CYP9Q3) were examined. Thiacloprid susceptibility was also detected. The results showed that treatment with thiacloprid at 20 mg/L and 4 mg/L induced 11 and five differentially expressed miRNAs (DEMs), respectively. Bioinformatic analysis suggested that the DEMs are mainly involved in the regulation of growth and development, metabolism, nerve conduction, and behavior. ame-miR-283-5p was downregulated by both concentrations, which was validated using quantitative real-time reverse transcription PCR analysis. Enhancing ame-miR-283-5p expression significantly inhibited CYP9Q2 mRNA and protein expression, and increased thiacloprid toxicity, while reducing ame-miR-283-5p expression significantly promoted CYP9Q2 expression, and decreased thiacloprid susceptibility. Our study revealed a novel role of miRNAs in insecticide resistance in honeybees.

A Genetic Compensation Phenomenon and Global Gene Expression Changes in Sex-miR-2766-3p Knockout Strain of Spodoptera exigua Hübner (Lepidoptera: Noctuidae)

MicroRNAs (miRNAs) drive the post-transcriptional repression of target mRNAs and play important roles in a variety of biological processes. miR-2766-3p is conserved and abundant in Lepidopteran species and may be involved in a variety of biological activities. In this study, Sex-miR-2766-3p was predicted to potentially bind to the 3' untranslated region (UTR) of cap 'n' collar isoform C (CncC) in Spodoptera exigua, and Sex-miR-2766-3p was confirmed to regulate the expression of SeCncC through screening with a luciferase reporter system. Although CRISPR/Cas9 has been extensively utilized to examine insect gene function, studies of miRNA function are still relatively uncommon. Thus, we employed CRISPR/Cas9 to knock out Sex-miR-2766-3p from S. exigua. However, the expression of SeCncC was not significantly altered in the knockout strain (2766-KO) compared with that of the WHS strain. This result suggested that a miRNA knockout might lack phenotypes because of genetic robustness. Additionally, we used transcriptome analysis to examine how the global gene expression patterns of the Sex-miR-2766-3p knockout strain varied. RNA-seq data revealed 1746 upregulated and 2183 downregulated differentially expressed genes (DEGs) in the 2766-KO strain, which might be the result of Sex-miR-2766-3p loss or DNA lesions as the trigger for transcriptional adaptation. GO function classification and KEGG pathway analyses showed that these DEGs were enriched for terms related to binding, catalytic activity, metabolic process, and signal transduction. Our findings demonstrated that S. exigua could compensate for the missing Sex-miR-2766-3p by maintaining the expression of SeCncC by other pathways.