Fenoxycarb and methoxyfenozide (RH-2485) affected development and chitin synthesis through disturbing glycometabolism in Lymantria dispar larvae

Chlorbenzuron downregulated HcLCP-17 expression by depressing two 20E-responsive transcription factors Br-C and βFTZ-F1 in Hyphantria cunea (Lepidoptera: Erebidae) larvae

BACKGROUND

Cuticular proteins (CPs) play essential roles in forming cuticular structures in insects. However, the specific functions and regulatory mechanisms of CPs remain largely unexplored. In this study, the Larval cuticular protein 17 (HcLCP-17) gene was identified from Hyphantria cunea, a highly destructive and polyphagous forest pest. To investigate the role of HcLCP-17 in cuticular function and transcriptional regulation mediated by 20E-responsive transcription factors (ERTFs), we employed RNA interference (RNAi) and yeast one-hybrid assay techniques. Additionally, we examined the molecular mechanism by which chlorbenzuron, a type of benzoylphenylurea (BPU) that functions as a chitin synthesis inhibitor (CSI), affects the 20E signaling pathway and ultimately regulates HcLCP-17 expression.

RESULTS

HcLCP-17 encodes a polypeptide consisting of 393 amino acids, which includes a chitin-binding domain. Silencing HcLCP-17 resulted in a disturbance in the structural organization of the larval cuticle and a notable reduction in chitin levels. HcLCP-17 expression was controlled by the interaction between Broad-Complex (Br-C) and beta Fushi Tarazu Factor-1 (βFTZ-F1) with its promoter fragment. Furthermore, the inhibitory effect of chlorbenzuron on HcLCP-17 expression was found to be potentially mediated by Br-C and βFTZ-F1.

CONCLUSION

The study presents a novel mode of action for the 20E signaling pathway in regulating the expression of CPs and reveals the potential mode-of-action of BPUs in insect cuticles. These findings provide a theoretical basis for future utilization of LCP-17 as a pesticide target making a significant contribution to the development of effective pest management strategies. © 2024 Society of Chemical Industry.

LdAMPKα2 knockdown accelerated the growth but depressed the chitin biosynthesis in Lymantria dispar larvae

AMPK (AMP-activated protein kinase) is a crucial cellular energy sensor across all eukaryotic species. Its multiple roles in maintaining energy homeostasis, regulating cellular metabolic processes have been widely investigated in mammals. In contrast, the function of AMPK in insects has been less reported. Here, we successfully identified three AMPK subunits from Lymantria dispar (L. dispar), a Lepidoptera pest in forestry. Based on that, in particular, the role of AMPK signaling in regulating larval development, as well as chitin biosynthesis was investigated by the application of RNAi-mediated LdAMPKα2 knockdown. The results indicated that knockdown of LdAMPKα2 significantly increased the body weight of L. dispar larvae, and dramatically upregulated the expression of LdmTOR, LdS6K and LdSREBP1, the key genes in mTOR (mammalian target of rapamycin) signaling pathway. While, it significantly reduced the expression of Ld4EBP, a critical repressor of mTOR pathway. Besides, the glucose level was increased and trehalose level was decreased in L. dispar after LdAMPKα2 silencing. Furthermore, we found that the chitin content in the epidermis, as well as the expressions of four key genes in the chitin biosynthesis pathway, LdGFAT, LdPAGM, LdUAP and LdCHSA, were significantly decreased after LdAMPKα2 knockdown. Taken together, these results revealed that AMPK signaling played a pivotal role in regulating the growth and development, as well as carbohydrate metabolism and chitin biosynthesis in L. dispar larvae. The findings expand our understanding of the comprehensive regulatory role of AMPK signaling in insects.

Unraveling the Role of Cuticular Protein 3-like (HvCP3L) in the Chitin Pathway through RNAi and Methoxyfenozide Stress Response in Heortia vitessoides Moore

Cuticle proteins (CPs) constitute a multifunctional family; however, the physiological role of Cuticle Protein 3-like (CP3L) in Heortia vitessoides Moore remains largely unclear. In this study, we cloned the HvCP3L gene from the transcriptional library of Heortia vitessoides Moore. RT-qPCR results revealed that HvCP3L exhibited high expression levels during the larval stage of Heortia vitessoides Moore, particularly at the L5D1 stage, observed in both larval and adult heads. Through RNA interference, we successfully silenced the HvCP3L gene, resulting in a significant reduction in the survival rate of Heortia vitessoides Moore, with the survival rate from larvae to adults plummeting to a mere 17.7%, accompanied by phenotypic abnormalities. Additionally, we observed that the knockdown of HvCP3L led to the inhibition of genes in the chitin pathway. Following exposure to methoxyfenozide stress, the HvCP3L gene exhibited significant overexpression, coinciding with phenotypic abnormalities. These findings underscore the pivotal role of HvCP3L in the growth and development of Heortia vitessoides Moore.

Genome-wide analysis of Panonychus citri microRNAs with a focus on potential insecticidal activity of 4 microRNAs to eggs and nymphs

Panonychus citri McGregor (Acari: Tetranychidae), a destructive citrus pest, causes considerable annual economic losses due to its short lifespan and rapid resistance development. MicroRNA (miRNA)-induced RNA interference is a promising approach for pest control because of endogenous regulation of pest growth and development. To search for miRNAs with potential insecticidal activity in P. citri, genome-wide analysis of miRNAs at different developmental stages was conducted, resulting in the identification of 136 miRNAs, including 73 known and 63 novel miRNAs. A total of 17 isomiRNAs and 12 duplicated miRNAs were characterized. MiR-1 and miR-252-5p were identified as reference miRNAs for P. citri and Tetranychus urticae. Based on differential expression analysis, treatments with miR-let-7a and miR-315 mimics and the miR-let-7a antagomir significantly reduced the egg hatch rate and resulted in abnormal egg development. Overexpression or downregulation of miR-34-5p and miR-305-5p through feeding significantly decreased the adult eclosion rate and caused molting defects. The 4 miRNAs, miR-let-7a, miR-315, miR-34-5p, and miR-305-5p, had important regulatory functions and insecticidal properties in egg hatching and adult eclosion. In general, these data advance our understanding of miRNAs in mite biology, which can assist future studies on insect-specific miRNA-based green pest control technology.

Silencing of Glutamine: Fructose-6-Phosphate Aminotransferase Impairs Growth and Development in Sogatella furcifera (Hemiptera: Delphacidae)

Glutamine: fructose-6-phosphate aminotransferase (GFAT), the fourth enzyme in the chitin synthesis pathway, exerts wide-ranging effects on the growth and development of organisms. However, the role of GFAT in Sogatella furcifera remains unknown. In this study, the functional significance of the GFAT gene of S. furcifera was analyzed using a reverse transcription-polymerase chain reaction and RNA interference (RNAi) analyses. The complementary DNA sequence of SfGFAT was 3162 bp in length and contained a 2067 bp open reading frame encoding 688 amino acid residues. Structural domain analysis indicated that the SfGFAT protein consisted of one glutamine aminotransferase class 2 domain and two sugar isomerase domains. Expression profile analysis revealed that SfGFAT was expressed throughout the egg, nymph, and adult phases and was strongly expressed on the first day of each nymph stage and in the integuments of five tissues. RNAi results revealed that SfGFAT gene silencing significantly inhibited the mRNA expression of the target gene and resulted in severe mortality among S. furcifera. In summary, these findings demonstrate that SfGFAT plays a critical role in the development of S. furcifera. Moreover, these results may aid in the development of methods to control the spread of S. furcifera.

Sublethal effects of halofenozide on larval development and detoxification in Phaedon brassicae (Coleoptera: Chrysomelidae)

The brassica leaf beetle, Phaedon brassicae, is a serious defoliator of cruciferous crops. Halofenozide (Hal), an ecdysone agonist, is a new class of insect growth-regulating insecticide. Our preliminary experiment revealed the outstanding larval toxicity of Hal against P. brassicae. However, the metabolic degradation of this compound in insects remains unclear. In this study, oral administration of Hal at LC10 and LC25 caused severe separation of the cuticle and epidermis, leading to larval molting failure. Sublethal dose exposure also significantly reduced the larval respiration rate as well as their pupation rates and pupal weights. Conversely, the activities of the multifunctional oxidase, carboxylesterase (CarE), and glutathione S-transferase (GST) were significantly enhanced in Hal-treated larvae. Further analysis using RNA sequencing identified 64 differentially expressed detoxifying enzyme genes, including 31 P450s, 13 GSTs, and 20 CarEs. Among the 25 upregulated P450s, 22 genes were clustered into the CYP3 clan, and the other 3 genes belonged to the CYP4 clan. Meanwhile, 3 sigma class GSTs and 7 epsilon class GSTs were dramatically increased, accounting for the majority of the upregulated GSTs. Moreover, 16 of the 18 overexpressed CarEs were clustered into the coleopteran xenobiotic-metabolizing group. These results showed the augmented expression of detoxification genes in P. brassicae after exposed to sublethal dose of Hal, and helped to better understand the potential metabolic pathways that could contribute to the reduced sensitivity to Hal in this pest. Overall, a deep insight into the detoxification mechanisms would provide practical guidance for the field management of P. brassicae.

Effects of lufenuron treatments on the growth and development of Spodoptera frugiperda (Lepidoptera: Noctuidae)

Lufenuron is an effective benzoylurea insecticide that inhibits the synthesis of chitin and regulates the growth of insects. However, little is known about the effects of lufenuron treatment on the development of Spodoptera frugiperda (J. E. Smith). In this study, we assessed the toxicity of lufenuron on S. frugiperda and evaluated the effects of lufenuron treatment on the growth and development of S. frugiperda. The results showed that lufenuron exhibits high insecticidal activity against S. frugiperda, with the LC₅₀ value of 0.99 mg L^-1. Lufenuron treatments can significantly prolong the larval developmental duration and reduce the rates of pupation and emergence. To further explore the underlying mechanism of this observation, the expression profiles of the chitin synthase gene (SfCHS) and chitinase gene (SfCHT), two key enzyme genes involved in the molting of S. frugiperda, were determined after exposure to lufenuron for 96 h. The results of qRT-PCR demonstrated that lufenuron treatments can significantly reduce the expression of SfCHT, while the expression of SfCHS remained relatively stable. Furthermore, we found that lufenuron strongly interacted with chitinase (SfCHT) (-10.8 kcal/mol) and chitin synthase (SfCHS) (R1: -9.7 kcal/mol; R2: -10.2 kcal/mol). Our results indicated that lufenuron has significant effects on the development of S. frugiperda that might be attributed to the differential expression of SfCHT and SfCHS.

Knockdown of GFAT disrupts chitin synthesis in Hyphantria cunea larvae

Glutamine-fructose-6-phosphate transaminase (GFAT) has been reported to regulate the hexosamine biosynthetic pathway as the first rate-limiting enzyme. As a key enzyme that catalyzes the substrate of glycosylation modification, which has a wide-ranging effect on cellular functions. However, there are few studies on the relationship between GFAT and chitin metabolism in insects. In the present study, the GFAT gene from Hyphantria cunea was identified based on transcriptome and bioinformatic analysis. The role of HcGFAT in regulating development and chitin synthesis was analyzed by RNA interference (RNAi) in H. cunea larvae. The full-length HcGFAT gene (2028 bp) encodes a 676 amino acid (aa) polypeptide had typical structural features of the SIS and Gn_AT_II superfamily. Phylogenetic analyses showed that GFAT of H. cunea shares the highest homology and identity with GFAT of Ostrinia furnacalis. Expression profiles indicated that HcGFAT was expressed throughout larval, pupal and three tissues (midgut, fat body, epidermis), and highly expressed in the last instar of larvae and strongly expressed in epidermis among three tissues. Bioassay results showed that knockdown of HcGFAT repressed larval growth and development, resulting in a significant loss of larval body weight. Meanwhile, HcGFAT knockdown also significantly caused larval developmental deformity. Knockdown of HcGFAT regulated the expression of four other critical genes in the chitin synthesis pathway (HcGNA, HcPAGM, HcUAP, HcCHSA), and ultimately resulted in decreased chitin content in the epidermis. In summary, these findings indicated that GFAT plays a critical role in larval growth and development, as well as chitin synthesis in H. cunea.

Transcriptome analysis of emamectin benzoate caused midgut damage by inducing oxidative stress, energy metabolism disorder and apoptosis in gypsy moth (Lymantria dispar)

BACKGROUND

Emamectin benzoate (EMB) is a semisynthetic bioinsecticide, which has been widely used in the control of forestry and agricultural pests. However, the mechanism of its toxic effects on the non-neural tissues has been rarely reported. Here, we explored the mechanism of the midgut damage induced by EMB in gypsy moth (Lymantria dispar) in order to better understand the toxicological mechanism of EMB.

RESULTS

Our results confirmed that EMB caused damage to the midgut of gypsy moth by inducing apoptosis. Transcriptome showed that 1469, 650 and 950 genes were significantly differentially expressed in the midgut of gypsy moth after 24, 48 and 72 h of EMB exposure, and oxidative stress, energy metabolism disorder and apoptosis may be related to the toxic effects of EMB. The indicators related to oxidative stress, energy metabolism and apoptosis were further examined. The results showed that EMB could cause oxidative stress by increasing ROS level and inhibiting antioxidant enzymes (P < 0.05), such as catalase (CAT), superoxide dismutase (SOD), and glutathione peroxidase (GPx), which in turn causes mitochondria injury. Subsequently, energy metabolism was inhibited by downregulating the activities and mRNA level of energy metabolism enzymes. Furthermore, the mitochondrial apoptosis pathway was activated, triggering apoptosis, and eventually causing midgut injury in gypsy moth.

CONCLUSION

Our results indicated that EMB caused damage to midgut by inducing oxidative stress, energy metabolism disorder and apoptosis in gypsy moth. Our findings shed new light on the toxicological mechanism of EMB on non-neural tissues from oxidative stress, energy metabolism and apoptosis perspectives. © 2022 Society of Chemical Industry.

Transcriptomic analysis of interactions between Lymantria dispar larvae and carvacrol

Due to its biological activity, carvacrol (CAR) is widely used in medicine, agriculture, and forestry. Our previous studies showed that in Lymantria dispar larvae, CAR treatment can induce the production of antifeedants and lead to growth inhibition and death of larvae. However, the effect CAR exerts on RNA levels in L. dispar larvae remains unclear. In this study, the Illumina HiSeq4000 sequencing platform was used to sequence the total RNA of L. dispar larvae. A total of six cDNA libraries (three treatments and three controls) were established and 39,807 genes were generated. Compared with the control group, 296 differentially expressed genes (DEGs) (142 up-regulated and 154 down-regulated) were identified after CAR treatment. GO and KEGG enrichment analyses showed that these DEGs mainly clustered in the metabolism of xenobiotics, carbohydrates, and lipids. Furthermore, 12 DEGs were found to be involved in detoxification, including six cytochrome P450s, two esterases, one glutathione peroxidase, one UDP-glycosyltransferase gene, and two genes encoding heat shock proteins. The expression levels of detoxification genes changed under CAR treatment (especially P450s), which further yielded candidate genes for explorations of the insecticidal mechanism of CAR. The reliability of transcriptome data was verified by qRT-PCR. The enzyme activities of CYP450 and acid phosphatase significantly increased (by 38.52 U/mg·prot and 0.12 μmol/min·mg, respectively) 72 h after CAR treatment. However, the activity of alkaline phosphatase did not change significantly. These changes in enzyme activity corroborated the reliability of the transcriptome data at the protein level. The results of GO enrichment analysis of DEGs indicated that CAR influenced the oxidation-reduction process in L. dispar larvae. Furthermore, CAR can cause oxidative stress in L. dispar larvae, identified through the determination of peroxidase and polyphenol oxidase activities, total antioxidant capacity, and hydrogen peroxide content. This study provides useful insight into the insecticidal mechanism of CAR.

3-Bromopyruvate-induced glycolysis inhibition impacts larval growth and development and carbohydrate homeostasis in fall webworm, Hyphantria cunea Drury

As a typical glycolytic inhibitor, 3-bromopyruvate (3-BrPA) has been extensively studied in cancer therapy in recent decades. However, few studies focused on 3-BrPA in regulating the growth and development of insects, and the relationship and regulatory mechanism between glycolysis and chitin biosynthesis remain largely unknown. The Hyphantria cunea, named fall webworm, is a notorious defoliator, which caused a huge economic loss to agriculture and forestry. Here, we investigated the effects of 3-BrPA on the growth and development, glycolysis, carbohydrate homeostasis, as well as chitin synthesis in H. cunea larvae. To elucidate the action mechanism of 3-BrPA on H. cunea will provide a new insight for the control of this pest. The results showed that 3-BrPA dramatically restrained the growth and development of H. cunea larvae and resulted in larval lethality. Meanwhile, we confirmed that 3-BrPA caused a significant decrease in carbohydrate, adenosine triphosphate (ATP), pyruvic acid (PA), and triglyceride (TG) levels by inhibiting glycolysis in H. cunea larvae. Further studies indicated that 3-BrPA significantly affected the activities of hexokinase (HK), phosphofructokinase (PFK), pyruvate kinase (PK), glucose 6-phosphate dehydrogenase (G6PDH) and trehalase, as well as expressions of the genes related to glycolysis, resulting in carbohydrate homeostasis disorder. Moreover, it was found that 3-BrPA enhanced 20-hydroxyecdysone (20E) signaling by upregulating HcCYP306A1 and HcCYP314A1, two critical genes in 20E synthesis pathway, and accelerated chitin synthesis by upregulating transcriptional levels of genes in the chitin synthesis pathway in H. cunea larvae. Taken together, our findings provide a novel insight into the mechanism of glycolytic inhibitor in regulating the growth and development of insects, and lay a foundation for the potential application of glycolytic inhibitors in pest control as well.

Determination of 12 insect growth regulator residues in foods of different matrixes by modified QuEChERS and UPLC-MS/MS

An analytical method was developed and validated for the simultaneous determination of 12 insect growth regulators (IGRs) (buprofezin, cyantraniliprole, flubendiamide, flonicamid, tolfenpyrad, chlorantraniliprole, RH-5849, methoxyfenozide, chromafenozide, tebufenozide, pyriproxyfen and fenoxycarb) in foods collected from different matrixes by modified QuEChERS and ultraperformance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). The samples were ultrasonically extracted with acetonitrile containing 0.5% formic acid, and different QuEChERS purification conditions were optimized for different matrixes (vegetable oil, fruit and tea). 12 IGRs were separated on a Plus C18 column, and detected by MS/MS under multiple reaction monitoring (MRM) mode. The developed method was validated in terms of linearity, matrix effect, accuracy and precision. Acceptable recoveries of IGRs in three different substrates (vegetable oil, tea and fruit) at three spiked levels were in the range of 65.47-95.17%, 80.55-110.15%, and 62.02-96.50%, respectively, with RSDs less than 11.58%. The method showed a good linearity (R 2 ≥ 0.9994) for all analytes in the range of 0.2-200 μg L-1. The LODs (S/N = 3) and LOQs (S/N = 10) of the method were 0.04-0.40 μg kg-1, and 0.13-1.24 μg kg-1, respectively. Owing to the advantages of simple operation, high accuracy and sensitivity, this method is suitable for the rapid and simultaneous detection of 12 IGRs in vegetable oil, tea and fruit.

One step extraction followed by HPLC-ESI-MS/MS for multi-residue analysis of diacylhydrazine insecticides in water, sediment, and aquatic products

A multi-residue analysis of six diacylhydrazine insecticides in water, sediment, and aquatic products was established by liquid chromatography triple quadrupole tandem mass spectrometry (LC-MS/MS). The water sample was extracted with acetonitrile by low-temperature enrichment liquid-liquid extraction technology. The sediment and aquatic products were prepared using QuEChERS technique. Method validation showed perfect linearity with correlation coefficients (R) more than 0.9992 for all insecticides, and the matrix effects were nearly negligible (-1.42% to -0.27%) for water, sediment and aquatic products. The recoveries were 80.0-99.7% at three spiked levels (0.02 ng·mL^-1, 0.1 ng·mL^-1, 0.5 ng·mL^-1; 2.0, 10, and 50 ng·g^-1) and the precisions (intra-day and inter-day precision) were lower than 5.28%, with the low LODs (3.8 ~ 9.6 pg·mL^-1; 0.38-0.96 ng·g^-1) and LOQs (12.7 ~ 32.0 pg·mL^-1; 1.27-3.20 ng·g^-1) for water, sediment, and aquatic products, indicating the good accuracy and precision of the proposed method. The applicability, efficiency, and sensitivity of this method have been proved in the analysis of six diacylhydrazine insecticides in water, sediment, and crucian carp in Rice- crucian carp - integrated planting system.

Dissecting the roles of FTZ-F1 in larval molting and pupation, and the sublethal effects of methoxyfenozide on Helicoverpa armigera

BACKGROUND

In holometabolous insects, the major developmental transitions - larval molting and pupation - are triggered by a pulse of 20-hydroxyecdysone (20E) and coordinated by juvenile hormone. Methoxyfenozide (MF), an ecdysteroid agonist, represents a new class of insect growth regulators and is effective against lepidopteran pests. Fushi-tarazu factor 1 (FTZ-F1) is an ecdysone-inducible transcription factor. To date, the effect of MF on 20E-response genes remains unclear, and we speculate the involvement of FTZ-F1 in MF's growth regulating effect.

RESULTS

MF at LC₂₅ and LC₁₀ caused severe ecdysis failure in Helicoverpa armigera, extended their larval duration, lowered their pupal weight, and reduced the respiratory, pupation and emergence rates. Furthermore, sublethal doses of MF inhibited ecdysteroidogenesis and lowered the intrinsic 20E titer, but showed an inductive effect on 20E-response genes including HaFTZ-F1. HaFTZ-F1, predominantly expressed in larval epidermis, was markedly upregulated before or right after larval ecdysis, and maintained a high level in prepupal stage. Knockdown of HaFTZ-F1 in 4th-instar larvae severely impaired larval ecdysis, whereas its knockdown in final-instar larvae caused abnormal pupation. Moreover, knocking down HaFTZ-F1 downregulated three critical ecdysteroidogenesis genes, lowered 20E titer, and suppressed the expression of 20E receptors and 20E-response genes. The introduction of 20E into HaFTZ-F1-RNAi larvae partly relieved the negative effects on the 20E-induced signaling cascade.

CONCLUSION

Our findings reveal the adverse effects of sublethal doses of MF on the development of H. armigera and elucidate the resulting perturbations on the 20E-induced signaling cascade; we propose that HaFTZ-F1 regulates ecdysis and pupation by mediating 20E titer and its signaling pathway. © 2020 Society of Chemical Industry.