The overexpression of three cytochrome P450 genes CYP6CY14, CYP6CY22 and CYP6UN1 contributed to metabolic resistance to dinotefuran in melon/cotton aphid, Aphis gossypii Glover

Nanoparticle-Mediated dsRNA Delivery Used as a Broad-Spectrum Synergistic Nanonucleic Acid Adjuvant to Control Sogatella furcifera

The enhanced detoxification capacity caused by the induction or constitutive overexpression of metabolic enzyme genes has complicated sustainable and efficient pest control strategies. This study clarified the detoxification effects of two P450 genes, CYP4CE3 and CYP6FJ3, on multiple insecticides in Sogatella furcifera. The chimeric double-stranded RNA (ch-dsRNA) of these two genes was obtained by using the L4440-HT1115 (DE3) RNase III- system, and the RNA interference (RNAi) effectiveness of ch-dsRNA was verified by microinjection. MON-NH2 was subsequently used to deliver dsRNA as a synergist (MON-NH2@ch-dsRNA) to effectively protect dsRNA from nuclease degradation and stably inhibit CYP4CE3 and CYP6FJ3 expression through insect sap-feeding. Compared with the single insecticide application, the addition of MON-NH2@ch-dsRNA led to an increase in the mortality rates of imidacloprid, clothianidin, dinotefuran, and sulfoxaflor by 22.22-38.90%, with the synergistic enhancement of nitenpyram, yielding a ratio of 1.90-fold. Moreover, the field experiment results revealed that the control effect of nitenpyram was significantly improved by 14.53 and 10.30% on days 3 and 7, respectively, following the application of MON-NH2@ch-dsRNA. Therefore, MON-NH2@ch-dsRNA can be used as a nucleic acid nanosynergist with a broad-spectrum synergistic effect on insecticides in controlling S. furcifera.

Application of omics technology in ecotoxicology of arthropod in farmland

Arthropods, abundant in farmland, have unique biological traits that make them valuable for studying the ecotoxicological impacts of pollutants. Recent advancements in multi-omics technologies have enhanced their use in assessing pollution risks and understanding toxicity mechanisms. This article reviews recent developments in applying omics technologies-genomics, transcriptomics, proteomics, metabolomics, and meta-omics-to ecotoxicological research on farmland arthropods. Agricultural arthropods manage genes and proteins, such as metallothioneins, antioxidant enzyme systems, heat shock proteins, cytochrome P450, carboxylesterases, and glutathione S-transferases, for detoxification and antioxidant purposes. They adjust amino acid, sugar, and lipid metabolism to counteract pollutant-induced energy drain and modify gut microbiota to aid in detoxification. This study advocates for enhanced analysis of compound pollution and emerging pollutants using multi-omics, especially meta-omics, to clarify the toxicological mechanisms underlying arthropod responses to these pollutants. Furthermore, it underscores the urgent need for subsequent gene function mining and validation to support biological control strategies and promote sustainable agricultural practices. The findings of this research provide significant insights into the toxicological impacts and mechanisms of pollutants within farmland ecosystems, thereby contributing to the preservation of arthropod diversity.

Cythochrome P450-mediated dinotefuran resistance in onion thrips, Thrips tabaci

Onion thrips, Thrips tabaci, have developed resistance to many insecticides, and over the last decade, resistant populations have spread widely across Japan. The cytochrome P450 (CYP) family, a widely conserved detoxification enzyme that metabolizes xenobiotics such as insecticides and phytochemicals, is believed to play important roles in the development of resistance in T. tabaci. However, CYPs involved in insecticide resistance in T. tabaci remain unclear. To comprehensively identify CYPs in T. tabaci, the genome sequences of the thelytokous T. tabaci (ANO strain) were constructed, and 18,965 genes (protein coding) were predicted. We identified 127 CYP genes in the predicted gene set by manual curation, and 38 of these CYP genes belonged to the CYP3 clan, including genes from the CYP6 family, which is one of the most important CYP families involved in resistance to neonicotinoids in many insect pests. To identify the CYPs involved in resistance to dinotefuran, which is one of the neonicotinoids used to control T. tabaci, RNA sequencing of dinotefuran-resistant and dinotefuran-susceptible strains was performed. Results revealed that, TtCYP3652A1, which belongs to the thrips-specific CYP3652A subfamily in the CYP3 clan, was significantly upregulated in the resistant strain. In vitro CYP metabolism assays using insect cells were conducted for TtCYP3652A1 and five highly expressed CYP6 genes. Only TtCYP3652A1 significantly metabolized dinotefuran, which is considered to contribute to detoxification of dinotefuran. As no amino acid mutations were identified in the known target-site genes of neonicotinoids, TtCYP3652A1 was considered to be the main factor involved in the resistance to dinotefuran.

Molecular insights on the function of CYP380C12 in Aphis gossypii Glover (Hemiptera: Aphididae): in silico and RNAi analyses

Aphis gossypii Glover is a serious pest that causes significant economic losses and is difficult to control due to the rapid development of resistance to neonicotinoids. Insect cytochrome P450s play an important role in detoxification of insecticides. In this study, we aimed to understand the function of CYP380C12 in A. gossypii. The CYP380C12 gene of A. gossypii was cloned and characterized, and its relative expression level differed among instars. The expression of CYP380C12 increased by 48.5% compared with the Water group under imidacloprid (IMI) stress for 48 h. Molecular docking predicted the binding free energy of CYP380C12 and IMI was -7.0 kcal/mol, indicating an excellent stability at the docked active site, which was verified by molecular dynamics simulations. Subsequently, silencing efficiency of CYP380C12 in the dsCYP380C12 treatment group reached 48.9%, 47.0%, and 40.0% at 24, 48, and 72 h, and the mortality of A. gossypii treated with IMI was 1.45- and 1.38-fold that of the Water and dsGFP control groups, respectively. Moreover, the reproductive period of aphids treated with dsCYP380C12 (9.67 ± 0.88) was significantly shorter than that of those sprayed with Water (13.67 ± 1.20). Taken together, these results indicated that silencing CYP380C12 not only increases sensitivity of A. gossypii to IMI but also shortens its reproductive period. Understanding the function of CYP380C12 in A. gossypii can provide new insights for developing innovative strategies to control A. gossypii.

Both insertion mutation and low expression of nicotinic acetylcholine receptor Nlα4 subunit are associated with sulfoxaflor resistance in Nilaparvata lugens

BACKGROUND

Sulfoximine insecticide sulfoxaflor acts on insect nicotinic acetylcholine receptors (nAChRs). Metabolic resistance arising from increased activity of detoxification enzymes has been extensively documented in insect populations. Prior research by the present authors demonstrated the involvement of cytochrome P450 monooxygenases in mediating metabolic resistance to sulfoxaflor in Nilaparvata lugens. Nevertheless, investigations into the target-site resistance mechanisms of insects to sulfoxaflor remain limited.

RESULTS

The coding sequence (CDS) of 13 nAChR subunits in N. lugens of sulfoxaflor-susceptible (SFX-S) and sulfoxaflor-resistant (SFX-R) strains were cloned. A 'TGAC' insertion mutation at position 1428-1431 of the Nlα4 CDS was identified in the SFX-R strain. Genotyping revealed that 60% of individuals in the SFX-R strain carried the homozygous mutation, while 40% were heterozygous. Additionally, a homozygous mutant (Nlα4-M) strain was established for further investigation. Compared with the SFX-S [median lethal concentration (LC50) = 3.32 mg/L] strain, the expression levels of Nlα4 in the SFX-R (LC50 = 505.64 mg/L) and Nlα4-M (LC50 = 352.72 mg/L) strains were significantly down-regulated by 83.02% and 46.38%, respectively. Genetic linkage analysis confirmed a co-segregation of the Nlα4 mutation and its reduced expression with sulfoxaflor resistance in N. lugens. Furthermore, RNA interference (RNAi) targeting Nlα4 expression in both the SFX-S and Nlα4-M strains significantly decreased susceptibility to sulfoxaflor.

CONCLUSION

The results indicate that both the insertion mutation and low expression of the Nlα4 subunit are strongly associated with sulfoxaflor resistance in N. lugens. The present study offers valuable theoretical insights for the rational design of novel insecticides and the effective management of insecticide resistance in N. lugens. © 2025 Society of Chemical Industry.

Transcription factor CREB/ATF regulates overexpression of CYP6CY14 conferring resistance to cycloxaprid in Aphis gossypii

Aphis gossypii Glover as a destructive agricultural pest has evolved resistance to various insecticides. Cycloxaprid is a novel structure neonicotinoid insecticide with excellent toxicity against A. gossypii. However, the resistance mechanism of A. gossypii to cycloxaprid was unclear. In the present study, a cycloxaprid-resistant (Cpd-R) strain (80.1-fold) of A. gossypii was obtained by continuous selection. Bioassay results showed that piperonyl butoxide significantly increased the toxicity of cycloxaprid by 10.5-fold to the Cpd-R strain. The activity of P450s was significantly higher in Cpd-R strain than in susceptible (Cpd-S) strain. The transcriptomic and qRT-PCR results showed that CYP6CY14, CYP380C44 and CYP303A1 were significantly upregulated in Cpd-R strain compared with Cpd-S strain. Furthermore, knockdown of CYP6CY14, CYP380C44 and CYP303A1 via RNA interference (RNAi) significantly increased the sensitivity of Cpd-R strain to cycloxaprid. Based on the higher expression of CYP6CY14 and RNAi results, transgenic Drosophila assay was conducted to further clarify the role of CYP6CY14 in cycloxaprid resistance, and results showed a significant increase in resistance to cycloxaprid in D. melanogaster. Additionally, the results of RNAi, dual-luciferase reporter and yeast one-hybrid (Y1H) indicated that CREB/ATF directly regulates CYP6CY14 expression. These findings provide necessary basis for clarifying the resistance mechanism of cycloxaprid in A. gossypii.

Endosymbionts as hidden players in tripartite pathosystem of interactions and potential candidates for sustainable viral disease management

The convoluted relationships between plants, viruses, and arthropod vectors housing bacterial endosymbionts are pivotal in the spread of harmful plant viral diseases. Endosymbionts play key roles in: manipulating host responses, influencing insect resistance to pesticides, shaping insect evolution, and bolstering virus acquisition, retention, and transmission. This interplay presents an innovative approach for developing sustainable strategies to manage plant diseases. Recent progress in targeting specific endosymbionts through genetic modifications, biotechnological advancements, and RNA interference shows potential for curbing viral spread and disease progression. Additionally, employing synthetic biology techniques like CRISPR/Cas9 to engineer endosymbionts and disrupt crucial interactions necessary for viral transmission in arthropod vectors holds promise for effective control measures. In this review, these obligate and facultative bacterial cruxes have been discussed to elaborate on their mechanistic involvement in the regulation and/or inhibition of tripartite pathways of interactions. Furthermore, we provide an in-depth understanding of endosymbionts' synergistic and antagonistic effects on: insect biology, plant immunity, and virus acquisition and transmission. Finally, we point out open questions for future research and provide research directions concerning the deployment of genetically engineered symbionts to affect plant-virus-vector interactions for sustainable disease management. By addressing existing knowledge gaps and charting future research paths, a deeper comprehension of the role of endosymbionts in plant-virus-vector interactions can pave the way for innovative and successful disease management strategies. The exploration of antiviral therapies, paratransgenesis, and pathogen-blocking tactics using engineered endosymbionts introduces pioneering solutions for lessening the impact of plant viral diseases and green pest management.

CYP4CE1 Metabolized Nitenpyram through Two Types of Oxidation Reaction, Hydroxylation, and N-Demethylation

Nitenpyram, taking the place of imidacloprid, is a widely used neonicotinoid insecticide to control Nilaparvata lugens in Asia. Two P450s, CYP4CE1 and CYP6ER1, are key factors in the metabolic resistance against nitenpyram and imidacloprid. In this study, we found that CYP4CE1 expression was strongly associated with nitenpyram resistance in 8 field-collected populations, whereas CYP6ER1 expression correlated with imidacloprid resistance. Hence, we focused on nitenpyram metabolism by CYP4CE1, due to that imidacloprid metabolism by CYP6ER1 has intensively investigated. Mass spectrometry analysis revealed that recombinant CYP4CE1 metabolized nitenpyram into three products, N-desmethyl nitenpyram, hydroxy-nitenpyram, and N-desmethyl hydroxy-nitenpyram, with a preference for hydroxylation. In contrast, CYP6ER1 metabolized nitenpyram into a single product, N-desmethyl nitenpyram. These results provide new insights into the specific catalytic mechanisms of P450 enzymes in neonicotinoid metabolism and underscore the importance of different catalytic reactions in neonicotinoid insecticide resistance.

UDP-Glycosyltransferases UGT350C3 and UGT344L7 Confer Tolerance to Neonicotinoids in Field Populations of Aphis gossypii

The cotton aphid, Aphis gossypii, is a polyphagous pest that stunts host plant growth via direct feeding or transmitting plant virus. Due to the long-term application of insecticides, A. gossypii has developed different levels of resistance to numerous insecticides. We found that five field populations had evolved multiple resistances to neonicotinoids. To explore the resistance mechanism mediated by uridine diphosphate glycosyltransferases (UGTs), two upregulated UGT genes in these five strains, UGT350C3 and UGT344L7, were selected for functional analysis of their roles in neonicotinoid detoxification. Transgenic Drosophila bioassay results indicated that compared with the control lines, the UGT350C3 and UGT344L7 overexpression lines were more tolerant to thiamethoxam, imidacloprid, and dinotefuran. Knockdown of UGT350C3 and UGT344L7 significantly increased A. gossypii sensitivity to thiamethoxam, imidacloprid, and dinotefuran. Molecular docking analysis demonstrated that these neonicotinoids could bind to the active pockets of UGT350C3 and UGT344L7. This study provides functional evidence of neonicotinoid detoxification mediated by UGTs and will facilitate further work to identify strategies for preventing the development of neonicotinoid resistance in insects.

Genome-Wide Comparative Analysis of the Cytochrome P450 Monooxygenase Family in 19 Aphid Species and Their Expression Analysis in 4 Cereal Crop Aphids

Cytochrome P450 monooxygenases (CYP450s) play a variety of physiological roles, including pesticide resistance, plant allelochemical detoxification, and hormone metabolism catalysis. However, limited information is available on the classification and expression profiles of the CYP450 gene family in aphid species. This is the first study to identify the cytochrome P450 gene family in 19 aphid species at the whole genome level. A total of 1100 CYP450 genes were identified in 19 aphid species. Three hundred CYP450 genes belonged to six cereal crop aphid species, which were further classified into four subfamilies according to the phylogenetic relationship. The conserved motifs, exon-intron structures, and genomic organization of the same subfamilies were similar. Predictions of subcellular localization revealed that the endoplasmic reticulum harbored the majority of CYP450 proteins. In Sitobion avenae and Rhopalosiphum maidis, the increase in the CYP450 gene was primarily caused by segmental duplication events. However, only tandem duplication occurred in the CYP450 gene family of Diuraphis noxia, Rhopalosiphum padi, Schizaphis graminum, and Sitobion miscanthi. Synteny analysis found three continuous colinear CYP450 gene pairs among six cereal crop aphid species. Furthermore, we obtained the expression profiles of four cereal crop aphids, including R. padi, D. noxia, S. graminum, and S. avenae. Differential expression analysis provided growth stage specificity genes, tissue specificity genes, organ specificity genes and some detoxification metabolic genes among these four cereal crop aphids. Meanwhile, their expression patterns were showed. The related functions and pathways of CYP450s were revealed by GO and KEGG enrichment analysis. Above all, we picked the differentially expressed CYP450 genes from all of the differentially expressed genes (DEGs). These differentially expressed CYP450 genes provided some new potential candidates for aphid control and management. This work establishes the foundation for further investigations into the regulatory functions of the CYP450 gene family in aphid species and beyond.

CF2-II Alternative Splicing Isoform Regulates the Expression of Xenobiotic Tolerance-Related Cytochrome P450 CYP6CY22 in Aphis gossypii Glover

The expression of P450 genes is regulated by trans-regulatory factors or cis-regulatory elements and influences how endogenous or xenobiotic substances are metabolized in an organism's tissues. In this study, we showed that overexpression of the cytochrome P450 gene, CYP6CY22, led to resistance to cyantraniliprole in Aphis gossypii. The expression of CYP6CY22 increased in the midgut and remaining carcass of the CyR strain, and after repressing the expression of CYP6CY22, the mortality of cotton aphids increased 2.08-fold after exposure to cyantraniliprole. Drosophila ectopically expressing CYP6CY22 exhibited tolerance to cyantraniliprole and cross-tolerance to xanthotoxin, quercetin, 2-tridecanone, tannic acid, and nicotine. Moreover, transcription factor CF2-II (XM_027994540.2) is transcribed only as the splicing variant isoform CF2-II-AS, which was found to be 504 nucleotides shorter than CF2-II in A. gossypii. RNAi and yeast one-hybrid (Y1H) results indicated that CF2-II-AS positively regulates CYP6CY22 and binds to cis-acting element p (-851/-842) of CYP6CY22 to regulate its overexpression. The above results indicated that CYP6CY22 was regulated by the splicing isoform CF2-II-AS, which will help us further understand the mechanism of transcriptional adaption of cross-tolerance between synthetic insecticides and plant secondary metabolites mediated by P450s.

A chromosome-level genome assembly of the Rhus gall aphid Schlechtendalia chinensis provides insight into the endogenization of Parvovirus-like DNA sequences

The Rhus gall aphid, Schlechtendalia chinensis, feeds on its primary host plant Rhus chinensis to induce galls, which have economic importance in medicines and the food industry. Rhus gall aphids have a unique life cycle and are economically beneficial but there is huge gap in genomic information about this group of aphids. Schlechtendalia chinensis induces rich-tannin galls on its host plant and is emerging as a model organism for both commercial applications and applied research in the context of gall production by insects. Here, we generated a high-quality chromosome-level assembly for the S. chinensis genome, enabling the comparison between S. chinensis and non-galling aphids. The final genome assembly is 344.59 Mb with 91.71% of the assembled sequences anchored into 13 chromosomes. We predicted 15,013 genes, of which 14,582 (97.13%) coding genes were annotated, and 99% of the predicted genes were anchored to the 13 chromosomes. This assembly reveals the endogenization of parvovirus-related DNA sequences (PRDs) in the S. chinensis genome, which could play a role in environmental adaptations. We demonstrated the characterization and classification of cytochrome P450s in the genome assembly, which are functionally crucial for sap-feeding insects and have roles in detoxification and insecticide resistance. This genome assembly also revealed the whole genome duplication events in S. chinensis, which can be considered in comparative evolutionary analysis. Our work represents a reference genome for gall-forming aphids that could be used for comparative genomic studies between galling and non-galling aphids and provides the first insight into the endogenization of PRDs in the genome of galling aphids. It also provides novel genetic information for future research on gall-formation and insect-plant interactions.

Validation of biomarkers for neonicotinoid exposure in Folsomia candida under mutual exposure to diethyl maleate

Neonicotinoid insecticides are harmful to non-target soil invertebrates, which are crucial for sustainable agriculture. Gene expression biomarkers could provide economic and high-throughput metrics of neonicotinoid exposure and toxicity to non-target invertebrates. Thereby, biomarkers can help guide remediation efforts or policy enforcement. Gene expression of Glutathione S-Transferase 3 (GST3) has previously been proposed as a biomarker for the neonicotinoid imidacloprid in the soil ecotoxicological model species Folsomia candida (Collembola). However, it remains unclear how reliably gene expression of neonicotinoid biomarkers, such as GST3, can indicate the exposure to the broader neonicotinoid family under putative GST enzymatic inhibition. In this work, we exposed springtails to two neonicotinoids, thiacloprid and imidacloprid, alongside diethyl maleate (DEM), a known GST metabolic inhibitor that imposes oxidative stress. First, we determined the influence of DEM on neonicotinoid toxicity to springtail fecundity. Second, we surveyed the gene expression of four biomarkers, including GST3, under mutual exposure to neonicotinoids and DEM. We observed no effect of DEM on springtail fecundity. Moreover, the expression of GST3 was only influenced by DEM under mutual exposure with thiacloprid but not with imidacloprid. The results indicate that GST3 is not a robust indicator of neonicotinoid exposure and that probable GST enzymatic inhibition mediates the toxicity of imidacloprid and thiacloprid differentially. Future research should investigate biomarker reliability under shifting metabolic conditions such as provided by DEM exposure.

Overexpression of NADPH-cytochrome P450 reductase is associated with sulfoxaflor resistance and neonicotinoid cross-resistance in Nilaparvata lugens (Stål)

Nicotinamide adenine dinucleotide phosphate (NADPH)-cytochrome P450 reductase (CPR), a crucial electron-transfer partner of P450 systems, is required for various biological reactions catalyzed by P450 monooxygenase. Our previous study indicated that enhanced P450 enzyme detoxification and CYP6ER1 overexpression contributed to sulfoxaflor resistance in Nilaparvata lugens. However, the association between CPR, sulfoxaflor resistance, and neonicotinoid cross-resistance in N. lugens remains unclear. In this study, the sulfoxaflor-resistant (SFX-SEL) (RR = 254.04-fold), resistance-decline (DESEL) (RR = 18.99-fold), and susceptible unselected (UNSEL) strains of N. lugens with the same genetic background were established. Real-time quantitative polymerase chain reaction (RT-qPCR) revealed that the N. lugens CPR (NlCPR) expression level in the SFX-SEL strain was 6.85-fold and 6.07-fold higher than in UNSEL and DESEL strains, respectively. NlCPR expression was significantly higher in the abdomens of UNSEL, DESEL, and SFX-SEL fourth-instar nymphs than in other tissues (thoraxes, heads, and legs). Additionally, sulfoxaflor stress significantly increased NlCPR mRNA levels in the UNSEL, SFX-SEL and DESEL strains. NlCPR silencing by RNA interference (RNAi) dramatically increased the susceptibility of the UNSEL, DESEL, and SFX-SEL strains to sulfoxaflor, but the recovery of SFX-SEL was more obvious. Furthermore, NlCPR silencing led to a significant recovery in susceptibility to nitenpyram, dinotefuran, clothianidin, and thiamethoxam across all strains (UNSEL, DESEL, and SFX-SEL), with the greatest degree of recovery in the sulfoxaflor-resistant strain (SFX-SEL). Our findings suggest that NlCPR overexpression contributes to sulfoxaflor resistance and neonicotinoid cross-resistance in N. lugens. This will aid in elucidating the significance of CPR in the evolution of P450-mediated metabolic resistance in N. lugens.

Chromosome-level genome assembly of the spotted alfalfa aphid Therioaphis trifolii

The spotted alfalfa aphid (SAA, Therioaphis trifolii) (Hemiptera: Aphididae) is a destructive pest of cultivated alfalfa (Medicago sativa L.) that leads to large financial losses in the livestock industry around the world. Here, we present a chromosome-scale genome assembly of T. trifolii, the first genome assembly for the aphid subfamily Calaphidinae. Using PacBio long-read sequencing, Illumina sequencing, and Hi-C scaffolding techniques, a 541.26 Mb genome was generated, with 90.01% of the assembly anchored into eight scaffolds, and the contig and scaffold N50 are 2.54 Mb and 44.77 Mb, respectively. BUSCO assessment showed a completeness score of 96.6%. A total of 13,684 protein-coding genes were predicted. The high-quality genome assembly of T. trifolii not only provides a genomic resource for the more complete analysis of aphid evolution, but also provides insights into the ecological adaptation and insecticide resistance of T. trifolii.

Resistance to dinotefuran in Bemisia tabaci in China: status and characteristics

BACKGROUND

Bemisia tabaci (Gennadius) is a serious agricultural pest worldwide. Neonicotinoids are the most important new class of synthetic insecticides used in the management of B. tabaci. However, B. tabaci populations have developed resistance to various active ingredients in neonicotinoids following long-term and widespread application.

RESULTS

Dinotefuran exhibited high toxicity against most B. tabaci field populations. One population (Din-R) with a high level of resistance to dinotefuran (255.6-fold) was first identified in the field. The Din-R population exhibited medium to high levels of resistance to all the tested neonicotinoid insecticides and a high level of resistance to spinetoram. Genetic inheritance analysis revealed that resistance to dinotefuran was incompletely recessive and polygenic. The synergist piperonyl butoxide significantly increased the toxicity of dinotefuran to Din-R. P450 activity in the Din-R population was 2.19-fold higher than in the susceptible population. RNA-sequencing analysis showed that 12 P450 genes were significantly upregulated in the Din-R population, of which CYP6DW5, CYP6JM1 and CYP306A1 were found to exhibit more than 3.00-fold higher expression in Din-R when using a reverse transcription quantitative real-time polymerase chain reaction. Expression of eight P450 genes was obviously induced by dinotefuran, and CYP6DW5 showed the highest expression level. After knockdown of CYP6DW5 in Din-R, the toxicity of dinotefuran increased significantly.

CONCLUSION

P450 had a crucial role in dinotefuran resistance in B. tabaci, and CYP6DW5 was involved in the resistance. These results provide important information for the management of resistance in B. tabaci and improve our understanding of the resistance mechanism of dinotefuran. © 2022 Society of Chemical Industry.

Effects of transgenic cotton lines expressing dsAgCYP6CY3-P1 on the growth and detoxification ability of Aphis gossypii glover

BACKGROUND

The pest Aphis gossypii Glover globally causes considerable economic losses on various crops by its feeding damage and disease transmission. Transgenic plants that produce double-stranded RNA (dsRNA) targeted to insect genes are being developed as a pest control strategy. In this study, we evaluated the effects of transgenic cotton-mediated RNA interference (RNAi) on the growth and detoxification ability of A. gossypii after the transgenic cotton lines expressing dsAgCYP6CY3-P1 (the TG cotton lines) were obtained on the basis of exploring the functions of CYP6CY3 in our previous research.

RESULTS

The developmental time of third- and fourth-instar nymphs which fed on the TG cotton lines were significantly prolonged. Life table parameters showed that the fitness of cotton aphids from the TG cotton lines decreased. Additionally, the relative expression level of CYP6CY3 in cotton aphids which fed on the TG cotton lines was significantly reduced by 47.3 % at 48 h compared with that from the nontransgenic cotton (the NT cotton). Bioassay showed that silencing of CYP6CY3 increased mortality of the nymphs to imidacloprid by 28.49 % (at 24 h) and to acetamiprid by 73.77 % (at 48 h), respectively.

CONCLUSION

These results indicated that the TG cotton lines delayed the growth and development of A. gossypii, but also decreased population density and increased its sensitivity to imidacloprid and acetamiprid, respectively. The results provide further support for the development and application of plant-mediated RNAi. © 2022 Society of Chemical Industry.

Engineering plant immune circuit: walking to the bright future with a novel toolbox

Plant pathogens destroy crops and cause severe yield losses, leading to an insufficient food supply to sustain the human population. Apart from relying on natural plant immune systems to combat biological agents or waiting for the appropriate evolutionary steps to occur over time, researchers are currently seeking new breakthrough methods to boost disease resistance in plants through genetic engineering. Here, we summarize the past two decades of research in disease resistance engineering against an assortment of pathogens through modifying the plant immune components (internal and external) with several biotechnological techniques. We also discuss potential strategies and provide perspectives on engineering plant immune systems for enhanced pathogen resistance and plant fitness.

Molecular Mechanisms Underlying Metabolic Resistance to Cyflumetofen and Bifenthrin in Tetranychus urticae Koch on Cowpea

Tetranychus urticae Koch (T. urticae) is one of the most tremendous herbivores due to its polyphagous characteristics, and is resistant to most acaricides. In this study, enzyme-linked immunosorbent assay (ELISA), transcriptome sequencing (RNA-seq) and quantitative real-time PCR (qRT-PCR) were carried out to analyze the mechanisms of T. urticae metabolic resistance to cyflumetofen and bifenthrin on cowpea. The enzyme activity of UDP-glucuronosyltransferases (UGTs) and carboxylesterases (CarEs) in the cyflumetofen-resistant (R_cfm) strain significantly decreased, while that of cytochrome P450 monooxygenases (P450s) significantly increased. Meanwhile, the activities of glutathione-S-transferases (GSTs), CarEs and P450s in the bifenthrin-resistant (R_bft) strain were significantly higher than those in the susceptible strain (Lab_SS). According to the Kyoto Encyclopedia of Genes and Genomes (KEGG) and Gene Ontology (GO) analyses, in the R_cfm mite strain, two carboxyl/cholinesterase (CCE) genes and two P450 genes were upregulated and one gene was downregulated, namely CYP392E7; in the R_bft mite strain, eleven CCE, nine UGT, two P450, four GST and three ABC genes were upregulated, while four CCE and three P450 genes were downregulated. Additionally, 94 differentially expressed genes (DEGs) were common to the two resistant groups. Specifically, TuCCE46 and TuCCE70 were upregulated in both resistant groups. Furthermore, the qRT-PCR validation data were consistent with those from the transcriptome sequencing analysis. Specifically, TuCCE46 (3.37-fold) was significantly upregulated in the R_cfm strain, while in the R_bft strain, TeturUGT22 (5.29-fold), teturUGT58p (1.74-fold), CYP392A11 (2.89-fold) and TuGSTd15 (5.12-fold) were significantly upregulated and TuCCE01 (0.13-fold) and CYP392A2p (0.07-fold) were significantly downregulated. Our study indicates that TuCCE46 might play the most important role in resistance to cyflumetofen, and TuCCE01, teturUGT58p, teturUGT22, CYP392A11, TuGSTd15, TuGSTm09 and TuABCG-13 were prominent in the resistance to bifenthrin. These findings provide further insight into the critical genes involved in the metabolic resistance of T. urticae to cyflumetofen and bifenthrin.

Functional Validation of the Roles of Cytochrome P450s in Tolerance to Thiamethoxam and Imidacloprid in a Field Population of Aphis gossypii

Field populations of Aphis gossypii (SDR) have evolved high resistance to neonicotinoids, including thiamethoxam and imidacloprid. Synergism bioassays and transcriptomic comparison of the SDR and susceptible (SS) strains revealed that the cytochrome P450s may contribute to the neonicotinoid resistance evolution. The transcripts of some P450s were constitutively overexpressed in the SDR strain, and many genes showed expression plasticity under insecticide exposure. Drosophila that ectopically expressed CYPC6Y9, CYP4CK1, CYP6DB1, and CYP6CZ1 showed greater resistance (>8.0-fold) to thiamethoxam, and Drosophila that expressed CYPC6Y9, CYP6CY22, CYP6CY18, and CYP6D subfamily genes showed greater resistance (>5-fold) to imidacloprid. Five P450 genes that caused thiamethoxam resistance also conferred resistance to α-cypermethrin. Furthermore, the knockdown of CYP4CK1, CYP6CY9, CYP6CY18, CYPC6Y22, CYP6CZ1, and CYP6DB1 dramatically increased the sensitivity of the SDR strain to thiamethoxam or imidacloprid. These results indicate the involvement of multiple P450 genes, rather than one key gene, in neonicotinoid resistance in field populations.

Cross-Resistance and Fitness Costs of the cis-Nitromethylene Neonicotinoid Cycloxaprid Resistance in Melon Aphid, Aphis gossypii (Hemiptera: Aphididae)

The melon aphid, Aphis gossypii Glover, is an important pest on various vegetables around the world and has developed resistance to neonicotinoids in fields. Cycloxaprid is a novel cis-nitromethylene configuration neonicotinoid insecticide that is different from trans-configuration neonicotinoids like imidacloprid and thiamethoxam. Herein, the cross-resistance to the other seven insecticides and fitness costs were investigated in the cycloxaprid-resistant A. gossypii strain (Cpd-R), which has developed 69.5-fold resistance to cycloxaprid. The results showed that the Cpd-R strain had very low levels of cross-resistance to imidacloprid (4.3-fold), acetamiprid (2.9-fold), thiamethoxam (3.7-fold), nitenpyram (6.1-fold), flupyradifurone (2.2-fold), and sulfoxaflor (4.5-fold), while it exhibited a cross-resistance to dinotefuran (10.6-fold). The fitness of the Cpd-R strain by life table analysis was only 0.799 compared to the susceptible strain (Cpd-S). This Cpd-R strain exhibited significantly reduction in fecundity, oviposition days, and developmental time of nymph stage compared to the Cpd-S strain. Moreover, the expression levels of some genes related to the development and reproduction, including EcR, USP, JHAMT, and JHEH were significantly up-regulated, while Vg was down-regulated in the Cpd-R strain. This study indicates that the Cpd-R strain possessed a certain fitness cost. The above research results are useful for rational application of cycloxaprid and implementing the appropriate resistance management strategy for A. gossypii.

The Cross-Resistance Pattern and the Metabolic Resistance Mechanism of Acetamiprid in the Brown Planthopper, Nilaparvata lugens (Stål)

Acetamiprid is widely used in paddy fields for controlling Nilaparvata lugens (Stål). However, the risk of resistance development, the cross-resistance pattern and the resistance mechanism of acetamiprid in this pest remain unclear. In this study, an acetamiprid-resistant strain (AC-R) was originated from a field strain (UNSEL) through successive selection with acetamiprid for 30 generations, which reached 60.0-fold resistance when compared with a laboratory susceptible strain (AC-S). The AC-R strain (G₃₀) exhibited cross-resistance to thiamethoxam (25.6-fold), nitenpyram (21.4-fold), imidacloprid (14.6-fold), cycloxaprid (11.8-fold), dinotefuran (8.7-fold), sulfoxaflor (7.6-fold) and isoprocarb (8.22-fold), while there was no cross-resistance to etofenprox, buprofezin and chlorpyrifos. Acetamiprid was synergized by the inhibitor piperonyl butoxide (2.2-fold) and the activity of cytochrome P450 monooxygenase was significantly higher in the AC-R strain compared with the AC-S strain, suggesting the critical role of P450. The gene expression results showed that the P450 gene CYP6ER1 was significantly overexpressed in AC-R compared with the AC-S and UNSEL strains. In addition, the RNA interference (RNAi) of CYP6ER1 significantly increased the susceptibility of AC-R to acetamiprid. Molecular docking predicted that acetamiprid and CYP6ER1 had close binding sites, and the nitrogen atoms had hydrogen bond interactions with CYP6ER1. These results demonstrated that the overexpression of CYP6ER1 contributed to acetamiprid resistance in N. lugens.

The Synergistic Effect of Thiamethoxam and Synapsin dsRNA Targets Neurotransmission to Induce Mortality in Aphis gossypii

Sublethal doses of insecticides have many impacts on pest control and agroecosystems. Insects that survive a sublethal dose of insecticide could adapt their physiological and behavioral functions and resist this environmental stress, which contributes to the challenge of pest management. In this study, the sublethal effects of thiamethoxam on gene expression were measured through RNA sequencing in the melon aphid Aphis gossypii. Genes regulating energy production were downregulated, while genes related to neural function were upregulated. To further address the function of genes related to neurotransmission, RNA interference (RNAi) was implemented by transdermal delivery of dsRNA targeting synapsin (syn), a gene regulating presynaptic vesicle clustering. The gene expression of synapsin was knocked down and the mortality of aphids was increased significantly over the duration of the assay. Co-delivery of syn-dsRNA and thiamethoxam reversed the upregulation of synapsin caused by low-dose thiamethoxam and resulted in lethality to melon aphids, suggesting that the decreased presynaptic function may contribute to this synergistic lethal effect. In addition, the nanocarrier star polycation, which could bind both dsRNA and thiamethoxam, greatly improved the efficacy of lethality. These results increase our knowledge of the gene regulation induced by sublethal exposure to neonicotinoids and indicated that synapsin could be a potential RNAi target for resistance management of the melon aphid.

Increasing the activities of protective enzymes is an important strategy to improve resistance in cucumber to powdery mildew disease and melon aphid under different infection/infestation patterns

Powdery mildew, caused by Sphaerotheca fuliginea (Schlecht.) Poll., and melon aphids (Aphis gossypii Glover) are a typical disease and insect pest, respectively, that affect cucumber production. Powdery mildew and melon aphid often occur together in greenhouse production, resulting in a reduction in cucumber yield. At present there are no reports on the physiological and biochemical effects of the combined disease and pest infection/infestation on cucumber. This study explored how cucumbers can regulate photosynthesis, protective enzyme activity, and basic metabolism to resist the fungal disease and aphids. After powdery mildew infection, the chlorophyll and free proline contents in cucumber leaves decreased, while the activities of POD (peroxidase) and SOD (superoxide dismutase) and the soluble protein and MDA (malondialdehyde) contents increased. Cucumber plants resist aphid attack by increasing the rates of photosynthesis and basal metabolism, and also by increasing the activities of protective enzymes. The combination of powdery mildew infection and aphid infestation reduced photosynthesis and basal metabolism in cucumber plants, although the activities of several protective enzymes increased. Aphid attack after powdery mildew infection or powdery mildew infection after aphid attack had the opposite effect on photosynthesis, protective enzyme activity, and basal metabolism regulation. Azoxystrobin and imidacloprid increased the contents of chlorophyll, free proline, and soluble protein, increased SOD activity, and decreased the MDA content in cucumber leaves. However, these compounds had the opposite effect on the soluble sugar content and POD and CAT (catalase) activities. The mixed ratio of the two single agents could improve the resistance of cucumber to the combined infection of powdery mildew and aphids. These results show that cucumber can enhance its pest/pathogen resistance by changing physiological metabolism when exposed to a complex infection system of pathogenic microorganisms and insect pests.

Early Transcriptional Response to Monensin in Sensitive and Resistant Strains of Eimeria tenella

Eimeria parasites are the causative agents of coccidiosis, a common parasitic disease in poultry and livestock that causes significant economic losses to the animal husbandry industry. Ionophore coccidiostats, such as monensin and salinomycin, are widely used for prophylaxis of coccidiosis in poultry. Unfortunately, widespread drug resistance has compromised their efficacy. As a result, there is an increasing need to understand the targets and resistance mechanisms to anticoccidials. However, how Eimeria parasite genes respond to ionophores remains unclear. In this study, resistance to monensin was induced in E. tenella through serial generations of selection. Both sensitive and resistant E. tenella sporozoites were treated with 5 μg/ml monensin for 0, 2, and 4 h, respectively. Gene transcription profiles were then compared by high-throughput sequencing. The results showed that protein translation-related genes were significantly downregulated after drug induction. A total of 1,848 DEGs were detected in the sensitive strain after 2 h of exposure, whereas only 31 were detected in the resistant strain. Among these DEGs in the sensitive strain, genes associated with protein degradation were significantly upregulated, supporting the autophagy-like parasite killing theory. Then, 4 h of exposure resulted in additional 626 and 621 DEGs for sensitive and resistant strains, respectively. This result implies that the gene transcription in sensitive strain is more susceptible to monensin treatment. Our results provide gene expression landscapes of E. tenella following monensin treatment. These data will contribute to a better understanding of the mechanism of drug resistance to polyether ionophores in coccidia.

Polylactic acid nanoparticles for co-delivery of dinotefuran and avermectin against pear tree pests with improved effective period and enhanced bioactivity

Pesticide compounding technology for disease and pest control emerges as an effective way to increase the effectiveness of pesticides while reducing pesticides resistance. Nanomaterials and encapsulation technology have offered a new insight into preparing efficient pesticide formulations, especially constructing a co-delivery nanoparticle for synergistic pesticides. In this study, a dinotefuran/avermectin co-delivery nanoparticles (DACNPs) against pear tree pests with polylactic acid (PLA) as the wall material were constructed by double-emulsion method combined with high-pressure homogenization technique. The drug content of the DACNPs was 39.1% with an average size of 245.7 ± 4.2 nm and the mean polymer dispersity index (PDI) value was 0.123. The DACNPs showed high foliar retention and good spread performance on target leaves due to the nanoscale effect. The obtained DACNPs showed a better control effect on Grapholitha molesta Busck and Psylla chinensis Yang et Li compared with the commercial formulations, which could significantly prolong the effective duration and enhance the bioactivity with lower amounts and application frequency of pesticides. This study may provide new insights into developing novel pesticide formulations to improve the utilization rate of pesticides, reduce environmental pollution and minimize the cost of farming.

Functionally characterized arthropod pest and pollinator cytochrome P450s associated with xenobiotic metabolism

The cytochrome P450 family (P450s) of arthropods includes diverse enzymes involved in endogenous essential physiological functions and in the oxidative metabolism of xenobiotics, insecticides and plant allelochemicals. P450s can also establish insecticide selectivity in bees and pollinators. Several arthropod P450s, distributed in different phylogenetic groups, have been associated with xenobiotic metabolism, and some of them have been functionally characterized, using different in vitro and in vivo systems. The purpose of this review is to summarize scientific publications on arthropod P450s from major insect and mite agricultural pests, pollinators and Papilio sp, which have been functionally characterized and shown to metabolize xenobiotics and/or their role (direct or indirect) in pesticide toxicity or resistance has been functionally validated. The phylogenetic relationships among these P450s, the functional systems employed for their characterization and their xenobiotic catalytic properties are presented, in a systematic approach, including critical aspects and limitations. The potential of the primary P450-based metabolic pathway of target and non-target organisms for the development of highly selective insecticides and resistance-breaking formulations may help to improve the efficiency and sustainability of pest control.

A Novel Reference for Bt-Resistance Mechanism in Plutella xylostella Based on Analysis of the Midgut Transcriptomes

Simple Summary

Plutella xylostella is a very serious pest to cruciferous vegetables. At present, the control methods used are mainly traditional insecticides and the cultivation of Bt crops. However, with the long-term and large-scale use of insecticides, the diamondback moth has developed strong resistance to many kinds of insecticides and Bt crops. The Cry1S1000 strain of P. xylostella used here is a strain with more than 8000 times resistance to Bt Cry1Ac protoxin. In this paper, we used transcriptome sequencing to determine the midgut transcriptome of the G88-susceptible strain, Cry1S1000-resistant strain and its corresponding toxin-induced strains to find more genes related to Bt resistance. Our results will provide a reference for optimizing the control strategy of diamondback moth resistance and improving the control efficiency of biopesticides and Bt crops.

Abstract

The diamondback moth, Plutella xylostella, is a lepidopteran insect that mainly harms cruciferous vegetables, with strong resistance to a variety of agrochemicals, including Bacillus thuringiensis (Bt) toxins. This study intended to screen genes associated with Bt resistance in P. xylostella by comparing the midgut transcriptome of Cry1Ac-susceptible and -resistant strains together with two toxin-treated strains 24 h before sampling. A total of 12 samples were analyzed by BGISEQ-500, and each sample obtained an average of 6.35 Gb data. Additionally, 3284 differentially expressed genes (DEGs) were identified in susceptible and resistant strains. Among them, five DEGs for cadherin, 14 for aminopeptidase, zero for alkaline phosphatase, 14 for ATP binding cassette transport, and five heat shock proteins were potentially involved in resistance to Cry1Ac in P. xylostella. Furthermore, DEGs associated with “binding”, “catalytic activity”, “cellular process”, “metabolic process”, and “cellular anatomical entity” were more likely to be responsible for resistance to Bt toxin. Thus, together with other omics data, our results will offer prospective genes for the development of Bt resistance, thereby providing a brand new reference for revealing the resistance mechanism to Bt of P. xylostella.

Mutations in the nAChR β1 subunit and overexpression of P450 genes are associated with high resistance to thiamethoxam in melon aphid, Aphis gossypii Glover

The TMXR is a strain of melon aphids (Aphis gossypii Glover) that has extremely high resistance (resistance ratio > 2300 fold) to thiamethoxam. We explored the basis of this resistance by examining differences in nicotinic acetylcholine receptors (nAChRs) and cytochrome P450 monooxygenase (CYP450s) between the TMXR and the susceptible strain. The results showed that two mutation sites of nAChR β1 subunit, V62I and R81T, were found in TMXR, with the mutation frequencies of the two mutation sites as 93.75%. Meanwhile, compared with the susceptible strain, the expression level of nAChR β1 subunit gene in the TMXR decreased by 38%. In addition, piperonyl butoxide (PBO) showed a synergistic ratio of 17.78-fold on TMX toxicity against the TMXR, which suggested the involvement of CYP450s in the TMX resistance of melon aphid. Moreover, the expression levels of 4 P450s genes were significantly higher in the TMXR than the susceptible strain. Through RNAi, we verified that down-regulating CYP6DA1 increased the sensitivity of TMXR to TMX toxicity, demonstrating that a decrease in CYP6DA1 expression may reduce resistance in vivo. These results suggest that A. gossypii has the capacity to develop extremely high resistance to TMX through aggregated resistance mechanisms including enhancement of detoxification by upregulation of CYP450s, and target insensitivity caused by alteration of nAChR β1 subunit with mutation and low expression. These findings provide basic information for further clarifying the molecular mechanism of insecticide resistance in A. gossypii.

Chromosome-level genome assemblies of two cotton-melon aphid Aphis gossypii biotypes unveil mechanisms of host adaption

The cotton-melon aphid Aphis gossypii is a sap-sucking insect that is considered a serious global pest. The species is distributed over a large geographical range and uses a wide variety of hosts, with some populations being specialized to attack different plant species. Here, we provide de novo chromosome-level genome assemblies of a cotton specialist population (Hap1) and a cucurbit specialist population (Hap3). We achieved this by using a combination of third-generation sequencing platforms, namely Illumina and Hi-C sequencing technologies. We were able to anchor a total of 334.89 Mb (scaffold N50 of 89.13 Mb) and 359.95 Mb (scaffold N50 of 68.88 Mb) to four chromosomes for Hap1 and Hap3, respectively. Moreover, our results showed that the X-chromosome of Hap3 (113.01 Mb) was significantly longer than that of Hap1 (100.26 Mb), with a high level of sequence conservation between the aphid species. We also report variation in the number of protein-coding genes and repeat sequences between Hap1 and Hap3. In particular, olfactory and gustatory receptor genes underwent a high level of gene duplication and expansion events in A. gossypii, including between Hap1 and Hap3. Moreover, we identified two glutathione S-transferase genes which underwent single gene duplications in Hap3, and tandem duplication and inversion events affecting the cytochrome P450 monooxygenase between Hap1 and Hap3, all of which include the CYP3 family. Our results illustrate the variance in the genomic composition of two specialized A. gossypii populations and provide a helpful resource for the study of aphid population evolution, host adaption and insecticide resistance.

Effects of elevated CO2 treatment of Populus davidiana × P. bolleana on growth and detoxifying enzymes in gypsy moth, Lymantria dispar

To date, elevated CO₂ concentrations in the environment caused by various human activities influence diverse areas of life, including the interactions between insects and plants. The Lymantria dispar is one of the most severely destructive pests, which further could inflict ecological and economical damage. In this experiment, one-year-old Populus davidiana × P. bolleana plants were grown in CO₂-enhanced environments for one month at three different CO₂ concentrations: 397 ppm (atmospheric CO₂ concentration), 550 ppm and 750 ppm (two predicted elevated CO₂ concentrations). The 3rd instar L. dispar larvae then fed on the treated poplar seedlings covered in a nylon bag. The L. dispar larvae fed on poplar seedling treated for 96 h showed the highest growth rate at all CO₂ concentrations. Enzymatic activity of treated larvae showed the highest GST and P450 activity at 750 ppm CO₂. The relative expressions of seven CYP and ten GST genes in L. dispar larvae were analyzed quantitatively using real-time RT-PCR, which the results were expressed variably. Compared to 397 ppm CO₂, the expression of CYP4L23 was down-regulated, while the expressions of other CYP genes were up-regulated. Meanwhile, only GSTo1 gene showed down-regulated at 48 h and 96 h in 750 ppm CO₂ treatment, while GST expression level for the other nine GST genes showed up-regulated at 48 h and 72 h. These results offer the insight into plant-insect interactions under global climate change and furthermore will provide essential information for strategic pest control based on biochemical and molecular levels changes in gypsy moths.

Overexpression of ATP-binding cassette transporters associated with sulfoxaflor resistance in Aphis gossypii glover

BACKGROUND

Sulfoxaflor is a new insecticide for controlling against Aphis gossypii in the field. ATP-binding cassette (ABC) transporters belong to a large superfamily of proteins and play an important role in the detoxification process. However, the potential role of ABC transporters in sulfoxaflor resistance in A. gossypii is unknown.

RESULTS

In this study, an ABC transporter inhibitor, verapamil, dramatically increased the toxicity of sulfoxaflor in the resistant population with a synergistic ratio of 8.55. However, verapamil did not synergize sulfoxaflor toxicity in the susceptible population. The contents of ABC transporters were significantly increased in the Sul-R population. Based on RT-qPCR analysis, 10 of 23 ABC transcripts, ABCA1, ABCA2, ABCB1, ABCB5, ABCD1, ABCG7, ABCG16, ABCG26, ABCG27, and MRP7, were up-regulated in the Sul-R population compared to the Sus population. Meanwhile, inductive effects of ABCA1, ABCD1, ABCG7 and ABCG26 by sulfoxaflor were found in A. gossypii. Furthermore, knockdown of ABCA1 and ABCD1 using RNAi significantly increased the sulfoxaflor sensitivity in Sul-R aphids.

CONCLUSION

These results suggested that ABC transporters, especially the ABCA1 and ABCD1 genes, might be related with sulfoxaflor resistance in A. gossypii. This study will promote further work to validate the functional roles of these ABCs in sulfoxaflor resistance and might be helpful for the management of sulfoxaflor-resistant A. gossypii.

Overexpression of Multiple UDP-Glycosyltransferase Genes Involved in Sulfoxaflor Resistance in Aphis gossypii Glover

UDP-glycosyltransferases (UGTs) are major phase II enzymes involved in the metabolic detoxification of xenobiotics. In this study, two UGT-inhibitors, 5-nitrouracil and sulfinpyrazone, significantly increased sulfoxaflor toxicity against sulfoxaflor-resistant (Sul-R) Aphis gossypii, whereas there were no synergistic effects in susceptible (Sus) A. gossypii. The activity of UGTs in the Sul-R strain was significantly higher (1.35-fold) than that in the Sus strain. Further, gene expression determination demonstrated that 11 of 23 UGT genes were significantly upregulated (1.40- to 5.46-fold) in the Sul-R strain, among which the expression levels of UGT350A2, UGT351A4, UGT350B2, UGT342C2, and UGT343C2 could be induced by sulfoxaflor. Additionally, knockdown of UGT350A2, UGT351A4, UGT350B2, and UGT343C2 using RNA interference (RNAi) significantly increased sensitivity (1.57- to 1.76-fold) to sulfoxaflor in the Sul-R strain. These results suggested that UGTs might be involved in sulfoxaflor resistance in A. gossypii. These findings will facilitate further work to validate the functional roles of these UGT genes in sulfoxaflor resistance.

Selection and Validation of Reference Genes For qRT-PCR Analysis of Rhopalosiphum padi (Hemiptera: Aphididae)

Rhopalosiphum padi (L.) (Hemiptera: Aphididae) is an important cosmopolitan pest in cereal crops. Reference genes can significantly affect qRT-PCR results. Therefore, selecting appropriate reference genes is a key prerequisite for qRT-PCR analyses. This study was conducted to identify suitable qRT-PCR reference genes in R. padi. We systematically analyzed the expression profiles of 11 commonly used reference genes. The ΔCt method, the BestKeeper, NormFinder, geNorm algorithms, and the RefFinder online tool were used to evaluate the suitability of these genes under diverse experimental conditions. The data indicated that the most appropriate sets of reference genes were β-actin and GAPDH (for developmental stages), AK and TATA (for populations), RPS18 and RPL13 (for tissues), TATA and GAPDH (for wing dimorphism), EF-1α and RPS6 (for antibiotic treatments), GAPDH and β-actin (for insecticide treatments), GAPDH, TATA, RPS18 (for starvation-induced stress), TATA, RPS6, and AK (for temperatures), and TATA and GAPDH (for all conditions). Our study findings, which revealed the reference genes suitable for various experimental conditions, will facilitate the standardization of qRT-PCR programs, while also improving the accuracy of qRT-PCR analyses, with implications for future research on R. padi gene functions.

Insecticide resistance and resistance mechanisms in the melon aphid, Aphis gossypii, in Shandong, China

The melon aphid, Aphis gossypii, is an important pest of vegetables. Insecticide resistance in A. gossypii has increased due to the frequent use of insecticides. We studied the levels and mechanisms of A. gossypii resistance to imidacloprid, acetamiprid and lambda-cyhalothrin here. The resistance levels of the three insecticides in 20 populations of A. gossypii varied. When compared to the susceptible strain (Lab-SS), there were two moderate resistance (MR) populations and nine low resistance (LR) populations to imidacloprid, respectively, two MR populations and two LR populations to acetamiprid, respectively, and, five MR populations and two LR populations to λ-cyhalothrin, respectively. Gene mutation detection in the MR level populations showed arginine to threonine substitution (R81T) in three populations and lysine to glutamine substitution (K264E) in the nicotinic acetylcholine receptor (nAChR) β1 subunit in one population, respectively. No valine to isoleucine substitution (V62I) was found in the nAChR β1 subunit in any of the tested populations. The leucine to phenylalanine substitution (L1014F) in sodium channel α subunit was found in five MR populations. The relative expression of the CYP6CY13 gene was significantly upregulated in the Daiyue and Shenxian populations. The CYP6CY14 gene was significantly upregulated in Daiyue, Dongchangfu, Shenxian, Mengyin and Anqiu populations. The CYP6CY19 gene was significantly upregulated in the Dongchangfu and Mengyin populations. The relative expressions of the esterase E4 or FE4 genes were significantly upregulated in most of the MR populations. These results provide insight into the current insecticide resistance of A. gossypii and may contribute to more effective resistance management strategies.

Knockdown of CYP301B1 and CYP6AX1v2 increases the susceptibility of the brown planthopper to beta-asarone, a potential plant-derived insecticide

The cytochrome P450 monooxygenases of insects play crucial roles in the metabolic detoxification of insecticides. Our previous finding showed that two cytochrome P450 genes, both CYP301B1 and CYP6AX1v2, in the BPH underwent overexpression due to β-asarone. In this study, we investigated the molecular characteristics, expression patterns and functions of these two cytochrome P450 genes. The results showed that CYP301B1 had the highest expression level in the eggs, while CYP6AX1v2 was expressed in macropterous female adults. Moreover, the expression level of CYP301B1 in the head was higher than that in the integument, fat body and gut. The expression level of CYP6AX1v2 in the fat body and gut was higher than that in head and integument. Importantly, silencing CYP301B1 and CYP6AX1v2 separately could increase the sensitivity, resulting in significant higher mortality of BPH following treatment with β-asarone. Our findings indicated that CYP301B1 and CYP6AX1v2 could contribute to the resistance of BPH to β-asarone, and these two genes may be involved in the detoxification metabolism of β-asarone in BPH.

Functional analysis of cytochrome P450 genes linked with acetamiprid resistance in melon aphid, Aphis gossypii

Cytochrome P450 monooxygenases (P450s) are highly conserved multifunctional enzymes that play crucial roles in insecticide resistance development. In this study, the molecular mechanisms of P450s in acetamiprid resistance development to melon aphid, Aphis gossypii was investigated. Acetamiprid resistant (32.64-fold resistance) population (Ace-R) of A. gossypii was established by continuous selection with acetamiprid for 24 generations. Quantitative Real Time PCR was carried out to analyze the expression of P450 genes in both acetamiprid resistant (Ace-R) and susceptible (Ace-S) strains. Result showed that nine genes (CYP6CY14, CYP6DC1, CYP6CZ1, CYP6DD1, CYP6CY5, CYP6CY9, CYP6DA1, CYP6CY18, and CYP6CY16) of CYP3 clade, four genes (CYP302A1, CYP315A1, CYP301A1, and CYP314A1) of CYP2 clade, two genes (CYP4CK1, CYP4G51) of CYP4 clade and three genes (CYP306A1, CYP305E1, CYP307A1) of mitochondrial clade (Mito clad) were significantly up-regulated, in Ace-R compared to Ace-S strain. Whilst CYP4CJ2 gene from (CYP4 clade) was significantly down-regulated in Ace-R strain. Furthermore, RNA interference-mediated knockdown of CYP6CY14, CYP6DC1, and CYP6CZ1 genes significantly increased the sensitivity of Ace-R strain to acetamiprid. Taken together, this study showed that P450 genes especially CYP6CY14, CYP6DC1 and CYP6CZ1 are potentially involved in acetamiprid resistance development in A. gossypii. This study could be useful to understand the molecular basis of acetamiprid resistance mechanism in A. gossypii.

Multiple Known Mechanisms and a Possible Role of an Enhanced Immune System in Bt-Resistance in a Field Population of the Bollworm, Helicoverpa zea: Differences in Gene Expression with RNAseq

Several different agricultural insect pests have developed field resistance to Bt (Bacillus thuringiensis) proteins (ex. Cry1Ac, Cry1F, etc.) expressed in crops, including corn and cotton. In the bollworm, Helicoverpa zea, resistance levels are increasing; recent reports in 2019 show up to 1000-fold levels of resistance to Cry1Ac, a major insecticidal protein in Bt-crops. A common method to analyze global differences in gene expression is RNA-seq. This technique was used to measure differences in global gene expression between a Bt-susceptible and Bt-resistant strain of the bollworm, where the differences in susceptibility to Cry1Ac insecticidal proteins were 100-fold. We found expected gene expression differences based on our current understanding of the Bt mode of action, including increased expression of proteases (trypsins and serine proteases) and reduced expression of Bt-interacting receptors (aminopeptidases and cadherins) in resistant bollworms. We also found additional expression differences for transcripts that were not previously investigated, i.e., transcripts from three immune pathways-Jak/STAT, Toll, and IMD. Immune pathway receptors (ex. PGRPs) and the IMD pathway demonstrated the highest differences in expression. Our analysis suggested that multiple mechanisms are involved in the development of Bt-resistance, including potentially unrecognized pathways.