Overexpression of UDP-glucuronosyltransferase and cytochrome P450 enzymes confers resistance to sulfoxaflor in field populations of the aphid, Myzus persicae

Physiological and transcriptomic responses of silkworms to graphene oxide exposure

The growing use of nanomaterials has sparked significant interest in assessing the insect toxicities of nanoparticles. The silkworm, as an economically important insect, serves as a promising model for studying how insects respond to harmful substances. Here, we conducted a comprehensive investigation on the impact of graphene oxide (GO) on silkworms using a combination of physiological and transcriptome analyses. GO can enter the midguts and posterior silk glands of silkworms. High GO concentrations (> 25 mg/L) significantly (P < 0.01) inhibited larval growth. Additionally, GO (> 5 mg/L) significantly reduced the cocooning rate, and GO (> 15 mg/L) hindered oviduct development and egg laying in silkworms. GO increased the reactive oxygen species content and regulated catalase activity, suggesting that it may affect insect growth by regulating reactive oxygen detoxification. The transcriptome data analysis showed that 35 metabolism-related genes and 20 ribosome biogenesis-related genes were differentially expressed in response to GO, and their expression levels were highly correlated. Finally, we propose that a Ribosome biogenesis-Metabolic signaling network is involved in responses to GO. The research provides a new perspective on the molecular responses of insects to GO.

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.

A UDP-glycosyltransferase gene PcUGT202A9 was associated with abamectin resistance in Panonychus citri (McGregor)

Panonychus citri (McGregor) strains have developed a high level of resistance to abamectin, but the underlying molecular mechanism is unknown. Uridine diphosphate (UDP)-glycosyltransferases (UGTs) are critical for the removal of a variety of exogenous and endogenous substances. In this study, an enzyme activity assay revealed that UGTs potentially contribute to P. citri abamectin resistance. Spatiotemporal expression profiles showed that only PcUGT202A9 was significantly overexpressed in the abamectin-resistant strain (AbR) at all developmental stages. Moreover, UGT activity decreased significantly, whereas abamectin susceptibility increased significantly, in AbR after PcUGT202A9 was silenced. Three-dimensional modeling and molecular docking analyses revealed that PcUGT202A9 can bind stably to abamectin. Recombinant PcUGT202A9 activity was detected when α-naphthol was used, but the enzymatic activity was inhibited by abamectin (50 % inhibitory concentration: 803.3 ± 14.20 μmol/L). High-performance liquid chromatography and mass spectrometry analyses indicated that recombinant PcUGT202A9 can effectively degrade abamectin and catalyze the conjugation of UDP-glucose to abamectin. These results imply PcUGT202A9 contributes to P. citri abamectin resistance.

Nicotinamide deficiency promotes imidacloprid resistance via activation of ROS/CncC signaling pathway-mediated UGT detoxification in Nilaparvata lugens

Metabolic alternation is a typical characteristic of insecticide resistance in insects. However, mechanisms underlying metabolic alternation and how altered metabolism in turn affects insecticide resistance are largely unknown. Here, we report that nicotinamide levels are decreased in the imidacloprid-resistant strain of Nilaparvata lugens, may due to reduced abundance of the symbiotic bacteria Arsenophonus. Importantly, the low levels of nicotinamide promote imidacloprid resistance via metabolic detoxification alternation, including elevations in UDP-glycosyltransferase enzymatic activity and enhancements in UGT386B2-mediated metabolism capability. Mechanistically, nicotinamide suppresses transcriptional regulatory activities of cap 'n' collar isoform C (CncC) and its partner small muscle aponeurosis fibromatosis isoform K (MafK) by scavenging the reactive oxygen species (ROS) and blocking the DNA binding domain of MafK. In imidacloprid-resistant N. lugens, nicotinamide deficiency re-activates the ROS/CncC signaling pathway to provoke UGT386B2 overexpression, thereby promoting imidacloprid detoxification. Thus, nicotinamide metabolism represents a promising target to counteract imidacloprid resistance in N. lugens.

Characterization and functional analysis of UDP-glycosyltransferases reveal their contribution to phytochemical flavone tolerance in Spodoptera litura

Efficient detoxification is the key factor for phytophagous insect to adapt to phytochemicals. However, the role of uridine diphosphate (UDP)-glycosyltransferases (UGTs) in insect anti-defense to phytochemical flavone is largely unknown. In this study, 52 UGT genes were identified in Spodoptera litura and they presented evident gene duplication. UGT played a crucial part in larval tolerance to flavone because the enzyme activity and transcriptional level of 77 % UGT members were remarkably upregulated by flavone administration and suppression of UGT enzyme activity and gene expressions significantly increased larval susceptibility to flavone. Bacteria coexpressing UGTs had high survival rates under flavone treatment and flavone was dramatically metabolized by UGT recombinant cells, which indicated the involvement of UGTs in flavone detoxification. What's more, ecdysone pathway was activated by flavone. Topical application of 20-hydroxyecdysone highly upregulated UGT enzyme activity and more than half of UGT expressions. The effects were opposite when ecdysone receptor (EcR) and ultraspiracle (USP)-mediated ecdysone signaling pathway was inhibited. Furtherly, promoter reporter assays of 5 UGT genes showed that their transcription activities were notably increased by cotransfection with EcR and USP. In consequence, this study suggested that UGTs were involved in flavone detoxification and their transcriptional expressions were regulated by ecdysone pathway.

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.

The evolving story of sulfoxaflor resistance in the green peach aphid, Myzus persicae (Sulzer)

BACKGROUND

The green peach aphid, Myzus persicae (Sulzer), is one of the most economically important crop pests worldwide. Insecticide resistance in this pest was first detected over 60 years ago, with resistance in M. persicae now spanning over 80 active ingredients. Sulfoxaflor is a relatively new insecticide that is primarily used to control sap-feeding insects. In 2018 resistance to sulfoxaflor was discovered in field populations of M. persicae in Australia. This study aimed to determine the current distribution and phenotypic levels of sulfoxaflor resistance in Australian clones of M. persicae and to investigate how these patterns relate to clonal type.

RESULTS

For the first time, we show there is low-level resistance (8-26-fold) distributed across Australia, with resistance being detected in aphids collected from approximately 20% of all M. persicae collected and screened. Furthermore, this study shows sulfoxaflor resistance is found in two M. persicae haplotypes, providing evidence that there have been multiple independent evolutionary events which have given rise to sulfoxaflor resistance in this species.

CONCLUSION

These findings have important implications for the chemical control of M. persicae in Australia, especially when considering the broader genetic background of these aphids which are known to harbour a number of other insecticide resistance mechanisms. We recommend continuous monitoring of sulfoxaflor resistance in field populations of M. persicae (in Australia and elsewhere) and further research into the underlying genetic mechanisms conferring resistance to sulfoxaflor in both clonal haplotypes. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Differential gene expression and microRNA profile in corpora allata-corpora cardiaca of Aedes aegypti mosquitoes with weak juvenile hormone signalling

The corpora allata-corpora cardiaca (CA-CC) is an endocrine gland complex that regulates mosquito development and reproduction through the synthesis of juvenile hormone (JH). Epoxidase (Epox) is a key enzyme in the production of JH. We recently utilized CRISPR/Cas9 to establish an epoxidase-deficient (epox-/-) Aedes aegypti line. The CA from epox-/- mutants do not synthesize epoxidated JH III but methyl farneosate (MF), a weak agonist of the JH receptor, and therefore have reduced JH signalling. Illumina sequencing was used to examine the differences in gene expression between the CA-CC from wild type (WT) and epox-/- adult female mosquitoes. From 18,034 identified genes, 317 were significantly differentially expressed. These genes are involved in many biological processes, including the regulation of cell proliferation and apoptosis, energy metabolism, and nutritional uptake. In addition, the same CA-CC samples were also used to examine the microRNA (miRNA) profiles of epox-/- and WT mosquitoes. A total of 197 miRNAs were detected, 24 of which were differentially regulated in epox-/- mutants. miRNA binding sites for these particular miRNAs were identified using an in silico approach; they target a total of 101 differentially expressed genes. Our results suggest that a lack of epoxidase, besides affecting JH synthesis, results in the diminishing of JH signalling that have significant effects on Ae. aegypti CA-CC transcriptome profiles, as well as its miRNA repertoire.

Comprehensive analysis of the overexpressed cytochrome P450-based insecticide resistance mechanism in Spodoptera litura

Cytochrome P450s play critical roles in the metabolic resistance of insecticides in insects. Previous findings showed that enhanced P450 activity was an important mechanism mediating indoxacarb resistance, and multiple P450 genes were upregulated in indoxacarb resistant strains of Spodoptera litura. However, the functions of these P450 genes in insecticide resistance remain unknown. Here, the P450 inhibitor PBO effectively decreased the resistance of S. litura to indoxacarb. Ten upregulated P450 genes were characterized, all of which were overexpressed in response to indoxacarb induction. Knockdown of nine P450 genes decreased cell viability against indoxacarb, and further silencing of three genes (CYP339A1, CYP340G2, CYP321A19) in larvae enhanced the sensitivity to indoxacarb. Transgenic overexpression of these three genes increased resistance to indoxacarb in Drosophila melanogaster. Moreover, molecular modeling and docking predicted that these three P450 proteins could bind tightly to indoxacarb and N-decarbomethoxylated metabolite (DCJW). Interestingly, these three P450 genes may also mediate cross-resistance to chlorantraniliprole, λ-cyhalothrin and imidacloprid. Additionally, heterologous expression and metabolic assays confirmed that three recombinant P450s could effectively metabolize indoxacarb and DCJW. This study strongly demonstrates that multiple overexpressed mitochondrial and microsomal P450 genes were involved in insecticide resistance in S. litura.

Discovery of piperonyl-tethered sulfoximines as novel low bee-toxicity aphicides targeting Amelα1/ratβ2 complex

Nicotinic acetylcholine receptor (nAChR) is recognized as a significant insecticide target for neonicotinoids and some agonists. In this study, the nAChR α1 subunit from Apis mellifera was first found to be narrowly tuned to different bee toxicity insecticides, namely, sulfoxaflor (SFX) and flupyradifurone (FPF). Hence, novel sulfoximine derivatives 7a-h were rationally designed and synthesized by introducing a benzo[d][1,3]dioxole moiety into a unique sulfoximine skeleton based on the binding cavity characteristics of Amelα1/ratβ2. The two electrode voltage clamp responses of 7a-h were obviously lower than that of SFX, indicating their potentially low bee toxicity. Besides, representative compounds 7b and 7g exhibited low bee toxicity (LD50 > 11.0 μg/bee at 48 h) revealed by acute contact toxicity bioassays. Molecular modelling results indicated that Ile152, Ala151, and Val160 from honeybee subunit Amelα1 and Lys144 and Trp80 from aphid subunit Mpα1 may be crucial for bee toxicity and aphicidal activity, respectively. These results clarify the toxic mechanism of agonist insecticides on nontargeted pollinators and reveal novel scaffold sulfoximine aphicidal candidates with low bee toxicity. These results will provide a new perspective on the rational design and highly effective development of novel eco-friendly insecticides based on the structure of the nAChR subunit.

Functional analysis of UDP-glycosyltransferase genes conferring indoxacarb resistance in Spodoptera litura

UDP-glycosyltransferase (UGT) is the major detoxification enzymes of phase II involved in xenobiotics metabolism, which potentially mediates the formation of insect resistance. Previous transcriptome sequencing studies have found that several UGT genes were upregulated in indoxacarb resistant strains of Spodoptera litura, but whether these UGT genes were involved in indoxacarb resistance and their functions in resistance were unclear. In this study, the UGTs inhibitor, 5-nitrouracil, enhanced the toxicity of indoxacarb against S. litura, preliminarily suggesting that UGTs were participated in indoxacarb resistance. Two UGT genes, UGT33J17 and UGT41D10 were upregulated in the resistant strains and could be induced by indoxacarb. Alignment of UGT protein sequences revealed two conserved donor-binding regions with several key residues that interact with catalytic sites and sugar donors. Further molecular modeling and docking analysis indicated that two UGT proteins were able to stably bind indoxacarb and N-decarbomethoxylated metabolite (DCJW). Furthermore, knockdown of UGT33J17 and UGT41D10 decreased viability of Spli-221 cells and enhanced susceptibility of larvae to indoxacarb. Transgenic overexpression of these genes reduced the toxicity of indoxacarb in Drosophila melanogaster. This work revealed that upregulation of UGT genes significantly contributes to indoxacarb resistance in S. litura, and is of great significance for the development of integrated and sustainable management strategies for resistant pests in the field.

A review of the molecular mechanisms of acaricide resistance in mites and ticks

The Arachnida subclass of Acari comprises many harmful pests that threaten agriculture as well as animal health, including herbivorous spider mites, the bee parasite Varroa, the poultry mite Dermanyssus and several species of ticks. Especially in agriculture, acaricides are often used intensively to minimize the damage they inflict, promoting the development of resistance. Beneficial predatory mites used in biological control are also subjected to acaricide selection in the field. The development and use of new genetic and genomic tools such as genome and transcriptome sequencing, bulked segregant analysis (QTL mapping), and reverse genetics via RNAi or CRISPR/Cas9, have greatly increased our understanding of the molecular genetic mechanisms of resistance in Acari, especially in the spider mite Tetranychus urticae which emerged as a model species. These new techniques allowed to uncover and validate new resistance mutations in a larger range of species. In addition, they provided an impetus to start elucidating more challenging questions on mechanisms of gene regulation of detoxification associated with resistance.

First monitoring of resistance and corresponding mechanisms in the green peach aphid, Myzus persicae (Sulzer), to registered and unregistered insecticides in Saudi Arabia

Insecticides are widely used as the primary management strategy for controlling Myzus persicae, the devastating pest ravaging various vegetables, fruits, crops, and ornamentals. This study examined the susceptibility of M. persicae field populations to bifenthrin, fosthiazate, acetamiprid, spirotetramat, afidopyropen, and flonicamid while exploring the possible metabolic mechanisms of resistance. The study findings revealed that M. persicae field populations exhibited susceptible-to-moderate resistance to bifenthrin (resistance ratio (RR) = 0.94-19.65) and acetamiprid (RR = 1.73-12.91), low-to-moderate resistance to fosthiazate (RR = 3.67-17.00), and susceptible-to-low resistance to spirotetramat (RR = 0.70-6.68). However, all M. persicae field populations were susceptible to afidopyropen (RR = 0.44-2.25) and flonicamid (RR = 0.40-2.08). As determined by the biochemical assays, carboxylesterases were involved in the resistance cases to bifenthrin and fosthiazate, whereas cytochrome P450 monooxygenases were implicated in the resistance cases to acetamiprid. However, glutathione S-transferases were not implicated in the documented resistance of M. persicae field populations. Overall, the susceptibility of M. persicae field populations to flonicamid and afidopyropen-two unregistered insecticides in Saudi Arabia-suggests their potential as promising chemicals that can expand the various alternatives available for controlling this devastating pest. Although the detected moderate levels of resistance to bifenthrin, fosthiazate, and acetamiprid indicate a shift in the selection pressure of insecticides for M. persicae due to Saudi regulations, which have resulted in eventual obsolescence of conventional insecticides in favor of novel insecticides. Finally, rotational use of aforementioned insecticides can help in managing insecticide resistance in M. persicae.

Overexpression of the UDP-glycosyltransferase UGT34A23 confers resistance to the diamide insecticide chlorantraniliprole in the tomato leafminer, Tuta absoluta

The tomato leafminer, Tuta absoluta, is an invasive crop pest that has evolved resistance to many of the insecticides used for its control. To facilitate the investigation of the underpinning mechanisms of resistance in this species we generated a contiguous genome assembly using long-read sequencing data. We leveraged this genomic resource to investigate the genetic basis of resistance to the diamide insecticide chlorantraniliprole in Spanish strains of T. absoluta that exhibit high levels of resistance to this insecticide. Transcriptomic analyses revealed that, in these strains, resistance is not associated with previously reported target-site mutations in the diamide target-site, the ryanodine receptor, but rather is associated with the marked overexpression (20- to >100-fold) of a gene encoding a UDP-glycosyltransferase (UGT). Functional expression of this UGT, UGT34A23, via ectopic expression in Drosophila melanogaster demonstrated that it confers strong and significant resistance in vivo. The genomic resources generated in this study provide a powerful resource for further research on T. absoluta. Our findings on the mechanisms underpinning resistance to chlorantraniliprole will inform the development of sustainable management strategies for this important pest.

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.

Expression profile of the entire detoxification gene inventory of the western honeybee, Apis mellifera across life stages

The western honeybee, Apis mellifera, is a managed pollinator of many crops and potentially exposed to a wide range of foreign compounds, including pesticides throughout its life cycle. Honeybees as well as other insects recruit molecular defense mechanisms to facilitate the detoxification of xenobiotic compounds. The inventory of detoxification genes (DETOXome) is comprised of five protein superfamilies: cytochrome P450 monooxygenases (P450), carboxylesterases, glutathione S-transferases (GST), UDP-glycosyl transferases (UGT) and ATP-binding cassette (ABC) transporters. Here we characterized the gene expression profile of the entire honeybee DETOXome by analyzing 47 transcriptomes across the honeybee life cycle, including different larval instars, pupae, and adults. All life stages were well separated by principal component analysis, and K-means clustering revealed distinct temporal patterns of gene expression. Indeed, >50% of the honeybee detoxification gene inventory is found in one cluster and follows strikingly similar expression profiles, i.e., increased expression during larval development, followed by a sharp decline after pupation and a steep increase again in adults. This cluster includes 29 P450 genes dominated by CYP3 and CYP4 clan members, 15 ABC transporter genes mostly belonging to the ABCC subfamily and 13 carboxylesterase genes including almost all members involved in dietary/detox and hormone/semiochemical processing. RT-qPCR analysis of selected detoxification genes from all families revealed high expression levels in various tissues, especially Malpighian tubules, fatbody and midgut, supporting the view that these tissues are essential for metabolic clearance of environmental toxins and pollutants in honeybees. Our study is meant to spark further research on the molecular basis of detoxification in this critical pollinator to better understand and evaluate negative impacts from potentially toxic substances. Additionally, the entire gene set of 47 transcriptomes collected and analyzed provides a valuable resource for future honeybee research across different disciplines.

The molecular mechanisms of insecticide resistance in aphid crop pests

Aphids are a group of hemipteran insects that include some of the world's most economically important agricultural pests. The control of pest aphids has relied heavily on the use of chemical insecticides, however, the evolution of resistance poses a serious threat to their sustainable control. Over 1000 cases of resistance have now been documented for aphids involving a remarkable diversity of mechanisms that, individually or in combination, allow the toxic effect of insecticides to be avoided or overcome. In addition to its applied importance as a growing threat to human food security, insecticide resistance in aphids also offers an exceptional opportunity to study evolution under strong selection and gain insight into the genetic variation fuelling rapid adaptation. In this review we summarise the biochemical and molecular mechanisms underlying resistance in the most economically important aphid pests worldwide and the insights study of this topic has provided on the genomic architecture of adaptive traits.

P450-mediated resistance in Myzus persicae (Sulzer) (Hemiptera: Aphididae) reduces the efficacy of neonicotinoid seed treatments in Brassica napus

BACKGROUND

The prophylactic use of seeds treated with neonicotinoid insecticides remains an important means of controlling aphid pests in canola (Brassica napus) crops in many countries. Yet, one of the most economically important aphid species worldwide, the peach potato aphid (Myzus persicae), has evolved mechanisms which confer resistance to neonicotinoids, including amplification of the cytochrome P450 gene, CYP6CY3. While CYP6CY3 amplification has been associated with low-level resistance to several neonicotinoids in laboratory acute toxicity bioassays, its impact on insecticide efficacy in the field remains unresolved. In this study, we investigated the impact of CYP6CY3 amplification on the ability of M. persicae to survive neonicotinoid exposure under laboratory and semi-field conditions.

RESULTS

Three M. persicae clones, possessing different copy numbers of CYP6CY3, were shown to respond differently when exposed to the neonicotinoids, imidacloprid and thiamethoxam, in laboratory bioassays. Two clones, EastNaernup209 and Osborne171, displayed low levels of resistance (3-20-fold), which is consistent with previous studies. However, in a large-scale semi-field trial, both clones showed a surprising ability to survive and reproduce on B. napus seedlings grown from commercial rates of neonicotinoid-treated seed. In contrast, an insecticide-susceptible clone, of wild-type CYP6CY3 copy number, was unable to survive on seedlings treated in the same manner.

CONCLUSION

Our findings suggest that amplification of CYP6CY3 in M. persicae clones substantially impairs the efficacy of neonicotinoid seed treatments when applied to B. napus. These findings highlight the potentially important real-world implications of resistances typically considered to be 'low level' as defined through laboratory bioassays. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Contribution of UDP-glycosyltransferases to chlorpyrifos resistance in Nilaparvata lugens

As a multigene superfamily of Phase II detoxification enzymes, uridine diphosphate (UDP)-glycosyltransferases (UGTs) play important roles in the metabolism of xenobiotics including insecticides. In this study, 5-nitrouracil, an inhibitor of UGT enzyme activity, effectively increased the toxicity of chlorpyrifos to the chlorpyrifos-resistant strain of Nilaparvata lugens, one of the most resistant rice pests. The enzyme content of UGT in the resistant strain was significantly higher than that in the susceptible strain. Among 20 identified UGT genes, UGT386H2, UGT386J2, UGT386N2 and UGT386P1 were found significantly overexpressed in the resistant strain and can be effectively induced by chlorpyrifos. These four UGT genes were most highly expressed in the midgut and/or fat body, two main insect detoxification tissues. Amino acid sequence alignments revealed that these four UGTs contained a variable N-terminal substrate-binding domain and a conserved C-terminal sugar donor-binding domain. Furthermore, homology modeling and molecular docking analyses showed that these UGTs could stably bind to chlorpyrifos and chlorpyrifos oxon, with the binding free energies from -19.4 to -110.62 kcal mol^-1. Knockdown of UGT386H2 or UGT386P1 by RNA interference dramatically increased the susceptibility of the resistant strain to chlorpyrifos. These findings suggest that overexpression of these two UGT genes contributes to chlorpyrifos resistance in N. lugens.

Spirotetramat resistance in Myzus persicae (Sulzer) (Hemiptera: Aphididae) and its association with the presence of the A2666V mutation

BACKGROUND

Chemicals are widely used to protect field crops against aphid pests and aphid-borne viral diseases. One such species is Myzus persicae (Sulzer), a global pest that attacks a broad array of agricultural crops and transmits many economically damaging plant viruses. This species has evolved resistance to a large number of insecticide compounds as a result of widespread and repeated chemical use in many parts of the world. In this study, we investigated the evolution of resistance to a new plant protection product, spirotetramat, following reported chemical control failures.

RESULTS

Our study provides clear phenotypic and genotypic evidence of spirotetramat resistance in populations of M. persicae from Australia. We show there is cross-resistance to other insecticides within the same chemical group, namely spiromesifen and spirodiclofen. We also demonstrate that resistance is associated with the previously reported mutation, A2226V in the target site of spirotetramat, acetyl-CoA carboxylase. Our genetic analysis found all resistant M. persicae populations belong to the same multi-locus clonal type and carry the A2226V mutation, which appears to be inherited as a dominant trait in this species.

CONCLUSION

Our findings provide new insight into the resistance conferred by A2226V and have implications for the control of M. persicae in Australia and worldwide. A diagnostic assay developed in this study should serve as a valuable tool for future resistance monitoring and to support the implementation of pest management strategies. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.