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

Uridine diphosphate glucosyltransferase is vital for fenpropathrin resistance in Bombyx mori (Lepidoptera)

The silkworm (Bombyx mori) is an important model lepidopteran insect and can be used to identify pesticide resistance-related genes of great significance for biological control of pests. Uridine diphosphate glucosyltransferases (UGTs), found in all organisms, are the main secondary enzymes involved in the metabolism of heterologous substances. However, it remains uncertain if silkworm resistance to fenpropathrin involves UGT. This study observes significant variations in BmUGT expression among B. mori strains with variable fenpropathrin resistance post-feeding, indicating BmUGT's role in fenpropathrin detoxification. Knockdown of BmUGT with RNA interference and overexpression of BmUGT significantly decreased and increased BmN cell activity, respectively, indicating that BmUGT plays an important role in the resistance of silkworms to fenpropathrin. In addition, fenpropathrin residues were significantly reduced after incubation for 12 h with different concentrations of a recombinant BmUGT fusion protein. Finally, we verified the conservation of UGT to detoxify fenpropathrin in Spodoptera exigua: Its resistance to fenpropathrin decreased significantly after knocking down SeUGT. In a word, UGT plays an important role in silkworm resistance to fenpropathrin by directly degrading the compound, a function seen across other insects. The results of this study are of great significance for breeding silkworm varieties with high resistance and for biological control of pests.

Resistance toward Triflumezopyrim Related to Overexpression of SfUGT35A1 and SfGSTd2 in Sogatella furcifera (Hemiptera: Delphacidae)

Sogatella furcifera is a migratory pest that harms rice cultivation. Triflumezopyrim (TFM), a novel insecticide, effectively controls S. furcifera. To guide its scientific application, we studied the TFM resistance mechanisms in resistant strains. Through cross-resistance determination, we found that the strain had cross-resistance to clothianidin. Synergistic and enzyme activities also demonstrated that the TFM resistance was related to the enhancement of glutathione S-transferases and UDP-glycosyltransferases. Meanwhile, SfGSTd2, SfUGT2, and SfUGT35A1 were invariably upregulated in the TFM-resistant strain. RNAi revealed that SfGSTd2 (mortality increasing 33.3-53.3%) and SfUGT35A1 (increasing 33.3-46.7%) significantly increased sensitivity on TFM, while SfUGT35A1 (increasing 40.0-46.7%) also clearly promoted sensitivity toward clothianidin in S. furcifera. The GAL4/UAS system further verified that the overexpression of SfUGT35A1 is involved in the formation of TFM (mortality descending 2.8-52.8%) and clothianidin resistance (mortality descending 11.1-41.7%). Therefore, all results showed that the overexpression of SfGSTd2- and SfUGT35A1-mediated resistance to TFM in S. furcifera.

Physiological effects of field concentrations and sublethal concentrations of sulfoxaflor on Apis mellifera

BACKGROUND

Bees (Apis mellifera), as important pollinators of agricultural crops, are at risk when pesticides are used. Sulfoxaflor is a new insecticide which acts on the nicotinic acetylcholine receptor (nAChR) in a similar way to neonicotinoids. The goal of this study is to evaluate the toxicity of sulfoxaflor and its effect on the A. mellifera exposure.

RESULTS

Initially, developmental indicators such as larval survival, pupation, and eclosion were inhibited by 5.0 mg/L (field concentration) sulfoxaflor. In the pupal stage, fat content was significantly increased, while the glycogen content decreased. In addition, A. mellifera heads were treated with 2.0 mg/L (sublethal concentration) of sulfoxaflor and analyzed by RNA sequencing. The transcriptome results indicated that 2.0 mg/L amounts of sulfoxaflor have adverse effects on the immune, digestive, and nervous systems. Sulfoxaflor down-regulated the expression of many genes involved in immunity, detoxification, the myosin cytoskeleton, sensory neurons, and odor-binding proteins.

CONCLUSION

Field concentration and sublethal concentration were used for the combined analysis of honeybees. The effect of sublethal concentration of sulfoxaflor on honeybees was studied for the first time from the perspective of transcriptome sequencing of honeybee head. A preliminary study was carried out on the stress of sulfoxaflor at sublethal concentration on honeybee workers, which has certain research significance and can provide theoretical basis for the use of sulfoxaflor in the field environment. © 2024 Society of Chemical Industry.

Knockout of two uridine diphosphate-glycosyltransferase genes increases the susceptibility of Spodoptera litura to Bacillus thuringiensis toxins

Uridine diphosphate-glycosyltransferases (UGTs) catalyze sugar conjugation of endogenous and exogenous molecules in insects. In this study, 45 putative UGT genes in 11 families were identified from the genome of S. litura. Exposure to Bt toxins in 5th-instar larvae of the WT strain led to a significant upregulation of midgut UGT40 expression, particularly of SlUGT40D20, SlUGT40D22, and SlUGT40F25. This upregulation was not observed following exposure to chemical pesticides. Knockout of the UGT genes SlUGT40D20 and SlUGT40D22 in S. litura (mutant strains SlUGT40D20-KO and SlUGT40D22-KO) via CRISPR/Cas9-mediated mutagenesis increased susceptibility of S. litura to Bacillus thuringiensis (Bt) insecticidal proteins. However, in comparison with the wild-type (WT) strain, the mutants did not change susceptibility to chemical pesticides. Observations of 5th-instar larval midgut by electron microscopy revealed severe damage to the midgut epithelium caused by Cry1Ac toxin at 10 μg/g in the SlUGT40D20-KO strain compared to the WT. SDS-PAGE and LC MS/MS analyses identified a specific protein band corresponding to putative proteoglycans in the peritrophic matrix of the WT strain, which was absent in the SlUGT40D20-KO strain. Our study suggests an inverse correlation between expression of some UGTs and the susceptibility of S. litura larvae to some Bt toxins.

Interplant communication increases aphid resistance and alters rhizospheric microbes in neighboring plants of aphid-infested cucumbers

BACKGROUND

Aphis gossypii Glover is a prevalent phytophagous insect that inflicts significant damage on cucumber plants. Recent studies have provided insights into plant communication and signal transduction within conspecifics. However, understanding of the effect of these communication mechanisms on adjacent cucumbers and their resident aphids, especially in the context of an aphid infestation, is still in its early stages.

RESULTS

Utilizing a partitioned root configuration, a tendency for aphids to gather on nearby cucumber leaves of non-infested plants was observed. Furthermore, neighboring plants near aphid-infested cucumber plants showed a reduction in aphid reproduction rates. Concurrently, these plants exhibited a significant increase in reactive oxygen species (ROS) levels, along with enhanced defensive and antioxidant enzymatic responses. Analysis of the microbial community in the rhizosphere showed significant differences in species composition among the samples. Among these, the bacterial families Microbacteriaceae and Rhizobiaceae, along with the fungal species Leucocoprinus ianthinus and Mortierella globalpina, exhibited increases in their relative abundance in cucumber seedlings located near aphid-infested plants. Significantly, this study unveiled robust correlations between dominant microbial phyla and physiological indicators, primarily associated with aphid resistance mechanisms in plants.

CONCLUSION

The results show that aphid-infested cucumber plants trigger oxidative stress responses in adjacent seedlings through complex interplant communication mechanisms. In addition, these plants cause changes in the composition of the rhizospheric microbial community and the physiological activity of neighboring plants, consequently boosting their natural resistance to aphids. This study provides essential theoretical foundations to guide the development of sustainable strategies for managing cucumber aphids. © 2024 Society of Chemical Industry.

UGT201H1 overexpression confers cyflumetofen resistance in Tetranychus cinnabarinus (Boisduval)

BACKGROUND

Tetranychus cinnabarinus is one of the most common polyphagous arthropod herbivores, and is primarily controlled by the application of acaricides. The heavy use of acaricides has led to high levels of resistance to acaricides such as cyflumetofen, which poses a threat to global resistance management programs. Cyflumetofen resistance is caused by an increase in metabolic detoxification; however, the role of uridine diphosphate (UDP)-glycosyltransferase (UGT) genes in cyflumetofen resistance remains to be determined.

RESULTS

Synergist 5-nitrouracil (5-Nul) significantly enhanced cyflumetofen toxicity in T. cinnabarinus, which indicated that UGTs are involved in the development of cyflumetofen resistance. Transcriptomic analysis and quantitative (q)PCR assays demonstrated that the UGT genes, especially UGT201H1, were highly expressed in the YN-CyR strain, compared to those of the YN-S strain. The RNA interference (RNAi)-mediated knockdown of UGT201H1 expression diminished the levels of cyflumetofen resistance in YN-CyR mites. The findings additionally revealed that the recombinant UGT201H1 protein plays a role in metabolizing cyflumetofen. Our results also suggested that the aromatic hydrocarbon receptor (AhR) probably regulates the overexpression of the UGT201H1 detoxification gene.

CONCLUSION

UGT201H1 is involved in cyflumetofen resistance, and AhR may regulates the overexpression of UGT201H1. These findings provide deeper insights into the molecular mechanisms underlying UGT-mediated metabolic resistance to chemical insecticides. © 2024 Society of Chemical Industry.

Survey of target site mutations linked with insecticide resistance in Italian populations of Aphis gossypii

BACKGROUND

Aphis gossypii is a worldwide agricultural pest that causes high levels of economic losses by feeding and transmitting virus diseases. It is usually controlled by chemical insecticides, but this could lead to the selection of resistant populations. Several single nucleotide polymorphisms (SNPs) have been identified associated with insecticide resistance. Monitoring activities to detect the presence of such mutations in field populations can have an important role in insect pest management but, currently, no information on Italian strains is available.

RESULTS

The presence of target site mutations conferring resistance to different insecticides was analysed in Italian field collected populations of A. gossypii with an allele specific approach (QSGG, Qualitative Sybr-Green Genotyping). Primers were designed to detect mutations in genes coding acetylcholinesterase (S431F), nicotinic acetylcholine receptor (R81T) and voltage-gated sodium channel (M918L and L1014F). S431F was widespread but with high variability across populations. R81T was detected for the first time in Italy but only in two populations. The L1014F mutation (kdr) was not found, while in the samples showing the M918L two different nucleotidic substitutions were detected. Mutant allele frequencies were, respectively, 0.70 (S431), 0.31 (M918) and 0.02 (R81). Further analysis on the voltage-gated sodium channel gene showed the presence of eight haplotypes and one non-synonymous mutation in the gene coding region.

CONCLUSION

Multiple target-site mutations were detected within Italian populations. The combinations of genotypes observed in certain locations could affect negatively the control of this pest. Preliminary insights on the genetic structure in the Italian populations of A. gossypii were acquired. © 2024 Society of Chemical Industry.

Overexpression of SmUGGT1 Confers Imidacloprid Resistance to Sitobion miscanthi (Takahashi)

Sitobion miscanthi, the main species of wheat aphids, is one kind of harmful pest. Chemical insecticides are the important agrochemical products to effectively control wheat aphids. However, the broad application has led to serious resistance of pests to several insecticides, and understanding insecticide resistance mechanisms is critical for integrated pest management. In this study, SmUGGT1, a new uridine diphosphate (UDP)-glycosyltransferase (UGT) gene, was cloned and more strongly expressed in the SM-R (the resistant strain to imidacloprid) than in the SM-S (the susceptible strain to imidacloprid). The increased susceptibility to imidacloprid was observed after silencing SmUGGT1, indicating that it can be related to the resistance to imidacloprid. Subsequently, SmUGGT1 regulated post-transcriptionally in the coding sequences (CDs) by miR-81 was verified and involved in the resistance to imidacloprid in S. miscanthi. This finding is crucial in the roles of UGT involved in insecticide resistance management in pests.

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.

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.

Mutation V65I in the β1 Subunit of the Nicotinic Acetylcholine Receptor Confers Neonicotinoid and Sulfoxaflor Resistance in Insects

Neonicotinoids have been widely used to control pests with remarkable effectiveness. Excessive insecticides have led to serious insect resistance. Mutations of the nicotinic acetylcholine receptor (nAChR) are one of the reasons for neonicotinoid resistance conferred in various agricultural pests. Two mutations, V65I and V104I, were found in the nAChR β1 subunit of two neonicotinoid-resistant aphid populations. However, the specific functions of the two mutations remain unclear. In this study, we cloned and identified four nAChR subunits (α1, α2, α8, and β1) of thrips and found them to be highly homologous to the nAChR subunits of other insects. Subsequently, we successfully expressed two subtypes nAChR (α1/α2/α8/β1 and α1/α8/β1) by coinjecting three cofactors for the first time in thrips, and α1/α8/β1 showed abundant current rapidly. Acetylcholine, neonicotinoids, and sulfoxaflor exhibited different activation capacities for the two subtypes of nAChRs. Finally, V65I was found to significantly reduce the binding ability of nAChR to neonicotinoids and sulfoxaflor through electrophysiology and computer simulations. V104I caused a decrease in agonist affinity (pEC50) but an increase in the efficacy (Imax) of nAChR against neonicotinoids and reduced the binding ability of nAChR to sulfoxaflor. This study provides theoretical and technical support for studying the molecular mechanisms of neonicotinoid resistance in pests.

Uridine diphosphate glucosyltransferases are involved in spinosad resistance in western flower thrips Frankliniella occidentalis (Pergande)

Uridine diphosphate glucosyltransferases (UGTs) play crucial roles in the insect detoxification system and are associated with pesticide resistance. Our previous transcriptomic analysis of spinosad-susceptible (Ivf03) and resistant (NIL-R) Frankliniella occidentalis revealed numerous upregulated UGT genes in the NIL-R strain, suggesting their potential contribution to spinosad resistance. To investigate this hypothesis, here we conducted UGT activity assays and spinosad induction experiments, employing RNA interference (RNAi) techniques for gene function validation. We found significantly elevated UGT activity in the NIL-R strain compared to Ivf03, with 5-nitrouracil showing a substantial synergistic effect on the resistant strain. Eighteen UGT genes were identified in F. occidentalis, with gene expansion and duplication observed within families UGT466, 467, and 468. Ten out of the eighteen UGTs exhibited higher expression levels in NIL-R, specifically FoUGT466B1, FoUGT468A3, and FoUGT468A4 consistently being upregulated across nymphs, males, and females. RNAi-based functional validation targeting these three UGT genes led to increased susceptibility to spinosad in a life stage-, sex-, and dose-dependent manner. These results indicate that UGTs are indeed involved in spinosad resistance in F. occidentalis, and the effects are dependent on life stage, sex, and dose. Therefore, sustainable control for F. occidentalis resistance should always consider these differential responses.

Improvement of Panax notoginseng saponin accumulation triggered by methyl jasmonate under arbuscular mycorrhizal fungi

Panax notoginseng is a highly valued perennial medicinal herb plant in Yunnan Province, China, and the taproots are the main medicinal parts that are rich in active substances of P. notoginseng saponins. The main purpose of this study is to uncover the physiological and molecular mechanism of Panax notoginseng saponin accumulation triggered by methyl jasmonate (MeJA) under arbuscular mycorrhizal fungi (AMF) by determining physiological indices, high-throughput sequencing and correlation analysis. Physiological results showed that the biomass and saponin contents of P. notoginseng, the concentrations of jasmonic acids (JAs) and the key enzyme activities involved in notoginsenoside biosynthesis significantly increased under AMF or MeJA, but the interactive treatment of AMF and MeJA weakened the effect of AMF, suggesting that a high concentration of endogenous JA have inhibitory effect. Transcriptome sequencing results indicated that differential expressed genes (DEGs) involved in notoginsenoside and JA biosynthesis were significantly enriched in response to AMF induction, e.g., upregulated genes of diphosphocytidyl-2-C-methyl-d-erythritol kinases (ISPEs), cytochrome P450 monooxygenases (CYP450s)_and glycosyltransferases (GTs), while treatments AMF-MeJA and salicylhydroxamic acid (SHAM) decreased the abundance of these DEGs. Interestingly, a high correlation presented between any two of saponin contents, key enzyme activities and expression levels of DEGs. Taken together, the inoculation of AMF can improve the growth and saponin accumulation of P. notoginseng by strengthening the activities of key enzymes and the expression levels of encoding genes, in which the JA regulatory pathway is a key link. This study provides references for implementing ecological planting of P. notoginseng, improving saponin accumulation and illustrating the biosynthesis mechanism.

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.

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.

Over-expression of UDP-glycosyltransferase UGT353G2 confers resistance to neonicotinoids in whitefly (Bemisia tabaci)

The whitefly, Bemisia tabaci, comes up high metabolic resistance to most neonicotinoids in long-term evolution, which is the key problem of pest control. UGT glycosyltransferase, as a secondary detoxification enzyme, plays an indispensable role in detoxification metabolism. In this study, UGT inhibitors, 5-nitrouracil and sulfinpyrazone, dramatically augmented the toxic damage of neonicotinoids to B. tabaci. A UGT named UGT353G2 was identified in whitefly, which was notably up-regulated in resistant strain (3.92 folds), and could be induced by most neonicotinoids. Additionally, the using of RNA interference (RNAi) suppresses UGT353G2 substantially increased sensitivity to neonicotinoids in resistant strain. Our results support that UGT353G2 may be involved in the neonicotinoids resistance of whitefly. These findings will help further verify the functional role of UGTs in neonicotinoid resistance.

UDP-glucuronosyltransferase is involved in susceptibility of Chironomus kiiensis Tokunaga, 1936 (Diptera: Chironomidae) to insecticides

UDP-glucuronosyltransferases (UGTs) could transform various exogenous and endogenous compounds, which help detoxification of pesticides in insects. To investigate the role of UGTs in the detoxification metabolism of insecticides in Chironomus kiiensis, CkUGT302M1, CkUGT302N1, CkUGT308N1 and CkUGT36J1 genes were identified with 1449-1599 bp encoding 482-532 amino acids. Four UGT genes shared 40.86∼53.36% identity with other homologous insect species, and expressed in all developmental stages, notably in the larval and adult stages. Expression of CkUGTs was higher in the gastric caecum, midgut and head. Moreover, CkUGTs expression and activity were significantly increased in C. kiiensis larvae in exposure to sublethal concentrations of carbaryl, deltamethrin and phoxim, respectively. To further explore the functions of UGT genes, the CkUGT308N1 was effectively silenced in 4th instar C. kiiensis larvae by RNA interference, which resulted in the mortality of dsCkUGT308N1 treated larvae increased by 71.43%, 111.11% and 62.50% under sublethal doses of carbaryl, deltamethrin and phoxim at the 24-h time point, respectively. The study revealed that the CkUGT308N1 gene in C. kiiensis could contribute to the metabolism of pesticides and provide a scientific basis for evaluating the water pollution of pesticides.

Hormesis effects of sulfoxaflor on Aphis gossypii feeding, growth, reproduction behaviour and the related mechanisms

Sulfoxaflor, an important alternative insecticide in integrated pest management (IPM) strategies, can effectively control sap-feeding insect pests such as Aphis gossypii. Although the side effects of sulfoxaflor have recently attracted widespread attention, its toxicological characteristics and mechanisms are still largely undefined. Therefore, the biological characteristics, life table and feeding behaviour of A. gossypii were studied to evaluate the hormesis effect of sulfoxaflor. Then, the potential mechanisms of induced fecundity associated with the vitellogenin (Ag. Vg) and vitellogenin receptor (Ag. VgR) genes were investigated. Although the LC₁₀ and LC₃₀ concentrations of sulfoxaflor significantly reduced the fecundity and net reproduction rate (R₀) of the directly exposed sulfoxaflor-resistant and susceptible aphids, hormesis effects on fecundity and R₀ were observed in the F₁ generation of Sus A. gossypii when the parental generation was exposed to the LC₁₀ of sulfoxaflor. Moreover, the hormesis effects of sulfoxaflor on phloem feeding were observed in both A. gossypii strains. Additionally, enhanced expression levels and protein content of Ag. Vg and Ag. VgR were observed in progeny generations when F₀ was subjected to the trans- and multigenerational sublethal sulfoxaflor exposure. Therefore, sulfoxaflor-induced resurgence might occur in A. gossypii after exposure to sublethal concentrations. Our study could contribute to a comprehensive risk assessment and provide convincing reference to optimize sulfoxaflor in IPM strategies.

Sulfoxaflor adversely influences the biological characteristics of Coccinella septempunctata by suppressing vitellogenin expression and predation activity

Sulfoxaflor is a widely used sulfoximine insecticide that has been regarded as an important alternative insecticide for IPM strategies, but a comprehensive study of its potential ecological toxicity is still lacking. In the present work, the growth, longevity, predation and reproduction toxicity of Coccinella septempunctata caused by sulfoxaflor were evaluated. In addition, the potential mechanisms of decreased fecundity in C. septempunctata were investigated by analyzing the transcriptional and protein levels of reproduction-related gene vitellogenin (Vg). In a 20-day acute contact toxicity test, decreased survival proportion, pupation rate, adult emergence ratio, and increased hazard quotient (HQ) values were observed. Moreover, sublethal dosages of sulfoxaflor significantly inhibited the predation, longevity, fecundity and net reproduction rate of progeny. In addition, LR₃₀ of sulfoxaflor dramatically down-regulate the mRNA-expression (F₀: 65.38-fold, F₁: 2.24-fold) and protein content (F₀: 1.35-fold, F₁: 1.36-fold) of Vg in the F₀ and F₁ generations. These results suggested that sulfoxaflor could inhibit the gene and protein content of Vg, thereby reducing the fecundity of C. septempunctata. Our study indicated that sulfoxaflor has potential risks to parent and progeny generations of C. septempunctata. These results provide valuable reference for optimal usage of sulfoxaflor in IPM systems.

AoSte12 Is Required for Mycelial Development, Conidiation, Trap Morphogenesis, and Secondary Metabolism by Regulating Hyphal Fusion in Nematode-Trapping Fungus Arthrobotrys oligospora

Nematode-trapping (NT) fungi are a unique group of carnivorous microorganisms that can capture and digest nematodes by producing ingenious trapping devices (traps). Arthrobotrys oligospora, a representative NT fungus, can develop adhesive three-dimensional networks for nematode predation. Hyphal fusion is indispensable for the trap formation of A. oligospora. Here, we characterized an orthologous Ste12 protein (AoSte12) in A. oligospora via gene disruption, DNA affinity purification sequencing (DAP-Seq), and multi-omics approaches. The disruption of the Aoste12 gene caused an increase in hyphal fusion and resulted in defects in mycelial growth, conidiation, trap morphology, and stress resistance, as well as reducing the number of nuclei and lipid droplet accumulation. Moreover, transcriptome and DAP-Seq analysis revealed that AoSte12 was involved in cellular processes associated with growth, cell fusion, the tricarboxylic acid cycle, vesicles, actin filaments, and lipid metabolism. In addition, combining metabolome with transcriptome and DAP-Seq analysis indicated that AoSte12 was involved in the mitogen-activated protein kinase signaling pathway, lipid metabolism, and secondary metabolites. A yeast two-hybrid assay revealed that AoSte12 can interact with diverse proteins, such as the MAK-2 orthologue protein Fus3, the vacuolar sorting protein Pep3, and UDP-glycosyltransferase. Our results suggest that AoSte12 plays an indispensable role in hyphal fusion and thus regulates sporulation and trap morphogenesis. These results provide deep insights into the connection between hyphal fusion and trap formation in NT fungi. IMPORTANCE Nematode-trapping (NT) fungi are an important natural enemy of nematodes and can capture their prey by producing traps. Hyphal anastomosis and fusion are important for mycelial growth and the colony morphological development of filamentous fungi and are also crucial for the trap morphogenesis of NT fungi. Arthrobotrys oligospora can form complex three-dimensional networks (traps) when sensing the presence of nematodes. This study revealed that AoSte12 is indispensable for hyphal fusion and that it regulates mycelial growth, conidiation, trap morphogenesis, stress resistance, the number of nuclei, and lipid droplet accumulation in A. oligospora. In addition, DNA affinity purification sequencing, transcriptome, and metabolome analyses further revealed that AoSte12 is involved in the mitogen-activated protein kinase pathway, lipid metabolism, and secondary metabolism. Overall, these findings expand the important role of AoSte12 in NT fungus A. oligospora and provide a broad foundation for elucidating the regulatory mechanism of trap development and the lifestyle transitions of pathogenic fungi.

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.

Identification and characterization of UDP-glycosyltransferase genes and the potential role in response to insecticides exposure in Bactrocera dorsalis

BACKGROUND

The oriental fruit fly, Bactrocera dorsalis (Hendel) is a worldwide pest damaging a wide range of hosts. Due to the long-term indiscriminate use of insecticides, B. dorsalis has developed serious resistance to several insecticides. UDP-glycosyltransferases (UGTs) are secondary metabolic enzymes involved in biotransformation and play an important role in the metabolism of plant secondary metabolites and synthetic insecticides in insects. Thus, we suspect that UGTs in B. dorsalis play an important role in insecticide tolerance.

RESULTS

In this study, 31 UGT genes were identified in the genome of B. dorsalis, belonging to 13 subfamilies. Real-time quantitative polymerase chain reaction (RT-qPCR) results revealed that 12 UGT genes were highly expressed in the antennae, midgut, Malpighian tubule and fat body. The mRNA expressions of 17 UGT genes were up-regulated upon exposure to λ-cyhalothrin, imidacloprid, abamectin and chlorpyrifos. Knockdown of the selected five UGT genes (BdUGT301D2, BdUGT35F2, BdUGT36K2, BdUGT49D2, BdUGT50B5) by RNA interference increased the mortality of B. dorsalis from 9.29% to 27.22% upon exposure to four insecticides.

CONCLUSION

The abundance of UGTs in B. dorsalis is similar to other insect species, and 12 out of 31 UGTs were specifically expressed in metabolic tissues, suggesting a key role in detoxification. Down-regulation of five selected UGT genes increased the susceptibility of B. dorsalis to various insecticides, indicating that UGTs may play an important role in tolerance of B. dorsalis to multiple insecticides. © 2022 Society of Chemical Industry.

Exogenously applied melatonin alleviates the damage in cucumber plants caused by Aphis goosypii through altering the insect behavior and inducing host plant resistance

BACKGROUND

Aphis gossypii Glover is the main pest found in most cucumber-producing areas. Melatonin (MT) has been widely studied in protecting plants from environmental stresses and pathogens. However, little knowledge is available on the impact of MT on insect resistance.

RESULTS

The fecundity of aphids on MT-treated cucumber leaves was inhibited. Interestingly, MT-treated plants were more attractive to aphids, which would prevent the large-scale transmission of viruses caused by the random movement of aphids. Meanwhile, MT caused varying degrees of change in enzyme activities related to methylesterified HG degradation, antioxidants, defense systems and membrane lipid peroxidation. Furthermore, transcriptomic analysis showed that MT induced 2360 differentially expressed genes (DEGs) compared with the control before aphid infection. These DEGs mainly were enriched in hormone signal transduction, MAPK signaling pathway, and plant-pathogen interaction, revealing that MT can help plants acquire inducible resistance and enhance plant immunity. Subsequently, 2397 DEGs were identified after aphid infection. Further analysis showed that MT-treated plants possessed stronger JA signal, reactive oxygen species stability, and the ability of flavonoid synthesis under aphid infection, while mediating plant growth and sucrose metabolism.

CONCLUSION

In summary, MT as an environmentally friendly substance mitigated aphid damage to cucumbers by affecting the aphids themselves and enhancing plant resistance. This will facilitate exploring sustainable MT-based strategies for cucumber aphid control. © 2022 Society of Chemical Industry.

Impact of the nicotinic acetylcholine receptor mutation R81T on the response of European Myzus persicae populations to imidacloprid and sulfoxaflor in laboratory and in the field

Sulfoxaflor (Isoclast™ active) is a sulfoximine insecticide that is active on a broad range of sap-feeding insects, including species that exhibit reduced susceptibility to currently available insecticides. Colonies of Myzus persicae (green peach aphid) were established from aphids collected in the field from peach (Prunus persica) and nectarine (Prunus persica var. nucipersica) orchards in France, Italy and Spain. The presence of the nicotinic acetylcholine receptor (nAChR) point mutation R81T was determined for all the colonies. Eight of the 35 colonies collected were susceptible relative to R81T (i.e., R81T absent), three of the colonies were found to be homozygous for R81T while 24 colonies had R81T present in some proportion (heterozygous). Sulfoxaflor and imidacloprid were tested in the laboratory against these M. persicae field colonies, which exhibited a wide range of susceptibilities (sulfoxaflor RR = 0.6 to 61, imidacloprid RR = 0.7 to 986) (resistance ratios, RR) to both insecticides. Although sulfoxaflor was consistently more active than imidacloprid against these field collected M. persicae, there was a statistically significant correlation across all colonies between the RRs for imidacloprid and sulfoxaflor (Pearson's r = 0.939, p < 0.0001). However, when a larger group of the colonies from Spain possessing R81T were analyzed, there was no correlation observed for the RRs between imidacloprid and sulfoxaflor (r = 0.2901, p = 0.3604). Thus, consistent with prior studies, the presence of R81T by itself is not well correlated with altered susceptibility to sulfoxaflor. In field trials, sulfoxaflor (24 and 36 gai/ha) was highly effective (~avg. 88-96% control) against M. persicae, demonstrating similar levels of efficacy as flonicamid (60-70 gai/ha) and spirotetramat (100-180 gai/ha) at 13-15 days after application, in contrast to imidacloprid (110-190 gai/ha) and acetamiprid (50-75 gai/ha) with lower levels of efficacy (~avg. 62-67% control). Consequently, sulfoxaflor is an effective tool for use in insect pest management programs for M. persicae. However, it is recommended that sulfoxaflor be used in the context of an insecticide resistance management program as advocated by the Insecticide Resistance Action Committee involving rotation with insecticides possessing other modes of action (i.e., avoiding rotation with other Group 4 insecticides) to minimize the chances for resistance development and to extend its future utility.

Sulfoxaflor - A sulfoximine insecticide: Review and analysis of mode of action, resistance and cross-resistance

The sulfoximines, as exemplified by sulfoxaflor (Isoclast™active), are a relatively new class of nicotinic acetylcholine receptor (nAChR) competitive modulator (Insecticide Resistance Action Committee [IRAC] Group 4C) insecticides that provide control of a wide range of sap-feeding insect pests. The sulfoximine chemistry and sulfoxaflor exhibits distinct interactions with metabolic enzymes and nAChRs compared to other IRAC Group 4 insecticides such as the neonicotinoids (Group 4A). These distinctions translate to notable differences in the frequency and degree of cross-resistance between sulfoxaflor and other insecticides. Most insect strains exhibiting resistance to a variety of insecticides, including neonicotinoids, exhibited little to no cross-resistance to sulfoxaflor. To date, only two laboratory-based studies involving four strains (Koo et al. 2014, Chen et al. 2017) have observed substantial cross-resistance (>100 fold) to sulfoxaflor in neonicotinoid resistant insects. Where higher levels of cross-resistance to sulfoxaflor are observed the magnitude of that resistance is far less than that of the selecting neonicotinoid. Importantly, there is no correlation between presence of resistance to neonicotinoids (i.e., imidacloprid, acetamiprid) and cross-resistance to sulfoxaflor. This phenomenon is consistent with and can be attributed to the unique and differentiated chemical class represented by sulfoxalfor. Recent studies have demonstrated that high levels of resistance (resistance ratio = 124-366) to sulfoxaflor can be selected for in the laboratory which thus far appear to be associated with enhanced metabolism by specific cytochrome P450s, although other resistance mechanisms have not yet been excluded. One hypothesis is that sulfoxaflor selects for and is susceptible to a subset of P450s with different substrate specificity. A range of chemoinformatic, molecular modeling, metabolism and target-site studies have been published. These studies point to distinctions in the chemistry of sulfoxaflor, and its metabolism by enzymes associated with resistance to other insecticides, as well as its interaction with insect nicotinic acetylcholine receptors, further supporting the subgrouping of sulfoxaflor (Group 4C) separate from that of other Group 4 insecticides. Herein is an expansion of an earlier review (Sparks et al. 2013), providing an update that considers prior and current studies focused on the mode of action of sulfoxaflor, along with an analysis of the presently available resistance / cross-resistance studies, and implications and recommendations regarding resistance management.

UDP-Glucosyltransferases Induced by Nosema bombycis Provide Resistance to Microsporidia in Silkworm (Bombyx mori)

Simple Summary

Nosema bombycis (N. bombycis), an obligate intracellular eukaryotic parasite, is a virulent pathogen of the silkworm, that causes major economic losses. Although many studies have reported on B. mori host response to this pathogen, little is known about which genes are induced by N. bombycis. Our results showed that two B. mori uridine diphosphate-glucosyltransferases (UGTs) (BmUGT10295 and BmUGT8453) could be activated by N. bombycis and provide resistance to the microsporidia in silkworms. These results will contribute to our understanding of host stress reaction to pathogens and the two pathogen-induced resistant genes will provide a target for promoting pathogen resistance.

Abstract

As a silkworm pathogen, the microsporidian N. bombycis can be transovarially transmitted from parent to offspring and seriously impedes sericulture industry development. Previous studies found that Uridine diphosphate (UDP)-glycosyltransferases (UGTs) are involved in regulating diverse cellular processes, such as detoxification, pigmentation, and odorant sensing. Our results showed that BmUGT10295 and BmUGT8453 genes were specifically induced in infected silkworms, but other BmUGTs were not. Tissue distribution analysis of the two BmUGTs showed that the transcriptions of the two BmUGTs were mainly activated in the midgut and Malpighian tubule of infected silkworms. Furthermore, there were significantly fewer microsporidia in over-expressed BmUGTs compared with the control, but there were significantly more microsporidia in RNA interference BmUGTs compared with the control. These findings indicate that the two BmUGTs were induced by N. bombycis and provided resistance to the microsporidia.