The Role of Cytochrome P450s in Insect Toxicology and Resistance

Impact of long-term cadmium exposure on insecticidal cross-resistance and biological traits of Brown planthopper Nilaparvata lugens (Hemiptera: Delphacidae)

Cadmium (Cd) pollution threatens ecosystems and agricultural productivity, especially in rice-growing regions. This study examines the effects of long-term Cd exposure on the brown planthopper (Nilaparvata lugens), a major rice pest, focusing on biological traits, physiological responses, and insecticide cross-resistance. Cd bioaccumulation occurred across the soil-plant-insect chain, with higher concentrations in advanced N. lugens stages. Cd exposure prolonged development, reduced fecundity, and altered life table parameters, impairing population fitness. Physiological analyses showed increased activities of antioxidant (SOD, CAT, POD) and detoxification enzymes (GST and P450) and neurotransmission-regulating enzyme AChE in Cd-exposed insects, indicating adaptive stress responses. Prolonged Cd exposure also induced cross-resistance to insecticides like triflumezopyrim, dinotefuran, and sulfoxaflor, evidenced by higher LC50 values. Energy reserves, including glycogen, triglycerides, and total cholesterol, were significantly reduced in Cd-exposed N. lugens, further affecting reproduction. These findings reveal the complex link between heavy metal stress and insecticide resistance, highlighting challenges for pest management in Cd-contaminated areas. The study emphasizes the need for integrated pest management and soil remediation to mitigate heavy metal pollution's ecological and agricultural impacts. Future research should explore molecular mechanisms of Cd-induced cross-resistance and their implications for sustainable agriculture.

NADPH-cytochrome P450 reductase mediates resistance to neonicotinoid insecticides in Bradysia odoriphaga

As a crucial electron transfer partner of the P450 system, NADPH-cytochrome P450 reductase (CPR) plays an influential role in P450-mediated detoxification metabolism of xenobiotics. CPR has been found to be associated with insecticide resistance in several insects. However, the role of CPR in the cross-resistance of Bradysia odoriphaga to clothianidin and neonicotinoid insecticides remains to be elucidated. In this study, the CPR gene (BoCPR) of B. odoriphaga was cloned and characterized. The expression of BoCPR was more abundant in the adult stage and in the midgut and Malpighian tubules of larvae, and BoCPR was significantly overexpressed in the clothianidin-resistant (CL-R) strain compared to the susceptible (SS) strain. Exposure to clothianidin significantly increased BoCPR expression in both the SS and CL-R strains. In addition, knockdown of BoCPR in SS and CL-R strains significantly reduced CPR and P450 enzyme activities, and resulted in a significant increase in larval susceptibility to clothianidin, imidacloprid, and thiamethoxam. These results suggest that BoCPR plays an important role in B. odoriphaga resistance to clothianidin and cross-resistance to neonicotinoid insecticides.

Regulation of detoxifying enzymes expression and restriction of picorna-like virus infection by natural polysaccharide extracts in Drosophila cells

The world is currently witnessing a rise in viral infections, while the availability of antiviral drugs remains limited. Traditional Chinese medicine (TCM) has historically served as a valuable source of novel compounds for disease treatment. In this study, we assessed the antiviral potential of various TCM compounds using Drosophila melanogaster as a model organism. Our findings reveal that natural polysaccharide extracts, prepared from 10 commonly used medicinal herbs or fungi, exhibit antiviral activity against two picorna-like viruses. Importantly, the antiviral effect is not directly attributable to the compound itself but is instead mediated by cellular responses induced by treatment with the extract. We observed that the polysaccharide extract triggers a broad transcriptional response, which partially overlaps with NF-κB pathway activation in Drosophila. However, the antiviral activity of the extract was independent of classical innate immune pathways, such as RNA interference or NF-κB signaling. Instead, the extract appears to uniquely stimulate detoxification pathways, including upregulation of cytochrome P450 and glutathione S-transferase genes, which correlates with its antiviral effects.

Towards a unified approach in managing resistance to vaccines, drugs, and pesticides

Everywhere, pests and pathogens evolve resistance to our control efforts, impairing human health and welfare. Developing sustainable solutions to this problem requires working with evolved immune and ecological systems, rather than against these evolutionary forces. We advocate a transdisciplinary approach to resistance based on an evolutionary foundation informed by the concepts of integrated pest management and One Health. Diverse, multimodal management approaches create a more challenging environment for the evolution of resistance. Given our permanent evolutionary and ecological relationships with pests and pathogens, responses to most biological threats to health and agriculture should seek sustainable harm reduction rather than eradication.

Identification of the CYPome associated with acetamiprid resistance based on the chromosome-level genome of Megalurothrips usitatus (Bagnall) (Thysanoptera: Thripidae)

BACKGROUND

The bean flower thrips, Megalurothrips usitatus, poses a great threat to cowpea and other legume cultivars. Chemical insecticides have been applied to control M. usitatus, but have resulted in little profit because of the rapid evolution of insecticide resistance. To characterize the potential insecticide resistance mechanisms in M. usitatus, we sequenced and assembled a chromosome-level genome of M. usitatus by combining PacBio sequencing and Hi-C technology using a susceptible population.

RESULTS

The genome size was 248.60 Mb and contained 14 128 protein-coding genes. The expansion genes of M. usitatus were enriched in the functional categories of heme binding and monooxygenase activity. We further identified 103 cytochrome P450 genes from the M. usitatus genome, 33 of which belonged to the CYP6 family. Ten CYP6 genes were significantly overexpressed in an acetamiprid-resistant population of M. usitatus. An RNA interference bioassay showed that knockdown of CYP6FW1, CYP6GM5, CYP6GM6, and CYP6GM7 significantly reduced acetamiprid resistance in the resistant population. In addition, the expression of all four genes could be induced by acetamiprid exposure. AlphaFold2-based homology modeling and molecular docking analysis showed that the proteins with relevance to acetamiprid resistance had relatively lower binding free energy with the acetamiprid molecule.

CONCLUSION

This study provides a reference genome and gene resources for future studies on the evolution of M. usitatus and related pest species, and highlights the importance of cytochrome P450s in insecticide resistance in this pest insect. © 2025 Society of Chemical Industry.

Proactive Resistance Management Studies Highlight the Role of Cytochrome P450 Genes in the Resistance of Tuta absoluta Against Tetraniliprole

The diamide insecticide tetraniliprole is a valuable tool for managing major insect pests like the invasive tomato pinworm, Tuta absoluta (Meyrick). However, the mechanisms underlying tetraniliprole resistance, as well as its associated fitness costs, remain unclear. In this study, we assessed the fitness of tetraniliprole-resistant (TetraRS) and susceptible (SS) strains of T. absoluta and conducted Illumina RNA-seq to compare their transcriptomes. We also used nanocarrier-mediated RNA interference (RNAi) to knockdown P450 genes and evaluate their role in tetraniliprole resistance. After eight generations of selection, T. absoluta developed a 20.80-fold resistance to tetraniliprole, accompanied by fitness costs. RNA-seq analysis revealed 3332 differentially expressed genes (DEGs), with 1707 upregulated and 1625 downregulated in the TetraRS compared to the SS strain. Gene Ontology (GO) annotations showed significant enrichment in categories related to metabolic processes, cellular processes, catalytic activity, cellular anatomical entity, and binding. These genes were also identified in key KEGG pathways such as cytochrome P450, drug metabolism, carbon metabolism, oxidative phosphorylation, fatty acid metabolism, and protein processing. RT-qPCR analysis confirmed that P450 genes (CYP405D1, CYP6AB269, and CYP4AU1) were upregulated in TetraRS insects, in line with the RNA-seq results. Cytochrome P450 activity was significantly higher in the TetraRS strain than in the SS strain. Notably, nano-encapsulated dsRNA targeting these overexpressed P450 genes increased the susceptibility of T. absoluta to tetraniliprole. Further, cytochrome P450 activity was significantly reduced following silencing of P450 genes. These findings suggest that multiple genes and pathways, particularly P450 genes, contribute to tetraniliprole resistance in T. absoluta. This study provides valuable insights into the molecular mechanisms underlying insecticide resistance in this key pest species.

Neuroprotective and Gastroprotective Effects of Rutin and Fluoxetine Co-Supplementation: A Biochemical Analysis in Nauphoeta cinerea

A significant portion of the global population is affected by depression, leading to considerable social and economic burdens. Although antidepressants such as fluoxetine are effective, their prolonged use is often associated with adverse side effects. This study investigated the biochemical effects of fluoxetine and rutin, individually and in combination, using the Nauphoeta cinerea model. Cockroaches were supplemented with the compounds for seven days, during which toxicity, body weight, and food intake were monitored. At the end of the treatment, neural and intestinal tissues were subjected to biochemical analyses, and in silico evaluations of the compounds were also performed. Co-supplementation with rutin (5mg/mL) and fluoxetine (20mg/mL) significantly reduced TBARS levels compared to fluoxetine alone and prevented the weight loss typically observed with fluoxetine treatment, despite similar food intake across groups. Rutin also mitigated the toxicity associated with fluoxetine administration. These findings suggest that rutin co-supplementation may attenuate fluoxetine-induced oxidative stress and toxicity, supporting its potential as a protective agent during antidepressant therapy.

A multi-omic meta-analysis reveals novel mechanisms of insecticide resistance in malaria vectors

Malaria control faces challenges from widespread insecticide resistance in major Anopheles species. This study, employing a cross-species approach, integrates RNA-Sequencing, whole-genome sequencing, and microarray data to elucidate drivers of insecticide resistance in Anopheles gambiae complex and An. funestus. Here we show an inverse relationship between genetic diversity and gene expression, with highly expressed genes experiencing stronger purifying selection. Gene expression clusters physically in the genome, revealing potential coordinated regulation, and we find that highly over-expressed genes are associated with selective sweep loci. We identify known and novel candidate insecticide resistance genes, enriched for metabolic, cuticular, and behavioural functioning. We also present AnoExpress, a Python package, and an online interface for user-friendly exploration of resistance candidate expression. Despite millions of years of speciation, convergent gene expression responses to insecticidal selection pressures are observed across Anopheles species, providing crucial insights for malaria vector control.

A self-assembled multicomponent RNA nano-biopesticide for increasing the susceptibility of destructive bean flower thrips to insecticides via dsNrf2

High resistance of bean flower thrips (BFT, Megalurothrips usitatus) has led to the unscientific application of insecticides to cause famous "toxic cowpea" incidents in China. Nuclear factor erythroid 2-related factor 2 (Nrf2) plays an important role in inducing antioxidant responses and drug detoxification. Therefore, the detoxification genes may be suppressed to control insecticide resistance via Nrf2. Herein, we demonstrated that the expression of most detoxification genes and enzyme activity were remarkably suppressed via nrf2 RNAi. Subsequently, a novel hydrophilic-lipophilic diblock polymer (HLDP) was developed to co-assemble with dsNrf2 and sulfoxaflor (SUL) into nanoscale SUL/HLDP/dsNrf2 complex (221.52 nm). Excitingly, the SUL/HLDP/dsNrf2 complex exhibited excellent leaf adhesion performance, with the smaller contact angle, reduced surface tension, amplified contact area, improved retention, and enhanced plant uptake. Meanwhile, theSUL/HLDP/dsNrf2 displayed high delivery efficiency in vitro and in vivo, and its insecticidal activity against BFTs was significantly higher than SUL. Furthermore, the required doses of SUL/HLDP/dsNrf2 to achieve similar insecticidal activity were 50.14% and 58.42% of SUL via immersion and oral feeding, respectively. Overall, this study elucidated the regulatory role of nrf2 in the detoxification and metabolism of BFTs and developed a self-assembled multicomponent RNA nano-biopesticide to increase the susceptibility of BFTs to insecticides.

Multigeneration Sublethal Chlorantraniliprole Treatment Disrupts Nutritional Metabolism and Inhibits Growth, Development, and Reproduction of Phthorimaea absoluta

Phthorimaea absoluta, an important pest of tomato crops, has reportedly developed high levels of resistance to the insecticide chlorantraniliprole, which has a unique mode of action and high efficacy. This study evaluated the sustained multigenerational effects of chlorantraniliprole on P. absoluta, focusing on resistance development, growth, development, reproductive capacity, population parameters, and nutritional indicators. After continuous selection with sublethal chlorantraniliprole for eight generations (CX-Sub8), bioassays showed that CX-Sub8 had 225.37-fold higher resistance than the susceptible strain. The age-stage, two-sex life table analysis revealed that the preadult development time and mean generation time were significantly prolonged, while population reproduction and pupal weight were reduced. Moreover, the relative fitness of CX-Sub8 was 0.62, and changes in the life table parameters correlated with an increase in the serial number of selection cycles. The second-instar larvae of CX-Sub8 presented lower triglyceride, glycerol, trehalose, free fatty acid, and protein contents than the unselected strain (CX-S8). Transcriptome analysis identified 2517 differentially expressed genes, with most being enriched in nutrient metabolism-related pathways, such as amino acid biosynthesis and fatty acid degradation metabolism. These results indicate that multigenerational sublethal chlorantraniliprole treatment disrupts the nutritional metabolism, and inhibits the growth, development, and reproduction of P. absoluta.

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.

CYP321F3 mediates metabolic resistance to methoxyfenozide in rice stem borer, Chilo suppressalis

The development of insecticide resistance in insect populations is a major challenge to sustainable agriculture and food security worldwide. Methoxyfenozide, an insect growth regulator that acts as an agonist of 20-hydroxyecdysone (20E), has severely declined in its efficacy against the rice stem borer (Chilo suppressalis), a notorious pest of rice crops in East and Southeast Asia. To date, however, the genes involved in methoxyfenozide resistance in target pests remain unclear. We conducted a long-term (seven years from 2017 to 2023) and large geographical scale (8 provinces and 45 cities in China) resistance monitoring program for methoxyfenozide in C. suppressalis. Resistance was seen to arise rapidly in this species, with >100-fold resistance being detected in nearly all the field populations after 2018. Piperonyl butoxide (PBO), an inhibitor of cytochrome P450 enzymes (P450s), significantly increased the sensitivity of resistant strains of C. suppressalis to methoxyfenozide, implicating P450s in resistance. Six P450 genes: CYP321F3, CYP6CV5, CYP9A68, CYP6AB45, CYP324A12 and CYP6SN2 were identified as highly expressed in resistant C. suppressalis by transcriptome profiling. Of these, ectopic expression of CYP321F3 in Drosophila melanogaster resulted in a 7.0-fold increase in resistance to methoxyfenozide demonstrating its causal role in resistance. Collectively, these findings provide insight into the mechanisms mediating resistance to insect growth regulators and will inform the development of future pest and resistance management strategies.

Prevalence of insecticide resistance and enhanced detoxifying enzymes in field populations of Tuta absoluta (Lepidoptera: Gelechiidae) in the major Tomato growing regions of South India

South American pinworm Tuta absoluta (Meyrick) is an invasive and major tomato pest that attained resistance or reduced susceptibility to most insecticides used in their management due to repeated and intensive applications. This study aimed to find the levels of resistance in T. absoluta populations collected from South Indian states against novel insecticides such as chlorantraniliprole 18.5% SC, flubendiamide 39.35% SC, spinosad 45% SC, indoxacarb 14.5% SC, and emamectin benzoate 5% SG using leaf dip bioassay. Among the eight populations collected from major tomato growing belts spanning three states of South India (Andhra Pradesh, Karnataka and Tamil Nadu), Krishnagiri of Tamil Nadu showed the highest level of resistance to flubendiamide and the least resistance was shown by the Tirupati population, with a resistance ratio of 174.89 and 2.24, respectively. Significant correlation was found between LC50 values of flubendiamide and chlorantraniliprole (0.859), emamectin benzoate and flubendiamide (0.855) and spinosad and emamectin benzoate (0.866). The biochemical assay conducted to quantify the mixed function oxidase (MFO), carboxyl/choline esterase (CCE) and glutathione S-transferase (GST) in the T. absoluta larval populations showed an increased level of MFO, CCE and GST in Krishnagiri population with 15.59, 1.72 and 6.02-fold, respectively compared to susceptible population. It showed that the detoxification enzyme plays an important role in the insecticide resistance of the field population of T. absoluta. The results serve as an initial assessment for further understanding of the molecular mechanisms of insecticide resistance at the genetic level to design and implement successful insecticide resistance management strategies.

Impact of a worker bee thoracic ganglion RIC-3 variant on the actions of acetylcholine and neonicotinoids on nicotinic receptors in Apis mellifera

A transmembrane thioredoxin (TMX3) enables the functional expression of insect nicotinic acetylcholine receptors (nAChRs) in Xenopus laevis oocytes, while co-factors RIC-3 and UNC-50 regulate the receptor expression level. RIC-3 (resistant to inhibitors of cholinesterase 3) has been shown to diversify by its differential mRNA splicing patterns. How such diversity influences neonicotinoid sensitivity of nAChRs of beneficial insect species remains poorly understood. We have identified a RIC-3 variant expressed most abundantly in the thoracic ganglia of honeybee (Apis mellifera) workers and investigated its effects on the functional expression and pharmacology of Amα1/Amα8/Amβ1 and Amα1/Amα2/Amα8/Amβ1 nAChRs expressed in X. laevis oocytes. The AmRIC-3 enhanced the response amplitude to the acetylcholine (ACh) of these A. mellifera nAChRs when its cRNA was injected into oocytes at low concentrations but suppressed the ACh response amplitude at high concentrations. Co-expression of the AmRIC-3 had a minimal impact on the affinity of ACh, but changed the efficacy of imidacloprid and clothianidin, suggesting that the presence and the level of RIC-3 expression can affect the nAChR responses to ACh and neonicotinoids, depending on nAChR subunit composition in honeybees. © 2024 Society of Chemical Industry.

Downregulation of carboxylesterase gene mediates resistance to indoxacarb in Spodoptera litura

Carboxylesterases (CarEs) play a critical role in metabolic resistance to insecticides of insects. But fewer CarEs were associated with insecticide bioactivation in insects. Previous findings showed that four CarE genes were downregulated in the indoxacarb resistant populations of Spodoptera litura. In this study, qPCR verification showed that the expression of SlituCOE067 was downregulated in the resistant strains and gradually decreased after exposure to indoxacarb. Silencing of SlituCOE067 increased the cells viability of S. litura against indoxacarb, and further knockdown of SlituCOE067 reduced the sensitivity of larvae to indoxacarb. Overexpression of SlituCOE067 in transgenic fruit flies decreased the tolerance to indoxacarb. Molecular modeling and insecticide docking predicted that SlituCOE067 protein can bind tightly to indoxacarb instead of its activated product N-decarbomethoxylated metabolite (DCJW). Heterologous expression and metabolism experiment proved that recombinant SlituCOE067 can promote the activation of indoxacarb into DCJW, but cannot metabolize DCJW. These results comprehensively demonstrate that downregulation of SlituCOE067 can reduce the activation metabolism of indoxacarb and mediate the resistance of S. litura to indoxacarb. This study reveals a new mechanism of insecticide resistance caused by blocking the activation of insecticides in lepidoptera insects.

Identification and functional characterization of CYP3002B2, a cytochrome P450 associated with amitraz and flumethrin resistance in the major bee parasite Varroa destructor

Beekeeping worldwide is increasingly threatened by the parasitic mite Varroa destructor, whose management relies heavily on synthetic acaricides such as amitraz and flumethrin. However, the growing incidence of acaricide resistance in V. destructor presents a significant global challenge to apiculture. In this study, we investigated the mechanisms underlying resistance to these compounds in a V. destructor population exhibiting reduced susceptibility to both amitraz and flumethrin. Specifically, bioassays revealed that the resistant population (IL-R) displayed 35.0 % mortality in response to amitraz and 39.5 % mortality to flumethrin, in contrast to >90 % mortality observed in the susceptible IL-L and ATH-S populations. The resistance phenotype was not strongly associated with any of the known target site mutations; the putative amitraz resistance mutation F290L in the Octβ2R gene, and the pyrethroid resistant mutation L925V in the vgsc gene, were found at low frequencies (8.6 % and 13.6 % respectively). Transcriptomic analysis, comparing gene expression levels between the resistant population and two susceptible populations, revealed that resistance is associated with the overexpression of several cuticle genes and the cytochrome P450 gene CYP3002B2. CYP3002B2 was functionally expressed in E. coli, exhibiting catalytic activity against multiple model substrates and effectively metabolizing both amitraz and flumethrin. The predominant product of amitraz metabolism is likely an inactive, hydroxylated form of the insecticide, rather than any of the known activated/toxic metabolites of amitraz. These findings are crucial for evidence-based V. destructor management, as CYP3002B2 is the first detoxification enzyme shown to metabolize two major acaricides from different modes of action classes.

Effects of Metarhizium anisopliae on lethality, transfer, behavior, and physiology in Eucryptorrhynchus scrobiculatus and E. brandti (Coleoptera: Curculionidae)

Eucryptorrhynchus scrobiculatus (Motschulsky) and E. brandti (Harold) are 2 serious pests inflicting damage on Ailanthus altissima (Mill.) Swingle. In the field, these species exhibit aggregation behavior. We hypothesized that this behavior facilitated the contact and horizontal transfer of Metarhizium anisopliae (Metschn.) Sorokin in weevil species. Little or no mortality in both E. scrobiculatus and E. brandti adult individuals exposed to low concentrations M. anisopliae (1 × 105, 1 × 106 conidia/ml). A mortality rate of 100% was observed in both E. scrobiculatus and E. brandti adults after 3 and 5 d of treatment with M. anisopliae at concentrations of 1 × 109 and 1 × 108 conidia/ml. The aggregation behavior of E. scrobiculatus and E. brandti adults was unaffected by M. anisopliae. In the transfer test of M. anisopliae, the mortality rate of recipients mixed with donors treated with M. anisopliae conidia was significantly higher compared to untreated donors and control recipients in laboratory and field experiments. Furthermore, the mortality of secondary recipients in both E. scrobiculatus and E. brandti was significantly higher than that of the control group. The findings suggested that horizontal transfer of M. anisopliae occurred in both species, which was further supported by microscopy observation and the activity of immune-related enzymes in the donor, recipient, and secondary recipient. Our findings demonstrated a specific method for improving pest control by combining aggregation behavior with the use of biopesticides, thereby enhancing the understanding of biological management strategies.

Responses of biological characteristics and detoxification enzymes in the fall armyworm to methoxyfenozide stress

Methoxyfenozide is an insecticide with a unique mode of action on the insect ecdysone receptor and has been registered for the control of insect pests all over the world. In the present work, Spodoptera frugiperda was exposed to sublethal and lethal concentrations of methoxyfenozide to determine its impact on specific biological traits, metabolic enzyme activity, and the expression of detoxification enzymes. The result showed that 72-h posttreatment with LC50 and LC70 of methoxyfenozide significantly reduced the fecundity (eggs/female) of the F0 generation compared to those of the control group. However, the duration of the prepupal period was significantly increased. The exposure to LC10, LC30, LC50, and LC70 concentrations of methoxyfenozide significantly extended the developmental duration of larvae in F1 individuals. The fecundity of the F1 generation was significantly decreased, and the population life table parameters of F1 were also significantly affected. The activity of carboxylesterases showed little significant change, whereas the activity of glutathione S-transferases (GSTs) and cytochrome P450 monooxygenases (P450s) was significantly altered after exposure to LC10, LC30, LC50, and LC70 of methoxyfenozide. In total, 24-, 48-, and 96-h posttreatment with LC10, LC30, LC50, and LC70 of methoxyfenozide could cause upregulation of P450 genes such as CYP6AE44, CYP6B39, CYP9A26, CYP9A58, CYP9A59, and CYP9A60, as well as GST genes including GSTe3, GSTe9, GSTe10, GSTe15, GSTo2, GSTs1, GSTs5, GSTm2, and GSTm3. These findings could be instrumental in elucidating the molecular mechanisms underlying the sublethal and lethal effects of methoxyfenozide to S. frugiperda.

Azoxystrobin-Induced Physiological and Biochemical Alterations in Apis mellifera Workers of Different Ages

Fungal diseases of agricultural crops cause severe economic losses to the growers. For the control of these diseases, azoxystrobin is one of the recommended fungicides. This fungicide is systemic in action and is expected to reach the floral part of the treated crop and its residue in the pollen and nectar, the natural food sources of honey bees, which could be collected and fed on by honey bees, thus affecting their health. The purpose of this study was to determine the physiological and chemical changes caused by this fungicide in honey bee workers (Apis mellifera L). Workers of this honey bee at 1, 8, and 21 days old were treated with 125, 167, and 250 mg/L concentrations of azoxystrobin for seven days; their survival rates, activities of carboxylesterase (CarE), glutathione S-transferases (GSTs), cytochrome P450 enzyme (CYP450), catalase (CAT), and superoxide dismutase (SOD) enzymes, and the expression levels of immune (Aba, Api, Def1, and Hym) and nutrition genes (Ilp1, Ilp2, and Vg) were detected. Our findings revealed that azoxystrobin affected the survival of workers, particularly 1- and 21-day-old workers, who responded to azoxystrobin stress with increased activities of detoxification and protective enzymes, which might have physiological costs. Additionally, azoxystrobin affected the expression of immune and nutrition genes, with a decreased expression trend in 21-day-old workers compared to the 1- and 8-day-old workers, leading to reduced resistance to external stressors and increased mortality rates. These findings provide important insights into the adverse effects of azoxystrobin on workers of different ages and emphasize the potential risks of this chemical to colony stability and individual health. This study recommends an urgent ban on such a harmful fungicide being used for fungi control in agriculture, especially during plant flowering.

Identification and expression of detoxification genes provide insights into host adaptation of the walnut pest Atrijuglans aristata

BACKGROUND

Despite the presence of a large number of toxic components, primarily juglone, in walnut green husks, these components have failed to prevent infestations of the specialized pest Atrijuglans aristata. At present, it remains unclear whether detoxification genes play a pivotal role in enhancing host fitness of A. aristata. In this study, we explored the adaptation mechanisms of A. aristata to host plants by identifying and expressing gene families associated with detoxification, as well as assessing the binding affinity of their protein products with juglone.

RESULTS

We identified 84 P450 (P450 monooxygenases), 48 COE (carboxylesterases), 34 GST (glutathione S-transferases), 26 UGT (UDP-glycosyltransferases), and 57 ABC (ATP-binding cassette) transporter genes in the genome of A. aristata. The P450 gene family of A. aristata was divided into four classes based on phylogenetic relationships. Comparative transcriptome analysis revealed that 383 genes in the larval guts of A. aristata were significantly down-regulated after starvation treatment compared with normal feeding. These genes were frequently enriched in pathways related to P450 detoxification metabolism. Through homology modeling and molecular docking analysis of the 12 significantly down-regulated P450 genes, it was found that all 12 proteins exhibited strong binding affinities with the ligand molecule juglone.

CONCLUSIONS

The gene number of the detoxification-related families in the A. aristata genome is close to that of other specialized insect species. Twelve candidate P450 genes identified in comparative transcriptome analysis are inferred to be involved in host adaptation of A. aristata. These results provide a theoretical basis for the management of walnut pests.

Contribution of Nilaparvata lugens Nicotinic Acetylcholine Receptor Subunits Toward Triflumezopyrim and Neonicotinoid Susceptibility

Nicotinic acetylcholine receptors (nAChRs) are the molecular targets of some important insecticides including triflumezopyrim and neonicotinoids. However, our understanding of insect nAChR pharmacology and the specific nAChR subunits targeted by these insecticides remains limited. Here, we cloned 11 nAChR subunit genes, comprising Nlα1 to Nlα8, Nlα10, Nlβ1 and Nlβ3, from Nilaparvata lugens, a highly damaging insect pest of rice crops worldwide. Analysis of the expression of these genes in different tissues of N. lugens by qPCR analysis identified the brain as the primary site of expression. Knock down of the expression of Nlα1, Nlα2, Nlα8 and Nlβ1 using RNAi reduced N. lugens sensitivity to triflumezopyrim, suggesting these genes encode potential target subunits for triflumezopyrim. Knock out of Nlα2 and Nlα8 nAChR subunits by CRISPR/Cas9 genome editing showed that their deletion significantly reduced the toxicity of triflumezopyrim toward N. lugens. Furthermore, the deletion of Nlα2 also increased N. lugens resistance to imidacloprid and dinotefuran. However, numerous attempts revealed that the Nlβ1 knockout was nonviable. In vitro expression of receptors composed of Drosophila homologous subunits showed that this all-insect nAChR was inhibited by nanomolar concentrations of triflumezopyrim. The present findings identify specific nAChR subunits that are important both as targets for monitoring resistance-associated mutations and as subjects for molecular studies aimed at developing novel insecticides targeting these essential ion channels.

The released micro/nano-plastics from plastic containers amplified the toxic response of disinfection by-products in human cells

Micro- and nanoplastics (MNPs) released from plastic containers pose significant food safety concerns; however, their release patterns in different containers along with their impacts on other pollutants remain poorly understood. This study revealed that feeding bottles, food containers, and paper cups released approximately 104 microplastics and 107 nanoplastics after hot water treatment. These released MNPs were nontoxic in six cell types, whereas they significantly amplified the toxicity of disinfection by-products (DBPs), a widely existing contaminant in drinking water. The joint toxicity was influenced by MNPs size, the types of cells and DBPs, with a maximum synergistic efficiency of 57.89 ± 4.64 % in human hepatic carcinoma cells (HepG2) exposed to nanoplastics from feeding bottles and iodoacetamide. Additionally, the exposure assessment indicated that released MNPs posed greater risks to infants. These findings suggested that while MNPs alone were nontoxic, their interactions with DBPs presented potential risks, particularly for sensitive populations.

A key amino acid substitution of vacuolar-type H+-ATPases A subunit (VATP-A) confers selective toxicity of a potential botanical insecticide, periplocoside P (PSP), in Mythimna separata and Spodoptera exigua

Periplocosides, extracted from the root bark of Periploca sepium, are plant secondary compounds known to inhibit the V-ATPase enzyme in susceptible insect species, such as Mythimna separata. However, many species, including Spodoptera exigua, show resistance to these compounds. Previous studies identified the V-ATPase subunit A (VATP-A) in the midgut epithelium of M. separata as the putative target of periplocoside P (PSP), but the specific amino acids involved in this interaction remained unclear. In this study, we demonstrate the selective toxicity of PSP and its inhibition effect on V-ATPase. Molecular docking identified potential interactions between PSP and three amino acids (K85, R171, E199) in MsVATP-A, with in vitro binding assays revealing that K85 and R171 serve as the primary binding sites. Notably, sequence alignment revealed that R171 in sensitive species is substituted with K in resistant species. To investigate the functional implications of this substitution, we performed in vitro site-directed mutagenesis to exchange the corresponding amino acids between the VATP-A orthologs of M. separata and S. exigua. The R171K mutation in MsVATP-A reduced binding to PSP, while the K170R mutation in SeVATP-A enhanced it. Furthermore, in vivo genome editing in Drosophila melanogaster, a PSP-sensitive species, revealed that the R168K mutation conferred 15.78-fold resistance to PSP compared to the wild-type strain (w1118). Our findings confirm the role of VATP-A as the target of PSP and elucidate the key amino acids influencing its insecticidal selectivity. This research enhances the understanding of the molecular interactions between natural compounds and insect targets, offering insights for the development of targeted pest control strategies.

Simulating dynamic insecticide selection pressures for resistance management in mosquitoes assuming polygenic resistance

Insecticide resistance management (IRM) is critical to maintain the operational effectiveness of insecticides used in public health vector control. Evaluating IRM strategies rests primarily on computational models. Most models assume monogenic resistance, but polygenic resistance may be a more appropriate assumption. Conventionally, polygenic models assume selection differentials are constant over successive generations. We present a dynamic method for calculating the selection differentials accounting for the level of resistance and insecticide efficacy. This allows the inclusion of key parameters namely insecticide dosing, insecticide decay and cross resistance, increasing biological and operational realism. Two methods for calculating the insecticide selection differential were compared: truncation (only the most resistant individuals in the population survive) and probabilistic (individual survival depends on their level of resistance). The probabilistic calculation is extendable to multiple gonotrophic cycles, whereby mosquitoes may encounter different insecticides over their life span. A range of IRM strategies of direct policy relevance can be simulated, including the implication of reduced dose mixtures. We describe in detail the calculation and calibration of these models. We demonstrate the ability of the models to simulate a variety of IRM strategies and implications of including these features of the models. In simple IRM strategy evaluations, the truncation and probabilistic models give comparable results to each other and against published polygenic and monogenic models. Analysis of model simulations indicates there is often little difference between sequences or rotations of insecticides. Full-dose mixtures remain the best evaluated IRM strategy. Consistency between models increases confidence in their predictions especially when demonstrating model assumptions do not significantly impact key operational decisions. Using the multiple-gonotrophic cycle model we calculate the age distributions of mosquitoes which provides a framework to link resistance management with disease transmission. Future applications will investigate more scenario-specific evaluations of IRM strategies to inform public health policy.

Functional Characterization of Cytochromes P450 Linked to Herbicide Detoxification and Selectivity in Winter Wheat and the Problem Competing Weed Blackgrass

The selective chemical control of wild grasses in wheat is primarily determined by the relative rates of herbicide metabolism, with the superfamily of cytochromes P450 (CYPs) playing a major role in catalyzing phase 1 detoxification reactions. This selectivity is enhanced by herbicide safeners, which induce CYP expression in cereals, or challenged by the evolution of nontarget site resistance (NTSR) in weeds such as blackgrass. Using transcriptomics, proteomics, and functional expression in recombinant yeast, CYPs linked to safener treatment and NTSR have been characterized in wheat and blackgrass. Safener treatment resulted in the induction of 13 families of CYPs in wheat and 5 in blackgrass, with CYP71, CYP72, CYP76, and CYP81 members active toward selective herbicides in the crop. Based on their expression and functional activities, three inducible TaCYP81s were shown to have major roles in safening in wheat. In contrast, a single AmCYP81 that was enhanced by NTSR, but not by safening, was found to dominate herbicide detoxification in blackgrass.

Binding site loops D and G make a stronger contribution than loop C to the actions of neonicotinoids on the NACHO-assisted, robustly expressed Drosophila melanogaster Dα1/Dβ1 nicotinic acetylcholine receptor

TMX3 is essential for the functional expression of insect nicotinic acetylcholine receptors (nAChRs) and RIC-3 and UNC-50 modulate it. In addition to these cofactors, NACHO has been shown to enhance functional expression of certain vertebrate nAChRs and an insect homomeric nAChR. Here, we have examined the impact of Drosophila melanogaster NACHO (DmNACHO) on the ACh-induced response amplitude of the fruit fly Dα1/Dβ1 nAChRs coexpressed in Xenopus laevis oocytes with DmRIC-3, DmTMX3 and DmUNC-50 and examined the actions of neonicotinoid insecticides. DmNACHO markedly enhanced the ACh and neonicotinoid-induced response amplitude of Dα1/Dβ1 nAChRs coexpressed with the three cofactors DmRIC-3, DmTMX3 and DmUNC-50, while scarcely influencing ligand affinity. Given the robust Dα1/Dβ1 nAChR expression with the aid of the four cofactors, we investigated the impact of mutations in loops C, D and G of the orthosteric ligand binding domain (LBD) on the actions of the neonicotinoids imidacloprid and thiacloprid. Both the R81T mutation in loop D and the A60S mutation in loop G significantly reduced the agonist actions of the neonicotinoids, whereas the S221E mutation in loop C had no significant effect on agonist actions on this nAChR. Further, no greater affinity and efficacy reducing effects were observed even when the S221E mutation in loop C was combined with the R81T mutation in loop D, the A60S mutation in loop G, or both, demonstrating that loop D and loop G are more critical than loop C in determining the target-site actions of imidacloprid and thiacloprid.

Increased expression of an isoform of the long non-coding RNA, lnc37707, is associated with malathion resistance in Bactrocera dorsalis

The oriental fruit fly, Bactrocera dorsalis (Hendel) is an invasive pest threatening global fruit industries. Field populations of B. dorsalis exhibit complex insecticide resistance, hindering pest control efforts and exacerbating damage. Long non-coding RNAs (lncRNAs) are critical regulators of multiple bioprocess in insects, including insecticide resistance, and have potentials as novel target for pest management. Here, the candidate lncRNAs associated with malathion resistance in B. dorsalis were identified through RNA-seq. One of the isoforms of lnc37707, designated as lnc37707.10, was significantly enriched in the detoxification tissues of malathion-resistant (MR) strain. A specific fragment of lnc37707.10 (sflnc37707) was strongly associated with malathion resistance, and silencing sflnc37707 increased the susceptibility, whereas overexpressing it decreased susceptibility to malathion. Silencing sflnc37707 resulted in the down-regulation of 248 genes, but none of them included the four adjacent genes as its potential target. Instead, pathway analysis revealed significant enrichment of down-regulated genes involved in drug and xenobiotics metabolism, including P450s and GSTs. Bioinformatic analysis suggested a potential regulatory role of miRNA in the function of lnc37707. Further combining silence or overexpression sflnc37707 with miRNA mimic treatment identified that BdGSTd10 (an important gene involved in malathion resistance) and miR-1000 was strongly linked to lnc37707.10. Finally, a ceRNA (competing endogenous RNA) regulatory axis was proposed, where lnc37707.10 might indirectly modulate BdGSTd10 by sponging miR-1000 to regulate the malathion resistance in B. dorsalis. These findings provide a new insight into insecticide resistance and a potential lncRNA target for the sustainable pest management.

Acute and repeated exposure toxicity of the insecticide sulfoxaflor on hymenopteran pollinators; sulfoxaflor environmental science review part III

To support regulatory risk assessment, standardized laboratory tests of toxicity to representative species including honeybees (Apis mellifera L.), orchard bees (Osmia spp.), and bumblebees (Bombus spp.) provide the benchmark toxicity values for use in preliminary Tier 1 assessments and more detailed and realistic higher-tier assessments. In this analysis, we summarize the results of studies of toxicity of SFX to pollinators conducted by the registrant as well as results published in the literature. The geometric mean of 48-hr adult acute oral LD50 values for SFX for honeybees was 0.0740 μg SFX bee-1 (n = 5). Toxicity values for technical grade SFX (SFX-T) and formulated products were not significantly different. The geometric mean 48 hr adult acute contact LD50 values for SFX-T and several formulated products were 0.432 (n = 2) and 0.202 (n = 3) μg SFX bee-1, respectively. Exposures sprayed foliage was not significant after the spray had dried did not cause significant toxicity. Transformation products were not significantly toxic to adult or larval honeybees or other representative bee species. Results showed that, to complete the risk assessment, higher-tier studies were required. Differences in results between standard test methods and the nonstandard methods used in published work affect the outcome of the risk assessment. An understanding of these differences reconciled the differences in the reported findings.

A quantitative Apis mellifera hazard and risk assessment model (AMHRA) illustrated with the insecticide sulfoxaflor: sulfoxaflor environmental science review part VI

In this paper, conceptual models of the exposure pathways outside the hive and the in-hive distribution of pesticide residues brought to the honeybee hive are presented. The conceptual model is based on the natural life history, behavior and diet of individual honeybees (Apis mellifera). Receptor groups of bees with similar diets and potential exposure are defined. From the conceptual model, a quantitative A. mellifera hazard and risk assessment model (AMHRA) is developed and illustrated using sulfoxaflor (SFX) as a case study. The model estimates the exposure of the receptor groups of honeybees within a colony via various routes of exposure. The user selects a deterministic mode to obtain hazard quotients (HQ) or a probabilistic mode to obtain risk quotients (RQ). The model was run in the deterministic mode using the pesticide concentrations in nectar and pollen from a field experiment in which SFX was applied to cotton crops at the highest permitted application rate of 101 g a.i. ha-1. Acute and chronic exposure HQ values were calculated for the adult and larval receptor groups. The results showed that the SFX applied at the highest single application rate following the label directions was not hazardous to honeybees. The probabilistic mode was described but not run.

Weight of evidence assessment of effects of sulfoxaflor on aquatic invertebrates: sulfoxaflor environmental science review part II

Effects of sulfoxaflor (SFX) on aquatic invertebrates were assessed by comparing concentrations predicted to occur in or measured in surface waters to thresholds for adverse effects. Due to the specific mode of toxic action, fishes are relatively tolerant of the effects of SFX. Daphnia magna with an LC50 of 378 mg SFX L-1 (SD = 19.13) was similarly tolerant of the effects of SFX, while the LOEC was > 110 mg SFX L-1. A threshold for effects on aquatic insects, based on the chironomid midge, C. tentans, had LOAEL and NOAEL values of 0.0455 and 0.0618 mg L-1, respectively. The acute-to-chronic ratio was 18. Simulation models and parameters selected for a range of applications to crops predicted environmental concentrations (EECs) in surface waters to range from 2.2 to 7.7 µg L-1. Based on these EECs, the maximum hazard quotient (HQ) was 0.11, which is less than the US EPA level of concern (LOC) of 0.5, which would normally be the threshold to trigger regulatory action or higher-tier assessments. The risks posed by SFX to aquatic organisms are predicted to be de minimis. Hazard quotients based on EEC values predicted in the standard, USEPA farm pond estimated by use of the Pesticides in Water Calculator (PWC version 1.52) for scenarios of maximum application rates for cotton and LOAEL and NOAEL values for aquatic insects for SFX were less than or similar to those for other insecticides including neonicotinoids and organophosphorus compounds.

Weight of evidence assessment from field studies on effects of the insecticide sulfoxaflor on hymenopteran pollinators: sulfoxaflor environmental science review part V

Field studies involve combinations of exposure, natural dynamics, and effects in natural and agricultural environments. To be more realistic, field studies focussed on pollinating insects must consider the details of biology, life history, behavior, and pollination ecology of the test species. While expensive and time-consuming, these tests provide the most realistic information, especially for social insects, but are valuable for solitary bee species as well. They are more realistic than laboratory studies because they determine the combined effects of natural stressors including weather, food availability, parasites, and pathogens with anthropogenic stressors, such as the pesticide treatment itself, within agroecosystem landscapes. Twenty-four field studies conducted with bees to support the registration of sulfoxaflor and published work are included, and a standardized rating system for the quality and relevance of the studies was used. The studies included Apis mellifera L., Bombus terrestris L., and Osmia bicornis L. The results show that, when SFX products are applied at the highest labeled application rate with bees actively foraging or fed in syrup at equivalent rates, the effects are minor and temporary. Sublethal effects included lethargy, disorientation, and reduced body mass at emergence. No new modes of action and no treatment-related effects on brood rearing were found.

The miRNA-275 Targeting RpABCG23L is Involved in Pyrethroid Resistance in the Bird Cherry-Oat Aphid, a Serious Agricultural Pest

Rhopalosiphum padi is a global agricultural pest which had developed resistance to different insecticides. The ATP-binding cassette (ABC) transporter plays an important role in insecticide resistance. However, ABC transporters' role and regulatory mechanism in mediating R. padi 's response to pyrethroids are unclear. In this study, we found that RpABCG23L was significantly overexpressed in the pyrethroid-resistant strains of R. padi. Knockdown of RpABCG23L significantly increased the susceptibility of R. padi to lambda-cyhalothrin and bifenthrin. Luciferase reporter gene analysis showed that miR-275 binds to the RpABCG23L coding region and down-regulates its expression. Injection of miR-275 mimics significantly reduced RpABCG23L expression and increased R. padi susceptibility to lambda-cyhalothrin and bifenthrin, while miR-275 inhibitor injection enhanced RpABCG23L expression and increased tolerance to both insecticides. The results provide a theoretical basis for understanding the mechanism of miRNA-mediated pyrethroid resistance, and open up a new way for the development of miRNA-based biopesticides.

A comparative genomic analysis at the chromosomal-level reveals evolutionary patterns of aphid chromosomes

Genomic rearrangements are primary drivers of evolution, promoting biodiversity. Aphids, an agricultural pest with high species diversity, exhibit rapid chromosomal evolution and diverse karyotypes. These variations have been attributed to their unique holocentric chromosomes and parthenogenesis, though this hypothesis has faced scrutiny. In this study, we generated a chromosomal-level reference genome assembly of the celery aphid (Semiaphis heraclei) and conducted comparative genomic analysis, revealing varying chromosomal evolution rates among aphid lineages, positively correlating with species diversity. Aphid X chromosomes have undergone frequent intra-chromosomal recombination, while autosomes show accelerated inter-chromosomal recombination. Moreover, considering both inter- and intra-chromosomal rearrangements, the increased autosomal rearrangement rates may be common across the Aphidomorpha. We identified that the expansion of DNA transposable elements and short interspersed nuclear elements (SINEs), coupled with gene loss and duplication associated with karyotypic instability (such as RIF1, BRD8, DMC1, and TERT), may play crucial roles in aphid chromosomal evolution. Additionally, our analysis revealed that the mutation and expansion of detoxification gene families in S. heraclei may be a key factor in adapting to host plant chemical defenses. Our results provide new insights into chromosomal evolutionary patterns and detoxification gene families evolution in aphids, aiding the understanding of species diversity and adaptive evolution.

Toxic effects of deltamethrin on oxidative stress, behavioural, organosomatic indices and histopathological changes in Digitonthophagus gazella (Coleoptera: Scarabaeinae)

Pyrethroids pose a great concern to the declining population of dung beetles and the sustainability of ecosystem services. This study aimed to investigate the toxic effects of deltamethrin on Digitonthophagus gazella. First, the LC50 value (0.275 ppm) was determined, and sub-lethal concentrations (LD; low dose-0.014ppm, MD; medium dose-0.028ppm, and HD; high dose-0.055ppm) were assessed for physiological effects. The findings showed a significant dose and time dependent increase in fluorescence intensity (DCF-DA staining) and a decrease in antioxidant activity, including superoxide dismutase (SOD), catalase (CAT), and glutathione (GSH). Furthermore, significant down regulation of cyp4g7, cyp6bq9, and cyp4q4 expression indicates enhanced oxidative stress. Additionally, a reduction in the organosomatic index, accompanied by histological changes in the brain, gut, and gonads, suggests potential functional disturbances. Overall, deltamethrin exposure had profound and irreversible pathological consequences on various vital organs and systems in D. gazella, affecting reproduction and nesting.

Functional analysis of AccCPR in Apis cerana cerana under pesticide and heavy metal stress

NADPH-cytochrome P450 reductase (CPR) plays important roles in the metabolism of both endogenous and exogenous compounds through cytochrome P450, and is also involved in the detoxification of insecticides mediated by cytochrome P450. However, the CPR from Apis cerana cerana has not been well characterized and its function is still undescribed. This study isolated the CPR gene from Apis cerana cerana and investigated its functional role in the resistance to pesticide and heavy metal stress. Bioinformatic analysis revealed significant homology between the gene and its counterparts in other species. Functional investigations demonstrated diverse expression and localization patterns of this gene, with AccCPR primarily expressed in muscular tissues and the gut, suggesting its potential roles in flight activities and intestinal barrier function of bees. Furthermore, the expression levels of this gene were significantly modulated under pesticide and heavy metal stress. Notably, the overexpression of AccCPR led to a marked alteration the tolerance to external stressors in E. coli. Additionally, the silencing of the AccCPR gene resulted in a significant decrease in antioxidant enzyme activity and the expression levels of genes associated with antioxidant functions. Consequently, the mortality rate of Apis cerana cerana under imidacloprid stress was significantly elevated. Taken together, our findings suggest that AccCPR may play a pivotal role in the resistance of Apis cerana cerana to abiotic stresses such as pesticides and heavy metals by regulating antioxidant pathways.

Comparative toxicity mechanisms of sulfoxaflor and lambda-cyhalothrin against Apolygus lucorum from enzymatic and transcriptomic perspectives: Efficient application of insecticides

The pyrethroid insecticide lambda-cyhalothrin is threatened by insecticide resistance and has been registered to control Apolygus lucorum. The sulfoximine insecticide sulfoxaflor as an excellent candidate is recommended for its management. Previous studies have mainly focused on identifying resistance genes and their sublethal effects on the biological characteristics of these two insecticides in this pest. However, the toxicity mechanism differences of lambda-cyhalothrin and sulfoxaflor exposures are largely unknown. The LD10 and LD30 values were measured with significant difference as 0.15, 0.46, 33.58, and 73.60 ng/insect for sulfoxaflor and lambda-cyhalothrin, respectively, indicating differences in the insecticide type. Exposure to sublethal sulfoxaflor resulted in a higher total number of differentially expressed genes (DEGs) (550 and 995 DEGs) than exposure to sublethal lambda-cyhalothrin (101 and 112 DEGs). Moreover, enrichment analysis showed that more metabolic and signaling pathways were involved in the toxicity of sulfoxaflor than that of lambda-cyhalothrin, and enzyme activities in the enriched pathways were induced by sulfoxaflor and inhibited by lambda-cyhalothrin. For transcriptome validation, DEGs encoding detoxification-related genes were identified and validated by quantitative real-time PCR (qRT-PCR). These results indicate that sulfoxaflor is more toxic than lambda-cyhalothrin due to different modes of action. Our findings not only first provide insight into the toxicity mechanism differences of lambda-cyhalothrin and sulfoxaflor action and detoxification in A. lucorum at molecular and biochemical levels but also offer data and techniques for registering candidate sulfoxaflor and efficient application of insecticides in the field.

Role of mutation G255A in modulating pyrethroid sensitivity in insect sodium channels

A voltage-gated sodium channel (VGSC) plays a crucial role in insect electrical signals, and it is a target for various naturally occurring and synthesized neurotoxins, including pyrethroids and dichlorodiphenyltrichloroethane. The type of agent is typically widely used to prevent and control sanitary and agricultural pests. The perennial use of insecticides has caused mutations in VGSCs that have given rise to resistance in most insects. These mutations are located among the two pyrethroid receptors, i.e., PyR1 and PyR2, as predicted by previous studies. The two binding regions are relatively symmetrical, and here we focus on the linkers between S4 and S5 of Domains I and II. The S4-S5 linker can promote a rapid increase in sodium current and the onset of action potential. By predicting mutations in 19 other amino acids at all the amino acids on S4-S5 linkers, their harmfulness is analyzed, and whether they affect protein stability and drug binding is determined. Through molecular docking and based on docking scores, four mutations were predicted to affect the binding of sodium channels to pyrethroids. Mutations G255V, G255A, A906V, and A906T were introduced into the VGSC of Blattella germanica (BgNav1-1), and their effects on channel gating and pyrethroid sensitivity in Xenopus oocytes were studied. The treatment of VGSCs with two types of pyrethroids (1 nM), Types I (permethrin, bifenthrin) and II (deltamethrin, λ-cyhalothrin), produced tail currents. Among the four, mutant G255A exhibited a certain degree of increased sensitivity to the two types of pyrethroids. This finding was in contrast with the three other mutations, which demonstrated a certain degree of sensitization to one or two pyrethroids. We predicted and validated the critical mutation G255A on the insect VGSC Domain I S4-S5 linker using by electrophysiological technology. In generally, under the pressure of many insecticides, gene modifications, such as transcriptional changes and point mutations in the coding region make insects resistant to insecticides. This phenomenon leads to a higher detoxification rate of insecticides and makes the target site insensitive. However, we found that G255A mutation could promote the combination of pyrethroid and VGSCs by changing the binding force with insecticides. This finding has potential application value in reversing insect resistance. The discovery of mutation G255A exhibits considerable significance for the current use of gene editing and gene drive technology to control pests and delay their resistance development.

Widespread resistance of the apple aphid Aphis spiraecola to pyrethroids in China

The apple aphid, Aphis spiraecola, is an important pest in apple orchards. Pyrethroids had been widely used for the control of apple aphid. To verify the resistance level of A. spiraecola against pyrethroid insecticides, 35 field populations from main apple-producing areas of China were collected, and the susceptibility to type I and type II pyrethroids were assessed. Bioassays showed that six populations were highly resistant to bifenthrin (RR = 40.97-93.88 fold), and 12 populations showed the extremely high resistance against permethrin (RR = 161.17-349.27-fold). Moreover, all field populations developed high to extremely high resistance against lambda-cyhalothrin, fenvalerate and deltamethrin, except the HNLY and SXYL populations. Toxicity assays indicated that A. spiraecola field populations have developed serious resistance to multiple pyrethroids, and the relative highest resistance occurred in SXQX population. Pre-exposure to different synergists did not significantly increased the toxicity of pyrethroids to SXQX population, indicating a minor role of metabolic resistance in the resistant A. spiraecola. Sequencing of voltage-gated sodium channel (VGSC) genes revealed two homozygous mutations (918V/V and 1014F/F) and six heterozygous mutations (918M/V, 1014L/F, 918M/V+1014L/F, 918V/V+1014L/F, 918M/V+1014F/F and 918M/L+1014L/F) in A. spiraecola. Moreover, 1014L/F and 918M/V+1014L/F mutations were the dominant genotypes with frequencies of 26.67 % and 33.33 % in field populations, respectively. These results indicate that A. spiraecola in China has developed resistance against pyrethroids, and the resistance are mainly caused by mutations in VGSC. Pyrethroid insecticides should not be employed in these fields-evolved resistance, where the practical resistance management is urgently needed.

Cuticle thickening mediates insecticide penetration resistance in Spodoptera litura

INTRODUCTION

Long-term and extensive use of chemical pesticides has led to the development of resistance in many important agricultural pests. The mechanisms of resistance formation in pests are complex and variable, and unraveling the resistance mechanisms is the key to control resistant pests. Insect cuticle, as the first line of defense for insecticides, plays a non-negligible role in insecticide penetration resistance. Although penetration resistance is widespread in insects, the multiple molecular mechanisms that impede insecticide penetration are unclear, especially in Spodoptera litura.

OBJECTIVES

This study aims to reveal the molecular mechanisms of insecticide penetration resistance in S. litura.

METHODS

The structure and thickness of cuticle were analyzed by TEM, and the role of cuticle in penetration resistance was determined by different application methods. The molecular mechanism of cuticular proteins overexpression was analyzed using RNAi, TEM, dual-luciferase assay and EMSA from cis- and trans-acting factors. In addition, the relationship between the chitin synthetic pathway and insecticide resistance was explored through enzyme activity, inhibitor assay, molecular docking and RNAi. Furthermore, the role of 20E in penetration resistance was analyzed.

RESULTS

The cuticle of the resistant populations was significantly thickened and accompanied by extrusion, which contributed significantly to indoxacarb resistance. Constitutive upregulation of trans-acting factor SlituFTZ-F1 co-regulates the overexpression of SlituCP26 with cis-acting elements in the SlituCP26 promoter (74 bp insertion), affecting the cuticle thickness‑mediated indoxacarb penetration resistance. Meanwhile, the overexpression of key genes in the chitin synthesis pathway increased the chitin content, which combined with SlituCP26 to participate in indoxacarb resistance. Moreover, 20E affected the SlituFTZ-F1-mediated regulatory pathway and chitin biosynthesis pathway in indoxacarb resistance.

CONCLUSION

This study comprehensively elucidated the molecular mechanism of cuticle thickening mediating penetration resistance to indoxacarb and confirmed its existence in the field populations of S. litura.

Ultrastructure of the Sensilla on Antennae and Mouthparts of Larval and Adult Cylas formicarius (Coleoptera: Brentidae)

The quarantine pest, Cylas formicarius, is a key pest of sweet potatoes during both production and storage, posing a major threat to food security in various countries. To investigate behavioral mechanisms, the ultrastructure of the heads of larval and adult stages was analyzed using scanning electron microscopy, with an emphasis on the sensilla of the mouthparts and antennae. The results reveal degeneration of the antennae and ocelli in larvae. The larval mouthparts are equipped with three types and six subtypes of sensilla. Both male and female adults have four types and six subtypes of sensilla on their mouthparts. Compared to larvae, the adult mouthparts display a greater diversity of sensilla types and higher numbers of sensilla basicaonica (SB), sensilla chaetica (SC), and sensilla digitiformia (SD). Adult antennae consist of a scape, a pedicel, and eight flagellomeres (F1-F8), with F8 showing sexual dimorphism. Seven types of sensilla, excluding SB and sensilla ligulate (SL), each with two subtypes, were identified on the antennae of adults of both sexes. SC, sensilla furcatea, Böhm bristles, and SL were newly observed in the antennae of C. formicarius adults. Additionally, one type and seven subtypes of sensilla on the adult antennae exhibit distinct sexual dimorphism in terms of structure or number. The relationship between the head structure and adaptability of C. formicarius was examined, and the functions of each sensilla were discussed, providing a theoretical basis for future studies on the behavior of this pest.

Integrative Analysis of Transcriptomics and Proteomics for Screening Genes and Regulatory Networks Associated with Lambda-Cyhalothrin Resistance in the Plant Bug Lygus pratensis Linnaeus (Hemiptera: Miridae)

The prolonged use of pyrethroid insecticides for controlling the plant bug Lygus pratensis has led to upward resistance. This study aims to elucidate the molecular mechanisms and potential regulatory pathways associated with lambda-cyhalothrin resistance in L. pratensis. In this study, we constructed a regulatory network by integrating transcriptome RNA-Seq and proteome iTRAQ sequencing analyses of one lambda-cyhalothrin-susceptible strain and two resistant strains, annotating key gene families associated with detoxification, identifying differentially expressed genes and proteins, screening for transcription factors involved in the regulation of detoxification metabolism, and examining the metabolic pathways involved in resistance. A total of 82,919 unigenes were generated following the assembly of transcriptome data. Of these, 24,859 unigenes received functional annotations, while 1064 differential proteins were functionally annotated, and 1499 transcription factors belonging to 64 distinct transcription factor families were identified. Notably, 66 transcription factors associated with the regulation of detoxification metabolism were classified within the zf-C2H2, Homeobox, THAP, MYB, bHLH, HTH, HMG, and bZIP families. Co-analysis revealed that the CYP6A13 gene was significantly up-regulated at both transcriptional and translational levels. The GO and KEGG enrichment analyses revealed that the co-up-regulated DEGs and DEPs were significantly enriched in pathways related to sphingolipid metabolism, Terpenoid backbone biosynthesis, ABC transporters, RNA transport, and peroxisome function, as well as other signaling pathways involved in detoxification metabolism. Conversely, the co-down-regulated DEGs and DEPs were primarily enriched in pathways associated with Oxidative phosphorylation, Fatty acid biosynthesis, Neuroactive ligand-receptor interactions, and other pathways pertinent to growth and development. The results revealed a series of physiological and biochemical adaptations exhibited by L. pratensis during the detoxification metabolism related to lambda-cyhalothrin resistance. This work provided a theoretical basis for further analysis of the molecular regulation mechanism underlying this resistance.

Functional investigation of CYP304F1 in Tuta absoluta (Lepidoptera: Gelechiidae) by RNA interference

Tuta absoluta has developed resistance to many biological insecticides, causing substantial agricultural and economic losses annually. P450s have been the most extensively studied enzymes in the context of insecticide metabolism in insect pests, and the detoxification metabolism of P450s in T. absoluta against biological insecticides remains poorly understood. In T. absoluta, CYP304F1 was screened from the comparative transcriptome of 2 regional populations in Xinjiang, China. The objective of the present study was to characterize and analyze CYP304F1 of T. absoluta and explore its role in detoxification of spinetoram as well as the growth and development of T. absoluta. Following cloning and sequence analysis of the target gene, it was named CYP304F1. Expression levels of CYP304F1 were then determined after spinetoram exposure and across various developmental instars and tissues. Finally, dsCYP304F1 was synthesized and utilized to assess the effects of post-RNAi on larval spinetoram susceptibility, growth, and development. Sequence analysis revealed that CYP304F1 harbors conserved domains characteristic of P450 proteins, exhibiting high conservation within the Lepidoptera clade. Treatment with an LC50 dose of spinetoram significantly upregulated CYP304F1 expression in T. absoluta larvae. Silencing CYP304F1 significantly enhanced larval susceptibility to spinetoram and prolonged leaf-mining duration and developmental time from the 2nd instar to 4th instar by 40% and 17.6%, respectively, compared to controls. And feeding on dsCYP304F1-treated leaves for 6 days resulted in 71% larval mortality. These results suggested that CYP304F1 played a crucial role in detoxification of spinetoram as well as in the growth and development of T. absoluta larvae.

Properties of "Stable" Mosquito Cytochrome P450 Enzymes

The use of insecticides is widespread in the control of debilitating mosquito-borne diseases. P450 enzymes (CYPs) play essential roles in mosquito physiological function but also in the enzymatic detoxification of xenobiotics. Broadly speaking, CYPs can be classified as "stable", meaning those that have no or very few paralogs, and "labile", constituting gene families with many paralogous members. The evolutionary dichotomy between "stable" and "labile" P450 genes is fuzzy and there is not a clear phylogenetic demarcation between P450s involved in detoxification and P450s involved in essential metabolic processes. In this study, bioinformatic methods were used to explore differences in the sequences of "stable" and "labile" P450s that may facilitate their functional classification. Genomic and sequence data of Anopheles gambiae (Agam), Aedes aegypti (Aaeg), and Culex quinquefasciatus (Cqui) CYPs were obtained from public databases. The results of this study show that "stable" CYPs are encoded by longer genes, have longer introns and more exons, and contain a higher proportion of hydrophobic amino acids than "labile" CYPs. Compared to "labile" CYPs, a significantly higher proportion of "stable" CYPs are associated with biosynthetic and developmental processes.

Exploiting Trap Type and Color for Monitoring Macadamia Felted Coccid Acanthococcus ironsidei (Williams) and Associated Parasitic Wasps in Macadamia Orchards in Hawai'i

Acanthococcus ironsidei (Williams) (Hemiptera: Eriococcidae) is an invasive pest of macadamia, Macadamia integrifolia, in Hawai'i, causing death to macadamia trees and decreased nut productivity. Monitoring relies on wrapping double-sided sticky tapes over tree branches to trap dispersing crawlers (i.e., mobile immature stage), but this is tedious for growers, especially in large orchards. From September to November 2022 and December 2022 to February 2023, at two commercial macadamia orchards on Hawai'i Island, the use of colored sticky cards was assessed for improving the monitoring of A. ironsidei and to investigate the Hymenopteran parasitoid complex that inhabits macadamia canopies. At each study site, four different colored sticky cards (yellow, lime green, dark green, and white) were placed on the lower canopy of five trees, and on each tree, a transparent double-sided sticky tape was deployed. At bi-weekly intervals, the sticky cards were replaced and re-randomized on each tree, and the double-sided sticky tapes were replaced. The results showed that the sticky cards captured both A. ironsidei crawlers and (winged) male adults, while the double-sided sticky tapes captured only crawlers. The trap color did not have significant effects on the captures of A. ironsidei male adults at the sites, while the captures of crawlers on sticky cards were lowest on the dark green sticky traps at one site. The captures of A. ironsidei adult males on white sticky traps were generally correlated with the number of crawlers captured on the double-sided sticky tapes. The parasitoid complex captured had disparities in the attraction to color; however, the yellow, lime green and dark green colors were seemingly more effective for monitoring Encarsia lounsburyi (Berlese & Paoli), a reported parasitoid of A. ironsidei. These results have useful practical implications for improved monitoring of A. ironsidei crawlers, male adults and associated natural enemies.

Differentially spliced mitochondrial CYP419A1 contributes to ethiprole resistance in Nilaparvata lugens

The brown planthopper Nilaparvata lugens is one of the most economically important pests of cultivated rice in Southeast Asia. Extensive use of insecticide treatments, such as imidacloprid, fipronil and ethiprole, has resulted in the emergence of multiple resistant strains of N. lugens. Previous investigation of the mechanisms of resistance to imidacloprid and ethiprole demonstrated that overexpression and qualitative changes in the cytochrome P450 gene CYP6ER1 lead to enhanced metabolic detoxification of these compounds. Here, we present the identification of a secondary mechanism enhancing ethiprole resistance mediated by differential splicing and overexpression of CYP419A1, a planthopper-specific, mitochondrial P450 gene. Although metabolic resistance to insecticides is usually mediated by overexpression of P450 genes belonging to either CYP 3 or 4 clades, we validate the protective effect of over-expression of CYP419A1, in vivo, using transgenic Drosophila melanogaster. Additionally, we report some unusual features of both the CYP419A1 gene locus and protein, which include, altered splicing associated with resistance, a non-canonical heme-binding motif and an extreme 5' end extension of the open reading frame. These results provide insight into the molecular mechanisms underpinning resistance to insecticides and have applied implications for the control of a highly damaging crop pest.

Strong resistance to β-cyfluthrin in a strain of the beetle Alphitobius diaperinus: a de novo transcriptome analysis

The lesser mealworm, Alphitobius diaperinus, is an invasive tenebrionid beetle and a vector of pathogens. Due to the emergence of insecticide resistance and consequent outbreaks that generate significant phytosanitary and energy costs for poultry farmers, it has become a major insect pest worldwide. To better understand the molecular mechanisms behind this resistance, we studied a strain of A. diaperinus from a poultry house in Brittany that was found to be highly resistant to the β-cyfluthrin. The strain survived β-cyfluthrin exposures corresponding to more than 100 times the recommended dose. We used a comparative de novo RNA-Seq approach to explore genes expression in resistant versus sensitive strains. Our de novo transcriptomic analyses showed that responses to β-cyfluthrin likely involved a whole set of resistance mechanisms. Genes related to detoxification, metabolic resistance, cuticular hydrocarbon biosynthesis and proteolysis were found to be constitutively overexpressed in the resistant compared to the sensitive strain. Follow-up enzymatic assays confirmed that the resistant strain exhibited high basal activities for detoxification enzymes such as cytochrome P450 monooxygenase and glutathione-S-transferase. The in-depth analysis of differentially expressed genes suggests the involvement of complex regulation of signaling pathways. Detailed knowledge of these resistance mechanisms is essential for the establishment of effective pest control.

Thermal modulation of insecticide-induced hormetic and oxidative responses in insect pests

Environmental global changes are dramatically affecting agroecosystems. Insects have been shown to present various responses to multi-stress conditions (i.e., increase in temperature and exposure to contaminants). However, there is a knowledge gap on how temperature can modulate the hormetic effects in individuals sublethally exposed to chemical stressors. Here, we investigated how temperature (15, 20, 25, and 28 °C) modulates the effects of lethal and sublethal exposure to insecticides (imidacloprid) on the longevity, fecundity, and oxidative stress of a pest insect, the aphid Mysus persicae. Our results showed additive and interactive effects of temperature and insecticide on the stimulatory and oxidative responses of the insect pest. Overall, imidacloprid was 2.4-fold less toxic at 15 °C (3.547 μg/ml) than at 20 °C (1.482 μg/ml) and 24.6 to 19.8-fold less toxic than at 25 °C (0.144 μg/ml) and 28 °C (0.179 μg/ml) respectively. Furthermore, although the exposure of female aphids to most sublethal concentrations resulted in a decrease in their longevity and fecundity compared to the control, some of the sublethal concentrations produced positive effects in these parameters for the exposed individuals. The magnitude of induced sublethal effects varied between temperatures and occurred in similar ranges of low concentrations at temperatures 15 °C and 20 °C, and at temperatures 25 °C and 28 °C. Additionally, imidacloprid low concentrations induced a temperature-dependent production of reactive oxygen species in exposed insects at 12 and 24 h after exposure indicating oxidative stress. Our study supplies valuable data on how temperature modulates pesticide-mediated hormesis that can alter ecological interactions and functions within agroecosystems with potential implications in pest management.

Evaluating the potential of Kalanchoe pinnata, Piper amalago amalago, and other botanicals as economical insecticidal synergists against Anopheles gambiae

BACKGROUND

Synergists reduce insecticide metabolism in mosquitoes by competing with insecticides for the active sites of metabolic enzymes, such as cytochrome P450s (CYPs). This increases the availability of the insecticide at its specific target site. The combination of both insecticides and synergists increases the toxicity of the mixture. Given the demonstrated resistance to the classical insecticides in numerous Anopheles spp., the use of synergists is becoming increasingly pertinent. Tropical plants synthesize diverse phytochemicals, presenting a repository of potential synergists.

METHODS

Extracts prepared from medicinal plants found in Jamaica were screened against recombinant Anopheles gambiae CYP6M2 and CYP6P3, and Anopheles funestus CYP6P9a, CYPs associated with anopheline resistance to pyrethroids and several other insecticide classes. The toxicity of these extracts alone or as synergists, was evaluated using bottle bioassays with the insecticide permethrin. RNA sequencing and in silico modelling were used to determine the mode of action of the extracts.

RESULTS

Aqueous extracts of Piper amalago var. amalago inhibited CYP6P9a, CYP6M2, and CYP6P3 with IC50s of 2.61 ± 0.17, 4.3 ± 0.42, and 5.84 ± 0.42 μg/ml, respectively, while extracts of Kalanchoe pinnata, inhibited CYP6M2 with an IC50 of 3.52 ± 0.68 μg/ml. Ethanol extracts of P. amalago var. amalago and K. pinnata displayed dose-dependent insecticidal activity against An. gambiae, with LD50s of 368.42 and 282.37 ng/mosquito, respectively. Additionally, An. gambiae pretreated with K. pinnata (dose: 1.43 μg/mosquito) demonstrated increased susceptibility (83.19 ± 6.14%) to permethrin in a bottle bioassay at 30 min compared to the permethrin only treatment (0% mortality). RNA sequencing demonstrated gene modulation for CYP genes in anopheline mosquitoes exposed to 715 ng of ethanolic plant extract at 24 h. In silico modelling showed good binding affinity between CYPs and the plants' secondary metabolites.

CONCLUSION

This study demonstrates that extracts from P. amalago var. amalago and K. pinnata, with inhibitory properties, IC50 < 6.95 μg/ml, against recombinant anopheline CYPs may be developed as natural synergists against anopheline mosquitoes. Novel synergists can help to overcome metabolic resistance to insecticides, which is increasingly reported in malaria vectors.

Genome sequences of four Ixodes species expands understanding of tick evolution

BACKGROUND

Ticks, hematophagous Acari, pose a significant threat by transmitting various pathogens to their vertebrate hosts during feeding. Despite advances in tick genomics, high-quality genomes were lacking until recently, particularly in the genus Ixodes, which includes the main vectors of Lyme disease.

RESULTS

Here, we present the genome sequences of four tick species, derived from a single female individual, with a particular focus on the European species Ixodes ricinus, achieving a chromosome-level assembly. Additionally, draft assemblies were generated for the three other Ixodes species, I. persulcatus, I. pacificus, and I. hexagonus. The quality of the four genomes and extensive annotation of several important gene families have allowed us to study the evolution of gene repertoires at the level of the genus Ixodes and of the tick group. We have determined gene families that have undergone major amplifications during the evolution of ticks, while an expression atlas obtained for I. ricinus reveals striking patterns of specialization both between and within gene families. Notably, several gene family amplifications are associated with a proliferation of single-exon genes-most strikingly for fatty acid elongases and sulfotransferases.

CONCLUSIONS

The integration of our data with existing genomes establishes a solid framework for the study of gene evolution, improving our understanding of tick biology. In addition, our work lays the foundations for applied research and innovative control targeting these organisms.

Long-Term Exposure to Lambda-Cyhalothrin Reveals Novel Genes Potentially Involved in Aedes aegypti Insecticide Resistance

Insecticide resistance in Aedes aegypti populations hinders vector control programs. Many studies have focused on the classical mechanisms, kdr mutations, and metabolic enzymes to understand the development of insecticide resistance. In this study, we subjected a strain of Ae. aegypti to selective pressure for 13 consecutive generations to understand the development and extent of insecticide resistance. We delved into the transcriptomics of this pressured strain to gain insights into the molecular changes underlying insecticide resistance in Ae. aegypti. Our data suggest mosquito resistance is influenced by additional mechanisms that are difficult to explain using only classical mechanisms. The response by mosquitoes varies depending on the exposure time. Initially, when mosquitoes are in contact with insecticides, they modulate the expression of metabolic enzymes and gain some point mutations in the sodium channel genes. After long-term exposure, the mosquitoes respond to insecticides by expressing different proteins involved in the cuticle, energetic metabolism, and synthesis of proteases. We propose a model that includes these novel mechanisms found after prolonged insecticide exposure, which work in conjunction with established mechanisms (kdr and metabolic resistance) but have a different timeline in terms of expression and appearance.