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

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.

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

BACKGROUND

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

RESULTS

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

CONCLUSION

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

P450 gene CYP321A8 is responsible for cross-resistance of insecticides in field populations of Spodoptera frugiperda

Continuous and long-term use of traditional and new pesticides can result in cross-resistance among pest populations in different fields. Study on the mechanism of cross-resistance and related genes will help resistance management and field pest control. In this study, the pesticide-resistance mechanism in Spodoptera frugiperda (FAW) was studied with field populations in 3 locations of South China. Field FAW populations were highly resistant to traditional insecticides, chlorpyrifos (organophosphate) and deltamethrin (pyrethroid), and had higher levels of cytochrome P450 activity than a non-resistant laboratory strain. Inhibition of P450 activity by piperonyl butoxide significantly increased the sensitivity of resistant FAW in 3 locations to chlorpyrifos, deltamethrin and chlorantraniliprole (amide), a new type of insecticide, suggesting that P450 detoxification is a critical factor for insecticide resistance in field FAW populations. Transcriptomic analysis indicated that 18 P450 genes were upregulated in the field FAW populations collected in 3 regions and in 2 consecutive years, with CYP321A8, the most significantly upregulated one. Knockdown of CYP321A8 messenger RNA by RNA interference resulted in an increased sensitivity to the 3 tested insecticides in the field FAW. Enzyme activity and molecular docking analyses indicated that CYP321A8 enzyme was able to metabolize the 3 tested insecticides and interact with 8 other types of insecticides, confirming that CYP321A8 is a key cross-resistance gene with a wide range of substrates in the field FAW populations across the different regions and can be used as a biomarker and target for management of FAW insecticide resistance in fields.

miRNAs modulate altered expression of cytochrome P450s and nicotinic acetylcholine receptor subunits conferring both metabolic and target resistance to sulfoxaflor in Nilaparvata lugens (Stål)

Understanding the insecticide resistance mechanisms and their underlying regulatory pathways is essential for pest management. Previous findings indicated that the overexpression of P450 gene, CYP6ER1, was a key mechanism for sulfoxaflor metabolic resistance in Nilaparvata lugens. However, it remains unclear whether quantitative changes in the target nicotinic acetylcholine receptors (nAChRs) contribute to sulfoxaflor resistance and the underlying regulatory mechanisms involved. Here, qRT-PCR, pairwise correlation analyses and RNAi confirmed that the down-regulation of Nlα4, along with the up-regulation of Nlα10 and Nlβ1, were linked to sulfoxaflor resistance in N. lugens. Four microRNAs, novel-m0262-5p, novel-m0071-3p and novel-m0196-3p, and miR-10471-x were found to target CYP6ER1, Nlα4 and Nlβ1, respectively. Subsequently, the binding activity between these miRNAs and their target genes was verified by dual fluorescence in vitro. Over-supplementation of novel-m0262-5p and miR-10471-x via miRNA agomir injections suppressed the expression of CYP6ER1 and Nlβ1, and decreased nymph resistance to sulfoxaflor. Conversely, novel-m0262-5p and miR-10471-x antagomirs treatment induced the expression of CYP6ER1 and Nlβ1, thereby enhancing sulfoxaflor resistance. Additionally, overexpression of novel-m0071-3p and novel-m0196-3p inhibited Nlα4 expression and increased sulfoxaflor resistance. These findings indicate that miRNAs regulate the differential expression of P450s and nAChRs, mediating both metabolic and target resistance to sulfoxaflor in N. lugens.

Two critical detoxification enzyme genes, NlCYP301B1 and NlGSTm2 confer pymetrozine resistance in the brown planthopper (BPH), Nilaparvata lugens Stål

The brown planthopper (BPH), Nilaparvata lugens Stål, is a notorious pest that infests rice across Asia. The rapid evolution of chemical pesticide resistance in BPH poses an ongoing threat to agriculture and human health. Currently, pymetrozine has emerged as a viable alternative to imidacloprid for managing N. lugens. The detoxification of insecticides in insects includes three major metabolic gene families: cytochrome P450 monooxygenases (P450s), glutathione S-transferases (GSTs), and carboxylesterases (CarEs). In this study, highly resistant strains of BPH to pymetrozine (BPH-R40: 705-fold) were created from the susceptible BPH strain through continuous multi-selection. The activities of detoxifying enzymes, including P450s, GSTs, and CarEs were measured. Notably, P450s and GSTs exhibited significantly higher activity in the pymetrozine-resistance strain than that of the susceptible BPH strain. Hence, we characterized P450s and GSTs genes in N. lugens and revealed their phylogeny, structure, motif analysis, and chromosome location. Subsequently, the expression profiles of 53 P450s and 11 GSTs genes were quantified, and two crucial detoxifying enzyme genes, NlCYP301B1 and NlGSTm2, were identified as being involved in pymetrozine resistance. Furthermore, RNA interference (RNAi)-mediated silencing of NlCYP301B1 and NlGSTm2 gene expression significantly increased larval mortality of BPH in response to pymetrozine. To our knowledge, enhancing the activity of key detoxification enzymes to resist insecticides represents a widespread and vital defense mechanism in insects.

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

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

Field-evolved resistance to neonicotinoids in the mosquito, Anopheles gambiae, is associated with downregulation and mutations of nicotinic acetylcholine receptor subunits combined with cytochrome P450-mediated detoxification

Neonicotinoid insecticides act selectively on their nicotinic receptor targets leading to variable sensitivity among arthropods. This study aimed to investigate the molecular mechanisms underlying contrasting susceptibility to neonicotinoids observed in wild populations of two mosquito sibling species. Bioassays and a synergism test revealed that the sister taxa, Anopheles gambiae and An. coluzzii, from Yaounde, Cameroon, rely on cytochrome P450s to detoxify neonicotinoids and develop resistance. However, contrary to An. coluzzii, An. gambiae populations are evolving stronger resistance to several active ingredients facilitated by mutations and reduced expression of nicotinic acetylcholine receptors. Six mutations were detected in coding sequences of the β1 and α6 subunits, including two substitutions in one of the loops that modulate ligand binding and sensitivity. Allele frequencies were strongly correlated with a susceptibility gradient between An. coluzzii and An. gambiae suggesting that the mutations may play a key role in sensitivity. Messenger RNA expression levels of the β1, α3, and α7 subunits decreased dramatically, on average by 23.27, 17.50, 15.80-fold, respectively, in wild An. gambiae populations compared to a susceptible insectary colony. By contrast, only the β2 and α9-1 subunits were moderately downregulated (5.28 and 2.67-fold change, respectively) in field-collected An. coluzzii adults relative to susceptible colonized mosquitoes. Our findings provide critical information for the application and resistance management of neonicotinoids in malaria prevention.

Adult mosquitoes of the sibling species Anopheles gambiae and Anopheles coluzzii exhibit contrasting patterns of susceptibility to four neonicotinoid insecticides along an urban-to-rural gradient in Yaoundé, Cameroon

BACKGROUND

Neonicotinoids are potential alternatives for controlling pyrethroid-resistant mosquitoes, but their efficacy against malaria vector populations of sub-Saharan Africa has yet to be investigated. The aim of the present study was to test the efficacy of four neonicotinoids against adult populations of the sibling species Anopheles gambiae and Anopheles coluzzii sampled along an urban-to-rural gradient.

METHODS

The lethal toxicity of three active ingredients for adults of two susceptible Anopheles strains was assessed using concentration-response assays, and their discriminating concentrations were calculated. The discriminating concentrations were then used to test the susceptibility of An. gambiae and An. coluzzii mosquitoes collected from urban, suburban and rural areas of Yaoundé, Cameroon, to acetamiprid, imidacloprid, clothianidin and thiamethoxam.

RESULTS

Lethal concentrations of neonicotinoids were relatively high suggesting that this class of insecticides has low toxicity against Anopheles mosquitoes. Reduced susceptibility to the four neonicotinoids tested was detected in An. gambiae populations collected from rural and suburban areas. By contrast, adults of An. coluzzii that occurred in urbanized settings were susceptible to neonicotinoids except acetamiprid for which 80% mortality was obtained within 72 h of insecticide exposure. The cytochrome inhibitor, piperonyl butoxide (PBO), significantly enhanced the activity of clothianidin and acetamiprid against An. gambiae mosquitoes.

CONCLUSIONS

These findings corroborate susceptibility profiles observed in larvae and highlight a significant variation in tolerance to neonicotinoids between An. gambiae and An. coluzzii populations from Yaoundé. Further studies are needed to disentangle the role of exposure to agricultural pesticides and of cross-resistance mechanisms in the development of neonicotinoid resistance in some Anopheles species.

Anopheles gambiae larvae's ability to grow and emerge in water containing lethal concentrations of clothianidin, acetamiprid, or imidacloprid is consistent with cross-resistance to neonicotinoids

BACKGROUND

For decades, various agrochemicals have been successfully repurposed for mosquito control. However, preexisting resistance caused in larval and adult populations by unintentional pesticide exposure or other cross-resistance mechanisms poses a challenge to the efficacy of this strategy. A better understanding of larval adaptation to the lethal and sublethal effects of residual pesticides in aquatic habitats would provide vital information for assessing the efficacy of repurposed agrochemicals against mosquitoes.

METHODS

We reared field-collected mosquito larvae in water containing a concentration of agrochemical causing 100% mortality in susceptible mosquitoes after 24 h (lethal concentration). Using this experimental setup, we tested the effect of lethal concentrations of a pyrrole (chlorfenapyr, 0.10 mg/l), a pyrethroid (deltamethrin, 1.5 mg/l), and three neonicotinoids including imidacloprid (0.075 mg/l), acetamiprid (0.15 mg/l), and clothianidin (0.035 mg/l) on mortality rates, growth, and survival in third-instar larvae of the two sibling species Anopheles gambiae and Anopheles coluzzii collected from Yaoundé, Cameroon.

RESULTS

We found that An. gambiae and An. coluzzii larvae were susceptible to chlorfenapyr and were killed within 24 h by a nominal concentration of 0.10 mg/l. Consistent with strong resistance, deltamethrin induced low mortality in both species. Lethal concentrations of acetamiprid, imidacloprid, and clothianidin strongly inhibited survival, growth, and emergence in An. coluzzii larvae. By contrast, depending on the active ingredient and the population tested, 5-60% of immature stages of An. gambiae were able to grow and emerge in water containing a lethal concentration of neonicotinoids, suggesting cross-resistance to this class of insecticides.

CONCLUSIONS

These findings corroborate susceptibility profiles observed in adults and suggest that unintentional pesticide exposure or other cross-resistance processes could contribute to the development of resistance to neonicotinoids in some Anopheles populations.

Molecular Evolutionary Mechanisms of CYP6ER1vA-Type Variant Associated with Resistance to Neonicotinoid Insecticides in Field Populations of Nilaparvata lugens

The evolution of insecticide resistance has threatened the control of Nilaparvata lugens. Research on mechanisms behind neonicotinoid resistance in N. lugens remains incomplete. This study examined P450-mediated resistance to neonicotinoids in a resistant N. lugens strain (XA-2017-3G). The overexpression of CYP6ER1 in the XA-2017-3G strain plays a role in neonicotinoid resistance, as confirmed by RNA interference. Phenotypic analyses of CYP6ER1-mediated resistance in strains, including laboratory-susceptible, field-collected, and imidacloprid-laboratory further-selected strains, revealed that the vA-type/vL-type genotype exhibited greater resistance to neonicotinoids compared to the vA-type/vA-type genotype. The mRNA expression levels of CYP6ER1vA-type were closely correlated with the levels of neonicotinoid resistance in N. lugens strains, in which CYP6ER1vA-type overexpression is in part attributed to increased copy numbers of CYP6ER1. CYP6ER1vA-type-mediated neonicotinoid resistance was further confirmed by a CYP6ER1vA-type transgenic Drosophila melanogaster line. Taken together, our findings strongly suggest that the overexpression of CYP6ER1vA-type, which can be partially attributed to copy number variations, plays a crucial role in N. lugens resistance to neonicotinoids.

Occurrence and water-sediment exchange of systemic insecticides and their transformation products in an agriculture-dominated basin

Neonicotinoids (NEOs) and fipronil (FIP) are ubiquitous in aquatic environment, yet the transformation and water-sediment exchange are largely unknown for these systemic insecticides and their transformation products (TPs). Herein, occurrence, field-based partitioning coefficients, and fugacity fractions (ff) of NEOs, FIP, and their TPs were analyzed in the drainage and receiving rivers near a rice paddy field. NEOs and FIPs were frequently detected in the sediments with concentrations of TPs being often higher than the parent compounds. Average ff values of NEOs (0.944-1.00) were larger than those of FIPs (0.399-0.716), indicating NEOs had a greater tendency to diffuse from sediment into water. Similar as well-studied hydrophobic compounds, hydrophobicity was the main factor impacting the water-sediment exchange of moderately hydrophobic FIPs. Alternatively, electrostatic interactions governed the fate of hydrophilic NEOs in water-sediment system. The log Kd values of NEOs were positively correlated with their N/C ratios (p < 0.05), possibly because the negatively charged sediments (zeta potential were from -19.1 ± 0.6 to -5.84 ± 0.57 mV) generated electrostatic attraction with amino functional group. Our study highlighted the ubiquitousness of TPs and distinct water-sediment interaction for moderately hydrophobic and hydrophilic insecticides in an agriculture-dominated watershed.

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

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

Baseline Susceptibility and Evidence of Resistance to Acetamiprid in Gill's Mealybug, Ferrisia gilli Gullan (Hemiptera: Pseudococcidae)

Gill's mealybug, Ferrisia gilli (Gullan) (Hemiptera: Pseudococcidae), is a major pest of pistachio in California. Insecticide treatment is the primary control method and acetamiprid is widely used to control this pest. However, there have been numerous reports of control failures for F. gilli after field applications of recommended insecticides in recent years. The purpose of this study was to develop a method for routine monitoring of F. gilli susceptibility and quantify current levels of F. gilli susceptibility to acetamiprid. A leaf-dip bioassay method using lima bean leaves was established and baseline susceptibility responses of 5 field populations were determined. Lethal concentrations to kill 50% of population (LC50) for second instar nymphs at 48 h ranged from 0.367 to 2.398 µg(AI)ml-1 of acetamiprid. Similarly, lethal concentrations to kill 90% of population (LC90) for second instar nymphs at 48 h ranged from 2.887 to 10.752 µg(AI)ml-1 of acetamiprid. The F. gilli population collected from Hanford area showed up to 6.5-fold significantly decreased mortality to acetamiprid compared to other populations. The resistance identified in this study, although relatively low, indicates that there has been repeated pressure to select for acetamiprid resistance and resistance levels can further magnify if effective management steps are not taken. The baseline susceptibility established in this study can be used to investigate potential cause of recent acetamiprid failures against F. gilli. In the long-term, results of this study will support the development of resistance management strategies by monitoring shifts in the susceptibility of F. gilli populations.

Importance of CYP6ER1 Was Different among Neonicotinoids in Their Susceptibility in Nilaparvata lugens

CYP6ER1 overexpression is a prevalent mechanism for neonicotinoid resistance in Nilaparvata lugens. Except for imidacloprid, the metabolism of other neonicotinoids by CYP6ER1 lacked direct evidence. In this study, a CYP6ER1 knockout strain (CYP6ER1^-/-) was constructed using the CRISPR/Cas9 strategy. The CYP6ER1^-/- strain showed much higher susceptibility to imidacloprid and thiacloprid with an SI (sensitivity index, LC₅₀ of WT/LC₅₀ of CYP6ER1^-/-) of over 100, which was 10-30 for four neonicotinoids (acetamiprid, nitenpyram, clothianidin, and dinotefuran) and less than 5 for flupyradifurone and sulfoxaflor. Recombinant CYP6ER1 showed the highest activity to metabolize imidacloprid and thiacloprid and moderate activity for the other four neonicotinoids. Main metabolite identification and oxidation site prediction revealed that CYP6ER1 activities were insecticide structure-dependent. The most potential oxidation site of imidacloprid and thiacloprid was located in the five-membered heterocycle with hydroxylation activity. For the other four neonicotinoids, the potential site was within the ring opening of a five-membered heterocycle, indicating N-desmethyl activity.