Insecticide Resistance Monitoring of the Diamondback Moth (Lepidoptera: Plutellidae) Populations in China

Knockout of silk fibroin genes in Plutella xylostella results in decreased fitness and performance

BACKGROUND

The ability of insects to spin silk is crucial for their survival, reproduction, and interactions with the environment. The diamondback moth (DBM), Plutella xylostella, a serious agricultural pest, relies on silk production, which influences its behavior and population dynamics.

RESULTS

This study employed CRISPR/Cas9 technology to knock out three genes, that is, silk fibroin heavy chain (PxFibH), silk fibroin light chain (PxFibL), and fibrohexamerin (PxP25), to investigate their roles in silk gland development and related biological traits. We successfully generated PxFibH, PxFibL, and PxP25 knockout mutants, which displayed defective cocoon formation and developed into naked pupae. Further analysis revealed significant alterations in silk gland structure and various biological parameters, including increased larval mortality, prolonged developmental time, reduced pupal weight, and shortened adult lifespan.

CONCLUSIONS

These findings highlight the importance of silk fibroin genes in silk production and growth development in P. xylostella, positioning them as potential targets for innovative pest control strategies. © 2025 Society of Chemical Industry.

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

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

Comprehensive Transcriptomic Analyses of Silk-Associated Genes and Functional Characterization of Key Silk Fibroins in Plutella xylostella

The diamondback moth (DBM), Plutella xylostella (Lepidoptera: Plutellidae), is a serious agricultural pest that utilizes silk as a defensive mechanism, with silk fibroins playing a pivotal role in this process. Through comprehensive transcriptomic analyses, we identified 3452 differentially expressed genes (DEGs) co-expressed in the silk gland of P. xylostella and associated with silk production. The Gene Ontology (GO) analysis revealed enrichment in categories related to protein synthesis, secretion, and extracellular matrix organization, while Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis linked these genes to amino acid metabolism and protein processing pathways. Additionally, we identified three key silk fibroin genes: silk fibroin heavy chain (FibH), silk fibroin light chain (FibL), and fibrohexamerin (P25). We characterized the structure of these genes and analyzed the phylogenetic relationships, amino acid composition, hydrophilicity, and other physicochemical properties of the encoded silk fibroin proteins. The expression profiles revealed peak expression levels of these genes in the silk glands of fourth instar larvae. This integrative study enhances our understanding of the molecular mechanisms underlying silk production in P. xylostella and provides a foundation for future research into the biological roles, evolutionary trajectories, and potential applications of these silk fibroin genes in agricultural pest management and biotechnology.

Baseline Susceptibility of Plutella xylostella and Spodoptera exigua to Fluxametamide in China

Fluxametamide, an innovative isoxazoline insecticide, acts as an antagonist of γ-aminobutyric acid-gated chloride channels. Its distinct mode of action sets it apart, lacking known cross-resistance with current insecticides. This positions fluxametamide as a promising tool for addressing insecticide resistance in Lepidoptera, thysanoptera, coleoptera, and diptera pest insects. To develop and implement successful resistance management strategies, it is crucial to establish the baseline susceptibility to this insecticide before it is registered and widely used in China. In this study, we assessed the baseline susceptibility of two widespread lepidopteran pest species, Plutella xylostella and Spodoptera exigua, to fluxametamide. The insecticide exhibited remarkably high efficacy against populations of the two lepidopteran species sampled in their primary distribution areas in China. For P. xylostella and S. exigua, the median lethal concentrations (LC50) ranged between 0.040 and 0.247 mg/L, and 0.211 and 0.761 mg/L, respectively. Among populations, there was a relative low variability in susceptibility to fluxametamide, showing a 6.18-fold difference for P. xylostella and 3.61-fold for S. exigua. The suggested diagnostic concentrations for P. xylostella and S. exigua were 10 and 15 mg/L, respectively. Fluxametamide exhibited high toxicity to the selected resistant strains, which displayed strong resistance to abamectin, emamectin benzoate, and deltamethrin. No cross-resistance to fluxametamide was detected in the laboratory diamide-resistant strain. Our findings offer essential insights for crafting successful resistance management initiatives to maintain the effectiveness of fluxametamide against these significant pests.

Transcriptomic analysis of male diamondback moth antennae: Response to female semiochemicals and allyl isothiocyanate

Female semiochemicals and allyl isothiocyanate (AITC) attract moths, and the moths use odorant-degrading enzymes (ODEs) to break down the excess odor. By identifying antennae-specific ODEs, researchers have established the molecular foundation for odorant degradation and signal inactivation in insects. This enables further exploration of new pest control methods. Currently, the degradation of female semiochemicals and AITC has received limited attention, inspiring this study to identify target ODEs in diamondback moths through transcriptome analysis. Sequencing of antennae from male adults (MA) exposed to female adults (FA) and AITC yielded a substantial 54.18 Gb of clean data, revealing 2276 differentially expressed genes (DEGs) between the MA and MA-FA treatments, and 629 DEGs between MA and MA-AITC treatments. The analysis of MAs exposed to FAs and AITC identified 29 and 17 ODEs, respectively, mainly involving aldehyde dehydrogenases (ALDHs), alcohol dehydrogenases (ADs), cytochrome P450s (CYPs), and UDP-glucuronosyltransferases (UGTs). Pathway analysis revealed primary enrichment in glycolysis/gluconeogenesis and fatty acid degradation in female adult treatments. In contrast, AITC treatments showed major enrichment in pathways related to pentose and glucuronate interconversions, retinol metabolism, and ascorbate and aldarate metabolism. Additionally, qRT-PCR analysis validated the expression patterns of 10 ODE genes in response to these treatments, with varying results observed among the genes. These findings indicate significant changes in ODE expression levels, providing a molecular foundation for identifying potential targets for behavioral inhibitors.

The I4790K mutation of the ryanodine receptor is responsible for anthranilic diamide resistance in field populations of Plutella xylostella (Lepidoptera: Plutellidae)

Insecticide resistance in Plutella xylostella (Linnaeus) (Lepidoptera: Plutellidae) is a major constraint on the global production of cruciferous crops. For effective management of insecticide resistance, it is necessary to develop a molecular detection tool for predicting insecticide resistance levels based on the mutation frequency of target sites. In this study, a susceptible strain (SHggt) of P. xylostella was subjected to chlorantraniliprole and tetraniliprole selection under laboratory conditions to obtain the CHLSel and TETSel strains, respectively, to determine their resistance development, cross-resistance and mutation frequencies of the P. xylostella ryanodine receptor (PxRyR). In addition, the tetraniliprole resistance and the mutation frequencies of the PxRyR from 7 field populations were evaluated. Continuous selection over 30 generations resulted in resistance ratios (RRs) of 7,073.2-fold and 6,971.0-fold for the CHLSel and TETSel strains, respectively, and thousandfold increases in cross-resistance to unexposed diamides, e.g., cyantraniliprole and flubendiamide, were observed. For the field populations, three out of seven populations have developed more than thousandfold resistance to tetraniliprole. Among the three investigated target site mutations in PxRyR, only I4790K was detected in both laboratory-selected strains. However, 2 mutations, I4790K and G4946E, were detected in field populations. A positive correlation between RRs and K allele frequencies was observed in the laboratory-selected/relaxed strains and field populations of P. xylostella. These results suggest a possible link between the development of anthranilic diamide resistance and the frequency of the PxRyR I4790K mutation, which can be used to develop effective strategies for diamide resistance management in P. xylostella.

Verification of AKT and CDK5 Gene and RNA Interference Combined with Irradiation to Mediate Fertility Changes in Plutella xylostella (Linnaeus)

Plutella xylostella (Linnaeus) mainly damages cruciferous crops and causes huge economic losses. Presently, chemical pesticides dominate its control, but prolonged use has led to the development of high resistance. In contrast, the sterile insect technique provides a preventive and control method to avoid the development of resistance. We discovered two genes related to the reproduction of Plutella xylostella and investigated the efficacy of combining irradiation with RNA interference for pest management. The results demonstrate that after injecting PxAKT and PxCDK5, there was a significant decrease of 28.06% and 25.64% in egg production, and a decrease of 19.09% and 15.35% in the hatching rate compared to the control. The ratio of eupyrene sperm bundles to apyrene sperm bundles also decreased. PxAKT and PxCDK5 were identified as pivotal genes influencing male reproductive processes. We established a dose-response relationship for irradiation (0-200 Gy and 200-400 Gy) and derived the irradiation dose equivalent to RNA interference targeting PxAKT and PxCDK5. Combining RNA interference with low-dose irradiation achieved a sub-sterile effect on Plutella xylostella, surpassing either irradiation or RNA interference alone. This study enhances our understanding of the genes associated with the reproduction of Plutella xylostella and proposes a novel approach for pest management by combining irradiation and RNA interference.

Comparative transcriptome analysis reveals the molecular mechanism of sterility induced by irradiation of Plutella xylostella (Linnaeus)

Plutella xylostella (Linnaeus) is an important pest of cruciferous plants, which is harmful all over the world, causing serious economic losses, and its drug resistance is increasing rapidly. The sterile insect technique (SIT) is a green control method and does not cause resistance. In this study, transcriptomics and bioinformatics were used to explore the effects of irradiation on the reproductive function of Plutella xylostella, and the response mechanism of sterility under irradiation was initially revealed. We identified 3342 (1682 up-regulated, 1660 down-regulated), 1963 (1042 up-regulated, 921 down-regulated) and 1531 (721 up-regulated, 810 down-regulated) differentially expressed genes (DEGs) in the 200 Gy vs CK (Control Check), 400 Gy vs CK and 400 Gy vs 200 Gy groups, respectively. GO and KEGG analyses were performed for DEGs in each group. The results showed that 200 Gy activated the downstream phosphorylation pathway and inhibited the cytochrome p450 immune response mechanism. 400 Gy promoted protein decomposition and absorption pathways, autophagy pathways, etc. Down-regulated genes were concentrated in the transformation process of energy metabolizing substances such as ATP, phosphorylation signaling pathway, and insulin, while up-regulated genes were concentrated in biological regulation and metabolic processes. Eight genes in the phosphorylation pathway were selected for qRT-PCR verification, and the results showed that the phosphorylation of different dose groups was regulated in different ways. 400 Gy used positive feedback regulation, while the phosphorylation of F1 used negative feedback regulation.

Development of a gold nanoparticle-based lateral flow immunoassay for the fast detection of diafenthiuron in cabbage and apples

Due to its unique insecticidal and acaricidal mechanism of action, and ability to mix with most insecticides and fungicides, diafenthiuron (DIAF) is widely used in the cultivation of fruits and vegetables. However, this insecticide can cause unacceptable harm to organisms, making the detection of DIAF residues in fruits and vegetables crucial. In this study, a novel hapten based on the structure of DIAF was utilized to prepare a monoclonal antibody (mAb) with high specificity and sensitivity. The half maximum inhibitory concentration (IC₅₀) of the anti-DIAF mAb was 20.96 μg kg^-1 as determined by ic-ELISA and little cross-reactivity with other analogues. Next, a GNP-based lateral flow immunoassay (LFIA) was developed to detect DIAF in cabbages and apples. The optimized LFIA, for cabbage samples, showed a visual limit of detection (vLOD), cut-off value and calculated limit of detection (cLOD) of 0.1 mg kg^-1, 10 mg kg^-1 and 1.5 μg kg^-1, respectively, and for apples 0.1 mg kg^-1, 5 mg kg^-1 and 3.4 μg kg^-1, respectively. Recovery rates in cabbage and apples were 89.4-105.0% and 105.3-112.0%, with a coefficient of variation of 2.73-5.71% and 2.15-7.56%, respectively. These results indicated that the established LFIA based on our anti-DIAF mAb was a reliable method for in situ rapid detection of DIAF in cabbage and apple samples.

A novel V263I mutation in the glutamate-gated chloride channel of Plutella xylostella (L.) confers a high level of resistance to abamectin

The frequent and extensive use of insecticides leads to the evolution of insecticide resistance, which has become one of the constraints on global agricultural production. Avermectins are microbial-derived insecticides that target a wide number of insect pests, including the diamondback moth Plutella xylostella, an important global pest of brassicaceous vegetables. However, field populations of P. xylostella have evolved serious resistance to avermectins, including abamectin, thereby threatening the efficiency of these insecticides. In this study, a novel valine to isoleucine mutation (V263I) was identified in the glutamate-gated chloride channel (GluCl) of field P. xylostella populations, which showed different levels of resistance to abamectin. Electrophysiological analysis revealed that the V263I mutation significantly reduced the sensitivity of PxGluCl to abamectin by 6.9-fold. Genome-modified Drosophila melanogaster carrying the V263I mutation exhibited 27.1-fold resistance to abamectin. Then, a knockin strain (V263I-KI) of P. xylostella expressing the homozygous V263I mutation was successfully constructed using the CRISPR/Cas9. The V263I-KI had high resistance to abamectin (106.3-fold), but significantly reduced fecundity. In this study, the function of V263I mutation in PxGluCl was verified for the first time. These findings provide a more comprehensive understanding of abamectin resistance mechanisms and lay the foundation for providing a new molecular detection method for abamectin resistance monitoring.

CRISPR/Cas9-mediated D472N substitution in the Rdl1 of Plutella xylostella confers low resistance to abamectin

BACKGROUND

Abamectin is one of the main insecticides used for the control of Plutella xylostella, a destructive pest of cruciferous crops. Target-site mutation plays an important role in insecticide resistance. A point mutation (D472N) has been reported in the Rdl1 γ-aminobutyric acid receptor (GABAR) in P. xylostella, but its roles in insecticide resistance remain unknown.

RESULTS

In this study, the D472N mutation of the Rdl1 GABAR was detected in several field populations of P. xylostella and showed a positive correlation with abamectin resistance. A knock-in homozygous mutation strain (D472N-KI) of P. xylostella was successfully constructed using CRISPR/Cas9 coupled with homology-directed repair, and the bioassay results demonstrated that compared with the susceptible strain, the D472N-KI strain had 11.1- and 3.7-fold increased resistance to abamectin and endosulfan, respectively. There was no difference in resistance to fipronil, broflanilide or isocycloseram, which also target the GABAR. In addition, the total fecundity of the D472N-KI strain was significantly reduced by 50.0%.

CONCLUSION

Our results suggest that the homozygous D472N mutation in Rdl1 confers a low level of resistance to abamectin in P. xylostella but causes significant fecundity disadvantages, which may delay the development of resistance to some extent. These results lay a foundation for further understanding the mechanisms of abamectin resistance in insect pests. © 2022 Society of Chemical Industry.

A comprehensive assessment of insecticide resistance mutations in source and immigrant populations of the diamondback moth Plutella xylostella (L.)

BACKGROUND

The diamondback moth (DBM) Plutella xylostella has developed resistance to almost all insecticides used to control it. Populations of DBM in temperate regions mainly migrate from annual breeding areas. However, the distribution pattern of insecticide resistance of DBM within the context of long-distance migration remains unclear.

RESULTS

In this study, we examined the frequency of 14 resistance mutations for 52 populations of DBM collected in 2010, 2011, 2017 and 2018 across China using a high-throughput KASP genotyping method. Mutations L1041F and T929I conferring pyrethroid resistance, and mutations G4946E and E1338D conferring chlorantraniliprole resistance were near fixation in most populations, whereas resistant alleles of F1020S, M918I, A309V and F1845Y were uncommon or absent in most populations. Resistance allele frequencies were relatively stable among different years, although the frequency of two mutations decreased. Principal component analysis based on resistant allele frequencies separated a southern population as an outlier, whereas the immigrants clustered with other populations, congruent with the migration pattern of northern immigrants coming from the Sichuan area of southwestern China. Most resistant mutations deviated from Hardy-Weinberg equilibrium due to a lower than expected frequency of heterozygotes. The deviation index of heterozygosity for resistant alleles was significantly higher than the index obtained from single nucleotide polymorphisms across the genome. These findings suggest heterogeneous selection pressures on resistant mutations.

CONCLUSION

Our results provide a picture of resistant mutation patterns in DBM shaped by insecticide usage and migration of this pest, and highlight the widespread distribution of resistance alleles in DBM. © 2022 Society of Chemical Industry.

Sublethal effects of chlorfenapyr on Plutella xylostella (Lepidoptera: Plutellidae)

BACKGROUND

The diamondback moth (DBM), Plutella xylostella (L.), is the most destructive pest of cruciferous vegetables worldwide. Chlorfenapyr is an important insecticide for controlling DBM. The impacts of three sublethal doses (LC₁ , LC₁₀ and LC₃₀ ) of chlorfenapyr on the chlorfenapyr-exposed DBM individuals and their unexposed F₁ and F₂ offspring were investigated in order to reveal the non-lethal deleterious effects of chlorfenapyr and its potential hormetic effects.

RESULTS

LC₁ significantly increased female pupa weight of F₀ and F₁ generations, and F₀ fecundity as well as F₁ gross reproduction rate (GRR). The LC₁ -elicited rise in emergency rate and fecundity was significantly greater in F₀ than in F₁ . By contrast, LC₃₀ significantly decreased age-specific survival rates, pupation rate, male pupal weight, emergence rate and fecundity of F₀ and F₁ generations as well as female adult proportion and GRR, net reproduction rate (R₀ ), intrinsic rate of increase (r_m ) and finite rate of increase (λ) of F₁ generation. The LC₃₀ -induced reductions in pupation rate, adult emergence rate, male and female pupa weight, and fecundity were greater in F₁ than in F₀ . While LC₁₀ elicited only a mild inhibition (extension of pupal duration) in F₀ , it yielded both deleterious (drops in female proportion and age-specific survivals) and hormetic effects (ups in male longevity and female fecundity) in F₁ .

CONCLUSION

The results demonstrate that the sublethal effects of chlorfenapyr on DBM vary from inhibition to stimulatory hormesis, depending on the dose and generation. © 2022 Society of Chemical Industry.

Influence of seasonal migration on evolution of insecticide resistance in Plutella xylostella

The diamondback moth, Plutella xylostella (L.), is one of the most destructive migratory pest species of cruciferous vegetables worldwide and has developed resistance to most of the insecticides used for its control. The migration regularity, migratory behavior, and relationship between flight and reproduction of P. xylostella have been widely reported. However, the effect of migration on insecticide resistance in this pest is still unclear. In this study, the effect of migration on P. xylostella resistance to seven insecticides was investigated using populations across the Bohai Sea that were collected in the early and late seasons during 2017-2019. The bioassay results showed that the early season populations of P. xylostella from south China possessed much higher resistance to insecticides because of intensive insecticide application; alternatively, the late season populations migrated from northeast China, where the insecticides were only used occasionally, showed much lower insecticide resistance. The genome re-sequencing results revealed that, among the eight mutations involved in insecticide resistance, the frequencies of two acetylcholinesterase mutations (A298S and G324A) responsible for organophosphorus insecticide resistance were significantly decreased in the late season populations. The results indicated that P. xylostella migration between tropical and temperate regions significantly delayed the development of insecticide resistance. These findings illustrated the effect of regional migration on the evolution of insecticide resistance in P. xylostella, and provided foundational information for further research on the relationship between migration and insecticide resistance development in other insects.

Biological Control of Diamondback Moth-Increased Efficacy with Mixtures of Beauveria Fungi

Diamondback moth (DBM) is an important horticultural pest worldwide as the larvae of these moths feed on the leaves of cruciferous vegetables. As DBM has developed resistance to more than 100 classes of synthetic insecticides, new biological control options are urgently required. Beauveria species are entomopathogenic fungi recognized as the most important fungal genus for controlling a wide range of agricultural, forestry, and veterinary arthropod pests. Previous research, aimed at developing new Beauveria-based biopesticides for DBM, has focused on screening single isolates of Beauveria bassiana. However, these fungal isolates have individual requirements, which may limit their effectiveness in some environments. This current study separately assessed 14 Beauveria isolates, from a range of habitats and aligned to four different species (Beauveria bassiana, B. caledonica, B. malawiensis, and B. pseudobassiana), to determine the most effective isolate for the control of DBM. Further assays then assessed whether selected combinations of these fungal isolates could increase the overall efficacy against DBM. Six Beauveria isolates (three B. bassiana and three B. pseudobassiana) achieved high DBM mortality at a low application rate with the first documented report of B. pseudobassiana able to kill 100% of DBM larvae. Further research determined that applications of low-virulent Beauveria isolates improved the control of DBM compared to mixtures containing high-virulent isolates. This novel approach increased the DBM pest mortality and shortened the time to kill.

The glutathione S-transferase (PxGST2L) may contribute to the detoxification metabolism of chlorantraniliprole in Plutella xylostella(L.)

The diamondback moth (Plutella xylostella L.), is an economic pest of cruciferous plants worldwide, which causes great economic loss to cruciferous plants production. However, the pest has developed resistance to insecticides. One of such insecticides is chlorantraniliprole. The study of the mechanisms underlying resistance is key for the effective management of resistance. In this study, a comparative proteomics approach was used to isolate and identify various proteins that differed between chlorantraniliprole-susceptible and -resistant strains of P. xylostella. Eleven proteins were significantly different and were successfully identified by MALDI-TOF-MS. Metabolism-related proteins accounted for the highest proportion among the eleven different proteins. The function of the PxGST2L protein was validated by RNAi. Knockdown of PxGST2L reduced the GST activity and increased the toxicity of chlorantraniliprole to the diamondback moth. The resistance ratio of diamondback moth to chlorantraniliprole was reduced from 1029 to 505. The results indicated that PxGST2L is partly responsible for chlorantraniliprole insecticide resistance in DBM. Our finding contributes to the understanding of the mechanism underlying resistance to chlorantraniliprole in the DBM, to develop effective resistance management tactics.