Plutella xylostella, a destructive crucifer pest, can rapidly develop resistance to most classes of pesticides. This study investigated the molecular resistance mechanisms to chlorpyrifos, an organophosphate pesticide. Two P. xylostella genes, ace1 and ace2, were described. The nucleotide sequence results revealed no variation in ace2, while the resistant strain (Kar-R) had four amino acid alterations in ace1, two of which (A298S and G324A) were previously shown to confer organophosphate resistance in P. xylostella. In the present study, the 3D model structures of both the wild-type (Gu-S) and mutant (Kar-R) of P. xylostella ace1 strains were studied through molecular dynamics (MDs) simulations and molecular docking. Molecular dynamics simulations of RMSD revealed less structural deviation in the ace1 mutant than in its wild-type counterpart. Higher flexibility in the 425–440 amino acid region in the mutant active site (Glu422 and Acyl pocket) increased the active site’s entropy, reducing the enzyme’s affinity for the inhibitors. Gene expression analysis revealed that the relative transcription levels of ace1 were significantly different in the Kar-R strain compared with the Gu-S strain. This study enhances the understanding of the mechanisms governing ace1′s resistance to insecticide and provides essential insights for new insecticides as well as valuable insights into environmentally conscious pest management techniques.

Detoxification genes are crucial to insect resistance against chemical pesticides, yet their expression may be altered by exposure to biopesticides such as spores and insecticidal proteins of Bacillus thuringiensis (Bt). Increased enzymatic levels of selected detoxification genes, including glutathione S-transferase (GST), cytochrome P450 (CYP450), and carboxylesterase (CarE), were detected in chlorantraniliprole (CAP)-resistant strains of the diamondback moth (DBM, Plutella xylostella) from China when compared to a reference susceptible strain. These CAP-resistant DBM strains displayed distinct expression patterns of GST 1, CYP6B7, and CarE-6 after treatment with CAP and a Bt pesticide (Bt-G033). In particular, the gene expression analysis demonstrated significant upregulation of the CYP6B7 gene in response to the CAP treatment, while the same gene was downregulated following the Bt-G033 treatment. Downregulation of CYP6B7 using RNAi resulted in increased susceptibility to CAP in resistant DBM strains, suggesting a role of this gene in the resistant phenotype. However, pretreatment with a sublethal dose of Bt-G033 inducing the downregulation of CYP6B7 did not significantly increase CAP potency against the resistant DBM strains. These results identify the DBM genes involved in the metabolic resistance to CAP and demonstrate how their expression is affected by exposure to Bt-G033.

In southern China, cowpea production is severely threatened by Megalurothrips usitatus due to its fast-evolving resistance to insecticides. The toxicity monitoring of commonly used insecticides against field populations provides key information for the resistance management of pests. In this study, field populations of Megalurothrips usitatus were collected from three locations (QY, YF, MM) in Guangdong, and the sensitivity of these populations against insecticides was determined by using a thrips insecticides bioassay system (TIBS) method. The bioassay results indicated there were sensitivity variances to insecticides between these three field populations. Among these 10 insecticides, spinetoram and spinosad both showed high toxicity against all three field populations. In addition, broflanilide for QY, emamectin benzoate for YF, and emamectin benzoate and cyantraniliprole for MM were suggested as alternate insecticides to alleviate selective pressure from insecticides on field populations. In field experiments, the corrected control efficacy of cyantraniliprole and spinetoram against M. usitatus was over 75% at 7 dpa, which proved to be ideal insecticides for field application. These field-based results provide guidance for chemical control against thrips and can be valuable in proposing appropriate strategies for thrips resistance management.

As two major pests of cowpea in South China, bean flower thrips [Megalurothrips usitatus (Bagnall)] and flower thrips [Frankliniella intonsa (Trybom)] always occur on the same plant. In this study, the two-sex life table parameters of these two species were investigated on three bean pods: cowpea (Vigna unguiculata L. var. Chunqiu Wujiadou), snap bean (Phaseolus vulgaris L. var. Yonglong 3), and green bean (Phaseolus vulgaris L. var. Linghangzhe) using standard cut bean protocols. Longevity of female adult M. usitatus showed no significant difference on cowpea and snap bean, but was shortest on green bean, with the highest fecundity on snap bean, followed by cowpea and green bean. Longevity and fecundity of female adult F. intonsa were both highest on cowpea, followed by snap bean and green bean. On snap bean, the population parameters (R₀, GRR, T) of M. usitatus were higher than F. intonsa, whereas r and λ were not different, suggesting that M. usitatus were more competitive on snap bean. On cowpea, the population parameters (R₀, GRR, r, λ) of F. intonsa were higher than M. usitatus, suggesting a competitive advantage of F. intonsa on cowpea. To better mimic field conditions, we investigated the survival and fecundity of adult M. usitatus under two distinct scenarios: when they could feed directly on cut surfaces of cowpeas (standard lab protocol), and when they could not. Adult survival of M. usitatus is not significantly influenced by whether or not they fed directly on cut surfaces of cowpeas. However, a notable decrease in fecundity was observed in M. usitatus that fed on surface-covered cut pods. This suggested that direct feeding on cut surfaces of cowpea did have an impact on thrips’ fecundity, offering fresh perspectives for future research into the growth and development of thrips in a laboratory. Our study suggests that experiments involving cut surfaces may be misleading, and further investigations are ongoing to address these concerns.

G protein-coupled receptors (GPCRs) are considered the largest and most variable family of transmembrane receptors regulating physiological processes such as toxicological responses and insecticide resistance development. The present study investigated the responses of Methuselah (Mth), belonging to GPCR family B in the Diamondback Moth (DBM), Plutella xylostella, to chlorantraniliprole (CAP). Genome-wide identification and phylogenetic analysis of Pxmth genes revealed their evolutionary relationships and functional classifications. Expression profiling demonstrated significant overexpression of Pxmth2 in the CAP-resistant strain. Additionally, the tertiary and secondary structures of Pxmth2 were characterized, providing insights into its functional role. Silencing Pxmth2 via RNA interference (RNAi) reduced resistance of DBM to CAP and suppressed downstream stress-associated genes (CYP6B6, CYP6B7, CYP6BF1), increasing susceptibility to the insecticide. The function of Pxmth2 was further explored using a transgenic line of Drosophila melanogaster engineered to overexpress the gene; flies overexpressing Pxmth2 exhibited a significantly increased resistance to CAP compared to controls. These findings indicate that Pxmth2 contributes to CAP resistance in DBM and highlights potential molecular targets for improving pest management strategies.