Resistance selection of triflumezopyrim in Laodelphax striatellus (fallén): Resistance risk, cross-resistance and metabolic mechanism

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

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

Insights into the role of non-coding RNAs in the development of insecticide resistance in insects

Pest control heavily relies on chemical pesticides has been going on for decades. However, the indiscriminate use of chemical pesticides often results in the development of resistance in pests. Almost all pests have developed some degree of resistance to pesticides. Research showed that the mechanisms of insecticide resistance in insects encompass metabolic resistance, behavioral resistance, penetration resistance and target-site resistance. Research on the these mechanisms has been mainly focused on the cis-regulatory or trans-regulatory for the insecticide resistance-related genes, with less attention paid to non-coding RNAs (ncRNAs), such as microRNA (miRNA), long non-coding RNA (lncRNA), and circular RNA (circRNA). There has been increased studies focus on understanding how these ncRNAs are involved in post-transcriptional regulation of insecticide resistance-related genes. Besides, the formatted endogenous RNA (ceRNA) regulatory networks (lncRNA/circRNA-miRNA-mRNA) has been identified as a key player in governing insect resistance formation. This review delves into the functions and underlying mechanisms of miRNA, lncRNA, and circRNA in regulating insect resistance. ncRNAs orchestrate insect resistance by modulating the expression of detoxification enzyme genes, insecticide target genes, as well as receptor genes, effectively regulating both target-site, metabolic and penetration resistance in insects. It also explores the regulatory mechanisms of ceRNA networks in the development of resistance. By enhancing our understanding of the mechanisms of ncRNAs in insecticide resistance, it will not only provide valuable insights into the new mechanisms of insecticide resistance but also help to enrich new directions in ncRNAs gene regulation research.

MicroRNA PC-5p-3991_515 mediates triflumezopyrim susceptibility in the small brown planthopper through regulating the post-transcriptional expression of P450 CYP417A2

BACKGROUND

Cytochrome P450 monooxygenases (P450s) are recognized as a major contributor to metabolic resistance in insects to most insecticides, through gene overexpressions and protein mutations. MicroRNA (miRNA), an important post-transcriptional regulator, has been reported to promote insecticide resistance by mediating the expression of detoxification enzyme genes.

RESULTS

In the present study, we reported that a novel microRNA PC-5p-3991_515 was involved in the post-transcriptional regulation of CYP417A2 and mediated the triflumezopyrim susceptibility in the small brown planthopper (SBPH), Laodelphax striatellus (Fallén). The tissue expression profiles showed that CYP417A2 was highly expressed in fat body. CYP417A2 was significantly up-regulated at 12, 36, 60, 84 and 108 h after the triflumezopyrim treatment. RNA interference (RNAi) against CYP417A2 significantly increased triflumezopyrim susceptibility in SBPH. According to the prediction by miRanda and TargetScan software, three miRNAs were indicated to bind to CYP417A2. However, when oversupply of agomir, only two miRNAs, PC-3p-625_4405 and PC-5p-3991_515, significantly increased the susceptibility to triflumezopyrim and decreased CYP417A2 levels. Furthermore, PC-5p-3991_515 was confirmed to be involved in the post-transcriptional regulation of CYP417A2 by dual luciferase reporter assay. Meanwhile, PC-5p-3991_515 was co-localized with CYP417A2 in the midgut in situ hybridization.

CONCLUSION

Our findings revealed that the novel microRNA, PC-5p-3991_515, post-transcriptionally regulated CYP417A2 expression, which then mediated the triflumezopyrim susceptibility in SBPH. © 2023 Society of Chemical Industry.

Enhancement of tolerance against flonicamid in Solenopsis invicta (Hymenoptera: Formicidae) through overexpression of CYP6A14

Solenopsis invicta is a main issue in southern China and is causing significant damage to the local ecological environment. The extensive use of insecticides has resulted in the development of tolerance in S. invicta. In our study, ten S. invicta colonies from Sichuan Province exhibited varying degrees of tolerance against flonicamid, with LC50 values from 0.49 mg/L to 8.54 mg/L. The sensitivity of S. invicta to flonicamid significantly increased after treatment with the P450 enzyme inhibitor piperonyl butoxide (PBO). Additionally, the activity of P450 in S. invicta was significantly enhanced after being treated with flonicamid. Flonicamid induced the expression levels of CYP4aa1, CYP9e2, CYP4C1, and CYP6A14. The expression levels of these P450 genes were significantly higher in the tolerant colonies compared to the sensitive colonies, and the relative copy numbers of CYP6A14 in the tolerant colonies were 2.01-2.15 fold. RNAi feeding treatment effectively inhibited the expression of P450 genes, thereby reducing the tolerance of S. invicta against flonicamid. In addition, the overexpression of CYP6A14 in D. melanogaster resulted in reduced sensitivity to flonicamid. Our investigations revealed hydrophobic interactions between flonicamid and seven amino acid residues of CYP6A14, along with the formation of a hydrogen bond between Glu306 and flonicamid. Our findings suggest that flonicamid can effectively control S. invicta and P450 plays a pivotal role in the tolerance of S. invicta against flonicamid. The overexpression of CYP6A14 also increased tolerance to flonicamid.

Risk of resistance and the metabolic resistance mechanism of Laodelphax striatellus (Fallén) to cyantraniliprole

Cyantraniliprole is a highly effective diamide insecticide used to control of Laodelphax striatellus (Fallén). This study aimed to assess the insecticide resistance risk of L. striatellus and its metabolic resistance mechanisms. After 25 continuous generations of selection, the resistance of L. striatellus to cyantraniliprole increased by 17.14-fold. The realistic heritability of resistance was 0.0751. After successive rearing for five generations without exposure to insecticides, the resistance ratio for the resistant strain of L. striatellus decreased by 3.47-fold, and the average resistance decline rate per generation was 0.0266. Cyantraniliprole-resistant strains did not exhibit cross-resistance to triflumezopyrim, pymetrozine, flonicamid, sulfoxaflor, dinotefuran, clothianidin, thiamethoxam, nitenpyram, or imidacloprid. Compared to those of the sensitive strain, the 2nd, 3rd, and 4th instars, nymphal stage durations, total preoviposition period, and average generation time of the resistant strain were markedly reduced. Furthermore, the activity of cytochrome P450 monooxygenase (P450) and carboxylesterase (CarE) were markedly increased. The upregulation of CYP419A1v2 expression was most evident among the P450 genes, with a 6.10-fold increase relative to that in the sensitive strain. The CarE gene LsCarE5 was significantly upregulated by 1.94-fold compared with that in the sensitive strain. With the continuous use of cyantraniliprole, L. striatellus may develop resistance to this insecticide. This resistance may be related to the increase in metabolic enzyme activities regulated by the overexpression of P450 and CarE genes.

A microRNA, PC-5p-30_205949, regulates triflumezopyrim susceptibility in Laodelphax striatellus (Fallén) by targeting CYP419A1 and ABCG23

MicroRNAs (miRNAs) are known to be important post-transcriptional regulators of gene expression and have been shown to be associated with insecticide resistance in insects. In this research, we show that a miRNA, PC-5p-30_205949, is involved in triflumezopyrim susceptibility via regulating expressive abundance of cytochrome P450 CYP419A1 and ATP-binding cassette transporters ABCG23 in the small brown planthopper (SBPH), Laodelphax striatellus (Fallén). Triflumezopyrim treatment significantly reduced the abundance of PC-5p-30_205949, feeding of agomir-PC-5p-30_205949 significantly increased the sensitivity of SBPH to triflumezopyrim, and its spatiotemporal expression profiles showed that PC-5p-30_205949 were expressed at all developmental stages and were highly expressed in head tissue. By software prediction and dual luciferase reporter assay, the target genes of PC-5p-30_205949 were identified as two detoxification metabolism genes CYP419A1 and ABCG23. The relative expressions of CYP419A1 and ABCG23 were significantly up-regulated after 24 h, 48 h and 72 h with triflumezopyrim exposure. CYP419A1 was highly expressed in the 4th-instar nymphs and male adults, with the highest expression level in fat body. ABCG23 was highly expressed in female adults, and had the highest expression in head. Furthermore, silencing of CYP419A1 and ABCG23 by RNA interference significantly increased the mortality of SBPH to triflumezopyrim, and molecular docking showed that CYP419A1 and ABCG23 could stably bind to triflumezopyrim with binding free energies of -171.5622 and - 103.3402 kcal mol^-1, respectively. These results suggest that SBPH has a strategy to enhance the resistance to triflumezopyrim by attenuating the expression of PC-5P-30_205949, thereby activating the detoxification metabolic pathway by targeting CYP419A1 and ABCG23.