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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. [ABSTRACT FROM AUTHOR]

BACKGROUND: Neonicotinoids, such as imidacloprid, are selective agonists of insect nicotinic acetylcholine receptors (nAChRs) used to control Nilaparvata lugens, a major rice insect pest. High imidacloprid resistance has been reported in N. lugens both in the laboratory and in the field. Cycloxaprid (CYC), an oxa‐bridged cis‐nitromethylene neonicotinoid, showed high insecticidal activity against N. lugens and low cross‐resistance in imidacloprid‐resistant strains and field populations. RESULTS: Binding studies demonstrated that imidacloprid has two binding sites with different affinities (Kd = 3.18 ± 0.43 pm and 1.78 ± 0.19 nm) in N. lugens nAChRs. CYC was poor at displacing [3H]imidacloprid at its high‐affinity binding site (Ki = 159.38 ± 20.43 nm), but quite efficient at the low‐affinity binding site (Ki = 1.27 ± 0.35 nm). These data showed that CYC had overlapping binding sites with imidacloprid only at its low‐affinity binding site. Therefore, the low displacement ability of CYC against imidacloprid binding at its high‐affinity site could partially explain the low cross‐resistance of CYC in imidacloprid‐resistant populations. CONCLUSION: The high insecticidal activity, low cross‐resistance and different binding properties on insect nAChRs of CYC show that it is a potential insecticide for the control of N. lugens and related insect pests, especially ones with high resistance to neonicotinoids. © 2018 Society of Chemical Industry Cycloxaprid is an oxa‐bridged cis‐nitromethylene neonicotinoid. This article shows that different binding properties on insect nicotinic acetylcholine receptors partially explain its low cross‐resistance with imidacloprid. [ABSTRACT FROM AUTHOR]

Abstract: BACKGROUND: Cycloxaprid is a new oxabridged cis‐configuration neonicotinoid insecticide, the resistance development potential and underlying resistance mechanism of which were investigated in the small brown planthopper, Laodelphax striatellus (Fallén), an important agricultural pest of rice. RESULTS: A cycloxaprid‐resistant strain (YN‐CPD) only achieved 10‐fold higher resistance, in contrast to 106‐fold higher resistance to buprofezin and 332‐fold higher resistance to chlorpyrifos achieved after exposure to similar selection pressure, and the cycloxaprid selected line showed no cross‐resistance to the buprofezin and chlorpyrifos‐selected resistance strains. Moreover, we identified 10 nicotinic acetylcholine receptor (nAChR) subunits from the transcriptome of L. striatellus, and six segments had open reading frames (ORFs). While we did not find mutations in the nAChR genes of L. striatellus, subunits Lsα1 and Lsβ1 exhibited, respectively, 9.60‐fold and 3.36‐fold higher expression in the resistant strain, while Lsα8 exhibited 0.44‐fold lower expression. Suppression of Lsα1 through ingestion of dsLsα1 led to an increase in susceptibility to cycloxaprid. CONCLUSION: The findings indicate that resistance to cycloxaprid develops slowly compared with resistance to other chemicals and without cross‐resistance to chlorpyrifos or buprofezin; over‐expressed Lsα1 is associated with low cycloxaprid resistance levels, but the importance of over‐expressed Lsβ1 and reduced expression of Lsα8 could not be excluded. © 2017 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

BACKGROUND Fitness costs associated with insecticide resistance in pest insects have mainly been studied under optimal laboratory conditions. However, resistant insects face more stressors than just insecticides in the field, and how the resistant population reacts to these stressors is of practical importance for the control of pest insects such as the brown planthopper Nilaparvata lugens. The aim of the present study was to explore the impact of population density on the competitiveness of resistant and susceptible individuals. RESULTS Two isogenic N. lugens populations, a highly imidacloprid-resistant population (HZ-R) with a resistance ratio (RR) of 227.10 and a relatively susceptible population (HZ-S) with an RR of 2.99, were created from a field-resistant population (HZ; RR 62.51). The high resistance levels of HZ-R and HZ were mainly attributable to the overexpression of multiple cytochrome P450 (CYP) genes such as CYP6ER1, CYP6AY1, CYP6CW1 and CYP4CE1 compared with HZ-S, this being supported by piperonyl butoxide synergism. HZ-R was observed to be more resistant to thiacloprid and etofenprox compared with HZ and HZ-S. Most interestingly, in high population density treatments, HZ-S individuals were much more competitive than HZ-R individuals. CONCLUSION Imidacloprid-resistant individuals of N. lugens are less competitive than their susceptible counterparts under density pressure. © 2017 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Background: The endocycle can generate cells referred to as 'polyploid'. Fizzy-related protein (Fzr) plays an important role in driving the mitosis-to-endocycle transition. The brown planthopper (BPH), Nilaparvata lugens (Stål), a serious insect pest, feeds exclusively on rice. However, polyploidy and its regulatory mechanisms are poorly understood in BPH., Results: Here, we found that the ploidy levels of follicles H (FH) and accessory gland (AG) significantly increased with BPH age when examining the polyploidy of FH and AG of salivary glands. Fzr was identified as an important regulator for polyploidy in BPH salivary gland. Knockdown of Fzr resulted in a decrease in cell size and DNA content in nymph salivary glands. Fzr knockdown transcriptionally upregulated cyclin-dependent kinase 1 (CDK1), CDK2, cyclin A (CycA) and CycB, and downregulated CycD, CycE, Myc and mini-chromosome maintenance protein 2-7 (MCM2-7). Phenotypically, Fzr knockdown significantly suppressed salivary protein production, feeding and survival in BPH nymphs., Conclusion: Our results show that BPH salivary glands exhibit obvious polyploidy, and Fzr positively regulates the endocycle in nymph salivary gland. These findings provide clues for the study of the regulatory mechanisms of insect polyploidy. © 2024 Society of Chemical Industry., (© 2024 Society of Chemical Industry.)

Background: The whitebacked planthopper (WBPH), Sogatella furcifera (Horváth), is a major rice pest in many parts of Asia. Fipronil has been widely used to control rice pests, and resistance to fipronil has been reported in some important species., Results: A field population (F) of WBPH was collected, with 50.5-fold resistance to fipronil, which increased to 137.5-fold (F-se) after continuous selection for 11 generations. The F-se population did not show significant cross-resistance to the insecticides examined by comparison with the F population. TPP (synergism ratio 1.9), DEM (1.5) and PBO (1.1) showed only slight synergism on fipronil in the F-se population. A large increase was found in esterase and P450 monooxygenase activity in the F-se population. In vitro, PBO inhibited both esterase and P450 monooxygenase activity, and TPP inhibited esterase activity in the F-se population., Conclusion: Synergistic study in vivo and biochemical study in vitro indicated that esterase and P450 monooxygenases might be important factors for fipronil resistance in the selected population F-se. However, these biochemical factors could not lead to such high resistance (137.5-fold) in the F-se population, and target-site insensitivity would be another or more important factor.

Background: The brown planthopper (BPH), Nilaparvata lugens Stål, is a major rice pest in many parts of Asia. Neonicotinoids such as imidacloprid and dinotefuran are widely used for control of this pest, and resistance to these insecticides has developed in recent years. This pest has also been widely exposed to triazophos and fenvalerate, although these insecticides are not used for the control of the pest directly. Here, the effects of sublethal doses of these four insecticides on the reproduction and wing formation in BPH were examined., Results: Imidacloprid and dinotefuran reduced the fecundity of BPH to 68.8% and 52.4% in macropterous families, and to 57.9% and 43.1% in brachypterous families, when compared with the untreated controls. By contrast, triazophos and fenvalerate increased fecundity. In both macropterous and brachypterous families, sublethal doses of imidacloprid and dinotefuran showed significant induction of macropterous adults., Conclusion: Imidacloprid and dinotefuran could reduce the fecundity of BPH to a significant extent, demonstrating further activity against this pest in addition to their direct toxicity. The significant induction of macropterous adults by sublethal doses of imidacloprid and dinotefuran is of importance in the management of this pest, particularly in the areas of predicting the size of emigrating populations and the numbers of insects likely to occur in newly colonized areas.

Imidacloprid has been used as a key insecticide to control the brown planthopper, Nilaparvata lugens Stål, for several years, but no obvious resistance has been identified in field populations as yet. To evaluate the risk, a field population was collected and selected with imidacloprid in the laboratory. After 37-generation selection a strain with 250-fold resistance had been successfully achieved. Fitness analysis by constructing life tables demonstrated that resistant hoppers had obvious disadvantages in their reproduction. The fitness of highly resistant hoppers had decreased dramatically (0.169 and 0.104) to only one-fifth to one-tenth of that of the susceptible strain. Hence it was concluded that the brown planthopper had the potential to develop high resistance to imidacloprid but that the lower fitness of resistant hoppers could result in a quick recovery of sensitivity when the population did not come into contact with imidacloprid. This means that a reasonable resistance management programme with less imidacloprid use may efficiently delay or even stop resistance development.