A review of physiological resistance to insecticide stress in Nilaparvata lugens

Nicotinamide deficiency promotes imidacloprid resistance via activation of ROS/CncC signaling pathway-mediated UGT detoxification in Nilaparvata lugens

Metabolic alternation is a typical characteristic of insecticide resistance in insects. However, mechanisms underlying metabolic alternation and how altered metabolism in turn affects insecticide resistance are largely unknown. Here, we report that nicotinamide levels are decreased in the imidacloprid-resistant strain of Nilaparvata lugens, may due to reduced abundance of the symbiotic bacteria Arsenophonus. Importantly, the low levels of nicotinamide promote imidacloprid resistance via metabolic detoxification alternation, including elevations in UDP-glycosyltransferase enzymatic activity and enhancements in UGT386B2-mediated metabolism capability. Mechanistically, nicotinamide suppresses transcriptional regulatory activities of cap 'n' collar isoform C (CncC) and its partner small muscle aponeurosis fibromatosis isoform K (MafK) by scavenging the reactive oxygen species (ROS) and blocking the DNA binding domain of MafK. In imidacloprid-resistant N. lugens, nicotinamide deficiency re-activates the ROS/CncC signaling pathway to provoke UGT386B2 overexpression, thereby promoting imidacloprid detoxification. Thus, nicotinamide metabolism represents a promising target to counteract imidacloprid resistance in N. lugens.

Contribution of UDP-glycosyltransferases to chlorpyrifos resistance in Nilaparvata lugens

As a multigene superfamily of Phase II detoxification enzymes, uridine diphosphate (UDP)-glycosyltransferases (UGTs) play important roles in the metabolism of xenobiotics including insecticides. In this study, 5-nitrouracil, an inhibitor of UGT enzyme activity, effectively increased the toxicity of chlorpyrifos to the chlorpyrifos-resistant strain of Nilaparvata lugens, one of the most resistant rice pests. The enzyme content of UGT in the resistant strain was significantly higher than that in the susceptible strain. Among 20 identified UGT genes, UGT386H2, UGT386J2, UGT386N2 and UGT386P1 were found significantly overexpressed in the resistant strain and can be effectively induced by chlorpyrifos. These four UGT genes were most highly expressed in the midgut and/or fat body, two main insect detoxification tissues. Amino acid sequence alignments revealed that these four UGTs contained a variable N-terminal substrate-binding domain and a conserved C-terminal sugar donor-binding domain. Furthermore, homology modeling and molecular docking analyses showed that these UGTs could stably bind to chlorpyrifos and chlorpyrifos oxon, with the binding free energies from -19.4 to -110.62 kcal mol^-1. Knockdown of UGT386H2 or UGT386P1 by RNA interference dramatically increased the susceptibility of the resistant strain to chlorpyrifos. These findings suggest that overexpression of these two UGT genes contributes to chlorpyrifos resistance in N. lugens.

The F-box protein OsEBF2 confers the resistance to the brown planthopper (Nilparvata lugens Stål)

The brown planthopper (BPH; Nilaparvata lugens) is a piercing-sucking insect pest specific to rice plants and may cause severe declines in rice yields. Therefore, it is of great theoretical significance and practical application value to elucidate the molecular mechanism of rice resistance to BPH. Previous studies have shown that an ethylene (ET) signaling pathway gene, OsEBF1, positively regulates BPH resistance in rice. OsEBF1 is an E3 ligase that mediates the degradation of another ET pathway gene, OsEIL1. OsEBF2 is the homologous gene of OsEBF1, and the sequence identity between the two genes is 78.5%. Our results indicated that OsEBF2 can directly interact with OsEIL1 and positively regulate rice resistance to BPH. More importantly, there were no obvious differences in agronomic traits between WT and OsEBF2OE transgenic lines. The resistance mechanism of the OsEBF2 gene may be to reduce the content of ET in rice by inhibiting the expression of ethylene response factor genes. This study revealed that OsEBF2 is an F-box protein that positively regulates the rice resistance to BPH and can be used as an effective target gene for rice BPH resistance breeding.

Insights into insecticide-resistance mechanisms in invasive species: Challenges and control strategies

Threatening the global community is a wide variety of potential threats, most notably invasive pest species. Invasive pest species are non-native organisms that humans have either accidentally or intentionally spread to new regions. One of the most effective and first lines of control strategies for controlling pests is the application of insecticides. These toxic chemicals are employed to get rid of pests, but they pose great risks to people, animals, and plants. Pesticides are heavily used in managing invasive pests in the current era. Due to the overuse of synthetic chemicals, numerous invasive species have already developed resistance. The resistance development is the main reason for the failure to manage the invasive species. Developing pesticide resistance management techniques necessitates a thorough understanding of the mechanisms through which insects acquire insecticide resistance. Insects use a variety of behavioral, biochemical, physiological, genetic, and metabolic methods to deal with toxic chemicals, which can lead to resistance through continuous overexpression of detoxifying enzymes. An overabundance of enzymes causes metabolic resistance, detoxifying pesticides and rendering them ineffective against pests. A key factor in the development of metabolic resistance is the amplification of certain metabolic enzymes, specifically esterases, Glutathione S-transferase, Cytochromes p450 monooxygenase, and hydrolyses. Additionally, insect guts offer unique habitats for microbial colonization, and gut bacteria may serve their hosts a variety of useful services. Most importantly, the detoxification of insecticides leads to resistance development. The complete knowledge of invasive pest species and their mechanisms of resistance development could be very helpful in coping with the challenges and effectively developing effective strategies for the control of invasive species. Integrated Pest Management is particularly effective at lowering the risk of chemical and environmental contaminants and the resulting health issues, and it may also offer the most effective ways to control insect pests.

Effects of phytocompound Precocene 1 on the expression and functionality of the P450 gene in λ-cyhalothrin-resistant Spodoptera litura (Fab.)

Spodoptera litura (Fabricius) is an agriculturally significant polyphagous insect pest that has evolved a high level of resistance to conventional insecticides. A dietary assay was used in this work to assess the resilience of field populations of S. litura to λ-cyhalothrin. Analysis of the function and expression of the cytochrome P450 gene was used to test the sensitivity of S. litura larvae to sub-lethal concentrations of the insecticidal plant chemical Precocene 1, both by itself and in combination with λ-cyhalothrin. The activity of esterase enzymes (α and β) was found to decrease 48 h post treatment with Precocene 1. The activity of GST enzyme and cytochrome P450 increased with Precocene 1 treatment post 48 h, however. Expression studies revealed the modulation by Precocene 1 of cytochrome P450 genes, CYP4M16, CYP4M15, CYP4S8V4, CYP4G31, and CYP4L10. While CYP4M16 expression was stimulated the most by the synergistic Precocene 1 + λ-cyhalothrin treatment, expression of CYP4G31 was the most down-regulated by Precocene 1 exposure. Hence, it is evident that λ-cyhalothrin-resistant pest populations are still sensitive to Precocene 1 at a sublethal concentration that is nevertheless capable of hindering their development. Precocene 1 can therefore be considered a potent candidate for the effective management of insecticide-resilient S. litura.

SPARC plays an important role in the oviposition and nymphal development in Nilaparvata lugens Stål

Background

The brown planthopper (Nilaparvata lugens Stål)is a notorious rice pest in many areas of Asia. Study on the molecular mechanisms underlying its development and reproduction will provide scientific basis for effective control. SPARC (Secreted Protein, Acidic and Rich in Cysteine) is one of structural component of the extracellular matrix, which influences a diverse array of biological functions. In this study, the gene for SPARC was identified and functionally analysed from N.lugens.

Results

The result showed that the NlSPARC mRNA was highly expressed in fat body, hemolymph and early embryo. The mortality increased significantly when NlSPARC was downregulated after RNA interference (RNAi) in 3 ~ 4^th instar nymphs. Downregulation of NlSPARC in adults significantly reduced the number of eggs and offspring, as well as the transcription level of NlSPARC in newly hatched nymphs and survival rate in progeny. The observation with microanatomy on individuals after NlSPARC RNAi showed smaller and less abundant fat body than that in control. No obvious morphological abnormalities in the nymphal development and no differences in development of internal reproductive organ were observed when compared with control.

Conclusion

NlSPARC is required for oviposition and nymphal development mainly through regulating the tissue of fat body in N.lugens. NlSPARC could be a new candidate target for controlling the rapid propagation of N.lugens population. Our results also demonstrated that the effect of NlSPARC RNAi can transfer to the next generation in N.lugens.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08903-z.

The metabolic resistance of Nilaparvata lugens to chlorpyrifos is mainly driven by the carboxylesterase CarE17

The involvement of carboxylesterases (CarEs) in resistance to chlorpyrifos has been confirmed by the synergism analysis in Nilaparvata lugens. However, the function of specific CarE gene in chlorpyrifos resistance and the transcriptional regulatory mechanism are obscure. Herein, the expression patterns of 29 CarE genes in the susceptible and chlorpyrifos-resistant strains were analyzed. Among them, CarE3, CarE17 and CarE19 were overexpressed in the resistant strain, and knockdown of either CarE gene by RNA interference significantly increased the susceptibility to chlorpyrifos. Remarkably, knockdown of CarE17 reduced the enzymatic activity of CarE by 88.63 % and showed a much greater effect on increasing chlorpyrifos toxicity than silencing other two CarE genes. Overexpression of CarE17 in Drosophila melanogaster decreased the toxicity of chlorpyrifos to transgenic fruit flies. Furthermore, the region between - 205 to + 256 of CarE17 promoter sequence showed the highest promoter activity, and 16 transcription factors (TFs) were predicted from this region. Among these TFs, Lim1β and C15 were overexpressed in the resistant strain. Knockdown of either TF resulted in reduced CarE17 expression and a decrease in resistance of N. lugens to chlorpyrifos. These results indicate that the constitutive overexpression of Lim1β and C15 induces CarE17 expression thus conferring chlorpyrifos resistance in N. lugens.