Monitoring, cross-resistance, inheritance, and fitness costs of brown planthoppers, Nilaparvata lugens, resistance to pymetrozine in China

Cross-resistance, inheritance and biochemical mechanism of abamectin resistance in a field-derived strain of the citrus red mite, Panonychus citri (Acari: Tetranychidae)

BACKGROUND

The citrus red mite, Panonychus citri (McGregor), a global pest of citrus, has developed different levels of resistance to various acaricides in the field. Abamectin is one of the most important insecticides/acaricides worldwide, targetting a wide number of insect and mite pests. The evolution of abamectin resistance in P. citri is threatening the sustainable use of abamectin for mite control.

RESULTS

The abamectin resistant strain (NN-Aba), derived from a field strain NN by consistent selection with abamectin, showed 4279-fold resistance to abamectin compared to a relatively susceptible strain (SS) of P. citri. Cross-resistance of NN-Aba was observed between abamectin and emamectin benzoate, pyridaben, fenpropathrin and cyflumetofen. Inheritance analyses indicated that abamectin resistance in the NN-Aba strain was autosomal, incompletely recessive and polygenic. The synergy experiment showed that abamectin toxicity was synergized by piperonyl butoxide (PBO), diethyl maleate (DEM) and tributyl phosphorotrithiotate (TPP) in the NN-Aba strain, and synergy ratios were 2.72-, 2.48- and 2.13-fold, respectively. The glutathione-S-transferases activity in the NN-Aba strain were significantly increased by 2.08-fold compared with the SS strain.

CONCLUSION

The abamectin resistance was autosomal, incompletely recessive and polygenic in P. citri. The NN-Aba strain showed cross-resistance to various acaricides with different modes of action. Metabolic detoxification mechanism participated in abamectin resistance in NN-Aba strain. These findings provide useful information for resistance management of P. citri in the field. © 2023 Society of Chemical Industry.

Reverse genetic study reveals the molecular targets of chordotonal organ TRPV channel modulators

Insecticides have been widely used for the control of insect pests that have a significant impact on agriculture and human health. A better understanding of insecticide targets is needed for effective insecticide design and resistance management. Pymetrozine, afidopyropen and flonicamid are reported to target on proteins that located on insect chordotonal organs, resulting in the disruption of insect coordination and the inhibition of feeding. In this study, we systematically examined the susceptibility of six Drosophila melanogaster mutants (five transient receptor potential channels and one mechanoreceptor) to three commercially used insecticides, in order to identify the receptor subunits critical to the insect's response to insecticides. Our results showed that iav1, nan36aand wtrw1 mutants exhibited significantly reduced susceptibility to pymetrozine and afidopyropen, but not to flonicamid. The number of eggs produced by the three mutant females were significantly less than that of the w1118 strain. Meanwhile, the longevity of all male mutants and females of nan36a and wtrw1 mutants was significantly shorter than that of the w1118 strain as the control. However, we observed no gravitaxis defects in wtrw1 mutants and the anti-gravitaxis of wtrw1 mutants was abolished by pymetrozine. Behavioral assays using thermogenetic tools further confirmed the bioassay results and supported the idea that Nan as a TRPV subfamily member located in Drosophila chordotonal neurons, acting as a target of pymetrozine, which interferes with Drosophila and causes motor deficits with gravitaxis defects. Taken together, this study elucidates the interactions of pymetrozine and afidopyropen with TRPV channels, Nan and Iav, and TRPA channel, Wtrw. Our research provides another evidence that pymetrozine and afidopyropen might target on nan, iav and wtrw channels and provides insights into the development of sustainable pest management strategies.

Metabolic Resistance of Sogatella furcifera (Hemiptera: Delphacidae) toward Pymetrozine Involves the Overexpression of CYP6FJ3

Sogatella furcifera (Horváth), which mainly threatens rice, shows various levels of pesticide resistance due to long-term overuse of pesticides. Our resistance monitoring of 20 field populations in Sichuan, China, revealed that they were susceptible to highly resistant toward pymetrozine (0.4-142.2 RR), and JL21 reached the highest level of resistance. The JL21 population exhibited cross-resistance to triflumezopyrim and dinotefuran but sensitivity to sulfoxaflor, acetamiprid, clothianidin, and nitenpyram. The increased P450 activity were support to involve in pymetrozine resistance by detoxification enzyme activities and synergist determination. Among 16 candidate P450 genes, CYP6FJ3 (5.25-fold) was the most up-regulated in JL21, while no significant change was found after LC25 pymetrozine treatment. Furthermore, the knockdown by RNAi and heterologous overexpression by the GAL4/UAS system confirmed that the CYP6FJ3 overexpression was involved in the pymetrozine resistance, and recombination in vitro confirmed that CYP6FJ3 could hydroxylate pymetrozine. Therefore, the overexpression of CYP6FJ3 promotes pymetrozine metabolic resistance in S. furcifera.

Overexpression of NADPH-cytochrome P450 reductase is associated with sulfoxaflor resistance and neonicotinoid cross-resistance in Nilaparvata lugens (Stål)

Nicotinamide adenine dinucleotide phosphate (NADPH)-cytochrome P450 reductase (CPR), a crucial electron-transfer partner of P450 systems, is required for various biological reactions catalyzed by P450 monooxygenase. Our previous study indicated that enhanced P450 enzyme detoxification and CYP6ER1 overexpression contributed to sulfoxaflor resistance in Nilaparvata lugens. However, the association between CPR, sulfoxaflor resistance, and neonicotinoid cross-resistance in N. lugens remains unclear. In this study, the sulfoxaflor-resistant (SFX-SEL) (RR = 254.04-fold), resistance-decline (DESEL) (RR = 18.99-fold), and susceptible unselected (UNSEL) strains of N. lugens with the same genetic background were established. Real-time quantitative polymerase chain reaction (RT-qPCR) revealed that the N. lugens CPR (NlCPR) expression level in the SFX-SEL strain was 6.85-fold and 6.07-fold higher than in UNSEL and DESEL strains, respectively. NlCPR expression was significantly higher in the abdomens of UNSEL, DESEL, and SFX-SEL fourth-instar nymphs than in other tissues (thoraxes, heads, and legs). Additionally, sulfoxaflor stress significantly increased NlCPR mRNA levels in the UNSEL, SFX-SEL and DESEL strains. NlCPR silencing by RNA interference (RNAi) dramatically increased the susceptibility of the UNSEL, DESEL, and SFX-SEL strains to sulfoxaflor, but the recovery of SFX-SEL was more obvious. Furthermore, NlCPR silencing led to a significant recovery in susceptibility to nitenpyram, dinotefuran, clothianidin, and thiamethoxam across all strains (UNSEL, DESEL, and SFX-SEL), with the greatest degree of recovery in the sulfoxaflor-resistant strain (SFX-SEL). Our findings suggest that NlCPR overexpression contributes to sulfoxaflor resistance and neonicotinoid cross-resistance in N. lugens. This will aid in elucidating the significance of CPR in the evolution of P450-mediated metabolic resistance in N. lugens.

CRISPR/Cas9-mediated knockout of NlCYP6CS1 gene reveals its role in detoxification of insecticides in Nilaparvata lugens (Hemiptera: Delphacidae)

BACKGROUND

The brown planthopper (Nilaparvata lugens) is one of the major rice insect pests in Asia. Recently, high levels of insecticide resistance have been frequently reported and cytochrome P450 monooxygenase (P450)-mediated metabolic detoxification is a common resistance mechanism in N. lugens. However, there has been no persuasive genetic method to prove the role of P450s in insecticide resistance in N. lugens.

RESULTS

Here, CRISPR/Cas9 system was used to disrupt the P450 gene NlCYP6CS1 to elucidate its role in insecticide resistance in field populations of N. lugens. We successfully constructed a homozygous strain (Nl6CS1-KO) with a 5-bp deletion and 1-bp insertion mutation of NlCYP6CS1. Compared with a background resistant strain (Nl-R), the susceptibility of knockout strain Nl6CS1-KO to imidacloprid, nitenpyram, thiamethoxam, dinotefuran, and pymetrozine was increased by 2.3-, 3.4-, 7.0-, 4.2- and 3.9-fold, respectively, but not significantly changed to triflumezopyrim, chlorpyrifos and buprofezin. Life table analysis demonstrated that the Nl6CS1-KO strain resembled the Nl-R strain in terms of egg and nymph developmental duration and adult lifespan, but differed from the Nl-R strain in the survival rate of eggs and nymphs, reproduction, and body weight.

CONCLUSIONS

Our study demonstrates the effect of functional deletion of NlCYP6CS1 on multiple insecticide resistance in N. lugens. For the first time, we applied CRISPR/Cas9 system to reveal the mechanism of insecticide resistance in N. lugens, which may shed light on similar studies in other hemipteran insects. © 2023 Society of Chemical Industry.

Resistance Monitoring of Nilaparvata lugens to Pymetrozine Based on Reproductive Behavior

On the basis of the inhibition effects of pymetrozine on the reproductive behavior of N. lugens, we established a bioassay method to accurately evaluate the toxicity of pymetrozine in N. lugens and clarified the level of pymetrozine resistance of N. lugens in the field. In this study, pymetrozine's effects on the fecundity of N. lugens were evaluated using the topical application method and rice-seedling-dipping method. Moreover, the resistance of N. lugens to pymetrozine in a pymetrozine-resistant strain (Pym-R) and two field populations (YZ21 and QS21) was determined using the rice-seedling-dipping method and fecundity assay methods. The results showed that treatment of N. lugens third-instar nymphs with LC₁₅, LC₅₀, and LC₈₅ doses of pymetrozine resulted in a significantly reduced fecundity of N. lugens. In addition, N. lugens adults treated with pymetrozine, using the rice-seedling-dipping and topical application method, also exhibited a significantly inhibited fecundity. Using the rice-stem-dipping method, pymetrozine resistance levels were shown to be high in Pym-R (194.6-fold), YZ21 (205.9-fold), and QS21 (212.8-fold), with LC₅₀ values of 522.520 mg/L (Pym-R), 552.962 mg/L (YZ21), and 571.315 (QS21) mg/L. However, when using the rice-seedling-dipping or topical application fecundity assay method, Pym-R (EC₅₀: 14.370 mg/L, RR = 12.4-fold; ED₅₀: 0.560 ng/adult, RR = 10.8-fold), YZ21 (EC₅₀: 12.890 mg/L, RR = 11.2-fold; ED₅₀: 0.280 ng/adult; RR = 5.4-fold), and QS21 (EC₅₀: 13.700 mg/L, RR = 11.9-fold) exhibited moderate or low levels of resistance to pymetrozine. Our studies show that pymetrozine can significantly inhibit the fecundity of N. lugens. The fecundity assay results showed that N. lugens only developed low to moderate levels of resistance to pymetrozine, indicating that pymetrozine can still achieve effective control on the next generation of N. lugens populations.

Timing of Fungal Insecticide Application to Avoid Solar Ultraviolet Irradiation Enhances Field Control of Rice Planthoppers

Thechemical control of rice planthoppers (RPH)is prohibited in annual rice-shrimp rotation paddy fields. Here, the fungal insecticides Beauveria bassiana ZJU435 and Metarizhium anisoplae CQ421 were tested for control of RPH populations dominated by Nilaparvata lugens in three field trials. During four-week field trials initiated from the harsh weather of high temperatures and strong sunlight, the rice crop at the stages from tillering to flowering was effectively protected by fungal sprays applied at 14-day intervals. The sprays of either fungal insecticide after 5:00 p.m. (solar UV avoidance) suppressed the RPH population better than those before 10 a.m. The ZJU435 and CQ421 sprays for UV avoidance versus UV exposure resulted in mean control efficacies of 60% and 56% versus 41% and 45% on day 7, 77% and 78% versus 63% and 67% on day 14, 84% and 82% versus 80% and 79% on day 21, and 84% and 81% versus 79% and 75 on day 28, respectively. These results indicate that fungal insecticides can control RPH in the rice-shrimp rotation fields and offer a novel insight into the significance of solar-UV-avoiding fungal application for improved pest control during sunny summers.

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 overexpression of cytochrome P450 genes confers buprofezin resistance in the brown planthopper, Nilaparvata lugens (Stål)

BACKGROUND

Buprofezin, an insect growth regulator, has been widely used to control brown planthopper (BPH), Nilaparvata lugens, one of the most destructive pests of rice crops in Asia. The intensive use of this compound has resulted in very high levels of resistance to buprofezin in the field, however, the underpinning mechanisms of resistance have not been fully resolved.

RESULTS

Insecticide bioassays using the P450 inhibitor piperonyl butoxide significantly synergized the toxicity of buprofezin in two resistant strains of BPH (BPR and YC2017) compared to a susceptible strain (Sus), suggesting P450s play a role in resistance to this compound. Whole transcriptome profiling identified 1110 genes that were upregulated in the BPR strain compared to the Sus strain, including 13 cytochrome P450 genes, eight esterases and one glutathione S-transferase. Subsequently, qPCR validation revealed that four of the P450 genes, CYP6ER1vA, CYP6CW1, CYP4C77, and CYP439A1 were significantly overexpressed in both the BRP and YC2017 strains compared with the Sus strain. Further functional analyses showed that only suppression of CYP6ER1vA, CYP6CW1, and CYP439A1 gene expression by RNA interference significantly increased the toxicity of buprofezin against BPH. However, only transgenic Drosophila melanogaster expressing CYP6ER1vA and CYP439A1 exhibited significant resistance to buprofezin. Finally, the BPR strain was found to exhibit modest but significant levels of resistance to acetamiprid, dinotefuran and pymetrozine.

CONCLUSIONS

Our findings provide strong evidence that the overexpression of CYP6ER1vA and CYP439A1 contribute to buprofezin resistance in BPH, and that resistance to this compound is associated with low-level resistance to acetamiprid, dinotefuran and pymetrozine. These results advance understanding of the molecular basis of BPH resistance to buprofezin and will inform the development of management strategies for the control of this highly damaging pest. © 2022 Society of Chemical Industry.