Biochemical mechanisms of imidacloprid resistance in Nilaparvata lugens: over-expression of cytochrome P450 CYP6AY1

Fitness cost and molecular basis of imidacloprid resistance in brown planthopper, Nilaparvata lugens (Stål) in India

This study aims to assess the fitness cost associated with imidacloprid resistance and expression of cytochrome P450 genes in brown planthopper, Nilaparvata lugens (Stål). After continuous selection with imidacloprid exposure over 10 generations in a glass house, N. lugens developed a 12.84-fold resistance. The demographic and life history parameters of imidacloprid resistant (IMI-R) and susceptible (IMI-S) strains of N. lugens were compared by age-stage, two-sex life table approach. The duration of egg, third instar, fifth instar, pre-adult and total pre-oviposition period were significantly prolonged in IMI-R strain. However, the fecundity of IMI-R strain (194.59) was significantly lower as compared to IMI-S strain (224.05). There was no significant effect on the duration of other nymphal instars and adult longevity. Whereas the intrinsic rate of increase and doubling time differed significantly in the IMI-R and IMI-S strains, the relative fitness of IMI-R strain was 0.74, clearly indicating a trade-off between imidacloprid resistance and fitness in N. lugens. In IMI-R strain, two P450 genes CYP6ER1 and CYP6AY1 were significantly upregulated by 5.85 and 3.35-fold, respectively compared to the IMI-S strain. Our results conclude that imidacloprid resistance in N. lugens has significant fitness cost due to prolonged developmental stages, reduced fecundity, altered demographic parameters and upregulation of P450 genes. Lower fitness of imidacloprid resistant strains has direct implication in management of N. lugens in rice ecosystems, as any withdrawal of exposure could potentially recover susceptibility.

CYP321F3 mediates metabolic resistance to methoxyfenozide in rice stem borer, Chilo suppressalis

The development of insecticide resistance in insect populations is a major challenge to sustainable agriculture and food security worldwide. Methoxyfenozide, an insect growth regulator that acts as an agonist of 20-hydroxyecdysone (20E), has severely declined in its efficacy against the rice stem borer (Chilo suppressalis), a notorious pest of rice crops in East and Southeast Asia. To date, however, the genes involved in methoxyfenozide resistance in target pests remain unclear. We conducted a long-term (seven years from 2017 to 2023) and large geographical scale (8 provinces and 45 cities in China) resistance monitoring program for methoxyfenozide in C. suppressalis. Resistance was seen to arise rapidly in this species, with >100-fold resistance being detected in nearly all the field populations after 2018. Piperonyl butoxide (PBO), an inhibitor of cytochrome P450 enzymes (P450s), significantly increased the sensitivity of resistant strains of C. suppressalis to methoxyfenozide, implicating P450s in resistance. Six P450 genes: CYP321F3, CYP6CV5, CYP9A68, CYP6AB45, CYP324A12 and CYP6SN2 were identified as highly expressed in resistant C. suppressalis by transcriptome profiling. Of these, ectopic expression of CYP321F3 in Drosophila melanogaster resulted in a 7.0-fold increase in resistance to methoxyfenozide demonstrating its causal role in resistance. Collectively, these findings provide insight into the mechanisms mediating resistance to insect growth regulators and will inform the development of future pest and resistance management strategies.

Investigating insecticide resistance in eggplant fruit and shoot borer: Multi-class insecticides and detoxification gene expression

Eggplant fruit and shoot borer, Leucinodes orbonalis (Lepidoptera: Crambidae), is a destructive borer pest that infests eggplant crop from nursery stage to fruiting. This study aimed to evaluate the current insecticide resistance status of L. orbonalis collected from ten different locations of Tamil Nadu, India, using a fruit dip bioassay. Late second instar larvae were exposed to spinosad, spinetoram, thiacloprid and emamectin benzoate. Median lethal concentration (LC50) and resistance ratios (RR) were estimated for each population using a susceptible NBAIR population as a reference. The results showed that emamectin benzoate was highly toxic to L. orbonalis. All field populations exhibited a low to high level of resistance against spinosad (7.4 to 72.1 fold) and spinetoram (6.6 to 67.8 fold), while susceptibility to low levels of resistance was observed against thiacloprid (0.89 to 5.06 fold) and emamectin benzoate (1.48 to 11.29 fold). Additionally, detoxification enzyme assays were conducted for cytochrome P450 monooxygenases (CYP/MFO), glutathione S-transferases (GST) and carboxylesterases (CarE) revealing high specific activity in the Dharmapuri (DMP) population, correlating with resistance. Furthermore, quantitative real-time PCR analysis was conducted to assess detoxification gene expression in resistant (DMP) and susceptible populations after insecticide exposure, revealing significant overexpression of cyp306a1 and ce125 across the studied insecticides, particularly after 48 h, indicating their key role in resistance. These findings highlight the need for insecticide rotation with different modes of action to mitigate resistance development in L. orbonalis, providing valuable insights for sustainable pest management in Tamil Nadu and similar agricultural contexts worldwide.

Overexpression of CYP6CY1 is Involved in Imidacloprid Resistance in Sitobion miscanthi (Takahashi) (Homoptera: Aphidae)

Sitobion miscanthi is a wheat aphid species that can damage seriously agricultural production. The effective management of wheat aphids has depended on chemical insecticides. However, their wide application led to severe resistance of wheat aphids to some insecticides, and cytochrome P450 as a detoxifying enzyme plays a crucial role in the insecticide resistance. In this study, CYP6CY1, a new P450 gene, was isolated and overexpressed in a S.miscanthi resistant strain to imidacloprid. The increased sensitivity to imidacloprid after silencing of CYP6CY1 indicated that its involvement in imidacloprid resistance. Subsequently, action of miR-3047-3p within the 3' UTR of the CYP6CY1 was confirmed at the posttranscriptional regulatory level, and was shown to be involved in the resistance to imidacloprid. These results provide opportunities for understanding the roles of P450 in insecticide resistance of pests.

Two detoxification enzyme genes, CYP6DA2 and CarFE4, mediate the susceptibility to afidopyropen in Semiaphis heraclei

Introduction

Semiaphis heraclei is an important economic pest affecting Caprifoliaceae and Apiaceae plants, and chemical control is still the main effective control method in the field. Afidopyropen is a new type of pyridine cyclopropyl insecticide, which can effectively control piercing-sucking mouthparts pests and is suitable for pest resistance management. However, the detoxification mechanism of S. heraclei to afidopyropen is still poorly cleared.

Methods

The insecticidal activity of afidopyropen against S. heraclei and the enzyme activity assay and synergism bioassay were evaluated. The detoxification enzyme genes were obtained by transcriptome and validated by quantitative real-time PCR (RT-qPCR). Furthermore, RNA interference was used to study the functions of detoxification enzyme genes.

Results

The activities of cytochrome P450 monooxygenases (P450s) and carboxylesterases (CarEs) were significantly increased under afidopyropen treatment. The toxicity of afidopyropen against S. heraclei was significantly increased after application the inhibitors of piperonyl butoxide and triphenyl phosphate. Sixteen P450 genes and three CarE genes were identified in the transcriptome of S. heraclei. The RT-qPCR results showed that eleven P450 genes and two CarE genes were significantly upregulated under afidopyropen treatment, and the expression of CYP6DA2 and CarFE4 was upregulated by more than 2.5 times. The expression pattern of CYP6DA2 and CarFE4 was further analyzed in different developmental stages of S. heraclei and knockdown of CYP6DA2 and CarFE4 significantly increased the susceptibility of S. heraclei to afidopyropen.

Conclusion

The results of this study uncover the key functions of CYP6DA2 and CarFE4 in the detoxification mechanism of S. heraclei to afidopyropen, and provide a theoretical basis for the scientific use of afidopyropen in the field.

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.

NADPH-cytochrome P450 reductase involved in the lambda-cyhalothrin susceptibility on the green mirid bug Apolygus lucorum

NADPH-cytochrome P450 reductase (CPR) is crucial for the detoxification process catalysed by cytochrome P450, which targets various exogenous xenobiotics, as well as pesticides. In our research, we successfully obtained the complete cDNA sequence of Apolygus lucorum's CPR (AlCPR) using reverse transcription PCR along with rapid amplification of cDNA ends technology. Bioinformatics analysis exhibited that the inferred amino acid sequence of AlCPR is characteristic of standard CPRs, featuring an N-terminal membrane anchor and three conserved FMN, FAD and NADP binding sites. Phylogenetic result revealed that AlCPR was positioned within the Hemiptera cluster, showing a close evolutionary relationship with the CPR of Cimex lectularius. The real-time quantitative PCR results demonstrated widespread expression of AlCPR across various life stages and tissues of A. lucorum, with the most prominent expression in adults and the abdominal region. Injecting double-stranded RNA of AlCPR only significantly increased the lambda-cyhalothrin susceptibility in lambda-cyhalothrin-resistant strain rather than the susceptible strain. These findings suggest a potential link between AlCPR and the P450-dependent defence mechanism against lambda-cyhalothrin in A. lucorum.

Trial and error: New insights into recombinant expression of membrane-bound insect cytochromes P450 in Escherichia coli systems

Insect cytochromes P450 (CYP450s) are key enzymes responsible for a wide array of oxidative transformations of both endogenous and exogenous substrates. However, there is currently no a universal guideline established for heterologous expression of membrane-bound CYP450s, which hampers their downstream biochemical and structural studies. In this study, we conducted large-scale screening of protein overexpression in Escherichia coli using 71 insect CYP450 sequences and optimized the expression of a difficult-to-express CYP450 (CYP6HX3) using eight different optimizations, including selection of host strains and expression vectors, alternative of leader signal peptides, and N-terminal modifications. We confirmed that 1) Only insect CYP450s belonging to the CYP347 family could be expressed with N-terminal fusion of ompA2+ signal peptide in E. coli expression system. 2) E. coli Lemo 21 (DE3) effectively improved the expression of CYP6HX3 in the plasma membrane. 3) A brick-red appearance occurred frequently in the expressed thallus or membrane proteins, but this phenomenon could not necessarily indicate successful overexpression of target CYP450s. These findings provide new insights into the recombinant expression of insect CYP450s in E. coli systems and will facilitate the theoretical approaches for functional expression and production of eukaryotic CYP450s.

microRNA-3037 targeting CYP6CY2 confers imidacloprid resistance to Sitobion miscanthi (Takahashi)

The wheat aphid Sitobion miscanthi is a dominant and destructive pest in agricultural production. Insecticides are the main substances used for effective control of wheat aphids. However, their extensive application has caused severe resistance of wheat aphids to some insecticides; therefore, exploring resistance mechanisms is essential for wheat aphid management. In the present study, CYP6CY2, a new P450 gene, was isolated and overexpressed in the imidacloprid-resistant strain (SM-R) compared to the imidacloprid-susceptible strain (SM-S). The increased sensitivity of S. miscanthi to imidacloprid after knockdown of CYP6CY2 indicates that it could be associated with imidacloprid resistance. Subsequently, the posttranscriptional regulation of CYP6CY2 in the 3' UTR by miR-3037 was confirmed, and CYP6CY2 participated in imidacloprid resistance. This finding is critical for determining the role of P450 in relation to the resistance of S. miscanthi to imidacloprid. It is of great significance to understand this regulatory mechanism of P450 expression in the resistance of S. miscanthi to neonicotinoids.

Assessment of toxic effects of imidacloprid on freshwater zooplankton: An experimental test for 27 species

The neonicotinoid pesticide imidacloprid has been used worldwide since 1992. As one of the most important chemicals used in pest control, there have been concerns that its run-off into rivers and lakes could adversely affect aquatic ecosystems, where zooplankton play a central role in the energy flow from primary to higher trophic levels. However, studies assessing the effects of pesticides at the species level have relied on a Daphnia-centric approach, and no studies have been conducted using species-level assessments on a broad range of zooplankton taxa. In the present study, we therefore investigated the acute toxicity of imidacloprid on 27 freshwater crustacean zooplankton (18 cladocerans, 3 calanoid copepods and 6 cyclopoid copepods). The experiment showed that a majority of calanoid copepods and cladocerans were not affected at all by imidacloprid, with the exception of one species each of Ceriodaphnia and Diaphasoma, while all six cyclopoid copepods showed high mortality rates, even at concentrations of imidacloprid typically found in nature. In addition, we found a remarkable intra-taxonomic variation in susceptibility to this chemical. As many cyclopoid copepods are omnivorous, they act as predators as well as competitors with other zooplankton. Accordingly, their susceptibility to imidacloprid is likely to cause different responses at the community level through changes in predation pressure as well as changes in competitive interactions. The present results demonstrate the need for species-level assessments of various zooplankton taxa to understand the complex responses of aquatic communities to pesticide disturbance.

Transcription Factors AhR and ARNT Regulate the Expression of CYP6SX1 and CYP3828A1 Involved in Insecticide Detoxification in Bradysia odoriphaga

Aryl hydrocarbon receptor (AhR) and aryl hydrocarbon receptor nuclear translocator (ARNT) mediate the responses of adaptive metabolism to various xenobiotics. Here, we found that BoAhR and BoARNT are highly expressed in the midgut of Bradysia odoriphaga larvae. The expression of BoAhR and BoARNT was significantly increased after exposure to imidacloprid and phoxim. The knockdown of BoAhR and BoARNT significantly decreased the expression of CYP6SX1 and CYP3828A1 as well as P450 enzyme activity and caused a significant increase in the sensitivity of larvae to imidacloprid and phoxim. Exposure to β-naphthoflavone (BNF) significantly increased the expression of BoAhR, BoARNT, CYP6SX1, and CYP3828A1 as well as P450 activity and decreased larval sensitivity to imidacloprid and phoxim. Furthermore, CYP6SX1 and CYP3828A1 were significantly induced by imidacloprid and phoxim, and the silencing of these two genes significantly reduced larval tolerance to imidacloprid and phoxim. Taken together, the BoAhR/BoARNT pathway plays key roles in larval tolerance to imidacloprid and phoxim by regulating the expression of CYP6SX1 and CYP3828A1.

Glutathione S-transferase directly metabolizes imidacloprid in the whitefly, Bemisia tabaci

The whitefly Bemisia tabaci poses a significant threat to various crops and ornamental plants and causes severe damage to the agricultural industry. Over the past few decades, B. tabaci has developed resistance to several pesticides, including imidacloprid. Therefore, elucidating the mechanism that leads to insecticide detoxification is very important for controlling B. tabaci and managing whitefly resistance to neonicotinoid insecticides. Among insect detoxification enzymes, glutathione S-transferase (GST) is an important phase II detoxification enzyme that helps detoxify exogenous toxic substances. In this study, we cloned the BtGSTz1 gene and observed that its expression level was greater in imidacloprid-resistant populations than sensitive populations of B. tabaci. By silencing BtGSTz1 via RNA interference, we found a significant increase in the mortality of imidacloprid-resistant B. tabaci. Additionally, prokaryotic expression and in vitro metabolism studies revealed that the recombinant BtGSTz1 protein could metabolize 36.36% of the total imidacloprid, providing direct evidence that BtGSTz1 plays a crucial role in the detoxification of imidacloprid. Overall, our study elucidated the role of GSTs in physiological activities related to insecticide resistance, which helps clarify the resistance mechanisms conferred by GSTs and provides useful insights for sustainable integrated pest management.

Cytochrome P450 CYP6EM1 Underpins Dinotefuran Resistance in the Whitefly Bemisia tabaci

Being a destructive pest worldwide, the whitefly Bemisia tabaci has evolved resistance to neonicotinoid insecticides. The third-generation neonicotinoid dinotefuran has commonly been applied to the control of the whitefly, but its underlying mechanism is currently unknown. On the base of our transcriptome data, here we aim to investigate whether the cytochrome P450 CYP6EM1 underlies dinotefuran resistance in the whitefly. Compared to the susceptible strain, the CYP6EM1 gene was found to be highly expressed in both laboratory and field dinotefuran-resistant populations. Upon exposure to dinotefuran, the mRNA levels of CYP6EM1 were increased. These results demonstrate the involvement of this gene in dinotefuran resistance. Loss and gain of functional studies in vivo were conducted through RNAi and transgenic Drosophila melanogaster assays, confirming the role of CYP6EM1 in conferring such resistance. In a metabolism assay in vitro, the CYP6EM1 protein could metabolize 28.11% of dinotefuran with a possible dinotefuran-dm-NNO metabolite via UPLC-QTOF/MS. Docking of dinotefuran to the CYP6EM1 protein showed a good binding affinity, with an energy of less than -6.0 kcal/mol. Overall, these results provide compelling evidence that CYP6EM1 plays a crucial role in the metabolic resistance of B. tabaci to dinotefuran. Our work provides new insights into the mechanism underlying neonicotinoid resistance and applied knowledge that can contribute to sustainable control of a global pest such as whitefly.

New insights into chlorantraniliprole metabolic resistance mechanisms mediated by the striped rice borer cytochrome P450 monooxygenases: A case study of metabolic differences

The anthranilic diamide insecticide chlorantraniliprole has been extensively applied to control Lepidoptera pests. However, its overuse leads to the development of resistance and accumulation of residue in the environment. Four P450s (CYP6CV5, CYP9A68, CYP321F3, and CYP324A12) were first found to be constitutively overexpressed in an SSB CAP-resistant strain. It is imperative to further elucidate the molecular mechanisms underlying P450s-mediated CAP resistance for mitigating its environmental contamination. Here, we heterologously expressed these four P450s in insect cells and evaluated their abilities to metabolize CAP. Western blotting and reduced CO difference spectrum tests showed that these four P450 proteins had been successfully expressed in Sf9 cells, which are indicative of active functional enzymes. The recombinant proteins CYP6CV5, CYP9A68, CYP321F3, and CYP324A12 exhibited a preference for metabolizing the fluorescent P450 model probe substrates EC, BFC, EFC, and EC with enzyme activities of 0.54, 0.67, 0.57, and 0.46 pmol/min/pmol P450, respectively. In vitro metabolism revealed distinct CAP metabolic rates (0.97, 0.86, 0.75, and 0.55 pmol/min/pmol P450) and efficiencies (0.45, 0.37, 0.30, and 0.17) of the four recombinant P450 enzymes, thereby elucidating different protein catalytic activities. Furthermore, molecular model docking confirmed metabolic differences and efficiencies of these P450s and unveiled the hydroxylation reaction in generating N-demethylation and methylphenyl hydroxylation during CAP metabolism. Our findings not only first provide new insights into the mechanisms of P450s-mediated metabolic resistance to CAP at the protein level in SSB but also demonstrate significant differences in the capacities of multiple P450s for insecticide degradation and facilitate the evaluation and mitigation of toxic risks associated with CAP application in the environment.

Insecticidal activity against rice pest of oxazosulfyl, a novel sulfyl insecticide

The development and commercialization of new chemical classes of insecticides are important for efficient crop protection, particularly for combatting insecticide resistance and providing sustainable agricultural production. This study reports on oxazosulfyl, a novel "sulfyl" class of insecticide, against a wide range of insect pests of rice. In the laboratory assay, oxazosulfyl showed insecticidal activity against all developmental stages of the brown planthopper Nilaparvata lugens (Stål). Phosphor imaging assays and soil drench bioassays demonstrated good systemic distribution in rice plants. Oxazosulfyl showed insecticidal activity against imidacloprid- and fipronil-resistant field populations of N. lugens, the white-backed planthopper Sogatella furcifera (Horváth), and the small brown planthopper Laodelphax striatellus (Fallén), as well as the respective susceptible strains. No cross-resistance was observed among oxazosulfyl, imidacloprid, and fipronil. Oxazosulfyl with a wide insecticidal spectrum is a potentially useful pest management tool for sustainable rice production.

CYP4CS5-mediated thiamethoxam and clothianidin resistance is accompanied by fitness cost in the whitefly Bemisia tabaci

BACKGROUND

Understanding the trade-offs between insecticide resistance and the associated fitness is of particular importance to sustainable pest control. One of the most devastating pest worldwide, the whitefly Bemisia tabaci, has developed resistance to various insecticides, especially the neonicotinoid group. Although neonicotinoid resistance often is conferred by P450s-mediated metabolic resistance, the relationship between such resistance and the associated fitness phenotype remains largely elusive. By gene cloning, quantitative reverse transcription (qRT)-PCR, RNA interference (RNAi), transgenic Drosophila melanogaster, metabolism capacity in vitro and 'two sex-age stage' life table study, this study aims to explore the molecular role of a P450 gene CYP4CS5 in neonicotinoid resistance and to investigate whether such resistance mechanism carries fitness costs in the whitefly.

RESULTS

Our bioassay tests showed that a total of 13 field-collected populations of B. tabaci MED biotype displayed low-to-moderate resistance to thiamethoxam and clothianidin. Compared to the laboratory susceptible strain, we then found that an important P450 CYP4CS5 was remarkably upregulated in the field resistant populations. Such overexpression of CYP4CS5 had a good match with the resistance level among the whitefly samples. Further exposure to the two neonicotinoids resulted in an increase in CYP4CS5 expression. These results implicate that overexpression of CYP4CS5 is closely correlated with thiamethoxam and clothianidin resistance. RNAi knockdown of CYP4CS5 increased mortality of the resistant and susceptible populations after treatment with thiamethoxam and clothianidin in bioassay, but obtained an opposite result when using a transgenic line of D. melanogaster expressing CYP4CS5. Metabolic assays in vitro revealed that CYP4CS5 exhibited certain capacity of metabolizing thiamethoxam and clothianidin. These in vivo and in vitro assays indicate an essential role of CYP4CS5 in conferring thiamethoxam and clothianidin resistance in whitefly. Additionally, our life-table analysis demonstrate that the field resistant whitefly exhibited a prolonged development time, shortened longevity and reduced fecundity compared to the susceptible, suggesting an existing fitness cost as a result of the resistance.

CONCLUSION

Collectively, in addition to the important role of CYP4CS5 in conferring thiamethoxam and clothianidin resistance, this resistance mechanism is associated with fitness costs in the whitefly. These findings not only contribute to the development of neonicotinoids resistance management strategies, but also provide a new target for sustainable whitefly control. © 2023 Society of Chemical Industry.

Two Point Mutations in CYP4CE1 Promoter Contributed to the Differential Regulation of CYP4CE1 Expression by FoxO between Susceptible and Nitenpyram-Resistant Nilaparvata lugens

Four P450s were reported to be important for imidacloprid resistance in Nilaparvata lugens, a major insect pest on rice, which was confirmed in this study in an imidacloprid-resistant strain (ImiR). Here we found that only two (CYP4CE1 and CYP6ER1) from these four P450 genes were overexpressed in a nitenpyram-resistant strain (NitR) when compared to a susceptible strain (SUS). CYP4CE1 RNAi reduced nitenpyram and imidacloprid resistance in NitR and ImiR strains, with a greater reduction in nitenpyram resistance. The transcription factor FoxO mediated nitenpyram resistance in NitR and ImiR strains, but it was not differentially expressed among strains. The potential reason for the differential regulation of FoxO on CYP4CE1 expression was mainly from sequence differences in the CYP4CE1 promoter between susceptible and resistant insects. In six FoxO response elements predicted in the CYP4CE1 promoter, the single-nucleotide polymorphisms were frequently detected in over 50% of NitR and ImiR individuals. The luciferase reporter assays showed that two mutations, -650T/G and -2205T/A in two response elements at the positions of -648 and -2200 bp, mainly contributed to the enhanced regulation on CYP4CE1 expression by FoxO in resistant insects. The frequency was over 69% for both -650T/G and -2205T/A detected in NitR and ImiR individuals but less than 20% in SUS insects. In conclusion, CYP4CE1 overexpression importantly contributed to nitenpyram resistance in N. lugens, and two mutations in the CYP4CE1 promoter of resistant insects led to an enhanced regulation on CYP4CE1 expression by FoxO.

Biochemical and molecular characterization of neonicotinoids resistance in the tarnished plant bug, Lygus lineolaris

In the southern United States, neonicotinoids are commonly applied as foliar insecticides to control sucking insect pests, such as the tarnished plant bug (TPB, Lygus lineolaris). In this study, spraying bioassays were conducted to determine the toxicity of five neonicotinoids and sulfoxaflor to susceptible and late fall field-collected TPB adults from Mississippi Delta region. Compared to a susceptible population, the field-collected TPBs exhibited the highest resistance to imidacloprid (up to 19.5-fold), a moderate resistance to acetamiprid (9.43-fold), clothianidin (13.68-fold), thiamethoxam (7.88-fold) and the least resistance to thiacloprid (4.61-fold) and sulfoxaflor (1.82-fold), respectively. A synergist study demonstrated that piperonyl butoxide (PBO) significantly increased the toxicity of imidacloprid and thiamethoxam by 22.2- and 15.3-fold, respectively, while triphenyl phosphate (TPP) and diethyl maleate (DEM) only showed 2-3-fold synergism to both neonicotinoids. In the field-collected TPBs, activities of the three detoxification enzymes esterase, glutathione S-transferase (GST) and CYP450 monooxygenase (P450) were significantly increased by 3.43-, 1.48- and 2.70-fold, respectively, when compared to the susceptible population. Additionally, after 48 h exposure to imidacloprid or thiamethoxam, resistant TPB adults exhibited elevated esterase activities, decreased GST activities, and no significant changes in P450 activities. Further examinations revealed that the expression of certain esterase and P450 detoxification genes were significantly elevated in resistant TPBs. Overall, these results suggest that elevated esterase and P450s expression and enzyme activity are key mechanisms for metabolic resistance in TPBs to neonicotinoids. Our findings also provide valuable information for selection and adoption of neonicotinoid insecticides for resistance management of TPBs and minimizing toxic risk to foraging bees.

20E biosynthesis gene CYP306A1 confers resistance to imidacloprid in the nymph stage of Bemisia tabaci by detoxification metabolism

BACKGROUND

Difference in physiology level between the immature and mature stages of insects likely contribute to different mechanisms of insecticide resistance. It is well acknowledged that insect 20-hydroxyecdysone (20E) plays an important role in many biological processes in the immature stage, whether 20E confers insecticide resistance at this specific stage is still poorly understood. By gene cloning, reverse transcription quantitative real-time PCR, RNA interference (RNAi) and in vitro metabolism experiments, this study aimed to investigate the potential role of 20E-related genes in conferring imidacloprid (IMD) resistance in the immature stage of the whitefly Bemisia tabaci Mediterranean.

RESULTS

After identification of low to moderate IMD resistance in the whitefly, we found CYP306A1 of the six 20E-related genes was overexpressed in the nymph stage of the three resistant strains compared to a laboratory reference susceptible strain, but not in the adult stage. Further exposure to IMD resulted in an increase in CYP306A1 expression in the nymph stage. These results together imply that CYP306A1 may be implicated in IMD resistance in the nymph stage of the whitefly. RNAi knockdown of CYP306A1 increased the mortality of nymphs after treatment with IMD in bioassay, suggesting a pivotal role of CYP306A1 in conferring IMD resistance in the nymph stage. Additionally, our metabolism experiments in vivo showed that the content of IMD reduced by 20% along with cytochrome P450 reductase and heterologously expressed CYP306A1, which provides additional evidence for the important function of CYP306A1 in metabolizing IMD that leads to the resistance.

CONCLUSION

This study uncovers a novel function of the 20E biosynthesis gene CYP306A1 in metabolizing imidacloprid, thus contributing to such resistance in the immature stage of the insect. These findings not only advance our understanding of 20E-mediated insecticide resistance, but also provide a new target for sustainable pest control of global insect pests such as whitefly. © 2023 Society of Chemical Industry.

The mechanisms of metabolic resistance to pyrethroids and neonicotinoids fade away without selection pressure in the tarnished plant bug Lygus lineolaris

BACKGROUND

Heavy selection pressure prompted the development of resistance in a serious cotton pest tarnished plant bug (TPB), Lygus Lineolaris in the mid-southern United States. Conversely, a laboratory resistant TPB strain lost its resistance to five pyrethroids and two neonicotinoids after 36 generations without exposure to any insecticide. It is worthwhile to examine why the resistance diminished in this population and determine whether the resistance fade away has practical value for insecticide resistance management in TPB populations.

RESULTS

A field-collected resistant TPB population in July (Field-R1) exhibited 3.90-14.37-fold resistance to five pyrethroids and two neonicotinoids, while another field-collected TPB population in April (Field-R2) showed much lower levels of resistance (0.84-3.78-fold) due to the absence of selection pressure. Interestingly, after 36 generations without exposure to insecticide, the resistance levels in the same population [laboratory resistant strain (Lab-R)] significantly decreased to 0.80-2.09-fold. The use of detoxification enzyme inhibitors had synergistic effects on permethrin, bifenthrin and imidacloprid in resistant populations of Lygus lineolaris. The synergism was more pronounced in Field-R2 than laboratory susceptible (Lab-S) and Lab-R TPB population. Moreover, esterase, glutathione S-transferase (GST), and cytochrome P450-monooxygenases (P450) enzyme activities increased significantly by approximately 1.92-, 1.43-, and 1.44-fold in Field-R1, respectively, and 1.38-fold increased P450 enzyme activities in Field-R2 TPB population, compared to the Lab-S TPB. In contrast, the three enzyme activities in the Lab-R strain were not significantly elevated anymore relative to the Lab-S population. Additionally, Field-R1 TPB showed elevated expression levels of certain esterase, GST and P450 genes, respectively, while Field-R2 TPB overexpressed only P450 genes. The elevation of these gene expression levels in Lab-R expectedly diminished to levels close to those of the Lab-S TPB populations.

CONCLUSION

Our results indicated that the major mechanism of resistance in TPB populations was metabolic detoxification, and the resistance development was likely conferred by increased gene expressions of esterase, GST, and P450 genes, the fadeaway of the resistance may be caused by reversing the overexpression of esterase, GST and P450. Without pesticide selection, resistant gene (esterase, GST, P450s) frequencies declined, and detoxification enzyme activities returned to Lab-S level, which resulted in the recovery of the susceptibility in the resistant TPB populations. Therefore, pest's self-purging of insecticide resistance becomes strategically desirable for managing resistance in pest populations. Published 2023. This article is a U.S. Government work and is in the public domain in the USA.

Functional roles of two novel P450 genes in the adaptability of Conogethes punctiferalis to three commonly used pesticides

Introduction: Insect cytochrome P450 (CYP450) genes play important roles in the detoxification and metabolism of xenobiotics, such as plant allelochemicals, mycotoxins and pesticides. The polyphagous Conogethes punctiferalis is a serious economic pest of fruit trees and agricultural crops, and it shows high adaptability to different living environments. Methods: The two novel P450 genes CYP6CV1 and CYP6AB51 were identified and characterized. Quantitative real-time PCR (qRT-PCR) technology was used to study the expression patterns of the two target genes in different larval developmental stages and tissues of C. punctiferalis. Furthermore, RNA interference (RNAi) technology was used to study the potential functions of the two P450 genes by treating RNAi-silenced larvae with three commonly used pesticides. Results: The CYP6CV1 and CYP6AB51 genes were expressed throughout various C. punctiferalis larval stages and in different tissues. Their expression levels increased along with larval development, and expression levels of the two target genes in the midgut were significantly higher than in other tissues. The toxicity bioassay results showed that the LC₅₀ values of chlorantraniliprole, emamectin benzoate and lambda-cyhalothrin on C. punctiferalis larvae were 0.2028 μg/g, 0.0683 μg/g and 0.6110 mg/L, respectively. After treating with different concentrations of chlorantraniliprole, emamectin benzoate and lambda-cyhalothrin (LC₁₀, LC₃₀, LC₅₀), independently, the relative expressions of the two genes CYP6CV1 and CYP6AB51 were significantly induced. After the dsRNA injection, the expression profiles of the two CYP genes were reduced 72.91% and 70.94%, respectively, and the mortality rates of the larvae significantly increased when treated with the three insecticides independently at LC₁₀ values. Discussion: In the summary, after interfering with the CYP6CV1 and CYP6AB51 in C. punctiferalis, respectively, the sensitivity of C. punctiferalis to chlorantraniliprole, emamectin benzoate and lambda-cyhalothrin was significantly increased, indicating that the two CYP6 genes were responsible for the adaptability of C. punctiferalis to the three chemical insecticides in C. punctiferalis. The results from this study demonstrated that CYP6CV1 and CYP6AB51 in C. punctiferalis play crucial roles in the detoxification of chlorantraniliprole, emamectin benzoate and lambda-cyhalothrin.

Evaluation of Transgenerational Effects of Sublethal Imidacloprid and Diversity of Symbiotic Bacteria on Acyrthosiphon gossypii

Symbiotic bacteria and hormesis in aphids are the driving forces for pesticide resistance. However, the mechanism remains unclear. In this study, the effects of imidacloprid on the population growth parameters and symbiotic bacterial communities of three successive generations of Acyrthosiphon gossypii were investigated. The bioassay results showed that imidacloprid had high toxicity to A. gossypii with an LC₅₀ of 1.46 mg·L^-1. The fecundity and longevity of the G0 generation of A. gossypii decreased when exposed to the LC₁₅ of imidacloprid. The net reproductive rate (R₀), intrinsic rate of increase (r_m), finite rate of increase (λ), and total reproductive rate (GRR) of G1 and G2 offspring were significantly increased, but those of the control and G3 offspring were not. In addition, sequencing data showed that the symbiotic bacteria of A. gossypii mainly belonged to Proteobacteria, with a relative abundance of 98.68%. The dominant genera of the symbiotic bacterial community were Buchnera and Arsenophonus. After treatment with the LC₁₅ of imidacloprid, the diversity and species number of bacterial communities of A. gossypii decreased for G1-G3 and the abundance of Candidatus-Hamiltonella decreased, but Buchnera increased. These results provide insight into the resistance mechanism of insecticides and the stress adaptation between symbiotic bacteria and aphids.

The neonicotinoid insecticide imidacloprid has unexpected effects on the growth and development of soil amoebae

Neonicotinoid pesticides are the most widely used insecticides worldwide and have become a global environmental issue. Previous studies have shown that imidacloprid, the most used neonicotinoid, can negatively affect a wide range of organisms, including non-target insects, fish, invertebrates, and mammals. Imidacloprid can also accumulate and persist in soils, posing threats to the terrestrial ecosystem. However, we know little about one ecologically important group of organisms, the single-celled soil protists. In this study, we used a soil amoeba, Dictyostelium discoideum, to test whether and how imidacloprid affects the growth and development of soil amoebae. We provide the first empirical evidence that environmental concentrations of imidacloprid negatively impact the fitness and development of soil amoebae. In addition, the adverse effects did not show a dose-response relationship with increased imidacloprid concentrations, where no significant difference was observed among the treatment groups. Further transcriptome analyses showed that imidacloprid affected amoeba's key DEGs related to phagocytosis, cell division, morphogenesis, and cytochrome P450. Moreover, soil amoebae show both conserved and novel transcriptional responses to imidacloprid. In conclusion, this study has expanded the non-target list of imidacloprid from animals and plants to single-celled protists, and we believe the impact of neonicotinoid pesticides on the microbiome is significantly underestimated and deserves more studies.

Importance of CYP6ER1 Was Different among Neonicotinoids in Their Susceptibility in Nilaparvata lugens

CYP6ER1 overexpression is a prevalent mechanism for neonicotinoid resistance in Nilaparvata lugens. Except for imidacloprid, the metabolism of other neonicotinoids by CYP6ER1 lacked direct evidence. In this study, a CYP6ER1 knockout strain (CYP6ER1^-/-) was constructed using the CRISPR/Cas9 strategy. The CYP6ER1^-/- strain showed much higher susceptibility to imidacloprid and thiacloprid with an SI (sensitivity index, LC₅₀ of WT/LC₅₀ of CYP6ER1^-/-) of over 100, which was 10-30 for four neonicotinoids (acetamiprid, nitenpyram, clothianidin, and dinotefuran) and less than 5 for flupyradifurone and sulfoxaflor. Recombinant CYP6ER1 showed the highest activity to metabolize imidacloprid and thiacloprid and moderate activity for the other four neonicotinoids. Main metabolite identification and oxidation site prediction revealed that CYP6ER1 activities were insecticide structure-dependent. The most potential oxidation site of imidacloprid and thiacloprid was located in the five-membered heterocycle with hydroxylation activity. For the other four neonicotinoids, the potential site was within the ring opening of a five-membered heterocycle, indicating N-desmethyl activity.

Alternative Splicing and Expression Reduction of P450 Genes Mediating the Oxidation of Chlorpyrifos Revealed a Novel Resistance Mechanism in Nilaparvata lugens

Cytochrome P450 enzymes metabolize various xenobiotics in insects. Compared to numerous P450s associated with insecticide detoxification and resistance, fewer have been identified to bioactivate proinsecticides in insects. Here we reported that two P450s, CYP4C62 and CYP6BD12, in Nilaparvata lugens could bioactivate chlorpyrifos, an organophosphorus insecticide, into its active ingredient chlorpyrifos-oxon in vivo and in vitro. RNAi knockdown of these two genes significantly reduced the sensitivity to chlorpyrifos and the formation of chlorpyrifos-oxon in N. lugens. Chlorpyrifos-oxon was generated when chlorpyrifos was incubated with the crude P450 enzyme prepared from N. lugens or recombinant CYP4C62 and CYP6BD12 enzymes. The expression reduction of CYP4C62 and CYP6BD12 and alternative splicing in CYP4C62 reduced the oxidation of chlorpyrifos into chlorpyrifos-oxon, which contributed importantly to chlorpyrifos resistance in N. lugens. This study revealed a novel mechanism of insecticide resistance due to the bioactivation reduction, which would be common for all currently used proinsecticides.

Acute and chronic toxicity of imidacloprid in the pollinator fly, Eristalis tenax L., assessed using a novel oral bioassay

Imidacloprid is a neonicotinoid neurotoxin that remains widely used worldwide and persists in the environment, resulting in chronic exposure to non-target insects. To accurately map dose-dependent effects of such exposure across taxa, toxicological assays need to assess relevant modes of exposure across indicator species. However, due to the difficulty of these experiments, contact bioassays are most frequently used to quantify dose. Here, we developed a novel naturalistic feeding bioassay to precisely measure imidacloprid ingestion and its toxicity for acute and chronic exposure in a dipteran, Eristalis tenax L., an important member of an under-represented pollinator group. Flies which ingested imidacloprid dosages lower than 12.1 ng/mg all showed consistent intake volumes and learned improved feeding efficiency over successive feeding sessions. In contrast, at doses of 12.1 ng/mg and higher flies showed a rapid onset of severe locomotive impairment which prevented them from completing the feeding task. Neither probability of survival nor severe locomotive impairment were significantly higher than the control group until doses of 1.43 ng/mg or higher were reached. We were unable to measure a median lethal dose for acute exposure (72 h) due to flies possessing a relatively high tolerance for imidacloprid. However, with chronic exposure (18 days), mortality went up and an LD50 of 0.41 ng/mg was estimated. Severe locomotive impairment (immobilisation) tended to occur earlier and at lower dosages than lethality, with ED50s of 7.82 ng/mg and 0.17 ng/mg for acute and chronic exposure, respectively. We conclude that adult Eristalis possess a much higher tolerance to this toxin than the honeybees that they mimic. The similarity of the LD50 to other dipterans such as the fruitfly and the housefly suggests that there may be a phylogenetic component to pesticide tolerance that merits further investigation. The absence of obvious adverse effects at sublethal dosages also underscores a need to develop better tools for quantifying animal behaviour to evaluate the impact of insecticides on foraging efficiency in economically important species.

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

The risk assessment and resistance mechanisms of insecticide resistance are critical for resistance management strategy before a new insecticide is widely used. Triflumezopyrim (TFM) is the first commercialized mesoionic insecticide, which can inhibit nicotinic acetylcholine receptor with high-performance against the small brown planthopper (SBPH), Laodelphax striatellus (Fallén). In our study, the resistance of SBPH to TFM increased 26.29-fold, and the actual heritability of resistance was 0.09 after 21 generations of continuous selection by TFM. After five generations of constant feeding under insecticide-free conditions from F16 generation, the resistance level decreased 2.05-fold, and the average resistance decline rate per generation was 0.01, but there were no statistical decline. The TFM resistant strains had no cross-resistance to imidacloprid, nitenpyram, thiamethoxam, dinotefuran, flonicamid, pymetrozine, and chlorfenapyr. The third and fifth nymphal stage duration, pre-adult stage, adult preoviposition period, longevity, emergence rate, and hatchability of the resistant strain were significantly lower than those of the susceptible strain, while the female-male ratio was considerably increased. The fitness cost was 0.89. Further, cytochrome P450 monooxygenase (P450) and carboxylesterase (CarE) activities were markedly increased, but only the enzyme inhibitor piperonyl butoxide (PBO) had a significant synergistic effect on the resistant strain. The expression of CYP303A1, CYP4CE2, and CYP419A1v2 of P450 genes was significantly increased. SBPH has a certain risk of resistance to TFM with continuous application. The TFM resistance may be due to the increased activity of P450 enzyme regulated by the overexpression of P450 genes.

Transcriptome and population structure of glassy-winged sharpshooters (Homalodisca vitripennis) with varying insecticide resistance in southern California

Background

Homalodisca vitripennis Germar, the glassy-winged sharpshooter, is an invasive insect in California and a critical threat to agriculture through its transmission of the plant pathogen, Xylella fastidiosa. Quarantine, broad-spectrum insecticides, and biological control have been used for population management of H. vitripennis since its invasion and subsequent proliferation throughout California. Recently wide-spread neonicotinoid resistance has been detected in populations of H. vitripennis in the southern portions of California’s Central Valley. In order to better understand potential mechanisms of H. vitripennis neonicotinoid resistance, we performed RNA sequencing on wild-caught insecticide-resistant and relatively susceptible sharpshooters to profile their transcriptome and population structure.

Results

We identified 81 differentially expressed genes with higher expression in resistant individuals. The significant largest differentially expressed candidate gene linked to resistance status was a cytochrome P450 gene with similarity to CYP6A9. Furthermore, we observed an over-enrichment of GO terms representing functions supportive of roles in resistance mechanisms (cytochrome P450s, M13 peptidases, and cuticle structural proteins). Finally, we saw no evidence of broad-scale population structure, perhaps due to H. vitripennis' relatively recent introduction to California or due to the relatively small geographic scale investigated here.

Conclusions

In this work, we characterized the transcriptome of insecticide-resistant and susceptible H. vitripennis and identified candidate genes that may be involved in resistance mechanisms for this species. Future work should seek to build on the transcriptome profiling performed here to confirm the role of the identified genes, particularly the cytochrome P450, in resistance in H. vitripennis. We hope this work helps aid future population management strategies for this and other species with growing insecticide resistance.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08939-1.

The Cross-Resistance Pattern and the Metabolic Resistance Mechanism of Acetamiprid in the Brown Planthopper, Nilaparvata lugens (Stål)

Acetamiprid is widely used in paddy fields for controlling Nilaparvata lugens (Stål). However, the risk of resistance development, the cross-resistance pattern and the resistance mechanism of acetamiprid in this pest remain unclear. In this study, an acetamiprid-resistant strain (AC-R) was originated from a field strain (UNSEL) through successive selection with acetamiprid for 30 generations, which reached 60.0-fold resistance when compared with a laboratory susceptible strain (AC-S). The AC-R strain (G₃₀) exhibited cross-resistance to thiamethoxam (25.6-fold), nitenpyram (21.4-fold), imidacloprid (14.6-fold), cycloxaprid (11.8-fold), dinotefuran (8.7-fold), sulfoxaflor (7.6-fold) and isoprocarb (8.22-fold), while there was no cross-resistance to etofenprox, buprofezin and chlorpyrifos. Acetamiprid was synergized by the inhibitor piperonyl butoxide (2.2-fold) and the activity of cytochrome P450 monooxygenase was significantly higher in the AC-R strain compared with the AC-S strain, suggesting the critical role of P450. The gene expression results showed that the P450 gene CYP6ER1 was significantly overexpressed in AC-R compared with the AC-S and UNSEL strains. In addition, the RNA interference (RNAi) of CYP6ER1 significantly increased the susceptibility of AC-R to acetamiprid. Molecular docking predicted that acetamiprid and CYP6ER1 had close binding sites, and the nitrogen atoms had hydrogen bond interactions with CYP6ER1. These results demonstrated that the overexpression of CYP6ER1 contributed to acetamiprid resistance in N. lugens.

Overexpression of ATP-binding cassette transporters ABCG10, ABCH3 and ABCH4 in Aphis craccivora (Koch) facilitates its tolerance to imidacloprid

Aphis craccivora (Koch), a globally pest that causes significant threat to the legumes, has developed different degrees of resistance to a variety of insecticides. The ATP-binding cassette (ABC) transporters comprise a multifunctional transporter protein superfamily which play important roles in the transport and detoxification of xenobiotic compounds in insects. However, whether ABC transporters take part in the tolerance of imidacloprid in A. craccivora is still unknown. In order to investigate the functions of ABC transporters in the imidacloprid tolerance, fifty- eight ABC transporters were identified in the transcriptome and genome of A. craccivora and the toxicity of imidacloprid against A. craccivora was significantly increased after application the inhibitors of verapamil and Ko143. The relative expression levels of ABCG5, ABCG6, ABCG10, ABCH3, ABCH4, ABCH8 and ABCH10 were significantly up-regulated in response to imidacloprid treatment with LC₁₅, LC₅₀ and LC₈₅ concentrations, and the expression patterns of these seven ABC transporters were further analyzed at different developmental stages and in different tissues of A. craccivora by quantitative real-time PCR (RT-qPCR). Furthermore, knockdown of ABCG10, ABCH3 and ABCH4 significantly increased the mortality of A. craccivora to imidacloprid. Our results reveal the key functions of ABC transporters in the tolerance of imidacloprid and provide valuable information regarding the development of improved management strategies in A. craccivora.

MicroRNA-190-5p confers chlorantraniliprole resistance by regulating CYP6K2 in Spodoptera frugiperda (Smith)

The fall armyworm Spodoptera frugiperda (Smith) (FAA) is responsible for considerable losses in grain production, and chemical control is the most effective strategy. However, frequent insecticide application can lead to the development of resistance. In insects, cytochrome P450 plays a crucial role in insecticide metabolism. CYP6K2 is related to FAA resistance to chlorantraniliprole. However, the regulatory mechanism of CYP6K2 expression is poorly understood. In this study, a conserved target of isolated miRNA-190-5p was located in the 3' UTR of CYP6K2 in FAA. A luciferase reporter analysis showed that in FAA, miRNA-190-5p can combine with the 3'UTR of CYP6K2 to suppress its expression. Injected miRNA-190-5p agomir significantly reduced CYP6K2 abundance by 54.6% and reduced tolerance to chlorantraniliprole in FAA larvae, whereas injected miRNA-190-5p antagomir significantly increased CYP6K2 abundance by 1.77-fold and thus improved chlorantraniliprole tolerance in FAA larvae. These results provide a basis for further research on the posttranscriptional regulatory mechanism of CYP6K2 and will facilitate further study on the function of miRNAs in regulating tolerance to chlorantraniliprole in FAA.

Intermittent induction of LEA peptide by lactose enhances the expression of insecticidal proteins in Bacillus thuringiensis

Cry toxins from Bacillus thuringiensis (Bt) have been extensively applied in agriculture to substitute the use of chemical insecticides. We have previously reported the use of a coexpression system in which late embryogenesis abundant (LEA) peptides under the control of the lac promoter increase the expression of insecticidal proteins in Bt. The use of lactose to induce the expression of LEA peptides may be a desirable alternative to isopropyl β‐D‐thiogalactopyranoside, the most frequently used inducer for recombinant protein expression. In this study we investigated the use of lactose as an inducer for optimal protein expression. We observed enhanced insecticidal Cry protein expression by applying a simple technique based on intermittent induction, and then optimized concentration and the point of induction time from the 11^th h to the 15^th h. Our data suggest that intermittent induction of lactose might be a new technique for the enhancement of bacterial protein expression.

Overexpression of ATP-binding cassette transporter Mdr49-like confers resistance to imidacloprid in the field populations of brown planthopper, Nilaparvata lugens

BACKGROUND

The brown planthopper (BPH), Nilaparvata lugens (Stål), is the most severe pest attacking rice crops using sucking mouthparts. It causes significant damages to rice growth and food production worldwide. With the long-term and wide use of insecticides, field populations of BPH have developed resistance to many insecticides.

RESULTS

Here, we showed that upregulation of an ATP-binding cassette transporter gene NlMdr49-like contributes to imidacloprid resistance in field populations of BPH. A comparative transcriptome analysis was performed to evaluate the gene expression in two field populations (JXSG18 and YNTC18). Compared with a susceptible strain (Sus), 202 upregulated genes and 170 downregulated genes were identified in both field populations. Functional enrichment analysis revealed that the differentially expressed genes (DEGs) are mainly linked to metabolic process and transmembrane transport. Among the candidate DEGs, NlMdr49-like was significantly upregulated in both field populations. Based on the genome and transcriptome of BPH, the full-length complementary DNA of NlMdr49-like was sequenced and its molecular characteristics were analyzed. Expression pattern analysis of various tissues showed that NlMdr49-like was predominantly expressed in midgut and Malpighian tubules which are important excretion organs. Knocking down NlMdr49-like reduced BPH resistance to imidacloprid, but did not affect its resistance to the other nine insecticides (chlorpyrifos, thiamethoxam, nitenpyram, dinotefuran, sulfoxaflor, triflumezopyrim, ethiprole, buprofezin and pymetrozine). Furthermore, a transgenic strain of Drosophila melanogaster overexpressing NlMdr49-like was less susceptible to imidacloprid.

CONCLUSIONS

Our findings indicate that upregulation of NlMdr49-like is another mechanism contributing to imidacloprid resistance in N. lugens. This result is helpful to further understand the resistance mechanism of N. lugens to imidacloprid. © 2021 Society of Chemical Industry.

Functionally characterized arthropod pest and pollinator cytochrome P450s associated with xenobiotic metabolism

The cytochrome P450 family (P450s) of arthropods includes diverse enzymes involved in endogenous essential physiological functions and in the oxidative metabolism of xenobiotics, insecticides and plant allelochemicals. P450s can also establish insecticide selectivity in bees and pollinators. Several arthropod P450s, distributed in different phylogenetic groups, have been associated with xenobiotic metabolism, and some of them have been functionally characterized, using different in vitro and in vivo systems. The purpose of this review is to summarize scientific publications on arthropod P450s from major insect and mite agricultural pests, pollinators and Papilio sp, which have been functionally characterized and shown to metabolize xenobiotics and/or their role (direct or indirect) in pesticide toxicity or resistance has been functionally validated. The phylogenetic relationships among these P450s, the functional systems employed for their characterization and their xenobiotic catalytic properties are presented, in a systematic approach, including critical aspects and limitations. The potential of the primary P450-based metabolic pathway of target and non-target organisms for the development of highly selective insecticides and resistance-breaking formulations may help to improve the efficiency and sustainability of pest control.

The Key Glutathione S-Transferase Family Genes Involved in the Detoxification of Rice Gramine in Brown Planthopper Nilaparvata lugens

Phytochemical toxins are considered a defense measure for herbivore invasion. To adapt this defensive strategy, herbivores use glutathione S-transferases (GSTs) as an important detoxification enzyme to cope with toxic compounds, but the underlying molecular basis for GST genes in this process remains unclear. Here, we investigated the basis of how GST genes in brown planthopper (BPH, Nilaparvata lugens (Stål)) participated in the detoxification of gramine by RNA interference. For BPH, the LC25 and LC50 concentrations of gramine were 7.11 and 14.99 μg/mL at 72 h after feeding, respectively. The transcriptions of seven of eight GST genes in BPH were induced by a low concentration of gramine, and GST activity was activated. Although interferences of seven genes reduced BPH tolerance to gramine, only the expression of NlGST1-1, NlGSTD2, and NlGSTE1 was positively correlated with GST activities, and silencing of these three genes inhibited GST activities in BPH. Our findings reveal that two new key genes, NlGSTD2 and NlGSTE1, play an essential role in the detoxification of gramine such as NlGST1-1 does in BPH, which not only provides the molecular evidence for the coevolution theory, but also provides new insight into the development of an environmentally friendly strategy for herbivore population management.

Genomic organization and expression pattern of cytochrome P450 genes in the wolf spider Pardosa pseudoannulata

As one of the dominant natural enemies for insect pests, the pond wolf spider, Pardosa pseudoannulata, plays important roles in pest control. Insecticide applications threaten P. pseudoannulata and consequently weaken its control effects. The roles of P450 monooxygenases in insecticide detoxifications have been richly reported in insects, but there are few reported in spiders. In this study, 120 transcripts encoding P. pseudoannulata P450s were identified based on whole genome sequencing. Compared to P450s of Aedes aegypti and Nilaparvata lugens, several novel P450 families were found, such as CYP3310. KEGG analysis of the CYP3310 family indicated that the family might be involved in the synthesis and metabolism of polyunsaturated fatty acids and hydrocarbons. The potential P450s involved in insecticide metabolism were obtained according to the high FPKM values in fat bodies based on transcriptome sequencing. However, none of the selected P450 genes was significantly upregulated by the treatments of deltamethrin or imidacloprid. The present study provides genomic and transcriptomic information of spider P450s, especially for their roles in the synthesis and metabolism of endogenous and exogenous compounds, such as polyunsaturated fatty acids, hydrocarbons and insecticides.

Mechanism of metabolic resistance to pymetrozine in Nilaparvata lugens: over-expression of cytochrome P450 CYP6CS1 confers pymetrozine resistance

BACKGROUND

Pymetrozine is commonly used for the control of Nilaparvata lugens, and resistance to pymetrozine has been frequently reported in the field populations in recent years. However, the mechanism of brown planthopper resistance to pymetrozine is still unknown.

RESULTS

In this study, a pymetrozine-resistant strain (PMR) was established, and the potential biochemical resistance mechanism of N. lugens to pymetrozine was investigated. Pymetrozine was synergized by the inhibitor piperonyl butoxide (PBO) in the PMR with 2.83-fold relative synergistic ratios compared with the susceptible strain (Sus). Compared with the Sus, the cytochrome P450 monooxygenase activity of PMR was increased by 1.7 times, and two P450 genes (NlCYP6CS1 and NlCYP301B1) were found to be significantly overexpressed more than 6.0-fold in the PMR. Pymetrozine exposure induced upregulation of NlCYP6CS1 expression in the Sus, but the expression of NlCYP301B1 did not change significantly. In addition, RNA interference (RNAi)-mediated suppression of NlCYP6CS1 gene expression dramatically increased the toxicity of pymetrozine against N. lugens. Moreover, transgenic lines of Drosophila melanogaster expressing NlCYP6CS1 were less susceptible to pymetrozine, and had a stronger ability to metabolize pymetrozine.

CONCLUSIONS

Taken together, our findings indicate that the overexpression of NlCYP6CS1 is one of the key factors contributing to pymetrozine resistance in N. lugens. And this result is helpful in proposing a management strategy for pymetrozine resistance.

Evaluation of Beta-Cyfluthrin Resistance of Cigarette Beetle (Coleoptera: Anobiidae) from Cigarette Manufacturing Factories of China and Underlying Metabolic Mechanisms Responsible for Resistance

Beta-cyfluthrin, as a synthetic pyrethroid, has been widely used in cigarette manufacturing factories in China to control Lasioderma serricorne (F.) (Coleoptera: Anobiidae). In this study, spray toxicity bioassays and filter paper residual contact toxicity bioassays were conducted to investigate the beta-cyfluthrin sensitivity level of five field strains of L. serricorne collected from cigarette manufacturing factories in China. Bioassay results indicated that five field strains had developed different levels of resistance to beta-cyfluthrin with RR50 of 3.51-10.20 at 2 hr after application and 4.05-49.50 at 24 hr after application in spray toxicity bioassays, and RR50 of 4.74-14.47 at 2 hr exposure in filter paper residual contact bioassays. In addition, we examined CarE, GST, and CYP450 enzyme activity and content of L. serricorne adults and larvae. Enzyme-linked immunosorbent assay results suggested that there was no significant difference in GST, CYP450, and CarE content of L. serricorne adults between field strains and reference sensitive strain. Biochemical assay results indicated that CYP450 activity of L. serricorne adults and larvae of five field strains was significantly higher than that of reference sensitive strain, with increased CYP450 activity of 1.08-1.82-fold in adults and 1.08-2.12-fold in larvae. The results implied that elevated CYP450 activity may contribute to metabolic resistance of L. serricorne to pyrethroid. Our study indicated that there was no clear evidence that the enhanced CarE and GST activity was associated with pyrethroid resistance of L. serricorne.

The roles of GSTs in fipronil resistance in Nilaparvata lugens: Over-expression and expression induction

As one of the most important detoxification enzymes in insects, Glutathione S-transferases (GSTs) play key roles in insecticide resistance via direct metabolism and protection against oxidative stress induced by insecticide exposure. Insect GSTs are often considered as the phase II detoxification enzymes, they have potential function to metabolize fipronil as well as its fipronil's metabolites. In the fipronil-resistant Nilaparvata lugens strain G28, GSTs' inhibitor DEM (diethyl maleate) showed the optimal synergistic effects (5.73-fold), indicating the essential roles of GSTs in the resistance to fipronil in this insect species. Four GST genes, NlGSTs1, NlGSTs2, NlGSTe1 and NlGSTd1, were found over-expressed in G28 when compared to its relative susceptible counterpart strain S28. The roles of these four GSTs in fipronil resistance were confirmed via RNAi. The four GST genes were highly over-expressed in the midgut and/or fat body with detoxification action, which might provide more chances for insects to metabolize fipronil and its metabolites. Additionally, the higher induction levels in the GST gene expression by insecticides in the midgut and/or fat body compared to the whole insect also supported the significant roles of the four GSTs in the detoxification. Above all, the results provided evidences to understand the functions of GSTs in fipronil resistance in N. lugens, and gave a reference for other insects in fipronil resistance.

Cytochrome P450s Are Essential for Insecticide Tolerance in the Endoparasitoid Wasp Meteorus pulchricornis (Hymenoptera: Braconidae)

With the widespread application of insecticides, parasitoid wasps may also be under risk when exposed to insecticides directly at their free-living stages. The endoparasitoid wasp Meteorus pulchricornis is the predominant natural enemy of many lepidopteran pests, such as Spodoptera litura and Helicoverpa armigera. The cytochrome P450 monooxygenases constitute a ubiquitous and complex superfamily of hydrophobic, haem-containing enzymes. P450s are involved in the detoxification of many xenobiotics. However, their exact roles in the tolerance mechanism in parasitoids toward insecticides has received less attention. Here, 28 P450 genes in M. pulchricornis were identified from a previously constructed transcriptome dataset. These P450 genes belonged to CYP2, -3, and -4, and mitochondrial clans. Subsequently, eight candidate MpulCYPs were selected from four CYP clans to validate their expression patterns under phoxim, cypermethrin, and chlorfenapyr exposure by qRT-PCR. The results showed that all three insecticides had significant effects on the expression of MpulCYPs. To further study the function of P450s, CYP369B3 was silenced, and its expression levels of CYP369B3 were significantly decreased. Survival analysis indicated that after dsRNA injection, the mortality rate of wasps was significantly increased when M. pulchricornis females were exposed to insecticides compared to control groups. Our findings provide a theoretical base for elucidating the mechanism of insecticide tolerance and promote functional research on P450 genes in parasitoid wasps.

Evaluation of sublethal and transgenerational effects of sulfoxaflor on Aphis gossypii via life table parameters and 16S rRNA sequencing

BACKGROUND

Aphis gossypii, a polyphagous and recurrent pest induced by pesticides, causes tremendous loss crop yields each year. Previous studies on the mechanism of pesticide-induced sublethal effects mainly focus on the gene level. The symbiotic bacteria are also important participants of this mechanism, but their roles in hormesis are still unclear.

RESULTS

In this study, life table parameters and 16S rRNA sequencing were applied to evaluate the sublethal and transgenerational effects of sulfoxaflor on adult A. gossypii after 24-h LC₂₀ (6.96 mg L^-1 ) concentration exposure. The results indicated that the LC₂₀ of sulfoxaflor significantly reduced the finite rate of increase (λ) and net reproductive rate (R₀ ) of parent generation (G0), and significantly increased mean generation time (T) of G1 and G2, but not of G3 and G4. Both reproductive period and fecundity of G1 and G2 were significantly higher than those of the control. Furthermore, our sequencing data revealed that more than 95% bacterial communities were dominated by the phylum Proteobacteria, in which the maximum proportion genus was the primary symbiont Buchnera and the facultative symbiont Arsenophonus. Compared to those of the control, the abundance and composition of symbiotic bacteria of A. gossypii for three successive generations (G0-G2) were changed after G0 A. gossypii was exposed to sulfoxaflor: the diversity of the bacterial community was decreased, but the abundance of Buchnera was increased (G0), while the abundance of Arsenophonus was decreased. Contrary to G0, G1 and G2 cotton aphid exhibited an increased relative abundance of Arsenophonus in the sublethal treatment group.

CONCLUSION

Taken together, our results provide an insight into the interactions among pesticide resistance, aphids, and symbionts, which will eventually help to better manage the resurgence of A. gossypii. © 2021 Society of Chemical Industry.

UDP-Glycosyltransferases from the UGT344 Family Are Involved in Sulfoxaflor Resistance in Aphis gossypii Glover

Simple Summary

The cotton aphid, Aphis gossypii Glover, is a notorious pest in cotton and cucurbit fields. The control of A. gossypii has typically relied on the application of chemical insecticides. Sulfoxaflor is the first commercially available sulfoximine insecticide, which exhibits great efficacy against sap-feeding insect pests and has been applied as an alternative insecticide for controlling of A. gossypii in China. Consequently, A. gossypii quickly developed resistance to this insecticide. Hence, in this study, to clarify the potential detoxifying roles of UGTs (one of the phase II detoxification enzymes) in resistance of A. gossypii against sulfoxaflor, the synergistic effects of two synergists (sulfinpyrazone and 5-nitrouracil) against sulfoxaflor were investigated using the susceptible and laboratory-established sulfoxaflor resistant strain (SulR), and the expression levels of 15 UGT genes were determined by qRT-PCR. Furthermore, the involvement of highly upregulated UGTs in sulfoxaflor-resistant strain was functionally tested by RNA interference (RNAi). Our results suggest that overexpression of UGTs contributes to sulfoxaflor resistance in A. gossypii, which should be useful for understanding sulfoxaflor resistance mechanisms.

Abstract

UDP-glycosyltransferases (UGTs) are major phase II detoxification enzymes that catalyze the transfer of glycosyl residues from activated nucleotide sugars to acceptor hydrophobic molecules and play very important roles in the biotransformation of various endogenous and exogenous compounds. Our previous studies demonstrated that UGTs participated in the detoxification of insecticides in Aphis gossypii. However, the potential roles of UGTs in A. gossypii resistance to sulfoxaflor are still unclear. In this study, two inhibitors of UGT enzymes, sulfinpyrazone and 5-nitrouracil, significantly increased the toxicity of sulfoxaflor to a resistant strain of A. gossypii, whereas there were no synergistic effects in the susceptible strain. Based on the transcriptome sequencing results, the expression levels of 15 UGTs were analyzed by quantitative real-time PCR, and we found that seven UGT genes were highly over-expressed in a sulfoxaflor-resistant strain compared to the susceptible strain, including UGT344B4, UGT344C5, UGT344A11, UGT344A14, and UGT344L2. Further suppressing the expression of UGT344B4, UGT344C5, and UGT344A11 by RNA interference significantly increased the sensitivity of resistant aphids to sulfoxaflor, indicating that the overexpression of UGT genes is potentially associated with sulfoxaflor resistance. These results could provide valuable information for further understanding the mechanisms of insecticide resistance.

Genome-wide assessment and development of molecular diagnostic methods for imidacloprid-resistance in the brown planthopper, Nilaparvata lugens (Hemiptera; Delphacidae)

BACKGROUND

The brown planthopper, Nilaparvata lugens (Stål), is one of the most notorious pests of rice throughout Asia. The brown planthopper has developed high resistance to imidacloprid, a member of neonicotinoid insecticides. Several genes and mutations conferring imidacloprid resistance in N. lugens, especially in eastern and southeastern Asia populations, have been reported. Thus, the key mechanisms of imidacloprid resistance need to be examined.

RESULTS

RNA-seq analyses revealed that only one cytochrome P450 monooxygenase gene, CYP6ER1, was commonly upregulated in the five resistant strains tested. Sequences of CYP6ER1, which were highly expressed in the imidacloprid-resistant strains, contained a three-nucleotide deletion in the coding region, and amino acid substitutions and deletion, compared to that in an imidacloprid-susceptible strain. RNAi-mediated gene knockdown of CYP6ER1 increased imidacloprid susceptibility in a resistant strain. Further, we established two simple and convenient PCR-based molecular diagnostic methods to detect the CYP6ER1 locus with the three-nucleotide deletion. Using these methods, the resistance of F₂ progenies derived from the crosses of F₁ siblings from susceptible and resistant parents was analyzed, showing that the imidacloprid resistance had a relationship to the CYP6ER1 locus with the three-nucleotide deletion.

CONCLUSION

The overexpression of a variant CYP6ER1 with amino acid substitutions and deletion was involved in imidacloprid resistance in N. lugens. Based on these findings, molecular diagnostic methods have been developed and are promising tools for monitoring imidacloprid resistance in paddy fields. © 2020 Society of Chemical Industry.

Changes in Transcriptome and Gene Expression in Sogatella furcifera (Hemiptera: Delphacidae) in Response to Cycloxaprid

The white-backed planthopper, Sogatella furcifera (Horváth), causes substantial damage to crops by direct feeding or virus transmission, especially southern rice black-streaked dwarf virus, which poses a serious threat to rice production. Cycloxaprid, a novel cis-nitromethylene neonicotinoid insecticide, has high efficacy against rice planthoppers, including imidacloprid-resistant populations. However, information about the influence of cycloxaprid on S. furcifera (Hemiptera: Delphacidae) at the molecular level is limited. Here, by de novo transcriptome sequencing and assembly, we constructed two transcriptomes of S. furcifera and profiled the changes in gene expression in response to cycloxaprid at the transcription level. We identified 157,906,456 nucleotides and 131,601 unigenes using the Illumina technology from cycloxaprid-treated and untreated S. furcifera. In total, 38,534 unigenes matched known proteins in at least one database, accounting for 29.28% of the total unigenes. The number of coding DNA sequences was 28,546 and that of amino acid sequences in the coding region was 22,299. In total, 15,868 simple sequence repeats (SSRs) were identified. The trinucleotide repeats accounted for 45.1% (7,157) of the total SSRs and (AAG/CTT)n were the most frequent motif. There were 359 differentially expressed genes that might have been induced by cycloxaprid. There were 131 upregulated and 228 downregulated genes. Twenty-two unigenes might be involved in resistance against cycloxaprid, such as cytochrome P450, glutathione S-transferase (GST), acid phosphatase (ACP), and cadherin. Our study provides vital information on cycloxaprid-induced resistance mechanisms, which will be useful to analyze the molecular mechanisms of cycloxaprid resistance and may lead to the development of novel strategies to manage S. furcifera.

Current susceptibilities of brown planthopper Nilaparvata lugens to triflumezopyrim and other frequently used insecticides in China

The brown planthopper is a notorious rice pest in many areas of Asia. The evolution of insecticide resistance in Nilaparvata lugens has become a serious problem in the effective control of this pest in the paddy field. In this article, the current susceptibility of N. lugens field populations to novel mesoionic insecticide triflumezopyrim and major classes of chemical insecticides was determined and compared. The monitoring results indicated that field populations of N. lugens had developed low resistance to triflumezopyrim (resistance ratio, RR: 1.3-7.3-fold) during 2015-2018 in China, and the median lethal concentration values varied from 0.05 to 0.29 mg/L. Additionally, during 2017 to 2018, field populations of N. lugens showed high resistance levels to thiamethoxam (RR: 456.1-1025.6-fold), imidacloprid (RR: 2195.3-6899.0-fold) and buprofezin (RR: 1241.5-4521.7-fold), moderate to high resistance levels to dinotefuran (RR: 97.6-320.1-fold), clothianidin (RR: 69.4-230.1-fold) and isoprocarb (RR: 44.1-108.0-fold), and low to moderate levels of resistance to chlorpyrifos (RR: 12.0-29.7-fold) and nitenpyram (RR: 6.9-24.1-fold). In contrast, N. lugens just showed low resistance to sulfoxaflor (RR: 3.3-8.5-fold) and etofenprox (RR: 5.0-9.1-fold) in the field. Additionally, the P450 gene CYP6ER1 was found to be significantly overexpressed in all five field populations of N. lugens collected in 2018 when compared with a laboratory susceptible strain. Our findings will provide useful information to delay the evolution of insecticide resistance in N. lugens.

Contribution of Glutathione S-Transferases to Imidacloprid Resistance in Nilaparvata lugens

The importance of glutathione S-transferases (GSTs) in imidacloprid resistance in Nilaparvata lugens, a major rice pest, and other insects was often excluded, mostly due to the slight effects of diethyl maleate (DEM) on synergizing imidacloprid in resistant populations. Here, we found that the synergistic effects of DEM were time-dependent. At 24 or 48 h, the time often selected to record mortalities in imidacloprid bioassay, DEM really did not cause an obvious increase in imidacloprid toxicity. However, significant effects were observed after 72 h. The results revealed that GSTs, as phase II detoxification enzymes to metabolize secondary products generated from phase I detoxification enzymes, were also important in imidacloprid resistance in N. lugens, but might have occurred a little later than that of P450s and CarEs as phase I enzymes. The constitutive overexpression in the imidacloprid-resistant strain G25 and expression induction by imidacloprid in the susceptible strain S25 indicated that four GST genes, NlGSTs1, NlGSTs2, NlGSTe1, and NlGSTm1, were important in imidacloprid resistance, which was confirmed by RNAi test. The higher expression levels and more expression induction by imidacloprid in the midgut and fat body compared to the whole insect supported the important roles of these four GSTs, which was also supported by the more overexpression times in the midgut and fat body versus the whole insect between G25 and S25 strains. Taking the data together, the study ascertained the roles of GSTs in imidacloprid resistance in N. lugens.

Characterization of flupyradifurone resistance in the whitefly Bemisia tabaci Mediterranean (Q biotype)

BACKGROUND

Bemisia tabaci is one of most notorious pests on various crops worldwide and many populations show high resistance to different types of insecticides. Flupyradifurone is a novel insecticide against sucking pests. B. tabaci resistance to flupyradifurone has been detected in the field, however the mechanism of flupyradifurone resistance has rarely been studied.

RESULTS

The flupyradifurone-resistant strain (FLU-SEL) was selected from the susceptible strain of B. tabaci (MED-S) using flupyradifurone for 24 generations. The FLU-SEL strain exhibited 105.56-fold resistance to flupyradifurone, and moderate cross-resistance to imidacloprid, but no cross-resistance to other tested neonicotinoids. Synergism tests and metabolic enzyme assays suggested that FLU-SEL resistance can be attributed to enhanced detoxification mediated by glutathione S-transferase (GST) and P450 monooxygenase (P450). Compared with MED-S strain, CYP6CX4 and GSTs2 were significantly overexpressed in FLU-SEL, and silencing CYP6CX4 or GSTs2 increased the mortality of whiteflies to flupyradifurone challenge in FLU-SEL. In addition, silencing CYP6CX4 also increased the mortality of whiteflies exposed to imidacloprid.

CONCLUSION

Overexpression of CYP6CX4 and GSTs2 was associated with flupyradifurone resistance, as confirmed by RNA interference. Our findings suggested that metabolic resistance to flupyradifurone might be mediated by P450s and GSTs. © 2020 Society of Chemical Industry.

Fly-Tox: A panel of transgenic flies expressing pest and pollinator cytochrome P450s

There is an on-going need to develop new insecticides that are not compromised by resistance and that have improved environmental profiles. However, the cost of developing novel compounds has increased significantly over the last two decades. This is in part due to increased regulatory requirements, including the need to screen both pest and pollinator insect species to ensure that pre-existing resistance will not hamper the efficacy of a new insecticide via cross-resistance, or adversely affect non-target insect species. To add to this problem the collection and maintenance of toxicologically relevant pest and pollinator species and strains is costly and often difficult. Here we present Fly-Tox, a panel of publicly available transgenic Drosophila melanogaster lines each containing one or more pest or pollinator P450 genes that have been previously shown to metabolise insecticides. We describe the range of ways these tools can be used, including in predictive screens to avoid pre-existing cross-resistance, to identify potential resistance-breaking inhibitors, in the initial assessment of potential insecticide toxicity to bee pollinators, and identifying harmful pesticide-pesticide interactions.

Realized heritability, inheritance and cross-resistance patterns in imidacloprid-resistant strain of Dysdercus koenigii (Fabricius) (Hemiptera: Pyrrhocoridae)

BACKGROUND

Imidacloprid, a neonicotinoid insecticide, is widely sprayed alone or mixed with other insecticides against Dysdercus koenigii, a potential pest of cotton in Pakistan. Recently, resistance to imidacloprid in field populations of D. koenigii has developed because of its overuse. Herein, we have investigated inheritance of imidacloprid resistance in D. koenigii and its cross-resistance to other insecticides.

RESULTS

The imidacloprid-selected population had a 91 421-fold increase in resistance to imidacloprid after six generations. Overlapping 95% fiducial limits of LC_50s of the F₁ (Imida-Sel ♂ × Sus-ST ♀) and F₁ ^† (Imida-Sel ♀ × Sus-ST ♂) suggested an autosomal and incomplete dominant resistance to imidacloprid (D_LC = 0.84 for F₁ and 0.86 for F₁ ^† ). Reciprocal backcrosses of the F₁ and F₁ ^† with Sus-ST predicted a polygenic inheritance. Realized heritability of imidacloprid resistance was 0.38. When mean slope = 1.74 and h² = 0.38, then 3-13 generations would be required for a ten-fold increase in LC_50s at 90-20% intensity of selection. Very high cross-resistance to emamectin benzoate (143-fold), deltamethrin (1675-fold) and lambda-cyhalothrin (140-fold), and moderate cross-resistance to acetamiprid (37-fold) in the imidacloprid-selected strain compared to the field population were observed.

CONCLUSION

Imidacloprid resistance developed very quickly under continuous selection pressure in the laboratory. These factors might lead to an increasing likelihood of resistance development in field populations, if imidacloprid is used continuously without insecticide rotation for prolonged periods. The present results would be supportive for better management of D. koenigii by devising an effective resistance management strategy. © 2020 Society of Chemical Industry.

The overexpression of three cytochrome P450 genes CYP6CY14, CYP6CY22 and CYP6UN1 contributed to metabolic resistance to dinotefuran in melon/cotton aphid, Aphis gossypii Glover

Dinotefuran, the third-generation neonicotinoid, has been applied against melon/cotton aphid Aphis gossypii Glover in China. The risk of resistance development, cross-resistance pattern and potential resistance mechanism of dinotefuran in A. gossypii were investigated. A dinotefuran-resistant strain of A. gossypii (DinR) with 74.7-fold resistance was established by continuous selection using dinotefuran. The DinR strain showed a medium level of cross resistance to thiamethoxam (15.2-fold), but no cross resistance to imidacloprid. The synergism assay indicated that piperonyl butoxide and triphenyl phosphate showed synergistic effects on dinotefuran toxicity to the DinR strain with a synergistic ratio of 8.3 and 2.5, respectively, while diethyl maleate showed no synergistic effect. The activities of cytochrome P450 monooxygenase and carboxylesterase were significantly higher in DinR strain than in susceptible strain (SS). Moreover, the gene expression results showed that CYP6CY14, CYP6CY22 and CYP6UN1 were significantly overexpressed in DinR strain compared with SS strain. The expression of CYP6CY14 was 5.8-fold higher in DinR strain than in SS strain. Additionally, the transcription of CYP6CY14, CYP6CY22 and CYP6UN1 in A. gossypii showed dose- and time-dependent responses to dinotefuran exposure. Furthermore, knockdown of CYP6CY14, CYP6CY22 and CYP6UN1 via RNA interference (RNAi) significantly increased mortality of A. gossypii, when A. gossypii was treated with dinotefuran. These results demonstrated the overexpression of CYP6CY14, CYP6CY22 and CYP6UN1 contributed to dinotefuran resistance in A. gossypii.