Comparative transcriptome and RNA interference reveal CYP6DC1 and CYP380C47 related to lambda-cyhalothrin resistance in Rhopalosiphum padi

Functional characterization of two DH44R genes associated with starvation and desiccation in Rhopalosiphum padi (Hemiptera: Aphididae)

CRF-like diuretic hormone receptor (CRF/DHR), also known as DH44R in insects, are G-protein coupled receptors (GPCRs) that play a role in regulating osmotic balance in various insect species. These receptors have the potential to be targeted for the development of insecticides. However, our understanding of the role of DHR genes in aphids, including Rhopalosiphum padi, a major wheat pest, is currently limited. In this study, we isolated and characterized two R. padi DHRs (RpDHR1 and RpDHR2). The expression levels of RpDHR1 increased after starvation and were restored after re-feeding. The expression levels of RpDHR1 gene decreased significantly 24 h after injection of dsRNA targeting the gene. Knockdown of RpDHR1 increased aphid mortality under starvation conditions (24, 36, 48 and 60 h). Under starvation and desiccation condition, the aphid mortality decreased after knockdown of RpDHR1. This is the first study to report the role of DHR genes in the starvation and desiccation response of aphids. The results suggest that RpDHR1 is involved in the resistance of R. padi to starvation and dehydration, making it a potential target for insecticide development. Novel insecticides could be created by utilizing DHR agonists to disrupt the physiological processes of insect pests.

A relaxin receptor gene RpGPCR41 is involved in the resistance of Rhopalosiphum padi to pyrethroids

Rhopalosiphum padi is a global pest that poses a significant threat to wheat crops and has developed resistance to various insecticides. G protein-coupled receptors (GPCRs), known for their crucial role in signaling and biological processes across insect species, have recently gained attention as a potential target for insecticides. GPCR has the potential to contribute to insect resistance through the regulation of P450 gene expression. However, GPCRs in R. padi remained unexplored until this study. We identified a total of 102 GPCRs in R. padi, including 81 receptors from family A, 10 receptors from family B, 8 receptors from family C, and 3 receptors from family D. Among these GPCR genes, 16 were up-regulated in both lambda-cyhalothrin and bifenthrin-resistant strains of R. padi (LC-R and BIF-R). A relaxin receptor gene, RpGPCR41, showed the highest up-regulated expression in both the resistant strains, with a significant increase of 14.3-fold and 22.7-fold compared to the susceptible strain (SS). RNA interference (RNAi) experiments targeting the relaxin receptor significantly increase the mortality of R. padi when exposed to the LC50 concentration of lambda-cyhalothrin and bifenthrin. The expression levels of five P450 genes (RpCYP6CY8, RpCYP6DC1, RpCYP380B1, RpCYP4CH2, and RpCYP4C1) were significantly down-regulated following knockdown of RpGPCR41 in LC-R and BIF-R strains. Our results highlight the involvement of GPCR gene overexpression in the resistance of R. padi to pyrethroids, providing valuable insights into the mechanisms underlying aphid resistance and a potential target for aphid control.

Uridine Diphosphate-Glycosyltransferase RpUGT344D38 Contributes to λ-Cyhalothrin Resistance in Rhopalosiphum padi

Uridine diphosphate-glycosyltransferase (UGT) is a key phase II enzyme in the insect detoxification system. Pyrethroids are commonly used to control the destructive wheat aphid Rhopalosiphum padi. In this study, we found a highly expressed UGT gene, RpUGT344D38, in both λ-cyhalothrin (LCR)- and bifenthrin (BTR)-resistant strains of R. padi. After exposure to λ-cyhalothrin and bifenthrin, the expression levels of RpUGT344D38 were significantly increased in the resistant strains. Knockdown of RpUGT344D38 did not affect the resistance of BTR, but it did significantly increase the susceptibility of LCR aphids to λ-cyhalothrin. Molecular docking analysis demonstrated that RpUGT344D38 had a stable binding interaction with both bifenthrin and λ-cyhalothrin. The recombinant RpUGT344D38 was able to metabolize 50% of λ-cyhalothrin. This study provides a comprehensive analysis of the role of RpUGT344D38 in the resistance of R. padi to bifenthrin and λ-cyhalothrin, contributing to a better understanding of aphid resistance to pyrethroids.

Functional Characterization of CYP6QE1 and CYP6FV21 in Resistance to λ-Cyhalothrin and Imidacloprid in Bradysia odoriphaga

Cytochrome P450 monooxygenases (P450s) belong to a family of metabolic enzymes that are involved in the detoxification of insecticides. In this study, our bioassay results showed that a field-collected population of Bradysia odoriphaga displayed a moderate resistance to λ-cyhalothrin and imidacloprid. Compared to susceptible population, CYP6QE1 and CYP6FV21 were significantly overexpressed in the field population. The expression of CYP6QE1 and CYP6FV21 was more abundant in the third and fourth larval stages, and CYP6QE1 and CYP6FV21 were most highly expressed in the midgut and Malpighian tubules. Exposure to λ-cyhalothrin and imidacloprid significantly increased the expression levels of CYP6QE1 and CYP6FV21. Furthermore, the silencing of CYP6QE1 and CYP6FV21 significantly increased the susceptibility of B. odoriphaga larvae to λ-cyhalothrin and imidacloprid. The overexpression of CYP6QE1 and CYP6FV21 significantly enhanced the tolerance of transgenic Drosophila melanogaster lines to λ-cyhalothrin and imidacloprid. In addition, molecular docking revealed that these two P450 proteins have strong binding affinity toward λ-cyhalothrin and imidacloprid insecticides. Taken together, these results indicate that the overexpression of CYP6QE1 and CYP6FV21 is responsible for resistance to λ-cyhalothrin and imidacloprid in B. odoriphaga.

Voltage-gated sodium channel gene mutation and P450 gene expression are associated with the resistance of Aphis spiraecola Patch (Hemiptera: Aphididae) to lambda-cyhalothrin

Aphis spiraecola Patch is one of the most economically important tree fruit pests worldwide. The pyrethroid insecticide lambda-cyhalothrin is commonly used to control A. spiraecola. In this 2-year study, we quantified the resistance level of A. spiraecola to lambda-cyhalothrin in different regions of the Shaanxi province, China. The results showed that A. spiraecola had reached extremely high resistance levels with a 174-fold resistance ratio (RR) found in the Xunyi region. In addition, we compared the enzymatic activity and expression level of P450 genes among eight A. spiraecola populations. The P450 activity of A. spiraecola was significantly increased in five regions (Xunyi, Liquan, Fengxiang, Luochuan, and Xinping) compared to susceptible strain (SS). The expression levels of CYP6CY7, CYP6CY14, CYP6CY22, P4504C1-like, P4506a13, CYP4CZ1, CYP380C47, and CYP4CJ2 genes were significantly increased under lambda-cyhalothrin treatment and in the resistant field populations. A L1014F mutation in the sodium channel gene was found and the mutation rate was positively correlated with the LC50 of lambda-cyhalothrin. In conclusion, the levels of lambda-cyhalothrin resistance of A. spiraecola field populations were associated with P450s and L1014F mutations. Our combined findings provide evidence on the resistance mechanism of A. spiraecola to lambda-cyhalothrin and give a theoretical basis for rational and effective control of this pest species.

Overexpression of the Chemosensory Protein CSP7 Gene Contributed to Lambda-Cyhalothrin Resistance in the Bird Cherry-Oat Aphid Rhopalosiphum padi

Lambda-cyhalothrin is one of the most important pyrethroids used for controlling wheat aphids. Extensive spraying of lambda-cyhalothrin has led to the development of high resistance to this pyrethroid inRhopalosiphum padi. The mechanisms of resistance are complex and not fully understood. In this study, we found that a laboratory-selected strain of R. padi showed extremely high resistance to lambda-cyhalothrin and cross-resistance to bifenthrin and deltamethrin. The expression level of RpCSP7 was significantly elevated in the resistant strain compared to that in the susceptible strain. Knockdown of RpCSP7 increased the susceptibility of R. padi to lambda-cyhalothrin, whereas the susceptibility to bifenthrin and deltamethrin was not significantly changed. The recombinant RpCSP7 displayed a high affinity for lambda-cyhalothrin but no affinities to bifenthrin and deltamethrin. These findings suggest that the overexpression of RpCSP7 contributes to the resistance of R. padi to lambda-cyhalothrin. This study provides valuable insights into CSP-mediated insecticide resistance in insects.

Characterization and fitness cost of bifenthrin resistance in Rhopalosiphum padi (Hemiptera: Aphididae)

Rhopalosiphum padi is an important global wheat pest. The pyrethroid insecticide bifenthrin is widely used in the control R. padi. We explored the resistance potential, cross-resistance, adaptive costs, and resistance mechanism of R. padi to bifenthrin using a bifenthrin-resistant strain (Rp-BIF) established in laboratory. The Rp-BIF strain developed extremely high resistance against bifenthrin (1033.036-fold). Cross-resistance analyses showed that the Rp-BIF strain had an extremely high level of cross-resistance to deltamethrin (974.483-fold), moderate levels of cross-resistance to chlorfenapyr (34.051-fold), isoprocarb (27.415-fold), imidacloprid (14.819-fold), and thiamethoxam (11.228-fold), whereas negative cross-resistance was observed to chlorpyrifos (0.379-fold). The enzymatic activity results suggested that P450 played an important role in bifenthrin resistance. A super-kdr mutation (M918L) of voltage-gated sodium channel (VGSC) was found in the bifenthrin-resistant individuals. When compared with the susceptible strain (Rp-SS), the Rp-BIF strain was significantly inferior in multiple life table parameters, exhibiting a relative fitness of 0.69. Our toxicological and biochemical studies indicated that multiple mechanisms of resistance might be involved in the resistance trait. Our results provide insight into the bifenthrin resistance of R. padi and can contribute to improve management of bifenthrin-resistant R. padi in the field.

UGT2B13 and UGT2C1 are involved in lambda-cyhalothrin resistance in Rhopalosiphum padi

Uridine diphosphate-glucuronosyltransferases (UGTs) are major multifunctional detoxification phase II enzymes involved in the metabolic detoxification of xenobiotics. However, their roles in insecticides resistance are still unclear. In this study, we identified two UGTs genes (UGT2B13 and UGT2C1) in Rhopalosiphum padi, a serious insect pest of wheat worldwide. Bioassays results showed that the resistance ratio of R. padi resistance strain (LC-R) to lambda-cyhalothrin (LC) was 2963.8 fold. The roles of UGT2B13 and UGT2C1 in lambda-cyhalothrin resistance were evaluated. Results indicated that the UGTs contents were significantly increased in the LC resistant strain of R. padi. UGT2B13 and UGT2C1 were significantly overexpressed in the LC-R strain. Transcription levels of UGT2B13 and UGT2C1 were relatively higher in the gut of LC-R strain. RNA interference (RNAi) of UGT2B13 or UGT2C1 significantly decreased the UGTs contents of the LC-R aphids and increased mortality of R. padi exposure to the LC50 concentration of LC. This study provides a new view that UGTs are involved in LC resistance of R. padi. The findings will promote further work to detailed the functions of UGTs in the metabolism resistance of insects to insecticides.

The molecular mechanisms of insecticide resistance in aphid crop pests

Aphids are a group of hemipteran insects that include some of the world's most economically important agricultural pests. The control of pest aphids has relied heavily on the use of chemical insecticides, however, the evolution of resistance poses a serious threat to their sustainable control. Over 1000 cases of resistance have now been documented for aphids involving a remarkable diversity of mechanisms that, individually or in combination, allow the toxic effect of insecticides to be avoided or overcome. In addition to its applied importance as a growing threat to human food security, insecticide resistance in aphids also offers an exceptional opportunity to study evolution under strong selection and gain insight into the genetic variation fuelling rapid adaptation. In this review we summarise the biochemical and molecular mechanisms underlying resistance in the most economically important aphid pests worldwide and the insights study of this topic has provided on the genomic architecture of adaptive traits.

Chemosensory proteins are associated with thiamethoxam tolerance in bird cherry-oat aphid Rhopalosiphum padi

Rhopalosiphum padi (L.) is an important cosmopolitan pest of cereal crops. Thiamethoxam is widely used for control R. padi in some regions. Chemosensory proteins (CSPs) are a class of transporter proteins in arthropods which play a key role in various physiological processes including response to insecticide exposure. However, the role of R. padi CSPs (RpCSPs) in insecticide binding and susceptibility has not been well clarified. In this study, we found that the expression levels of RpCSP1, RpCSP4, RpCSP5, RpCSP7, RpCSP10 were dramatically upregulated after exposure to thiamethoxam. Suppression of RpCSP4 and RpCSP5 transcription by RNA interference significantly enhanced the susceptibility of R. padi to thiamethoxam. Molecular docking and fluorescence competitive binding showed that RpCSP4 and RpCSP5 had high binding affinity with thiamethoxam. The present results prove that RpCSP4 and RpCSP5 are related to insecticide resistance through high binding affinity to reduce the toxicity of insecticide.

Transcriptome Analysis to Identify Responsive Genes under Sublethal Concentration of Bifenazate in the Diamondback Moth, Plutella xylostella (Linnaeus, 1758) (Lepidoptera: Plutellidae)

Bifenazate is a novel acaricide that has been widely used to control spider mites. Interestingly, we found bifenazate had a biological activity against the diamondback moth (Plutella xylostella), one of the most economically important pests on crucifer crops around the world. However, the molecular mechanisms underlying the response of P. xylostella to bifenazate treatment are not clear. In this study, we first estimated the LC₃₀ dose of bifenazate for third-instar P. xylostella larvae. Then, in order to identify genes that respond to the treatment of this insecticide, the comparative transcriptome profiles were used to analyze the gene expression changes in P. xylostella larvae after exposure to LC₃₀ of bifenazate. In total, 757 differentially expressed genes (DEGs) between bifenazate-treated and control P. xylostella larvae were identified, in which 526 and 231 genes were up-regulated and down-regulated, respectively. The further Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis showed that the xenobiotics metabolisms pathway was significantly enriched, with ten detoxifying enzyme genes (four P450s, five glutathione S-transferases (GSTs), and one UDP-Glucuronosyltransferase (UGT)) were up-regulated, and their expression patterns were validated by qRT-PCR as well. Interestingly, the present results showed that 17 cuticular protein (CP) genes were also remarkably up-regulated, including 15 CPR family genes. Additionally, the oxidative phosphorylation pathway was found to be activated with eight mitochondrial genes up-regulated in bifenazate-treated larvae. In contrast, we found some genes that were involved in tyrosine metabolism and purine pathways were down-regulated, indicating these two pathways of bifenazate-exposed larvae were significantly inhibited. In conclusion, the present study would help us to better understand the molecular mechanisms of sublethal doses of bifenazate detoxification and action in P. xylostella.

Down-Regulation of P450 Genes Enhances Susceptibility to Indoxacarb and Alters Physiology and Development of Fall Armyworm, Spodoptera frugipreda (Lepidoptera: Noctuidae)

The fall armyworm (FAW), Spodoptera frugiperda (J.E. Smith), is a pest of many important crops globally. Effective control is challenging, with the pest exhibiting resistance to different synthetic pesticides across various groups. However, the mechanisms employed by resistant insects for overexpression of relevant detoxification genes remain unclear. The activity of detoxification enzymes was investigated in this study. Additionally, using RNA interference (RNAi), a functional analysis was completed of two P450s genes in an indoxacarb resistant population of fall armyworms. Elevated resistance levels (resistance ratio = 31.37-fold) in indoxacarb-selected populations of FAW were observed after 14 generations. The qRT-PCR showed higher expression of two cytochrome P450 genes, CYP321A7 and CYP6AE43, in this selected population compared to the control population. RNAi was applied to knock down the P450 dsCYP321A7 and dsCYP6AE43 genes in the FAW larvae. Droplet feeding of the dsRNAs (CYP321A7 and CYP6AE43) via an artificial diet significantly increased mortality rates in the indoxacarb treated population. A shorter larval developmental time of FAW was detected in all dsRNAs-fed larvae. Correspondingly, larval mass was reduced by dsRNAs in indoxacarb resistant populations of fall armyworm. Larval feeding assays demonstrate that dsRNAs targeting, specifically of CYP321A7 and CYP6AE43 enzymes, could be a beneficial technique in the management of indoxacarb resistant populations. Further study on the potential use of dsRNA and its application should be conducted in efforts to counter the development of resistance in FAW against various insecticides in the field.