P450s in plant–insect interactions

Physiological and transcriptomic responses of silkworms to graphene oxide exposure

The growing use of nanomaterials has sparked significant interest in assessing the insect toxicities of nanoparticles. The silkworm, as an economically important insect, serves as a promising model for studying how insects respond to harmful substances. Here, we conducted a comprehensive investigation on the impact of graphene oxide (GO) on silkworms using a combination of physiological and transcriptome analyses. GO can enter the midguts and posterior silk glands of silkworms. High GO concentrations (> 25 mg/L) significantly (P < 0.01) inhibited larval growth. Additionally, GO (> 5 mg/L) significantly reduced the cocooning rate, and GO (> 15 mg/L) hindered oviduct development and egg laying in silkworms. GO increased the reactive oxygen species content and regulated catalase activity, suggesting that it may affect insect growth by regulating reactive oxygen detoxification. The transcriptome data analysis showed that 35 metabolism-related genes and 20 ribosome biogenesis-related genes were differentially expressed in response to GO, and their expression levels were highly correlated. Finally, we propose that a Ribosome biogenesis-Metabolic signaling network is involved in responses to GO. The research provides a new perspective on the molecular responses of insects to GO.

Keap1 Negatively Regulates Transcription of Three Counter-Defense Genes and Susceptibility to Plant Toxin Gossypol in Helicoverpa armigera

Expressions of a wide range of cytoprotective counter-defense genes are mainly regulated by the Keap1-Nrf2-ARE signaling pathway in response to oxidative stress from xenobiotics. Gossypol is the major antiherbivore secondary metabolite of cotton, but how the polyphagous pest Helicoverpa armigera copes with this phytochemical to utilize its favorite host plant cotton remains largely elusive. In this study, we first suppressed the Keap1 gene in newly hatched larvae of cotton bollworm by feeding them the siRNA diet for 4 days. All of the larvae were subsequently fed the artificial diet supplied with gossypol or the control diet for 5 days. We identified that the knockdown of the Keap1 gene significantly decreased larval mortality and significantly increased the percentages of larval survival, reaching the fourth instar, compared with ncsiRNA when exposed to a diet containing gossypol. Three counter-defense genes CYP9A17, CYP4L11 and UGT41B3, which were related to the induction or metabolism of gossypol according to the report before, were all significantly up-regulated after the knockdown of the Keap1 gene. The Antioxidant Response Elements (AREs) were also detected in the promoter regions of the three counter-defense genes above. These data indicate that the suppression of the Keap1 gene activates the Keap1-Nrf2-ARE signaling pathway, up-regulates the expressions of counter-defense genes involved in the resistance of oxidative stress and finally contributes to reducing the susceptibility of gossypol. Our results provide more knowledge about the transcriptional regulation mechanisms of counter-defense genes that enable the cotton bollworm to adapt to the diversity of host plants including cotton.

Metabolomics-driven investigation of plant defense response against pest and pathogen attack

The advancement of metabolomics has assisted in the identification of various bewildering characteristics of the biological system. Metabolomics is a standard approach, facilitating crucial aspects of system biology with absolute quantification of metabolites using minimum samples, based on liquid/gas chromatography, mass spectrometry and nuclear magnetic resonance. The metabolome profiling has narrowed the wide gaps of missing information and has enhanced the understanding of a wide spectrum of plant-environment interactions by highlighting the complex pathways regulating biochemical reactions and cellular physiology under a particular set of conditions. This high throughput technique also plays a prominent role in combined analyses of plant metabolomics and other omics datasets. Plant metabolomics has opened a wide paradigm of opportunities for developing stress-tolerant plants, ensuring better food quality and quantity. However, despite advantageous methods and databases, the technique has a few limitations, such as ineffective 3D capturing of metabolites, low comprehensiveness, and lack of cell-based sampling. In the future, an expansion of plant-pathogen and plant-pest response towards the metabolite architecture is necessary to understand the intricacies of plant defence against invaders, elucidation of metabolic pathway operational during defence and developing a direct correlation between metabolites and biotic stresses. Our aim is to provide an overview of metabolomics and its utilities for the identification of biomarkers or key metabolites associated with biotic stress, devising improved diagnostic methods to efficiently assess pest and pathogen attack and generating improved crop varieties with the help of combined application of analytical and molecular tools.

RNA interference of NADPH-cytochrome P450 reductase increases the susceptibility of Aphis gossypii Glover to sulfoxaflor

NADPH-cytochrome P450 reductase (CPR) is essential for the detoxification of endogenous and exogenous substances mediated by cytochrome P450. While several insect CPRs have been found to be associated with insecticide resistance, the CPR of Aphis gossypii has not been characterized, and its functional role in insecticide resistance remains undefined. In this study, we cloned and characterized the full-length sequence of A. gossypii CPR (AgCPR). The deduced amino acid sequence of AgCPR contains all conserved domains of CPR, which shows high similarity to other insect CPRs and was clustered into a same branch of aphids according to phylogenetic analysis. The transcript of AgCPR was present in all developmental stages, with the highest expression in the adult stage. Furthermore, the expression of AgCPR could be induced by sulfoxaflor, a commonly used insecticide, in a time- and dose-dependent manner. Further silencing of AgCPR by feeding dsRNA significantly increased the susceptibility of A. gossypii to this insecticide. These findings suggest that AgCPR may play a significant role in the susceptibility of A. gossypii to sulfoxaflor and in the development of P450-mediated resistance to sulfoxaflor.

The genome sequence of a spider mite, Tetranychus truncatus, provides insights into interspecific host range variation and the genetic basis of adaptation to a low-quality host plant

The phytophagous mite Tetranychus truncatus is a serious pest in East Asia but has a relatively narrower host range than the pest mite Tetranychus urticae, which can feed on over 1200 plant species. Here, we generated a high-quality chromosomal level genome of T. truncatus and compared it with that of T. urticae, with an emphasis on the genes related to detoxification and chemoreception, to explore the genomic basis underlying the evolution of host range. We also conducted population genetics analyses (in 86 females from 10 populations) and host transfer experiments (in 4 populations) to investigate transcription changes following transfer to a low-quality host (Solanum melongena, eggplant), and we established possible connections between fitness on eggplant and genes related to detoxification and chemoreception. We found that T. truncatus has fewer genes related to detoxification, transport, and chemoreception than T. urticae, with a particularly strong reduction in gustatory receptor (GR) genes. We also found widespread transcriptional variation among T. truncatus populations, which varied in fitness on eggplant. We characterized selection on detoxification-related genes through ω values and found a negative correlation between expression levels and ω values. Based on the transcription results, as well as the fitness and genetic differences among populations, we identified genes potentially involved in adaptation to eggplant in T. truncatus. Our work provides a genomic resource for this pest mite and new insights into mechanisms underlying the adaptation of herbivorous mites to host plants.

Expression Analysis Reveals Differentially Expressed Genes in BPH and WBPH Associated with Resistance in Rice RILs Derived from a Cross between RP2068 and TN1

BPH (brown planthopper) and WBPH (white backed planthopper) are significant rice pests that often co-occur as sympatric species and cause substantial yield loss. Despite their genetic similarities, different host-resistance genes confer resistance against these two hoppers. The defense mechanisms in rice against these pests are complex, and the molecular processes regulating their responses remain largely unknown. This study used specific recombinant inbred lines (RILs) derived from a cross between rice varieties RP2068-18-3-5 (BPH- and WBPH-resistant) and TN1 (BPH- and WBPH-susceptible) to investigate the mechanisms of interaction between these planthoppers and their rice hosts. WBPH and BPH were allowed to feed on specific RILs, and RNA-Seq was carried out on WBPH insects. Transcriptome profiling and qRT-PCR results revealed differential expression of genes involved in detoxification, digestion, transportation, cuticle formation, splicing, and RNA processing. A higher expression of sugar transporters was observed in both hoppers feeding on rice with resistance against either hopper. This is the first comparative analysis of gene expressions in these insects fed on genetically similar hosts but with differential resistance to BPH and WBPH. These results complement our earlier findings on the differential gene expression of the same RILs (BPH- or WBPH-infested) utilized in this study. Moreover, identifying insect genes and pathways responsible for countering host defense would augment our understanding of BPH and WBPH interaction with their rice hosts and enable us to develop lasting strategies to control these significant pests.

Identification and functional study of detoxification-related genes in response to tolfenpyrad stress in Glyphodes pyloalis Walker (Lepidoptera: Pyralidae)

Glyphodes pyloalis Walker (G. pyloalis) is a common destructive mulberry pest. Due to the long-term and frequent use of insecticides, it has developed tolerance to commonly used insecticides. Tolfenpyrad (TFP) is a novel pyrazole heterocyclic insecticide. In order to understand the TFP detoxification mechanism of G. pyloalis larvae, we first estimated the LC30 dose of TFP for 3rd instar G. pyloalis larvae. Next, we identified genes that were differentially expressed in 3rd instar G. pyloalis larvae treated with TFP compared to the control group by transcriptome sequencing. In total, 86,949,569 and 67,442,028 clean reads were obtained from TFP-treated and control G. pyloalis larvae, respectively. A total of 5588 differentially expressed genes (DEGs) were identified in TFP-treated and control G. pyloalis larvae, of which 3084 genes were upregulated and 2504 genes were downregulated. We analyzed the expression of 43 candidate detoxification enzyme genes associated with insecticide tolerance using qPCR. According to the spatiotemporal expression pattern of DEGs, we found that CYP6ABE1, CYP333A36 and GST-epsilon8 were highly expressed in the midgut, while CarEs14 was strongly expressed in haemolymph. Furthermore, we successfully knocked down these genes by RNA interference. After silencing CYP6ABE1 and CYP333A36, bioassay showed that the mortality rate of TFP-treated G. pyloalis larvae was significantly higher compared to the control group. This study provides a theoretical foundation for understanding the sensitivity of G. pyloalis to TFP and establish the basis for the effective and green management of this pest.

Ecotoxicological effects of common fungicides on the eastern honeybee Apis cerana cerana (Hymenoptera)

The widespread use of fungicides for plant protection has increased the potential for pollinator exposure. This study therefore aimed at assessing the acute and chronic effects of fungicides on pollinators. For this purpose, the acute oral toxicity of the common fungicides azoxystrobin, pyraclostrobin, and boscalid to Eastern honeybee Apis cerana cerena was first evaluated, and the chronic effects on multiple aspects were investigated after exposure to a one-tenth medium lethal dose (LD₅₀) for 10 days. This study revealed that the LD₅₀ values of azoxystrobin, pyraclostrobin and boscalid for adult Eastern honeybees were 12.7 μg/bee, 36.6 μg/bee, and >119 μg/bee, respectively. Midgut epithelial cells revealed that fungicide exposure caused increased intercellular spaces and varying degrees of vacuolization. Exposure to these three fungicides and their binary mixtures significantly affected glycerophospholipid, alanine, aspartate, and glutamate metabolism in Eastern honeybee midguts. Additionally, the relative composition of Lactobacillus, the dominant functional genus in Eastern honeybee guts decreased and microbial balance was disrupted. All fungicides and their mixtures induced strong transcriptional upregulation of genes associated with the immune response and encoding enzymes related to oxidative phosphorylation and metabolism, including abaecin, apidaecin, hymenotaecin, cyp4c3, cyp6a2 and hbg3. Our study provides important insight for understanding the effects of commonly used fungicides on nontarget pollinator and contributes to a more comprehensive assessment of fungicide effects on ecological and environmental safety.

Combined PacBio Iso-Seq and Illumina RNA-Seq Analysis of the Tuta absoluta (Meyrick) Transcriptome and Cytochrome P450 Genes

Tuta absoluta (Meyrick) is a devastating invasive pest worldwide. The abamectin and chlorantraniliprole complex have become an alternative option for chemical control because they can enhance insecticidal activity and delay increased drug resistance. Notably, pests are inevitably resistant to various types of insecticides, and compound insecticides are no exception. To identify potential genes involved in the detoxification of abamectin and chlorantraniliprole complex in T. absoluta, PacBio SMRT-seq transcriptome sequencing and Illumina RNA-seq analysis of abamectin and chlorantraniliprole complex-treated T. absoluta were performed. We obtained 80,492 non-redundant transcripts, 62,762 (77.97%) transcripts that were successfully annotated, and 15,524 differentially expressed transcripts (DETs). GO annotation results showed that most of these DETs were involved in the biological processes of life-sustaining activities, such as cellular, metabolic, and single-organism processes. The KEGG pathway enrichment results showed that the pathways related to glutathione metabolism, fatty acid and amino acid synthesis, and metabolism were related to the response to abamectin and chlorantraniliprole complex in T. absoluta. Among these, 21 P450s were differentially expressed (11 upregulated and 10 downregulated). The qRT-PCR results for the eight upregulated P450 genes after abamectin and chlorantraniliprole complex treatment were consistent with the RNA-Seq data. Our findings provide new full-length transcriptional data and information for further studies on detoxification-related genes in T. absoluta.

RNAi-mediated silencing of AccCYP6k1 revealed its role in the metabolic detoxification of Apis cerana cerana

Insect cytochrome P450 monooxygenases (P450s or CYPs) perform important functions in the metabolic detoxification of both endogenous and exogenous substrates. However, the mechanism of action of the P450 genes in bees is unclear. In this study, we investigated the effects of AccCYP6k1 on the metabolism and detoxification of Apis cerana cerana. Spatiotemporal expression profiling revealed that the expression of AccCYP6k1 was the highest in foragers (A15) and was mainly expressed in the leg, midgut and head. RT-qPCR results showed that AccCYP6k1 exhibited different expression patterns following exposure to xenobiotics. In addition, silencing AccCYP6k1 increased the pesticides sensitivity and affected the detoxification system and antioxidant process of A. cerana cerana. In brief, the induced expression of AccCYP6k1 is related to the resistance of A. cerana cerana, while knockdown AccCYP6k1 affect the pesticides resistance and metabolic detoxification system of A. cerana cerana. These findings not only support the theoretical basis of metabolic detoxification in bees but also provide a better understanding of P450-mediated resistance to pesticides in insects.

Changes in life history parameters and transcriptome profile of Serangium japonicum associated with feeding on natural prey (Bemisia tabaci) and alternate host (Corcyra cephalonica eggs)

BACKGROUND

The mass production of natural predators with prolonged shelf life is a prerequisite for their field application as pest control agents. The traditional methods used for the mass production of Serangium japonicum rely heavily on the consistent supply of natural prey. This study explains the effects of B. tabaci (natural prey) and C. cephalonica eggs (alternative food) on life history and transcriptome profile of S. japanicum.

METHODS

This study compares the effects of B. tabaci (natural prey) and C. cephalonica eggs (alternative food) on biology, reproduction, and predatory efficacy, and transcriptome profile of S. japanicum.

RESULTS

This study revealed that S. japonicum was able to successfully complete its life cycle while feeding on B. tabaci (natural prey) and C. cephalonica eggs (alternative food). The C. cephalonica eggs fed S. japonicum individuals had longer developmental period and lower fecundity as compared to those feeding on whitefly but the survival rates (3rd instar nymphs, 4th instar nymphs and pupae) and predatory efficacy of C. cephalonica eggs fed S. japonicum individuals were significantly similar to to those feeding on whitefly.Transcriptome analysis showed that when faced with dietary changes, S. japanicum could successfully feed on C. cephalonica eggs by regulating genes related to nutrient transport, metabolism, and detoxification. Moreover, S. japanicum degraded excess cellular components through ribosomal autophagy and apoptosis, which provided sufficient materials and energy for survival and basic metabolism.

CONCLUSION

Corcyra cephalonica eggs can be used as an alternate host for the predator, Serangium japonicum, as the survival rates and predatory efficacy of the predator are similar to those feeding on the natural host (B.tabaci). When faced with dietary changes, S. japanicum could successfully feed on C. cephalonica eggs as revealed by upregulation of genes related to nutrient transport, metabolism, and detoxification. These findings are of great significance for studying the functional evolution of S. japonicum in response to dietary changes.

Ternary Mixture of Azoxystrobin, Boscalid and Pyraclostrobin Disrupts the Gut Microbiota and Metabolic Balance of Honeybees (Apis cerana cerana)

There is a growing risk of pollinators being exposed to multiple fungicides due to the widespread use of fungicides for plant protection. A safety assessment of honeybees exposed to multiple commonly used fungicides is urgently required. Therefore, the acute oral toxicity of the ternary mixed fungicide of ABP (azoxystrobin: boscalid: pyraclostrobin = 1:1:1, m/m/m) was tested on honeybees (Apis cerana cerana), and its sublethal effect on foragers’ guts was evaluated. The results showed that the acute oral median lethal concentration (LD50) of ABP for foragers was 12.6 μg a.i./bee. ABP caused disorder of the morphological structure of midgut tissue and affected the intestinal metabolism; the composition and structure of the intestinal microbial community was perturbed, which altered its function. Moreover, the transcripts of genes involved in detoxification and immunity were strongly upregulated with ABP treatment. The study implies that exposure to a fungicide mixture of ABP can cause a series of negative effects on the health of foragers. This work provides a comprehensive understanding of the comprehensive effects of common fungicides on non-target pollinators in the context of ecological risk assessment and the future use of fungicides in agriculture.

CYP6DW3 Metabolizes Imidacloprid to Imidacloprid-urea in Whitefly (Bemisia tabaci)

Bemisia tabaci has developed high resistance to many insecticides and causes substantial agricultural and economic losses annually. The insecticide resistance of whitefly has been widely reported in previous studies; however, the underlying mechanism remains little known. In this study, we cloned two P450 genes: CYP6DW3 and CYP6DW5v1; these genes were markedly overexpressed in imidacloprid-resistant whitefly populations compared with susceptible populations, and knockdown of these genes decreased the imidacloprid resistance of whitefly. Moreover, heterologous expression of whitefly P450 genes in SF9 cells and metabolic studies showed that the CYP6DW3 protein could metabolize 14.11% imidacloprid and produced imidacloprid-urea in vitro. Collectively, the expression levels of CYP6DW3 and CYP6DW5v1 are positively correlated with imidacloprid resistance in B. tabaci. Our study further reveals that cytochrome P450 enzymes affect the physiological activities related to resistance in insects, which helps scholars more deeply understand the resistance mechanism, and contributes to the development of integrated pest management framework.

Functional analysis of 3 genes in xenobiotic detoxification pathway of Bursaphelenchus xylophilus against matrine

Bursaphelenchus xylophilus is the causative agent of pine wilt disease. It has caused devastating damage to ecosystems worldwide, owing to the characteristic of being widely spread and uncontrollable. However, the current methods of control are mainly based on pesticides, which can cause irreversible damage to the ecosystem. Therefore, the search for new drug targets and the development of environmentally friendly nematicides is especially valuable. In this study, three key genes of the xenobiotic detoxification pathways were cloned from B. xylophilus, which were subsequently subjected to bioinformatic analysis. The bioassay experiment was carried out to determine the concentration of matrine required for further tests. Subsequently, enzyme activity detection and three gene expression pattern analysis were performed on matrine treated nematodes. Finally, RNA interference was conducted to verify the functions carried out by the three genes in combating matrine. The results indicated that cytochrome P450 and glutathione S-transferase of B. xylophilus were activated by matrine, which induced high expression of BxCYP33C4, BxGST1, and BxGST3. After RNA interference of three genes of B. xylophilus, the sensitivity of B. xylophilus to matrine was increased and the survival rate of nematodes was reduced to various degrees in comparison to the control group. Overall, the results fully demonstrated that BxCYP33C4, BxGST1, and BxGST3 are valuable drug targets for B. xylophilus. Furthermore, the results suggested that matrine has value for development and exploitation in the prevention and treatment of B. xylophilus.

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

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

Functional validation of CYP304A1 associated with haedoxan A detoxification in Aedes albopictus by RNAi and transgenic drosophila

BACKGROUND

Insect cytochrome P450 monooxygenases play important roles in the detoxification metabolism of endogenous and exogenous compounds. Haedoxan A (HA) from Phryma leptostachya L. is a highly efficient natural pesticide used to control houseflies and mosquitos. CYP4C21 and CYP304A1 were previously demonstrated to be transcriptionally increased in Aedes albopictus in response to HA exposure, but their involvement in HA metabolism is unknown.

RESULTS

Our data showed that CYP304A1 expression levels in A. albopictus were highest in third-instar larvae, and the expression level of CYP4C21 decreased significantly with the growth of instars, with the lowest occurring in the pupal stage. Compared with the control, the silencing of CYP304A1 and CYP4C21 genes by chitosan nanoparticle-mediated RNA interference could deplete 58.2% and 54.0% of the expression of corresponding genes, respectively. The bioassay data showed that knocking down the expression of CYP304A1 increased the mortality of A. albopictus when exposed to HA at LC₃₀ and LC₅₀ doses, but did not significantly increase mortality after silencing CYP4C21. Our data demonstrated that CYP304A1, but not CYP4C21, may be involved in HA detoxification. Moreover, the resistance ratio of CYP304A1 overexpressing flies was approximately 2-fold higher than that of the control line. The metabolized product of HA by CYP304A1 needs to be further confirmed by in vitro expression.

CONCLUSION

This finding showed that inducibility was not always linked to detoxifying capabilities, and enhanced our understanding of the molecular basis of HA metabolic detoxification in A. albopictus. © 2022 Society of Chemical Industry.

CYP4CJ6-mediated resistance to two neonicotinoid insecticides in Sitobion miscanthi (Takahashi)

The wheat aphid Sitobion miscanthi (CWA) is an important harmful pest in wheat fields. Insecticide application is the main method to effectively control wheat aphids. However, CWA has developed resistance to some insecticides due to its extensive application, and understanding resistance mechanisms is crucial for the management of CWA. In our study, a new P450 gene, CYP4CJ6, was identified from CWA and showed a positive response to imidacloprid and thiamethoxam. Transcription of CYP4CJ6 was significantly induced by both imidacloprid and thiamethoxam, and overexpression of CYP4CJ6 in the imidacloprid-resistant strain was also observed. The sensitivity of CWA to these two insecticides was increased after the knockdown of CYP4CJ6. These results indicated that CYP4CJ6 could be associated with CWA resistance to imidacloprid and thiamethoxam. Subsequently, the posttranscriptional regulatory mechanism was assessed, and miR-316 was confirmed to participate in the posttranscriptional regulation of CYP4CJ6. These results are crucial for clarifying the roles of P450 in the resistance of CWA to insecticides.

Knockdown of CYP6CR2 and CYP6DE5 reduces tolerance to host plant allelochemicals in the Chinese white pine beetle Dendroctonus armandi

Bark beetles rely on detoxifying enzymes to resist the defensive terpenoids of the host tree. Insect cytochrome P450 (CYPs) plays a key role in the detoxification of pesticides and plant allelochemicals. CYP6 family is unique to Insecta, and its biochemical function is basically related to the metabolism of exogenous substances. In this study, we sequenced and characterized the full-length cDNAs of two CYP6 genes from Chinese white pine beetle, Dendroctonus armandi. Spatiotemporal expression profiling revealed that the expression of CYP6CR2 and CYP6DE5 was higher in larval and adult stages of D. armandi than that in other developmental stages, and that two genes predominantly expressed in brain, midgut, fat body, Malpighian tubules or hemolymph. The expression of CYP6CR2 and CYP6DE5 was significantly induced after feeding on the phloem of Pinus armandii and exposure to six stimuli [(±)- α -pinene, (-)-α-pinene, (-)-β-pinene, (+)-3-carene, (±)-limonene and turpentine]. Importantly, silencing CYP6CR2 and CYP6DE5 separately could increase the sensitivity, led to a significant reduction of the activity of P450, resulting a significant increase in adult mortality after treatment with terpenoids. The comprehensive results of this study showed that in the process of host selection and colonization, the functions of CYPs were mainly to hydrolyze the chemical defense of the host and degrade odor molecules. These findings may help to develop new treatments to control this important pest.

Cytochrome P450 Genes Expressed in Phasmatodea Midguts

Cytochrome P450s (CYPs) are xenobiotic detoxification genes found in most eukaryotes, and linked in insects to the tolerance of plant secondary chemicals and insecticide resistance. The number and diversity of CYP clans, families, and subfamilies that an organism produces could correlate with its dietary breadth or specialization. This study examined the CYP diversity expressed in the midguts of six species of folivorous stick insects (Phasmatodea), to identify their CYP complement and see if any CYPs correlate with diet toxicity or specialization, and see what factors influenced their evolution in this insect order. CYP genes were mined from six published Phasmatodea transcriptomes and analyzed phylogenetically. The Phasmatodea CYP complement resembles that of other insects, though with relatively low numbers, and with significant expansions in the CYP clades 6J1, 6A13/14, 4C1, and 15A1. The CYP6 group is known to be the dominant CYP family in insects, but most insects have no more than one CYP15 gene, so the function of the multiple CYP15A1 genes in Phasmatodea is unknown, with neofunctionalization following gene duplication hypothesized. No correlation was found between CYPs and diet specialization or toxicity, with some CYP clades expanding within the Phasmatodea and others likely inherited from a common ancestor.

De Novo Transcription Responses Describe Host-Related Differentiation of Paracoccus marginatus (Hemiptera: Pseudococcidae)

Paracoccus marginatus (Hemiptera: Pseudococcidae) is an invasive pest with a diverse host range, strong diffusion, and high fecundity. It has been observed that P. marginatus feeding on Carica papaya have a higher survival rate, fecundity, and longer lifespan than P. marginatus feeding on Solanum tuberosum, indicating their successful adaptation to C. papaya; however, the mechanisms underlying host plant adaptation remain unclear. Therefore, RNA-seq was performed to study the transcriptional responses of P. marginatus feeding on C. papaya and S. tuberosum plants. A total of 408 genes with significant differential expression were defined; most of them were downregulated in S. tuberosum, including those of digestive enzymes, detoxifying enzymes, ribosomes, and reproductive-related genes, which may result from the adaptation of the host to nutritional needs and changes in toxic chemical levels. Enrichment analysis of the Kyoto Encyclopedia of Genes and Genomes showed that lysosome and longevity regulating pathways related to digestion, detoxification, and longevity were enriched. We suggest that C. papaya is a more suitable host than S. tuberosum, and downregulated target genes may have important effects on the adaptation of P. marginatus to host transfer.

Transcriptome analysis of Mythimna separata: De novo assembly and detection of genes related to beta-cypermethrin resistance

The oriental armyworm Mythimna separata (Walker) is a devastating pest of cereal crops mainly in Asia and Oceania and recently become resistant to beta-cypermethrin (beta-CP). However, molecular biological studies of its response to beta-CP are scarce, and related genomic information is not available. In this study, we sequenced and de novo assembled the transcriptome of beta-CP susceptible M. separata (MsS-whole, abbr. MsS-W). A total of 30,486 unigenes were obtained, with an N50 length of 506 bp. A number of 21,051 unigenes were matched to public databases, of which 10,107 were classified into 59 gene ontology subcategories, 5792 were assigned into 25 clusters of orthologous groups of proteins subgroups and 12,123 were assigned to 257 Kyoto Encyclopedia of Genes and Genomes pathways. A total of 729 simple sequence repeats were detected. In addition, a total of 323 cytochrome P450-associated sequences from nine lepidopterous species, of which 130 were from M. separata, were analyzed using the maximum likelihood method and Bayesian inference. Among the 130 cytochrome P450-associated sequences from M. separata, 60 were dropped into CYP3 clan, which is associated with metabolizing xenobiotics and plant natural compounds. Furthermore, the beta-CP susceptible (MsS-2) and resistant (MsR-2) M. separata population transcriptomes were sequenced. Certain critical genes involved in beta-CP detoxification were detected and verified by quantitative real-time polymerase chain reaction. Collectively, our results provided a basis for further studies of the molecular mechanism of insecticide resistance in M. separata.

Family dinner: Transcriptional plasticity of five Noctuidae (Lepidoptera) feeding on three host plant species

Polyphagous insects often show specialization in feeding on different host plants in terms of survival and growth and, therefore, can be considered minor or major pests of particular hosts. Whether polyphagous insects employ a common transcriptional response to cope with defenses from diverse host plants is under‐studied. We focused on patterns of transcriptional plasticity in polyphagous moths (Noctuidae), of which many species are notorious pests, in relation to herbivore performance on different host plants. We compared the transcriptional plasticity of five polyphagous moth species feeding and developing on three different host plant species. Using a comparative phylogenetic framework, we evaluated if successful herbivory, as measured by larval performance, is determined by a shared or lineage‐specific transcriptional response. The upregulated transcriptional activity, or gene expression pattern, of larvae feeding on the different host plants and artificial control diet was highly plastic and moth species‐specific. Specialization, defined as high herbivore success for specific host plants, was not generally linked to a lower number of induced genes. Moths that were more distantly related and showing high herbivore success for certain host plants showed shared expression of multiple homologous genes, indicating convergence. We further observed specific transcriptional responses within phylogenetic lineages. These expression patterns for specific host plant species are likely caused by shared evolutionary histories, for example, symplesiomorphic patterns, and could therefore not be associated with herbivore success alone. Multiple gene families, with roles in plant digestion and detoxification, were widely expressed in response to host plant feeding but again showed highly moth species‐specific. Consequently, high herbivore success for specific host plants is also driven by species‐specific transcriptional plasticity. Thus, potential pest moths display a complex and species‐specific transcriptional plasticity.

Three cytochrome P450 CYP4 family genes regulated by the CncC signaling pathway mediate phytochemical susceptibility in the red flour beetle, Tribolium castaneum

BACKGROUND

Insect cytochrome P450 monooxygenases (P450s) play a crucial role in phytochemical metabolism and tolerance. Three P450 genes (TcCYP4Q3, TcCYP4Q5, and TcCYP4Q7) are associated with the response of eugenol in Tribolium castaneum. However, the responding mechanisms of these P450 genes to eugenol remain unknown.

RESULTS

Here, spatiotemporal expression profiling revealed that TcCYP4Q3 and TcCYP4Q5 were most highly expressed in late adult, while TcCYP4Q7 was predominantly expressed in late larva; and all of these three P450 genes were mainly expressed in the fat body of larvae. Furthermore, the expressions of these three P450 genes were significantly up-regulated after exposure to eugenol, and depletion of them enhanced the susceptibility of beetles to eugenol. Interestingly, RNA interference (RNAi) against the CncC gene, a transcription factor of CncC signaling pathway associated with regulation of insect P450s in response to phytochemicals, reduced the transcripts of these three P450 genes following exposure to eugenol. Investigation of CncC signaling pathway showed that this pathway could be activated by eugenol.

CONCLUSION

Altogether, the results indicate that these three P450 genes are regulated by CncC signaling pathway to participate in the susceptibility of Tribolium castaneum to phytochemicals. These findings will aid implications for the development of novel therapeutics to control pest. © 2022 Society of Chemical Industry.

Mammalian cytochrome P450 biodiversity: Physiological importance, function, and protein and genomic structures of cytochromes P4502B in multiple species of woodrats with different dietary preferences

The vast diversity of cytochrome P450 enzymes in mammals has been proposed to result in large measure from plant-animal warfare, whereby evolution of chemical defenses such as phenolics and terpenoids in plants led to duplication and divergence of P450 genes in herbivores. Over evolutionary time, natural selection is predicted to have produced P450s with high affinity and enhanced metabolism of substrates that are ingested regularly by herbivores. Interestingly, however, almost all knowledge of the interactions of mammalian P450 enzymes with substrates stems from studies of the metabolism of drugs and model compounds rather than studies on wild mammalian herbivores and their respective PSMs. A question of particular interest centers on the role of individual P450 enzymes in the ability of certain herbivores to specialize on plants that are lethal to most other species, including those from the same genus as the specialists. We tackled this intricate problem using a tractable natural system (herbivorous woodrats, genus Neotoma) focusing on comparisons of the specialist N. stephensi, the facultative specialist N. lepida, and the generalist N. albigula, and employing a cross-disciplinary approach involving ecology, biochemistry, pharmacology, structural biology, and genomics. Based on multiple findings suggesting the importance of CYP2B enzymes for ingestion of juniper and a major constituent, α-pinene, we characterized the structure, function and activity of several CYP2B enzymes in woodrats with different dietary habits. Results to date suggest that differences in CYP2B gene copy number may contribute to differential tolerance of PSMs among woodrat species, although additional work is warranted to firmly link gene copy number to juniper tolerance.

Overexpression of Multiple Cytochrome P450 Genes Conferring Clothianidin Resistance in Bradysia odoriphaga

Cytochrome P450 monooxygenases (P450s) play important roles in the detoxification metabolism of xenobiotics and are involved in the resistance of insects to many insecticides. In this study, piperonyl butoxide (PBO), an inhibitor of P450 enzyme activity, significantly increased the toxicity of clothianidin in the clothianidin-resistant (CL-R) population of Bradysia odoriphaga. The enzyme activity of P450 in the CL-R population was significantly higher than that in the SS population. Furthermore, four P450 genes were found to be significantly overexpressed in the CL-R population. Tissue-specific expression analysis indicates that CYP9J57, CYP3828A1, CYP6SX1, and CYP6QE1 were most highly expressed in the midgut and/or Malpighian tubules. After exposure to LC₃₀ of clothianidin, the expression levels of the four P450 genes were significantly upregulated. The RNAi-mediated knockdown of CYP9J57, CYP3828A1, and CYP6QE1 significantly increased the susceptibility of B. odoriphaga to clothianidin. These results suggest that P450 genes are involved in clothianidin resistance in B. odoriphaga. This provides a better understanding of P450-mediated clothianidin resistance in B. odoriphaga and will contribute to the management of insect resistance to insecticides.

Review of molecular and biochemical responses during stress induced stimulation and hormesis in insects

The biphasic hormetic response to stress, defined by low-dose stimulation and high-dose inhibition is frequently observed in insects. Various molecular and biochemical responses associated with hormesis in insects have been reported in many studies, but no synthesis of all these findings has been undertaken. We conducted a systematic literature review, analyzing papers demonstrating phenotypic stimulatory effect(s) following exposure to stress where molecular or biochemical response(s) were also examined. Responses observed included stimulation of reproduction, survival and longevity, growth and development, and tolerance to temperature, chemical, or starvation and desiccation, in response to stressors including pesticides, oxidative stress, temperature, crowding and starvation, and radiation. Phenotypic stimulation ranged from <25% increased above controls to >100%. Reproductive stimulation was frequently <25% increased above controls, while stimulated temperature tolerance was frequently >100% increased. Molecular and biochemical responses had obvious direct connections to phenotypic responses in many cases, although not in all instances. Increased expression of heat shock proteins occurred in association with stimulated temperature tolerance, and increased expression of detoxification genes with stimulated pesticide or chemical tolerance, but also stimulated reproduction. Changes in the expression or activity of antioxidants were frequently associated with stimulation of longevity and reproduction. Stress induced changes in vitellogenin and juvenile hormone and genes in the IIS/TOR signalling pathway - which are directly responsible for regulating growth, development, and reproduction - were also reported. Our analysis showed that coordination of expression of genes or proteins associated with protection from oxidative stress and DNA and protein damage is important in the hormetic responses of insects.

Caterpillar-Induced Rice Volatile (E)-β-Farnesene Impairs the Development and Survival of Chilo suppressalis Larvae by Disrupting Insect Hormone Balance

Significant research progress has recently been made on establishing the roles of tps46 in rice defense. (E)-β-farnesene (Eβf) is a major product of tps46 activity but its physiological functions and potential mechanisms against Chilo suppressalis have not yet been clarified. In the present study, C. suppressalis larvae were artificially fed a diet containing 0.8 g/kg Eβf and the physiological performance of the larvae was evaluated. In response to Eβf treatment, the average 2nd instar duration significantly increased from 4.78 d to 6.31 d while that of the 3rd instar significantly increased from 5.70 d to 8.00 d compared with the control. There were no significant differences between the control and Eβf-fed 4th and 5th instars in terms of their durations. The mortalities of the 2nd and 3rd Eβf-fed instars were 21.00-fold and 6.39-fold higher, respectively, than that of the control. A comparative transcriptome analysis revealed that multiple differentially expressed genes are involved in insect hormone biosynthesis. An insect hormone assay on the 3rd instars disclosed that Eβf disrupted the balance between the juvenile hormone and ecdysteroid levels. Eβf treatment increased the juvenile hormones titers but not those of the ecdysteroids. The qPCR results were consistent with those of the RNA-Seq. The foregoing findings suggested that Eβf impairs development and survival in C. suppressalis larvae by disrupting their hormone balance. Moreover, Eβf altered the pathways associated with carbohydrate and xenobiotic metabolism as well as those related to cofactors and vitamins in C. suppressalis larvae. The discoveries of this study may contribute to the development and implementation of an integrated control system for C. suppressalis infestations in rice.

Transcriptomic profile of the predatory mite Amblyseius swirskii (Acari: Phytoseiidae) on different host plants

Amblyseius swirskii Athias-Henriot (Acari: Phytoseiidae) is a predatory mite, effective at controlling whiteflies and thrips in protected crops. However, on tomato its efficacy as a biocontrol agent is hindered, most probably by the plant trichomes and their exudates. Our aim was to characterize the response of A. swirskii to the tomato trichome exudates and identify three major detoxification gene sets in this species: cytochromes P450 (CYPs), glutathione S-transferases (GSTs) and carboxyl/cholinesterases (CCEs). Mites were exposed separately to tomato and pepper, a favourable host plant for A. swirskii, after which their transcriptional responses were analysed and compared. The de novo transcriptome assembly resulted in 71,336 unigenes with 66.1% of them annotated. Thirty-nine A. swirskii genes were differentially expressed after transfer on tomato leaves when compared to pepper leaves; some of the expressed genes were associated with the metabolism of tomato exudates. Our results illustrate that the detoxification gene sets CYPs, GSTs and CCEs are abundant in A. swirskii, but do not play a significant role when in contact with the tomato exudates.

The phylogenetic and evolutionary analyses of detoxification gene families in Aphidinae species

Detoxification enzymes play significant roles in the interactions between insects and host plants, wherein detoxification-related genes make great contributions. As herbivorous pests, aphids reproduce rapidly due to parthenogenesis. They are good biological materials for studying the mechanisms that allow insect adaptation to host plants. Insect detoxification gene families are associated with insect adaptation to host plants. The Aphidinae is the largest subfamily in the Aphididae with at least 2483 species in 256 genera in 2 tribes: the Macrosiphini (with 3/4 of the species) and the Aphidini. Most aphid pests on crops and ornamental plants are Aphidinae. Members of the Aphidinae occur in nearly every region of the world. The body shape and colour vary significantly. To research the role that detoxification gene families played in the process of aphid adaptation to host evolution, we analyzed the phylogeny and evolution of these detoxification gene families in Aphidinae. In general, the P450/GST/CCE gene families contract, whereas the ABC/UGT families are conserved in Aphidinae species compared to these families in other herbivorous insects. Genus-specific expansions of P450 CYP4, and GST Delta have occurred in the genus Acyrthosiphon. In addition, the evolutionary rates of five detoxification gene families in the evolution process of Aphidinae are different. The comparison of five detoxification gene families among nine Aphidinae species and the estimated relative evolutionary rates provided herein support an understanding of the interaction between and the co-evolution of Aphidinae and plants.

Biochemical profiling of functionally expressed CYP6P9 variants of the malaria vector Anopheles funestus with special reference to cytochrome b5 and its role in pyrethroid and coumarin substrate metabolism

Cytochrome P450 monooxygenases (P450s) are well studied enzymes catalyzing the oxidative metabolism of xenobiotics in insects including mosquitoes. Their duplication and upregulation in agricultural and public health pests such as anopheline mosquitoes often leads to an enhanced metabolism of insecticides which confers resistance. In the laboratory strain Anopheles funestus FUMOZ-R the duplicated P450s CYP6P9a and CYP6P9b are highly upregulated and proven to confer pyrethroid resistance. Microsomal P450 activity is regulated by NADPH cytochrome P450 oxidoreductase (CPR) required for electron transfer, whereas the modulatory role of cytochrome b₅ (CYB5) on insect P450 activity is less clear. In previous studies CYP6P9a and CYP6P9b were recombinantly expressed in tandem with An. gambiae CPR using E. coli-expression systems and CYB5 added to the reaction mix to enhance activity. However, the precise role of CYB5 on substrate turn-over when combined with CYP6P9a and CYP6P9b remains poorly investigated, thus one objective of our study was to address this knowledge gap. In contrast to the CYP6P9 variants, the expression levels of both CYB5 and CPR were not upregulated in the pyrethroid resistant FUMOZ-R strain when compared to the susceptible FANG strain, suggesting no immediate regulatory role of these genes in pyrethroid resistance in FUMOZ-R. Here, for the first time we recombinantly expressed CYP6P9a and CYP6P9b from An. funestus in a baculovirus expression system using High-5 insect cells. Co-expression of each enzyme with CPR from either An. gambiae or An. funestus did not reveal noteworthy differences in catalytic capacity. Whereas the co-expression of An. funestus CYB5 - tested at different multiplicity of infection (MOI) ratios - resulted in a significantly higher metabolization of coumarin substrates as measured by fluorescence assays. This was confirmed by Michaelis-Menten kinetics using the most active substrate, 7-benzyloxymethoxy-4-trifluoromethylcoumarin (BOMFC). We observed a similar increase in coumarin substrate turnover by adding human CYB5 to the reaction mix. Finally, we compared by UPLC-MS/MS analysis the depletion rate of deltamethrin and the formation of 4'OH-deltamethrin by recombinantly expressed CYP6P9a and CYP6P9b with and without CYB5 and detected no difference in the extent of deltamethrin metabolism. Our results suggest that co-expression (or addition) of CYB5 with CYP6P9 variants, recombinantly expressed in insect cells, can significantly enhance their metabolic capacity to oxidize coumarins, but not deltamethrin.

Transcriptomic analysis of salivary gland and proteomic analysis of oral secretion in Helicoverpa armigera under cotton plant leaves, gossypol, and tannin stresses

Gossypol and tannin are involved in important chemical defense processes in cotton plants. In this study, we used transcriptomics and proteomics to explore the changes in salivary gland functional genes and oral secretion (OS) proteins after feeding with artificial diet (containing gossypols and tannins) and cotton plant leaves. We found that dietary cotton plant leaves, gossypols and tannins exerted adverse impacts on the genes that regulated the functions of peptidase, GTPase, glycosyl hydrolases in the salivary glands of the Helicoverpa armigera (H. armigera). However, GST, UGT, hydrolases, and lipase genes were up-regulated to participate in the detoxification and digestive of H. armigera. The oral secretory proteins of H. armigera were significantly inhibited under the stress of gossypol and tannin, such as enzyme activity, but some proteins (such as PZC71358.1) were up-regulated and involved in immune and digestive functions. The combined analysis of transcriptomics and metabolomics showed a weak correlation, and the genes and proteins involved were mainly in digestive enzyme activities. Our work clarifies the deleterious physiological impacts of gossypols and tannins on H. armigera and reveals the mechanism by which H. armigera effectively mitigate the phytotoxic effects through detoxification and immune systems.

Expanding the Menu: Are Polyphagy and Gene Family Expansions Linked across Lepidoptera?

Evolutionary expansions and contractions of gene families are often correlated with key innovations and/or ecological characteristics. In butterflies and moths (Lepidoptera), expansions of gene families involved in detoxification of plant specialized metabolites are hypothesized to facilitate a polyphagous feeding style. However, analyses supporting this hypothesis are mostly based on a limited number of lepidopteran species. We applied a phylogenomics approach, using 37 lepidopteran genomes, to analyze if gene family evolution (gene gain and loss) is associated with the evolution of polyphagy. Specifically, we compared gene counts and evolutionary gene gain and loss rates of gene families involved in adaptations with plant feeding. We correlated gene evolution to host plant family range (phylogenetic diversity) and specialized metabolite content of plant families (functional metabolite diversity). We found a higher rate for gene loss than gene gain in Lepidoptera, a potential consequence of genomic rearrangements and deletions after (potentially small-scale) duplication events. Gene family expansions and contractions varied across lepidopteran families, and were associated to host plant use and specialization levels. Within the family Noctuidae, a higher expansion rate for gene families involved in detoxification can be related to the large number of polyphagous species. However, gene family expansions are observed in both polyphagous and monophagous lepidopteran species and thus seem to be species-specific in the taxa sampled. Nevertheless, a significant positive correlation of gene counts of the carboxyl- and choline esterase and glutathione-S-transferase detoxification gene families with the level of polyphagy was identified across Lepidoptera.

A Comprehensive Analysis of Calmodulin-Like Proteins of Glycine max Indicates Their Role in Calcium Signaling and Plant Defense Against Insect Attack

The calcium (Ca²⁺) signaling is a crucial event during plant-herbivore interaction, which involves a transient change in cytosolic Ca²⁺ concentration, which is sensed by Ca²⁺-sensors, and the received message is transduced to downstream target proteins leading to appropriate defense response. Calmodulin-like proteins (CMLs) are calcium-sensing plant-specific proteins. Although CMLs have been identified in a few plants, they remained uncharacterized in leguminous crop plants. Therefore, a wide-range analysis of CMLs of soybean was performed, which identified 41 true CMLs with greater than 50% similarity with Arabidopsis CMLs. The phylogenetic study revealed their evolutionary relatedness with known CMLs. Further, the identification of conserved motifs, gene structure analysis, and identification of cis-acting elements strongly supported their identity as members of this family and their involvement in stress responses. Only a few Glycine max CMLs (GmCMLs) exhibited differential expression in different tissue types, and rest of them had minimal expression. Additionally, differential expression patterns of GmCMLs were observed during Spodoptera litura-feeding, wounding, and signaling compound treatments, indicating their role in plant defense. The three-dimensional structure prediction, identification of interactive domains, and docking with Ca²⁺ ions of S. litura-inducible GmCMLs, indicated their identity as calcium sensors. This study on the characterization of GmCMLs provided insights into their roles in calcium signaling and plant defense during herbivory.

Molecular characterization and functional analysis of cytochrome P450-mediated detoxification CYP302A1 gene involved in host plant adaptation in Spodoptera frugieprda

The fall armyworm (FAW) Spodoptera frugiperda is a destructive and polyphagous pest of many essential food crops including maize and rice. The FAW is hard to manage, control, or eradicate, due to its polyphagous nature and voracity of feeding. Here, we report the characterization and functional analysis of the detoxification gene CYP302A1 and how S. frugieprda larvae use a detoxification mechanism to adapt host plants. Results demonstrated that CYP302A1 expression levels were much higher in midgut tissue and the older S. frugiperda larvae. Our current studies revealed the enhanced P450 activity in the midguts of S. frugiperda larvae after exposure to rice plants as compared to corn plants and an artificial diet. Furthermore, higher mortality was observed in PBO treated larvae followed by the exposure of rice plants as compared to the corn plant. The dsRNA-fed larvae showed downregulation of CYP302A1 gene in the midgut. At the same time, higher mortality, reduced larval weight and shorter developmental time was observed in the dsRNA-fed larvae followed by the exposure of rice plant as compared to the corn plant and DEPC-water treated plants as a control. These results concluded that the inducible P450 enzyme system and related genes could provide herbivores with an ecological opportunity to adapt to diverse host plants by utilizing secondary compounds present in their host plants.

Metabolic-based insecticide resistance mechanism and ecofriendly approaches for controlling of beet armyworm Spodoptera exigua: a review

The beet army worm, Spodoptera exigua, is a widely distributed polyphagous pest of economically important crops worldwide. The management of this pest insect continues to face many challenges. Despite synthetic chemicals posing a serious threat to the environment, these remain the conventional approach for controlling S. exigua in the field. An over-reliance on chemical control has not only led to selection for resistance to insecticides and to a reduction of natural enemies, but has also polluted various components of ecosystem. Given these increasing pressures on the ecosystem, there is a need to implement integrated pest management (IPM) approaches exploiting a wider range of tools (biotechnological approaches, microbial control, biological control, cultural control, and use of host plant resistance) for an alternative to chemical control. The IPM approach can not only reduce the hazard of chemical residues in the environment and associated health problems, but may also provide best strategies to control insect pests. This review synthesizes published information on insecticide resistance of S. exigua and explores alternative IPM approaches to control S. exigua.

Silencing of cytochrome P450 gene CYP321A1 effects tannin detoxification and metabolism in Spodoptera litura

Cytochrome P450 monooxygenase (P450 or CYP) plays an important role in the metabolism of insecticides and plant allelochemicals by insects. CYP321B1, a novel Spodoptera litura P450 gene, was identified and characterized. CYP321B1 contains a 1488 bp open reading frame (ORF) that encodes a 495 amino acid protein. In fourth instar larvae, the highest CYP321B1 expression levels were found in the midgut and fat body. In the tannin feeding test, tannin can significantly induce the expression of CYP321B1 in the midgut and fat body of 4th instar larvae. To verify the function of CYP321B1, RNA interference and metabolome analysis were performed. The results showed that silencing CYP321B1 significantly reduced the rate of weight gain under tannin induction. Metabolome analysis showed silencing affected 47 different metabolites, mainly involved in secondary metabolite biosynthesis and amino acid metabolism, including amino acids, lipid fatty acids, organic acids and their derivatives. Henoxyacetic acid and cysteamine are the most highly regulated metabolites, respectively. These findings demonstrate that CYP321B1 plays an important role in tannin detoxification and metabolism. Functional knowledge about metabolite detoxification genes in this major herbivorous insect pest can provide new insights into this biological process and provide new targets for agricultural pest control.

Rapid specialization of counter defenses enables two-spotted spider mite to adapt to novel plant hosts

Genetic adaptation, occurring over a long evolutionary time, enables host-specialized herbivores to develop novel resistance traits and to efficiently counteract the defenses of a narrow range of host plants. In contrast, physiological acclimation, leading to the suppression and/or detoxification of host defenses, is hypothesized to enable broad generalists to shift between plant hosts. However, the host adaptation mechanisms used by generalists composed of host-adapted populations are not known. Two-spotted spider mite (TSSM; Tetranychus urticae) is an extreme generalist herbivore whose individual populations perform well only on a subset of potential hosts. We combined experimental evolution, Arabidopsis thaliana genetics, mite reverse genetics, and pharmacological approaches to examine mite host adaptation upon the shift of a bean (Phaseolus vulgaris)-adapted population to Arabidopsis. We showed that cytochrome P450 monooxygenases are required for mite adaptation to Arabidopsis. We identified activities of two tiers of P450s: general xenobiotic-responsive P450s that have a limited contribution to mite adaptation to Arabidopsis and adaptation-associated P450s that efficiently counteract Arabidopsis defenses. In approximately 25 generations of mite selection on Arabidopsis plants, mites evolved highly efficient detoxification-based adaptation, characteristic of specialist herbivores. This demonstrates that specialization to plant resistance traits can occur within the ecological timescale, enabling the TSSM to shift to novel plant hosts.

Construction and analysis of the protein-protein interaction network for the detoxification enzymes of the silkworm, Bombyx mori

Detoxification enzymes are necessary for insects to metabolize toxic substances and maintain physiological activities. Cytochromes P450 (CYPs), glutathione S-transferases (GSTs), and carboxylesterase (CarEs) are the main detoxification enzymes in insects. In addition, UDP-glucosyltransferase and ATP-binding cassette transporter also participate in the process of material metabolism. This study collected proteins related to detoxification in the silkworm, Bombyx mori (Lepidoptera: Bombycidae). And we performed Gene Ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis on these proteins to understand their biological function. We constructed the protein-protein interaction network for the silkworm's detoxification enzymes and analyzed the network's topological properties. We found that BGIBMGA014046-TA, BGIBMGA003221-TA, BGIBMGA011092-TA, BGIBMGA000074-TA, and LOC732976 are the essential proteins in the network. These proteins are primarily involved in the process of ribosome biogenesis and may be related to protein synthesis. We integrated GO, KEGG, and network analysis and found that ribosome-associated protein and GSTs played a vital role in the detoxification process.

Effects of elevated CO2 treatment of Populus davidiana × P. bolleana on growth and detoxifying enzymes in gypsy moth, Lymantria dispar

To date, elevated CO₂ concentrations in the environment caused by various human activities influence diverse areas of life, including the interactions between insects and plants. The Lymantria dispar is one of the most severely destructive pests, which further could inflict ecological and economical damage. In this experiment, one-year-old Populus davidiana × P. bolleana plants were grown in CO₂-enhanced environments for one month at three different CO₂ concentrations: 397 ppm (atmospheric CO₂ concentration), 550 ppm and 750 ppm (two predicted elevated CO₂ concentrations). The 3rd instar L. dispar larvae then fed on the treated poplar seedlings covered in a nylon bag. The L. dispar larvae fed on poplar seedling treated for 96 h showed the highest growth rate at all CO₂ concentrations. Enzymatic activity of treated larvae showed the highest GST and P450 activity at 750 ppm CO₂. The relative expressions of seven CYP and ten GST genes in L. dispar larvae were analyzed quantitatively using real-time RT-PCR, which the results were expressed variably. Compared to 397 ppm CO₂, the expression of CYP4L23 was down-regulated, while the expressions of other CYP genes were up-regulated. Meanwhile, only GSTo1 gene showed down-regulated at 48 h and 96 h in 750 ppm CO₂ treatment, while GST expression level for the other nine GST genes showed up-regulated at 48 h and 72 h. These results offer the insight into plant-insect interactions under global climate change and furthermore will provide essential information for strategic pest control based on biochemical and molecular levels changes in gypsy moths.

A new P450 involved in the furanocoumarin pathway underlies a recent case of convergent evolution

Furanocoumarins are phytoalexins often cited as an example to illustrate the arms race between plants and herbivorous insects. They are distributed in a limited number of phylogenetically distant plant lineages, but synthesized through a similar pathway, which raised the question of a unique or multiple emergence in higher plants. The furanocoumarin pathway was investigated in the fig tree (Ficus carica, Moraceae). Transcriptomic and metabolomic approaches led to the identification of CYP76F112, a cytochrome P450 catalyzing an original reaction. CYP76F112 emergence was inquired using phylogenetics combined with in silico modeling and site-directed mutagenesis. CYP76F112 was found to convert demethylsuberosin into marmesin with a very high affinity. This atypical cyclization reaction represents a key step within the polyphenol biosynthesis pathway. CYP76F112 evolutionary patterns suggests that the marmesin synthase activity appeared recently in the Moraceae family, through a lineage-specific expansion and diversification. The characterization of CYP76F112 as the first known marmesin synthase opens new prospects for the use of the furanocoumarin pathway. It also supports the multiple acquisition of furanocoumarin in angiosperms by convergent evolution, and opens new perspectives regarding the ability of cytochromes P450 to evolve new functions related to plant adaptation to their environment.

Functional validation of key cytochrome P450 monooxygenase and UDP-glycosyltransferase genes conferring cyantraniliprole resistance in Aphis gossypii Glover

Cytochrome P450 monooxygenases (P450s) and UDP-glycosyltransferases (UGTs) are major detoxifying enzymes that metabolize plant toxins and insecticides. In the present study, the synergists of piperonyl butoxide, sulfinpyrazone and 5-nitrouracil significantly increased cyantraniliprole and α-cypermethrin toxicity against the resistant strain. The transcripts of UGT341A4, UGT344B4, UGT344D6, UGT344J2 and UGT344M2 increased significantly in the CyR strain compared with the susceptible strain. Among these upregulated genes (including P450s), CYP6CY7 and UGT344B4 were highly expressed in the midgut. Transgenic expression of the P450 and UGT genes in broad body tissues in Drosophila melanogaster indicated that the expression of CYP380C6, CYP4CJ1, UGT341A4, UGT344B4 and UGT344M2 is sufficient to confer cyantraniliprole resistance, and CYP380C6, CYP6CY7, CYP6CY21, UGT341A4 and UGT344M2 are related to α-cypermethrin cross-resistance. The midgut-specific overexpression of CYP380C6, CYP6CY7, CYP6CY21, CYP4CJ1, UGT341A4, UGT344B4 and UGT344M2 significantly increased insensitivity to cyantraniliprole, and CYP380C6, CYP6CY7, CYP6CY21, UGT344B4 and UGT344M2 confer α-cypermethrin cross-resistance. The expression of CYP380C6, CYP4CJ1, UGT341A4 and UGT344M2 in broad tissues or in midgut has similar effects on insensitivity to insecticides; however, CYP6CY7, CYP6CY21 and UGT344B4 are more effective in the midgut. This result indicates that broad body tissues and midgut tissue are involved in insecticide resistance mediated by the candidate P450s and UGTs examined.

Comparative analyses of transcriptional responses of Dectes texanus LeConte (Coleoptera: Cerambycidae) larvae fed on three different host plants and artificial diet

Dectes texanus is an important coleopteran pest of soybeans and cultivated sunflowers in the Midwestern United States that causes yield losses by girdling stems of their host plants. Although sunflower and giant ragweed are primary hosts of D. texanus, they began colonizing soybeans approximately 50 years ago and no reliable management method has been established to prevent or reduce losses by this pest. To identify genes putatively involved when feeding soybean, we compared gene expression of D. texanus third-instar larvae fed soybean to those fed sunflower, giant ragweed, or artificial diet. Dectes texanus larvae differentially expressed 514 unigenes when fed on soybean compared to those fed the other diet treatments. Enrichment analyses of gene ontology terms from up-regulated unigenes in soybean-fed larvae compared to those fed both primary hosts highlighted unigenes involved in oxidoreductase and polygalacturonase activities. Cytochrome P450s, carboxylesterases, major facilitator superfamily transporters, lipocalins, apolipoproteins, glycoside hydrolases 1 and 28, and lytic monooxygenases were among the most commonly up-regulated unigenes in soybean-fed larvae compared to those fed their primary hosts. These results suggest that D. texanus larvae differentially expressed unigenes involved in biotransformation of allelochemicals, digestion of plant cell walls and transport of small solutes and lipids when feeding in soybean.

Proteomic analysis of Laodelphax striatellus in response to Rice stripe virus infection reveal a potential role of ZFP36L1 in restriction of viral proliferation

Persistent plant viruses multiply and circulate inside insect vectors following the route of midgut-hemolymph-salivary gland. Currently, how viruses interact with insect vectors after they are released into hemolymph is not entirely clear. In this study, we found that the hemolymph and fat body (HF) contained the highest Rice stripe virus (RSV) levels. Proteomic analysis on RSV-free and RSV-infected HF identified 156 differentially expressed proteins (DEPs), with the majority of them participating in metabolism, transportation, and detoxification. The RNA binding protein esf2 was the most downregulated protein. Knocking down the expression of esf2 did not influence the RSV burden, but caused the lethal effect to L. striatellus. In contrast, the mRNA decay protein ZFP36L1 was 69% more abundant upon RSV infection, and suppression of ZFP36L1 significantly increased the RSV burden. Our results reveal the potential role of ZFP36L1 in restricting the viral proliferation, and provide valuable clues for unravelling the interaction between RSV and L. striatellus in HF. SIGNIFICANCE: More than 76% of plant viruses are transmitted by insect vectors. For persistent propagative transmission, plant viruses multiply and circulate inside insects following the route of midgut-hemolymph-salivary gland. However, how viruses interact with vector insects after they are released into hemolymph is not entirely clear. Our study investigated the influence of rice stripe virus (RSV) on insect hemolymph and fat body by iTRAQ labeling method. Among the 156 differentially expressed proteins (DEPs) identified, two proteins associated with mRNA metabolism were selected for function analysis. We found that the mRNA decay activator protein ZFP36L1 influenced the RSV proliferation, and RNA binding protein esf2 caused the lethal effect to L. striatellus. Our results provide valuable clues for unveiling the interaction between RSV and L. striatellus, and might be useful in pest management.

Landscape-dependent effects of varietal mixtures on insect pest control and implications for farmer profits

Intraspecific plant diversity can significantly impact insect herbivore populations in natural systems. Yet, its role as an insect pest control strategy in agriculture has received less attention, and little is known about which crop traits are important to herbivores in different landscape contexts. Moreover, empirical economic analyses on the cost-effectiveness of varietal mixtures are lacking. We used varietal mixtures of Brassica oleracea crops on working farms to examine how two metrics of intraspecific crop diversity, varietal richness and number of plant colors (color richness), affect crop damage and the incidence and abundance of two insect pest species: Pieris rapae and Phyllotreta spp. We evaluated the context-dependency of varietal mixtures by sampling early- and late-season plantings of B. oleracea crops in farms across a gradient of landscape composition. We developed crop budgets and used a net present value analysis to assess the impact of varietal mixtures on input and labor costs, crop revenues, and profit. We found context-dependent effects of varietal mixtures on both pests. In early-season plantings, color richness did not affect Phyllotreta spp. populations. However, increasing varietal richness reduced Phyllotreta spp. incidence in simple landscapes dominated by cropland, but this trend was reversed in complex landscapes dominated by natural habitats. In late-season plantings, color richness reduced the incidence and abundance of P. rapae larvae, but only in complex landscapes where their populations were highest. Varietal richness had the same effect on P. rapae larvae as color richness. Unexpectedly, we consistently found lower pest pressure and reduced crop damage in simple landscapes. Although varietal mixtures did not affect crop damage, increasing color richness corresponded with increased profits, due to increased revenue and a marginal reduction in labor and input costs. We demonstrate varietal mixtures can significantly impact pest populations, and this effect can be mediated by intraspecific variation in crop color. However, the strength and direction of these effects vary by season, landscape composition, and pest species. The association between varietal color richness and profitability indicates farmers could design mixtures to enhance economic returns. We recommend additional research on the benefits of intraspecific trait variation for farmers.

The role of cytochrome P450-mediated detoxification in insect adaptation to xenobiotics

Insect cytochrome P450 monooxygenases (P450s) are well known to be involved in metabolic detoxification of xenobiotics, such as phytochemicals, insecticides and environmental pollutants. Enhanced metabolic detoxification is closely associated with the constitutive overexpression and induction of P450s. In general, multiple insect P450s are co-responsible for xenobiotic detoxification. Considering the capacity of P450s to respond to a wide range of xenobiotics, synergistic interactions between natural and synthetic xenobiotics and P450-mediated cross-tolerance/resistance are ubiquitous. Recent studies have indicated that both transcription factors and signaling pathways are involved in the regulation of P450 genes in xenobiotic responses. This article reviews our current understanding of P450-mediated detoxification in insect adaptation to xenobiotics and highlights recent progress in the molecular basis of P450 regulation.

Cytochrome P450s CYP380C6 and CYP380C9 in green peach aphid facilitate its adaptation to indole glucosinolate-mediated plant defense

BACKGROUND

Overexpressing CIRCADIAN CLOCK ASSOCIATED1 in Arabidopsis thaliana (CCA1-ox) increases indole glucosinolate production and resistance to green peach aphid (Myzus persicae). Little is known of how aphids respond to this group of plant defense compounds or of the underlying molecular mechanism.

RESULTS

Aphids reared on CCA1-ox for over 40 generations (namely the CCA population) became less susceptible to CCA1-ox than aphids maintained on the wild-type Col-0 (namely the COL population). This elevated tolerance was transgenerational as it remained for at least eight generations after the CCA population was transferred to Col-0. Intriguingly, transcriptome analysis indicated that all differential cytochrome P450 monooxygenase genes (MpCYPs), primarily MpCYP4s, MpCYP380s and MpCYP6s, were more highly expressed in the CCA population. Application of a P450 inhibitor to the CCA population resulted in decreased aphid reproduction on CCA1-ox, which was not observed if aphids were reared on Col-0. When indole glucosinolate biosynthesis in CCA1-ox was blocked using virus-induced gene silencing, the effect of the P450 inhibitor on the CCA population was attenuated, affirming the essential role played by MpCYPs in counteracting the defense mechanism in CCA1-ox that is low or absent in Col-0. Furthermore, we used host-induced gene silencing to identify MpCYP380C6 and MpCYP380C9 that specifically facilitated the CCA population to cope with CCA1-mediated plant defense. Expression profiles revealed their possible contribution to the transgenerational tolerance observed in aphids.

CONCLUSION

MpCYP380C6 and MpCYP380C9 in aphids play a crucial role in mitigating indole glucosinolate-mediated plant defense, and this effect is transgenerational.

Plant flavonoids enhance the tolerance to thiamethoxam and flupyradifurone in whitefly Bemisia tabaci (Hemiptera: Aleyrodidae)

The sweetpotato whitefly Bemisia tabaci is a polyphagous crop pest distributed worldwide and frequent exposure to many different defensive secondary metabolites in its host plants. To counteract these defensive plant secondary metabolites, B. tabaci elevate their production of detoxification enzymes, including cytochrome P450 monooxygenases. Besides their tolerance to phytotoxin, B. tabaci have quickly developed resistance to various insecticides in the field. However, the relationship between host plant secondary metabolites and insecticide resistance in B. tabaci is not fully understood. In this study, the influence of plant flavonoid ingestion on B. tabaci tolerance to thiamethoxam and flupyradifurone insecticides and its possible mechanism were examined. Eight plant flavonoids were screened to evaluate their effects on B. tabaci adult sensitivity to thiamethoxam and flupyradifurone. Of which rutin, quercetin, kaempferol, myricetin and catechin significantly reduced adult sensitivity to thiamethoxam and flupyradifurone. Application of cytochrome P450 inhibitor piperonyl butoxide significantly increased the mortality of B. tabaci adults treated with thiamethoxam and flupyradifurone. Moreover, flavonoid ingestion predominantly enhanced the activity of cytochrome P450 enzyme in B. tabaci adults. Meanwhile, the expression level of three cytochrome P450 genes, CYP6CM1, CYP6CX4 and CYP4C64 were induced by the flavonoids in B. tabaci adults. In conclusion, plant flavonoids enhanced the tolerance to thiamethoxam and flupyradifurone in B. tabaci and cytochrome P450s may contribute the flavonoid adaptation. The reduced sensitivity of thiamethoxam and flupyradifurone in flavonoid-fed B. tabaci adults suggested that previous exposure to the host plant-derived flavonoids is likely to compromise the efficacy of insecticides.

Genetic and evolution analysis of extrafloral nectary in cotton

Extrafloral nectaries are a defence trait that plays important roles in plant-animal interactions. Gossypium species are characterized by cellular grooves in leaf midribs that secret large amounts of nectar. Here, with a panel of 215 G. arboreum accessions, we compared extrafloral nectaries to nectariless accessions to identify a region of Chr12 that showed strong differentiation and overlapped with signals from GWAS of nectaries. Fine mapping of an F2 population identified GaNEC1, encoding a PB1 domain-containing protein, as a positive regulator of nectary formation. An InDel, encoding a five amino acid deletion, together with a nonsynonymous substitution, was predicted to cause 3D structural changes in GaNEC1 protein that could confer the nectariless phenotype. mRNA-Seq analysis showed that JA-related genes are up-regulated and cell wall-related genes are down-regulated in the nectary. Silencing of GaNEC1 led to a smaller size of foliar nectary phenotype. Metabolomics analysis identified more than 400 metabolites in nectar, including expected saccharides and amino acids. The identification of GaNEC1 helps establish the network regulating nectary formation and nectar secretion, and has implications for understanding the production of secondary metabolites in nectar. Our results will deepen our understanding of plant-mutualism co-evolution and interactions, and will enable utilization of a plant defence trait in cotton breeding efforts.

Responses of detoxification enzymes in the midgut of Bombyx mori after exposure to low-dose of acetamiprid

Bombyx mori is an important economic insect. However, the environmental pollution caused by the widespread use of neonicotinoid insecticides has significantly affected the safe production of sericulture. In this paper, we determined the LC₅₀ of acetamiprid, a kind of neonicotinoid insecticides, to 5th instar silkworm larvae, examined its residues in hemolymph and midgut of silkworm after continuous exposure to low-dose of acetamiprid, and investigated the transcription level of detoxifying-related genes and the activity of detoxifying enzymes. The results showed that acetamiprid was highly toxic (24-h LC₅₀, 1.50 mg/L) to silkworm larvae. After continuous exposure to low-dose of acetamiprid (0.15 mg/L), the acetamiprid residue concentrations in hemolymph and midgut were 0.90 and 0.58 μg/mg, respectively, at 48 h, but all decreased at 96 h. At 24 h of acetamiprid exposure, the transcription levels of CYP4M5 and CYP6AB4 and the P450 enzyme activity were significantly enhanced. However, the transcription levels of CarE and CarE-11 and the activity of CarE enzymes were both inhibited by acetamiprid exposure. After 24 h-72 h of acetamiprid exposure, the transcription levels of GSTe3 and GSTd1 were significantly up-regulated, and the GST enzyme activity was also significantly elevated from 48 h to 96 h. Furthermore, the expression levels of FoxO, CncC and Keap1, the key upstream genes of detoxification enzymes, showed a similar trend as the GST genes. These results indicated that acetamiprid was reduced in midgut and the expression of GSTs was upregulated may via FoxO/CncC/Keap1 signaling pathway, which plays a key role in detoxification responses.

Impact of alkaloids in food consumption, metabolism and survival in a blood-sucking insect

The sense of taste provides information about the “good” or “bad” quality of a food source, which may be potentially nutritious or toxic. Most alkaloids taste bitter to humans, and because bitter taste is synonymous of noxious food, they are generally rejected. This response may be due to an innate low palatability or due to a malaise that occurs after food ingestion, which could even lead to death. We investigated in the kissing bug Rhodnius prolixus, whether alkaloids such as quinine, caffeine and theophylline, are merely distasteful, or if anti-appetitive responses are caused by a post-ingestion physiological effect, or both of these options. Although anti-appetitive responses were observed for the three alkaloids, only caffeine and theophylline affect metabolic and respiratory parameters that reflected an underlying physiological stress following their ingestion. Furthermore, caffeine caused the highest mortality. In contrast, quinine appears to be a merely unpalatable compound. The sense of taste helps insects to avoid making wrong feeding decisions, such as the intake of bitter/toxic foods, and thus avoid potentially harmful effects on health, a mechanism preserved in obligate hematophagous insects.