Molecular mechanisms of insect adaptation to plant secondary compounds

Divergent Response of Two Bark Beetle-Fungal Symbiotic Systems to Host Monoterpenes Reflects Niche Partitioning Strategies

The successful establishment of bark beetle-fungus symbionts on plants is required to overcome host defenses. However, little is known about how different bark beetle-fungus symbionts adapt to different niches on the same host plant. Here, we investigated the niche partitioning mechanism of two co-occurring bark beetle-fungus symbiotic systems, Ips nitidus-Ophiostoma bicolor and Dendroctonus micans-Endoconidiophora laricicola, on Qinghai spruce (Picea crassifolia) tree. The lower niche of the spruce trunk inhabited by D. micans showed a higher content of monoterpenes than the upper niche of the trunk inhabited by I. nitidus. Dendroctonus micans showed greater tolerance and higher metabolic efficiency toward monoterpenes than I. nitidus. However, both beetle species showed a similar metabolic profile toward α-pinene, albeit with different levels of metabolites. Additionally, O. bicolor, transmitted by I. nitidus, showed a significantly higher tolerance to monoterpenes and pathogenicity to spruce trees than E. laricicola, transmitted by D. micans. In particular, monoterpenoid metabolites were observed to attenuate the inhibitory effect of high-dose α-pinene on E. laricicola, thus increasing its fitness in a high-dose monoterpene microhabitat. These results show that these two bark beetle-fungus symbionts have adapted to different niches, leading to fitness differences in niche distribution that are at least partly related to the different distribution of monoterpene concentration in the spruce trunk. This research provides a novel perspective for understanding the coevolution between bark beetle-fungus symbionts and their host plants.

Identification and in vivo functional analysis of furanocoumarin-responsive cytochrome P450s in a Rutaceae-feeding Papilio butterfly

The Order Lepidoptera contains nearly 160,000 described species and most of them are specialist herbivores that use restricted plant species as hosts. Speciation that originated from host shift is one of the important factors for the diversification of Lepidoptera. Because plants prepare secondary metabolites for defense against herbivores, with varying profiles of the components among different plant taxa, the specialist herbivores need to be adapted to the toxic substances unique to their host plants. Swallowtail butterflies of the genus Papilio consist of over 200 species. Approximately 80% of them utilize Rutaceae plants, and among the remaining species, a specific subgroup uses phylogenetically distant Apiaceae plants as larval hosts. Rutaceae and Apiaceae commonly contain toxic secondary metabolites, furanocoumarins, and molecular phylogenetic studies support the concept that Apiaceae feeders were derived from Rutaceae feeders. Molecular mechanisms underlying furanocoumarin tolerance in Papilio butterflies have been investigated almost exclusively in an Apiaceae feeder by an in vitro assay. In contrast, there is little information regarding the Rutaceae feeders. Here, we focused on a Rutaceae feeder, Papilio xuthus, and identified two furanocoumarin-responsive cytochrome P450-6B (CYP6B) genes, of which one was an ortholog of a furanocoumarin-metabolizing enzyme identified in the Apiaceae-feeding Papilio while the other was previously unreported. We further conducted in vivo functional analysis using the CRISPR/Cas9 system, revealing a contribution of these CYP6Bs to furanocoumarin tolerance of P. xuthus larvae. Our findings suggest that co-option of furanocoumarin-metabolizing CYP6B enzymes at least partially contributed to the host shift from Rutaceae to Apiaceae in Papilio butterflies.

High nitrogen application in maize enhances insecticide tolerance of the polyphagous herbivore Spodoptera litura by induction of detoxification enzymes and intensification of cuticle

Nitrogen (N) is one of the most intensively used fertilizers in cropping system and could exert a variety of bottom-up effects on the ecological fitness of herbivores. However, the effects of increased N inputs on insect pesticide tolerance have not been comprehensively understood. Bioassays showed that high N (HN) applied to maize plants significantly increased larval tolerance of Spodoptera litura to multiple insecticides. Activities of detoxification enzymes were significantly higher in the larvae fed on maize plants supplied with HN. RNA-seq analysis showed that numerous GST and cuticle-related genes were induced in the larvae fed on HN maize. RT-qPCR analysis further confirmed four GST genes and larval-specific cuticle gene LCP167. Furthermore, when injected with dsRNA specific to GSTe1, GSTs5, and LCP167, the mortality of larvae treated with methomyl was about 3-fold higher than that of dsGFP-injected larvae. Electron microscope observation showed that cuticle of the larvae fed on HN maize was thicker than the medium level of N. These findings suggest that increased application of N fertilizer enhances insecticide tolerance of lepidopteran pests via induction of detoxification enzymes and intensification of cuticle. Thus, overuse of N fertilizer may increase pest insecticide tolerance and usage of chemical insecticides.

Dimethyl sulfoxide, an alternative for control of Nosema ceranae infection in honey bees (Apis mellifera)

Nosema ceranae is a microsporidian parasite that threatens current apiculture. N. ceranae-infected honey bees (Apis mellifera) exhibit morbid physiological impairments and reduced honey production, malnutrition, shorter life span, and higher mortality than healthy honey bees. In this study, we found that dimethyl sulfoxide (DMSO) could enhance the survival rate of N. ceranae-infected honey bees. Therefore, we investigated the effect of DMSO on N. ceranae-infected honey bees using comparative RNA sequencing analysis. Our results revealed that DMSO was able to affect several biochemical pathways, especially the metabolic-related pathways in N. ceranae-infected honey bees. Based on these findings, we conclude that DMSO may be a useful alternative for treating N. ceranae infection in apiculture.

Gut microbiota metagenomics and mediation of phenol degradation in Bactrocera minax (Diptera, Tephritidae)

BACKGROUND

Gut microbiota mediating insect-plant interactions have many manifestations, either by provisioning missing nutrients, or by overcoming plant defensive reactions. However, the mechanism by which gut microbiota empower insects to survive by overcoming a variety of plant secondary metabolites remains largely unknown. Bactrocera minax larvae develop in immature citrus fruits, which present numerous phenolic compounds that challenge the larvae. To explore the role of gut microbes in host use and adaptability, we uncovered the mechanisms of phenol degradation by gut microbes using metagenomic and metatranscriptomic analyses, and verified the degradation ability of isolated and cultured bacteria. Research on this subject can help develop potential strain for the environmental friendly pest management operations.

RESULTS

We demonstrated the ability of gut microbes in B. minax larvae to degrade phenols in unripe citrus. After antibiotic treatment, coniferyl alcohol and coumaric aldehyde significantly reduced the survival rate, body length and body weight of the larvae. The metagenomic and metatranscriptomic analyses in B. minax provided evidence for the presence of genes in bacteria and the related pathway involved in phenol degradation. Among them, Enterococcus faecalis and Serratia marcescens, isolated from the gut of B. minax larvae, played critical roles in phenol degradation. Furthermore, supplementation of E. faecalis and S. marcescens in artificial diets containing coniferyl alcohol and coumaric aldehyde increased the survival rate of larvae.

CONCLUSION

In summary, our results provided the first comprehensive analysis of gut bacterial communities by high-throughput sequencing and elucidated the role of bacteria in phenol degradation in B. minax, which shed light on the mechanism underlying specialist insect adaption to host secondary metabolites via gut bacteria. © 2024 Society of Chemical Industry.

Plasticity for the win: Flexible transcriptional response to host plant switches in the comma butterfly (Polygonia c-album)

Generalist plant-feeding insects are characterised by a broad host repertoire that can comprise several families or even different orders of plants. The genetic and physiological mechanisms underlying the use of such a wide host range are still not fully understood. Earlier studies indicate that the consumption of different host plants is associated with host-specific gene expression profiles. It remained, however, unclear if and how larvae can alter these profiles in the case of a changing host environment. Using the polyphagous comma butterfly (Polygonia c-album) we show that larvae can adjust their transcriptional profiles in response to a new host plant. The switch to some of the host plants, however, resulted in a larger transcriptional response and, thus, seems to be more challenging. At a physiological level, no correspondence for these patterns could be found in larval performance. This suggests that a high transcriptional but also phenotypic flexibility are essential for the use of a broad and diverse host range. We furthermore propose that host switch tests in the laboratory followed by transcriptomic investigations can be a valuable tool to examine not only plasticity in host use but also subtle and/or transient trade-offs in the evolution of host plant repertoires.

Jasmonic Acid and Salicylic Acid improved resistance against Spodoptera frugiperda Infestation in maize by modulating growth and regulating redox homeostasis

Exploring host plant resistance and elevating plant defense mechanisms through the application of exogenous elicitors stands as a promising strategy for integrated pest management. The fall armyworm, a pernicious menace to grain crops in tropical and subtropical regions, stands as a formidable threat due to its capacity for devastation and a wide-ranging spectrum of host plants. There is no literature regarding artificially induced resistance in maize against fall armyworm (Spodoptera frugiperda) by exogenous application of phytohormones. The present investigation was performed to evaluate the role of jasmonic acid (JA) and salicylic acid (SA) on two maize hybrids namely FH-1046 and YH-1898 against fall armyworm. Results showed that plant height, biomass and lengths, fresh and dry weight of root shoot which decreased with armyworm infestation improved with phytohormonal application. JA treatment resulted in a higher increase in all attributes as compared to SA treatment. Improvement in relative water contents, photosynthetic pigments and pronounced levels of phenol and proline accumulation were observed in infested plants after JA treatment. Infested plants recovered from oxidative stress as JA application activated and increased the antioxidant enzyme activity of superoxide dismutase, peroxidase and polyphenol oxidase activity in both FH-1046 and YH-1898 . The oxidative stress reduction in infested plants after JA treatment was also evident from a fair decrease in MDA and H2O2 in both varieties. The SA and JA mediated genes expression was studied and it was found that in FH1046 maize cultivar, JA dependent genes, particularly marker genes PR1 and Lox5 were highly expressed along with TPS10 and BBT12. Whereas SPI, WRKY28, ICS and PAL were shown to be activated upon SA application. Evidently, both JA and SA elicited a robust defensive response within the maize plants against the voracious S. frugiperda, which in consequence exerted a discernible influence over the pest's developmental trajectory and physiological dynamics. A decrease in detoxification enzyme activity of the insects was observed after feeding on treated plants. Moreover, it was recorded that the survival and weight gain of FAW feeding on phytohormone treated maize plants also decelerated. In conclusion, FH-1046 was found to be more tolerant than YH-1898 against fall armyworm infestation and 1 mM JA was more effective than 1 mM SA for alleviation of fall armyworm stress. Therefore, it was inferred that phytohormones regulated redox homeostasis to circumvent oxidative damage and mediate essential metabolic events in maize under stress. To our current understanding, this study is the very first presentation of induced resistance in maize against S. frugiperda with the phytohormonal application (JA and SA).

Comparative Genomics and the Salivary Transcriptome of the Redbanded Stink Bug Shed Light on Its High Damage Potential to Soybean

The redbanded stink bug, Piezodorus guildinii (Westwood) (Hemiptera: Pentatomidae), is a significant soybean pest in the Americas, which inflicts more physical damage on soybean than other native stink bugs. Studies suggest that its heightened impact is attributed to the aggressive digestive properties of its saliva. Despite its agricultural importance, the factors driving its greater ability to degrade plant tissues have remained unexplored in a genomic evolutionary context. In this study, we hypothesized that lineage-specific gene family expansions have increased the copy number of digestive genes expressed in the salivary glands. To investigate this, we annotated a previously published genome assembly of the redbanded stink bug, performed a comparative genomic analysis on 11 hemipteran species, and reconstructed patterns of gene duplication, gain, and loss in the redbanded stink bug. We also performed RNA-seq on the redbanded stink bug's salivary tissues, along with the rest of the body without salivary glands. We identified hundreds of differentially expressed salivary genes, including a subset lost in other stink bug lineages, but retained and expressed in the redbanded stink bug's salivary glands. These genes were significantly enriched with protein families involved in proteolysis, potentially explaining the redbanded stink bug's heightened damage to soybeans. Contrary to our hypothesis, we found no support for an enrichment of duplicated digestive genes that are also differentially expressed in the salivary glands of the redbanded stink bug. Nonetheless, these results provide insight into the evolution of this important crop pest, establishing a link between its genomic history and its agriculturally important physiology.

Screening and functional validation of the core detoxification genes conferring broad-spectrum response to insecticides in Spodoptera frugiperda

BACKGROUND

Fall armyworm, Spodoptera frugiperda, a formidable agricultural pest, has developed resistance to various synthetic insecticides. However, how S. frugiperda utilizes its limited energy and resources to deal with various insecticides remains largely unexplored.

RESULTS

We utilized transcriptome sequencing to decipher the broad-spectrum adaptation mechanism of S. frugiperda to eight insecticides with distinct modes-of-action. Analysis of the Venn diagram revealed that 1014 upregulated genes and 778 downregulated genes were present in S. frugiperda treated with at least five different insecticides, compared to the control group. Exposure to various insecticides led to the significant upregulation of eight cytochrome P450 monooxygenases (P450s), four UDP glucosyltransferases (UGTs), two glutathione-S-transferases (GSTs) and two ATP-binding cassette transporters (ABCs). Among them, the sfCYP340AD3 and sfCYP4G74 genes were demonstrated to respond to stress from six different insecticides in S. frugiperda, as evidenced by RNA interference and toxicity bioassays. Furthermore, homology modeling and molecular docking analyses showed that sfCYP340AD3 and sfCYP4G74 possess strong binding affinities to a variety of insecticides.

CONCLUSION

Collectively, these findings showed that S. frugiperda utilizes a battery of core detoxification genes to cope with the exposure of synthetic insecticides. This study also sheds light on the identification of efficient insecticidal targets gene and the development of resistance management strategies in S. frugiperda, thereby facilitating the sustainable control of this serious pest. © 2024 Society of Chemical Industry.

Duplications and Losses of the Detoxification Enzyme Glycosyltransferase 1 Are Related to Insect Adaptations to Plant Feeding

Insects have developed sophisticated detoxification systems to protect them from plant secondary metabolites while feeding on plants to obtain necessary nutrients. As an important enzyme in the system, glycosyltransferase 1 (GT1) conjugates toxic compounds to mitigate their harm to insects. However, the evolutionary link between GT1s and insect plant feeding remains elusive. In this study, we explored the evolution of GT1s across different insect orders and feeding niches using publicly available insect genomes. GT1 is widely present in insect species; however, its gene number differs among insect orders. Notably, plant-sap-feeding species have the highest GT1 gene numbers, whereas blood-feeding species display the lowest. GT1s appear to be associated with insect adaptations to different plant substrates in different orders, while the shift to non-plant feeding is related to several losses of GT1s. Most large gene numbers are likely the consequence of tandem duplications showing variations in collinearity among insect orders. These results reveal the potential relationships between the evolution of GT1s and insect adaptation to plant feeding, facilitating our understanding of the molecular mechanisms underlying insect-plant interactions.

Metabolomic Profiling Reveals the Anti-Herbivore Mechanisms of Rice (Oryza sativa)

The use of secondary metabolites of rice to control pests has become a research hotspot, but little is known about the mechanism of rice self-resistance. In this study, metabolomics analysis was performed on two groups of rice (T1, with insect pests; T2, without pests), indicating that fatty acids, alkaloids, and phenolic acids were significantly up-regulated in T1. The up-regulated metabolites (p-value < 0.1) were enriched in linoleic acid metabolism, terpene, piperidine, and pyridine alkaloid biosynthesis, α-linolenic acid metabolism, and tryptophan metabolism. Six significantly up-regulated differential metabolites in T1 were screened out: N-trans-feruloyl-3-methoxytyramine (1), N-trans-feruloyltyramine (2), N-trans-p-coumaroyltyramine (3), N-cis-feruloyltyramine (4), N-phenylacetyl-L-glutamine (5), and benzamide (6). The insect growth inhibitory activities of these six different metabolites were determined, and the results show that compound 1 had the highest activity, which significantly inhibited the growth of Chilo suppressalis by 59.63%. Compounds 2-4 also showed a good inhibitory effect on the growth of Chilo suppressalis, while the other compounds had no significant effect. RNA-seq analyses showed that larval exposure to compound 1 up-regulated the genes that were significantly enriched in ribosome biogenesis in eukaryotes, the cell cycle, ribosomes, and other pathways. The down-regulated genes were significantly enriched in metabolic pathways, oxidative phosphorylation, the citrate cycle (TCA cycle), and other pathways. Eighteen up-regulated genes and fifteen down-regulated genes from the above significantly enriched pathways were screened out and verified by real-time quantitative PCR. The activities of detoxification enzymes (glutathione S-transferase (GST); UDP-glucuronosyltransferase (UGT); and carboxylesterase (CarE)) under larval exposure to compound 1 were measured, which indicated that the activity of GST was significantly inhibited by compound 1, while the activities of the UGT and CarE enzymes did not significantly change. As determined by UPLC-MS, the contents of compound 1 in the T1 and T2 groups were 8.55 ng/g and 0.53 ng/g, respectively, which indicated that pest insects significantly induced the synthesis of compound 1. Compound 1 may enhance rice insect resistance by inhibiting the detoxification enzyme activity and metabolism of Chilo suppressalis, as well as promoting cell proliferation to affect its normal growth and development process. The chemical-ecological mechanism of the insect resistance of rice is preliminarily clarified in this paper.

Molecular basis of host plant recognition by silkworm larvae

Herbivorous insects can identify their host plants by sensing plant secondary metabolites as chemical cues. We previously reported the two-factor host acceptance system of the silkworm Bombyx mori larvae. The chemosensory neurons in the maxillary palp (MP) of the larvae detect mulberry secondary metabolites, chlorogenic acid (CGA), and isoquercetin (ISQ), with ultrahigh sensitivity, for host plant recognition and feeding initiation. Nevertheless, the molecular basis for the ultrasensitive sensing of these compounds remains unknown. In this study, we demonstrated that two gustatory receptors (Grs), BmGr6 and BmGr9, are responsible for sensing the mulberry compounds with attomolar sensitivity for host plant recognition by silkworm larvae. Calcium imaging assay using cultured cells expressing the silkworm putative sugar receptors (BmGr4-10) revealed that BmGr6 and BmGr9 serve as receptors for CGA and ISQ with attomolar sensitivity in human embryonic kidney 293T cells. CRISPR/Cas9-mediated knockout (KO) of BmGr6 and BmGr9 resulted in a low probability of making a test bite of the mulberry leaves, suggesting that they lost the ability to recognize host leaves. Electrophysiological recordings showed that the loss of host recognition ability in the Gr-KO strains was due to a drastic decrease in MP sensitivity toward ISQ in BmGr6-KO larvae and toward CGA and ISQ in BmGr9-KO larvae. Our findings have revealed that the two Grs, previously considered to be sugar receptors, are molecules responsible for detecting plant phenolics in host plant recognition.

CRISPR/Cas9-Based Functional Characterization of SfUGT50A15 Reveals Its Roles in the Resistance of Spodoptera frugiperda to Chlorantraniliprole, Emamectin Benzoate, and Benzoxazinoids

UDP-glycosyltransferases (UGTs) are a diverse superfamily of enzymes. Insects utilize uridine diphosphate-glucose (UDP-glucose) as a glycosyl donor for glycosylation in vivo, involved in the glycosylation of lipophilic endosymbionts and xenobiotics, including phytotoxins. UGTs act as second-stage detoxification metabolizing enzymes, which are essential for the detoxification metabolism of insecticides and benzoxazine compounds. However, the UGT genes responsible for specific glycosylation functions in S. frugiperda are unclear at present. In this study, we utilized CRISPR/Cas9 to produce a SfUGT50A15-KO strain to explore its possible function in governing sensitivity to chemical insecticides or benzoxazinoids. The bioassay results suggested that the SfUGT50A15-KO strain was significantly more sensitive to chlorantraniliprole, emamectin benzoate, and benzoxazinoids than the wild-type strains. This finding suggests that the overexpression of the SfUGT50A15 gene may be linked to S. frugiperda resistance to pesticides (chlorantraniliprole and emamectin benzoate) as well as benzoxazinoids (BXDs).

Glutathione S-Transferase Genes Involved in Response to Short-Term Heat Stress in Tetranychus urticae (Koch)

Tetranychus urticae, a globally ubiquitous mite, poses a significant threat to agriculture. Elevated temperatures exacerbate the growth, development, and reproduction of T. urticae, leading to substantial crop damage. In this study, we employed comparative transcriptomic approaches with whole-genome information of T. urticae to identify six Glutathione S-transferase genes (GSTs) implicated in heat stress response. Through comprehensive bioinformatics analyses, we elucidated the tertiary structure and active sites of the corresponding proteins, providing a thorough characterization of these GST genes. Furthermore, we investigated the expression patterns of these six GST genes under short-term heat shock conditions. Our findings unveiled the involvement of T. urticae GST genes in combating oxidative stress induced by heat, underscoring their role in antioxidant defense mechanisms. This study contributes valuable insights into the molecular mechanisms underlying the response of T. urticae to heat stress, laying a foundation for the development of strategies aimed at mitigating its impact in high-temperature environments.

Chromosome-level genome assembly of the aster leafhopper (Macrosteles quadrilineatus) reveals the role of environment and microbial symbiosis in shaping pest insect genome evolution

Leafhoppers comprise over 20,000 plant-sap feeding species, many of which are important agricultural pests. Most species rely on two ancestral bacterial symbionts, Sulcia and Nasuia, for essential nutrition lacking in their phloem and xylem plant sap diets. To understand how pest leafhopper genomes evolve and are shaped by microbial symbioses, we completed a chromosomal-level assembly of the aster leafhopper's genome (ALF; Macrosteles quadrilineatus). We compared ALF's genome to three other pest leafhoppers, Nephotettix cincticeps, Homalodisca vitripennis, and Empoasca onukii, which have distinct ecologies and symbiotic relationships. Despite diverging ~155 million years ago, leafhoppers have high levels of chromosomal synteny and gene family conservation. Conserved genes include those involved in plant chemical detoxification, resistance to various insecticides, and defence against environmental stress. Positive selection acting upon these genes further points to ongoing adaptive evolution in response to agricultural environments. In relation to leafhoppers' general dependence on symbionts, species that retain the ancestral symbiont, Sulcia, displayed gene enrichment of metabolic processes in their genomes. Leafhoppers with both Sulcia and its ancient partner, Nasuia, showed genomic enrichment in genes related to microbial population regulation and immune responses. Finally, horizontally transferred genes (HTGs) associated with symbiont support of Sulcia and Nasuia are only observed in leafhoppers that maintain symbionts. In contrast, HTGs involved in non-symbiotic functions are conserved across all species. The high-quality ALF genome provides deep insights into how host ecology and symbioses shape genome evolution and a wealth of genetic resources for pest control targets.

A chromosome-level genome assembly of yellow stem borer (Scirpophaga incertulas)

The yellow stem borer Scirpophaga incertulas is the dominant pest of rice in tropical Asia. However, the lack of genomic resources makes it difficult to understand their invasiveness and ecological adaptation. A high-quality chromosome-level genome of S. incertulas, a monophagous rice pest, was assembled by combining Illumina short reads, PacBio HiFi long sequencing, and Hi-C scaffolding technology. The final genome size was 695.65 Mb, with a scaffold N50 of 28.02 Mb, and 93.50% of the assembled sequences were anchored to 22 chromosomes. BUSCO analysis demonstrated that this genome assembly had a high level of completeness, with 97.65% gene coverage. A total of 14,850 protein-coding genes and 366.98 Mb of transposable elements were identified. In addition, comparative genomic analyses indicated that chemosensory processes and detoxification capacity may play critical roles in the specialized host preference of S. incertulas. In summary, the chromosome-level genome assembly of S. incertulas provides a valuable genetic resource for understanding the biological characteristics of its invasiveness and developing an efficient management strategy.

Molecular Characterization Analysis and Adaptive Responses of Spodoptera frugiperda (Lepidoptera: Noctuidae) to Nutritional and Enzymatic Variabilities in Various Maize Cultivars

The fall armyworm, Spodoptera frugiperda Smith (Lepidoptera: Noctuidae), a common agricultural pest known for its extensive migration and wide host ranges, causes considerable harm to maize (Zea mays L.). In this study, we utilized two molecular marker genes, COI and Tpi, to compare the genetic characteristics of the collected original samples. Additionally, through an interactive study between S. frugiperda larvae and six maize varieties aiming to understand the insect's adaptability and resistance mechanisms, our analysis revealed that both the COI and Tpi genes identified S. frugiperda as the corn strain. Further examination of the larvae showed significant differences in nutritional indices, digestive, and detoxification enzyme activities. Special maize varieties were found to offer higher efficiency in nutrient conversion and assimilation compared with common varieties. This study revealed adaptations in S. frugiperda's digestive and detoxification processes in response to the different maize varieties. For instance, larvae reared on common maize exhibited elevated amylase and lipase activities. Interestingly, detoxification enzyme activities exhibited different patterns of variation in different maize varieties. The Pearson correlation analysis between nutritional indices, enzyme activities, and the nutritional content and secondary metabolites of maize leaves provided deeper insights into the pest's adaptability. The results highlighted significant relationships between specific nutritional components in maize and the physiological responses of S. frugiperda. Overall, our findings contribute substantially to the understanding of S. frugiperda's host plant adaptability, offering critical insights for the development of sustainable pest management strategies.

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

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

Microbial changes and associated metabolic responses modify host plant adaptation in Stephanitis nashi

Symbiotic microorganisms are essential for the physiological processes of herbivorous pests, including the pear lace bug Stephanitis nashi, which is known for causing extensive damage to garden plants and fruit trees due to its exceptional adaptability to diverse host plants. However, the specific functional effects of the microbiome on the adaptation of S. nashi to its host plants remains unclear. Here, we identified significant microbial changes in S. nashi on 2 different host plants, crabapple and cherry blossom, characterized by the differences in fungal diversity as well as bacterial and fungal community structures, with abundant correlations between bacteria or fungi. Consistent with the microbiome changes, S. nashi that fed on cherry blossom demonstrated decreased metabolites and downregulated key metabolic pathways, such as the arginine and mitogen-activated protein kinase signaling pathway, which were crucial for host plant adaptation. Furthermore, correlation analysis unveiled numerous correlations between differential microorganisms and differential metabolites, which were influenced by the interactions between bacteria or fungi. These differential bacteria, fungi, and associated metabolites may modify the key metabolic pathways in S. nashi, aiding its adaptation to different host plants. These results provide valuable insights into the alteration in microbiome and function of S. nashi adapted to different host plants, contributing to a better understanding of pest invasion and dispersal from a microbial perspective.

First report on evaluation of commercial eugenol and piperine against Aedes aegypti L (Diptera: Culicidae) larvae: Mortality, detoxifying enzyme, and histopathological changes in the midgut

Dengue fever is a worldwide public health problem, and efforts to eradicate it have focused on controlling the dengue vector, Aedes aegypti. This study aims to assess the toxicity and effect of commercial eugenol and piperine on Ae. aegypti larvae through enzyme detoxification and histopathological changes in the midgut. Laboratory-reared Ae. aegypti larvae were treated with various concentrations of commercial eugenol and piperine and observed after 24, 48, and 72 h. Biochemical methods were used to assess detoxification enzyme activity for acetylcholinesterase, glutathione S-transferase, and oxidase, and changes in the midgut were examined using routine histological examination. In terms of larvicidal activity, piperine exceeded eugenol. Piperine and eugenol had LC50 and LC90 values of 3.057 and 5.543 μM, respectively, and 6.421 and 44.722 μM at 24 h. Piperine and eugenol reduced oxidase activity significantly (p < 0.05), but increased acetylcholinesterase and glutathione S-transferase activity significantly (p < 0.05). After being exposed to piperine and eugenol, the food bolus and peritrophic membrane ruptured, the epithelial layer was interrupted and irregular, the epithelial cells shrank and formed irregularly, and the microvilli became irregular in shape. Commercial piperine and eugenol behave as potential larvicides, with processes involving altered detoxifying enzymes, specifically decreased oxidase function and increased GST activity, as well as midgut histological abnormalities.

Identification and potential application of key insecticidal metabolites in Tilia amurensis, a low-preference host of Hyphantria cunea

Developing effective insecticidal strategies is an important means of reducing the spread and host plant damage by Hyphantria cunea. In this study, key metabolites with insecticidal activity against H. cunea were screened by targeted metabolomics in Tilia amurensis, a low-preference host plant. Subsequently, the potential of key metabolites that could be used as botanical pesticides was evaluated. The results showed that coumarin was the key insecticidal metabolite of T. amurensis and had a significant insecticidal effect and weight inhibition effect on H. cunea larvae. Coumarin treatment significantly decreased the larval nutrient content and the gene expression of rate-limiting enzymes in the glycolytic pathway and tricarboxylic acid cycle. A significantly enhanced detoxification enzyme activity (CarE and GST), antioxidant oxidase activity (SOD and CAT), non-enzymatic antioxidant levels (GSH), and total antioxidant capacity were observed in coumarin-treated larvae. Coumarin treatment resulted in a significant increase in the expression levels of detoxification enzyme genes (CarE1, CarE2, CarE3, GST2, and GST3) and antioxidant oxidase genes (SOD1, CAT1, and CAT2) in H. cunea larvae. Coumarin treatment significantly increased the levels of MDA and H2O2 in larvae but did not cause pathological changes in the ultrastructure of the larval midgut. Coumarin solution sprayed directly or as a microcapsule suspension formulation with coumarin as the active ingredient had significant insecticidal activity against the H. cunea larvae. Overall, coumarin, a key anti-insect metabolite identified from T. amurensis, can significantly inhibit the growth and survival of H. cunea larvae and has the potential to be developed as a botanical pesticide.

Comparative genomics reveals evolutionary drivers of the dietary shift in Hemiptera

Hemiptera insects exhibit a close relationship to plants and demonstrate a diverse range of dietary preferences, encompassing phytophagy as the predominant feeding habit while a minority engages in carnivorous or haematophagous behaviour. To counteract the challenges posed by phytophagous insects, plants have developed an array of toxic compounds, causing significant evolutionary selection pressure on these insects. In this study, we employed a comparative genomics approach to analyse the expansion and contraction of gene families specific to phytophagous insect lineages, along with their adaptive evolutionary traits, utilising representative species from the Hemiptera order. Our investigation revealed substantial expansions of gene families within the phytophagous lineages, especially in the Pentatomomorpha branch represented by Oncopeltus fasciatus and Riptortus pedestris. Notably, these expansions of gene families encoding enzymes are potentially involved in hemipteran-plant interactions. Moreover, the adaptive evolutionary analysis of these lineages revealed a higher prevalence of adaptively evolved genes in the Pentatomomorpha branch. The observed branch-specific gene expansions and adaptive evolution likely contribute significantly to the diversification of species within Hemiptera. These results help enhance our understanding of the genomic characteristics of the evolution of different feeding habits in hemipteran insects.

Evolutionary genomics of three agricultural pest moths reveals rapid evolution of host adaptation and immune-related genes

BACKGROUND

Understanding the genotype of pest species provides an important baseline for designing integrated pest management (IPM) strategies. Recently developed long-read sequence technologies make it possible to compare genomic features of nonmodel pest species to disclose the evolutionary path underlying the pest species profiles. Here we sequenced and assembled genomes for 3 agricultural pest gelechiid moths: Phthorimaea absoluta (tomato leafminer), Keiferia lycopersicella (tomato pinworm), and Scrobipalpa atriplicella (goosefoot groundling moth). We also compared genomes of tomato leafminer and tomato pinworm with published genomes of Phthorimaea operculella and Pectinophora gossypiella to investigate the gene family evolution related to the pest species profiles.

RESULTS

We found that the 3 solanaceous feeding species, P. absoluta, K. lycopersicella, and P. operculella, are clustered together. Gene family evolution analyses with the 4 species show clear gene family expansions on host plant-associated genes for the 3 solanaceous feeding species. These genes are involved in host compound sensing (e.g., gustatory receptors), detoxification (e.g., ABC transporter C family, cytochrome P450, glucose-methanol-choline oxidoreductase, insect cuticle proteins, and UDP-glucuronosyl), and digestion (e.g., serine proteases and peptidase family S1). A gene ontology enrichment analysis of rapid evolving genes also suggests enriched functions in host sensing and immunity.

CONCLUSIONS

Our results of family evolution analyses indicate that host plant adaptation and pathogen defense could be important drivers in species diversification among gelechiid moths.

The role of the Bemisia tabaci and Trialeurodes vaporariorum cytochrome-P450 clade CYP6DPx in resistance to nicotine and neonicotinoids

The alkaloid, nicotine, produced by tobacco and other Solanaceae as an anti-herbivore defence chemical is one of the most toxic natural insecticides in nature. However, some insects, such as the whitefly species, Trialeurodes vaporariorum and Bemisia tabaci show strong tolerance to this allelochemical and can utilise tobacco as a host. Here, we used biological, molecular and functional approaches to investigate the role of cytochrome P450 enzymes in nicotine tolerance in T. vaporariorum and B. tabaci. Insecticide bioassays revealed that feeding on tobacco resulted in strong induced tolerance to nicotine in both species. Transcriptome profiling of both species reared on tobacco and bean hosts revealed profound differences in the transcriptional response these host plants. Interrogation of the expression of P450 genes in the host-adapted lines revealed that P450 genes belonging to the CYP6DP subfamily are strongly upregulated in lines reared on tobacco. Functional characterisation of these P450s revealed that CYP6DP1 and CYP6DP2 of T. vaporariorum and CYP6DP3 of B. tabaci confer resistance to nicotine in vivo. These three genes, in addition to the B. tabaci P450 CYP6DP5, were also found to confer resistance to the neonicotinoid imidacloprid. Our data provide new insight into the molecular basis of nicotine resistance in insects and illustrates how divergence in the evolution of P450 genes in this subfamily in whiteflies may have impacted the extent to which different species can tolerate a potent natural insecticide.

The brown planthopper NlDHRS11 is involved in the detoxification of rice secondary compounds

BACKGROUND

The brown planthopper (Nilaparvata lugens, BPH) is the most destructive serious pest in rice production. Resistant varieties are effective means to defend against BPH, but the impact of the ingestion of resistant rice on BPH transcriptional regulation is still unclear. Here, we explore the molecular basis of the regulation by BPH feeding on resistant rice.

RESULTS

BPH nymphs preferentially selected susceptible rice TN1 at 24 h after release in a choice test. Feeding on resistant rice IR56 under nonselective conditions increased mortality, decreased growth rate, and prolonged the molting time of BPH. Transcriptomic sequencing revealed 38 dysregulated genes, including 31 down-regulated and seven up-regulated genes in BPH feeding on resistant rice for 7 days compared with feeding on susceptible rice TN1. These genes were mainly involved in the pathways of growth and development, metabolism, energy synthesis, and transport. Finally, we showed that the toxicities of rice defensive compounds to BPH were dose-dependent, and silencing of the BPH gene dehydrogenase/reductase SDR family member 11 (NlDHRS11) increased sensibility to the rice secondary compounds ferulic acid and resorcinol.

CONCLUSION

The adaption of BPH feeding on resistant rice is orchestrated by dynamically regulating gene expressions, and NlDHRS11 is a gene involved in the detoxification of plant defensive chemicals. The current work provides new insights into the interaction between insects and plants, and will help to develop novel BPH control strategies. © 2023 Society of Chemical Industry.

Functional characterization of four antenna-biased chemosensory proteins in Dioryctria abietella reveals a broadly tuned olfactory DabiCSP1 and its key residues in ligand-binding

The orientation of the oligophagous cone-feeding moth Dioryctria abietella (Lepidoptera: Pyralidae) to host plants primarily relies on olfactory-related proteins, particularly those candidates highly expressed in antennae. Here, through a combination of expression profile, ligand-binding assay, molecular docking and site-directed mutagenesis strategies, we characterized the chemosensory protein (CSP) gene family in D. abietella. Quantitative real-time PCR (qPCR) analyses revealed the detectable expression of all 22 DabiCSPs in the antennae, of which seven genes were significantly enriched in this tissue. In addition, the majority of the genes (19/22 relatives) had the expression in at least one reproductive tissue. In the interactions of four antenna-dominant DabiCSPs and different chemical classes, DabiCSP1 was broadly tuned to 27 plant-derived odors, three man-made insecticides and one herbicide with high affinities (Ki < 6.60 μM). By contrast, three other DabiCSPs (DabiCSP4, CSP6 and CSP17) exhibited a narrow odor binding spectrum, in response to six compounds for each protein. Our mutation analyses combined with molecular docking simulations and binding assays further identified four key residues (Tyr25, Thr26, Ile65 and Val69) in the interactions of DabiCSP1 and ligands, of which binding abilities of this protein to 12, 15, 16 and three compounds were significantly decreased compared to the wildtype protein, respectively. Our study reveals different odor binding spectra of four DabiCSPs enriched in antennae and identifies key residues responsible for the binding of DabiCSP1 and potentially active compounds for the control of this pest.

Host adaptation and specialization in Tetranychidae mites

Composite generalist herbivores are comprised of host-adapted populations that retain the ability to shift hosts. The degree and overlap of mechanisms used by host-adapted generalist and specialist herbivores to overcome the same host plant defenses are largely unknown. Tetranychidae mites are exceptionally suited to address the relationship between host adaptation and specialization in herbivores as this group harbors closely related species with remarkably different host ranges-an extreme generalist the two-spotted spider mite (Tetranychus urticae Koch [Tu]) and the Solanaceous specialist Tetranychus evansi (Te). Here, we used tomato-adapted two-spotted spider mite (Tu-A) and Te populations to compare mechanisms underlying their host adaptation and specialization. We show that both mites attenuate induced tomato defenses, including protease inhibitors (PIs) that target mite cathepsin L digestive proteases. While Te solely relies on transcriptional attenuation of PI induction, Tu and Tu-A have elevated constitutive activity of cathepsin L proteases, making them less susceptible to plant anti-digestive proteins. Tu-A and Te also rely on detoxification of tomato constitutive defenses. Te uses esterase and P450 activities, while Tu-A depends on the activity of all major detoxification enzymatic classes to disarm tomato defensive compounds to a lesser extent. Thus, even though both Tu-A and Te use similar mechanisms to counteract tomato defenses, Te can better cope with them. This finding is congruent with the ecological and evolutionary times required to establish mite adaptation and specialization states, respectively.

The Capsicum terpenoid biosynthetic module is affected by spider-mite herbivory

In response to herbivory, Capsicum annuum leaves adapt their specialized metabolome that may protect the plant against herbivore feeding either directly or indirectly through volatile metabolites acting as cues for natural enemies of the herbivore. The volatile blend of spider-mite infested leaves differs from non-challenged leaves predominantly by a higher contribution of mono- and sesquiterpenes. In addition to these terpenoids released into the headspace, the terpenoid composition of the leaves alters upon herbivory. All this suggests an important role for terpenoids and their biosynthetic machinery in the defence against herbivory. Here, we show that the C. annuum genome contains a terpene synthase (TPS) gene family of 103 putative members of which structural analysis revealed that 27 encode functional enzymes. Transcriptome analysis showed that several TPS loci were differentially expressed upon herbivory in leaves of two C. annuum genotypes, that differ in susceptibility towards spider mites. The relative expression of upstream biosynthetic genes from the mevalonate and the methylerythritol phosphate pathway also altered upon herbivory, revealing a shift in the metabolic flux through the terpene biosynthetic module. The expression of multiple genes potentially acting downstream of the TPSs, including cytochrome P450 monooxygenases, UDP-glucosyl transferases, and transcription factors strongly correlated with the herbivory-induced TPS genes. A selection of herbivory-induced TPS genes was functionally characterized through heterologous expression and the products that these enzymes catalysed matched with the volatile and non-volatile terpenoids induced in response to herbivory.

The host plant strongly modulates acaricide resistance levels to mitochondrial complex II inhibitors in a multi-resistant field population of Tetranychus urticae

The two-spotted spider mite Tetranychus urticae is a polyphagous pest with an extraordinary ability to develop acaricide resistance. Here, we characterize the resistance mechanisms in a T. urticae population (VR-BE) collected from a Belgian tomato greenhouse, where the grower was unsuccessful in chemically controlling the mite population resulting in crop loss. Upon arrival in the laboratory, the VR-BE population was established both on bean and tomato plants as hosts. Toxicity bioassays on both populations confirmed that the population was highly multi-resistant, recording resistance to 12 out of 13 compounds tested from various mode of action groups. DNA sequencing revealed the presence of multiple target-site resistance mutations, but these could not explain resistance to all compounds. In addition, striking differences in toxicity for six acaricides were observed between the populations on bean and tomato. The highest difference was recorded for the complex II inhibitors cyenopyrafen and cyflumetofen, which were 4.4 and 3.3-fold less toxic for VR-BE mites on tomato versus bean. PBO synergism bioassays suggested increased P450 based detoxification contribute to the host-dependent toxicity. Given the involvement of increased detoxification, we subsequently determined genome-wide gene expression levels of VR-BE on both hosts, in comparison to a reference susceptible population, revealing overexpression of a large set of detoxification genes in VR-BE on both hosts compared to the reference. In addition, a number of mainly detoxification genes with higher expression in VR-BE on tomato compared to bean was identified, including several cytochrome P450s. Together, our work suggests that multi-resistant field populations can accumulate a striking number of target-site resistance mutations. We also show that the host plant can have a profound effect on the P450-associated resistance levels to cyenopyrafen and cyflumetofen.

Characterisation and localisation of plant metabolites involved in pharmacophagy in the turnip sawfly

Several herbivorous insects consume certain metabolites from plants for other purposes than nutrition, such as defence. Adults of the turnip sawfly, Athalia rosae take up specific terpenoids, called clerodanoids, from Ajuga reptans. These metabolites are slightly modified by the sawflies and influence their mating behaviour and defence against predators. We characterised these metabolites and investigated their localisation in the insect and the specificity of the uptake and metabolite modification. Therefore, we performed feeding assays with adults and larvae of A. rosae as well as larvae of Spodoptera exigua, followed by chemical analyses. Two main clerodanoid-derived metabolites were detected in the abdomen and thorax but also on the surface of the adults. Small amounts were also found in larvae of the sawfly, while they were not detectable in S. exigua. Our findings provide new insights into the peculiarities of pharmacophagy and specialised metabolism in A. rosae.

Tetraose steroidal glycoalkaloids from potato provide resistance against Alternaria solani and Colorado potato beetle

Plants with innate disease and pest resistance can contribute to more sustainable agriculture. Natural defence compounds produced by plants have the potential to provide a general protective effect against pathogens and pests, but they are not a primary target in resistance breeding. Here, we identified a wild relative of potato, Solanum commersonii, that provides us with unique insight in the role of glycoalkaloids in plant immunity. We cloned two atypical resistance genes that provide resistance to Alternaria solani and Colorado potato beetle through the production of tetraose steroidal glycoalkaloids (SGA). Moreover, we provide in vitro evidence to show that these compounds have potential against a range of different (potato pathogenic) fungi. This research links structural variation in SGAs to resistance against potato diseases and pests. Further research on the biosynthesis of plant defence compounds in different tissues, their toxicity, and the mechanisms for detoxification, can aid the effective use of such compounds to improve sustainability of our food production.

Evolution of chemosensory and detoxification gene families across herbivorous Drosophilidae

Herbivorous insects are exceptionally diverse, accounting for a quarter of all known eukaryotic species, but the genomic basis of adaptations that enabled this dietary transition remains poorly understood. Many studies have suggested that expansions and contractions of chemosensory and detoxification gene families-genes directly mediating interactions with plant chemical defenses-underlie successful plant colonization. However, this hypothesis has been challenging to test because the origins of herbivory in many insect lineages are ancient (>150 million years ago (mya)), obscuring genomic evolutionary patterns. Here, we characterized chemosensory and detoxification gene family evolution across Scaptomyza, a genus nested within Drosophila that includes a recently derived (<15 mya) herbivore lineage of mustard (Brassicales) specialists and carnation (Caryophyllaceae) specialists, and several nonherbivorous species. Comparative genomic analyses revealed that herbivorous Scaptomyza has among the smallest chemosensory and detoxification gene repertoires across 12 drosophilid species surveyed. Rates of gene turnover averaged across the herbivore clade were significantly higher than background rates in over half of the surveyed gene families. However, gene turnover was more limited along the ancestral herbivore branch, with only gustatory receptors and odorant-binding proteins experiencing strong losses. The genes most significantly impacted by gene loss, duplication, or changes in selective constraint were those involved in detecting compounds associated with feeding on living plants (bitter or electrophilic phytotoxins) or their ancestral diet (fermenting plant volatiles). These results provide insight into the molecular and evolutionary mechanisms of plant-feeding adaptations and highlight gene candidates that have also been linked to other dietary transitions in Drosophila.

Green Manure Crops as Food Source: Impact on the Performance of the Migratory Beet Webworm, Loxostege sticticalis (Lepidoptera: Pyralidae)

The application of green manure is crucial for achieving sustainable agriculture and animal husbandry, but pest management is often overlooked. Conducting a risk assessment for insect pests in green manure is essential. The beet webworm, Loxostege sticticalis, a polyphagous insect, is currently experiencing an outbreak in northern China, and represents a significant migratory pest. A two-sex life table and flight mill test approach was used to comprehensively evaluate the effects of three major legume green manure crops (Pisum sativam, Vicia sativa, and Vicia villosa) on the growth, development, fecundity, and flight ability of L. sticticalis in China. Our findings indicate that L. sticticalis cannot utilize V. villosa for generational development. L. sticticalis shows reduced performance on P. sativam and V. sativa compared to its suitable host Chenopodium album. However, both the population parameters (R0, r, λ, and T) and the population prediction results suggest that L. sticticalis can adapt to P. sativam and V. sativa. In the process of promoting green manure, careful consideration should be given to the selection of appropriate green manure varieties and the implementation of effective pest control measures during their planting. Our findings lay the groundwork for the promotion of green manure and implementation of an ecological management plan for L. sticticalis.

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.

High-quality chromosome-level scaffolds of the plant bug Pachypeltis micranthus provide insights into the availability of Mikania micrantha control

BACKGROUND

The plant bug, Pachypeltis micranthus Mu et Liu (Hemiptera: Miridae), is an effective potential biological control agent for Mikania micrantha H.B.K. (Asteraceae; one of the most notorious invasive weeds worldwide). However, limited knowledge about this species hindered its practical application and research. Accordingly, sequencing the genome of this mirid bug holds great significance in controlling M. micrantha.

RESULTS

Here, 712.72 Mb high-quality chromosome-level scaffolds of P. micranthus were generated, of which 707.51 Mb (99.27%) of assembled sequences were anchored onto 15 chromosome-level scaffolds with contig N50 of 16.84 Mb. The P. micranthus genome had the highest GC content (42.43%) and the second highest proportion of repetitive sequences (375.82 Mb, 52.73%) than the three other mirid bugs (i.e., Apolygus lucorum, Cyrtorhinus lividipennis, and Nesidiocoris tenuis). Phylogenetic analysis showed that P. micranthus clustered with other mirid bugs and diverged from the common ancestor approximately 200 million years ago. Gene family expansion and/or contraction were analyzed, and significantly expanded gene families associated with P. micranthus feeding and adaptation to M. micrantha were manually identified. Compared with the whole body, transcriptome analysis of the salivary gland revealed that most of the upregulated genes were significantly associated with metabolism pathways and peptidase activity, particularly among cysteine peptidase, serine peptidase, and polygalacturonase; this could be one of the reasons for precisely and highly efficient feeding by the oligophagous bug P. micranthus on M. micrantha.

CONCLUSION

Collectively, this work provides a crucial chromosome-level scaffolds resource to study the evolutionary adaptation between mirid bug and their host. It is also helpful in searching for novel environment-friendly biological strategies to control M. micrantha.

Caterpillars Detoxify Diterpenoid from Nepeta stewartiana by the Molting Hormone Gene CYP306A1

Herbivorous insects are well known for detoxifying a broad range of the defense compounds produced by the plants that they feed on, but knowledge of the mechanisms of detoxification is still very limited. Here, we describe a system in which two species of lepidopteran caterpillars metabolize an abietane diterpene from the plants of Nepeta stewartiana Diels to an oxygenated derivative that is less active biologically. We found that this transformation could be catalyzed by a cytochrome P450 enzyme in caterpillars, which are associated with molting. Most interestingly, abietane diterpene targets the molting-associated gene CYP306A1 to alter the content of molting hormones in the insect at specific developmental stages and competitively inhibit molting hormone metabolism. These findings identify the mechanism by which caterpillars are able to detoxify abietane diterpenoid through hydroxylation at the C-19 position, which may be opening up exciting research questions into the mechanisms of interaction between plants and insects.

Transcription factor CncC potentially regulates cytochrome P450 CYP321A1-mediated flavone tolerance in Helicoverpa armigera

Insect P450s play crucial roles in metabolizing insecticides and toxic plant allelochemicals. In this study, our results demonstrate that Helicoverpa armigera can adapt to a lower concentration of flavone (a flavonoid phytochemical), and P450 activities and CYP321A1 transcript levels significantly increase after exposure to flavone. RNAi-mediated knockdown of CYP321A1 significantly reduced the tolerance of H. armigera larvae to flavone. In addition, the regulatory mechanisms driving CYP321A1 induction following exposure to flavone were investigated. Flavone exposure significantly increased H₂O₂ generation in the larval midgut. The mRNA levels of HaCncC and HaMaf-s significantly increased in the midgut of H. armigera after exposure to flavone. Knockdown of HaCncC significantly inhibited expression of flavone-induced CYP321A1 and resulted in a decrease in flavone induction of CYP321A1. HaCncC knockdown significantly reduced the tolerance of H. armigera larvae to flavone. Taken together, these results indicate that HaCncC regulates expression of the CYP321A1 gene responsible for flavone tolerance in H. armigera.

Cytochrome P450 gene CYP6BQ8 mediates terpinen-4-ol susceptibility in the red flour beetle, Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae)

Cytochrome P450 proteins (CYPs) in insects can encode various detoxification enzymes and catabolize heterologous substances, conferring tolerance to insecticides. This study describes the identification of a P450 gene (CYP6BQ8) from Tribolium castaneum (Herbst) and investigation of its spatiotemporal expression profile and potential role in the detoxification of terpinen-4-ol, a component of plant essential oils. The developmental expression profile showed that TcCYP6BQ8 expression was relatively higher in early- and late-larval stages of T. castaneum compared with other developmental stages. Tissue expression profiles showed that TcCYP6BQ8 was mainly expressed in the head and integument of both larvae and adults. The expression profiling of TcCYP6BQ8 in developmental stages and tissues is closely related to the detoxification of heterologous substances. TcCYP6BQ8 expression was significantly induced after exposure to terpinen-4-ol, and RNA interference against TcCYP6BQ8 increased terpinen-4-ol-induced larval mortality from 47.78 to 66.67%. This indicates that TcCYP6BQ8 may be involved in T. castaneum's metabolism of terpinen-4-ol. Correlation investigation between the CYP6BQ8 gene and terpinen-4-ol resistance in T. castaneum revealed that the TcCYP6BQ8 gene was one of the factors behind T. castaneum's resistance to terpinen-4-ol. This discovery may provide a new theoretical foundation for future regulation of T. castaneum.

Evolution of chemosensory and detoxification gene families across herbivorous Drosophilidae

Herbivorous insects are exceptionally diverse, accounting for a quarter of all known eukaryotic species, but the genetic basis of adaptations that enabled this dietary transition remains poorly understood. Many studies have suggested that expansions and contractions of chemosensory and detoxification gene families - genes directly mediating interactions with plant chemical defenses - underlie successful plant colonization. However, this hypothesis has been challenging to test because the origins of herbivory in many lineages are ancient (>150 million years ago [mya]), obscuring genomic evolutionary patterns. Here, we characterized chemosensory and detoxification gene family evolution across Scaptomyza, a genus nested within Drosophila that includes a recently derived (<15 mya) herbivore lineage of mustard (Brassicales) specialists and carnation (Caryophyllaceae) specialists, and several non-herbivorous species. Comparative genomic analyses revealed that herbivorous Scaptomyza have among the smallest chemosensory and detoxification gene repertoires across 12 drosophilid species surveyed. Rates of gene turnover averaged across the herbivore clade were significantly higher than background rates in over half of the surveyed gene families. However, gene turnover was more limited along the ancestral herbivore branch, with only gustatory receptors and odorant binding proteins experiencing strong losses. The genes most significantly impacted by gene loss, duplication, or changes in selective constraint were those involved in detecting compounds associated with feeding on plants (bitter or electrophilic phytotoxins) or their ancestral diet (yeast and fruit volatiles). These results provide insight into the molecular and evolutionary mechanisms of plant-feeding adaptations and highlight strong gene candidates that have also been linked to other dietary transitions in Drosophila .

Effects of Methyl Jasmonate Fumigation on the Growth and Detoxification Ability of Spodoptera litura to Xanthotoxin

Methyl jasmonate (MeJA) is a volatile substance derived from jasmonic acid (JA), and it responds to interbiotic and abiotic stresses by participating in interplant communication. Despite its function in interplant communication, the specific role of MeJA in insect defense responses is poorly understood. In this study, we found that carboxylesterase (CarE) activities, glutathione-S-transferase (GSTs) activities, and cytochrome mono-oxygenases (P450s) content increased more after the feeding of diets containing xanthotoxin, while larvae exposed to MeJA fumigation also showed higher enzyme activity in a dose-dependent manner: lower and medium concentrations of MeJA induced higher detoxification enzyme activities than higher concentrations of MeJA. Moreover, MeJA improved the growth of larvae fed on the control diet without toxins and diets with lower concentrations of xanthotoxin (0.05%); however, MeJA could not protect the larvae against higher concentrations of xanthotoxin (0.1%, 0.2%). In summary, we demonstrated that MeJA is effective at inducing S. litura defense response, but the enhanced detoxifying ability could not overcome the strong toxins.

Molecular Mechanisms Underlying Host Plant Specificity in Aphids

Aphids are serious pests of agricultural and ornamental plants and important model systems for hemipteran-plant interactions. The long evolutionary history of aphids with their host plants has resulted in a variety of systems that provide insight into the different adaptation strategies of aphids to plants and vice versa. In the past, various plant-aphid interactions have been documented, but lack of functional tools has limited molecular studies on the mechanisms of plant-aphid interactions. Recent technological advances have begun to reveal plant-aphid interactions at the molecular level and to increase our knowledge of the mechanisms of aphid adaptation or specialization to different host plants. In this article, we compile and analyze available information on plant-aphid interactions, discuss the limitations of current knowledge, and argue for new research directions. We advocate for more work that takes advantage of natural systems and recently established molecular techniques to obtain a comprehensive view of plant-aphid interaction mechanisms.

Exogenous methyl jasmonate induced cassava defense response and enhanced resistance to Tetranychus urticae

Exogenous application of methyl jasmonate (MeJA) could activate plant defense response against the two-spotted spider mite (TSSM), Tetranychus urticae Koch, in different plants. However, whether MeJA can also serve as an elicitor in cassava (Manihot esculenta Crantz) remains unknown. In this study, induced defense responses were investigated in TSSM-resistant cassava variety C1115 and TSSM-susceptible cassava variety KU50 when applied with MeJA. The performance of TSSM feeding on cassava plants that were pre-treated with various concentrations of MeJA was first evaluated. Subsequently, the activities of antioxidative enzymes (superoxide dismutase and catalase), detoxification enzymes (glutathione S-transferase, cytochrome P450 and carboxylesterase) and digestive enzymes (protease, amylase and invertase) in TSSM were analyzed at days 1, 2, 4 and 8 post-feeding. The results showed that MeJA treatment can induce cassava defense responses to TSSM in terms of reducing egg production and adult longevity as well as slowing development and prolonging the egg stage. Noticeably, C1115 exhibited stronger inhibition of TSSM development and reproduction than KU50. In addition, the activities of all the tested enzymes were induced in both C1115 and KU50, the most in C1115. We conclude that exogenous methyl jasmonate can induce cassava defense responses and enhance resistance to TSSM.

UHPLC-MS/MS Analysis of the Accumulation and Excretion of Steroidal Glycoalkaloids Consumed by Potato Tuber Moth (Phthorimaea operculella) Larvae under Different Feeding Treatments

Food poisoning caused by potato glycoside alkaloids (SGA) remains a critical factor that affects potato production safety. The potato tuber moth (Phthorimaea operculella) is a notorious pest that displays good adaptability to SGA in potato tissues. Studies that explore the mechanisms underlying SGA homeostasis in potato tuber moth larvae are urgently needed. In this study, ultra-high-performance liquid chromatography (UHPLC)-triple quadrupole mass spectrometry (MS/MS) was applied to detect the dominant SGA substances α-solanine and α-chaconine in potato leaves and PTM larval tissues. From the highest to lowest SGA concentrations, the potato cultivars studied were ranked as follows: DS47, LS6, DS23 and QS9. To exclude the influence of nutrients within different potato varieties, different SGA containing (0%, 0.1%, 0.2%, 0.3% and 0.4%) the artificial diet treatment groups were added. DS47 and 0.3% SGA-containing artificial diets presented the best conditions for PTM growth, development and reproduction compared to other potato cultivars and artificial diet controls. The potato tuber moth larva tissues were dissected and the SGA content within different tissues were detected using an UHPLC machine. The results showed that α-chaconine was dispersed in the feces, midgut, hindgut, head and cuticle, and α-solanine was distributed only in the feces and midgut. Antibiotic-treated insects exhibited higher concentrations of SGA than the normal microbiome group. Furthermore, the SGA concentrations of 100 newly-hatched PTM larvae and puparia were detected, with both of them found to contain small amounts of SGA. The results showed that ecdysis and the excretion process were effective approaches used by the potato tuber moth to equilibrate internal SGA accumulation. The microorganism-decreased SGA concentrations were excited in their gut. SGA may transfer from adults to the next generation, and SGAs in PTM are inheritable. In this study, we demonstrated that the potato tuber moth possessed an effective method to preliminarily decrease high SGA accumulation in potato.

Comparative transcriptome analysis reveals differences in gene expression in whitefly following individual or combined applications of Akanthomyces attenuatus (Zare & Gams) and matrine

BACKGROUND

Bemisia tabaci Gennadius (Hemiptera: Aleyrodidae) is a serious pest of crops in different regions of the world. Our recent studies on the joint application of Akanthomyces attenuatus (a pathogenic insect fungus) and matrine (a botanical insecticide) against B. tabaci have shown promising results. Using RNA sequencing (RNA-Seq), we identified differentially expressed genes involved in whitefly responses to single or mixed applications of A. attenuatus and matrine.

METHODS

In this study, we compared the transcriptome profiles of B. tabaci treated with individual and combined treatments of A. attenuatus and matrine to determine variations in gene expression among whiteflies in response to different treatments.

RESULTS

Transcriptomic data analysis showed differential expression of 71, 1194, and 51 genes in response to A. attenuatus (BtA), matrine (BtM), and A. attenuatus + matrine (BtAM) treatment, respectively. A total of 65 common differentially expressed genes (DEGs) were identified between whiteflies treated with A. attenuatus (BtA) and matrine (BtM). A comparison of DEGs across the three treatments (BtA, BtM, and BtAM) revealed two common DEGs. The results also revealed that AMPK signaling, apoptosis, and drug metabolism pathways are likely involved in whitefly defense responses against A. attenuatus and matrine infection. Furthermore, a notable suppression of general metabolism and immune response genes was observed in whiteflies treated with A. attenuatus + matrine (BtAM) compared to whiteflies treated with individual A. attenuatus (BtA) or matrine (BtM) treatments.

CONCLUSION

Dynamic changes in the number of differentially expressed genes were observed in B. tabaci subjected to different treatments (BtA, BtM, and BtAM). To the best of our knowledge, this is the first report on the molecular interactions between whitefly and individual or combined treatments of A. attenuatus and matrine. These results will further improve our knowledge of the infection mechanism and complex biochemical processes involved in the synergistic action of A. attenuatus and matrine against B. tabaci.

Biodegradation of Free Gossypol by Helicoverpa armigera Carboxylesterase Expressed in Pichia pastoris

Gossypol is a polyphenolic toxic secondary metabolite derived from cotton. Free gossypol in cotton meal is remarkably harmful to animals. Furthermore, microbial degradation of gossypol produces metabolites that reduce feed quality. We adopted an enzymatic method to degrade free gossypol safely and effectively. We cloned the gene cce001a encoding carboxylesterase (CarE) into pPICZαA and transformed it into Pichia pastoris GS115. The target protein was successfully obtained, and CarE CCE001a could effectively degrade free gossypol with a degradation rate of 89%. When esterase was added, the exposed toxic groups of gossypol reacted with different amino acids and amines to form bound gossypol, generating substances with (M + H) m/z ratios of 560.15, 600.25, and 713.46. The molecular formula was C₂₇H₂₈O₁₃, C₃₄H₃₆N₂O₆, and C₄₇H₅₉N₃O₃. The observed instability of the hydroxyl groups caused the substitution and shedding of the group, forming a substance with m/z of 488.26 and molecular formula C₃₁H₃₆O₅. These properties render the CarE CCE001a a valid candidate for the detoxification of cotton meal. Furthermore, the findings help elucidate the degradation process of gossypol in vitro.

Trans-driven variation in expression is common among detoxification genes in the extreme generalist herbivore Tetranychus urticae

The extreme adaptation potential of the generalist herbivore Tetranychus urticae (the two-spotted spider mite) to pesticides as well as diverse host plants has been associated with clade-specific gene expansions in known detoxifying enzyme families, and with extensive and rapid transcriptional responses. However, how this broad transcriptional potential is regulated remains largely unknown. Using a parental/F1 design in which four inbred strains were crossed to a common inbred strain, we assessed the genetic basis and inheritance of gene expression variation in T. urticae. Mirroring known phenotypic variation in the progenitor strains of the inbreds, we confirmed that the inbred strains we created were genetically distinct, varied markedly in pesticide resistance, and also captured variation in host plant fitness as is commonly observed in this species. By examining differences in gene expression between parents and allele-specific expression in F1s, we found that variation in RNA abundance was more often explained in trans as compared to cis, with the former associated with dominance in inheritance. Strikingly, in a gene ontology analysis, detoxification genes of the cytochrome P450 monooxygenase (CYP) family, as well as dioxygenases (DOGs) acquired from horizontal gene transfer from fungi, were specifically enriched at the extremes of trans-driven up- and downregulation. In particular, multiple CYPs and DOGs with broad substrate-specificities for pesticides or plant specialized compounds were exceptionally highly upregulated as a result of trans-regulatory variation, or in some cases synergism of cis and trans, in the most multi-pesticide resistant strains. Collectively, our findings highlight the potential importance of trans-driven expression variation in genes associated with xenobiotic metabolism and host plant use for rapid adaptation in T. urticae, and also suggests modular control of these genes, a regulatory architecture that might ameliorate negative pleiotropic effects.

Effects of Elevated CO2 Concentration on Host Adaptability and Chlorantraniliprole Susceptibility in Spodoptera frugiperda

Elevated atmospheric carbon dioxide concentrations (eCO2) can affect both herbivorous insects and their host plants. The fall armyworm (FAW), Spodoptera frugiperda, is a highly polyphagous agricultural pest that may attack more than 350 host plant species and has developed resistance to both conventional and novel-action insecticides. However, the effects of eCO2 on host adaptability and insecticide resistance of FAW are unclear. We hypothesized that eCO2 might affect insecticide resistance of FAW by affecting its host plants. To test this hypothesis, we investigated the effect of eCO2 on (1) FAW's susceptibility to chlorantraniliprole after feeding on wheat, (2) FAW's population performance traits (including the growth and reproduction), and (3) changes in gene expression in the FAW by transcriptome sequencing. The toxicity of chlorantraniliprole against the FAW under eCO2 (800 µL/L) stress showed that the LC50 values were 2.40, 2.06, and 1.46 times the values at the ambient CO2 concentration (400 µL/L, aCO2) for the three generations, respectively. Under eCO2, the life span of pupae and adults and the total number of generations were significantly shorter than the FAW under aCO2. Compared to the aCO2 treatment, the weights of the 3rd and 4th instar larvae and pupae of FAW under eCO2 were significantly heavier. Transcriptome sequencing results showed that more than 79 detoxification enzyme genes in FAW were upregulated under eCO2 treatment, including 40 P450, 5 CarE, 17 ABC, and 7 UGT genes. Our results showed that eCO2 increased the population performance of FAW on wheat and reduced its susceptibility to chlorantraniliprole by inducing the expression of detoxification enzyme genes. This study has important implications for assessing the damage of FAW in the future under the environment of increasing atmospheric CO2 concentration.

Enhanced top-down control of herbivore population growth on plants with impaired defences

Herbivore densities can be regulated by bottom-up and top-down forces such as plant defences and natural enemies, respectively. These forces can interact with each other to increase plant protection against herbivores; however, how much complementarity exists between bottom-up and top-down forces still remains to be fully elucidated. Particularly, because plant defences can hinder natural enemies, how these interactions affect herbivore performance and dynamics remains elusive.To address this topic, we performed laboratory and greenhouse bioassays with herbivorous mite pests and predatory mites on mutant tomato plants that lack defensive hairs on stems and leaves. Particularly, we investigated the behaviour and population dynamics of different phytophagous mite species in the absence and presence of predatory mites.We show that predatory mites do not only perform better on tomatoes lacking defensive hairs but also that they can suppress herbivore densities better and faster on these hairless plants. Hence, top-down control of herbivores by natural enemies more than compensated the reduced bottom-up herbivore control by plant defences.Our results lead to the counter-intuitive insight that removing, instead of introducing, plant defence traits can result in superior protection against important pests through biological control. Read the free Plain Language Summary for this article on the Journal blog.

Rosa chinensis Cultivars Affect Fitness-Related Characteristics and Digestive Physiology of the Western Flower Thrips, Frankliniella occidentalis Pergande (Thysanoptera: Thripidae)

Host plant species will influence the population and physiological performance of insects. Frankliniella occidentalis is a well-known invasive pest commonly found on flowering plants. Herein, the population development of F. occidentalis was investigated on the flowers of different Rosa chinensis cultivars (Ruby, Love, Parade, Pink Peace, and Mohana), and the digestive enzyme activities in thrips were measured after feeding on these flowers. The developmental times of F. occidentalis from egg to adult were 10.07, 10.37, 11.64, 10.66, and 10.90 d on Ruby, Love, Parade, Pink Peace, and Mohana, respectively. Significant differences in fecundity were also observed, with the greatest fecundity levels of F. occidentalis on Ruby (82.96) and the lowest on Mohana (63.40). F. occidentalis showed the greatest R0 on Ruby (43.57), followed by Love (36.46), Parade (33.00), Pink Peace (27.97), and Mohana (23.21). The rm showed a similar trend, with values of 0.156, 0.145, 0.141, 0.134, and 0.130, respectively. There were significant differences in digestive enzyme activities in F. occidentalis on different flowers, and different digestive enzymes showed different performance among these plants. The highest amylase and lipase activities in F. occidentalis were on Ruby, on which F. occidentalis had the fastest development rate and the highest R0, whereas the highest trypsin activity was on Pink Peace. All three digestive enzymes in thrips showed the lowest activities on Mohana. The varied population development of F. occidentalis associated with R. chinensis cultivars may be related to their digestive enzyme performance, which plays important roles in nutrient metabolism and insect growth.