Metabolic enzymes associated with xenobiotic and chemosensory responses in Nasonia vitripennis

Comparative Genomics Uncovers the Evolutionary Dynamics of Detoxification and Insecticide Target Genes Across 11 Phlebotomine Sand Flies

Sand flies infect more than 1 million people annually with Leishmania parasites and other bacterial and viral pathogens. Progress in understanding sand fly adaptations to xenobiotics has been hampered by the limited availability of genomic resources. To address this gap, we sequenced, assembled, and annotated the transcriptomes of 11 phlebotomine sand fly species. Subsequently, we leveraged these genomic resources to generate novel evolutionary insights pertaining to their adaptations to xenobiotics, including those contributing to insecticide resistance. Specifically, we annotated over 2,700 sand fly detoxification genes and conducted large-scale phylogenetic comparisons to uncover the evolutionary dynamics of the five major detoxification gene families: cytochrome P450s (CYPs), glutathione-S-transferases (GSTs), UDP-glycosyltransferases (UGTs), carboxyl/cholinesterases (CCEs), and ATP-binding cassette (ABC) transporters. Using this comparative approach, we show that sand flies have evolved diverse CYP and GST gene repertoires, with notable lineage-specific expansions in gene groups evolutionarily related to known xenobiotic metabolizers. Furthermore, we show that sand flies have conserved orthologs of (i) CYP4G genes involved in cuticular hydrocarbon biosynthesis, (ii) ABCB genes involved in xenobiotic toxicity, and (iii) two primary insecticide targets, acetylcholinesterase-1 (Ace1) and voltage gated sodium channel (VGSC). The biological insights and genomic resources produced in this study provide a foundation for generating and testing hypotheses regarding the molecular mechanisms underlying sand fly adaptations to xenobiotics.

Identification and expression dynamics of CYPome across different developmental stages of Maconellicoccus hirsutus (Green)

Maconellicoccus hirsutus is a highly polyphagous insect pest, posing a substantial threat to various crop sp., especially in the tropical and sub-tropical regions of the world. While extensive physiological and biological studies have been conducted on this pest, the lack of genetic information has hindered our understanding of the molecular mechanisms underlying its growth, development, and xenobiotic metabolism. The Cytochrome P450 gene, a member of the CYP gene superfamily ubiquitous in living organisms is associated with growth, development, and the metabolism of both endogenous and exogenous substances, contributing to the insect's adaptability in diverse environments. To elucidate the specific role of the CYP450 gene family in M. hirsutus which has remained largely unexplored, a de novo transcriptome assembly of the pink mealybug was constructed. A total of 120 proteins were annotated as CYP450 genes through homology search of the predicted protein sequences across different databases. Phylogenetic studies resulted in categorizing 120 CYP450 genes into four CYP clans. A total of 22 CYP450 families and 30 subfamilies were categorized, with CYP6 forming the dominant family. The study also revealed five genes (Halloween genes) associated with the insect hormone biosynthesis pathway. Further, the expression of ten selected CYP450 genes was studied using qRT-PCR across crawler, nymph, and adult stages, and identified genes that were expressed at specific stages of the insects. Thus, the findings of this study reveal the expression dynamics and possible function of the CYP450 gene family in the growth, development, and adaptive strategies of M. hirsutus which can be further functionally validated.

The genomic and cellular basis of biosynthetic innovation in rove beetles

How evolution at the cellular level potentiates macroevolutionary change is central to understanding biological diversification. The >66,000 rove beetle species (Staphylinidae) form the largest metazoan family. Combining genomic and cell type transcriptomic insights spanning the largest clade, Aleocharinae, we retrace evolution of two cell types comprising a defensive gland-a putative catalyst behind staphylinid megadiversity. We identify molecular evolutionary steps leading to benzoquinone production by one cell type via a mechanism convergent with plant toxin release systems, and synthesis by the second cell type of a solvent that weaponizes the total secretion. This cooperative system has been conserved since the Early Cretaceous as Aleocharinae radiated into tens of thousands of lineages. Reprogramming each cell type yielded biochemical novelties enabling ecological specialization-most dramatically in symbionts that infiltrate social insect colonies via host-manipulating secretions. Our findings uncover cell type evolutionary processes underlying the origin and evolvability of a beetle chemical innovation.

Overexpression of an Integument Esterase Gene LbEST-inte4 Infers the Malathion Detoxification in Liposcelis bostrychophila (Psocoptera: Liposcelididae)

Liposcelis bostrychophila, commonly known as booklouse, is an important stored-product pest worldwide. Studies have demonstrated that booklices have developed resistance to several insecticides. In this study, an integument esterase gene, LbEST-inte4, with upregulated expression, was characterized in L. bostrychophila. Knockdown of LbEST-inte4 resulted in a substantial increase in the booklice susceptibility to malathion. Overexpression of LbEST-inte4 in Drosophila melanogaster significantly enhanced its malathion tolerance. Molecular modeling and docking analysis suggested potential interactions between LbEST-inte4 and malathion. When overexpressed LbEST-inte4 in Sf9 cells, a notable elevation in esterase activity and malathion tolerance was observed. HPLC analysis indicated that the LbEST-inte4 enzyme could effectively degrade malathion. Taken together, the upregulated LbEST-inte4 appears to contribute to malathion tolerance in L. bostrychophila by facilitating the depletion of malathion. This study elucidates the molecular mechanism underlying malathion detoxification and provides the foundations for the development of effective prevention and control measures against psocids.

Identification and biochemical characterization of a carboxylesterase gene associated with β-cypermethrin resistance in Dermanyssus gallinae

Dermanyssus gallinae is a major hematophagous ectoparasite in layer hens. Although the acaricide β-cypermethrin has been used to control mites worldwide, D. gallinae has developed resistance to this compound. Carboxylesterases (CarEs) are important detoxification enzymes that confer resistance to β-cypermethrin in arthropods. However, CarEs associated with β-cypermethrin resistance in D. gallinae have not yet been functionally characterized. Here, we isolated a CarE gene (Deg-CarE) from D. gallinae and assayed its activity. The results revealed significantly higher expression of Deg-CarE in the β-cypermethrin-resistant strain (RS) than in the susceptible strain (SS) toward α-naphthyl acetate (α-NA) and β-naphthyl acetate (β-NA). These findings suggest that enhanced esterase activities might have contributed to β-cypermethrin resistance in D. gallinae. Quantitative real-time PCR analysis revealed that Deg-CarE expression levels were significantly higher in adults than in other life stages. Although Deg-CarE was upregulated in the RS, significant differences in gene copy numbers were not observed. Additionally, Deg-CarE expression was significantly induced by β-cypermethrin in both the SS and RS. Moreover, silencing Deg-CarE via RNA interference decreased the enzyme activity and increased the susceptibility of the RS to β-cypermethrin, confirming that Deg-CarE is crucial for β-cypermethrin detoxification. Finally, recombinant Deg-CarE (rDeg-CarE) expressed in Escherichia coli displayed high enzymatic activity toward α/β-NA. However, metabolic analysis indicated that rDeg-CarE did not directly metabolize β-cypermethrin. The collective findings indicate that D. gallinae resistance to β-cypermethrin is associated with elevated CarEs protein activity and increased Deg-CarE expression levels. These findings provide insights into the metabolic resistance of D. gallinae and offer scientific guidance for the management and control of D. gallinae.

Unveiling Molecular Effects of the Secondary Metabolite 2-Dodecanone in the Model Hymenopteran Nasonia vitripennis

Over the past decade, multiple studies have suggested that the secondary metabolites produced by plants against herbivorous insects could be used as biopesticides. However, as the molecular mechanism of action of these compounds remains unknown, it is difficult to predict how they would affect non-target insects; thus, their innocuity needs to be clarified. Here, we investigate, from the molecular level to the organism, the responses of a useful parasitic insect Nasonia vitripennis (Walker, 1836) being exposed at the pupae stage for 48 h (up to 6 days) to sublethal doses (5 µg/L and 500 µg/L) of 2-Dodecanone. 2-Dodecanone altered the gene expression of genes related to ecdysone-related pathways, biotransformation, and cell homeostasis. A significant induction of ecdysone response-genes (EcR, usp, E78, Hr4, Hr38) was detected, despite no significant differences in ecdysteroid levels. Regarding the cell homeostasis processes, the gene l(2)efl was differentially altered in both experimental conditions, and a dose-dependent induction of hex81 was observed. 2-Dodecanone also triggered an induction of Cyp6aQ5 activity. Finally, 2-Dodecanone exposure had a significant effect on neither development time, energy reserves, nor egg-laying capacity; no potential genotoxicity was detected. For the first time, this study shows evidence that 2-Dodecanone can modulate gene expression and interfere with the ecdysone signalling pathway in N. vitripennis. This could lead to potential endocrine alterations and highlight the suitability of this organism to improve our general understanding of the molecular effects of plant defences in insects. Our findings provide new insights into the toxicity of 2-Dodecanone that could potentially be explored in other species and under field conditions for plant protection and pest management as a means to reduce reliance on synthetic pesticides.

Gene expression plasticity facilitates different host feeding in Ips sexdentatus (Coleoptera: Curculionidae: Scolytinae)

Host shift is ecologically advantageous and a crucial driver for herbivore insect speciation. Insects on the non-native host obtain enemy-free space and confront reduced competition, but they must adapt to survive. Such signatures of adaptations can often be detected at the gene expression level. It is astonishing how bark beetles cope with distinct chemical environments while feeding on various conifers. Hence, we aim to disentangle the six-toothed bark beetle (Ips sexdentatus) response against two different conifer defences upon host shift (Scots pine to Norway spruce). We conducted bioassay and metabolomic analysis followed by RNA-seq experiments to comprehend the beetle's ability to surpass two different terpene-based conifer defence systems. Beetle growth rate and fecundity were increased when reared exclusively on spruce logs (alternative host) compared to pine logs (native host). Comparative gene expression analysis identified differentially expressed genes (DEGs) related to digestion, detoxification, transporter activity, growth, signalling, and stress response in the spruce-feeding beetle gut. Transporter genes were highly abundant during spruce feeding, suggesting they could play a role in pumping a wide variety of endogenous and xenobiotic compounds or allelochemicals out. Trehalose transporter (TRET) is also up-regulated in the spruce-fed beetle gut to maintain homeostasis and stress tolerance. RT-qPCR and enzymatic assays further corroborated some of our findings. Taken together, the transcriptional plasticity of key physiological genes plays a crucial role after the host shift and provides vital clues for the adaptive potential of bark beetles on different conifer hosts.

The Molecular Resistance Mechanisms of European Earwigs from Apple Orchards Subjected to Different Management Strategies

To date, apple orchards are among the most treated crops in Europe with up to 35 chemical treatments per year. Combining control methods that reduce the number of pesticide treatments is essential for agriculture and more respectful of the environment, and the use of predatory insects such as earwigs may be valuable to achieve this goal. European earwigs, Forficula auricularia (Dermaptera: Forficulidae) are considered beneficial insects in apple orchards where they can feed on many pests like aphids. The aim of this study was to investigate the potential impact of orchards' insecticide treatments on resistance-associated molecular processes in natural populations of earwigs. Because very few molecular data are presently available on earwigs, our first goal was to identify earwig resistance-associated genes and potential mutations. Using earwigs from organic, integrated pest management or conventional orchards, we identified mutations in acetylcholinesterase 2, α1 and β2 nicotinic acetylcholine receptors. In addition, the expression level of these targets and of some essential detoxification genes were monitored using RT-qPCR. Unexpectedly, earwigs collected in organic orchards showed the highest expression for acetylcholinesterase 2. Four cytochromes P450, one esterase and one glutathione S-transferases were over-expressed in earwigs exposed to various management strategies in orchards. This first study on resistance-associated genes in Forficula auricularia paves the way for future experimental studies aimed at better understanding the potential competition between natural enemies in apple orchards in order to optimize the efficiency of biocontrol.

Functional orthologs of honeybee CYP6AQ1 in stingless bees degrade the butenolide insecticide flupyradifurone

Flupyradifurone (FPF), a novel butenolide insecticide binding to nicotinic acetylcholine receptors (nAChRs), has been shown to be less acutely toxic to western honey bees (Apis mellifera) than other insecticides such as neonicotinoids sharing the same target-site. A previous study revealed that this is due to enhanced oxidative metabolism of FPF, mediated by three cytochrome P450 monooxygenases (P450s), including CYP6AQ1. Therefore, we followed a toxicogenomics approach and investigated the potential role of functional CYP6AQ1 orthologs in FPF metabolism from eight different bee species, including stingless bees (Tribe: Meliponini). We conducted a phylogenetic analysis on four stingless bee species, including Frieseomelitta varia, Heterotrigona itama, Melipona quadrifasciata and Tetragonula carbonaria to identify CYP6AQ1-like functional orthologs. Three non-Meliponini, but tropical bee species, i.e., Ammobates syriacus, Euglossa dilemma and Megalopta genalis were analyzed as well. We identified candidate P450s in all (neo)tropical species with greater than 61% and 67% predicted protein sequence identities when compared to A. mellifera CYP6AQ1 and Bombus terrestris CYP6AQ26, respectively. Heterologous expression in High Five insect cells of these functional orthologs revealed a common coumarin substrate profile and a preference for the O-debenzylation of bulkier substrates. Competition assays using the fluorescent probe substrate 7-benzyloxymethoxy-4-trifluoromethylcoumarin (BOMFC) with these enzymes indicated inhibition of BOMFC metabolism by increasing concentrations of FPF. Furthermore, UPLC-MS/MS analysis revealed the capacity of all CYP6AQ1-like orthologs to metabolize FPF by hydroxylation in vitro at various levels, indicating a conserved FPF detoxification potential in different (neo)tropical bee species including Meliponini. This research, employing a toxicogenomics approach, provides important insights into the potential of stingless and other tropical bee species to detoxify FPF, and highlights the significance of investigating the detoxification mechanisms of insecticides in non-Apis bee species by molecular tools to inform risk assessment and conservation efforts.

Role of the epsilon glutathione S-transferases in xanthotoxin tolerance in Spodoptera litura

Spodoptera litura, a polyphagous lepidopteran pest, demonstrates a remarkable capacity to adapt to varying host plants by efficiently detoxifying phytochemicals. However, the underlying mechanism for this adaptation is not well understood. Herein, twenty eplison glutathione S-transferase genes (GSTes) were characterized and their roles in phytochemical tolerance were analyzed in S. litura. Most of the GSTe genes were mainly expressed in the larval midgut and fat body. Exposure to the phytochemicals, especially xanthotoxin, induced the expression of most GSTe genes. Molecular docking analysis revealed that xanthotoxin could form stable bonds with six xanthotoxin-responsive GSTes, with binding free energies ranging from -36.44 to -68.83 kcal mol-1. Knockdown of these six GSTe genes increased the larval susceptibility to xanthotoxin. Furthermore, xanthotoxin exposure significantly upregulated the expression of two transcription factor genes CncC and MafK. Silencing of either CncC or MafK reduced the expression of GSTe16, which exhibited the largest change in response to xanthotoxin. Additionally, analysis of the promoter sequence of GSTe16 revealed the presence of seven CncC/Maf binding sites. Luciferase reporter assays showed that CncC and MafK enhanced the expression of GSTe16, leading to the increased xanthotoxin tolerance in S. litura. These findings provide insight into the functions and transcriptional regulatory mechanisms of GSTes, thereby enhancing our understanding of the role of GSTs in the adaptation of lepidopteran pests to phytochemicals.

Evolution of five environmentally responsive gene families in a pine-feeding sawfly, Neodiprion lecontei (Hymenoptera: Diprionidae)

A central goal in evolutionary biology is to determine the predictability of adaptive genetic changes. Despite many documented cases of convergent evolution at individual loci, little is known about the repeatability of gene family expansions and contractions. To address this void, we examined gene family evolution in the redheaded pine sawfly Neodiprion lecontei, a noneusocial hymenopteran and exemplar of a pine-specialized lineage evolved from angiosperm-feeding ancestors. After assembling and annotating a draft genome, we manually annotated multiple gene families with chemosensory, detoxification, or immunity functions before characterizing their genomic distributions and molecular evolution. We find evidence of recent expansions of bitter gustatory receptor, clan 3 cytochrome P450, olfactory receptor, and antimicrobial peptide subfamilies, with strong evidence of positive selection among paralogs in a clade of gustatory receptors possibly involved in the detection of bitter compounds. In contrast, these gene families had little evidence of recent contraction via pseudogenization. Overall, our results are consistent with the hypothesis that in response to novel selection pressures, gene families that mediate ecological interactions may expand and contract predictably. Testing this hypothesis will require the comparative analysis of high-quality annotation data from phylogenetically and ecologically diverse insect species and functionally diverse gene families. To this end, increasing sampling in under-sampled hymenopteran lineages and environmentally responsive gene families and standardizing manual annotation methods should be prioritized.

Sublethal effects of halofenozide on larval development and detoxification in Phaedon brassicae (Coleoptera: Chrysomelidae)

The brassica leaf beetle, Phaedon brassicae, is a serious defoliator of cruciferous crops. Halofenozide (Hal), an ecdysone agonist, is a new class of insect growth-regulating insecticide. Our preliminary experiment revealed the outstanding larval toxicity of Hal against P. brassicae. However, the metabolic degradation of this compound in insects remains unclear. In this study, oral administration of Hal at LC10 and LC25 caused severe separation of the cuticle and epidermis, leading to larval molting failure. Sublethal dose exposure also significantly reduced the larval respiration rate as well as their pupation rates and pupal weights. Conversely, the activities of the multifunctional oxidase, carboxylesterase (CarE), and glutathione S-transferase (GST) were significantly enhanced in Hal-treated larvae. Further analysis using RNA sequencing identified 64 differentially expressed detoxifying enzyme genes, including 31 P450s, 13 GSTs, and 20 CarEs. Among the 25 upregulated P450s, 22 genes were clustered into the CYP3 clan, and the other 3 genes belonged to the CYP4 clan. Meanwhile, 3 sigma class GSTs and 7 epsilon class GSTs were dramatically increased, accounting for the majority of the upregulated GSTs. Moreover, 16 of the 18 overexpressed CarEs were clustered into the coleopteran xenobiotic-metabolizing group. These results showed the augmented expression of detoxification genes in P. brassicae after exposed to sublethal dose of Hal, and helped to better understand the potential metabolic pathways that could contribute to the reduced sensitivity to Hal in this pest. Overall, a deep insight into the detoxification mechanisms would provide practical guidance for the field management of P. brassicae.

Identification of metabolizing enzyme genes associated with xenobiotics and odorants in the predatory stink bug Arma custos based on transcriptome analysis

The predatory stink bug, Arma custos, is a highly effective beneficial predator of crop pests. The lack of gene information related to xenobiotic detoxification and odorant degrading enzymes in the predator stink bugs to date has limited our ability for more in-depth studies of biological control. Hence, we conducted de novo assembly of the A. custos transcriptome from guts, antennae, and other tiussue samples of 5th instar larvae using Illumina sequencing technology. A total of 91, 50 and 23 genes of cytochrome P450 monooxygenases (CYPs), carboxyl/choline esterases (CCEs) and glutathione S-transferases (GSTs) genes were identified, respectively. Gene expansions of CYP3 and CYP4 clans and the hormone and pheromone processing CCE class were found in A. custos. Analysis of tissue-specific expression patterns showed that 37 CYPs, 14 CCEs and 8 GSTs were enriched in guts, and 6 CYPs, 5 CCEs and 2 GSTs were up-regulated in antennae, suggesting their potential roles on xenobiotics detoxification and ordorant degradation. Gene information data presented here could be useful for a deeper understanding of the ecology, physiology and behavior of this beneficial species and could be helpful to improve their bio-control efficiency.

Identification, expression profiles and involvement in insecticides tolerance and detoxification of carboxylesterase genes in Bactrocera dorsalis

Carboxylesterases (CarEs) are a multifunctional superfamily of enzymes and play an important role in detoxification of various insecticides in insects. The oriental fruit fly, Bactrocera dorsalis, is one of the most destructive agricultural pests and has developed different degrees of resistance to organophosphates in field. However, the involvement of BdCarEs in tolerance or resistance to other alternative insecticides are still unclear. In the present study, 33 BdCarEs genes were identified based on the genome database of B. dorsalis. Phylogenetic analysis demonstrated that they were classified into nine clades, with abundance of α-esterases. Meanwhile, the sequence characterization and the chromosome distribution were also analyzed. The spatiotemporal expression analysis of BdCarEs genes suggested that the diversity of potential function in different physiological processes. With the exception of BdCarE21, all BdCarEs genes responded to at least one insecticide exposure, and BdCarE20 was found to be up-regulated after exposure to all five tested insecticides individually. Eight BdCarEs genes were overexpressed in MR strain when compared to that in SS strain. Subsequently, knockdown the expression of representative BdCarEs genes significantly increased the susceptibility of the oriental fruit fly to corresponding insecticides, which indicated that the tested BdCarEs genes contributed to one or multiple insecticide detoxification. These findings provide valuable insights into the potential role in respond to tolerance or resistance to insecticides with different mode of action, and will facilitate development of efficiency management strategy for B. dorsalis.

The genomic and cellular basis of biosynthetic innovation in rove beetles

How evolution at the cellular level potentiates change at the macroevolutionary level is a major question in evolutionary biology. With >66,000 described species, rove beetles (Staphylinidae) comprise the largest metazoan family. Their exceptional radiation has been coupled to pervasive biosynthetic innovation whereby numerous lineages bear defensive glands with diverse chemistries. Here, we combine comparative genomic and single-cell transcriptomic data from across the largest rove beetle clade, Aleocharinae. We retrace the functional evolution of two novel secretory cell types that together comprise the tergal gland-a putative catalyst behind Aleocharinae's megadiversity. We identify key genomic contingencies that were critical to the assembly of each cell type and their organ-level partnership in manufacturing the beetle's defensive secretion. This process hinged on evolving a mechanism for regulated production of noxious benzoquinones that appears convergent with plant toxin release systems, and synthesis of an effective benzoquinone solvent that weaponized the total secretion. We show that this cooperative biosynthetic system arose at the Jurassic-Cretaceous boundary, and that following its establishment, both cell types underwent ∼150 million years of stasis, their chemistry and core molecular architecture maintained almost clade-wide as Aleocharinae radiated globally into tens of thousands of lineages. Despite this deep conservation, we show that the two cell types have acted as substrates for the emergence of adaptive, biochemical novelties-most dramatically in symbiotic lineages that have infiltrated social insect colonies and produce host behavior-manipulating secretions. Our findings uncover genomic and cell type evolutionary processes underlying the origin, functional conservation and evolvability of a chemical innovation in beetles.

Inducible Gut-Specific Carboxylesterase SlCOE030 in Polyphagous Pests of Spodoptera litura Conferring Tolerance between Nicotine and Cyantraniliprole

Insecticides tolerance in herbivorous arthropods is associated with preadaptation to host plant allelochemicals. However, how plant secondary metabolites activate detoxifying metabolic genes to develop tolerance remains unclear. Herein, the tolerance of Spodoptera litura larvae to cyantraniliprole was increased after nicotine exposure. An S. litura α esterase, SlCOE030, was predominantly expressed in the midgut and induced after exposure to cyantraniliprole, nicotine, and cyantraniliprole plus nicotine. Drosophila melanogaster with ectopically overexpressed SlCOE030 enhanced cyantraniliprole and nicotine tolerance by 4.91- and 2.12-fold, respectively. Compared to UAS-SlCOE030 and Esg-GAL4 lines, the Esg > SlCOE030 line laid more eggs after nicotine exposure. SlCOE030 knockdown decreased the sensitivity of nicotine-treated S. litura larvae to cyantraniliprole. Metabolism assays indicated that recombinant SlCOE030 protein metabolizes cyantraniliprole. Homology modeling and molecular docking analysis demonstrated that SlCOE030 exhibits effective affinities for cyantraniliprole and nicotine. Thus, insect CarEs may result in the development of cross-tolerance between synthetic insecticides and plant secondary metabolites.

Dynamic Roles of Insect Carboxyl/Cholinesterases in Chemical Adaptation

Insects have evolved several intricate defense mechanisms to adapt to their chemical environment. Due to their versatile capabilities in hydrolytic biotransformation, insect carboxyl/cholinesterases (CCEs) play vital roles in the development of pesticide resistance, facilitating the adaptation of insects to their host plants, and manipulating insect behaviors through the olfaction system. CCEs confer insecticide resistance through the mechanisms of qualitative or quantitative changes of CCE-mediated enhanced metabolism or target-site insensitivity, and may contribute to the host plant adaptation. CCEs represent the first odorant-degrading enzymes (ODEs) discovered to degrade insect pheromones and plant odors and remain the most promising ODE candidates. Here, we summarize insect CCE classification, currently characterized insect CCE protein structure characteristics, and the dynamic roles of insect CCEs in chemical adaptation.

Role of Insect and Mammal Glutathione Transferases in Chemoperception

Glutathione transferases (GSTs) are ubiquitous key enzymes with different activities as transferases or isomerases. As key detoxifying enzymes, GSTs are expressed in the chemosensory organs. They fulfill an essential protective role because the chemosensory organs are located in the main entry paths of exogenous compounds within the body. In addition to this protective function, they modulate the perception process by metabolizing exogenous molecules, including tastants and odorants. Chemosensory detection involves the interaction of chemosensory molecules with receptors. GST contributes to signal termination by metabolizing these molecules. By reducing the concentration of chemosensory molecules before receptor binding, GST modulates receptor activation and, therefore, the perception of these molecules. The balance of chemoperception by GSTs has been shown in insects as well as in mammals, although their chemosensory systems are not evolutionarily connected. This review will provide knowledge supporting the involvement of GSTs in chemoperception, describing their localization in these systems as well as their enzymatic capacity toward odorants, sapid molecules, and pheromones in insects and mammals. Their different roles in chemosensory organs will be discussed in light of the evolutionary advantage of the coupling of the detoxification system and chemosensory system through GSTs.

Antennal transcriptomic analysis of carboxylesterases and glutathione S-transferases associated with odorant degradation in the tea gray geometrid, Ectropis grisescens (Lepidoptera, Geometridae)

Introduction: Carboxylesterases (CXEs) and glutathione S-transferases (GSTs) can terminate olfactory signals during chemosensation by rapid degradation of odorants in the vicinity of receptors. The tea grey geometrid, Ectropis grisescens (Lepidoptera, Geometridae), one of the most devastating insect herbivores of tea plants in China, relies heavily on plant volatiles to locate the host plants as well as the oviposition sites. However, CXEs and GSTs involved in signal termination and odorant clearance in E. grisescens remains unknown. Methods: In this study, identification and spatial expression profiles of CXEs and GSTs in this major tea pest were investigated by transcriptomics and qRT-PCR, respectively. Results: As a result, we identified 28 CXEs and 16 GSTs from female and male antennal transcriptomes. Phylogenetic analyses clustered these candidates into several clades, among which antennal CXEs, mitochondrial and cytosolic CXEs, and delta group GSTs contained genes commonly associated with odorants degradation. Spatial expression profiles showed that most CXEs (26) were expressed in antennae. In comparison, putative GSTs exhibited a diverse expression pattern across different tissues, with one GST expressed specifically in the male antennae. Disscussion: These combined results suggest that 12 CXEs (EgriCXE1, 2, 4, 6, 8, 18, 20-22, 24, 26, and 29) and 5 GSTs (EgriGST1 and EgriGST delta group) provide a major source of candidate genes for odorants degradation in E. grisescens.

Comparative genomic analysis of carboxylesterase genes in Tenebrio molitor and other four tenebrionids

Carboxylesterases (COEs) have various functions in wide taxons of organisms. In insects, COEs are important enzymes involved in the hydrolysis of a variety of ester-containing xenobiotics, neural signal transmission, pheromone degradation, and reproductive development. Understanding the diversity of COEs is basic to illustrate their functions. In this study, we identified 53, 105, 37, and 39 COEs from the genomes of Tenebrio molitor, Asbolus verucosus, Hycleus cichorii, and H. phaleratus in the superfamily of Tenebrionidea, respectively. Phylogenetic analysis showed that 234 COEs from these four species and those reported in Tribolium castaneum (63) could be divided into 12 clades and three major classes. The α-esterases significantly expanded in T. molitor, A. verucosus, and T. castaneum compared to dipteran and hymenopteran insects. In T. molitor, most COEs showed tissue and stage-specific but not a sex-biased expression. Our results provide insights into the diversity and evolutionary characteristics of COEs in tenebrionids, and lay a foundation for the functional characterization of COEs in the yellow mealworm.

A full-length transcriptome and gene expression analysis of three detoxification gene families in a predatory stink bug, Picromerus lewisi

The predatory stink bug P. Lewisi shows potential for Integrated Pest Management programs for controlling Lepidoptera pest insects in crops and forests. The importance of this insect for biological control has stimulated several studies into its biology and ecology. However, P. lewisi has little genetic information available. In the present study, PacBio single-molecule real-time (SMRT) sequencing and Illumina RNA-seq sequencing technologies were used to reveal the full-length transcriptome profiling and tissue-specific expression patterns of P. lewisi. A total of 12,997 high-quality transcripts with an average length of 2,292 bp were obtained from different stages of P. lewisi using SMRT sequencing. Among these, 12,101 were successfully annotated in seven public databases. A total of 67 genes of cytochrome P450 monooxygenases, 43 carboxylesterase genes, and 18 glutathione S-transferase genes were identified, most of which were obtained with full-length ORFs. Then, tissue-specific expression patterns of 5th instar nymphs were analyzed using Illumina sequencing. Several candidate genes related to detoxification of insecticides and other xenobiotics as well as the degradation of odors, were identified in the guts and antennae of P. lewisi. The current study offered in-depth knowledge to understand the biology and ecology of this beneficial predator and related species.

Identification and characterization of candidate detoxification genes in Pharsalia antennata Gahan (Coleoptera: Cerambycidae)

The wood-boring beetles, including the majority of Cerambycidae, have developed the ability to metabolize a variety of toxic compounds derived from host plants and the surrounding environment. However, detoxification mechanisms underlying the evolutionary adaptation of a cerambycid beetle Pharsalia antennata to hosts and habitats are largely unexplored. Here, we characterized three key gene families in relation to detoxification (cytochrome P450 monooxygenases: P450s, carboxylesterases: COEs and glutathione-S-transferases: GSTs), by combinations of transcriptomics, gene identification, phylogenetics and expression profiles. Illumina sequencing generated 668,701,566 filtered reads in 12 tissues of P. antennata, summing to 100.28 gigabases data. From the transcriptome, 215 genes encoding 106 P450s, 77 COEs and 32 GSTs were identified, of which 107 relatives were differentially expressed genes. Of the identified 215 genes, a number of relatives showed the orthology to those in Anoplophora glabripennis, revealing 1:1 relationships in 94 phylogenetic clades. In the trees, P. antennata detoxification genes mainly clustered into one or two subfamilies, including 64 P450s in the CYP3 clan, 33 COEs in clade A, and 20 GSTs in Delta and Epsilon subclasses. Combining transcriptomic data and PCR approaches, the numbers of detoxification genes expressed in abdomens, antennae and legs were 188, 148 and 141, respectively. Notably, some genes exhibited significantly sex-biased levels in antennae or legs of both sexes. The findings provide valuable reference resources for further exploring xenobiotics metabolism and odorant detection in P. antennata.

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.

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

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

Gut transcriptome of two bark beetle species stimulated with the same kairomones reveals molecular differences in detoxification pathways

Dendroctonus bark beetles are the most destructive agents in coniferous forests. These beetles come into contact with the toxic compounds of their host's chemical defenses throughout their life cycle, some of which are also used by the insects as kairomones to select their host trees during the colonization process. However, little is known about the molecular mechanisms by which the insects counteract the toxicity of these compounds. Here, two sibling species of bark beetles, D. valens and D. rhizophagus, were stimulated with vapors of a blend of their main kairomones (α-pinene, β-pinene and 3-carene), in order to compare the transcriptional response of their gut. A total of 48 180 unigenes were identified in D. valens and 43 704 in D. rhizophagus, in response to kairomones blend. The analysis of differential gene expression showed a transcriptional response in D. valens (739 unigenes, 0.58–10.36 Log2FC) related to digestive process and in D. rhizophagus (322 unigenes 0.87–13.08 Log2FC) related to xenobiotics metabolism. The expression profiles of detoxification genes mainly evidenced the up-regulation of COEs and GSTs in D. valens, and the up-regulation of P450s in D. rhizophagus. Results suggest that terpenes metabolism comes accompanied by an integral hormetic response, result of compensatory mechanisms, including the activation of other metabolic pathways, to ensure the supply of energy and the survival of organisms which is specific for each species, according to its life history and ecological strategy.

Detoxification gene families in Phylloxera: Endogenous functions and roles in response to the environment

Phylloxera, Daktulosphaira vitifoliae, is an agronomic pest that feeds monophagously on grapevine, Vitis spp. host plants. Phylloxera manipulates primary and secondary plant metabolism to establish either leaf or root galls. We manually annotated 198 detoxification genes potentially involved in plant host manipulation, including cytochrome P450 (66 CYPs), carboxylesterase (20 CCEs), glutathione-S-transferase (10 GSTs), uridine diphosphate-glycosyltransferase (35 UGTs) and ABC transporter (67 ABCs) families. Transcriptomic expression patterns of these detoxification genes were analyzed for root and leaf galls. In addition to these transcriptomic analyses, we reanalyzed recent data from L1 and L2-3 stages feeding on tolerant and resistant rootstock. Data from two agricultural pest aphids, the generalist Myzus persicae and the Fabaceae specialist Acyrthosiphon pisum, and from the true bug vector of Chagas disease, Rhodnius prolixus, were used to perform phylogenetic analyses for each detoxification gene family. We found expansions of several gene sub-families in the genome of D. vitifoliae. Phylogenetically close genes were found to be organized in clusters in the same genomic position and orientation suggesting recent successive duplications. These results highlight the roles of the phylloxera detoxification gene repertoire in insect physiology and in adaptation to plant secondary metabolites, and provide gene candidates for further functional analyses.

The Birth-and-Death Evolution of Cytochrome P450 Genes in Bees

The birth-and-death model of multigene family evolution describes how gene families evolve and diversify through duplication and deletion. The cytochrome P450s are one of the most diverse and well-studied multigene families, involved in both physiological and xenobiotic functions. Extensive studies of insect P450 genes have demonstrated their role in insecticide resistance. Bees are thought to experience toxin exposure through their diet of nectar and pollen, as well as the resin-collecting behavior exhibited by some species. Here, we describe the repertoire of P450 genes in the orchid bee Euglossa dilemma. Male orchid bees form perfume bouquets used in courtship displays by collecting volatile compounds, resulting in exposure to compounds known to be toxic. In addition, we conducted phylogenetic and selection analyses across ten bee species encompassing three bee families. We find that social behavior and resin collection are not correlated with the repertoire of P450 present in a bee species. However, our analyses revealed that P450 clades can be classified as stable and unstable, and that genes involved in xenobiotic metabolism are more likely to belong to unstable clades. Furthermore, we find that unstable clades are under more dynamic evolutionary pressures and exhibit signals of adaptive evolution. This work highlights the complexity of multigene family evolution, revealing that multiple factors contribute to the diversification, stability, and dynamics of this gene family. Furthermore, we provide a resource for future detailed studies investigating the function of different P450s in economically important bee species.

Two single mutations in carboxylesterase 001C improve fenvalerate hydrolase activity in Helicoverpa armigera

Carboxylesterases (CarEs) usually play critical roles in the detoxification of toxic chemicals and therefore may be involved in insecticide resistance in agricultural pests. Previous work has shown that CarE 001C from Helicoverpa armigera was able to metabolize the isomers of cypermethrin and fenvalerate. In this study, seven mutants of CarE 001C with single amino acid substitution were produced and expressed in the Escherichia coli. Enzyme kinetic analysis indicated that all seven mutations dramatically reduced enzymatic activities toward the generic substrate α-naphthyl acetate, but in vitro metabolism assay showed that two of the mutations, H423I and R322L, significantly improved hydrolase activities toward fenvalerate, with their recorded specific activities being 3.5 and 5.1 nM·s^-1·mg ^-1 proteins, respectively. Further, thermostability assay showed that the stability of one mutant enzyme was enhanced. This study will help us better understand the potential of CarEs in insecticide detoxification and resistance in H. armigera.

Genomic analysis of the carboxylesterase family in the salmon louse (Lepeophtheirus salmonis)

The pyrethroid deltamethrin and the macrocyclic lactone emamectin benzoate (EMB) are used to treat infestations of farmed salmon by parasitic salmon lice, Lepeophtheirus salmonis. While the efficacy of both compounds against Atlantic populations of the parasite has decreased as a result of the evolution of resistance, the molecular mechanisms of drug resistance in L. salmonis are currently not fully understood. The functionally diverse carboxylesterases (CaE) family includes members involved in pesticide resistance phenotypes of terrestrial arthropods. The present study had the objective to characterize the CaE family in L. salmonis and assess its role in drug resistance. L. salmonis CaE homologues were identified by homology searches in the parasite's transcriptome and genome. The transcript expression of CaEs predicted to be catalytically competent was studied using quantitative reverse-transcription PCR in drug susceptible and multi-resistant L. salmonis. The above strategy led to the identification of 21 CaEs genes/pseudogenes. Phylogenetic analyses assigned 13 CaEs to clades involved in neurodevelopmental signaling and cell adhesion, while three sequences were predicted to encode secreted enzymes. Ten CaEs were identified as being potentially catalytically competent. Transcript expression of acetylcholinesterase (ace1b) was significantly increased in multi-resistant lice compared to drug-susceptible L. salmonis, with transcript abundance further increased in preadult-II females following EMB exposure. In summary, results from the present study demonstrate that L. salmonis possesses fewer CaE gene family members than most arthropods characterized so far. Drug resistance in L. salmonis was associated with overexpression of ace1b.

Carboxylesterase genes in nitenpyram-resistant brown planthoppers, Nilaparvata lugens

Carboxylesterases (CarEs) represent one of the major detoxification enzyme families involved in insecticide resistance. However, the function of specific CarE genes in insecticide resistance is still unclear in the insect Nilaparvata lugens (Stål), a notorious rice crop pest in Asia. In this study, a total of 29 putative CarE genes in N. lugens were identified, and they were divided into seven clades; further, the β-esterase clade was significantly expanded. Tissue-specific expression analysis found that 17 CarE genes were abundantly distributed in the midgut and fat body, while 12 CarE genes were highly expressed in the head. The expression of most CarE genes was significantly induced in response to the challenge of nitenpyram, triflumezopyrim, chlorpyrifos, isoprocarb and etofenprox. Among these, the expression levels of NlCarE2, NlCarE4, NlCarE9, NlCarE17 and NlCarE24 were increased by each insecticide. Real-time quantitative polymerase chain reaction and RNA interference assays revealed the NlCarE1 gene to be a candidate gene mainly involved in nitenpyram resistance, while simultaneously silencing NlCarE1 and NlCarE19 produced a stronger effect than silencing either one individually, suggesting a cooperative relationship in resistance formation. These findings lay the foundation for further clarification of insecticide resistance mediated by CarE in N. lugens.

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

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

Resistance in the Genus Spodoptera: Key Insect Detoxification Genes

The genus Spodoptera (Lepidoptera: Noctuidae) includes species that are among the most important crop pests in the world. These polyphagous species are able to feed on many plants, including corn, rice and cotton. In addition to their ability to adapt to toxic compounds produced by plants, they have developed resistance to the chemical insecticides used for their control. One of the main mechanisms developed by insects to become resistant involves detoxification enzymes. In this review, we illustrate some examples of the role of major families of detoxification enzymes such as cytochromes P450, carboxyl/cholinesterases, glutathione S-transferases (GST) and transporters such as ATP-binding cassette (ABC) transporters in insecticide resistance. We compare available data for four species, Spodoptera exigua, S. frugiperda, S. littoralis and S. litura. Molecular mechanisms underlying the involvement of these genes in resistance will be described, including the duplication of the CYP9A cluster, over-expression of GST epsilon or point mutations in acetylcholinesterase and ABCC2. This review is not intended to be exhaustive but to highlight the key roles of certain genes.

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.

Identification of key residues of carboxylesterase PxEst-6 involved in pyrethroid metabolism in Plutella xylostella (L.)

The long-term and excessive use of insecticides has led to severe environmental problems and the evolution of insecticide resistance in insects. Carboxylesterases (CarEs) are important detoxification enzymes conferring insecticide resistance on insects. Herein, the detoxification process of Plutella xylostella (L.) carboxylesterase 6 (PxEst-6), one representative P. xylostella carboxylesterase, is investigated with cypermethrin, bifenthrin, cyfluthrin and λ-cyhalothrin. RT-qPCR shows that PxEst-6 is highly expressed in the midgut and cuticles of the third instar larvae. Exposure to pyrethroid insecticides resulted in PxEst-6 up-regulation in a short time. Metabolic assays indicate that PxEst-6 has the capacity to metabolize these pyrethroid insecticides. The combination of molecular docking, binding mode analyses and alanine mutations demonstrated that His451, Lys458 and Gln431 were key residues of PxEst-6 for metabolizing pyrethroids and the acetate groups derived from pyrethroids were key sites for being metabolized by PxEst-6. H451- and K458-derived hydrogen bond (H-bond) interactions with the pyrethroid acetate groups and the polar interactions with the pyrethroid acetate group provided by the Q431 sidechain were crucial to the pyrethroids' metabolism by PxEst-6. Our study contributes to revealing the reasons for pyrethroid resistance in P. xylostella, and provides a fundamental basis for the development of novel pyrethroid insecticides.

A chromosome-level genome of the spider Trichonephila antipodiana reveals the genetic basis of its polyphagy and evidence of an ancient whole-genome duplication event

Background

The spider Trichonephila antipodiana (Araneidae), commonly known as the batik golden web spider, preys on arthropods with body sizes ranging from ∼2 mm in length to insects larger than itself (>20‒50 mm), indicating its polyphagy and strong dietary detoxification abilities. Although it has been reported that an ancient whole-genome duplication event occurred in spiders, lack of a high-quality genome has limited characterization of this event.

Results

We present a chromosome‐level T. antipodiana genome constructed on the basis of PacBio and Hi-C sequencing. The assembled genome is 2.29 Gb in size with a scaffold N50 of 172.89 Mb. Hi‐C scaffolding assigned 98.5% of the bases to 13 pseudo-chromosomes, and BUSCO completeness analysis revealed that the assembly included 94.8% of the complete arthropod universal single-copy orthologs (n = 1,066). Repetitive elements account for 59.21% of the genome. We predicted 19,001 protein-coding genes, of which 96.78% were supported by transcriptome-based evidence and 96.32% matched protein records in the UniProt database. The genome also shows substantial expansions in several detoxification-associated gene families, including cytochrome P450 mono-oxygenases, carboxyl/cholinesterases, glutathione-S-transferases, and ATP-binding cassette transporters, reflecting the possible genomic basis of polyphagy. Further analysis of the T. antipodiana genome architecture reveals an ancient whole-genome duplication event, based on 2 lines of evidence: (i) large-scale duplications from inter-chromosome synteny analysis and (ii) duplicated clusters of Hox genes.

Conclusions

The high-quality T. antipodiana genome represents a valuable resource for spider research and provides insights into this species’ adaptation to the environment.

Genome Mining and Expression Analysis of Carboxylesterase and Glutathione S-Transferase Genes Involved in Insecticide Resistance in Eggplant Shoot and Fruit Borer, Leucinodes orbonalis (Lepidoptera: Crambidae)

The shoot and fruit borer, Leucinodes orbonalis (Lepidoptera: Crambidae) is the major cause of low productivity in eggplant and insecticides being the mainstay of management of L. orbonalis. However, field control failures are widespread due to the evolution of insecticide resistance. Taking advantage of the whole genome sequence information, the present study investigated the level of insecticide resistance and the expression pattern of individual carboxylesterase (CE) and glutathione S-transferases (GSTs) genes in various field collected populations of L. orbonalis. Dose-mortality bioassays revealed a very high level of resistance development against fenvalerate (48.2–160-fold), phosalone (94-534.6-fold), emamectin benzoate (7.2–55-fold), thiodicarb (9.64–22.7-fold), flubendiamide (187.4–303.0-fold), and chlorantraniliprole (1.6–8.6-fold) in field populations as compared to laboratory-reared susceptible iso-female colony (Lo-S). Over-production of detoxification enzymes viz., CE and GST were evident upon enzyme assays. Mining of the draft genome of L. orbonalis yielded large number of genes potentially belonging to the CE and GST gene families with known history of insecticide resistance in other insects. Subsequent RT-qPCR studies on relative contribution of individual genes revealed over-expression of numerous GSTs and few CEs in field populations, indicating their possible involvement of metabolic enzymes in insecticide resistance. The genomic information will facilitate the development of novel resistance management strategies against this pest.

Transcriptome analysis of putative detoxification genes in the Asian citrus psyllid, Diaphorina citri

BACKGROUND

The Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Psyllidae), is a notorious pest that transmits the causal agent of huanglongbing (also called citrus greening disease). Resistance to insecticide in this destructive pest poses a serious threat to the citrus industry. To date, no systemic studies on genes coding for detoxification enzymes has been carried out on D. citri.

RESULTS

Multiple transcriptomes were generated through deep sequencing of RNA libraries. Candidate genes potentially involved in detoxification including cytochrome P450 monooxygenases (CYPs), glutathione S-transferases (GSTs), and esterases (ESTs) were systematically identified by searching the transcriptomes and a draft genome assembly. A total of 49, 14 and 20 genes were found encoding CYPs, GSTs, and ESTs, respectively, in D. citri. The total numbers of candidate detoxification genes were much smaller than the counterparts reported in other insect species, which may reflect the strict oligophagy of this insect species. Developmental stage- and tissue-specific expression patterns of the identified genes as well as their responses to insecticide treatments identified a small set of genes that could participate in detoxifying plant secondary metabolites and insecticides.

CONCLUSION

Our studies represent the most comprehensive investigation to date on identification, characterization and expression profiling of detoxification genes in D. citri. The information revealed in this study shall be useful in designing strategies to manage this important insect pest. © 2020 Society of Chemical Industry.

Genome-enabled insights into the biology of thrips as crop pests

BACKGROUND

The western flower thrips, Frankliniella occidentalis (Pergande), is a globally invasive pest and plant virus vector on a wide array of food, fiber, and ornamental crops. The underlying genetic mechanisms of the processes governing thrips pest and vector biology, feeding behaviors, ecology, and insecticide resistance are largely unknown. To address this gap, we present the F. occidentalis draft genome assembly and official gene set.

RESULTS

We report on the first genome sequence for any member of the insect order Thysanoptera. Benchmarking Universal Single-Copy Ortholog (BUSCO) assessments of the genome assembly (size = 415.8 Mb, scaffold N50 = 948.9 kb) revealed a relatively complete and well-annotated assembly in comparison to other insect genomes. The genome is unusually GC-rich (50%) compared to other insect genomes to date. The official gene set (OGS v1.0) contains 16,859 genes, of which ~ 10% were manually verified and corrected by our consortium. We focused on manual annotation, phylogenetic, and expression evidence analyses for gene sets centered on primary themes in the life histories and activities of plant-colonizing insects. Highlights include the following: (1) divergent clades and large expansions in genes associated with environmental sensing (chemosensory receptors) and detoxification (CYP4, CYP6, and CCE enzymes) of substances encountered in agricultural environments; (2) a comprehensive set of salivary gland genes supported by enriched expression; (3) apparent absence of members of the IMD innate immune defense pathway; and (4) developmental- and sex-specific expression analyses of genes associated with progression from larvae to adulthood through neometaboly, a distinct form of maturation differing from either incomplete or complete metamorphosis in the Insecta.

CONCLUSIONS

Analysis of the F. occidentalis genome offers insights into the polyphagous behavior of this insect pest that finds, colonizes, and survives on a widely diverse array of plants. The genomic resources presented here enable a more complete analysis of insect evolution and biology, providing a missing taxon for contemporary insect genomics-based analyses. Our study also offers a genomic benchmark for molecular and evolutionary investigations of other Thysanoptera species.

Antennal Proteome of the Solenopsis invicta (Hymenoptera: Formicidae): Caste Differences in Olfactory Receptors and Chemosensory Support Proteins

Little is known about the expression pattern of odorant and pheromone transporters, receptors, and deactivation enzymes in the antennae of ants carrying out different tasks. In order to begin filling in this information gap, we compared the proteomes of the antennae of workers and males of the red fire ant, Solenopsis invicta Buren (Hymenoptera: Formicidae). Male ants do not perform any colony work, and their only activity is to leave the nest on a mating flight. Previous studies showed that male ants express fewer types of odorant receptors than workers. Thus, we expected to find large differences between male and worker antennae for expression of receptors, transporters, and deactivators of signaling chemicals. We found that the abundance of receptors was consistent with the expected caste-specific signaling complexity, but the numbers of different antenna-specific transporters and deactivating enzymes in males and workers were similar. It is possible that some of these proteins have antenna-specific functions that are unrelated to chemosensory reception. Alternatively, the similar complexity could be a vestige of ant progenitors that had more behaviorally active males. As the reduced behavior of male ants evolved, the selection process may have favored a complex repertoire of transporters and deactivating enzymes alongside a limited repertoire of odorant receptors.

Identification and characterization of detoxification genes in two cerambycid beetles, Rhaphuma horsfieldi and Xylotrechus quadripes (Coleoptera: Cerambycidae: Clytini)

The longhorned beetles, Rhaphuma horsfieldi and Xylotrechus quadripes, are two polyphagous insects with larvae feeding on different host plants. In this study, we identified and characterized three gene superfamilies of cytochrome P450s (CYPs), carboxylesterases (COEs) and glutathione-S-transferases (GSTs) involved in the detoxification of endobiotics (e.g., hormones and steroids) and xenobiotics (e.g., insecticides, sex pheromones and plant allelochemicals) through a combination approach of bioinformatics, phylogenetics, expression profiles and genomics. Transcriptome analyses led to the identification of 281 transcripts encoding 135 P450s, 108 COEs and 38 GSTs from the two beetles, coupled with comparative studies of detoxification genes among coleopteran species, suggesting a correlation between host range and the sizes of P450 or COE gene repertoires. The P450s of two beetles were phylogenetically classified into four clades, representing the majority of genes in the CYP3 clan. The COEs from R. horsfieldi and X. quadripes were separately grouped into 11 and 10 clades, and the GST superfamily was assigned into six clades. Expression profiles revealed that the detoxification genes were broadly expressed in various tissues as an implication of functional diversities. Ultimately and more importantly, five alternative splicing events in the Epsilon GSTs, including RhorGSTe7.1/GSTe7.2 and XquaGSTe3.1/GST3.2, were acquired in Coleoptera, in which these genes and their orthologs shared highly conserved gene structure. Our current study has complemented the resources for the detoxification genes in the family Cerambycidae, and allows for functional experiments to identify candidate molecular targets involved in pest resistance to insecticides like organophosphates, organochlorines and pyrethroids.

Functional characterization of a novel λ-cyhalothrin metabolizing glutathione S-transferase, CpGSTe3, from the codling moth Cydia pomonella

BACKGROUND

Recent work has shown that two codling moth (Cydia pomonella) glutathione S-transferase genes (GSTs), CpGSTd1 and CpGSTd3, can metabolize λ-cyhalothrin, one of the recommended insecticides for C. pomonella control worldwide. However, systematical characterization of delta and epsilon GSTs, especially their potential contributions in the metabolism of λ-cyhalothrin, is currently still lacking in C. pomonella.

RESULTS

In this study, a total of nine cDNA sequences were identified in C. pomonella, including four in the delta and five in the epsilon subclasses. RT-qPCR showed that seven GSTs were ubiquitously expressed at all developmental stages, and CpGSTe2, CpGSTe3, and CpGSTe4 were mainly expressed in larvae. The mRNA levels of CpGSTd2, CpGSTd4, and CpGSTe5 were significantly higher in male than in female adults. Tissue-specific expression analysis revealed that the CpGSTe2, CpGSTe3, and CpGSTe4 were highly expressed in the midgut while CpGSTd2 and CpGSTd4 were predominantly expressed in the Malpighian tubules. The transcripts of these GSTs (except CpGSTe1) were co-expressed following exposure to LD₁₀ of λ-cyhalothrin for 3 h. Recombinant CpGSTd4, CpGSTe2, and CpGSTe3 proteins expressed in Escherichia coli displayed glutathione-conjugating activity toward 1-chloro-2,4-dinitrobenzene. In addition, λ-cyhalothrin could inhibit the activity of recombinant CpGSTd4, CpGSTe2, and CpGSTe3 enzymes, but only recombinant CpGSTe3 showed λ-cyhalothrin metabolic capacity, with 21.88 ± 1.09% of parental compound being depleted within 1 h.

CONCLUSION

These data show that CpGSTe3 is a third GST gene, encoding an enzyme that metabolizes λ-cyhalothrin in C. pomonella. © 2019 Society of Chemical Industry.

Diverse patterns of constitutive and inducible overexpression of detoxifying enzyme genes among resistant Aphis glycines populations

Understanding the mechanisms of pyrethroid resistance is essential to the effective management of pesticide resistance in Aphis glycines Matsumura (Hemiptera: Aphididae). We mined putative detoxifying enzyme genes in the draft genome sequence of A. glycines for cytochrome oxidase P450 (CYP), glutathione-S-transferase (GST) and esterases (E4 and carboxylesterases-CES). Aphids from clonal populations resistant to pyrethroids from three sites in Minnesota, USA, were screened against a diagnostic LC99 concentration of either λ-cyhalothrin or bifenthrin and detoxifying enzyme genes expression in survivors was analyzed by qPCR. Their expression profiles were compared relative to a susceptible clonal population. We found 61 CYP (40 full-length), seven GST (all full-length), seven E4 (five full-length) and three CES (two full-length) genes, including 24 possible pseudogenes. The detoxifying enzymes had different expression profiles across resistant aphid populations, possibly reflecting differences in the genetic background and pyrethroid selection pressures as the number of constitutively overexpressed detoxifying enzyme genes was correlated with the level of resistance. Our findings will strengthen the understanding of the pyrethroid resistance mechanisms in A. glycines.

Genomic and transcriptomic analyses of glutathione S-transferases in an endoparasitoid wasp, Pteromalus puparum

Pteromalus puparum is a gregarious pupal endoparasitoid with a wide host range. It deposits eggs into pierid and papilionid butterfly pupae. Glutathione S-transferases (GSTs) are a family of multifunctional detoxification enzymes that act in xenobiotic metabolism in insects. Insect genome projects have facilitated identification and characterization of GST family members. We identified 20 putative GSTs in the P. puparum genome, including 19 cytosolic and one microsomal. Phylogenetic analysis showed that P. puparum GSTs are clustered into Hymenoptera-specific branches. Transcriptomic data of embryos, larvae, female pupae, male pupae, female adults, male adults, venom glands, carcass, salivary glands, and ovaries revealed stage-, sex-, and tissue-specific expression patterns of GSTs in P. puparum. This is the most comprehensive study of genome-wide identification, characterization, and expression profiling of GST family in hymenopterans. Our results provide valuable information for understanding the metabolic adaptation of this wasp.

Characterisation of GST genes from the Hyphantria cunea and their response to the oxidative stress caused by the infection of Hyphantria cunea nucleopolyhedrovirus (HcNPV)

The fall webworm, Hyphantria cunea (Drury) (Lepidoptera: Noctuidae), is a major pest found in forests. In this study, the effects of Hyphantria cunea nucleopolyhedrovirus (HcNPV) infection on the transcription levels and activities of glutathione S-transferases (GSTs) in H. cunea were determined. In the present study, 18 GST family genes were identified from the H. cunea transcriptome dataset by using bioinformatic analyses. These GST genes were classified into cytosolic (15 genes) and microsomal (three genes) classes. The 15 cytosolic GST genes belonged to four different subclasses (epsilon, sigma and delta). The all GST genes, especially GSTe4, showed high expression levels in egg and 1st~4th instar larval stage while their low expression levels in 5th~7th instar larvae using real-time quantitative PCR analysis. However, the expression levels of the 18 GST genes were varied after exposure to sublethal doses of HcNPV. The expression levels of most GSTs were downregulated and upregulated at low and high concentrations of HcNPV, respectively. The corresponding total GST activities also showed similar patterns. In H. cunea, changes in the expression levels and enzymatic activities of GSTs after exposure to HcNPV indicated that they may have important functions in the defense against HcNPV, and the stress, which may be reflected by the high GST enzymatic activities.

Expression Patterns, Molecular Characterization, and Response to Host Stress of CYP Genes from Phenacoccus solenopsis (Hemiptera: Pseudococcidae)

The quarantine insect pest Phenacoccus solenopsis (Hemiptera: Pseudococcidae) has a broad host range and is distributed worldwide. Each year, P. solenopsis causes significant crop losses. The detoxification of various xenobiotic compounds involves the cytochrome P450 monooxygenase (CYP) superfamily of enzymes. However, the functions of CYPs in P. solenopsis are poorly understood. In the present study, P. solenopsis was reared from the egg to the adult stage on three host plants: Tomato, cotton, and hibiscus. Thirty-seven P. solenopsis CYP genes were identified and their phylogenetic relationships were analyzed. Eleven CYP genes (PsCYP4NT1, PsCYP4G219, PsCYP6PZ1, PsCYP6PZ5, PsCYP301B1, PsCYP302A1, PsCYP305A22, PsCYP315A1, PsCYP353F1, PsCYP3634A1, and PsCYP3635A2) were selected for quantitative real-time PCR analysis. The results demonstrated marked differences in CYP expression levels in P. solenopsis grown on different host plants. The results will aid the molecular characterization of CYPs and will increase our understanding of CYP expression patterns in P. solenopsis during development and growth on different hosts.

Identification of glutathione-S-transferase genes by transcriptome analysis in Meteorus pulchricornis (Hymenoptera: Braconidae) and their expression patterns under stress of phoxim and cypermethrin

Meteorus pulchricornis (Wesmael) (Hymenoptera: Braconidae) is a preponderant endoparasitoid wasp, attacking the larvae of many lepidopteran pests. We present the first body transcriptome dataset for M. pulchricornis. In total, 50,781,796 clean reads were obtained and 33,144 unigenes were assembled; 15,458 unigenes showed a significant similarity (E value < 10^-5) to known proteins in the NCBI non-redundant protein database. Gene ontology and cluster of orthologous group analyses were performed to classify the functions of genes. To better understand the role of glutathione-S-transferases (GSTs) in detoxification mechanism in M. pulchricornis, we identified seventeen GST genes (MpulGSTs) from the body transcriptome. Among these, fifteen MpulGSTs belonged to cytosolic GSTs and the other two belonged to microsomal classes. The cytosolic GSTs were classified into four different clades: four in delta, three in omega, seven in sigma, and one in zeta. The expression levels of these MpulGSTs after exposure to sub-lethal concentrations of phoxim and cypermethrin were determined using real-time quantitative polymerase chain reaction: seven MpulGSTs (MpulGSTD3, MpulGSTS1, MpulGSTS2, MpulGSTS4, MpulGSTS6 MpulGSTO3, and MpulGSTmic1) and 11 MpulGSTs (MpulGSTD1, MpulGSTD2, MpulGSTD3, MpulGSTO2, MpulGSTS1, MpulGSTS2, MpulGSTS3, MpulGSTS4, MpulGSTS5, MpulGSTS7, and MpulGSTmic1) were highly expressed, respectively. These results suggested that GST genes may play a pivotal role in detoxification process in M. pulchricornis. Our findings would provide a theoretical base for elucidating insecticide susceptibility and should promote functional research on specific GST genes in parasitoid wasps.

Identification of detoxification genes in imidacloprid-resistant Asian citrus psyllid (Hemiptera: Lividae) and their expression patterns under stress of eight insecticides

BACKGROUND

The Asian citrus psyllid, Diaphorina citri, is one of the major pests in citrus-growing areas around the world. The application of insecticides is the most effective method to reduce the population of D. citri. However, D. citri has developed resistance to multiple classes of insecticides. Understanding resistance mechanisms is crucial to the management of D. citri. In this study, molecular assays were performed to characterize imidacloprid resistance mechanisms.

RESULTS

Based on the D. citri transcriptome database and other known insect resistance genes, 16 cytochrome P450, eight glutathione-S-transferase and six esterase genes were selected for cloning and sequencing. The gene expression analysis of 30 detoxification genes demonstrated that the relative expression of CYP4g15, CYP303A1, CYP4C62, CYP6BD5, GSTS1 and EST-6 were moderately high (>5-fold increase) in the imidacloprid-resistant strain. Feeding of double-stranded RNA (dsRNA) reduced the expression of the six genes (46.7%-72.1%) and resulted in significant adult mortality (65.62%-82.76%). We also determined the ability of different insecticides to induce the six selected genes. The expression of CYP4C62 and GSTS1 genes were the most significantly upregulated in adults treated with all insecticides, except for chlorfenapyr. In chlorfenapyr-treated D. citri, expression of CYP4g15 and CYP303A1 were the most highly induced.

CONCLUSION

Overexpressed detoxification genes were associated with imidacloprid resistance, as confirmed by RNA interference feeding tests. The induction of the six selected genes when exposed to different insecticides supported the hypothesis that they were involved in the metabolism of the tested insecticides. © 2018 Society of Chemical Industry.