Identification of Candidate Olfactory Genes in the Antennal Transcriptome of the Stink Bug Halyomorpha halys

Genomic identification and evolutionary analysis of chemosensory receptor gene families in two Phthorimaea pest species: insights into chemical ecology and host adaptation

BACKGROUND

Insects rely on sophisticated sensitive chemosensory systems to sense their complex chemical environment. This sensory process involves a combination of odorant receptors (ORs), gustatory receptors (GRs) and ionotropic receptors (IRs) in the chemosensory system. This study focused on the identification and characterization of these three types of chemosensory receptor genes in two closely related Phthorimaea pest species, Phthorimaea operculella (potato tuber moth) and Phthorimaea absoluta (tomato leaf miner).

RESULTS

Based on manual annotation of the genome, we identified a total of 349 chemoreceptor genes from the genome of P. operculella, including 93 OR, 206 GR and 50 IR genes, while for P. absoluta, we identified 72 OR, 122 GR and 46 IR genes. Through phylogenetic analysis, we observed minimal differences in the number and types of ORs and IRs between the potato tuber moth and tomato leaf miner. In addition, we found that compared with those of tomato leaf miners, the gustatory receptor branch of P. operculella has undergone a large expansion, which may be related to P. absoluta having a narrower host range than P. operculella. Through analysis of differentially expressed genes (DEGs) of male and female antennae, we uncovered 45 DEGs (including 32ORs, 9 GRs, and 4 IRs).

CONCLUSIONS

Our research provides a foundation for exploring the chemical ecology of these two pests and offers new insights into the dietary differentiation of lepidopteran insects, while simultaneously providing molecular targets for developing environmentally friendly pest control methods based on insect chemoreception.

Transcriptome-wide analysis uncovers regulatory elements of the antennal transcriptome repertoire of bumblebee at different life stages

Bumblebees are crucial pollinators, providing essential ecosystem services and global food production. The success of pollination services relies on the interaction between sensory organs and the environment. The antenna functions as a versatile multi-sensory organ, pivotal in mediating chemosensory/olfactory information, and governs adaptive responses to environmental changes. Despite an increasing number of RNA-sequencing studies on insect antenna, comprehensive antennal transcriptome studies at the different life stages were not elucidated systematically. Here, we quantified the expression profile and dynamics of coding/microRNA genes of larval head and antennal tissues from early- and late-stage pupa to the adult of Bombus terrestris as suitable model organism among pollinators. We further performed Pearson correlation analyses on the gene expression profiles of the antennal transcriptome from larval head tissue to adult stages, exploring both positive and negative expression trends. The positively correlated coding genes were primarily enriched in sensory perception of chemical stimuli, ion transport, transmembrane transport processes and olfactory receptor activity. Negatively correlated genes were mainly enriched in organic substance biosynthesis and regulatory mechanisms underlying larval body patterning and the formation of juvenile antennal structures. As post-transcriptional regulators, miR-1000-5p, miR-13b-3p, miR-263-5p and miR-252-5p showed positive correlations, whereas miR-315-5p, miR-92b-3p, miR-137-3p, miR-11-3p and miR-10-3p exhibited negative correlations in antennal tissue. Notably, based on the inverse expression relationship, positively and negatively correlated microRNA (miRNA)-mRNA target pairs revealed that differentially expressed miRNAs predictively targeted genes involved in antennal development, shaping antennal structures and regulating antenna-specific functions. Our data serve as a foundation for understanding stage-specific antennal transcriptomes and large-scale comparative analysis of transcriptomes in different insects.

Identification of candidate chemosensory genes in Bactrocera cucurbitae based on antennal transcriptome analysis

The melon fly, Bactrocera cucurbitae (Coquillett) (Tephritidae: Diptera), is an invasive pest that poses a significant threat to agriculture in Africa and other regions. Flies are known to use their olfactory systems to recognise environmental chemical cues. However, the molecular components of the chemosensory system of B. cucurbitae are poorly characterised. To address this knowledge gap, we have used next-generation sequencing to analyse the antenna transcriptomes of sexually immature B. cucurbitae adults. The results have identified 160 potential chemosensory genes, including 35 odourant-binding proteins (OBPs), one chemosensory protein (CSP), three sensory neuron membrane proteins (SNMPs), 70 odourant receptors (ORs), 30 ionotropic receptors (IRs), and 21 gustatory receptors (GRs). Quantitative real-time polymerase chain reaction quantitative polymerase chain reaction was used to validate the results by assessing the expression profiles of 25 ORs and 15 OBPs. Notably, high expression levels for BcucOBP5/9/10/18/21/23/26 were observed in both the female and male antennae. Furthermore, BcucOROrco/6/7/9/13/15/25/27/28/42/62 exhibited biased expression in the male antennae, whereas BcucOR55 showed biased expression in the female antennae. This comprehensive investigation provides valuable insights into insect olfaction at the molecular level and will, thus, help to facilitate the development of enhanced pest management strategies in the future.

Genome-wide identification of candidate chemosensory receptors in the bean bug Riptortus pedestris (Hemiptera: Alydidae) and the functional verification of its odorant receptor co-receptor (Orco) in recognizing aggregation pheromone

A sophisticated and sensitive olfactory system plays a vital role in the survival and reproduction of insects. Chemosensory receptors are indispensable for the molecular recognition and discrimination of semiochemicals. Riptortus pedestris is a notorious pest of legume plants, resulting in yield losses and quality decreases in soybeans. It is well accepted that R. pedestris highly relies on its olfactory system in detecting aggregation pheromones, host volatiles, and pesticides; however, little research focused on its chemosensory receptors. In the present study, we identified 237 odorant receptors (ORs), 42 gustatory receptors (GRs), and 31 ionotropic receptors (IRs) from the reported genome of R. pedestris, and analyzed their phylogenetic relationship with other hemipteran species. Through the results of RNA-seq and real-time quantitative PCR (qRT-PCR), we found that RpedORs displayed different expression levels in the antennae of R. pedestris at different development stages. To further verify the function of odorant receptor co-receptor (Orco), an obligate and unique insect OR, we silenced RpedOrco by RNA interference (RNAi) method. The results showed that silencing RpedOrco could significantly impair the response to aggregation pheromone in R. pedestris, indicating that RpedOrco plays an essential role in odorant detection. Our results can provide the theoretical foundations for revealing the olfactory recognition mechanism of R. pedestris and help explore and develop novel olfactory-based agents against this pest.

Identification and Comparative Expression Profiles of Candidate Olfactory Receptors in the Transcriptomes of the Important Egg Parasitoid Wasp Anastatus japonicus Ashmead (Hymenoptera: Eupelmidae)

Anastatus japonicus Ashmead is an egg parasitoid wasp important for the biological control of fruit crop pests. The olfaction of parasitoids is crucial to searching for host pests in fruit crops. In this study, we sequenced and analyzed the antennal and abdominal transcriptomes of A. japonicus to better understand the olfactory mechanisms in this species. A total of 201 putative olfactory receptor genes were identified, including 184 odorant receptors (ORs) and 17 ionotropic receptors (IRs). Then, we assayed the tissue-specific and sex-biased expression profiles of those genes based on the transcriptional levels. In total, 165 ORs and 15 IRs had upregulated expression in the antennae. The expression levels of 133 ORs, including odorant receptor co-receptor (AjapORco), and 10 IRs, including AjapIR8a, were significantly different between the female and male antennae. Our results provide valuable information for further studies on the molecular mechanisms of the olfactory system in A. japonicus.

Exploration of Candidate Genes Involved in the Biosynthesis, Regulation and Recognition of the Male-Produced Aggregation Pheromone of Halyomorpha halys

The aggregation pheromone of the brown marmorated stink bug, Halyomorpha halys (Stål), is produced by adult males, and plays an important role in the behavioral regulation of H. halys. However, information on the molecular mechanisms underlying this pheromone's biosynthesis is limited. In this study, HhTPS1, a key candidate synthase gene in the aggregation pheromone biosynthesis pathway of H. halys, was identified. Then, through weighted gene co-expression network analysis, the candidate P450 enzyme genes in the biosynthetic downstream of this pheromone and the related candidate transcription factor in this pathway were also identified. In addition, two olfactory-related genes, HhCSP5 and HhOr85b, involved in the recognition of the aggregation pheromone of H. halys, were detected. We further identified the key amino acid sites of HhTPS1 and HhCSP5 that interact with substrates by using molecular docking analysis. This study provides basic information for further investigations into the biosynthesis pathways and recognition mechanisms of aggregation pheromones in H. halys. It also provides key candidate genes for bioengineering bioactive aggregation pheromones necessary for the development of technologies for the monitoring and control of H. halys.

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.

The antennal transcriptome of Triatoma infestans reveals substantial expression changes triggered by a blood meal

BACKGROUND

Triatoma infestans is the main vector of Chagas disease in the Americas, currently transmitting it in Argentina, Paraguay, and Bolivia. Many T. infestans populations present insecticide resistance, reducing the efficiency of control campaigns. Alternative vector control methods are needed, and molecular targets mediating fundamental physiological processes can be a promising option to manipulate kissing bug behavior. Therefore, it is necessary to characterize the main sensory targets, as well as to determine whether they are modulated by physiological factors. In order to identify gene candidates potentially mediating host cue detection, the antennal transcripts of T. infestans fifth instar larvae were sequenced and assembled. Besides, we evaluated whether a blood meal had an effect on transcriptional profiles, as responsiveness to host-emitted sensory cues depends on bug starvation.

RESULTS

The sensory-related gene families of T. infestans were annotated (127 odorant receptors, 38 ionotropic receptors, 11 gustatory receptors, 41 odorant binding proteins, and 25 chemosensory proteins, among others) and compared to those of several other hemipterans, including four triatomine species. Several triatomine-specific lineages representing sensory adaptations developed through the evolution of these blood-feeding heteropterans were identified. As well, we report here various conserved sensory gene orthogroups shared by heteropterans. The absence of the thermosensor pyrexia, of pickpocket receptor subfamilies IV and VII, together with clearly expanded takeout repertoires, are revealed features of the molecular bases of heteropteran antennal physiology. Finally, out of 2,122 genes whose antennal expression was significantly altered by the ingestion of a blood meal, a set of 41 T. infestans sensory-related genes (9 up-regulated; 32 down-regulated) was detected.

CONCLUSIONS

We propose that the set of genes presenting nutritionally-triggered modulation on their expression represent candidates to mediate triatomine host-seeking behavior. Besides, the triatomine-specific gene lineages found represent molecular adaptations to their risky natural history that involves stealing blood from an enormously diverse set of vertebrates. Heteropteran gene orthogroups identified may represent unknown features of the sensory specificities of this largest group of hemipteroids. Our work is the first molecular characterization of the peripheral modulation of sensory processes in a non-dipteran vector of human disease.

Identification of Chemosensory Genes, Including Candidate Pheromone Receptors, in Phauda flammans (Walker) (Lepidoptera: Phaudidae) Through Transcriptomic Analyses

Olfactory and gustatory systems play an irreplaceable role in all cycles of growth of insects, such as host location, mating, and oviposition. Many chemosensory genes in many nocturnal moths have been identified via omics technology, but knowledge of these genes in diurnal moths is lacking. In our recent studies, we reported two sex pheromone compounds and three host plant volatiles that play a vital role in attracting the diurnal moth, Phauda flammans. The antennal full-length transcriptome sequence of P. flammans was obtained using the Pacbio sequencing to further explore the process of sex pheromone and host plant volatile recognition in P. flammans. Transcriptome analysis identified 166 candidate olfactory and gustatory genes, including 58 odorant-binding proteins (OBPs), 19 chemosensory proteins (CSPs), 59 olfactory receptors (ORs), 16 ionotropic receptors (IRs), 14 gustatory receptors (GRs), and 2 sensory neuron membrane proteins (SNMPs). Subsequently, a phylogenetic tree was established using P. flammans and other lepidopteran species to investigate orthologs. Among the 17 candidate pheromone receptor (PR) genes, the expression levels of PflaOR21, PflaOR25, PflaOR35, PflaOR40, PflaOR41, PflaOR42, PflaOR44, PflaOR49, PflaOR51, PflaOR61, and PflaOR63 in the antennae were significantly higher than those in other non-antennae tissues. Among these PR genes, PflaOR21, PflaOR27, PflaOR29, PflaOR35, PflaOR37, PflaOR40, PflaOR42, PflaOR44, PflaOR60, and PflaOR62 showed male-biased expression, whereas PflaOR49, PflaOR61, and PflaOR63 revealed female-biased expression. The functions of related OR genes were also discussed. This research filled the gap of the chemosensory genes of P. flammans and provided basic data for future functional molecular mechanisms studies on P. flammans olfaction.

Characterizations of botanical attractant of Halyomorpha halys and selection of relevant deorphanization candidates via computational approach

Halyomorpha halys has been recognized as a global cross-border pest species. Along with well-established pheromone trapping approaches, there have been many attempts to utilize botanical odorant baits for field monitoring. Due to sensitivity, ecological friendliness, and cost-effectiveness for large-scale implementation, the selection of botanical volatiles as luring ingredients and/or synergists for H. halys is needed. In the current work, botanical volatiles were tested by olfactometer and electrophysiological tests. Results showed that linalool oxide was a potential candidate for application as a behavioral modifying chemical. It drove remarkable attractiveness toward H. halys adults in Y-tube assays, as well as eliciting robust electroantennographic responsiveness towards antennae. A computational pipeline was carried out to screen olfactory proteins related to the reception of linalool oxide. Simulated docking activities of four H. halys odorant receptors and two odorant binding proteins to linalool oxide and nerolidol were performed. Results showed that all tested olfactory genes were likely to be involved in plant volatile-sensing pathways, and they tuned broadly to tested components. The current work provides insights into the later development of field demonstration strategies using linalool oxide and its molecular targets.

Binding Affinity Characterization of Four Antennae-Enriched Odorant-Binding Proteins From Harmonia axyridis (Coleoptera: Coccinellidae)

Harmonia axyridis is an important natural enemy that consumes many agricultural and forestry pests. It relies on a sensitive olfactory system to find prey and mates. Odorant-binding proteins (OBPs) as the first-step of recognizing volatiles, transport odors through sensillum lymph to odorant receptors (ORs). However, little is known about the molecular mechanisms of H. axyridis olfaction. In this study, four H. axyridis antenna specific OBP genes, HaxyOBP3, 5, 12, and 15, were bacterially expressed and the binding features of the four recombinant proteins to 40 substances were investigated using fluorescence competitive binding assays. Three-dimensional structure modeling and molecular docking analysis predicted the binding sites between HaxyOBPs and candidate volatiles. Developmental expression analyses showed that the four HaxyOBP genes displayed a variety of expression patterns at different development stages. The expression levels of HaxyOBP3 and HaxyOBP15 were higher in the adult stage than in the other developmental stages, and HaxyOBP15 was significantly transcriptionally enriched in adult stage. Ligand-binding analysis demonstrated that HaxyOBP3 and HaxyOBP12 only combined with two compounds, β-ionone and p-anisaldehyde. HaxyOBP5 protein displayed binding affinities with methyl salicylate, β-ionone, and p-anisaldehyde (K_i = 18.15, 11.71, and 13.45 μM). HaxyOBP15 protein had a broad binding profile with (E)-β-farnesene, β-ionone, α-ionone, geranyl acetate, nonyl aldehyde, dihydro-β-ionone, and linalyl acetate (K_i = 4.33–31.01 μM), and hydrophobic interactions played a key role in the binding of HaxyOBP15 to these substances according to molecular docking. Taken together, HaxyOBP15 exhibited a broader ligand-binding spectrum and a higher expression in adult stage than HaxyOBP3, 5, and 12, indicating HaxyOBP15 may play a greater role in binding volatiles than other three HaxyOBPs. The results will increase our understanding of the molecular mechanism of H. axyridis olfaction and may also result in new management strategies (attractants/repellents) that increase the biological control efficacy of H. axyridis.

Characterization of Antennal Chemosensilla and Associated Chemosensory Genes in the Orange Spiny Whitefly, Aleurocanthus spiniferus (Quaintanca)

The insect chemosensory system plays an important role in many aspects of insects' behaviors necessary for their survival. Despite the complexity of this system, an increasing number of studies have begun to understand its structure and function in different insect species. Nonetheless, the chemosensory system in the orange spiny whitefly Aleurocanthus spiniferus, as one of the most destructive insect pests of citrus in tropical Asia, has not been investigated yet. In this study, the sensillum types, morphologies and distributions of the male and female antennae of A. spiniferus were characterized using scanning electron microscopy. In both sexes, six different sensilla types were observed: trichodea sensilla, chaetica sensilla, microtrichia sensilla, coeloconic sensilla, basiconic sensilla, and finger-like sensilla. Moreover, we identified a total of 48 chemosensory genes, including 5 odorant-binding proteins (OBPs), 12 chemosensory proteins (CSPs), 3 sensory neuron membrane proteins (SNMPs), 6 odorant receptors (ORs), 8 gustatory receptors (GRs), and 14 ionotropic receptors (IRs) using transcriptome data analysis. Tissue-specific transcriptome analysis of these genes showed predominantly expression in the head (including antennae), whereas CSPs were broadly expressed in both head (including the antennae) and body tissue of adult A. spiniferus. In addition, the expression profiling of selected chemosensory genes at different developmental stages was examined by quantitative real time-PCR which was mapped to the transcriptome. We found that the majority of these genes were highly expressed in adults, while AspiORco, AspiGR1, AspiGR2, and AspiIR4 genes were only detected in the pupal stage. Together, this study provides a basis for future chemosensory and genomic studies in A. spiniferus and closely related species. Furthermore, this study not only provides insights for further research on the molecular mechanisms of A. spiniferus-plant interactions but also provides extensive potential targets for pest control.

Diversity and Molecular Evolution of Odorant Receptor in Hemipteran Insects

Simple Summary

Insects’ behavior and ecology are closely related to their chemosensory systems, during which odorant receptors (ORs) play an essential role in host recognition. Although OR gene evolution has been studied in many insect orders, a comprehensive evolutionary analysis and expression of OR gene gain and loss events among diverse hemipteran species are still needed. In this study, we identified and analyzed the OR genes from hemipteran species systematically. The number of OR genes discovered in each species ranged from less than ten to hundreds. Gene gain and loss events of OR have occurred in several species in the seven major clades classified through phylogenetic analysis. Then, we discovered the amino acid differences between species to understand the molecular evolution of OR in the order Hemiptera through positive selection. This study lays a foundation for subsequent investigations into the molecular mechanisms of Hemiptera olfactory receptors involved in host recognition.

Abstract

Olfaction is a critical physiologic process for insects to interact with the environment, especially plant-emitted volatiles, during which odorant receptors (ORs) play an essential role in host recognition. Although OR gene evolution has been studied in many insect orders, a comprehensive evolutionary analysis and expression of OR gene gain and loss events among diverse hemipteran species are still required. In this study, we identified and analyzed 887 OR genes from 11 hemipteran species. The number of OR genes discovered in each species ranged from less than ten to hundreds. Phylogenetic analysis revealed that all identified Hemiptera OR genes were classified into seven major clades. Gene gain and loss events of OR have occurred in several species. Then, by positive selection, we discovered the amino acid differences between species to understand the molecular evolution of OR in the order Hemiptera. Additionally, we discussed how evolutionary analysis can aid the study of insect–plant communication. This study lays a foundation for subsequent investigations into the molecular mechanisms of Hemiptera olfactory receptors involved in host recognition.

Transcriptome Analysis for Identification of Genes Related to Growth and Development, Digestion and Detoxification, Olfaction in the Litchi Stink Bug Tessaratoma papillosa

Tessaratoma papillosa is a major pest of Litchi chinensis and Dimocarpus longan. Adult and nymph secretions are not only harmful to plants but also to humans. At present, there are not a lot of research on T. papillosa, especially omics research. We used high-throughput sequencing technology to sequence the T. papillosa transcriptome and obtained 67,597 unigenes homologous to Halyomorpha halys (88.03%). Subsequently, RNA-SEQ and comparative analyses were performed on the 14 different developmental stages and tissues. A total of 462 unigenes related to growth and development, 1,851 unigenes related to digestion and detoxification, and 70 unigenes related to olfaction were obtained. Moreover, expression analysis showed that the T. papillosa major life activities genes are uniformly expressed across all developmental states. However, the adult midgut gene expression patterns were utterly different from that of the nymphs. Similarly, female fat body genes exhibited distinct expression patterns compared to that of males and nymphs. Thus, different developmental stages and physiological functions affect gene expression patterns. We also found that most of the differential genes were associated with cellular maintenance. This study will help understand the growth and development of litchi stink bugs, their choice of host plants, food digestion and detoxification, and their reproductive behavior. In addition, this result can provide reference information for some target genes in the process of control of T. papillosa.

Stink Bug Communication and Signal Detection in a Plant Environment

Plants influenced the evolution of plant-dwelling stink bugs' systems underlying communication with chemical and substrate-borne vibratory signals. Plant volatiles provides cues that increase attractiveness or interfere with the probability of finding a mate in the field. Mechanical properties of herbaceous hosts and associated plants alter the frequency, amplitude, and temporal characteristics of stink bug species and sex-specific vibratory signals. The specificity of pheromone odor tuning has evolved through highly specific odorant receptors located within the receptor membrane. The narrow-band low-frequency characteristics of the signals produced by abdomen vibration and the frequency tuning of the highly sensitive subgenual organ vibration receptors match with filtering properties of the plants enabling optimized communication. A range of less sensitive mechanoreceptors, tuned to lower vibration frequencies, detect signals produced by other mechanisms used at less species-specific levels of communication in a plant environment. Whereas the encoding of frequency-intensity and temporal parameters of stink bug vibratory signals is relatively well investigated at low levels of processing in the ventral nerve cord, processing of this information and its integration with other modalities at higher neuronal levels still needs research attention.

Expression Profiles and Functional Characterization of Chemosensory Protein 15 (HhalCSP15) in the Brown Marmorated Stink Bug Halyomorpha halys

Chemosensory proteins (CSPs) have been identified in the sensory tissues of various insect species and are believed to be involved in chemical communication in insects. However, the physiological roles of CSPs in Halyomorpha halys, a highly invasive insect species, are rarely reported. Here, we focused on one of the antennal CSPs (HhalCSP15) and determined whether it was involved in olfactory perception. Reverse transcription PCR (RT-PCR) and quantitative real-time PCR (qRT-PCR) analysis showed that HhalCSP15 was enriched in nymph and male and female adult antennae, indicating its possible involvement in the chemosensory process. Fluorescence competitive binding assays revealed that three of 43 natural compounds showed binding abilities with HhalCSP15, including β-ionone (K_i=11.9±0.6μM), cis-3-hexen-1-yl benzoate (K_i=10.5±0.4μM), and methyl (2E,4E,6Z)-decatrienoate (EEZ-MDT; K_i=9.6±0.8μM). Docking analysis supported the experimental affinity for the three ligands. Additionally, the electrophysiological activities of the three ligands were further confirmed using electroantennography (EAG). EEZ-MDT is particularly interesting, as it serves as a kairomone when H. halys forages for host plants. We therefore conclude that HhalCSP15 might be involved in the detection of host-related volatiles. Our data provide a basis for further investigation of the physiological roles of CSPs in H. halys, and extend the olfactory function of CSPs in stink bugs.

Olfactory Reception of Host Alarm Pheromone Component by the Odorant-Binding Proteins in the Samurai Wasp, Trissolcus japonicus (Hymenoptera: Scelionidae)

The samurai wasp, Trissolcus japonicus, is the predominant egg parasitoid of the brown marmorated stink bug, Halyomorpha halys, in its native range in China. (E)-2-Decenal is a major component of the alarm pheromone of H. halys, an important invasive insect pest with significant economic importance. T. japonicus can be strongly repelled by (E)-2-decenal, and thus its host location efficiency would be reduced in the field. Better understanding on the molecular basis of olfactory reception of this host alarm pheromone component by T. japonicus may provide opportunities to develop novel approaches to enhance biological control efficacy of the parasitoid against H. halys. We identified six Odorant Binding Proteins (OBPs) from T. japonicus by transcriptome sequencing, within which three classical OBPs were expressed in a heterologous expression system with E. coli, harvested, and then challenged with (E)-2-decenal in binding assay experiments. TjapOBP2 showed the highest binding ability to (E)-2-decenal, compared to TjapOBP1 and TjapOBP3. Our results unambiguously suggest that TjapOBP2 would play an important role in discriminating (E)-2-decenal and could be a possible target for further intervention in the parasitoid-host system.