The oriental fruit fly, Bactrocera dorsalis, is a devastating fruit fly pest in tropical and sub-tropical countries. Like other insects, this fly uses its chemosensory system to efficiently interact with its environment. However, our understanding of the molecular components comprising B. dorsalis chemosensory system is limited. Using next generation sequencing technologies, we sequenced the transcriptome of four B. dorsalis developmental stages: egg, larva, pupa and adult chemosensory tissues. A total of 31 candidate odorant binding proteins (OBPs), 4 candidate chemosensory proteins (CSPs), 23 candidate odorant receptors (ORs), 11 candidate ionotropic receptors (IRs), 6 candidate gustatory receptors (GRs) and 3 candidate sensory neuron membrane proteins (SNMPs) were identified. The tissue distributions of the OBP and CSP transcripts were determined by RT-PCR and a subset of nine genes were further characterized. The predicted proteins from these genes shared high sequence similarity to Drosophila melanogaster pheromone binding protein related proteins (PBPRPs). Interestingly, one OBP (BdorOBP19c) was exclusively expressed in the sex pheromone glands of mature females. RT-PCR was also used to compare the expression of the candidate genes in the antennae of male and female B. dorsalis adults. These antennae-enriched OBPs, CSPs, ORs, IRs and SNMPs could play a role in the detection of pheromones and general odorants and thus could be useful target genes for the integrated pest management of B. dorsalis and other agricultural pests.

Olfactory transduction is a process by which olfactory sensory neurons (OSNs) transform odor information into neuronal electrical signals. This process begins with the binding of odor molecules to receptor proteins on olfactory receptor neuron (ORN) dendrites. The major molecular components involved in olfaction include odorant-binding proteins (OBPs), chemosensory proteins (CSPs), odorant receptors (ORs), gustatory receptors (GRs), ionotropic receptors (IRs), sensory neuron membrane proteins (SNMPs) and odorant-degrading enzymes (ODEs). More importantly, as potential molecular targets, chemosensory proteins are used to identify novel attractants or repellants for environmental-friendly pest management. In this study we analyzed the transcriptome of the flea beetle, Phyllotreta striolata (Coleoptera, Chrysomelidae), a serious pest of Brassicaceae crops, to better understand the molecular mechanisms of olfactory recognition in this pest. The analysis of transcriptomes from the antennae and terminal abdomens of specimens of both sexes identified transcripts from several key molecular components of chemoreception including 73 ORs, 36 GRs, 49 IRs, 2 SNMPs, 32 OBPs, 8 CSPs, and four candidate odorant degrading enzymes (ODEs): 143 cytochrome P450s (CYPs), 68 esterases (ESTs), 27 glutathione S-transferases (GSTs) and 8 UDP-glycosyltransferases (UGTs). Bioinformatic analyses indicated that a large number of chemosensory genes were up-regulated in the antennae. This was consistent with a potential role in olfaction. To validate the differential abundance analyses, the expression of 19 genes encoding various ORs, CSPs, and OBPs was assessed via qRT-PCR between non-chemosensory tissue and antennae. Consistent with the bioinformatic analyses, transcripts for all of the genes in the qRT-PCR subset were elevated in antennae. These findings provide the first insights into the molecular basis of chemoreception in the striped flea beetle.

BACKGROUNDOdorant‐binding proteins (OBPs) and chemosensory proteins (CSPs) are two families of small water‐soluble proteins involved in odor detection and subsequent signal transmission. Determination of their binding mechanisms and specificity towards different odorants is important for developing OBPs/CSPs as targets in pest control management.RESULTSWe re‐annotated genes encoding putative OBPs and CSPs in the Asian citrus psyllid (Diaphorina citri) draft genome using various bioinformatic tools. Genes encoding nine OBPs (seven Classic and two Plus‐C) and 12 CSPs were identified, consistent with our previous transcriptomic results. Tissue‐specific and developmental expression analyses suggested that genes encoding six OBPs and four CSPs were predominantly expressed in antennae, and displayed various expression patterns in different development stages, suggesting potential involvement in olfactory perception. Competitive fluorescence binding assays with 13 candidate ligands, including known host plant volatiles, sex pheromone components and repellents, showed that DcitOBP3 could bind to various odorants, whereas DcitOBP6, 8 and 9 bound specifically to host plant terpenoids. DcitCSP1 and 12 could also bind to certain terpenoids with high binding specificity.CONCLUSIONOBP‐ and CSP‐encoding genes were systematically identified by annotating the draft D. citri genome and those potentially involved in odorant detection and signal transmission were identified by analyzing their tissue‐expression profiles and odorant‐binding affinities, particularly to the peripheral molecular perception of host plant terpenoids. The identified genes may provide potential targets for efficient pest control. © 2020 Society of Chemical Industry

The Asian citrus psyllid, Diaphorina citri is the principal vector of the highly destructive citrus disease called Huanglongbing (HLB) or citrus greening, which is a major threat to citrus cultivation worldwide. More effective pest control strategies against this pest entail the identification of potential chemosensory proteins that could be used in the development of attractants or repellents. However, the molecular basis of olfaction in the Asian citrus psyllid is not completely understood. Therefore, we performed this study to analyze the antennal and abdominal transcriptome of the Asian citrus psyllid. We identified a large number of transcripts belonging to nine chemoreception-related gene families and compared their expression in male and female adult antennae and terminal abdomen. In total, 9 odorant binding proteins (OBPs), 12 chemosensory proteins (CSPs), 46 odorant receptors (ORs), 20 gustatory receptors (GRs), 35 ionotropic receptors (IRs), 4 sensory neuron membrane proteins (SNMPs) and 4 different gene families encoding odorant-degrading enzymes (ODEs): 80 cytochrome P450s (CYPs), 12 esterase (ESTs), and 5 aldehyde dehydrogenases (ADE) were annotated in the D. citri antennal and abdominal transcriptomes. Our results revealed that a large proportion of chemosensory genes exhibited no distinct differences in their expression patterns in the antennae and terminal abdominal tissues. Notably, RNA sequencing (RNA-seq) data and quantitative real time-PCR (qPCR) analyses showed that 4 DictOBPs, 4 DictCSPs, 4 DictIRs, 1 DictSNMP, and 2 DictCYPs were upregulated in the antennae relative to that in terminal abdominal tissues. Furthermore, 2 DictOBPs (DictOBP8 and DictOBP9), 2 DictCSPs (DictOBP8 and DictOBP12), 4 DictIRs (DictIR3, DictIR6, DictIR10, and DictIR35), and 1 DictCYP (DictCYP57) were expressed at higher levels in the male antennae than in the female antennae. Our study provides the first insights into the molecular basis of chemoreception in this insect pest. Further studies on the identified differentially expressed genes would facilitate the understanding of insect olfaction and their role in the interactions between olfactory system and biological processes.

Background The males of many Bactrocera species (Diptera: Tephritidae) respond strongly to plant-derived chemicals (male lures) and can be divided into cue lure/raspberry ketone (CL/RK) responders, methyl eugenol (ME) responders and non-responders. Representing a non-responders, Bactrocera minax display unique olfactory sensory characteristics compared with other Bactrocera species. The chemical senses of insects mediate behaviors that are associated with survival and reproduction. Here, we report the generation of transcriptomes from antennae and the rectal glands of both male and female adults of B. minax using Illumina sequencing technology, and annotated gene families potentially responsible for chemosensory. Results We developed four transcriptomes from different tissues of B. minax and identified a set of candidate genes potentially responsible for chemosensory by analyzing the transcriptomic data. The candidates included 40 unigenes coding for odorant receptors (ORs), 30 for ionotropic receptors (IRs), 17 for gustatory receptors (GRs), three for sensory neuron membrane proteins (SNMPs), 33 for odorant-binding proteins (OBPs), four for chemosensory proteins (CSPs). Sex- and tissue-specific expression profiles for candidate chemosensory genes were analyzed via transcriptomic data analyses, and expression profiles of all ORs and antennal IRs were investigated by real-time quantitative PCR (RT-qPCR). Phylogenetic analyses were also conducted on gene families and paralogs from other insect species together. Conclusions A large number of chemosensory genes were identified from transcriptomic data. Identification of these candidate genes and their expression profiles in various tissues provide useful information for future studies towards revealing their function in B. minax. Electronic supplementary material The online version of this article (10.1186/s12864-019-6022-5) contains supplementary material, which is available to authorized users.

The oriental fruit fly, Bactrocera dorsalis (Diptera: Tephritidae), is one of the most destructive pests throughout tropical and subtropical regions in Asia. This insect displays remarkable changes during different developmental phases in olfactory behavior between sexually immature and mated adults. The olfactory behavioral changes provide clues to examine physiological and molecular bases of olfactory perception in this insect. We comparatively analyzed behavioral and neuronal responses of B. dorsalis adults to attractant semiochemicals, and the expression profiles of antenna chemosensory genes. We found that some odorant-binding proteins (OBPs) were upregulated in mated adults in association with their behavioral and neuronal responses. Ligand-binding assays further showed that one of OBP83a orthologs, BdorOBP83a-2, binds with high affinity to attractant semiochemicals. Functional analyses confirmed that the reduction in BdorOBP83a-2 transcript abundance led to a decrease in neuronal and behavioral responses to selected attractants. This study suggests that BdorOBP83a-2 mediates behavioral responses to attractant semiochemicals and could be a potential efficient target for pest control.

The sweetpotato weevil, Cylas formicarius (Fabricius), is a serious pest of sweetpotato. Olfaction-based approaches, such as use of synthetic sex pheromones to monitor populations and the bait-and-kill method to eliminate males, have been applied successfully for population management of C. formicarius. However, the molecular basis of olfaction in C. formicarius remains unknown. In this study, we produced antennal transcriptomes from males and females of C. formicarius using high-throughput sequencing to identify gene families associated with odorant detection. A total of 54 odorant receptors (ORs), 11 gustatory receptors (GRs), 15 ionotropic receptors (IRs), 3 sensory neuron membrane proteins (SNMPs), 33 odorant binding proteins (OBPs), and 12 chemosensory proteins (CSPs) were identified. Tissue-specific expression patterns revealed that all 54 ORs and 11 antennal IRs, one SNMP, and three OBPs were primarily expressed in antennae, suggesting their putative roles in olfaction. Sex-specific expression patterns of these antenna-predominant genes suggest that they have potential functions in sexual behaviors. This study provides a framework for understanding olfaction in coleopterans as well as future strategies for controlling the sweetpotato weevil pest.

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