Chemosensory genes identified in the antennal transcriptome of the blowfly Calliphora stygia

Molecular Characterization, Evolution and Expression Analysis of Ammonium Transporter from Four Closely Related Bactrocera Species (Tephritidae)

Numerous insects are attracted to low levels of ammonia, utilizing it as a cue to locate food sources. The Ammonium Transporter (Amt), a highly conserved, atypical olfactory receptor, has been shown to mediate the detection of ammonia in insects. While the attraction of Tephritidae to ammonia is well established, knowledge about the Amt in this family is limited. The species Bactrocera dorsalis (Hendel 1912), Bactrocera cucurbitae (Coquillett 1899), Bactrocera correcta Bezzi 1916 and Bactrocera tau (Walker 1849), which are common agricultural pests within Tephritidae, exhibit numerous ecological similarities, offering a solid foundation for studying Amt characteristics in this family. In this study, we elucidated the sequences, evolutionary relationships, and expression patterns of Amt in these four species. The results indicated that these Amts share the same open reading frame, containing 1770 bp that encode a protein of 589 amino acid residues. These Amt proteins exhibit the typical structural characteristics of Amts, including an 11-transmembrane domain with an extracellular N-terminus and an intracellular C-terminus. They also have the ability to form trimers in the membrane. Additionally, they contain three conserved amino acid residues essential for ammonia transport: A189, H195, and H352. Phylogenetic and expression pattern analyses showed that they are highly conserved in Diptera and are significantly expressed in antennae. This study is the first report characterizing the Amt gene in four Tephritidae species. These findings provide a foundation for further exploration into the roles of these genes in their particular biological contexts.

Antennal transcriptome analysis reveals sensory receptors potentially associated with host detection in the livestock pest Lucilia cuprina

BACKGROUND

Lucilia cuprina (Wiedemann, 1830) (Diptera: Calliphoridae) is the main causative agent of flystrike of sheep in Australia and New Zealand. Female flies lay eggs in an open wound or natural orifice, and the developing larvae eat the host's tissues, a condition called myiasis. To improve our understanding of host-seeking behavior, we quantified gene expression in male and female antennae based on their behavior.

METHODS

A spatial olfactometer was used to evaluate the olfactory response of L. cuprina mated males and gravid females to fresh or rotting beef. Antennal RNA-Seq analysis was used to identify sensory receptors differentially expressed between groups.

RESULTS

Lucilia cuprina females were more attracted to rotten compared to fresh beef (> fivefold increase). However, males and some females did not respond to either type of beef. RNA-Seq analysis was performed on antennae dissected from attracted females, non-attracted females and males. Transcripts encoding sensory receptors from 11 gene families were identified above a threshold (≥ 5 transcript per million) including 49 ATP-binding cassette transporters (ABCs), two ammonium transporters (AMTs), 37 odorant receptors (ORs), 16 ionotropic receptors (IRs), 5 gustatory receptors (GRs), 22 odorant-binding proteins (OBPs), 9 CD36-sensory neuron membrane proteins (CD36/SNMPs), 4 chemosensory proteins (CSPs), 4 myeloid lipid-recognition (ML) and Niemann-Pick C2 disease proteins (ML/NPC2), 2 pickpocket receptors (PPKs) and 3 transient receptor potential channels (TRPs). Differential expression analyses identified sex-biased sensory receptors.

CONCLUSIONS

We identified sensory receptors that were differentially expressed between the antennae of both sexes and hence may be associated with host detection by female flies. The most promising for future investigations were as follows: an odorant receptor (LcupOR46) which is female-biased in L. cuprina and Cochliomyia hominivorax Coquerel, 1858; an ABC transporter (ABC G23.1) that was the sole sensory receptor upregulated in the antennae of females attracted to rotting beef compared to non-attracted females; a female-biased ammonia transporter (AMT_Rh50), which was previously associated with ammonium detection in Drosophila melanogaster Meigen, 1830. This is the first report suggesting a possible role for ABC transporters in L. cuprina olfaction and potentially in other insects.

Identification and sex expression profiles of candidate chemosensory genes from Atherigona orientalis via the antennae and leg transcriptome analysis

Atherigona orientalis Schiner (1868) is an acknowledged agricultural pest owing to its feeding habits and breeding locations. This insect is a tropical and subtropical pest in fruits and vegetables, in which >50 varieties of fruits and vegetables in 26 families, such as Capsicum annuum, Lycopersicon esculentum, and Cucumis melo have been attacked. Moreover, A. orientalis may also develop in rotten crops and feces or insect carcasses, which are also considered one kind of sanitary pest and medical insect. At present, the invasion ranges of A. orientalis are still increasing and more preventive and management measures are to be processed. To gain a better understanding of the molecular mechanisms involved in olfactory reception in A. orientalis, the transcriptome of male and female antennae and legs was systematically analyzed. In total, 131 chemosensory-related genes, including 63 odorant receptors (ORs), 20 gustatory receptors (GRs), 18 ionotropic receptors (IRs), 27 odorant binding proteins (OBPs), 1 chemosensory protein (CSP), and 2 sensory neuron membrane proteins (SNMPs), were identified. The analysis focused on obtaining expression information of candidate olfactory genes at the transcriptomic level by examining the differentially expressed genes (DEGs) in all samples. Totally, 41 DEGs were identified between male antennae (MA) and female antennae (FA), including 32 ORs, 5 OBPs, 1 IR, 2 GRs and 1 SNMP. In MA versus male legs (ML), 78 DEGs were identified (45 ORs, 18 OBPs, 6 GRs, 6 IRs, 1 CSP and 2 SNMPs). In FA and female legs (FL), 96 DEGs were identified (51 ORs, 21 OBPs, 9 GRs, 12 IRs, 1 CSP and 2 SNMPs). For ML and FL, 3 DEGs were identified, including 2 ORs and 1 SNMP. Our results supplement valuable insights for future research on the chemoreception mechanisms in A. orientalis.

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.

Comparative transcriptome analysis of the antenna and proboscis reveals feeding state-dependent chemosensory genes in Eupeodes corollae

The physiological state of an insect can affect its olfactory system. However, the molecular mechanism underlying the effect of nutrition-dependent states on odour-guided behaviours in hoverflies remains unclear. In this study, comparative transcriptome analysis of the antenna and proboscis from Eupeodes corollae under different feeding states was conducted. Compared with the previously published antennal transcriptome, a total of 32 novel chemosensory genes were identified, including 4 ionotropic receptors, 17 gustatory receptors, 9 odorant binding proteins and 2 chemosensory proteins. Analysis of differences in gene expression between different feeding states in male and female antennae and proboscises revealed that the expression levels of chemosensory genes were impacted by feeding state. For instance, the expression levels of EcorOBP19 in female antennae, EcorOBP6 in female proboscis, and EcorOR6, EcorOR14, EcorIR5 and EcorIR84a in male antennae were significantly upregulated after feeding. On the other hand, the expression levels of EcorCSP7 in male proboscis and EcorOR40 in male antennae were significantly downregulated. These findings suggest that nutritional state plays a role in the adaptation of hoverflies' olfactory system to food availability. Overall, our study provides important insights into the plasticity and adaptation of chemosensory systems in hoverflies.

Application of omics techniques in forensic entomology research

With the advent of the post-genome era, omics technologies have developed rapidly and are widely used, including in genomics, transcriptomics, proteomics, metabolomics, and microbiome research. These omics techniques are often based on comprehensive and systematic analysis of biological samples using high-throughput analysis methods and bioinformatics, to provide new insights into biological phenomena. Currently, omics techniques are gradually being applied to forensic entomology research and are useful in species identification, phylogenetics, screening for developmentally relevant differentially expressed genes, and the interpretation of behavioral characteristics of forensic-related species at the genetic level. These all provide valuable information for estimating the postmortem interval (PMI). This review mainly discusses the available omics techniques, summarizes the application of omics techniques in forensic entomology, and their future in the field.

Current Knowledge on Chemosensory-Related Candidate Molecules Potentially Involved in Tick Olfaction via Haller's Organ

Ticks are obligatory hematophagous ectoparasites and vectors of many animal and human pathogens. Chemosensation plays a significant role in tick communication with their environment, including seeking out blood meal hosts. Studies on the structure and function of Haller's organ and its components have improved our understanding regarding tick olfaction and its chemical ecology. Compared with the knowledge on insect olfaction, less is known about the molecular basis of olfaction in ticks. This review focused on the chemosensory-related candidate molecules likely involved in tick olfaction. Members of the ionotropic receptor family and a new class of odorant-binding proteins are now known to be involved in tick olfaction, which appear to differ from that of insects. These candidate molecules are more closely related to those of mites and spiders than to other arthropods. The amino acid sequences of candidate niemann-pick type C2 and microplusin-like proteins in ticks exhibit features indicating their potential role as binding proteins. In the future, more comprehensive pertinent research considering the existing shortcomings will be required to fully understand the molecular basis of tick olfactory chemoreception. This information may contribute to the development of new molecular-based control mechanisms to reduce tick populations and related disease transmission.

Transcriptome Analysis and Identification of Chemosensory Genes in Baryscapus dioryctriae (Hymenoptera: Eulophidae)

Baryscapus dioryctriae is a pupal endoparasitoid of many Pyralidae pests and has been used as a biocontrol agent against insect pests that heavily damage the cone and seed of the Korean pine. The olfactory system of wasps plays an essential role in sensing the chemical signals during their foraging, mating, host location, etc., and the chemosensory genes are involved in detecting and transducing these signals. Many chemosensory genes have been identified from the antennae of Hymenoptera; however, there are few reports on the chemosensory genes of Eulophidae wasps. In this study, the transcriptome databases based on ten different tissues of B. dioryctriae were first constructed, and 274 putative chemosensory genes, consisting of 27 OBPs, 9 CSPs, 3 NPC2s, 155 ORs, 49 GRs, 23 IRs and 8 SNMPs genes, were identified based on the transcriptomes and manual annotation. Phylogenetic trees of the chemosensory genes were constructed to investigate the orthologs between B. dioryctriae and other insect species. Additionally, twenty-eight chemosensory genes showed female antennae- and ovipositor-biased expression, which was validated by RT-qPCR. These findings not only built a molecular basis for further research on the processes of chemosensory perception in B. dioryctriae, but also enriched the identification of chemosensory genes from various tissues of Eulophidae wasps.

Insights Into Chemosensory Proteins From Non-Model Insects: Advances and Perspectives in the Context of Pest Management

Nowadays, insect chemosensation represents a key aspect of integrated pest management in the Anthropocene epoch. Olfaction-related proteins have been the focus of studies due to their function in vital processes, such ashost finding and reproduction behavior. Hence, most research has been based on the study of model insects, namely Drosophila melanogaster, Bombyx mori or Tribolium castaneum. Over the passage of time and the advance of new molecular techniques, insects considered non-models have been studied, contributing greatly to the knowledge of insect olfactory systems and enhanced pest control methods. In this review, a reference point for non-model insects is proposed and the concept of model and non-model insects is discussed. Likewise, it summarizes and discusses the progress and contribution in the olfaction field of both model and non-model insects considered pests in agriculture.

Identification and functional analysis of a chemosensory protein from Bactrocera minax (Diptera: Tephritidae)

BACKGROUND

Olfaction has an indispensable role in insect behavior, enabling location of suitable host plants and oviposition sites, finding mates and evasion of natural enemies. Chemosensory proteins (CSPs) function to screen external odorants and transport them to olfactory receptor neurons, thereby increasing the sensitivity of the olfactory system. At present, CSP genes have been identified in many insect species, but there are relatively few studies on the function of CSP, especially in Tephritidae.

RESULTS

In this study, we sequenced and analyzed 12 transcriptomes of Bactrocera minax and identified five CSP genes. The results of polymerase chain reactions with reverse transcription showed that BminCSP3 was highly expressed only in antennae. Results from competitive binding experiments showed that BminCSP3 has good binding ability to citral compared with 23 other volatile organic compounds. The docking model with citral showed hydrogen bond formation with residues (ARG97); however, no hydrogen bonds were formed in the docking of five other ligands (furfuryl alcohol, linalool, cis-3-hexenyl acetate, (R)-(+)-limonene and (+)-carvone). Electroantennogram (EAG) analyses revealed that citral was active in B. minax at the antennal level, and the EAG response value of female adults was significantly higher than that of male adults. Furthermore, the results of behavioral bioassays showed that females were significantly attracted to citral.

CONCLUSION

Our results suggest that BminCSP3 plays an important role in the recognition of citral by B. minax adults. © 2022 Society of Chemical Industry.

Neuroligin 3 from common cutworm enhances the GABA-induced current of recombinant SlRDL1 channel

BACKGROUND

Neuroligin (NLG) protein is a nerve cell adhesion molecule and plays a key role in the precision apposition of presynaptic domains on inhibitory and excitatory synapses. Existing studies mainly focused on the function of NLG3 against the excitatory channel. However, the interaction between insect NLG3 and ionotropic GABA receptor, which is the main inhibitory channel, remains unclear. In this study, the Nlg3 of common cutworm (CCW), Spodoptera litura Fabricius, one important agricultural Lepidopteron, is selected to explore its function in the inhibitory channel.

RESULTS

The SlNlg3 was obtained and the SlNLG3 contains the characteristic features including transmembrane domain, PDZ-binding motif and type-B carboxylesterases signature 2 motif. The SlNlg3 messenger RNA (mRNA) was most abundant in midgut, and exhibited multiple expression patterns in different developmental stages and tissues or body parts. Compared with the single injection of SlRDL1, the median effective concentration value of GABA in activating currents was smaller in Xenopus laevis oocytes co-injected with SlRDL1 and SlNlg3. In addition, SlNlg3 could enhance the GABA-induced current of homomeric SlRDL1 channel from -391.86 ± 15.41 to -2152.51 ± 30.09 nA. DsSlNlg3 depressed the expression level of SlNlg3 mRNA more than 64.29% at 6 h. After exposure to median lethal dose of fluralaner, the mortality of CCW injected with dsSlNlg3 was significantly decreased by 13.34% and 30.00% at 24 and 48 h, respectively, compared to injection of dsEGFP.

CONCLUSION

NLG3 should have physiological function on ionotropic GABA receptor in vitro, which provided a favorable foundation for further research on the physiological function of Nlg gene in Lepidopteron. © 2021 Society of Chemical Industry.

The metabolism and role of free fatty acids in key physiological processes in insects of medical, veterinary and forensic importance

Insects are the most widespread group of organisms and more than one million species have been described. These animals have significant ecological functions, for example they are pollinators of many types of plants. However, they also have direct influence on human life in different manners. They have high medical and veterinary significance, stemming from their role as vectors of disease and infection of wounds and necrotic tissue; they are also plant pests, parasitoids and predators whose activities can influence agriculture. In addition, their use in medical treatments, such as maggot therapy of gangrene and wounds, has grown considerably. They also have many uses in forensic science to determine the minimum post-mortem interval and provide valuable information about the movement of the body, cause of the death, drug use, or poisoning. It has also been proposed that they may be used as model organisms to replace mammal systems in research. The present review describes the role of free fatty acids (FFAs) in key physiological processes in insects. By focusing on insects of medical, veterinary significance, we have limited our description of the physiological processes to those most important from the point of view of insect control; the study examines their effects on insect reproduction and resistance to the adverse effects of abiotic (low temperature) and biotic (pathogens) factors.

Identification and analysis of olfactory genes in Dioryctria abietella based on the antennal transcriptome

The coneworm Dioryctria abietella (Lepidoptera: Pyralidae) is an economy devastating pest that infests many valuable conifer species in the Holarctic regions, such as Pinus koraiensis Siebold and Zucc. The chemosensory system plays a crucial role in the mating, foraging, and ovipositing of this pest, and therefore it is desirable to identify chemosensory molecules for pest control. However, little is known at molecular level about the olfactory mechanisms in D. abietella. In the present study, we first established antennal transcriptomes of D. abietella and identified 132 putative chemosensory genes, including 15 odorant-binding proteins, 18 chemosensory proteins, 65 odorant receptors, 5 sensory neuron membrane proteins, 24 ionotropic receptors, and 5 gustatory receptors. In addition, phylogenetic trees were constructed for chemosensory genes to investigate the orthologs between D. abietella and other species of insects. Furthermore, we also compared the patterns of motifs between OBPs and CSPs using MEME. Additionally, we observed that most of DabiOBPs and DabiCSPs had the antenna-biased expression by quantitative real-time PCR (RT-qPCR), and there was a higher expression of DabiPBP1 and DabiPBP2 in male antennae than in female antennae. The binding sites of DabiPBPs (DabiPBP1, DabiPBP2) and DabiPRs (DabiOR19, DabiOR31) to the sex pheromone were predicted well by three-dimensional docking structure modelling and molecular docking. Our finding supplied a foundation for further research on the binding process of OBPs or CSPs and sensing process of ORs, SNMPs, IRs or GRs in D. abietella.

Transcriptome Characterization and Expression Analysis of Chemosensory Genes in Chilo sacchariphagus (Lepidoptera Crambidae), a Key Pest of Sugarcane

Insect chemoreception involves many families of genes, including odourant/pheromone binding proteins (OBP/PBPs), chemosensory proteins (CSPs), odourant receptors (ORs), ionotropic receptors (IRs), and sensory neuron membrane proteins (SNMPs), which play irreplaceable roles in mediating insect behaviors such as host location, foraging, mating, oviposition, and avoidance of danger. However, little is known about the molecular mechanism of olfactory reception in Chilo sacchariphagus, which is a major pest of sugarcane. A set of 72 candidate chemosensory genes, including 31 OBPs/PBPs, 15 CSPs, 11 ORs, 13 IRs, and two SNMPs, were identified in four transcriptomes from different tissues and genders of C. sacchariphagus. Phylogenetic analysis was conducted on gene families and paralogs from other model insect species. Quantitative real-time PCR (qRT-PCR) showed that most of these chemosensory genes exhibited antennae-biased expression, but some had high expression in bodies. Most of the identified chemosensory genes were likely involved in chemoreception. This study provides a molecular foundation for the function of chemosensory proteins, and an opportunity for understanding how C. sacchariphagus behaviors are mediated via chemical cues. This research might facilitate the discovery of novel strategies for pest management in agricultural ecosystems.

Antennal Transcriptome Analysis and Identification of Candidate Chemosensory Genes of the Harlequin Ladybird Beetle, Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae)

Simple Summary

The predatory harlequin ladybird Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae) has been widely released for classical and augmentative biological control programs of insect herbivores and is now distributed worldwide. Because of its invasive behavior and the threat it can pose to local biodiversity, this ladybird has been adopted as a model species for invasive biocontrol predators. A huge amount of existing literature is available on this species. However, little is known about the mechanisms underlying H. axyridis smell and taste, even though these senses are important in this ladybird for courtship, mating, and for locating suitable habitats for feeding and oviposition. Here we describe the first chemosensory gene repertoire that is expressed in the antennae of male and female H. axyridis. Our findings would likely represent the basis for future functional studies aiming at increasing the efficacy of H. axyridis in biological control or at reducing its populations in those areas where the ladybird has become a matter of concern due to its invasiveness.

Abstract

In predatory ladybirds (Coleoptera: Coccinellidae), antennae are important for chemosensory reception used during food and mate location, and for finding a suitable oviposition habitat. Based on NextSeq 550 Illumina sequencing, we assembled the antennal transcriptome of mated Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae) males and females and described the first chemosensory gene repertoire expressed in this species. We annotated candidate chemosensory sequences encoding 26 odorant receptors (including the coreceptor, Orco), 17 gustatory receptors, 27 ionotropic receptors, 31 odorant-binding proteins, 12 chemosensory proteins, and 4 sensory neuron membrane proteins. Maximum-likelihood phylogenetic analyses allowed to assign candidate H. axyridis chemosensory genes to previously described groups in each of these families. Differential expression analysis between males and females revealed low variability between sexes, possibly reflecting the known absence of relevant sexual dimorphism in the structure of the antennae and in the distribution and abundance of the sensilla. However, we revealed significant differences in expression of three chemosensory genes, namely two male-biased odorant-binding proteins and one male-biased odorant receptor, suggesting their possible involvement in pheromone detection. Our data pave the way for improving the understanding of the molecular basis of chemosensory reception in Coccinellidae.

Identification of olfactory genes of a forensically important blow fly, Aldrichina grahami (Diptera: Calliphoridae)

Background

The time-length between the first colonization of necrophagous insect on the corpse and the beginning of investigation represents the most important forensic concept of minimum post-mortem inference (PMImin). Before colonization, the time spent by an insect to detect and locate a corpse could significantly influence the PMImin estimation. The olfactory system plays an important role in insect food foraging behavior. Proteins like odorant binding proteins (OBPs), chemosensory proteins (CSPs), odorant receptors (ORs), ionotropic receptors (IRs) and sensory neuron membrane proteins (SNMPs) represent the most important parts of this system. Exploration of the above genes and their necrophagous products should facilitate not only the understanding of their roles in forging but also their influence on the period before PMImin. Transcriptome sequencing has been wildly utilized to reveal the expression of particular genes under different temporal and spatial condition in a high throughput way. In this study, transcriptomic study was implemented on antennae of adult Aldrichina grahami (Aldrich) (Diptera: Calliphoridae), a necrophagous insect with forensic significance, to reveal the composition and expression feature of OBPs, CSPs, ORs, IRs and SNMPs genes at transcriptome level.

Method

Antennae transcriptome sequencing of A. grahami was performed using next-generation deep sequencing on the platform of BGISEQ-500. The raw data were deposited into NCBI (PRJNA513084). All the transcripts were functionally annotated using Gene Ontology (GO) and the Kyoto Encyclopedia of Genes and Genomes (KEGG) database. Differentially expressed genes (DEGs) were analyzed between female and male antennae. The transcripts of OBPs, CSPs, ORs, IRs and SNMPs were identified based on sequence feature. Phylogenetic development of olfactory genes of A. grahami with other species was analyzed using MEGA 5.0. RT-qPCR was utilized to verify gene expression generated from the transcriptome sequencing.

Results

In total, 14,193 genes were annotated in the antennae transcriptome based on the GO and the KEGG databases. We found that 740 DEGs were differently expressed between female and male antennae. Among those, 195 transcripts were annotated as candidate olfactory genes then checked by sequence feature. Of these, 27 OBPs, one CSPs, 49 ORs, six IRs and two SNMPs were finally identified in antennae of A. grahami. Phylogenetic development suggested that some olfactory genes may play a role in food forging, perception of pheromone and decomposing odors.

Conclusion

Overall, our results suggest the existence of gender and spatial expression differences in olfactory genes from antennae of A. grahami. Such differences are likely to greatly influence insect behavior around a corpse. In addition, candidate olfactory genes with predicted function provide valuable information for further studies of the molecular mechanisms of olfactory detection of forensically important fly species and thus deepen our understanding of the period before PMImin.

Identification and preliminary characterization of chemosensory-related proteins in the gall fly, Procecidochares utilis by transcriptomic analysis

Chemoreception is critical for insect behaviors such as foraging, host searching and oviposition. The process of chemoreception is mediated by a series of proteins, including odorant-binding proteins (OBPs), gustatory receptors (GRs), odorant receptors (ORs), ionotropic receptors (IRs), chemosensory proteins (CSPs) and sensory neuron membrane proteins (SNMPs). The tephritid stem gall fly, Procecidochares utilis Stone, is a type of egg parasitic insect, which is an effective biological control agent for the invasive weed Ageratina adenophora in many countries. However, the study of molecular components related to the olfactory system of P. utilis has not been investigated. Here, we conducted the developmental transcriptome (egg, first-third instar larva, pupa, female and male adult) of P. utilis using next-generation sequencing technology and identified a total of 133 chemosensory genes, including 40 OBPs, 29 GRs, 24 ORs, 28 IRs, 6 CSPs, and 6 SNMPs. The sequences of these candidate chemosensory genes were confirmed by BLAST, and phylogenetic analysis was performed. Quantitative real-time PCR (qRT-PCR) confirmed that the expression levels of the candidate OBPs varied at the different developmental stages of P. utilis with most OBPs expressed mainly in the pupae, female and male adults but scarcely in eggs and larvae, which was consistent with the differentially expressed genes (DEGs) analysis using the fragments per kilobase per million fragments (FPKM) value. Our results provide a significant contribution towards the knowledge of the set of chemosensory proteins and help advance the use of P. utilis as biological control agents.

Characterization of a specific odorant receptor for linalool in the Chinese citrus fly Bactrocera minax (Diptera: Tephritidae)

Insect sensing of odorants plays important roles in various behaviors, including host location, mate attraction, and oviposition site selection. The odorant receptor (OR) is a key protein in insect environmental odor recognition. Most Diptera studies of ORs have focused on Drosophila and mosquitos, so there little known about ORs in the agricultural pest insects Tephritidae. To understand the olfactory recognition mechanism of Bactrocera minax, we sequenced and analyzed 12 B. minax transcriptomes to identify a total of 59 OR genes. Semi-quantitative reverse transcription PCR (RT-PCR) showed that several BminORs were highly expressed in antennae. Available with a complete open reading frame and expressed in the antennae of both sexes at a higher level than those of other BminORs, BminOR24 was selected for further functional analyses. BminOR24/BminOrco expressed in Xenopus oocytes responded significantly to linalool. The identification of B. minax OR genes lays a foundation for further functional studies of OR genes, and functional characterization of BminOR24 provides insight for improving methods for controlling B. minax, a devastating pest insects.

Identification and Expression Profiling of Chemosensory Genes in Hermetia illucens via a Transcriptomic Analysis

The black soldier fly, Hermetia illucens, is a cosmopolitan insect of the family Stratiomyidae (Diptera). Chemosensory genes encode proteins involved directly in the detection of odorants. In this study, we sequenced the antennal transcriptome of H. illucens adults to identify chemosensory genes. Putative unigenes encoding 27 odorant binding proteins (OBPs), five chemosensory proteins (CSPs), 70 odorant receptors (ORs), 25 ionotropic receptors (IRs), 10 gustatory receptors (GRs) and two sensory neuron membrane proteins (SNMPs) were identified. Tissue-specific expression profiles of the identified OBPs, CSPs and SNMPs were investigated using RT-PCR. Eight OBPs (HillOBP1-2, 9, 11-14, and 17), one CSP (HillCSP5) and one SNMP (HillSNMP1) were predominantly expressed in antennae. Further real-time quantitative PCR analyses revealed that the antennae-enriched unigenes also exhibited significant differences in expression between males and females. Among the sex-biased unigenes, six ORs showed female-biased expression, suggesting that these genes might participate in female-specific behaviors such as oviposition site searching. Sixteen ORs and two OBPs showed male-biased expression, indicating that they may play key roles in the detection of female sex pheromones. Our study is the first attempt to delineate the molecular basis of chemoreception in H. illucens. Our data provide useful information for comparative studies on the differentiation and evolution of Dipteran chemosensory gene families.

Cloning and Functional Characterization of Three Odorant Receptors From the Chinese Citrus fly Bactrocera minax (Diptera: Tephritidae)

Insect olfactory sensing is crucial for finding food, mating, and oviposition preference. Odorant receptors (ORs) play a central role in the transmission of odorant signals into the environment by the peripheral olfactory system. Therefore, the identification and functional study of ORs are essential to better understand olfactory mechanisms in insects. OR studies on Diptera insects are primarily performed on Drosophila and mosquitoes, but few studies have been reported in Tephritidae. In this study, we examined three candidate ORs (BminOR3, BminOR12, and BminOR16) from Bactrocera minax. Our analysis of tissue expression revealed that the three BminORs were expressed in the antennae, with no difference between the male and female. In in vitro heterologous expression system of Xenopus oocytes. BminOR3/BminOrco responded strongly to 1-octen-3-ol, BminOR12/BminOrco responded to eight compounds [methyl salicylate, benzaldehyde, (Z)-3-hexenyl acetate, butyl acrylate, butyl propionate, 1-octanol, (S)-(+)-carvone and benzyl alcohol], and BminOR16/BminOrco slightly responded to undecanol. Our results concluded that BminOR3, BimOR12, and BminOR16 could play an important role in host-finding and oviposition positioning in B. minax.

Modulation of Sex Pheromone Discrimination by A UDP-Glycosyltransferase in Drosophila melanogaster

The detection and processing of chemical stimuli involve coordinated neuronal networks that process sensory information. This allows animals, such as the model species Drosophila melanogaster, to detect food sources and to choose a potential mate. In peripheral olfactory tissues, several classes of proteins are acting to modulate the detection of chemosensory signals. This includes odorant-binding proteins together with odorant-degrading enzymes (ODEs). These enzymes, which primarily act to eliminate toxic compounds from the whole organism also modulate chemodetection. ODEs are thought to neutralize the stimulus molecule concurrently to its detection, avoiding receptor saturation thus allowing chemosensory neurons to respond to the next stimulus. Here, we show that one UDP-glycosyltransferase (UGT36E1) expressed in D. melanogaster antennal olfactory sensory neurons (OSNs) is involved in sex pheromone discrimination. UGT36E1 overexpression caused by an insertion mutation affected male behavioral ability to discriminate sex pheromones while it increased OSN electrophysiological activity to male pheromones. Reciprocally, the decreased expression of UGT36E1, controlled by an RNAi transgene, improved male ability to discriminate sex pheromones whereas it decreased electrophysiological activity in the relevant OSNs. When we combined the two genotypes (mutation and RNAi), we restored wild-type-like levels both for the behavioral discrimination and UGT36E1 expression. Taken together, our results strongly suggest that this UGT plays a pivotal role in Drosophila pheromonal detection.

Antennal transcriptome analyses and olfactory protein identification in an important wood-boring moth pest, Streltzoviella insularis (Lepidoptera: Cossidae)

Olfaction plays key roles in insect survival and reproduction, such as feeding, courtship, mating, and oviposition. The olfactory-based control strategies have been developed an important means for pest management. Streltzoviella insularis is a destructive insect pest of many street tree species, and characterization of its olfactory proteins could provide targets for the disruption of their odour recognition processes and for urban forestry protection. In this study, we assembled the antennal transcriptome of S. insularis by next-generation sequencing and annotated the main olfactory multi-gene families, including 28 odorant-binding proteins (OBPs), 12 chemosensory proteins (CSPs), 56 odorant receptors (ORs), 11 ionotropic receptors (IRs), two sensory neuron membrane proteins (SNMPs), and 101 odorant-degrading enzymes (ODEs). Sequence and phylogenetic analyses confirmed the characteristics of these proteins. We further detected tissue- and sex-specific expression patterns of OBPs, CSPs and SNMPs by quantitative real time-PCR. Most OBPs were highly and differentially expressed in the antennae of both sexes. SinsCSP10 was expressed more highly in male antennae than in other tissues. Two SNMPs were highly expressed in the antennae, with no significant difference in expression between the sexes. Our results lay a solid foundation for understanding the precise molecular mechanisms underlying S. insularis odour recognition.

Latrophilin participates in insecticide susceptibility through positively regulating CSP10 and partially compensated by OBPC01 in Tribolium castaneum

Latrophilin (LPH) is an adhesion G protein-coupled receptor (aGPCR) that participates in multiple essential physiological processes. Our previous studies have shown that lph is not only indispensable for the development and reproduction of red flour beetles (Tribolium castaneum), but also for their resistance against dichlorvos or carbofuran insecticides. However, the regulatory mechanism of lph-mediated insecticide susceptibility remains unclear. Here, we revealed that knockdown of lph in beetles resulted in opposing changes in two chemoreception genes, chemosensory protein 10 (CSP10) and odorant-binding protein C01 (OBPC01), in which the expression of TcCSP10 was downregulated, whereas the expression of TcOBPC01 was upregulated. TcCSP10 and TcOBPC01 were expressed at the highest levels in early pupal and late larval stages, respectively. High levels of expression of both these genes were observed in the heads (without antennae) of adults. TcCSP10 and TcOBPC01 were significantly induced by dichlorvos or carbofuran between 12 and 72 h (hrs) after exposure, suggesting that they are likely associated with increasing the binding affinity of insecticides, leading to a decrease in sensitivity to the insecticides. Moreover, once these two genes were knocked down, the susceptibility of the beetles to dichlorvos or carbofuran was enhanced. Additionally, RNA interference (RNAi) targeting of lph followed by exposure to dichlorvos or carbofuran also caused the opposing expression levels of TcCSP10 and TcOBPC01 compared to the expression levels of wild-type larvae treated with insecticides alone. All these results indicate that lph is involved in insecticide susceptibility through positively regulating TcCSP10; and the susceptibility could also further partially compensated for through the negative regulation of TcOBPC01 when lph was knockdown in the red flour beetle. Our studies shed new light on the molecular regulatory mechanisms of lph related to insecticide susceptibility.

Transcriptomics reveal the molecular underpinnings of chemosensory proteins in Chlorops oryzae

BACKGROUND

Chemosensory proteins are a family of insect-specific chemical sensors that sense specific chemical cues and regulate insect behavior. Chemosensory proteins have been identified and analyzed in many insect species, such as Drosophila melanogaster, Bactrocera dorsalis and Calliphora stygia. This research has revealed that these proteins play a crucial role in insect orientation, predation and oviposition. However, little is known about the chemosensory proteins of Chlorops oryzae, a major pest of rice crops throughout Asia.

RESULTS

Comparative transcription analysis of the genes of Chlorops oryzae larvae, pupae and adults identified a total of 104 chemosensory genes, including 25 odorant receptors (ORs), 26 odorant-binding proteins (OBPs), 19 ionotropic receptors (IRs), 23 gustatory receptors (GRs) and 11 sensory neuron membrane proteins (SNMPs). The sequences of these candidate chemosensory genes were confirmed and used to construct phylogenetic trees. Quantitative real-time PCR (qRT-PCR) confirmed that the expression of candidate OR genes in different developmental stages was consistent with the fragments per kilobase per million fragments (FPKM) values of differentially expressed genes (DEGs).

CONCLUSIONS

The identification of chemosensory genes in C. oryzae provides a foundation for the investigation of the function of chemosensory proteins in this species, which, in turn, could allow the development of new, improved methods of controlling this pest.

Odorant Receptors and Odorant-Binding Proteins as Insect Pest Control Targets: A Comparative Analysis

Recently, two alternative targets in insect periphery nerve system have been explored for environmentally-friendly approaches in insect pest management, namely odorant-binding proteins (OBPs) and odorant receptors (ORs). Located in insect antennae, OBPs are thought to be involved in the transport of odorants to ORs for the specific signal transduction of behaviorally active odorants. There is rich information on OBP binding affinity and molecular docking to bioactive compounds as well as ample 3D crystal structures due to feasible production of recombinant proteins. Although these provide excellent opportunities for them to be considered as pest control targets and a tool to design pest control agents, the debates on their binding specificity represent an obstacle. On the other hand, ORs have recently been functionally characterized with increasing evidence for their specificity, sensitivity and functional roles in pest behaviors. However, a major barrier to use ORs for semiochemical discovery is the lack of 3D crystal structures. Thus, OBPs and ORs have not been analyzed comparatively together so far for their feasibility as pest control targets. Here, we summarize the state of OBPs and ORs research in terms of its application in insect pest management. We discuss the suitability of both proteins as pest control targets and their selection toward the discovery of new potent semiochemicals. We argue that both proteins represent promising targets for pest control and can be used to identify new super-ligands likely present in nature and with reduced risk of resistance development than insect pesticides currently used in agriculture. We discuss that with the massive identification of OBPs through RNA-seq and improved binding affinity measurements, these proteins could be reconsidered as suitable targets for semiochemical discovery.

Identification of candidate chemosensory genes in Mythimna separata by transcriptomic analysis

Background

The oriental armyworm, Mythimna separata, is an economically important and common Lepidopteran pest of cereal crops. Chemoreception plays a key role in insect life, such as foraging, oviposition site selection, and mating partners. To better understand the chemosensory mechanisms in M. separata, transcriptomic analysis of antennae, labial palps, and proboscises were conducted using next-generation sequencing technology to identify members of the major chemosensory related genes.

Results

In this study, 62 putative odorant receptors (OR), 20 ionotropic receptors (IR), 16 gustatory receptors (GR), 38 odorant binding proteins (OBP), 26 chemosensory proteins (CSP), and 2 sensory neuron membrane proteins (SNMP) were identified in M. separata by bioinformatics analysis. Phylogenetic analysis of these candidate proteins was performed. Differentially expressed genes (DEGs) analysis was used to determine the expressions of all candidate chemosensory genes and then the expression profiles of the three families of receptor genes were confirmed by real-time quantitative RT-PCR (qPCR).

Conclusions

The important genes for chemoreception have now been identified in M. separata. This study will provide valuable information for further functional studies of chemoreception mechanisms in this important agricultural pest.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-4898-0) contains supplementary material, which is available to authorized users.

Sex- and Tissue-Specific Expression Profiles of Odorant Binding Protein and Chemosensory Protein Genes in Bradysia odoriphaga (Diptera: Sciaridae)

Bradysia odoriphaga is an agricultural pest insect affecting the production of Chinese chive and other liliaceous vegetables in China, and it is significantly attracted by sex pheromones and the volatiles derived from host plants. Despite verification of this chemosensory behavior, however, it is still unknown how B. odoriphaga recognizes these volatile compounds on the molecular level. Many of odorant binding proteins (OBPs) and chemosensory proteins (CSPs) play crucial roles in olfactory perception. Here, we identified 49 OBP and 5 CSP genes from the antennae and body transcriptomes of female and male adults of B. odoriphaga, respectively. Sequence alignment and phylogenetic analysis among Dipteran OBPs and CSPs were analyzed. The sex- and tissue-specific expression profiles of 54 putative chemosensory genes among different tissues were investigated by quantitative real-time PCR (qRT-PCR). qRT-PCR analysis results suggested that 22 OBP and 3 CSP genes were enriched in the antennae, indicating they might be essential for detection of general odorants and pheromones. Among these antennae-enriched genes, nine OBPs (BodoOBP2/4/6/8/12/13/20/28/33) were enriched in the male antennae and may play crucial roles in the detection of sex pheromones. Moreover, some OBP and CSP genes were enriched in non-antennae tissues, such as in the legs (BodoOBP3/9/19/21/34/35/38/39/45 and BodoCSP1), wings (BodoOBP17/30/32/37/44), abdomens and thoraxes (BodoOBP29/36), and heads (BodoOBP14/23/31 and BodoCSP2), suggesting that these genes might be involved in olfactory, gustatory, or other physiological processes. Our findings provide a starting point to facilitate functional research of these chemosensory genes in B. odoriphaga at the molecular level.

Identification of chemosensory genes from the antennal transcriptome of Indian meal moth Plodia interpunctella

Olfaction plays an indispensable role in mediating insect behavior, such as locating host plants, mating partners, and avoidance of toxins and predators. Olfactory-related proteins are required for olfactory perception of insects. However, very few olfactory-related genes have been reported in Plodia interpunctella up to now. In the present study, we sequenced the antennae transcriptome of P. interpunctella using the next-generation sequencing technology, and identified 117 candidate olfactory-related genes, including 29 odorant-binding proteins (OBPs), 15 chemosensory proteins (CSPs), three sensory neuron membrane proteins (SNMPs), 47 odorant receptors (ORs), 14 ionotropic receptors (IRs) and nine gustatory receptors (GRs). Further analysis of qRT-PCR revealed that nine OBPs, three CSPs, two SNMPs, nine ORs and two GRs were specifically expressed in the male antennae, whereas eight OBPs, six CSPs, one SNMP, 16 ORs, two GRs and seven IRs significantly expressed in the female antennae. Taken together, our results provided useful information for further functional studies on insect genes related to recognition of pheromone and odorant, which might be meaningful targets for pest management.

Identification and Characterization of Odorant Binding Proteins in the Forelegs of Adelphocoris lineolatus (Goeze)

The chemosensory system is essential for insects to detect exogenous compounds, and odorant binding proteins (OBPs) play crucial roles in odorant binding and transduction. In the alfalfa plant bug Adelphocoris lineolatus, an important pest of multiple crops, our understanding of the physiological roles of antenna-biased OBPs has increased dramatically, whereas OBPs related to gustation have remained mostly unexplored. In this study, we employed RNA sequencing and RACE PCR methods to identify putative OBPs from the adult forelegs of both sexes. Eight candidate OBPs were identified, and three OBPs (AlinOBP15, 16, and 17) were novel. Full-length sequence alignment and phylogenetic analyses suggested that these three candidate OBPs had characteristics typical of the insect OBP family. AlinOBP16 and 17 displayed six highly conserved cysteines, placing them in the classic OBP subfamily, whereas AlinOBP15 resembled AlinOBP14 and clustered with the Plus-C clade. Quantitative real-time PCR (qRT-PCR) revealed distinct and significant tissue- and sex-biased expression patterns. AlinOBP15 was highly expressed in female heads, and AlinOBP16 and 17 were strongly expressed in female antennae. In particular, AlinOBP11, the most abundant OBP gene in our foreleg transcriptome dataset, was predominately expressed in adult legs. Furthermore, four types of sensilla hairs were observed on the forelegs of adult A. lineolatus, including sensilla trichodea, setae, and two types of sensilla chaetica (Sch1 and Sch2). Anti-AlinOBP11 antiserum strongly labeled the outer sensillum lymph of Sch2, implying that it has important gustatory functions in A. lineolatus. Our current findings provide evidence that OBPs can be functionally expressed in the tarsal gustatory sensilla of hemipteran mirid species, broadening our understanding of OBP chemosensory function in insects and facilitating the discovery of new functional targets for the regulation of insect host-searching behaviors.

Antennal transcriptome and expression analyses of olfactory genes in the sweetpotato weevil Cylas formicarius

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.

Chemosensory genes in the antennal transcriptome of two syrphid species, Episyrphus balteatus and Eupeodes corollae (Diptera: Syrphidae)

BACKGROUND

Predatory syrphid larvae are an important natural enemy of aphids in cotton agro-ecosystems in China. Their behaviors in prey foraging, localization and oviposition greatly rely on the perception of chemical cues. As a first step to better understand syrphid olfaction at the molecular level, we have performed a systematic identification of their major chemosensory genes.

RESULTS

Male and female antennal transcriptomes of Episyrphus balteatus and Eupeodes corollae were sequenced and assembled using Illumina HiSeq2000 technology. A total of 154 chemosensory genes in E. balteatus transcriptome, including candidate 51 odorant receptors (ORs), 32 ionotropic receptors (IRs), 14 gustatory receptors (GRs), 49 odorant-binding proteins (OBPs), 6 chemosensory proteins (CSPs) and 2 sensory neuron membrane proteins (SNMPs) were identified. In E. corollae transcriptome, we identified 134 genes including 42 ORs, 23 IRs, 16 GRs, 44 OBPs, 7 CSPs and 2 SNMPs. We have provided full-length sequences of the highly conserved co-receptor Orco, IR8a/25a family and carbon dioxide gustatory receptor in both syrphid species. The expression of candidate OR genes in the two syrphid species was evaluated by semi-quantitative reverse transcription PCR. There were no significant differences of transcript abundances in the respective male and female antenna, which is consistent with differentially expressed genes (DEGs) analysis using the FPKM value. The sequences of candidate chemosensory genes were confirmed and phylogenetic analysis was performed.

CONCLUSIONS

This research comprehensively analyzed and identified many novel candidate chemosensory genes regarding syrphid olfaction. It provides an opportunity for understanding how syrphid insects use chemical cues to conduct their behaviors among tritrophic interactions of plants, herbivorous insects, and natural enemies in agricultural ecosystems.

Transcriptome sequencing of Tessaratoma papillosa antennae to identify and analyze expression patterns of putative olfaction genes

Studies on insect olfaction have increased our understanding of insect's chemosensory system and chemical ecology, and have improved pest control strategies based on insect behavior. In this study, we assembled the antennal transcriptomes of the lychee giant stink bug, Tessaratoma papillosa, by using next generation sequencing to identify the major olfaction gene families in this species. In total, 59 odorant receptors, 14 ionotropic receptors (8 antennal IRs), and 33 odorant binding proteins (28 classic OBPs and 5 plus-C OBPs) were identified from the male and female antennal transcriptomes. Analyses of tissue expression profiles revealed that all 59 OR transcripts, 2 of the 8 antennal IRs, and 6 of the 33 OBPs were primarily expressed in the antennae, suggesting their putative role in olfaction. The sex-biased expression patterns of these antenna-predominant genes suggested that they may have important functions in the reproductive behavior of these insects. This is the first report that provides a comprehensive resource to future studies on olfaction in the lychee giant stink bug.

Characterization of the Adult Head Transcriptome and Identification of Migration and Olfaction Genes in the Oriental Armyworm Mythimna separate

The oriental armyworm Mythimna separate is an economically important insect with a wide distribution and strong migratory activity. However, knowledge about the molecular mechanisms regulating the physiological and behavioural responses of the oriental armyworm is scarce. In the present study, we took a transcriptomic approach to characterize the gene network in the adult head of M. separate. The sequencing and de novo assembly yielded 63,499 transcripts, which were further assembled into 46,459 unigenes with an N50 of 1,153 bp. In the head transcriptome data, unigenes involved in the 'signal transduction mechanism' are the most abundant. In total, 937 signal transduction unigenes were assigned to 22 signalling pathways. The circadian clock, melanin synthesis, and non-receptor protein of olfactory gene families were then identified, and phylogenetic analyses were performed with these M. separate genes, the model insect Bombyx mori and other insects. Furthermore, 1,372 simple sequence repeats of 2-6 bp in unit length were identified. The transcriptome data represent a comprehensive molecular resource for the adult head of M. separate, and these identified genes can be valid targets for further gene function research to address the molecular mechanisms regulating the migratory and olfaction genes of the oriental armyworm.

The Battle Against Flystrike - Past Research and New Prospects Through Genomics

Flystrike, or cutaneous myiasis, is caused by blow fly larvae of the genus Lucilia. This disease is a major problem in countries with large sheep populations. In Australia, Lucilia cuprina (Wiedemann, 1830) is the principal fly involved in flystrike. While much research has been conducted on L. cuprina, including physical, chemical, immunological, genetic and biological investigations, the molecular biology of this fly is still poorly understood. The recent sequencing, assembly and annotation of the draft genome and analyses of selected transcriptomes of L. cuprina have given a first global glimpse of its molecular biology and insights into host-fly interactions, insecticide resistance genes and intervention targets. The present article introduces L. cuprina, flystrike and associated issues, details past control efforts and research foci, reviews salient aspects of the L. cuprina genome project and discusses how the new genomic and transcriptomic resources for this fly might accelerate fundamental molecular research of L. cuprina towards developing new methods for the treatment and control of flystrike.

Sensory genes identification with head transcriptome of the migratory armyworm, Mythimna separata

Sensory system plays important roles in a wide array of insect’s behavior and physiological events, including the host landing and locating, feeding, flying, sex responding, mating and oviposition which happen independently and in sequence. The armyworm Mythimna separata (Lepidoptera: Noctuidae) of migratory insect is destructive for alimentarn crop and economic crop throughout the world. Here we present the high throughput sequencing of the head transcriptome and identify members of the major sensory genes which are crucial for armyworm’s success worldwide, including 8 opsins, 22 chemosensory proteins, 50 odorant binding proteins, 60 odorant receptors, 8 gustatory receptors, 24 ionotropic receptors, and 2 sensory neuron membrane proteins. It is worth noting that a duplication of the LW opsin gene exists in this insect. Several genes were clustered with functionally validated genes, such as Co-receptors of OR and IR, PBPs, PRs, CO2 GRs, bitter GRs and sweet GRs, were also identified. The transcriptome gene library provided the basis for further studies that elucidate the fundamental molecular mechanism of biology and control in M. separata. Our research exhibits the first comprehensive catalogue of the sensory genes fundamental for success and distribution in M. separata, which are potential novel targets for pest control strategies.

Expression and modulation of neuroligin and neurexin in the olfactory organ of the cotton leaf worm Spodoptera littoralis

Carboxylesterases are enzymes widely distributed within living organisms. In insects, they have been mainly involved in dietary metabolism and detoxification function. Interestingly, several members of this family called carboxylesterase-like adhesion molecules (CLAMs) have lost their catalytic properties and are mainly involved in neuro/developmental functions. CLAMs include gliotactins, neurotactins, glutactins, and neuroligins. The latter have for binding partner the neurexin. In insects, the function of these proteins has been mainly studied in Drosophila central nervous system or neuromuscular junction. Some studies suggested a role of neuroligins and neurexin in sensory processing but CLAM expression within sensory systems has not been investigated. Here, we reported the identification of 5 putative CLAMs expressed in the olfactory system of the model pest insect Spodoptera littoralis. One neuroligin, Slnlg4-yll and its putative binding partner neurexin SlnrxI were the most expressed in the antennae and were surprisingly associated with olfactory sensilla. In addition, both transcripts were upregulated in male antennae after mating, known to modulate the sensitivity of the peripheral olfactory system in S. littoralis, suggesting that these molecules could be involved in sensory plasticity.

The molecular sensory machinery of a Chagas disease vector: expression changes through imaginal moult and sexually dimorphic features

The triatomine bug Rhodnius prolixus is a main vector of Chagas disease, which affects several million people, mostly in Latin-America. Host searching, pheromone communication, and microclimatic preferences are aspects of its behaviour that depend on multimodal sensory inputs. The molecular bases of these sensory processes are largely unknown. The expression levels of genes transcribed in antennae were compared between 5^th instar larvae, and female and male adults by means of RNA-Seq. The antennae of R. prolixus showed increased expression of several chemosensory-related genes in imaginal bugs, while both sexes had similar expression patterns for most target genes. Few cases suggest involvement of target genes in sexually dimorphic functions. Most odorant and ionotropic receptor genes seemed to be expressed in all libraries. OBPs and CSPs showed very high expression levels. Other sensory-related genes such as TRPs, PPKs and mechanoreceptors had consistent levels of expression in all libraries. Our study characterises most of the sensory gene repertoire of these insects, opening an avenue for functional genetics studies. The increase in expression of chemosensory genes suggests an enhanced role in adult bugs. This knowledge allows developing new behaviour interfering strategies, increasing the options for translational research in the vector control field.

Morphological and Transcriptomic Analysis of a Beetle Chemosensory System Reveals a Gnathal Olfactory Center

BACKGROUND

The red flour beetle Tribolium castaneum is an emerging insect model organism representing the largest insect order, Coleoptera, which encompasses several serious agricultural and forest pests. Despite the ecological and economic importance of beetles, most insect olfaction studies have so far focused on dipteran, lepidopteran, or hymenopteran systems.

RESULTS

Here, we present the first detailed morphological description of a coleopteran olfactory pathway in combination with genome-wide expression analysis of the relevant gene families involved in chemoreception. Our study revealed that besides the antennae, also the mouthparts are highly involved in olfaction and that their respective contribution is processed separately. In this beetle, olfactory sensory neurons from the mouthparts project to the lobus glomerulatus, a structure so far only characterized in hemimetabolous insects, as well as to a so far non-described unpaired glomerularly organized olfactory neuropil in the gnathal ganglion, which we term the gnathal olfactory center. The high number of functional odorant receptor genes expressed in the mouthparts also supports the importance of the maxillary and labial palps in olfaction of this beetle. Moreover, gustatory perception seems equally distributed between antenna and mouthparts, since the number of expressed gustatory receptors is similar for both organs.

CONCLUSIONS

Our analysis of the T. castaneum chemosensory system confirms that olfactory and gustatory perception are not organotopically separated to the antennae and mouthparts, respectively. The identification of additional olfactory processing centers, the lobus glomerulatus and the gnathal olfactory center, is in contrast to the current picture that in holometabolous insects all olfactory inputs allegedly converge in the antennal lobe. These findings indicate that Holometabola have evolved a wider variety of solutions to chemoreception than previously assumed.

BdorOBP83a-2 Mediates Responses of the Oriental Fruit Fly to Semiochemicals

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.

Reproductive switching analysis of Daphnia similoides between sexual female and parthenogenetic female by transcriptome comparison

The water flea Daphnia are planktonic crustaceans commonly found in freshwater environment that can switch their reproduction mode from parthenogenesis to sexual reproduction to adapt to the external environment. As such, Daphnia are great model organisms to study the mechanism of reproductive switching, the underlying mechanism of reproduction and development in cladocerans and other animals. However, little is known about the Daphnia's reproductive behaviour at a molecular level. We constructed a genetic database of the genes expressed in a sexual female (SF) and a parthenogenetic female (PF) of D. similoides using Illumina HiSeq 2500. A total of 1,763 differentially expressed genes (865 up- and 898 down-regulated) were detected in SF. Of the top 30 up-regulated SF unigenes, the top 4 unigenes belonged to the Chitin_bind_4 family. In contrast, of the top down-regulated SF unigenes, the top 3 unigenes belonged to the Vitellogenin_N family. This is the first study to indicate genes that may have a crucial role in reproductive switching of D. similoides, which could be used as candidate genes for further functional studies. Thus, this study provides a rich resource for investigation and elucidation of reproductive switching in D. similoides.

De Novo Transcriptome Analysis of the Common New Zealand Stick Insect Clitarchus hookeri (Phasmatodea) Reveals Genes Involved in Olfaction, Digestion and Sexual Reproduction

Phasmatodea, more commonly known as stick insects, have been poorly studied at the molecular level for several key traits, such as components of the sensory system and regulators of reproduction and development, impeding a deeper understanding of their functional biology. Here, we employ de novo transcriptome analysis to identify genes with primary functions related to female odour reception, digestion, and male sexual traits in the New Zealand common stick insect Clitarchus hookeri (White). The female olfactory gene repertoire revealed ten odorant binding proteins with three recently duplicated, 12 chemosensory proteins, 16 odorant receptors, and 17 ionotropic receptors. The majority of these olfactory genes were over-expressed in female antennae and have the inferred function of odorant reception. Others that were predominantly expressed in male terminalia (n = 3) and female midgut (n = 1) suggest they have a role in sexual reproduction and digestion, respectively. Over-represented transcripts in the midgut were enriched with digestive enzyme gene families. Clitarchus hookeri is likely to harbour nine members of an endogenous cellulase family (glycoside hydrolase family 9), two of which appear to be specific to the C. hookeri lineage. All of these cellulase sequences fall into four main phasmid clades and show gene duplication events occurred early in the diversification of Phasmatodea. In addition, C. hookeri genome is likely to express γ-proteobacteria pectinase transcripts that have recently been shown to be the result of horizontal transfer. We also predicted 711 male terminalia-enriched transcripts that are candidate accessory gland proteins, 28 of which were annotated to have molecular functions of peptidase activity and peptidase inhibitor activity, two groups being widely reported to regulate female reproduction through proteolytic cascades. Our study has yielded new insights into the genetic basis of odour detection, nutrient digestion, and male sexual traits in stick insects. The C. hookeri reference transcriptome, together with identified gene families, provides a comprehensive resource for studying the evolution of sensory perception, digestive systems, and reproductive success in phasmids.

Molecular Characterization and Sex Distribution of Chemosensory Receptor Gene Family Based on Transcriptome Analysis of Scaeva pyrastri

Chemosensory receptors play key roles in insect behavior. Thus, genes encoding these receptors have great potential for use in integrated pest management. The hover fly Scaeva pyrastri (L.) is an important pollinating insect and a natural enemy of aphids, mainly distributed in the Palearctic and Nearctic regions. However, a systematic identification of their chemosensory receptor genes in the antennae has not been reported. In the present study, we assembled the antennal transcriptome of S. pyrastri by using Illumina sequencing technology. Analysis of the transcriptome data identified 60 candidate chemosensory genes, including 38 for odorant receptors (ORs), 16 for ionotropic receptors (IRs), and 6 for gustatory receptors (GRs). The numbers are similar to those of other Diptera species, suggesting that we were able to successfully identify S. pyrastri chemosensory genes. We analyzed the expression patterns of all genes by using reverse transcriptase PCR (RT-PCR), and found that some genes exhibited sex-biased or sex-specific expression. These candidate chemosensory genes and their tissue expression profiles provide information for further studies aimed at fully understanding the molecular basis behind chemoreception-related behaviors in S. pyrastri.

Gene set of chemosensory receptors in the polyembryonic endoparasitoid Macrocentrus cingulum

Insects are extremely successful animals whose odor perception is very prominent due to their sophisticated olfactory system. The main chemosensory organ, antennae play a critical role in detecting odor in ambient environment before initiating appropriate behavioral responses. The antennal chemosensory receptor genes families have been suggested to be involved in olfactory signal transduction pathway as a sensory neuron response. The Macrocentrus cingulum is deployed successfully as a biological control agent for corn pest insects from the Lepidopteran genus Ostrinia. In this research, we assembled antennal transcriptomes of M. cingulum by using next generation sequencing to identify the major chemosensory receptors gene families. In total, 112 olfactory receptors candidates (79 odorant receptors, 20 gustatory receptors, and 13 ionotropic receptors) have been identified from the male and female antennal transcriptome. The sequences of all of these transcripts were confirmed by RT-PCR, and direct DNA sequencing. Expression profiles of gustatory receptors in olfactory and non-olfactory tissues were measured by RT-qPCR. The sex-specific and sex-biased chemoreceptors expression patterns suggested that they may have important functions in sense detection which behaviorally relevant to odor molecules. This reported result provides a comprehensive resource of the foundation in semiochemicals driven behaviors at molecular level in polyembryonic endoparasitoid.

Identification of Male- and Female-Specific Olfaction Genes in Antennae of the Oriental Fruit Fly (Bactrocera dorsalis)

The oriental fruit fly (Bactrocera dorsalis) is a species of tephritid fruit fly, endemic to Southeast Asia but also introduced to many regions of the US, and it is one of the major pest species with a broad host range of cultivated and wild fruits. Although males of B. dorsalis respond strongly to methyl eugenol and this is used for monitoring and estimating populations, the molecular mechanism of the oriental fruit fly olfaction has not been elucidated yet. Therefore, in this project, using next generation sequencing technologies, we sequenced the transcriptome of the antennae of male and female adults of B. dorsalis. We identified a total of 20 candidate odorant binding proteins (OBPs), 5 candidate chemosensory proteins (CSPs), 35 candidate odorant receptors (ORs), 12 candidate ionotropic receptors (IRs) and 4 candidate sensory neuron membrane proteins (SNMPs). The sex-specific expression of these genes was determined and a subset of 9 OR genes was further characterized by qPCR with male and female antenna, head, thorax, abdomen, leg and wing samples. In the male antennae, 595 genes showed a higher expression, while 128 genes demonstrated a higher expression in the female antennae. Interestingly, 2 ORs (BdorOR13 and BdorOR14) were highly and specifically expressed in the antennae of males, and 4 ORs (BdorOR13, BdorOR16, BdorOR18 and BdorOR35) clustered with DmOR677, suggesting pheromone reception. We believe this study with these antennae-enriched OBPs, CSPs, ORs, IRs and SNMPs can play an important role in the detection of pheromones and general odorants, and so in turn our data improve our current understanding of insect olfaction at the molecular level and provide important information for disrupting the behavior of the oriental fruit fly using chemical communication methods.

Identification of Putative Chemosensory Receptor Genes from the Athetis dissimilis Antennal Transcriptome

Olfaction plays a crucial role in insect population survival and reproduction. Identification of the genes associated with the olfactory system, without the doubt will promote studying the insect chemical communication system. In this study, RNA-seq technology was used to sequence the antennae transcriptome of Athetis dissimilis, an emerging crop pest in China with limited genomic information, with the purpose of identifying the gene set involved in olfactory recognition. Analysis of the transcriptome of female and male antennae generated 13.74 Gb clean reads in total from which 98,001 unigenes were assembled, and 25,930 unigenes were annotated. Total of 60 olfactory receptors (ORs), 18 gustatory receptors (GRs), and 12 ionotropic receptors (IRs) were identified by Blast and sequence similarity analyzes. One obligated olfactory receptor co-receptor (Orco) and four conserved sex pheromone receptors (PRs) were annotated in 60 ORs. Among the putative GRs, five genes (AdisGR1, 6, 7, 8 and 94) clustered in the sugar receptor family, and two genes (AdisGR3 and 93) involved in CO₂ detection were identified. Finally, AdisIR8a.1 and AdisIR8a.2 co-receptors were identified in the group of candidate IRs. Furthermore, expression levels of these chemosensory receptor genes in female and male antennae were analyzed by mapping the Illumina reads.