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Aphidophagous syrphids are important for pest control and pollination in various agroecosystems. However, the mechanism underlying olfaction, which is critical for insect' behavioral processes and fitness, has not been well understood in the family Syrphidae. Hence, we performed a systematic identification and characterisation of the antennal sensilla and two groups of soluble proteins, odorant-binding proteins (OBPs) and chemosensory proteins (CSPs), in the hoverfly Eupeodes corollae. (i) With scanning electron microscopy, four major types of sensilla (chaetic sensilla [two subtypes], trichoid sensilla, basiconic sensilla [two subtypes] and coeloconic sensilla), with numerous microtrichia, were first observed along the entire surface of aristate antennae of both sexes of E. corollae. Of these, only chaetic sensillum was found on the first two antennal segments, scape and pedicel, while the other types of sensilla were located on the flagellum. No marked difference was observed in the morphological structure or distributional pattern of any of the sensilla between the two sexes. (ii) By molecular cloning and bioinformatic analysis, 7 EcorCSPs and 28 EcorOBPs (20 classic OBPs, 5 minus-C OBPs, and 3 plus-C OBPs) were directly identified from the species, which all share the characteristic hallmarks of their family, including the presence of a signal peptide and conserved cysteine signature. (iii) RT-qPCR of these chemosensory genes showed predominately tissue-biased expression patterns; 32 of the 35 EcorOBPs/CSPs were uniquely or primarily expressed in the main olfactory organs, either the antennae or head. (iv) Among these, several genes (EcorCSP2 and EcorOBP1, 9, 12, 15-17, 20) appeared to be antenna-biased. In situ hybridization assays indicated that each antenna-biased chemosensory gene was expressed in a different number of cells, suggesting they might play a more vital role in odour recognition and perception and could be potential candidates to study their biological functions in vivo and in vitro. Together, our current findings provide a basis for future studies on how syrphids utilize chemical cues to regulate their behavior during interactions among the natural enemy, its prey, and host plant in agro-ecosystems., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

A cDNA clone coding for pheromone binding protein was isolated from the antennae of Helicoverpa armigera by RT-PCR and (5'/3')-RACE technique. The full-length of H. armigera pheromone binding protein (HarmPBP) was 952 bp, possessing 162 amino acid residues including a signal peptide of 20 amino acids. Its predicted molecular weight and isoelectric point were 18.26 kDa and 5.23, respectively. This deduced amino acid sequence shared some common structural features with odorant-binding proteins from several moth species, including the six conserved cysteine motif, a typical characteristic of insect's odorant-binding proteins. Northern blot showed that HarmPBP is specifically expressed in the antennae of Helicoverpa armigera and more abundantly expressed in male than female. During the antennal development, HarmPBP is first expressed about 4 days prior to adult eclosion and rises to a plateau 2 days prior to adult eclosion. In order to obtain sufficient PBP for further determining its biochemical and physiological properties, a bacterical expression vector of PBP was constructed and successfully expressed in Escherichia coli. The recombinant PBP was shown to cross-react with an anti-PBP antiserum from Antheraea polyphemus. Polyclonal antibodies against HarmPBP were used to mark the distribution of the protein in olfactory sensilla. Very strong labeling was observed in the sensillum lymph of the hair lumen and of the sensillum-lymph cavity. In the male, HarmPBP is expressed in sensilla trichodea and not in sensilla basiconica, while in the female, it is expressed both in sensilla basiconica and sensilla trichodea.

Aphidophagous syrphids (Diptera: Syrphidae) are important insects in agroecosystems for pollination and biological control. Insect chemoreception is essential for these processes and for insect survival and reproduction; however, molecular determinants is not well understood for these beneficial insects. Here, we used recent transcriptome data for the common hoverfly, Episyrphus balteatus , to characterize key molecular components of chemoreception: odorant-binding proteins (OBPs) and chemosensory proteins (CSPs). Six EbalCSPs and 44 EbalOBPs were cloned from this species, and sequence analysis showed that most share the characteristic hallmarks of their protein family, including a signal peptide and conserved cysteine signature. Some regular patterns and key conserved motifs of OBPs and CSPs in Diptera were identified using the online tool MEME. Motifs were also compared among the three OBP subgroups. Quantitative real-time PCR (qRT-PCR) showed that most of these chemosensory genes were expressed in chemosensory organs, suggesting these genes have chemoreceptive functions. An overall comparison of the Ka/Ks values of orthologous genes in E. balteatus and another predatory hoverfly species to analyze the evolution of these olfactory genes showed that OBPs and CSPs are under strong purifying selection. Overall, our results provide a molecular basis for further exploring the chemosensory mechanisms of E. balteatus , and consequently, may help us to understand the tritrophic interactions among plants, herbivorous insects, and natural enemies. [ABSTRACT FROM AUTHOR]

Insects use their sensitive and selective olfactory system to detect outside chemical odorants, such as female sex pheromones and host plant volatiles. Several groups of olfactory proteins participate in the odorant detection process, including odorant binding proteins (OBPs), chemosensory proteins (CSPs), odorant receptors (ORs), ionotropic receptors (IRs) and sensory neuron membrane proteins (SNMPs). The identification and functional characterization of these olfactory proteins will enhance our knowledge of the molecular basis of insect chemoreception. In this study, we report the identification and differential expression profiles of these olfactory genes in the black cutworm moth Agrotis ipsilon. In total, 33 OBPs, 12 CSPs, 42 ORs, 24 IRs, 2 SNMPs and 1 gustatory receptor (GR) were annotated from the A. ipsilon antennal transcriptomes, and further RT-PCR and RT-qPCR revealed that 22 OBPs, 3 CSPs, 35 ORs, 14 IRs and the 2 SNMPs are uniquely or primarily expressed in the male and female antennae. Furthermore, one OBP (AipsOBP6) and one CSP (AipsCSP2) were exclusively expressed in the female sex pheromone gland. These antennae-enriched OBPs, CSPs, ORs, IRs and SNMPs were suggested to be responsible for pheromone and general odorant detection and thus could be meaningful target genes for us to study their biological functions in vivo and in vitro. [ABSTRACT FROM AUTHOR]

Insects interact with their environment and respond to the changes in host plant conditions using semiochemicals. Such ecological interactions are facilitated by the olfactory sensilla and the use of olfactory recognition proteins. The cotton aphid Aphis gossypii can change its phenotype in response to ecological conditions. They reproduce mainly as wingless asexual morphs but develop wings to find mates or new plant hosts under the influence of environmental factors such as temperature, plant nutrition and population density. Two groups of small soluble proteins, odorant binding proteins (OBPs) and chemosensory proteins (CSPs) are believed to be involved in the initial biochemical recognition steps in semiochemical perception. However, the exact molecular roles that these proteins play in insect olfaction remain to be discovered. In this study, we compared the transcriptomes of three asexual developmental stages (wingless spring and summer morphs and winged adults) and characterised 9 OBP and 9 CSP genes. The gene structure analysis showed that the number and length of introns in these genes are much higher and this appears to be unique feature of aphid OBP and CSP genes in general. Another unique feature in aphids is a higher abundance of CSP transcripts than OBP transcripts, suggesting an important role of CSPs in aphid physiology and ecology. We showed that some of the transcripts are overexpressed in the antennae in comparison to the bodies and highly expressed in the winged aphids compared to wingless morphs, suggesting a role in host location. We examined the differential expression of these olfactory genes in ten aphid species and compared the expression profile with the RNA-seq analyses of 25 pea aphid transcriptome libraries hosted on AphidBase. [ABSTRACT FROM AUTHOR]

Insects use their sensitive and selective olfactory system to detect outside chemical odorants, such as female sex pheromones and host plant volatiles. Several groups of olfactory proteins participate in the odorant detection process, including odorant binding proteins (OBPs), chemosensory proteins (CSPs), odorant receptors (ORs), ionotropic receptors (IRs) and sensory neuron membrane proteins (SNMPs). The identification and functional characterization of these olfactory proteins will enhance our knowledge of the molecular basis of insect chemoreception. In this study, we report the identification and differential expression profiles of these olfactory genes in the black cutworm moth Agrotis ipsilon. In total, 33 OBPs, 12 CSPs, 42 ORs, 24 IRs, 2 SNMPs and 1 gustatory receptor (GR) were annotated from the A. ipsilon antennal transcriptomes, and further RT-PCR and RT-qPCR revealed that 22 OBPs, 3 CSPs, 35 ORs, 14 IRs and the 2 SNMPs are uniquely or primarily expressed in the male and female antennae. Furthermore, one OBP (AipsOBP6) and one CSP (AipsCSP2) were exclusively expressed in the female sex pheromone gland. These antennae-enriched OBPs, CSPs, ORs, IRs and SNMPs were suggested to be responsible for pheromone and general odorant detection and thus could be meaningful target genes for us to study their biological functions in vivo and in vitro. [ABSTRACT FROM AUTHOR]

Abstract: Insect odorant binding proteins (OBPs) are required for insect olfaction perception and play a key role in transporting hydrophobic semiochemicals across the sensillum lymph to the olfactory receptors (Ors). We constructed two high-quality cDNA libraries from the male and female antennae of the lucerne plant bug, Adelphocoris lineolatus (Goeze) (Hemiptera: Miridae), a hemipteran species in a large and economically important phylogenetic group of phytophagous insects. A total of 1538 male ESTs and 1576 female ESTs were sequenced and analyzed, which produced 2915 high-quality ESTs for further analysis. The 2915 ESTs were assembled to 1423 unigenes. Of the 1423 unigenes, 895 (63%) showed no significant similarity with any known GenBank entry. The most prevalent transcripts in the cDNA libraries are OBPs, chemosensory proteins (CSPs), protein takeout precursors, antennae-specific proteins. We identified 14 genes encoding 12 “classical OBPs” with only six conserved cysteines and 2 “Plus-C OBPs” with two additional conserved cysteines and a conserved proline immediately after the sixth cysteine. AlinOBP4 has a very high amino acid identity of 89% to LAP, a well studied OBP of the tarnished plant bug Lygus lineolaris. The expression profiles of the 14 OBPs in different tissues (antennae, heads, thoraxes, abdomens, legs and wings) were measured by real-time qPCR. The results revealed some OBP genes are highly and differentially expressed in male and female antennae, and four OBP genes have an extremely high transcript level in the legs. Of two Plus-C OBP genes, one (AlinOBP14) is highly expressed only in the heads and another (AlinOBP7) is expressed in all olfactory tissues with much lower transcript levels comparing to other OBPs. The possible physiological functions of these OBPs are discussed. [Copyright &y& Elsevier]