In order to acquire enough nutrients and energy for further development, larvae need to invest a large portion of their sensory equipments to identify food sources. Yet, the molecular basis of odor-driven behavior in larvae has been poorly investigated. Information on olfactory genes, particularly odorant binding proteins (OBPs) and chemosensory proteins (CSPs) which are involved in the initial steps of olfaction is very scarce. In this study, we have identified 26 OBP and 21 CSP genes from the transcriptomes of Helicoverpa armigera larval antennae and mouthparts. A comparison with the 34 OBP and 18 CSP genes of the adult antenna, revealed four novel OBPs and seven novel CSPs. Similarly, 27 OBPs (six novel OBPs) and 20 CSPs (6 novel CSPs) were identified in the transcriptomes of Helicoverpa assulta larval antennae and mouthparts. Tissue-specific profiles of these soluble proteins in H. armigera showed that 6 OBP and 4 CSP genes are larval tissue-specific, 15 OBPs and 13 CSPs are expressed in both larvae and adult, while the rest are adult- specific. Our data provide useful information for functional studies of genes involved in larval foraging.
Citation: Chang H, Ai D, Zhang J, Dong S, Liu Y, Wang G (2017) Candidate odorant binding proteins and chemosensory proteins in the larval chemosensory tissues of two closely related noctuidae moths, Helicoverpa armigera and H. assulta. PLoS ONE 12(6): e0179243. https://doi.org/10.1371/journal.pone.0179243
Editor: Joseph Clifton Dickens, USDA-ARS Beltsville Agricultural Research Center, UNITED STATES
Received: January 4, 2017; Accepted: May 28, 2017; Published: June 8, 2017
Copyright: © 2017 Chang et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Data Availability: All relevant data are within the paper and its Supporting Information files.
Funding: This work was supported by National Natural Science Foundation of China (31372264 to SD, 31230062 to GW, 31321004 to GW&YL, and 31471833 to YL). The funder had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing interests: The authors have declared that no competing interests exist.
For survival, insects need a specialised sensory system to monitor environmental odors. Olfactory stimuli in Lepidoptera can be divided into intra-specific pheromones, mainly mediating communication between sexes, and plant volatiles used as cues for larval foraging and oviposition [1–3]. Odor detection is achieved by ten thousand chemosensilla on the two main sensory organs, antenna and mouthparts, housing olfactory sensory neurons (OSNs) that respond to volatiles and send electrical impulses to antennal lobes. From these organs cognate project neurons (PN) convey electric signals to the mushroom bodies and lateral horn of the protocerebron, triggering behavioral responses [4–6]. At the periphery, several protein families are involved in odor detection: odorant binding proteins (OBPs), chemosensory proteins (CSP), odorant receptors (OR) and ionotropic receptors (IR) [7–9]. Of these genes, the receptor families including ORs and IRs are the key elements which determine both sensitivity and specificity of chemical recognition. ORs are seven trans-membrane domain receptors expressed in the dendrite membrane of olfactory sensory neurons. OR perform their function as heterodimer with a specific ligand-binding ORx and a highly conserved co-receptor named Orco [10–12]. IRs belong to the ionotropic glutamate receptor (iGluR)-like protein family and can be activated by small molecules like acetates and amine-like volatile compounds [13–15].
Apart from receptors, two families of soluble proteins, OBPs and CSPs, also play essential roles in the first step of olfactory detection. OBPs are small soluble proteins generally with 135–220 amino acids. To maintain a compact and conserved structure, six conserved cysteines are paired in three interlocked disulphide bridges. Six α-helices envelop a hydrophobic binding pocket [16–18]. OBPs are present at high concentrations (up to 10mM) in the lymph between the dendritic membrane and the cuticular wall [7, 19]. More interesting, there are some evidences that OBPs contribute to odorant recognition, rather than being passive odorant shuttles [20, 21]. Some studies have shown that OBPs perform the first filtering function in olfactory discrimination [19,20], besides a more general role in ferrying ligands through the sensillum lymph to the membrane of OSN dendrites. OBPs have also been shown to influence the response of ORx/ORco complexes to specific odors [21, 22]. CSPs represent another class of small soluble proteins abundant in the lymph of chemosensilla . They are different from OBPs in amino acid sequence and structure, but appear to be similar in functions, although better evidence is needed to clarify their role in olfaction.
In Lepidoptera, both larvae and adults use their olfactory system to detect volatile chemicals, but their olfactory organs are completely different in morphology. In adults, a pair of antennae bear tens of thousands of sensilla, each of them housing two or more OSNs [24, 25]. Larvae are equipped with two different olfactory organs, antennae and mouthparts [26,27]. Unlike adult antennae, larval antennae and mouthparts contain few sensilla, but each of them houses a cluster of OSNs [28, 29]. With the rapid development of next generation sequence techniques, a large number of olfactory genes including IRs, ORs, OBPs and CSPs have been recently identified in the antennae of several moths, such as Manduca sexta [15, 30–32], Helicoverpa armigera [33–35], Helicoverpa assulta [34, 36], Cydia pomonella , Spodoptera littoralis [38, 39] and Chilo suppressalis , and many others. However, limited information is available for larval antennae and mouthparts.
Two Helicoverpa species, H. armigera and H. assulta are worldwide agricultural pests . The behaviors of larvae and adults are largely triggered by olfactory stimuli. Previously, we performed a transcriptome analysis on adult antennae in both species. A total of 131 putative chemosensory unigenes were identified in H. armigera including 60 ORs, 19 IRs, 34 OBPs and18 CSPs. Similarly, in H. assulta we found 129 putative chemosensory unigenes, including 64 ORs, 19 IRs, 29 OBPs and 17 CSPs . Skiri et al. (2005) have identified 65 glomeruli in each sex of H. armigera and 66 glomeruli in females of H. assulta , later supplemented by 15 new glomeruli in H. armigera . Assuming that the number of glomeruli is equal to the number of ORs and IRs [43, 44], almost all olfactory receptors were identified in the two species. These data also agree with another study focused on both adults and larvae of H. armigera chemosensory tissues . However, the repertoires of OBPs and CSPs in these two species may be incomplete by comparison with the numbers of OBPs and CSPs identified in the genome of B. mori (46 OBPs and 24 CSPs) . This suggests that some OBP and CSP sources may occur in other chemosensory tissues, such as larval antennae and mouthparts. In this study, we performed a transcriptome analysis to identify OBP and CSP genes in larval chemosensory organs of H. armigera and H. assulta. Moreover, we conducted RT-PCR assays on H. armigera adult and larval olfactory organs to find OBP and CSP genes with specific expression in larval antennae or mouthparts.
H. armigera were reared at the Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing, China. The H. assulta larvae were collected from the tobacco fields with the permission of the Experiment Station of Henan University of Science and Technology in Xuchang, Henan Province, China. Larvae were reared on an artificial diet and placed on a 16:8 h (light: dark) photoperiod at 27 ± 1°C, 55–65% RH. Pupae were sexed and male and female individuals were placed in separate cages for eclosion. The adults were fed on 10% honey solution. In expression profile studies, all adult tissues were collected from 3-day-old male and female moths, all larval tissues were collected from fifth instar larvae.
Fresh larval antennae and mouthparts were grinded in a liquid nitrogen cooled homogenizer, later adding 1mL of TriZol reagent (Invitrogen, Carlsbad, CA, USA) and the total RNA extraction were performed following the manufacturer’s instructions. The RNA sediment was dissolved in 20μL RNase-free water, RNA integrity was verified by gel electrophoresis. RNA quantity were measured on a Nanodrop ND-2000 spectrophotometer (NanoDrop products, Wilmington, DE, USA) and purity was verified by gel electrophoresis.
cDNA library construction and sequencing
Five micrograms total RNA of each samples (H. armigera larval antennae, H. armigera larval mouthparts, H. assulta larval antennae, and H. assulta larval mouthparts,) was used to construct the cDNA library respectively. cDNA library construction and Illumina HiSeq 2000 (Illumina, San Diego, CA, USA) sequencing of the samples were performed at Beijing Genomics Institute (BGI, Shenzhen, China). The length of insert sequence was around 200 bp. The libraries were paired-end sequenced using PE90 strategy. The detailed procedures have been described in previous work from our laboratory [33, 34].
Assembly and functional annotation
After removing low quality reads, trimming low quality nucleotides of both ends, trimming 3 adaptors and poly-A/T tails, the remainder raw-reads were considered as clean-reads. De novo assembly in each sample was conducted using Trinity (version 20120608). Then the unigenes derived from the Trinity outputs were clustered by TGICL [46,47]. The consensus cluster sequences and singletons make up the unigenes dataset. The annotation of unigenes were performed via a NCBI blastx against non-redundant (nr) and SwissProt database. Candidate unigenes encoding putative OBPs and CSPs, were identified according to nr and SwissProt annotation results.
Sequence and phylogenetic analysis
The open reading frames (ORFs) of the putative chemosensory genes were predicted by using ORF finder (http://www.ncbi.nlm.nih.gov/gorf/gorf.html). Putative N-terminal signal peptides of OBPs and CSPs were predicted by Signal IP 4.0 (http://www.cbs.dtu.dk/services/SignalP/). Alignments of amino acid sequences (without signal peptides) were performed by ClustalX 2.0. The phylogenetic trees of OBPs and CSPs were constructed using MEGA5 software by the neighbor-joining method with Jones-Taylor-Thornton (JTT) model and the node support was assessed using a bootstrap procedure of 1000 replicates. The OBP data set contained OBP sequences identified in Lepidoptera (37 from H. armigera, 35 from H. assulta, 14 from H. virescens, 47 from M. sexta and 35 from B. mori. The CSP data set contained 25 sequences from H. armigera, 23 from H. assulta, 9 from H. virescens, 13 from C. suppressalis, and 16 from B. mori. The protein name and accession number of the genes used for phylogenetic tree building are listed in S1 Material.
Expression analysis by semi-quantitative reverse transcription PCR
Semi-quantitative reverse transcription PCR was performed to compare the expression levels of candidate chemosensory genes in larval antennae, larval mouthparts, adult antennae and adult abdomen in H. armigera. Total RNA was extracted from each sample as mentioned above. Before cDNA synthesis, total RNA was treated with DNase I (Fermentas, Vilnius, Lithuania) to remove residual genomic DNA. The cDNA was synthesized from total RNA using RevertAid First Strand cDNA Synthesis Kit (Thermo Scientific, Waltham, MA, USA). Gene specific primers were designed using Primer-BLAST (http://www.ncbi.nlm.nih.gov/tools/primer-blast/) (S2 Material) and synthesized by Sangon Biotech Co., Ltd (Shanghai, China). Taq MasterMix (CWBIO, Beijing, China) was used for PCR reactions under general 3-step amplification of 94°C for 30s, 60°C for 30s, 72°C for 30s. For most chemosensory genes, the PCR cycle-numbers were 28. PCR products were run on a 2% agarose gel and verified by DNA sequencing. The experiment was repeated using two independently prepared cDNA templates.
Illumina sequencing and functional annotation
In this study, the transcriptomes of larval antennae and mouthparts in H. armigera and H. assulta were sequenced by Illumina HiSeq 2000 platform. After filtering, 51.1 million and 45.5 million clean-reads of 4.6 and 4.1 gigabases were generated for larval antennae and mouthparts of H. armigera, respectively. Meanwhile, 50.2 million and 52.9 million clean-reads of 4.5 and 4.8 gigabases were generated for larval antennae and mouthparts of H. assulta. These clean reads were assembled into 47,331, 41,705, 57,789 and 47,423 unigenes in H. armigera larval antennae and mouthparts, and in H. assulta larval antennae and mouthparts, respectively. After clustering and merging, 39,371 unigenes consisting of 12,724 distinct clusters and 26,647 distinct singletons were obtained for H. armigera and 44,352 unigenes consisting of 11,179 distinct clusters and 33,173 distinct singletons were obtained for H. assulta (Table 1).
A blastx homology search against the NCBI nr protein database revealed that 22,628 (57.5%) and 22,724 (51.2%) unigenes from H. armigera and H. assulta, respectively, showed sequence similarities to known proteins, with a cut-off E-value of 10−5. In the nr homologous species distribution, 46.78% (H. armigera) and 48.42% (H. assulta) annotated sequences closely matched the sequences of B. mori. The next most similar species was D. plexippus whose sequences matched 26.25% of those of H. armigera and 27.13% of H. assulta. Only a low percentage (<5%) of H. armigera and H. assulta sequences had orthologues in other species (S3 Material).
Identification of putative odorant-binding proteins
Based on the blastx sequence homology searching, a total of 26 and 27 OBP genes were obtained from H. armigera and H. assulta larval transcriptome respectively. Of these genes, 22 HarmOBPs and HassOBPs presented intact ORFs encoding for proteins of 135 to 195 aa, all exhibiting signal peptides at their N-termini (Table 2). A comparison with known OBPs of H. armigera adult antenna revealed four novel OBPs in larvae, that we named as HarmOBP31, HarmOBP33, HarmOBP35 and HarmOBP36, and six new OBPs in H. assulta, named as HassOBP33 to HassOBP38. All these novel genes were deposited in the GeneBank databases with the following accession numbers: HarmOBP31: KY810175, HarmOBP33: KY810179, HarmOBP35: KY810176, HarmOBP36: KY810177, HassOBP33: KY810180, HassOBP34: KY810178, HassOBP35: KY810181, HassOBP36: KY810182, HassOBP37: KY810183, HassOBP38: KY815028.
Insect OBPs are generally grouped into three main subfamilies: “Classic” OBPs with six conserved cysteines, “Minus-C” with only four cysteines, and “Plus-C” with more cysteines in addition to those of the conserved motif [45, 48, 49]. Among the larval OBPs, 14 of H. armigera and 17 of H. assulta were assigned to the Classic OBP group, while 3 can be classified as Minus-C OBPs in both species. 7 OBPs in both species belong to the Plus-C group, while others could not be assigned due to incomplete sequences (Fig 1).
The conserved cysteine residues were marked with “▽”. All these OBPs were assignment into CRLBP with six conserved cysteine residues, Minus-C with four conserved cysteine residues and Plus-C with more than more than six conserved cysteine residues.
A phylogenetic tree was constructed using OBP sequences from H. armigera, H. assulta, H. virescens, M sexta and B. mori (Fig 2). Accordingly, the OBPs can be grouped into ABPI (antennal binding protein I), ABPII (antennal binding protein II), CRLBP (classic OBP), Minus-C, Plus-C, and PBP/GOBP (general odorant binding protein/pheromone binding protein) clusters based on the classification of OBPs from B. mori . At the same time, most OBPs of H. armigera and H. assulta defined as Minus-C and Plus-C clustered with B. mori proteins of the same groups. However, among “classic” OBPs, only two sequences were found in the CRLBP branch, the others in the ABPX branches. Based on the bootstrap values on the tree, for all novel HarmOBPs we could find orthologous genes in H. assulta with more than 90% sequence identity. Only for HassOBP38 we could not identify an orthologue in H. armigera.
Harm: H. armigera (red), Hass: H. assulta (blue), Hvir: H. virescens (black), Bm: B. mori (aquamarine), Msex: M. sexta (cyan) The whole tree can be divided into six branches including GOBP/PBP, CRLBP, Plus-C, Minus-C, ABPI and ABPII. The red and blue circles represented newly identified HarmOBPs and HassOBPs respectively.
Identification of candidate chemosensory proteins
In our transcription sets, a total of 21 sequences in H. armigera and 20 sequences in H. assulta can be matched with sequences of known CSPs in other Lepidoptera species. Of these, 17 HarmCSPs and HassCSPs had full-length ORFs and predicted signal peptides. Their lengths range from 107 to 292 amino acids (Table 3). A comparison with CSPs previously reported for H. armigera and H. assulta adult antenna revealed seven new sequences in H. armigera (HarmCSP20 to HarmCSP26) and six in H. assulta (HassCSP20 to HassCSP25). All candidate CSPs exhibit the four conversed cysteine pattern characteristic of this family (Fig 3). These sequences were used to build a neighbor-joining tree with the CSPs of C. suppressalis, B. mori and H. virescens. In the tree we could recognize four groups of genes clustered together with a 99% bootstrap value, while the remaining sequences could not be grouped. Based on this homology analysis, we named the novel CSPs as HarmCSP20/HassCSP20, HarmCSP21/HassCSP21, HarmCSP22/HassOBP22, HarmCSP23/HassCSP23, HarmCSP24, HarmCSP25, HarmCSP26, HassCSP24 and HassCSP25 following the numbers assigned to previously reported CSPs (Fig 4). All these novel genes were deposited in the GeneBank: HarmCSP20-26 (GeneBank accession numbers: KY810184, KY810185, KY810186, KY810187, KY810188, KY815026, KY815027), HassCSP20-25 (GeneBank accession numbers: KY810189, KY810190, KY810191, KY810192, KY810193, KY810194).
All these CSPs were characteristic of four conserved cysteine residues marked with “▽”.
Expression of the OBPs and CSPs in larva and adult H. armigera
To better understand the functional role of OBPs and CSPs in larval olfactory systems, we investigated the expression patterns of all candidate HarmOBPs and HarmCSPs via semi-quantitative reverse transcription PCR. The tissues used were larval antenna, larval mouthpart, adult antenna and adult abdomen. The results reported in Fig 5 show that all OBPs except HarmOBP16 were successfully detected in target tissues. Six OBPs were exclusive to larval tissues including HarmOBP36, HarmOBP27 and HarmOBP19 specific for larval mouthparts, while HarmOBP26, HarmOBP31 and HarmOBP35 were expressed in both larval antennae and mouthparts. On the other hand, we found that five OBPs (HarmOBP2, HarmOBP15 and HarmOBP21, HarmOBP22 and HarmOBP23) are exclusively expressed in adult antenna. The remaining 13 OBPs showed expression in both larval and adult tissues. Of this latter group HarmGOBP2, HarmOBP4, HarmOBP9, HarmOBP17 and HarmOBP25 where were preferentially expressed in adult antenna, while the others did not show significant differences between larval and adult tissues. Compared to OBPs, CSPs were more expressed in non-olfactory tissues suggesting diverse functions. Eight of them showed similar expression levels in all tissues, while the others were specifically detected in olfactory organs. In particular, four genes (HarmCSP20, 22, 23 and 24) were specific of larval olfactory tissues, one (HarmCSP14) was detected only in adult antenna, and three (HarmCSP7, HarmCSP15 and HarmCSP25) were found in both larval and adult olfactory organs with no significant differences.
In Lepidoptera, the main tasks of adults are reproduction and species dispersal. To accomplish them they use a sophisticated olfactory system for correct mating and oviposition on the suitable host plant [50, 51]. Compared to adults, larvae show limited activity, their major tasks being feeding, growing and accumulating energy [52,53]. Therefore larvae are expected to harbor a simpler olfactory system than adults. One of the characteristics of monophagous insects is the strict specificity to their host, a typical example being the specialization of M. sexta for Solanaceous plants . In this case, the mother choses the host plant while ovipositing and larvae may not need to move away through their life [54, 55]. In contrast, larvae of polyphagous speciesoften ignore their mother’s choices, disperse actively, and often move between different host plants for feeding [56, 57]. For example, sometimes larvae need to abandon their prior host and select another one, because the plant resources are exhausted, or because of competition with other herbivores, or else because the plant has become infected [58–61]. Such differences in foraging behaviors are genetically determined .
H. armigera and H. assulta are two closely related species both representing serious pests in China and other countries. H. armigera is a polyphagous insect which attacks about 180 species of plants , while H. assulta is oligophagous, mainly feeding on tobacco . In both species antennae and mouthparts are the main chemosensory structures guiding the larvae to their host plants. Thus, a study of larval antennae and mouthparts at the molecular level can provide useful information for larva-based pest control.
In this work, we focused on two families of soluble protein OBPs and CSPs which play some roles in the interactions between odorant molecules and olfactory receptors. We identified a total of 26 OBPs and 21 CSPs in the larval chemosensory tissues of H. armigera as well as 27 OBPs and 20 CSPs in H. assulta. Combined with the data available for in adult antennae, the total number of OBP genes identified in H. armigera and H. assulta are 38 and 35 respectively. These numbers are lower, although in the same order, than those reported for other species (46 in B. mori) . The total number of CSP genes identified in H. armigera (25) and H. assulta (23) are also in the same order of magnitude as in other species such as B. mori (21), and S. littoralis (23) [39, 45].
For most of HarmOBPs and HarmCSPs we could find homologue genes in H. assulta. The high similarities in sequence between pairs of orthologous genes suggest that H. armigera and H. assulta larvae detect similar volatile substances. This idea is supported by the observation that often mixed populations of the two species are present on tobacco and some solanaceous plants . However, for some genes we could not find orthologs in the sister species. This fact, if confirmed, could suggest that during evolution, the two species can have developed some unique characteristics in their chemosensory systems to become adapted to different ecosystems. For nearly half of the HarmCSPs, we detected expression in non-olfactory organ, such as adult abdomen, suggesting roles different from chemosensing. Similarly, in other species, some CSPs were found to be expressed in non-olfactory tissues, such as the pheromone glands, where they likely assist delivery of semiochemicals in the environment [64–67], or in reproductive organs, with putative roles in egg and embryo development [68, 69]. Most of OBPs and CSPs are expressed both in adults and in larvae chemosensory organs, suggesting some common olfactory related behaviors. In particular, the gene encoding GOBP2 is expressed in larval antenna, where it might bind pheromone cues. Such hypothesis was originated from what was observed in Plutella xylostella . However, for all PBP genes we could not find their expression in H. armigera larval tissues. This case, although being inconsistent with what was observed in S. littoralis , was common in other species. We also found three OBPs and six CSPs presenting larva-specific expression, suggesting that they may be involved in larval-foraging behaviors. Three OBPs and ten CSPs were found to be expressed more in larval antennae than in mouthparts, whereas the other proteins were only detected in larval mouthparts, suggesting that these genes may be involved in taste.
Our results contribute to a better understanding of the chemoreception mechanisms of larvae at the molecular level and might help the development of larva-targeted strategies for population control in these two important agricultural pests.
S1 Material. Accession numbers for amino acid sequences of OBPs and CSPs used in phylogenetic analyses.
S2 Material. Primers for RT-PCR expression analyses of H. armigera OBPs and CSPs.
We thank Dr. Junfeng Dong (Henan University of Science and Technology) for providing the H. assulta and Miss Liyan Yang for insect rearing. This work was supported by National Natural Science Foundation of China (31372264 to SD, 31230062 to GW, 31321004 to GW&YL, and 31471833 to YL).
- Conceptualization: SD YL GW.
- Data curation: HC YL.
- Formal analysis: HC DA YL.
- Funding acquisition: SD YL GW.
- Investigation: HC DA JZ YL.
- Methodology: HC SD YL GW.
- Project administration: SD YL GW.
- Resources: HC DA JZ.
- Software: HC YL.
- Supervision: SD YL GW.
- Validation: SD YL GW.
- Visualization: HC DA.
- Writing – original draft: HC SD YL GW.
- Writing – review & editing: HC SD YL GW.
- 1. Knolhoff LM, Heckel DG. Behavioral assays for studies of host plant choice and adaption in herbrivorous insects. Annual Review of Entomology. 2014; 59: 263–78. pmid:24160429
- 2. Ando T, Inomata S, Yamamoto M. Lepidopteran sex pheromones. Topics in Current Chemistry. 2004; 239:51–96. pmid:22160231
- 3. Hansson BS. Olfaction in Lepidoptera. Reviews. 1995; 51:11, pp1003–1027.
- 4. Zhao XC, Tang QB, Liu Y, Wang YR, Yan FM, Wang GR. Fine structure and primary sensory projections of sensilla located in the labial-palp pit organ of Helicoverpa armigera (Insecta). Cell & Tissue Research. 2013; 353: 399–408. pmid:23736380
- 5. Hansson BS, Anton S. Function and morphology of the antenna lobe:New Developments. Annu Rev Entomol. 2000; 45: 203–31. pmid:10761576
- 6. Skiri HT, Rø H, Berg BG, Mustaparta H. Consistent organization of glomeruli in the antennal lobes of related species of Heliothine moths. J Comp Neurol, 2005; 491: 367–80. pmid:16175552.
- 7. Leal WS. Odorant reception in insects: roles of receptors, binding proteins, and degrading enzymes. Annual Review of Entomology. 2003; 58:373–391. pmid:23020622
- 8. Hallem EA, Dahanukar A, Carlson JR. Insect odor and taste receptors. Annual Review of Entomology. 2006; 51:113–135. pmid:16332206
- 9. Touhara K, Vosshall LB. Sensing odorants and pheromones with chemosensory receptors. Annual Review of Physiology. 2009; 71: 307–332. pmid:19575682
- 10. Benton R., Sachse S, Michnick SW, Vosshall LB. Atypical membrane topology and heteromeric function of Drosophila odorant receptors in vivo. PLoS Biology 2006; 4: e20. pmid:16402857
- 11. Sato K, Pellegrino M, Nakagawa T, Vosshall LB, Touhara K. Insect olfactory receptors are heteromeric ligand-gated ion channels. Nature. 2008; 452: 1002–6. pmid:18408712
- 12. Wicher D, Schäfer R, Bauernfeind R, Stensmyr MC, Heller R, et al. Drosophila odorant receptors are both ligand-gated and cyclic-nucleotide-activated cation channels. Nature, 2008; 452: 1007–1. pmid:18408711
- 13. Benton R, Vannice KS, Gomez-Diaz C, Vosshall LB. Variant ionotropic glutamate receptors as chemosensory receptors in Drosophila. Cell, 2009; 136:149–62. pmid:19135896
- 14. Croset V, Rytz R, Cummins SF, Budd A, Brawand D, Kaessmann H. Ancient protostome origin of chemosensory ionotropic glutamate receptors and the evolution of insect taste and olfaction. PLoS Genet. 2010; 6: e1001064. pmid:20808886
- 15. Grosse-Wilde E, Kuebler LS, Buck S, Vogel H, Wicher D. Antennal transcriptome of Manduca sexta. Proc Natl Acad Sci U S A. 2011; 108: 7449–54. pmid:21498690
- 16. Pelosi P, Iovinella I, Feliciolim A, Dani FR. Soluble proteins of chemical communication: an overview across arthropods. Front Physiol. 2014; 5: 320. pmid:25221516
- 17. Sandler BH, Nikonova L, Leal WS, Clardy J. Sexual attraction in the silkworm moth: structure of the pheromone-binding-protein-bombykol complex. Chem Biol. 2002; 7:143–51. pmid:10662696
- 18. Scaloni A, Monti M, Angeli S, Pelosi P. Structural analysis and disulfide-bridge pairing of two odorant-binding proteins from Bombyx mori. Biochem Biophys Res Commun. 1999; 266: 386–91. pmid:10600513
- 19. Klein U. Sensillum-lymph proteins from antennal olfactory hairs of the moth Antheraea polyphemus (Saturniidae). Insect Biochem. 1987; 17:1193–1204.
- 20. Plettner E, Lazar J, Prestwich EG, Prestwich GD. Discrimination of pheromone enantiomers by two pheromone binding proteins from the gypsy moth Lymantria dispar. Biochemistry. 2000; 39:8953–62. pmid:10913308
- 21. Chang HT, Liu Y, Yang T, Pelosi P, Dong SL, Wang GR. Pheromone binding proteins enhance the sensitivity of olfactory receptors to sex pheromones in Chilo suppressalis. Sci Rep. 2015; 5:13093. pmid:26310773
- 22. Sun MJ, Liu Y, Walker WB, Liu CC, Lin KJ, Wang GR. Identification and characterization of pheromone receptors and interplay between receptors and pheromone binding proteins in the diamondback moth, Plutella xyllostella. PLoS One. 2013; 8: e62098. pmid:23626773
- 23. Pelosi P, Zhou JJ, Ban LP, Calvello M. Soluble proteins in insect chemical communication. Cellular and Molecular Life Sciences. 2006; 63: 1658–1676. pmid:16786224
- 24. Ljungberg H, Anderson P, Hansson BS. Physiology and morphology of pheromone-specific sensilla on the antennae of male and female Spodoptera littoralis (Lepidoptera: Noctuidae). J Insect Physiol.1993; 39:253–260.
- 25. Chang HT, Guo MB, Wang B, Liu Y, Dong SL, Wang GR. Sensillar expression and responses of olfactory receptors reveal different peripheral coding in two Helicoverpa species using the same pheromone components. Sci Rep. 2016; 6:18742. pmid:26744070
- 26. Dethier VG, Choonhoven LM. Olfactory coding by lepidopterous larvae. Entomol Exp Appl. 1969; 12: 535–543.
- 27. Laue M. Immunolocalization of general odorant-binding protein in antennal sensilla of moth caterpillars. Arthropod Struct Dev. 2000; 29: 57–73. pmid:18088914
- 28. Schoonhoven LM, Dethier VG. Sensory aspects of host-plant discrimination by lepidopterous larvae. Arch Neerl ZooI. 1964; 16: 497–530.
- 29. Roessingh P, Xu S, Menken SB. Olfactory receptors on the maxillary palps of small ermine moth larvae: evolutionary history of benzaldehyde sensitivity. J Comp Physiol A Neuroethol Sens Neural Behav Physiol. 2007; 193: 635–47. pmid:17372741
- 30. Kanost MR, Arrese EL, Cao X. Chen YR, Chellapilla S, Goldsmith MR, et al. Multifaceted biological insights from a draft genome sequence of the tobacco hornworm moth, Manduca sexta. Insect Biochem Mol Biol. 2016; 76:118–47. pmid:27522922.
- 31. Vogt RG, Große-Wilde E, Zhou JJ. The Lepidoptera Odorant Binding Protein gene family: Gene gain and loss within the GOBP/PBP complex of moths and butterfiles. Insect Biochem Mol Biol. 2015; 62: 142–53. pmid:25784631.
- 32. Koenig C, Bretschneider A, Heckel DG, Große-Wilde E, Hansson BS, Vogel H. The plastic response of Manduca sexta to host and non-host plants. Insect Biochem Mol Biol. 2015; 63:72–85. pmid:26070471
- 33. Liu Y, Gu SH, Zhang YJ, Guo YY, Wang GR. Candidate Olfaction Genes Identified within the Helicoverpa armigera Antennal Transcriptome. PLoS One. 2012; 7: e48260. pmid:23110222
- 34. Zhang J, Wang B, Dong SL, Cao DP, Dong JF, Walker WS, et al. Antennal transcriptome analysis and comparison of chemosensory gene families in two closely related noctuidae moths, Helicoverpa armigera and H. assulta. PLoS One. 2015; 10: e0117054. pmid:25659090
- 35. Liu NY, X W, Papanicolaou A, Dong SL, Anderson A. Identification and characterization of three chemosensory receptor families in the cotton bollworm Helicoverpa armigera. BMC Genomics. 2014; 15:597. pmid:25027790
- 36. Xu W, Papanicolaou A, Liu NY, Dong SL, Anderson A. Chemosensory receptor genes in the Oriental tobacco budworm Helicoverpa assulta. Insect Mol Biol. 2015; 24:253–63. pmid:25430896
- 37. Bengtsson JM, Trona F, Montagné N, Anfora G, Ignell R, Witzgall P, et al. Putative chemosensory receptors of the codling moth, Cydia pomonella, identified by antennal transcriptome analysis. PLoS One. 2012; 7: e31620. pmid:22363688.
- 38. Poivet E, Gallot A, Montagné N, Glaser N, Legeai F, Jacquin-Joly E. A comparison of the olfactory gene repertoires of adults and larvae in the noctuid moth Spodoptera littoralis. PLoS One. 2013; 8: e60263. pmid:23565215
- 39. Jacquin-Joly E, Legeai F, Montagné N, Monsempes C, Francois M, Poulain J, et al. Candidate chemosensory genes in female antennae of the noctuid moth Spodoptera littoralis. Int J Biol Sci. 2012; 8:1036–50. pmid:22904672
- 40. Cao DP, Liu Y, Wei JJ, Liao XY, Walker WB, Li JH, et al. Identification of Candidate Olfactory Genes in Chilo suppressalis by Antennal Transcriptome Analysis. Int J Biol Sci. 2004; 10:846–60. pmid:25076861
- 41. Fitt GP. The ecology of Heliothis species in relation to agroecosystems. Annu Rev Entomol. 1989; 34: 17–53.
- 42. Zhao XC, Ma BW, Berg BG, Xie GY, Tang QB, Guo XR. A global-wide search for sexual dimorphism of glomeruli in the antennal lobe of female and male Helicoverpa armigera. Sci Rep. 2016; 6: 35204. pmid:27725758.
- 43. Carlsson MA, Galizia CG, Hansson BS. Spatial representation of odours in the antennal lobe of the moth Spodoptera littoralis (Lepidoptera: Noctuidae). Chem Senses. 2002; 27: 231–244. pmid:11923186
- 44. Fishilevich E, Vosshall LB. Genetic and functional subdivision of the Drosophila antennal lobe. Current Biology 15: 1548–1553. pmid:16139209
- 45. Gong DP, Zhang HJ, Zhao P, Xia QY, Xiang ZH. The Odorant Binding Protein Gene Family from the Genome of Silkworm, Bombyx mori. BMC Genetics. 2009; 10: 332. pmid:19624863
- 46. Ma DK, Li ZJ, Lu AY, Sun F, Chen S, Rothe M, et al. Acyl-CoA Dehydrogenase Drives Heat Adaptation by Sequestering Fatty Acids. Cell. 2015; 161: 1152–63. pmid:25981666
- 47. Grabherr MG, Haas BJ, Yassour M, Levin JZ, Thompson DA, Amit I, et al. Full-length transcriptome assembly from RNA-Seq data without a reference genome. Nature Biotechnology. 2011; 29: 644–652. pmid:21572440
- 48. Liu NY, Zhang T, Ye ZF, Li F, Dong SL. Identification and Characterization of Candidate Chemosensory Gene Families from Spodoptera exigua Developmental Transcriptomes. Int J Biol Sci. 2015; 11:1036–48. pmid:26221071
- 49. Yin XW, Iovinella I, Marangoni R, Cattonaro F, Flamini G, Sagona S, et al. Odorant-binding proteins and olfactory coding in the solitary bee Osmia cornuta. Cell and Mol Life Sci. 2013; 70: 3029–39. pmid:23512006
- 50. Thompson JN. Evolutionary ecology of the relationship between oviposition preference and performance of offspring in phytophagous insects. Entomol Exp Appl. 1988; 47: 3–14.
- 51. Marion-Poll F, Descoins C. Taste detection of phytoecdysteroids in larvae of Bombyx mori, Spodoptera littoralis and Ostrinia nubilalis. J Insect Physiol. 2002; 48: 467–476. pmid:12770096
- 52. Wiklund C. The evolutionary relationship between adult oviposition preferences and larval host plant range in Papilio machaon L. Oecologia. 1975; 18: 185–197. pmid:28308676
- 53. Poivet E, Rharrabe K, Monsempes C, Glaser N, Rochat D, Renou M, et al. The use of the sex pheromone as an evolutionary solution to food source selection in caterpillars. Nat Commun. 2012; 3:1047. pmid:22948829
- 54. Hovanitz W, Chang VC. Three factors affecting larval choice of food plant. J Res Lepidoptera. 1962; 1
- 55. Wiklund C. Host plant suitability and the mechanism of host selection in larvae of Papilio machaon. Ent exp appl. 1973; 16: 232–242.
- 56. Wiklund C. Oviposition preferences in Papilio machaon in relation to the host plants of the larvae. Ent exp appl. 1974; 17: 189–198.
- 57. Clark M, Malcolm SB. Ecology and behavior of first instar larval Lepidoptera. Annu Rev Entomol. 2002; 47: 361–393. pmid:11729079
- 58. Jackson RE, Mahaffey JS, Jrjr B, VAN Duyn JW, Sorensen CE. The impact of transgenic cottons expressing one or two proteins from Bacillus thuringiensis on survival and damage potential of first and second instars of Ostrinia nubilalis (Lepidoptera: Crambidae). J Cotton Sci. 2005; 9:199–203
- 59. Pats P, Ekbom B. Infestation and dispersal of early instars of Chilo partellus (Lepidoptera, Pyralidae) at different densities. Environm Entomol. 1992; 21:1110–1113
- 60. Kester KM, Peterson SC, Hanson F, Jackson DM. The roles of nicotine and natural enemies in determining larval feeding site distributions of Manduca sexta L. and Manduca quinquemaculata (Haworth) on tobacco. Chemoecology. 2002; 12:1–10.
- 61. Bernays EA. Feeding by lepidopteran larvae is dangerous. Ecol Entomol. 1997; 22:121–123.
- 62. Singh AK, Mullick S. Leaf volatiles as attractants for neonate Helicoverpa armigera Hbn. (Lep., Noctuidae) larvae. J Appl Ent. 2002. 126:14–19.
- 63. Wang HL, Ming QL, Zhao CH, Wang CZ. Genetic basis of sex pheromone blend difference between Helicoverpa armigera (Hubner) and Helicoverpa assulta (Guenee) (Lepidoptera: Noctuidae). J Insect Physiol. 2008; 54:813–7. pmid:18405915
- 64. Iovinella I, Dani FR, Niccolini A, Sagona S, Michelucci E, Gazzano A, et al. Differential expression of odorant binding proteins in the mandibular glands of the honey bee according to caste and age. J Proteome Res. 2011; 10(8):3439–49. pmid:21707107
- 65. Zhou XH, Ban LP, Iovinella I, Zhao L, Gao Q, Felicioli A, et al. Diversity, abundance, and sex-specific expression of chemosensory proteins in the reproductive organs of the locust Locusta migratoria manilensis. Biol Chem. 2013; 394: 43–54. pmid:23096575
- 66. Gu SH, Wu KM, Guo YY, Pickett JA, Field LM, Zhou JJ, et al. Identification of genes expressed in the sex pheromone gland of the black cutworm Agrotis ipsilon with putative roles in sex pheromone biosynthesis and transport. BMC Genomics. 2013; 14:636. pmid:24053512
- 67. Dani FR, Michelucci E, Francese S, Mastrobuoni G, Cappellozza S, La MG, et al. Odorant-binding proteins and chemosensory proteins in pheromone detection and release in the silkmoth Bombyx mori. Chem Senses. 2011; 36:335–44. pmid:21220518.
- 68. Marinotti O, Ngo T, Kojin BB, Chou SP, Nguyen B, Juhn J, et al. Integrated proteomic and transcriptomic analysis of the Aedes aegypti egg shell. BMC Dev Biol. 2014; 14:15. pmid:24707823
- 69. Maleszka J, Forêt S, Saint R, Maleszka R. RNAi-induced phenotypes suggest a novel role for a chemosensory protein CSP5 in the development of embryonic integument in the honeybee (Apis mellifera). Dev Genes Evol. 2007; 217:189–96. pmid:17216269
- 70. Zhu J, Ban LP, Song LM, Liu Y, Pelosi P, Wang GR. General odorant-binding proteins and sex pheromone guide larvae of Plutella xylostella to better food. Insect Biochem Mol Biol. 2016; 72:10–9. pmid:27001069