# De Novo Transcriptome Identifies Olfactory Genes in _Diachassimomorpha Ionigicaudata_ (Ashmead)
## 4 Discussion  
This project was initiated in an effort to identify the olfactory proteins of parasitoid wasps. In recent years, many aspects about the perception of pheromones and other odorants have been elucidated [36]. Olfaction is used by insects to recognize volatile cues that allow the detection of food, predators, and mates [37]. We identified 43 OBPs, 69 CSPs, 60 GRs, 689 ORs, 26 IRs, and 14 SNMPs in _D. longicaudata_ (Table 2, Table S2) and some of them were differentially expressed when they were maintained with fruit flies fed with different fruits (Figure 4C, Table S4). This is the first time the chemosensory genes in _D. longicaudata_ have been investigated and our findings provide a basis for elucidating the molecular mechanisms of the olfactory-related behaviors of parasitoid wasps. OBPs are a group of proteins that specialize in the transport of lipids. In this study, we identified 43 transcripts encoding OBPs and this number is similar to the number of genes encoding OBPs in the _Drosophila_ genome [38]. Additionally, classic OBPs have been reported to contain six Cys in their sequences [38; 39]. Because all the identified OBPs in this study were general OBPs (GOBPs) (Table S2), we found conserved Cys in their sequences (Figure S1), which increased the confidence of using the transcriptome to identify the OBPs in _D. longicaudata_. In detail, the _D. longicaudata_ OBPs were grouped into four subfamilies: OBP-56, -69, -72, and -83 (Table S2). However, no studies have been demonstrated to distinguish their functions. In general, according to their names, they are called GOBPs because they bind general odorants that are likely to be represented by the same volatiles for most of the species [40]. We also showed the differential expression of nine transcripts encoding OBPs in parasitoid wasps in response to the fruit flies with different scents (Figure 4, Table S4). This might indicate that some specific OBPs are expressed to discriminate different scents. Similar to OBPs, CSPs are another group of proteins that mediate the olfactory recognition in insects [41]. They are thought to be expressed during nearly the whole life circle of insects [42; 43]. The number of CSP genes varies in species. For example, only 4-8 CSP genes in ants, flies, bees, wasps, and anopheline mosquitoes [44]; 19-20 in butterfly, moth, and beetle [45; 46; 47]; and 27 to 83 in _Culex_ mosquito species [48]. We identified 69 CSP transcripts produced by 58 genes (Table S2), the number of which is similar to _Culex_ mosquito species. CSPs function not only in the chemical communication between insects and the environment but also in some other cellular processes, such as lipid transport, general immunity, insecticide resistance, and xenobiotic degradation [45; 49]. In ants, CSPs have been proposed to mediate the recognition of chemical signatures composed of cuticular lipids [50]. The differential expression of CSP transcripts identified in this study (Table S4) may support the ability to recognize different scents from their hosts. In the present study, we also identified some other olfactory gene families, such as OR, IR, GR, and SNMP, which were differentially expressed in response to the fruit fly with different scents (Table S2, Table S4). OR is the name for all molecules that are expressed in the cell membranes of olfactory receptor neurons and are responsible for the detection of odorants. The ORs form a multigene family consisting of around 800 genes in humans and 1400 genes in mice [51]. We identified 689 OR  
\begin{table}
\begin{tabular}{l l r r r} \hline \hline  & & **TRINITY_DN1020\_el\_gl\_13** & **TRINITY_DN1284\_co\_gl\_111** & **TRINITY_DN500\_o\_gl\_12** \\ \hline \multirow{2}{*}{Primers} & Forward & CAACTICAAGAACAACTCCAACC & ACTATAGACGACTCCAAGACC & GACTGCCTGCTATGAACCGTTG \\  & Reverse & CCACAG  
transcripts derived from 637 genes (Table 2, Table S2). The diversity of ORs might help insects to discriminate as many different odors as possible. GRs are found be expressed exclusively in gustatory receptor neurons [52].