*Article* **De Novo Transcriptome Identifies Olfactory Genes in** *Diachasmimorpha longicaudata* **(Ashmead)**

#### **Liangde Tang 1,**†**, Jimin Liu 2,**†**, Lihui Liu 2, Yonghao Yu 2, Haiyan Zhao 3,4,\* and Wen Lu 5,\***


Received: 3 January 2020; Accepted: 22 January 2020; Published: 29 January 2020

**Abstract:***Diachasmimoorpha longicaudata* (Ashmead,*D. longicaudata*) (Hymenoptera: Braconidae)is a solitary species of parasitoid wasp and widely used in integrated pest managemen<sup>t</sup> (IPM) programs as a biological control agen<sup>t</sup> in order to suppress tephritid fruit flies of economic importance. Although many studies have investigated the behaviors in the detection of their hosts, little is known of the molecular information of their chemosensory system. We assembled the first transcriptome of *D. longgicaudata* using transcriptome sequencing and identified 162,621 unigenes for the Ashmead insects in response to fruit flies fed with different fruits (guava, mango, and carambola). We annotated these transcripts on both the gene and protein levels by aligning them to databases (e.g., NR, NT, KEGG, GO, PFAM, UniProt/SwissProt) and prediction software (e.g., SignalP, RNAMMER, TMHMM Sever). CPC2 and MIREAP were used to predict the potential noncoding RNAs and microRNAs, respectively. Based on these annotations, we found 43, 69, 60, 689, 26 and 14 transcripts encoding odorant-binding protein (OBP), chemosensory proteins (CSPs), gustatory receptor (GR), odorant receptor (OR), odorant ionotropic receptor (IR), and sensory neuron membrane protein (SNMP), respectively. Sequence analysis identified the conserved six Cys in OBP sequences and phylogenetic analysis further supported the identification of OBPs and CSPs. Furthermore, 9 OBPs, 13 CSPs, 3 GRs, 4IRs, 25 ORs, and 4 SNMPs were differentially expressed in the insects in response to fruit flies with different scents. These results support that the olfactory genes of the parasitoid wasps were specifically expressed in response to their hosts with different scents. Our findings improve our understanding of the behaviors of insects in the detection of their hosts on the molecular level. More importantly, it provides a valuable resource for *D. longicaudata* research and will benefit the IPM programs and other researchers in this filed.

**Keywords:** *Diachasmimorpha longicaudata*; Ashmead; parasitoid wasps; transcriptome; olfactory protein; odorant-binding protein; chemosensory protein
