Anagrus nilaparvatae is an important egg parasitoid wasp of pests such as the rice planthopper. Based on the powerful olfactory system of sensing chemical information in nature, A . nilaparvatae shows complicated life activities and behaviors, such as feeding, mating, and hosting. We constructed a full‐length transcriptome library and used this to identify the characteristics of soluble chemical communication proteins. Through full‐length transcriptome sequencing, splicing, assembly, and data correction by Illumina, we obtained 163.59 Mb of transcriptome data and 501,179 items with annotation information. We then performed Gene Ontology (GO) functional classification of the transcriptome's unigenes. We analyzed the sequence characteristics of soluble chemical communication protein genes and identified eight genes: AnilOBP2 , AnilOBP9 , AnilOBP23 , AnilOBP56 , AnilOBP83 , AnilCSP5 , AnilCSP6 , and AnilNPC2 . After sequence alignment and conserved domain prediction, the eight proteins encoded by the eight genes above were found to be consistent with the typical characteristics of odorant‐binding proteins (OBPs), chemosensory proteins (CSPs), and Niemann‐pick type C2 proteins (NPC2s) in other insects. Phylogenetic tree analysis showed that the eight genes share low homology with other species of Hymenoptera. Quantitative real‐time polymerase chain reaction (RT‐qPCR) was used to analyze the expression responses of the eight genes in different sexes and upon stimulation by volatile organic compounds. The relative expression levels of AnilOBP9 , AnilOBP26 , AnilOBP83 , AnilCSP5 , and AnilNPC2 in males were significantly higher than those in females, while the relative expression level of AnilCSP6 was higher in females. The expression levels of AnilOBP9 and AnilCSP6 were significantly altered by the stimulation of β‐caryophyllene, suggesting that these two genes may be related to host detection. This study provides the first data for A . nilaparvatae's transcriptome and the molecular characteristics of soluble chemical communication proteins, as well as an opportunity for understanding how A . nilaparvatae behaviors are mediated via soluble chemical communication proteins.

Background Mymaridae is an ancient insect group and is a basal lineage of the superfamily Chalcidoidea. Species of Mymaridae have great potential for biological control. Anagrus nilaparvatae, a representative species of Mymaridae, is ideal for controlling rice planthopper due to its high rate of parasitism and ability to find hosts efficiently in paddy ridges and fields. Results Using both PacBio single-molecule real-time and Illumina sequencing, we sequenced and assembled the whole genome of A. nilaparvatae, a first for the family Mymaridae. The assembly consists of 394 scaffolds, totaling 488.8 Mb. The assembly is of high continuity and completeness, indicated by the N50 value of 25.4 Mb and 98.2% mapping rate of Benchmarking Universal Single-Copy Orthologs. In total, 16,894 protein-coding genes in the genome were annotated. A phylogenomic tree constructed for A. nilaparvatae and other 12 species of Hymenoptera confirmed that the family Mymaridae is sister to all remaining chalcidoids. The divergence time between A. nilaparvatae and the other seven Chalcidoidea species was dated at ~ 126.9 Mya. Chemoreceptor and mechanoreceptor genes are important in explaining parasitic behavior. We identified 17 odorant binding proteins, 11 chemosensory proteins, four Niemann-Pick type C2 proteins, 88 olfactory receptors, 12 gustatory receptors, 22 ionotropic receptors and 13 sensory neuron membrane proteins in the genome of A. nilaparvatae, which are associated with the chemosensory functions. Strikingly, there is only one pickpocket receptors and nine transient receptor potential genes in the genome that have a mechanosensory function. Conclusions We obtained a high-quality genome assembly for A. nilaparvatae using PacBio single-molecule real-time sequencing, which provides phylogenomic insights for its evolutionary history. The small numbers of chemo- and mechanosensory genes in A. nilaparvatae indicate the species-specific host detection and oviposition behavior of A. nilaparvatae might be regulated by relatively simple molecular pathways.

Background Mymaridae is an ancient insect group, which is a basal lineage in the Chalcidoidea phylogeny. The species of Mymaridae have great potential for biological control. Anagrus nilaparvatae, a representative specie of Mymaridae, is ideal for controlling rice planthopper due to its high rate of parasitism by finding hosts efficiently from paddy ridges to fields. Results Using both single-molecule real-time and Illumina sequencing, we sequenced and assembled the whole genome of A. nilaparvatae, which is the first genome sequenced in family Mymaridae. The assembly consists of 394 scaffolds accumulated to 488.8Mb. The assembly is of high continuity and completeness, indicated by the N50 value of 25,368,259bp and 98.4% mapping rate of BUSCO orthologs. 16894 protein-coding genes in the genome were annotated. The phylogenomic tree constructed for A. nilaparvatae and other 12 species of Hymenoptera confirmed that family Mymaridae is basal in the Chalcidoidea superfamily and sister to all the remaining Chalcidoidea species. The divergence between A. nilaparvatae and the other seven Chalcidoidea species was dated at ~ 126.9 Mya. Chemoreceptor and mechanoreceptor genes are important in the parasitic behavior. We identified 17 OBPs, 11 CSPs, 4 NPC2s, 88 ORs, 7 GRs, 22 IRs and 13 SNMPs in the genome of A. nilaparvatae, which are associated with the chemosensory function. Strikingly, there are only 1 PPK and 3 TRP genes in the genome that are relevant to the mechanosensory function. Conclusions The small numbers of chemo- and mechano-sensory genes in A. nilaparvatae indicate the species-specific host detection and oviposition behavior of A. nilaparvatae might be regulated by relatively simple molecular pathways.

Anagrus nilaparvatae is an important egg parasitoid wasps of rice pests rice planthopper. Based on the powerful olfactory system of sensing chemical information in nature, A. nilaparvatae shows complicated life activities and behaviors, such as feeding, mating and hosting. In this study, we constructed a full-length transcriptome library and further to identify the characteristics of olfactory binding proteins, the first participant in the olfactory system. Through full-length transcriptome sequencing, splicing, assembly, and data correction by Illumina, we obtained 163.59Mb of transcriptome data and 501,179 items of annotation information, and performed GO functional classification of unigenes of the transcriptome. We analyzed the sequence characteristics of olfactory binding protein genes, and 8 genes (AnilOBP2, AnilOBP9 AnilOBP23, AnilOBP56, AnilOBP83, AnilCSP5, AnilCSP6 and AnilNPC2) were identified. After sequence alignment and conserved domain prediction, the 8 proteins were consistent with the typical characteristics of OBPs, CSPs and NPC2s in insects. The phylogenetic tree analysis showed that the 8 genes share low homology relationship with other species in Hymenopteran. Finally, RT-qPCR was used to analyze the expression responses of the 8 genes in different genders and stimulated by volatiles. The relative expression levels of AnilOBP9, AnilOBP26, AnilOBP83, AnilCSP5 and AnilNPC2 in males were significantly higher than those in female, while the relative expression levels of AnilCSP6 were opposite. The expression levels of AnilOBP9 and AnilCSP6 were significantly altered by the stimulation of β-caryophylene, suggesting the two genes may be related to host searching. In this study, the transcriptome data of parasitoid wasps A. nilaparvatae could provide a reference for the molecular biology research of the parasitoids, and the identification and analysis of olfactory binding proteins not only help us further clarify the physiological characteristics and parasitic mechanism of the parasitoids, but also promote the utilization of natural enemy resources.