The Genome of Rice Planthopper Egg Parasitoid Wasps Anagrus Nilaparvatae (Hymenoptera: Mymaridae) Casts Light on the Chemo- and Mechano-Sensing in Parasitism

Abstract 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.