Genome-Wide Identification and Evolutionary Analysis of Chemosensory-Related Gene Families in the Solitary Wasp Rhynchium brunneum (Hymenoptera: Vespidae: Eumeninae).

The solitary predatory wasp Rhynchium brunneum is an important natural enemy of lepidopteran pests. In the present study, we systematically identified its chemosensory gene families, comprising 11 odorant-binding proteins (OBPs), 9 chemosensory proteins (CSPs), 147 odorant receptors (ORs), 21 gustatory receptors (GRs) and 28 ionotropic receptors (IRs). Multiple sequence alignment confirmed that OBPs and CSPs contain conserved cysteines motifs. Further alignment analysis revealed that certain genes within the GR family form high similarity clusters (up to 81%) on the same chromosome, indicative of recent tandem duplications. The IR family displays a dispersed similarity gradient (31-87%) and the OR family shows a broader spectrum (18-78%), suggesting a composite history of both recent and ancient duplication events. Phylogenetic and selection pressure analyses indicated that OBPs and CSPs are highly conserved within the Eumeninae, whereas ORs, GRs, and IRs have undergone lineage-specific expansions. All orthologous gene pairs shared with the social wasp Vespa mandarinia are subject to purifying selection (Ka/Ks < 1), consistent with evolutionary constraint. Numerous species-specific genes were also detected. The observed patterns suggest the hypotheses about ecological adaptations such as specific prey pheromones, location of suitable nesting sites, and so on. Resolving these relative contributions will require broader taxon sampling and functional validation assays. These results in the present study provide a genomic resource for chemosensory gene characterization in Vespidae and a foundation for future olfactory-based pest management strategies.