Exploring the olfactory repertoire of the ecologically important parasitoid wasp <i>Microplitis mediator</i> (Hymenoptera: Braconidae): from gene structures to expression analysis

The ability of parasitoid wasps to precisely locate hosts in complex environments is a key factor in suppressing pest populations. Chemical communication plays an essential role in mediating insect behaviors such as locating food sources, hosts, and mates. Odorant receptors (ORs) are the key connection between external odors and olfactory nerves. Through full-length antennal transcriptome sequencing, we identified an expanded repertoire of 177 ORs from the antenna of Microplitis mediator Haliday (Hymenoptera: Braconidae), including 75 previously undocumented complete open reading frames, significantly advancing our understanding beyond the 169 ORs reported in earlier studies. Phylogenetic analysis revealed that M. mediator odorant receptors (MmedORs) were divided into 24 subfamilies, and most of the MmedORs in the subfamilies showed high sequence identity with the Microplitis demolitor Wilkinson (Hymenoptera: Braconidae) ORs, indicating a conserved function of the ORs in both homologous species. Moreover, the OR genes structure within the same cluster is highly conserved. Semi-quantitative PCR results showed that 83 ORs were predominantly expressed in the antennae and 34 ORs were mainly expressed in other tissues, suggesting their primary function in olfactory perception. More precisely, real-time quantitative PCR results further indicated that 54 ORs were preferentially expressed in female antennae, and 22 ORs in male antennae, suggesting a specialized function in behaviors exclusive to females, including host location and oviposition. This study comprehensively characterizes and analyzes the expression analysis of M. mediator ORs, addressing key knowledge gaps in parasitoid chemoreception and providing a molecular framework for the conservation and utilization of natural enemies.