Identification of Odorant-Binding Protein AjapOBP26 as the Key Mediator of 2-Ethyl-1-hexanol Avoidance in the Egg Parasitoid Anastatus japonicus

The efficacy of parasitoid wasps as biological control agents depends on their perception of environmental chemical cues. The plant volatile 2-ethyl-1-hexanol (2EH) repels many insects; however, the molecular mechanisms by which natural enemies detect it remain unknown, hindering the development of precise behavioral manipulation strategies. Here, we identify AjapOBP26 as the key odorant-binding protein (OBP) mediating 2EH-triggered avoidance in the egg parasitoid Anastatus japonicus. Transcriptomic screening of 2EH-exposed wasps identified AjapOBP26 as a responsive candidate specifically expressed in the antennae of females. RNAi-mediated knockdown of AjapOBP26 impaired antennal electrophysiological responses to 2EH and eliminated avoidance behavior. A fluorescence competitive binding assay confirmed high-affinity binding, substantiating docking predictions. Therefore, AjapOBP26 is an essential molecular determinant for 2EH perception in A. japonicus. Our study identifies a specific OBP that mediates behavioral avoidance of a repellent in a parasitoid wasp and establishes a precise molecular target for refining behavior-based control strategies.