Deciphering the Chemical Fingerprint of Astragalus membranaceus: Volatile Components Attractive to Bruchophagus huonchili Wasps

SIMPLE SUMMARY: Bruchophagus huonchili is a serious threat to the yield and quality of the Chinese medicinal herb Astragalus membranaceus seeds. Plant volatile organic compounds (VOCs) are essential signaling substances for herbivorous insects when searching for host plants and mating partners. In this study, we collected and identified the VOCs emitted from A. membranaceus pods and evaluated the attraction of individual and combined compounds to B. huonchili. Our results showed that specific concentrations of five VOCs (cis-β-ocimene, hexyl acetate, hexanal, decanal, and β-caryophyllene) attract B. huonchili wasps. Moreover, our findings revealed that three formulations exhibited strong attraction to B. huonchili in Y-tube olfactometer assays and in the field. This study suggests that a blend with specific VOCs and ratios emitted from A. membranaceus could be used as attractants in traps for B. huonchili monitoring in the field. ABSTRACT: Bruchophagus huonchili is a pest that poses a serious threat to the yield and quality of Astragalus membranaceus seeds. In this study, we employed solid-phase microextraction (SPME) and gas chromatography-mass spectrometry (GC-MS) to identify volatile organic compounds (VOCs) in A. membranaceus pods during the pod-filled period. Additionally, we utilized a Y-tube olfactometer to measure the behavioral response of B. huonchili to different individual VOCs and specific VOC-based formulations. The most effective formulations were further evaluated for their effectiveness in attracting wasps in the field. Our findings revealed that A. membranaceus pods emit 25 VOCs, including green leaf volatiles (GLVs) and terpenoid and aromatic compounds. Among these compounds, five were found to be most attractive to B. huonchili at the following concentrations: 10 µg/µL cis-β-ocimene, 500 µg/µL hexyl acetate, 100 µg/µL hexanal, 1 µg/µL decanal, and 10 µg/µL β-caryophyllene, with respective response rates of 67.65%, 67.74%, 65.12%, 67.57%, and 66.67%. In addition, we evaluated 26 mixed VOC formulations, and three of them were effective at attracting B. huonchili. Furthermore, field experiments showed that one of the formulations was significantly more effective than the others, which could be used for monitoring B. huonchili populations.