Holotrichia parallela is one of the agriculturally important scarab beetle pests in China. In this study, HparOBP14 was cloned, which is the most abundantly expressed among the OBP genes in the legs of female H. parallela adults. Sequence comparison and phylogenetic analysis showed that HparOBP14 has a Plus-C structure motif. The expression profile analysis revealed that HparOBP14 expression was the highest in the female antennae and then in the legs. The fluorescence competitive binding experiment of the recombinant HparOBP14 protein showed that HparOBP14 had an affinity with 6-methyl-5-heptene-2-one (plant volatile), 3-methylindole, p-cymene, methanol, formaldehyde, α-pinene, and geraniol (organic fertilizer volatile). Knockdown HparOBP14 expression decreased significantly the EAG response of the injected female adults to p-cymene, methanol, formaldehyde, α-pinene, and geraniol. Similarly, the injected female adults were significantly less attracted to geraniol and methanol. Therefore, HparOBP14 might bind organic matter volatiles during oviposition. These results are not only helpful to analyze the olfactory recognition mechanism of female adult H. parallela when choosing suitable oviposition sites, but also to provide target genes for green prevention and control of H. parallela in the future.

Soybean root rot, primarily caused by Fusarium oxysporum, leads to severe root decay and substantial yield losses in Glycine max. This study screened ten entomopathogenic nematode-associated symbiotic bacteria for antagonistic activity against F. oxysporum. Among them, Xenorhabdus budapestensis XH-4 exhibited the strongest in vitro inhibition, suppressing mycelial growth by more than 73%. Antifungal activity was primarily attributed to extracellular metabolites, as both fermentation broth and cell-free culture supernatant were effective, whereas bacterial cell suspensions showed no significant inhibition. In greenhouse experiments, 40% (v/v) XH-4 reduced the disease index by 75–80%, comparable to the chemical fungicide metalaxyl–hymexazol. Genome mining revealed 20 biosynthetic gene clusters encoding diverse secondary metabolites, including fabclavine, fabclavine pyrrolizixenamide A, and putrebactin/avaroferrin, which likely underpin the strain antifungal efficacy. Additionally, XH-4 enhanced soybean antioxidant capacity and activated the phenylpropanoid pathway, indicating a dual mechanism involving direct antagonism and induced systemic resistance. These findings support the development of XH-4 as an environmentally friendly biofungicide for sustainable management of soybean root rot.