Endophytes induce volatile emission in olive trees with repellent activity against Bactrocera oleae

Abstract The olive fruit fly, Bactrocera oleae (Rossi), is a key pest of the olive tree worldwide. This study explores whether the endophytes Alcaligenes faecalis , Aureobasidium pullulans , Bacillus amyloliquefaciens , and Penicillium commune can trigger the emission of repellent volatile organic compounds (VOCs) in olive trees, targeting B. oleae . Accordingly, olive trees were inoculated with each endophyte or with buffer (control), and after 3 months, both fruits and leaves were collected to perform olfactometer assays and to evaluate VOCs by HS-SPME and GC–MS. Alcaligenes faecalis , A. pullulans , and B. amyloliquefaciens were found to significantly repel B. oleae females, with each treatment inducing a distinct VOC profile. Alcaligenes faecalis and B. amyloliquefaciens were characterized by higher levels of alkenes, including o-cymene and d-limonene, while P. commune and A. pullulans induced the emission of alkanes. Six VOCs were found to be negatively correlated with fly entries in the olfactometer assays, with beta-myrcene being the most prominent, followed by d-limonene, o-cymene, and 5-octadecene (E). These repellent VOCs were positively correlated with each other, indicating that their combined emission may produce synergistic effects, potentially enhancing their repellency. In contrast, 1, 4-hexadiene, 5-methyl-3-(1-methyl ethylidene) was identified as an attractant, showing a strong positive correlation with fly entries, and appeared to be produced through different biosynthetic pathways than the repellent VOCs. Overall, this work identifies three endophytes and a combination of repellent VOCs as promising new strategies for sustainable management of the olive fruit fly.