Antimicrobial treatment of egg-infested olives is associated with perturbation and carry-over changes on bacterial communities in the olive fly Bactrocera oleae (Diptera, Tephritidae)

The olive fly Bactrocera oleae (Rossi) is one of the most destructive olive pests, threatening olive and olive oil production worldwide. Traditionally managed with synthetic insecticides, its control now requires alternative strategies due to regulatory restrictions. The disruption of the obligate association between the pest and its primary symbiont Candidatus Erwinia dacicola has been reported following the application of a Zn–Cu–citric acid bio-complex compound (Dentamet) to olives infested with newly laid eggs. In this study, the effects of Dentamet exposure on the composition and structure of the B. oleae bacterial community were evaluated by comparing flies from treated (Dentamet-treated, DT) olives, with untreated (non-treated, NT) olives under laboratory conditions, and olives collected from untreated orchards (wild-in-controlled-environment). Bacterial communities were characterized by 16S rRNA gene sequencing on an Illumina MiSeq platform, and quantitative Real-Time PCR (qPCR) was used to estimate the abundance of Ca. E. dacicola and 4 additional bacterial genera involved in detoxification and nutrient metabolism. Metabarcoding analyses revealed differences between DT and NT samples, including reduced bacterial diversity in DT larvae and a shift in the adult bacterial community structure supported by beta diversity analyses. qPCR analysis showed a lower abundance of Ca. E. dacicola in DT larvae (significant), pupae, and adults, alongside decreases in the 4 investigated bacterial genera. Overall, these findings suggest that Dentamet exposure is associated with changes not only in the primary symbiont but also in the broader bacterial community, with potential implications for key microbial interactions.