## 4 Discussion
While we did not find strong microbially induced specific fruit volatile profiles, the overall abundance of volatiles (i.e., esters, terpenes, alcohol, and aromatics, which were previously described in other fruits commonly attractive to Tephritidae fruit flies [45; 46; 47]) was enhanced with incubation time with Enterobacteriaceae. For instance, a positive correlation was found between the proportion of compounds emitted by kiwifruit and the incubation time (e.g., more D-limonene was produced at 24 h post-inoculation). Given that such fruit volatiles were previously shown to be behaviorally attractive to QFF [6; 48; 49], we can suppose that the presence of Enterobacteriaceae participates in the fruit attraction. Altogether, our results corroborate the findings that chemical profiles of MVOCs are influenced by the presence of different sources of precursors in the culture media and pH [18; 22; 25; 37; 50; 51], and they could provide an explanation for the polyphgous capacity of female QFF to exploit several host-plants and adapt to various environmental conditions. Because female fruit flies may exhibit a delay in sexual maturation and reduced sexual performance and lifespan if they are unable to acquire sufficient protein [10], virgin females are expected to actively search for bacteria as a source of protein. In our study, females exhibited the greatest antennal responses to extracts of KO and EC, which is in line with a previous study showing that KO was the most attractive among several culturable bacterial symbionts of _B. zonata_[52]. Moreover, KO extracts attracted relatively more QFF females compared to CF, similarly to _B. cucurbite_ females, for which KO was more attractive than CF in field experiments [44]. It is noteworthy that CF was previously shown to produce large amounts of ammonia [22], a compound negatively correlated with QFF attraction to _Prowidencia rettgeri_[51] and other fly species [53; 54]. We suggest that the weak attraction to CF in our study may be due to the lack of detection of this compound, as a result of extreme volatility, such as demonstrated in other fruit fly species [55]. While ammonia could not be measured by GC/MS in our study, we acknowledge the existence of kits that enable easy, fast, and reliable detection of ammonia production (e.g., Ammonia Assay Kit, Megazyme, Neogen(r), and could help understand whether ammonia might be involved in the differential behavioral activity observed between CF and KO. Among the most abundant volatiles detected in our bacterial extracts, several alcohols (2-phenylethanol, isoamyl alcohol, and phenol), one aromatic (indole), and various pyrazines, triggered antennal responses from virgin females. No differences in the number of attracted _A. ludens_ between the solvent and 2-phenylethanol, isoamyl alcohol (syn. 3-methyl butanol) or phenol were previously found [22], while, in another study, negative correlations were found between the production of indole, 2,5-dimethylpyrazine, and 2-phenylethanol by EC, and fly attraction [56]. In contrast, we found that the proportion of EAD-active indole increased with longer incubation times in kiwifruit. While mature fruits were previously described as the most prone to risk of oviposition from -fruit flies [57], we suggest that mature fruits may also be at risk from immature fruit flies searching for protein source. From our Y-tube choice assays with synthetic compounds, we found neither a strong attraction nor repulsion to indole nor 2-phenylethanol (at the concentration tested), but phenol, as well as isoamyl alcohol, 2-methyl pyrazine, 2-ethyl 3-methyl pyrazine, and nonanal, appeared to be repellent to virgin female QFF. Moreover, the monoterpene D-limonene, which was the second most abundant compound detected in EC- and KO-inoculated fruits, triggered a strong attraction of virgin females.