## 4 Discussion  
The identification of unknown components is a tedious and time-consuming process. The use of GC-Orbitrap MS and supporting software Compound Discoverer and Mass Frontier accelerates this process significantly. Key in this respect is the accuracy of the mass measurements, which is typically \(<\)1 ppm, and drastically reduces the number of candidate element compositions that is able to match the mass-to-charge ratio of the molecular ion. As each elemental composition may give rise to a multitude of chemical structures, it is fair to conclude that the list of seemingly valid elemental compositions should be as small as possible prior to starting the identification exercise. In that respect, pre-screening with GC-EAD is an important step. Additionally, Kovats RI is a valuable tool, even in combination with Orbitrap MS data. Indeed, when isomeric components, such as terpenoids, are to be confirmed, (high resolution) spectral matching alone is not enough for positive identification (see Table 1). In fact, these components are better designated as 'unknown knowns', requiring retention verification for definitive confirmation. In case of \(\beta\)-caryophyllene, the calculated Kovats RI was 1424, which is close to the 1420 average value for non-polar columns from the NIST v20 database (as summarized by NCBI (2020)), and well within the \(\pm\)10 RI that can be expected for terpenoids on a 5% phenyl column [35]. In the current proof-of-principle, GC-EAD and GC-Orbitrap MS were used sequentially. However, it is easily possible to combine EAD and MS in parallel [36, 37] and omit the need to compare chromatograms [38]. In combination with Orbitrap MS, the method becomes even more powerful. The odor of pomegranate contains a large amount of secondary plant compounds, mainly green leaf volatiles (GLV) and terpenoids [39, 40, 41]. We identified 11 of these compounds that were evoking a response in the antenna of female caro moth. GLVs were also present but not causing consistent GC-EAD responses. This might be related to the low levels present (see Table 1). The low GLV levels (except for _cis_-3-hexen-1-ol) were not unexpected, since these compounds are mainly induced by stresses, such as senescence [42] and in particular herbivorous attack [43, 44]. However, we cannot fully exclude the possibility that that the low levels of green odors we found were the result of losing some of these more  
Figure 2: Behavioral responses of mated female and virgin female and male caro moths to a series of plant materials (pomegranate and pistachio) and their headspace extracts (HE) in wind tunnel bioassays. Differences between the odor sources and controls at each behavioral step are depicted using the following codes: ***\(p\leq 0.001\), ***\(p\leq 0.01\), *\(p\leq 0.05\), \(\circ\)\(p\leq 0.1\). volatile compounds during the relatively long sampling phase (22 h) or during the evaporation under a gentle nitrogen stream needed to sufficiently increase the concentrations in the eluate from the trap for analytical and electrophysiological measurements. All identified compounds have known ecological roles. Pentadecane is present in flower odors of many plant families [45], and is also found in pomegranate [41]. It can act as a repellent [46]. Pentadecane levels are changing during the development of grapevines [47], and differ between pomegranate plant parts [41]. However, since the component was used as an injection standard, no conclusions can be drawn regarding its presence in our headspace samples. Ethyl-4-ethoxy benzoate has antibacterial properties, is involved in root competition, and is highly elevated under drought stress [48; 49]. These ecological links make the compounds probably good indicators of plant health. All other active compounds were terpenoids, and in particular sesquiterpenes. Over 55,000 terpenoids are known [50].