## 3 Volatile Pheromones
### Does Host-Preference Affect the Volatile Pheromone Bouquet?  
Pheromone precursors are acquired from four main sources: (i) _de novo_ synthesis, (ii) conversion of precursors that insects acquire from host plants or substrate, (iii) direct incorporation from the host plants, and/or (iv) from endosymbionts [21; 251; 252; 253; 254]. Thus, it is likely that different variables influence the pheromone blend.  
The chemical classes of their pheromone components and their specific identity are more similar among species of _Anastrepha_, _Ceratitis_ and _Rhagoletis_ genera, and rather different from species of the genus _Bactrocera_. The monophagous _B. oleae_ is the most diverse species among the genus, with the majority of its pheromone volatiles being species-specific. To elucidate whether the composition of the pheromone components is related to feeding strategies of different species, we analysed the lists of volatile compounds identified in all species of the genera _Anastrepha_, _Ceratitis_, _Bactrocera_ and _Zeugodacus_. This analysis could not be extended to _Rhagoletis_ genus, as only the volatiles emitted by _R. cerasi_ have been identified [226] so far, and a single compound has been isolated in _R. batava_[61].  
The species with a monophagous or oligophagous feeding strategy mostly emit chemicals that are not shared with other species with the only exception of nonanal, \(\alpha\)-pinene and \(p\)-cymene, which are in common between _B. oleae_ and _R. cerasi_. Figure 5 shows the number of chemicals identified in each species as well as the intersections of overlapping compounds, represented by connected dots (see Table S2 for the complete lists of unique and overlapping chemicals).  
The polyphagous species shared more compounds, as shown by the higher number of connected dots in Figure 6 (see Table S2 for the complete lists of unique and overlapping chemicals). This finding is particularly evident between species belonging to the same genus.  
Figure 5: Comparison among the chemicals identified in the headspace emissions of monophagous and oligophagous tephritid species. UpSet plot showing unique and overlapping chemicals across five species belonging to the _Zeugodacus_, _Bactrocera_, _Anastrepha_ and _Rhagoletis_ genera. The intersection matrix is sorted in descending order. Connected dots represent intersections of overlapping chemicals and horizontal bars show the total number of compounds identified in each species headspace. The plot was generated using the UpSetR package in R [255].  
Figure 6 also reports the identity of the chemicals that are shared between different genera. It generally appears that the members of the _Anastrepha_ and _Ceratitis_ genera share a higher number of compounds, with chemicals belonging to the phenol lipids class being most frequently in common. Conversely, _Bactrocera_ species display quite unique pheromone blend features. The only two compounds to be shared belong to the diazine class and are in common with _Ceratitis_ species. This suggests that at least two major evolutionary forces, i.e., genomic background and host feeding strategy, interacting in a complex manner, have shaped the pheromone blend in these species. A comprehensive molecular phylogeny of rephritid species will be of great help in disentangling the effects of genome evolution and environmental selective pressures in shaping seminochemical-based behaviour in these species. Further research is required to deeply investigate how feeding strategies affect the production of semicohemicals, also with respect to the capacity of colonizing new hosts, a feature that characterises several invasive rephritid pests. A strong effect of larval host on the pheromone bouquet produced by the polyphag species _A. ludens_ and _A. obliquau_ has been recently demonstrated [245].