# Identification of Blackberry (_Rubus fritticosus_) Volatiles as _Drosophila suzukii_ Attractants
## 4 Discussion  
Our aim in this study was to identify the key compounds which mediate the attraction of \(D\). _suzukii_ to the berries of \(R\). _fruticosus_-one of the preferred hosts of spotted wing drosophila [28,29]. Using MHS-SPME GC-MS we identified a total of 38 volatile compounds, half of them were already identified in a different \(R\). _fruticosus_ cultivar using similar detection methods [39]. 33 of the 38 identified compounds were commercially available and tested for \(D\). _suzukii_ attractiveness [30, 31, 32]. This resulted in six individual compounds that significantly attracted \(D\). _suzukii_: acetaldehyde, hexyl acetate, camphene, linalool, myrtenol and \(L\)-limonene. Because acetaldehyde, hexyl acetate, linalool and myrtenol had a higher choice factor, i.e., causing a higher percentage of the \(D\). _suzukii_ flies to actually choose to move to either the control or treatment chamber, these compounds have the best potential of being a good lure. Earlier, hexyl acetate, limonene and linalool have also been shown to induce marked electroantennographic responses in \(D\). _suzukii_[25,27,38,40,41]. As yet, no electroantennography, however, has been performed in any _Drosophila_ spp. for  
Figure 4: Results from two-choice preference tests of all the here identified and commercially available _Rubus fruticosus_ volatiles. Column plot shows the attractivity (=the percentage of flies that chose the treatment vs. the control side) of each individual compound to _Drosophila. suzukii_ females. Attractivity was tested against a 50:50 distribution, shown as a horizontal dotted line (binomial GLMM, _FDR_ corrected, mean \(\pm\) SE, *: \(p\) < 0.05). any of the other three attractive components here identified. Nevertheless, the fact that we measure significant behavioral effects for those evidently implies that these compounds are sensed by the flies. In total, at least sixteen of the compounds identified here have been shown to be actively detected by \(D\). _suzukii_[21; 25; 27; 40; 42; 43], even though the detection of a single compound does not need to be associated with evoking a visible behavioral response [42]. Earlier, [PERSON] et al. [43] also showed that hexyl acetate is attractive to both \(D\). _melanogaster_ and \(D\). _suzukii_. This reduces the utility of this compound for \(D\). _suzukii_ lures, as it might display poor selectivity. Another study documented a small but nonsignificant attractive effect of hexyl acetate on \(D\). _suzukii_[41]. Dose-dependent behavioral effects and/or differences in statistical power to detect attractive effects with the setup used likely explain some of these discrepancies [42; 44]. Lastly, hexyl acetate has also been shown to play an important role in the attraction of _Rlugoletis pomonella_[45]. Acetaldehyde is a known fruit fermentation product, originating as an intermediate in the conversion of ethanol to acetic acid [46]. Both acetaldehyde and limonene are known to be attractive to _Drosophila melanogaster_[47; 48]. However, as yet, their attractive effect had not been demonstrated for \(D\). _suzukii_. A four-component blend with limonene has been shown to have great potential for mass trapping the Mexican fruit fly (_Anastrepha ludens_) [49]. Linalool might be a good candidate to improve the attractiveness or selectivity of existing \(D\). _suzukii_ lures, already hinted at by [PERSON] et al., who identified this compound as one of the most abundant in raspberry [27]. In that study, raspberry was also shown to be the most attractive fruit to \(D\). _suzukii_ of all the tested fruits. Around the same time, linalool was shown to have a strong insecticidal effect on \(D\). _suzukii_ when used at a high concentration as a fumigant [50]. Linalool is also recognized by and has shown to be attractive to other Diptera such as Tephritidae and the housefly (_Musca domestica_) [51; 52; 53; 54].