## 3 Results
### Concentrations of VOC Classes  
The distribution of the mean concentrations of each VOC class found in Sugar Belle scion leaves that were grown on each rootstock, comparing the non-infested control trees with the _D. citri_ infested trees is shown in box-and-whisker plots (Figure 4). The compounds that were associated with each VOC class can be found in Table 1. Interestingly, the total VOCs levels were not significantly different in the scion leaves that were grown on the three rootstocks with or without _D. citri_-infestation (Figure 4A), although shifts in the concentrations within the different VOC classes occurred (Figure 4B-D,F-H). The infestation resulted in moderate alterations in the total VOC content with fold increases of 1.16 and 1.08 for US-897 and SO, respectively, while C-35 total VOCs decreased slightly (\(-\)1.02-fold change) compared to the non-infested control trees. The monoterpenes levels were significantly higher in C-35 and US-897 compared to the SO, led by higher levels of \(\beta\)-pinene and p-cymene in C-35, and \(\gamma\)-terpinene and \(\beta\)-codimene in US-897. In fact, all of the monoterpenes except _allo_-ocimene were higher in US-897 after infestation with _D. citri_. Terpene alcohols increased in both SO and US-897 due to higher levels of thymol and phytol in SO, and linalool and thymol in US-897 (Figure 4C). Sesquiterpenes (Figure 4D) increased significantly (\(p\) < 0.0001) in the scion leaves that were grown only on SO primarily due to \(\beta\)-elemene and \(\beta\)-caryophyllene. C-35 sesquiterpenes trended higher after infestation (40.97 \(\upmu\)g-g\({}^{-1}\)) compared to 35.73 \(\upmu\)g-g\({}^{-1}\) in the controls (\(p\) = 0.0554). The fatty acids/esters group (Figure 4F) saw the most dramatic effects of infestation. The total fatty acids in the controls decreased from 169.8 \(\pm\) 31.1, 144.7 \(\pm\) 105.5, and 159.2 \(\pm\) 87.6 \(\upmu\)g-g\({}^{-1}\) in C-35, SO,  
Figure 3: Relative percentages of VOCs by compound class that were detected in the hexane extracts of mature leaves from Sugar Belle mandarin hybrids on three different rootstocks (US-897, C-35 trifoliate, and sour orange), and their changes due to infestation with _Diaphorina citri_. and US-897, respectively, to 9.3 \(\pm\) 5.9, 12.1 \(\pm\) 7.5, and 5.1 \(\pm\) 3.5 \(\upmu\)g\(\cdot\)g\({}^{-1}\), respectively, in the infested samples. Interestingly, the aldehyde levels were higher overall in SO, but were unchanged as a class after infestation (Figure 4E). The group that was designated as other (thymoquinone, ethyl 4-ethoxybenzoate, geranyl acetate, and coumarin) increased significantly in C-35 and SO rootstocks but decreased significantly in US-897 (Figure 4G). In C-35, all four of the compounds increased, three significantly totaling 43.0 \(\pm\) 7.5, 54.6 \(\pm\) 7.9, and 24.8 \(\pm\) 5.65 \(\upmu\)g\(\cdot\)g\({}^{-1}\) in C-35, SO, and US-897, respectively, whereas the control levels were 33.7 \(\pm\) 3.0, 37.0 \(\pm\) 12.6, and 36.3 \(\pm\) 5.3 \(\upmu\)g\(\cdot\)g\({}^{-1}\), respectively. In SO, thymoquinone increased the most, by 3.57-fold. Geranyl acetate decreased in both US-897 and SO with infection. In US-897, coumarin decreased from 17.5 \(\pm\) 2.5 \(\upmu\)g\(\cdot\)g\({}^{-1}\) to 12.0 \(\pm\) 2.6 \(\upmu\)g\(\cdot\)g\({}^{-1}\) although it increased in C-35 and SO more than 1.3-fold (Figure 4G, Table 2). The mean concentration of the unknowns (Figure 4H) were higher in the infested C-35 and SO, but lower in US-897 with respect to the control means. Figure 4: Box plots of the total VOCs levels in each chemical class that were detected in Sugar Belle leaves following infestation with _Diphorina citri_ and the influence of rootstock: (**A**) total VOC content, (**B**) monoterpenes, (**C**) terpene alcohols, (**D**) sesquiterpenenes, (**E**) aldehydes, (**F**) fatty acids and their methyl esters, (**G**) other compounds, and (**H**) unknowns. Refer to Table 1 for the VOC classifications.