## Results
### Volatile Organic Compounds  
No significant change was found in volatile composition between _B. tabaci_-infested and uninfested eggplant (Pillai test: F\({}_{(2,\,114)}=0.100\), \(p=0.905\)). The volatile Unknown 1 was only detected in eggplant (Table 1). PCA results indicated that the first and second components explained 48.78% and 28.75% of the total variability, respectively (Figure 6A). According to the component matrix in PCA, the most important compounds were 2,6,10-trimethyl-tetradecane, Tridecane and Pentadecane for PC1; however, 3-methyl pentadecane and Hepadecane were the main substances for PC2 (Figure 6A). These results are consistent with the change in the relative content of volatiles in Table 1. The volatiles of uninfested and _B. tabaci_-infested eggplants were not distinguished by the PCA (Figure 6A).  
Figure 6: Principal component analysis (PCA) of volatile compounds from uninfested and _Bemisia tabaci_-infested host plant species. PCA with a factor loading plot was used to analyze single plant species, including eggplant (**A**), cucumber (**B**) and cotton (**C**). (**D**) PCA for three plant species, namely eggplant (circles), cucumber (triangles) and cotton (diamonds) based on the 25 identified volatile components. Score plots of PC1 and PC2 with the percentage of total variance explained by each axis are shown. Each point represents an individual plant. Compound numbers in Figure 6 correspond with compound numbers in Table 1.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**N**} & \multirow{2}{*}{**Chemical Compounds**} & \multicolumn{5}{c}{**Relative Content (\%)**} \\ \cline{2-9}  & & **Unifested** & _B.tabaci-Infested_ & **Unifested** & _B.tabaci-Infested_ & **Unifested** & _B.tabaci-Infested_ \\  & & **Eggplant** & **Eggplant** & **Cu  
Fifteen volatiles were detected from uninfested and _B. tabaci_-infested cucumber (Table 1). The volatile composition did not vary between _B. tabaci_-infested and uninfested cucumber plants (Pillai test: F\({}_{\left(2,\,136\right)}\) = 0.770, \(p\) = 0.926; Figure 6). The first two components of the PCA explained 62.79% of the total variability. Three components were unidentified. Unknown 2, Unknown 3 and 7-methyl-pentadecane were present in the blend of uninfested or _B. tabaci_-infested cucumber plants, but they were not found in eggplant or cotton. Heptadecane and tert-Hexadecanethiol had remarkable effects in terms of explaining PC2, and 2-ethenyl-1,1-dimethyl-3-methylene-cyclohexane, 2,6,10-trimethyl-tetradacane and 7-methyl-pentadecane played more important roles in explaining PC1 (Figure 6B). The volatiles of uninfested and _B. tabaci_-infested cucumber were not distinguished by the PCA (Figure 6B).  
Cotton emitted more volatile species compared with those emitted by eggplant and cucumber plants (Table 1). There was no significant difference in volatile composition between _B. tabaci_-infested and uninfested cotton (Pillai test: F\({}_{\left(2,\,183\right)}\) = 0.620, \(p\) = 0.539, Figure 6C). The first two components of the PCA explained 64.32% of the total variability. \(\beta\)-Myrcene,1-Caryophyllene, Heptadecane and Humulene had remarkable effects in terms of explaining the first components of the PCA, and Pentadecane and Benzothiazole played a more important role in explaining the second components of the PCA (Figure 6C). The volatiles of uninfested and _B. tabaci_-infested cotton failed to be distinguished by the PCA (Figure 6C).  
PCA showed the apparent separation of plant volatiles among eggplant, cucumber and cotton, but obvious overlaps were found in uninfested and _B. tabaci_-infested plants of the same species (Figure 6D). The first and second PCs explained 39.94% and 24.3% of the total variance of the plant volatiles, respectively. Not all compounds could be detected in different plant species; only nine common compounds were detected in all groups in this experiment (Table 1).