## 4 Discussion  
To be widespread volatile, the function of geraniol in plants has been well studied. It has been shown to induce apoptosis-like cell death as a defense reaction against bacterial infection [30; 31; 32] and to play roles in attracting beneficial insects such as sarcophagid flies and braconid wasps [33]. In tea plants, geraniol is one of the herbivore-induced volatiles in aphid-damaged tea plants [11]. Our study confirmed that the emitted geraniol would be induced by _E. (M.) onukii_ attack. Geraniol was reported to be the symbolic aroma which could be used to differentiate different black tea [34]. To be the important flavor-related volatile, the induced geraniol by insect may affect the tea flavor. The pathway of geraniol biosynthesis has been elucidated; it is an acyclic monoterepene alcohol that is synthesized from GPP, the universal precursor of all monoterepenes. The GES from sweet basil was the first GES to be isolated, purified, and functionally characterized. It was shown to generate geraniol from GPP, and to be localized exclusively or almost exclusively to glands [35]. Since then, GESs have been identified \begin{table}
\begin{tabular}{c c} \hline \hline
**Geraniol Concentration (ug/mL)** & **OD\({}_{600}\)** \\ \hline
0 & \(>\)3 \\
100 & \(>\)3 \\
250 & \(11.980\pm 0.232\) \\
500 & \(0.018\pm 0.006\) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Antibacterial activity assay of geraniol. Figure 7: Phylogenetic analysis of the isolated endobacteria. The 16S ribosomal RNA (rRNA) sequences were aligned with ClustalX and neighbor-joining tree were created with MEGA software. Bootstrap values were calculated for 1000 replicates. and characterized from the evergreen camphor tree _Cinnamoun tentuipilum_[36], perilla [37; 38], and Madagascar periwinkle [39]. However, GES had not been isolated from tea leaves. Terpenes are structurally diverse natural products that have diverse functions in the ecological interactions of many living organisms. Terpenes are biosynthesized by terpene synthases, which have been widely studied in plants and eukaryotic fungi. Recently, terpene synthases in insects have attracted the interest of researchers. The terpene synthase in insect was found to be an evolutionarily novel family, and the sesquiterpene aggregation pheromone synthase was identified in _Phyllotre striolata_[22]. Most reported terpene synthases in insects are sesquiterpene synthases, while monoterpene synthases are rare. As one of monoterpene, geraniol has been found texist in many insects [40; 41; 42; 43; 44]. In the larvae of chrysomelid beetles, geraniol was presumed to be synthesized in fat body [43]. It could serve as a precursor of defense compound called iridoids [41; 42]. Moreover, geraniol has been proven to be the active component in Nassanoff glands to attract each other in honey bees [40]. It was also reported as caste determining compound from labial glands in _Melipona_ bees [44]. Although these important roles of geraniol had been reported, GES was not identified in the insect. In the present study, GES, a monoterpene synthase specifically producing geraniol, was extracted from _E. (M.) onukii_ (Figure 2). Moreover, GES was found to exist in many insects in the present study (Figure 6). These observations indicate that not only sesquiterpene synthases but also monoterpene synthases occur more widely among eukaryotes than previously thought. The higher crude enzyme activity of GES was found in the body part (Figure 2), which indicated that the GES protein may be mainly located in fat body as previously reported [43] or digested system. [PERSON] [45] reported that the mevalonate pathway genes in midgut were upregulated after phloem feeding, which may be responsible for monoterenoid pheromone component ipsdienol de novo synthesis. Our study further identified a TPS gene _EoTPS_ in _E. (M.) onukii_, which could produce geraniol with GPP as substrate in vitro.