## Materials and Methods
### Extraction and Activity Assay of Geraniol Synthase from Other Insects  
Two major pests of tea plants and one major pest of sweet potato were used to assay the GES activity of crude enzymes extracted from the insects. These insects were larvae of _Ectropis oblique_ and _Euproctis pseudoconsversa_, and adult of _Cylas formiciarus_. Briefly, one _E. oblique/E. pseudoconsversa_ larvae or ten C. _formicarius_ adults were homogenized with 250 \(\upmu\)L buffer (50 mM Tris HCl, 10 mM MgCl\({}_{2}\), 5 mM DTT, pH 7.5) on ice. The supernatant was transferred to a new tube and saved as crude enzyme after centrifuge at 12,000 g for 20 min. The reaction volume was 1 mL containing 50 mM Tris HCl (pH 7.5), 10 mM MgCl\({}_{2}\), 5 mM DTT, 100 \(\upmu\)c crude enzyme, and 5 \(\upmu\)g GPP. The reaction was incubated at 30 \({}^{\circ}\)C for 90 min. The volatile product was collected by SPME for 30 min at 42 \({}^{\circ}\)C. The volatiles absorbed by SPME were analyzed using GC-MS. Column: SUPELCOWAXTM 10 column, 30 m \(\times\) 0.25 mm, film thickness 0.25 \(\upmu\)m, Supelco Inc. The carrier gas was helium (flow rate, 1.0 mL/min). The injection port temperature was 230 \({}^{\circ}\)C and operated in splitless mode. The splitless time was 1 min. The initial temperature of the oven was 60 \({}^{\circ}\)C and kept for 3 min, then programmed to 240 \({}^{\circ}\)C at 10 \({}^{\circ}\)C/min, and held at 240 \({}^{\circ}\)C for 10 min. Full scan mode was applied with a mass range of _m/z_ 40-200. The experiments were performed in three replicates.  
Empoasca (Matsumurasca) onukii Endobateria Isolation, Identification, and Antibacterial Activity Assay of Geraniol  
The _E. (M.) onukii_ adults were anaest with CO\({}_{2}\), and then placed on ice. The anaest insects were collected in 1.5 mL eppendorf tube and washed with 70% ethanol for 1 min to kill the external bacterial. Then, the insects were washed with ddH\({}_{2}\)O twice. The washed insects were cut into pieces with dissecting forceps. The dissected insects were placed in a Luria Broth plate and incubated at 30 \({}^{\circ}\)C for two days. The bacteria were growing around the insect pieces. The single colonies were further isolated by plate streaking. The genomic DNA was extracted and the bacterial was identified by 165 ribosomal RNA (rRNA) sequencing. DNA was extracted with TIANamp Bacteria DNA kit (Tiangen, Beijing, China) according to the manufacturer's instruction. The forward primer used to amplify 16S rRNA is 5'-AGTTTGATCMTGGCTCAG-3'. The reverse primer is 5'-GGTTACCTTGTTACGACTT-3'. The length of the sequenced fragment is about 1500 bp. The obtained sequences were blasted in the NCBI database to identify the similarity with other reported species and the 16S rRNA sequences were aligned using ClustalX program with the available sequences. Phylogenetic tree was generated by MEGA with the neighbor-joining method. The statistical robustness of the clusters was evaluated by bootstrap analysis after 1000 replicates.  
The isolated endobacteria _Acinetobacter johnsonii_ was used for antibacterial activity assay of geraniol. The geraniol was dissolved in Tween 20. The final concentration of geraniol in LB medium was 0, 100, 250, and 500 \(\upmu\)g/mL, respectively. The final concentration of Tween 20 in the LB medium was 1%. One hundred microliters of the exponentially growing bacterial cells (OD\({}_{600}\) = 0.3) was inoculated into 10 mL LB medium containing geraniol with different concentration. Then, the cultures were incubated at 30 \({}^{\circ}\)C for another 6 h. Then, OD\({}_{600}\) was analyzed to evaluate the antibacterial activity.