## 1 Introduction  
The interaction between insects and plants mediated by plant volatiles has attracted much interest [1; 2], and many studies have revealed details of the early and late events related to plant volatile emissions after insect attack [3]. When plants are attacked by insects, mechanical damage is one of the first events. Although simple mechanical damage (single damage, such as one needle sting) may induce a plant response, it may be insufficient to induce the full response to insect attack because insect damage is usually continuous. Therefore, various automatic machines have been designed to simulate continuous wounding by insects [4; 5]. Continuous mechanical wounding resembling insect feeding can induce the production of volatiles similar to those induced by insects [4; 5]. Another important early event in the interaction between insects and plants is the entry of insect-derived elicitors into plant tissues. The most frequently reported insect-derived elicitors that induce the formation and emission of plant volatiles are fatty acid-amino acid conjugates [6; 7]. Other elicitors such as \(\beta\)-glucosidase [8], inception [9], caeliferins [6], and an unidentified heat-labile constituent [10] have also been identifiedand shown to induce the formation and emission of plant volatiles. These elicitors have mainly been identified in chewing insects, and rarely in piercing-sucking insects. This may be because the amount of elicitors produced by small piercing-sucking insects is insufficient for analysis and difficult to obtain [2]. In addition, the first events in the interaction between insects and plants have mainly been studied in model plants, rather than horticultural crop plants. Tea (_Camellia sinensis_) is an important horticultural crop in almost 30 countries, including China, Japan, India, and Kenya. Abundant volatiles compounds such as fatty acid-derivatives including (\(Z\))-3-hexen-1-ol, (\(Z\))-3-hexenyl acetate, (\(E\))-2-hexenal, and (\(E\))-2-hexenoic acid; volatile phenylpropanoids/benzenoids including benzyl nitrile, benzaldehyde, and indole; and volatile terpen including geraniol, farnesene, ocimenes, linalool, and nerolidol were found in tea [5; 11; 12; 13]. These volatile compounds are important quality components of teas and contribute to tea flavor [14]. Among these volatiles, terpenes are major floral and honey flavor-related volatiles [14]. During tea plant growth, many pest insects such as tea green leafhoppers, tea geometrid, tea aphids, smaller tea tortrix, and Kanzawa spider mites attack tea leaves and affect the yield and quality of the crop [13]. In response to these insect attacks, tea plants emit numerous compounds. Insect-induced volatiles may play important roles in defense [11; 12]. On the other hand, insect-induced volatiles may change the flavor the tea and increase the tea quality. As a classical example, a famous oolong tea (oriental beauty), which is manufactured from tea leaves infected with tea green leafhoppers, contains characteristic volatile monoterenes and has a unique ripe fruit and honey aroma [5; 15]. In our previous study, we elucidated the effect of tea green leafhopper (_Empoasca (Matsumurasca) onukii_ Matsuda) attack on the formation and emission of linalool in tea leaves. We found that continuous wounding was a key factor in the formation and emission of linalool from tea leaves exposed to _E. (M.) onukii_ attack [5]. In addition, we found that _E. (M.) onukii_ attack also significantly induced the emission of geraniol from tea leaves, but did not affect the enzyme activity of geraniol synthase (GES) in tea leaves. However, the reason is unknown. Geraniol is an acyclic monoterpene and contributes to the characteristic floral aroma and flavor in many fruits including _Citrus_, _Vitis vinifera_, and _Litchi chinesis_[16; 17; 18]. It is also an important floral aroma contributor in tea [14]. To find out whether _E. (M.) onukii_ contains GES, _E.