The Emission Of Tea Plant Volatiles Induced By Three Herbivore Insect Pests

Plant volatiles are the chemical information existing popularly in nature, and could mediate the tritrophic plant-herbivore-carnivore interaction and influenc the structure and composition of insect community in the ecosystem. In this research, the volatiles of healthy tea plants, intact tea shoots and mechanically damaged tea leaves were analyzed, the emission of volatiles emitted from tea plants damaged by tea weevil (Myllocerinus aurolineatus), tea leafhopper (Empoasca vitis) and tea geometrid (Ectropis oblique) were investigated, and the seasonal variation of volatiles emitted from tea plant damaged by E. obliqua was monitored by electronic nose (zNoseTM) in situ under field condition..The volatiles emitted from healthy tea plants were composed of 6 compounds. Healthy tea plants emitted much high levels of these volatile compounds at noon (12:00-13:00), and extremely low levels before the dawn (04:00-05:00). The volatiles emitted from intact tea shoots were composed of 19 compounds. But it changed at different times when tea shoots were plucked. The relative content of (Z)-3-hexenyl acetate was 81.31% at 0.5h after tea shoots were plucked, and the relative contents of (E)-β-ocimene and DMNT were 52.09, 27.80% respectively at 7.5h after tea shoots were plucked.It was found with SPME-GC-MS method that five green leaf volatiles were emitted immediately from tea leaves after mechanical damage, and (Z)-3-hexenal, (Z)-3-hexenol or (Z)-3-hexenyl acetate were the major volatiles emitted from mechanically wounded tea leaves. However, some novel compounds were induced by mechanical damage also. A further investigation by using zNoseTM showed that more mechanical damage level resulted in the more emission of (Z)-3-hexenal, (Z)-3-hexenol and (Z)-3-hexenyl acetate emitted from young leaves; the emission of them produced by the same mechanical damage on old leaves and young leaves was different; and the emission peak of them appeared at different time after mechanical damage.A different volatiles could be emitted from the plants damaged by the different tea pststs including M. aurolineatus, E. vitis and E. oblique. The volatiles induced by M. aurolineatus adults composed of 4 constitutional compounds and 47 novel compounds; the volatiles induced by E. vitis adults composed of 2 constitutional compounds, 1 induced compound and 29 novel compounds; the volatiles induced by E. oblique larvae composed of 4 constitutional compounds and 53 novel compounds. Most of the novel compounds induced by three herbivore species were similar, however there were some specific novel compounds induced respectively by different pests.β-bisabolene only induced by the larvae of E. oblique, TMTT only induced by E. vitis adults, andγ-terpinene induced by M. aurolineatus adults and E. vitis adults. These specific novel volatile compounds steadily induced by these three herbivore species under any densities tested, and their emission amounts were relatively low (the relative contents were less than 1%). However, there was great difference in quantity of the tea plants volatiles induced by these three herbivore species. The emission of benzyl nitrile was the highest from tea plants continuously infested by first-instar larvae of E. obliqua for 28h; the emission of (E)-β-ocimene was the highest from tea plants continuously infested by M. aurolineatus adults for 28h; and the volatile emitted from tea plants damaged by E. vitis adults continuously were mainly made up of (E)-β-ocimene, DMNT and (E,E)-α-farnesene.Density and the damaging period as well as the feeding style influenced the emission of herbivore-induced tea plants volatiles. The higher density of herbivore induced the more abundant volatiles in both quantity and quality. The damaging period influenced the liberated amounts of volatiles from the tea plant. Under the damage by tea pest for 6 hrs, the emission of inducible volatiles emitted from damaged tea plants on the next day was significantly lower than those tea plants damaged continuously. With regarding the damaging type, investigation showed that the constitutional compounds and novel compounds induced by the insects with chewing mouthparts (M. aurolineatus and E. oblique) were more than those induced by the insects with piercing-sucking mouthparts (E. vitis). Beacause of the difference in the size of mouthparts, the different type of damage caused by the different instars of E. oblique influnced the emission of tea plants volatiles. The volatiles induced by first-instar larvae of E. obliqua were more abundant in both quantity and quality than those damaged by the third-instar larvae.Investigated showed that the emission dynamics of volatiles emitted from tea plants damaged by different diensities of three herbivore species were similar. Constitutional compounds were emitted from tea plants immediately after insects inoculated. As damage proceeded,abundant volatiles were emitted from damaged tea plants. The emission of volatiles reached a relatively stable state at 24-28h after insects inoculated. Since then, the emission of most novel compounds followed diurnal cycles with increased emission during light period and reduced emission during darkness. However, 1,3,8-p-menthatriene induced by M. aurolineatus adults and (E)-β-ocimene induced by first-instar larvae of E. oblique were emitted in an opposite diurnal fashion, the emission of indole induced by three herbivore species was slowly reduced after reached the emission peak, and the emission of other individual compounds slowly increased as damage proceeded. After insects removed from continuously damaged tea plants, the emission of the novel compounds induced by high density of insect ceased later than those induced by low density of insect.In laboratory the tea plants volatiles induced by E. oblique was analyzed synchronously with GC-MS and zNoseTM. The qualitative analysis with GC-MS or zNoseTM showed similar results, but there was different in the quantity analysis with GC-MS and zNoseTM. Under field condition, the seasonal variation of voaltiles emitted from tea plant damaged by E. Obliqua larvae was monitored with zNoseTM in situ. The emission of most novel compounds were significant higher in spring than in autumn, but the emission of (E, E)-α-farnesene in spring were significant lower than in autumn.In summary, the components, contents, emission dynamics, and the influencing factors on emission of volatiles emitted from tea plants damaged by M. aurolineatus, E. vitis and E. oblique were investigated in this study. These results offered an important reference for studying the tritrophic tea plant- herbivore-carnivore interaction.