| Scale insects belong to Insecta, Hemiptera, Coccoidea. Scale insects damage plants by sucking mouthparts, causing direct damage, and most scale insects can secrete honeydew, induce sooty blotch, causing secondary damage, is a major pest of agricultural and forestry in worldwide. Because most of Scale have thick wax shell which can protect it from abiotic and Biotic stress making the general chemical control is very difficult to work, but kill a large number of natural enemies, Pollute the environment. On the other hand they have high reproductive capacity, Population increased very rapidly, make it is more difficult to controlled.Jasmonic acid (JA) and methyl jasmonate (MeJA) are plant Semiochemicals, the inducer of plant resistance. Exogenous application can induce plant produce more defence enzymes, secondary metabolites and change of volatile substances, produce direct defence and indirect defence on the herbivores, enhanced resistance to insect. Because it is a plant Semiochemicals and would not pollute the environment, so as an Exogenous signal moleculeto induce plant defence to control scale insects,the JA and MeJA have a good prospect.For study the feasibility of control scale insects, MeJA was applied to kumquat and persimmon trees respectively. The effection of the plant resistance to insect induced by MeJA were assaied. This study is divided into two parts:1. The effect of MeJA on the tritrophic relationship of Kumquat-scale insects-ParasitoidMeJA as an exogenous signal molecule was applied to treat the host plant to investigate the effect on the tritrophic relationship of Kumquat-scale-parasitoid and, confirm the significance in the biological control of the scale insect. The results showed that, under the damage of C. hesperidun, kumquat plants were induced and produced more chrymoltrypsin proteinase inhabitor (ChymPI) and polyphenol oxidase (PPO). Compared with the healthy plants, ChymPI was increased by 3.48 times and the activity of PPO was promoted by 1.11 times in the leaves of the slight damaged plants, however, these two kinds of materials increased by 6.93 times and 1.33 times, respectively, in the heavy damaged leaves. After treated with MeJA, the ChymPI and PPO were further promoted by 73.4% and 28.4%, respectively, in the slight damaged leaves. And the two values increased by 2.8% and 3.1%, respectively, in the heavy damaged leaves. Healthy plants were treated by MeJA, its PI values in the 1st-7th day, were always at a higher level, compared with the untreated healthy plants, the PI values increased by 4.17-5.89 times, the highest PI values was 4.83 on 5th day, the PPO activity in 1st-7th day only on 1st day was significant (P<0.05) increased by 52.6%.The trials showed that the crawlers of C. hesperidun preferred to settle on those leaves from the plants untreated with MeJA and the rate reached 63.8%. In contrast, the percentage of the scale insect was 22.6% selected on the leaves treated with MeJA. It indicated that the leaves treated with MeJA exhibited repellency effect to the nymphs of the scale insect. In the trend test MeJA treated kumquat produce repellency effects, made 1st and 2nd instar nymphsmadeof Drosicha contrahens tend to untreated plants. However,59.6% of the parasitoid, Coccophagus yoshidae, ran to the volatile source from the plants treated with MeJA, it was more one times than that to the untreated one. This result argued that the volatiles from the kumquat plants treated with MeJA have possessed of the attraction to the parasitoid of the scale insect.2. The resistance of persimmon trees to scale insects induced by MeJAThe persimmon trees were treated with MeJA during June and July which was a key phase for the scale control. In the experiment, MeJA was applied in three concentrations,0.05%,0.1% and 0.25%. The lipoxygenase (LOX), polyphenol oxidase (PPO) activity and the content of tannin were measured after 1-7 d of the treatment. Moreover, Using the circular method measure the change of volatile emissions from persimmon trees at different distance from flavor source of 1 mL MeJA. And the attraction of MeJA treatment Persimmon on the Harmonia axyridis in forest were studied. The results showed that MeJA was able to stimulate the persimmon trees to change the activity of LOX, PPO and content of tannin. The activity of LOX increased significantly in 1st day after treatment with the activity values reached 144.6 U.g-1 and 129.6 U.g-1 in the 0.05% and 0.1% MeJA treatement sections, respectively. In compare, the LOX activity reached 145.1 Ug-1 in 5th day after treatment in the 0.25% MeJA treated section, and the induction effect lasted longer. Similar to the LOX, the PPO activity of the 0.05% and 0.1% MeJA treated group reached top which were 146.3 U.g-1 and 149.4 U.g-1 respectively in 1st day after treatment. While the maximum of PPO activity of the 0.25% MeJA treated group was 133.8 Ug-1, appeared in 3rd day after treatment. The variety of tannin content induced by MeJA presented the wave-like trend. Meanwhile, Treatment persimmon by fumigation method using flavor source of 1 mL methyl jasmonate, and taste the change of volatile compounds of the persimmon trees which were from flavor source 0 m,5 m,10 m respectively, The results show that in the 10 m range, MeJA as a volatile substances can induce changes of persimmon volatile compounds, especially the terpenes which be considered associated with the effection of Attractive natural enemies were significantly increased, however also found that between the three distance points, induced by MeJA had different effects, in this 5 m from the flavor source, persimmon trees had the best effect, and the location of persimmon 0 m 10 m from the flavor source, had lower effect compare with the 5 m. Use 0.1% MeJA spray Persimmon which damaged by Ceroplastes japonicus (Green) and compared with the corresponding persimmon did not treat by MeJA, the effects of attracted H. axyridis had a significant increase, the ladybug number increase by 84.4% in the Persimmon treated by MeJA compared with the did not treat.
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