| Tomicus piniperda is a world-wide serious pine shoot beetle, and occurs throughout China, but it has been most destructive in southwestern China, in Yunnan province, where it attacks primarily Yunnan pine,Pinus yunnanensis. The beetle attacks not only by itself, some pathogenetic fungi associated with the beetle also invade to pathogen. Tree resistance is an important factor regulating bark beetle dynamics. So the level of Tomicus attack results from the interaction among the competence of Tomicus attack, the virulence of its associated fungi and the resistance of the host tree. The Yunnan pine, P.yunnanensis, is heavily attacked and often killed by Tomicus piniperda in certain parts in Yunnan province of Southwest China. Tomicus piniperda is also known as the "cancer"of Yunnan pine, and has resulted in tremendous losses in ecology and economic. Yunnan pine is the pioneer specie of renewing and sylviculturing in Yunnan altiplano mountainous. It has important social, economic and ecological benefits in afforesting in barren mountains and in dry and hot valleys, in preserving of water and soil, in amending of the ecological environment, and in adjusting the climate. Therefore, protecting the Yunnan pines will have important significance for the construction and sustainable development of ecology and economics in Yunnan and in Changjiang River upper stream region. For further opening out the mechanisms of Tomicus attack, and providing basic information and scientific basis for effective, long-term and sustainable integrated management of the beetles, the paper mainly studies on the interaction between Leptographium yunnanense, a blue-stain fungus associated with Tomicus piniperda attacking P.yunnanensis and Yunnan pine, and thus synthetically analyses the causes of the beetles occur, and the strategy of sustainable integrated management of the beetles from the point of view of system consisted of "Yunnan pine, Tomicus piniperda and its associated fungus". Results are as follows: 1. L. yunnanense is the main pathogenic fungus associated with Tomicus piniperda attacking P. yunnanensis, which can assist the beetles in overcoming the resistance of the host tree. During its growth and invasion in the host, it can produce phytotoxin, pectinase and cellulase to overcome the tree resistance and stain the host's tissues to blue, inducing the disease symptoms, such as phloem necrosis , namely phloem reaction zone, etc. The phytotoxin of L.yunnanense belongs to protein with no heat stability. Under the cool-store or room temperature, its activity can maintain about 20-40d. With the increase of temperature, its activity loses gradually. At the temperature of 60℃, the phytotoxin can still maintain some activities, but loses fully when the temperature exceeds 80℃. The phytotoxin can pathogenesis not only to Yunnan pine, but also to Shimao pine,P.kesiya var. langbianensis and Huasan pine, P. armandi. The phytotoxin's pathogenicity correlates with its concentration, the higher concentration, the higher pathogenicity, and the longer reaction zone induced by it. The phytotoxin can still maintain a certain activities when diluting it 5 times; this indicates that the phytototoxin has stronger pathogenicity. The phytotoxin can restrain the activities of peroxidase(PO),polyphenol oxidase(PPO)and phenylalanine ammonia lyase(PAL) that existed in the tree, and so reduce the resistance of the host tree and benefit the fungus to intrude into the tree successfully. Besides pathotoxin, L.yunnanense can also produce pectinase and cellulase to decompose the tree's cell wall. And this makes the fungus easy intruding into the tree cell to incept nutrition. With the effect of phytotoxin and pathogenetic enzymes of L.yunnanense, the tree's physiological functions have been maladjusted and to be diseased. From this, an important base established for Tomicus piniperda to attack and breed successfully. 2. Yunnan pine resistance to the beetles and its associated fungus is an important factor for regulating the level of Tomicus attack. The cell wall and the resin ducts are the tree's natural barriers to hold up the intrusion of L.yunnanense. After the invasion of the fungus, the traumatic resin duct will gradually form to enhance the resistance of the tree, the activities of PO,PPO and PAL of the tree will also increase distinctly and may maintain a longer time, thus the tree could constrain or poison the fungus intruded. These are the important resistant response of the tree to the fungus'invasion. There is an important correlation between the tree's resistance and its density of resin ducts, traumatic resin duct formation and the enzymes'activities related withtree's resistance after being invaded by L.yunnanense. The higher density of resin ducts and rate of traumatic resin duct's formation, higher enzymes'activities related to tree's resistance and longer the enzymes'activities maintain, the stronger of the tree's resistance to the fungus. These characteristics'variation between pine species is the main reason for Tomicus piniperda and its associated fungus to select different pine species as host and infest it, and thus results in different level of Tomicus attacks between pine species, so these characteristics are the important referent index for cultivating resistant variety. The resin ducts'density of Huasan pine is higher than that of Yunnan pine, and the enzymes'activities related with resistance in Huasan pine also higher than in Yunnan pine, and can maintain a longer time. So the resistance of Huasan pine is higher than that of Yunan pine. Therefore, it's difficult for the beetles and its associated fungi to intrude and breed in Huasan pine successfully, so the beetles and its associated fungi are tend to select Yunan pine as their host. And this is one of the important reasons for Tomicus piniperda attacking Yunnan pine very serious, but rarely attacking Huasan pine. 3. Water and heat conditions will restrict the growth and development of the trees and the beetles and its associated fungus, and therefore influences the spatial and temporal distribution of the beetles'attacks. With the temperature from 8 to 20℃, The growth length of L.yunnanense (FGL) has a positive correlation with the temperature(r=0.9424,r0.01=0.917,p<0.01), and also a certain positive correlation with the tree's water content. The resistance of Yunnan pine has a certain negative correlation with the temperature and precipitation, the correlation coefficient are r=-0.4627 and r=-0.7798(|r0.05|=0.811,p>0.05)respectively,this indicates that a certain drought and low temperature can enhance the Yunnan pine resistance. Of course this correlation comes into existence only in a certain range. When the variation of temperature and precipitation influences the tree's normal growth and development, the tree's resistance will be further weakened. So in the doughtier area such as ridge area, Tomicus attacks more serious. Under lower temperature(<10℃)and higher temperature(>30℃), the growth and virulence of L.yunnanense has been inhibited more than that of Yunnan pine tree resistance. However, With temperature from 15℃to 30℃, the resistance of Yunnan pine is relatively weaker. These indicate that in warmer climates, the growth and virulence of L.yunnanensehas been relatively strengthened, but the resistance of Yunnan pine has been relatively weakened. These indicate that climatic condition is an important factor regulating the spatial and temporal distribution of Tomicus attacks. In warm and humid climate, the resistance of Yunnan pine is relatively weaker, but the fungus'growth and its virulence are relatively stronger, so in these areas, the beetles attack (especially trunk attacks) very serious, and even killed the trees in large area. However, in the area with higher temperature or lower temperature and doughtier, the growth and development of the tree, the bark beetle and its associated fungi are all restricted to a certain degree. But more restricts on the beetles and its associated fungus, the resistance of Yunnan pine becomes relatively stronger, so the beetles attack not serious in these area. Thus forms the spatial distribution of Tomicus attacks in Yunnan. Tomicus attacks very serious, and often outbreaks in the south and central area of Yunnan, such as in the region of Kunming, Menzi, Yuqi, Honghe, etc., where the temperature and the precipitation are all higher. However, in the northwest area of Yunnan, such as Lijiang, Zhongdian ect., where both temperatures and precipitations are lower, Tomicus attacks occurs seldom. See from the temporal distribution of Tomicus attacks, in the earlier drought season, both temperatures and precipitations are relatively low, and the water content of Yunnan pine is also relatively low, under these conditions, the fungus'growth and its virulence are relatively weaker, the Yunnan pine's resistance is relatively stronger, so the Tomicus attacks not serious; however, in the later drought season, the temperature rises gradually, and the precipitation also increases, so does the water content of Yunnan pine, under these conditions, the Yunnan pine's resistance is relatively weaker , but the fungus'growth and its virulence are relatively stronger, so during this period, the Tomicus attacks ,especially trunk attacks, very serious. From Tomicus attacks in a year to see, the co-evolution has been come into being among the Yunnan pine and Tomicus piniperda and its associated fungus through a long-term interaction among them in a certain area. For example, in the central area of Yunnan, the beetles'seriously assembling attacks and the trees'being killed by the beetles in large area usually take place in drought season, in which both temperature and precipitation are all lower. However, the resistance of Yunnan pine is also stronger in this season, the beetles'attacks and its associated fungus'invasion will be hold up to a certain degree, the Tomicus attacks will also be controlled in a certain range.4. The interaction between the tree, Tomicus piniperda and its associated fungus is the inner fundamental mechanism making for the system balance. From the bigger environment point of view, in recent years, the environmental variation such as greenhouse effect, climatic change abnormally, ect., has resulted in the system balance largely leaning to the side which is in favor of the beetles and its associated fungus, and this is an important reason for the beetles outbreak. 5. The prevention and cure of Tomicus attacks should be taken integrated management strategies combining short-term targets with long-term targets. In the short-term, it should be strengthened the beetle attacks'monitor and adopted protecting measures integrated with biology, chemic, ect. From this can the Tomicus attacks be prevented and controlled timely. In the long-term, it should be protected and ameliorated the forest environment, protected and utilize the enemies of the beetle, made use of the directional mechanisms of the beetles attacking P. yunnanensis and of the tempt mechanisms of P.yunnanensis which may be existed, cultivated and applied the resistant variety. Only from these can the Tomicus attacks be sustainable managed, and promote ecology and economics developing in harmony.
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