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영어

Bursaphelenchus xylophilus is the causative agent of pine wilt disease. It is a devastating forest disease that has caused huge economic losses and has become a serious worldwide threat to forest ecosystems. Pine wilt disease was first discovered in Nanjing Sun Yat-sen Mausoleum in China in 1982. In a few short years, this disease also happened in Jiangsu, Anhui, Shandong, Zhejiang, Guangdong, Hubei, Hunan, Taiwan, Hong Kong et al. And now it has been found in Dalian, which is in the northeast of China. After invading healthy trees, B. xylophilus feeds on parenchymal cells and migrate through the tissues to spread over the tree, leading to wilting symptoms that result in the death of the tree within a year of infection. When the tree is dying, B. xylophilus feeds on fungi which invade the tree and reproduces quickly. While food is available, B. xylophilus develops through four moults (ie. four larval stages L1, L2, L3, L4 and adult) and reproduce within wood tissue. When conditions are adverse (ie. food becomes limiting), B. xylophilus enters specialized third-stage dauer larva (DL3). When stimulated by the presence of the vector beetle, the DL3 molts to become the fourth-stage dispersal larva (DL4) in preparation to board the vector. As the adult beetle emerges, the nematodes move and settle beneath the elytra or within the trachea of the beetles and are transported to another food source. It was found that dauer diapause was controlled by endocrine signals in response to environmental cues. Up to now, based on the study of B. xylophilus genome, 23 DL3 formation related genes were found. Those DL3 formation related genes were from three signaling pathways: cyclic guanosine monophosphate, transforming growth factor β and insulin-like signaling.