**2.2 Association with the pine wood nematodes**

70 Zoology

portion of Yunnan is the western margin of the Yunnan-Guizhou altiplano, where most of the terrain are plains with low hills with an altitude lower than the central portion of Yunnan as well as most of the LRGR (S.Y. Wang & W. Zhang, 2005). The subdued slope of this area also allows non-local organisms to enter Yunnan from the adjacent areas of China. Meanwhile, Yunnan also plays an important role in preventing invasive alien species from entering China, as the mountains lie in northern portion are natural barriers to obstruct the populations of non-local organisms from expanding. Therefore, Yunnan bears a vital strategic function of regional ecosecurity defined by the combination of terrestrial pathway

To enhance relevant research in detecting exotic species and/or non-local populations in Yunnan, research on invasive alien species has been conducted to reveal origin, expansion, and the mechanisms of invasion. For cases of invasive insects, researches on two exotic tephritid pests, *Bactrocera dorsalis* (Hendel) and *B. correcta* (Bezzi) have achieved the goals of population recognition and route reestablishment via modern molecular techniques (Shi et al., 2010; Liu, unpublished data). These studies demonstrated that the invasion of the two fruit flies represented the mode of natural and long-term invasion, inhabitation, and expansion. Moreover, the merits of these important research also provided ideas for the research on biological invasion in the new era. We used molecular techniques to detect nonlocal populations of a forest pest in southwestern Yunnan which strongly suggested another

The Japanese pine sawyer, *Monochamus alternatus* Hope (Coleoptera: Cerambycidae), is a stem-boring beetle widely distributed in eastern Asia and the northern portion of the Indochinese peninsula (Davis et al., 2008). This polyphagous beetle feeds on conifers throughout the life history, including many unrelated species of *Pinus*, *Picea*, *Abies*, *Cedrus*, *Larix*, and *Cupressus* (Ning et al., 2004; Davis et al., 2008). *M. alternatus* is a univoltine species, which produces only one generation per year (Togashi, 1989; L.P. Wang, 2004; Zhao et al., 2004). After copulation, the female adults gnaw ovipositing wounds in the bark of host trees, and lay eggs in the space between the phloem and the xylem (Anbutsu & Togashi, 2000). The newly hatched larvae ingest wood tissue from both the phloem and the xylem, and start to excavate "U" shaped tunnels from the third instar. The final instar larvae build oval pupal chambers at the end of the tunnels to pupate. The newly eclosed adults feed on shoots, needles, and bark to obtain nutrients for maturation (Shibata, 1987). Copulation usually takes place five to ten days after emergence, each adult is able to mate more than once (L.P. Wang, 2004; H. Yang et al., 2006). As a typical secondary stem-boring species, the female adults tend to select stressed hosts for oviposition (S.J. Hu et al., 2009), which is induced by the volatile chemicals (i.e., *α*-pinene, *β*-pinene, 3-carnine, and ethanol) emitted from the hosts (Ikeda et al., 1986; Yamasaki et al., 1989), but often influenced and deterred by bark thickness, branch diameter, ovipositing scars from other female adults, and larval frass (Nakamura et al., 1995a, 1995b; Anbutsu & Togashi, 2000; Li & Z.N. Zhang, 2006; S.J. Hu et al., 2009; Z.X. Yang et

and frontier prevention of biological invasion.

possible mode of biological invasion.

**2. Background information 2.1 The Japanese pine sawyer** 

al., 2010).

The pine wood nematode, *Bursaphelenchus xylophilus* (Steiner et Buhrer) (Nematoda: Aphelenchoididae), is a quarantine phytopathogenic organism of conifers indigenous to northern America but casually spread to Eurasia and southern Japan in last century (CABI & EPPO, 1997). The nematode, like other species of genus *Bursaphelenchus*, lives in the vascular tissue of their coniferous hosts, which decreases the transportation of water and resin, and subsequently weakens the hosts and causes a syndrome named the pine wilt disease (Mamiya, 1983). The pathogenicity of *B. xylophilus* varies significantly. In North America, reports on its damages are rarely seen (Wingfield et al., 1986). However, in the vast majority of Japan and China, where *B. xylophilus* is considered as an invasive species, the infestation is often fatal, and has caused catastrophic timber loss (Mamiya, 1988; X.B. Hu et al., 1997). In nature, the relocation of *Bursaphelenchus* nematodes depends on coleopterous vectors, but the association between nematodes and vectors differs with taxa (Linit, 1988). For *B. xylophilus*, the longhorned beetles of genus *Monochamus* are the major vector (Linit et al., 1983; Evans et al., 1996; Kulinich & Orlinskii, 1998), and research has confirmed that *M. alternatus* is the key vector of *B. xylophilus* in eastern Asia (Mamiya & Enda, 1972; Kobayashi et al., 1984). In infested hosts, the immature pine wood nematodes are able to locate the pupae of *M. alternatus* and board into the tracheae, and the newly eclosed adults carry the nematodes when seeking food and new hosts. During the course of feeding and ovipositing, the nematodes detach from the beetles and enter the new hosts through the feeding and ovipositing wounds to initiate a new round of infestation (Edwards & Linit, 1992; Naves et al., 2007).
