Dear Editor, The pinewood nematode （PWN） Bursaphelenchus xylophilus （Steiner and Buhrer, 1934） Nickle, 1970, the causal agent of Pine Wilt Disease （PWD）, is an invasive species known to have originated from North America, where it was not re- ported to cause large-scale outbreaks （Wingfield et al., 1984）. Ecological conditions encountered by B. xylophilus in China are different from conditions in its native North American range. Ecological differences, together with short generation times, improve the chances that changes in developmental traits may occur during lengthy invasive processes.
