Spread Of An Introduced Tree Pest Organism – The Pinewood Nematode

Invasions of exotic species sometimes cause devastating effects in ecosystems they have invaded. Nowadays worldwide economic activity increases the flow of people and trading materials within and between continents, resulting in increasing occurrence of invasion of exotic species. The invasion process generally involves four phases: arrival, establishment in the new habitat, range expansion, and saturation (Liebhold et al. 1995). The spread pattern of invading organisms has been studied empirically and theoretically by many authors (Andow et al. 1990, Shigesada et al. 1995, Veit and Lewis 1996, Yamamoto et al. 2000). Pinewood nematode, Bursaphelenchus xylophilus (Steiner et Buhrer) Nickle, is the causative agent of pine wilt disease (Kiyohara and Tokushige 1971). The infection of the nematode induces a rapid tree mortality of susceptible pine species such as Pinus densiflora, P. thunbergii, and P. sylvestris (Kiyohara and Tokushige 1971, Kondo et al. 1982). The nematode is inferred to be native to North America and introduced into Japan at the beginning of 20th century (Mamiya 1988). Since then it has spread to Korea, Taiwan, and China and devastated pine forests in East Asia. In Japan, for example, the annual loss of pines reached a maximum value of 2,430,000 m3 in 1979 (Mamiya 1988), and then was held at a level of about 1,000,000 m3 in the early half of 1990’s. It was also found in Portugal in 1999 (Mota et al. 1999). The objective of this article was to determine the spread pattern of pinewood nematode at within-stand, local, and regional levels in Japan. For this purpose, we summarized the biology of the nematode and its vectors first.