Possible altitude and temperature limits on pine wilt disease: the reproduction of vector sawyer beetles (Monochamus alternatus), survival of causal nematode (Bursaphelenchus xylophilus), and occurrence of damage caused by the disease

Pine wilt disease is caused by the pine wood nematode [Bursaphelenchus xylophilus (Steiner et Buhrer) Nickle]. In East Asia, an important vector of the nematode is Monochamus alternatus Hope. We determined the tolerance and reproductive ability of sawyer beetles and the nematode to altitude and temperature at elevations between 850 and 1,450 m on Mt. Fuji in Japan. The number of emergent adults decreased markedly along the altitudinal gradient, but the beetle could still reproduce at 1,050 m (8.2 A degrees C annual mean temperature). Beetles with a 2-year life cycle increased rapidly in number with increasing altitude. The pine wood nematode survived through winter at all altitudes tested (850-1,450 m). The beetle population decreased between 950 (9.1 A degrees C) and 1,150 m (8.3 A degrees C). Therefore, the beetle population seems to be stable at 850 m (10.2 A degrees C) and lower altitudes (higher temperatures) but cannot be maintained from 950 (9.1 A degrees C) to 1,150 m (8.3 A degrees C) without constant immigration of beetles from lower altitudes. The beetles could not reproduce at altitudes above 1,150 m (lower than 8.2 A degrees C). From the mean and effective cumulative temperatures, we concluded that the beetle (and its population) can endure temperatures lower than those previously reported. Pine wilt disease also occurred at lower temperatures and higher altitudes than expected. We have summarized the principal strategies for controlling the disease at high altitudes based on these results.