Effect of feeding by Monochumus alternatus on pine tree vitality : (2) A case of natural young Japanese red pine stands under different air pollution levels

Six and nine individuals of the vector (Moncochamus alternatus) of pinewood nematode Bursaphelenchus xylophilus were placed into their own respective frames, which were covered with sheets of white nylon netting in order to prevent escape, for one month (June 24 to July 23,1998) at both natural young Japanese red pine (Pinus densiflora) stands located at Hachihonmatsu in Higashi-Hiroshima and Fukutomi-cho in Hiroshima Pref., where the air pollution levels were different from each other. The feeding effect of the vectors on was then traced in the field during 10 months (June 1998 to March 1999). Sixty-four of 67 trees in the four frames at the both stands, into which six or nine vectors were placed, were fed on by the vectors. However, only one of these 64 died in the frame of nine vectors at Hachihonmatsu site under heavy air pollution, even though the vectors has about 4,000 nemotode on average. No nematode could be found out in the most hardly fed pine tree in each frame, including dead pine tree. This suggests that the damage killing young pine trees is not caused by the feeding of vectors even in a population density of 6-9 individuals/25m^2 employed in the study, which may be extremely higher than that in the field