Two, four and six individuals of the vector (Monochamus alternatus) of pinewood nematode Bursaphelenchus xylophilus were placed into their own respective frames for four weeks (July 11 to August 6,1996), and covered with sheets of white nylon netting in order to prevent escape at the experimental farm of Hiroshima University in Higashi-Hiroshima, west Japan. The feeding effect of the vectors on 40 Japanese black pine (Pinus thunbergii) seedlings in pots placed in each frame was then traced during four months (August to November, 1996). The area and numbers of feeding scars on the seedlings increased with the increase of the individual numbers of vectors in the frame. Sixty-Seven of 120 seedlings in the three frames were fed on by the vectors. However, none of these 67 died even though the vectors had about 3,000 nemotoda on average. This suggests that the damage killing pine seedlings is not caused by the feeding of vectors even in a population density of 2∿6 individuals/21.6m^2 employed in the study, which may be higher than that in the field.