Abstract
Pine wilt caused by Bursaphelenchus xylophilus has heavily damaged Pinus densiflora and P. thumbergii forests in Japan. The degree of susceptibility of pine stands to the disease sometimes varies even between stands that are located near to one another. We constructed a simple time-delayed model in which a transmission coefficient is used as an index of the stand's susceptibility to the disease. By applying the model to field data, we showed the usefulness of this coefficient as the susceptibility index. It may, thus, be helpful in evaluating the effectiveness of control techniques used against the disease over a period of some years.
