Infection behavior and distribution of Bursaphelenchus xylophilus in Pinus densiflora trees

Pine wood nematodes (PWN), Bursaphelenchus xylophilus , infect the pine host tree through maturation feeding wounds caused by Monochamus saltuarius (a long-horned beetle) and kill the host. This study investigated characteristics of the wound by M. saltuarius , infection behavior of PWN on the wound and distribution of PWN in stem tissues of 20-year-old Pinus densiflora that was artificially inoculated but not showing wilt symptoms. The vector beetle sucked resin and exposed cortical tissues, resin canals, phloem, cambium, ray parenchymatous cells and tracheids in xylem, while it fed on the bark of current shoots of pine tree. When PWN were inoculated on the fed shoot, they infected all of the exposed tissues. When placed on a cut current shoot disc with flowing resin profusely, PWN moved down the resin duct into the cortical layer gravitationally before the resin became sticky due to evaporation. In the artificially inoculated three-year-old stem of 20-year-old P. densiflora , PWN were distributed mostly in resin canals, some in cortical tissues and pith, but very rarely in tracheids. In conclusion, PWN can initially infect resin canals in cortical tissues of pine shoot after feeding by the long-horned beetle.