POPULATION-DYNAMICS OF THE PINE WOOD NEMATODE, BURSAPHELENCHUS-XYLOPHILUS, IN EXCISED BRANCH SEGMENTS OF WESTERN NORTH-AMERICAN CONIFERS

The population dynamics of two strains of the pine wood nematode, Burs aphelenchus xylophilus, were studied in excised branch segments of Pin us contorta, Abies grandis, Pseudotsuga menziesii, Tsuga heterophylla and Thuja plicata inoculated with the blue-stain fungus, Ophiostoma pi ceae. Nematodes were inoculated into small holes drilled into the cent er of the branch segments. Size and age-structure of the nematode popu lations were determined at regular intervals after inoculation. Nemato de population growth occurred in branch segments of all tree species t ested. However, population densities were significantly greater in P. contorta than in the other species. In one experiment, respective popu lation densities in branch segments of P. contorta, A. grandis, P. men ziesii T. heterophylla and T. plicata increased from 2, 0.02, 0.1, 0.0 4 and 0.05 nematodes/g dry wood at 2 weeks after inoculation to 57, 15 , 11, 13 and 6 nematodes/g dry wood after 16 weeks. The relative abund ance of persistent third-stage juveniles (J3P) increased through time in all tree species and was greatest in P. contorta at most sample dat es. The relative abundance of J3P was significantly greater in P. cont orta than in the other species in one of two experiments only.