Abstract Bursaphelenchus xylophilus was found only in declining or dead jack pine infested with Arceuthobium americanum. All trees containing Bursaphelenchus xylophilus were also infested with cerambycid beetles, bark beetles, and blue stain fungi. Arceuthobium americanum appeared to be the primary cause of tree mortality. Bursaphelenchus xylophilus was extracted from a dead jack pine, then increased on Botrytis cinerea and inoculated into 3-year-old seedlings of jack pine, red pine, Japanese red pine, and eastern white pine. After 6 weeks, 87, 13, 23, and 10 percent of the inoculated seedlings were dead or declining for those species, respectively. Forest Sci. 31:866-870.