To clarify the effect of the volatiles of Pinus densiflora on the temporal pattern of departure of Bursaphelenchus xylophilus from Monochamus alternatus adults (nematode departure curve), autoclaved or normal pine twigs were provided to the beetles. Monoterpenoids were not detected from the air of rearing containers with autoclaved pine twigs. A Kolmogorov-Smirnov test showed that there were significant differences in the averaged nematode departure curve between the 2 beetle groups supplied with different foods. The time of 50% nematode departure was shorter in the beetles supplied with autoclaved twigs. The proportion of nematodes which remained in the bodies of 5l-day-old M. alternatus was significantly smaller in the beetles supplied with autoclaved pine twigs. Consequently, it is suggested that B. xylophilus had a trait of spontaneous departure from M. alternatus and that the volatiles from excised normal P. densiflora twigs repressed B. xylophilus departure from M. alternatus.