Disclosed are (1) pest control chemicals against the pine wood nematodes containing an extract from a pine tree with an organic solvent, (2) a repellent against the pine wood nematodes containing alpha -humulene or a mixture of alpha -humulene and beta -bisabolene, (3) a repellent against the pine wood nematodes containing a mixture of alpha -pinene and calarene, (4) a nematicide against the pine wood nematodes containing methyl ferulate, (+)-pinoresinol or a mixture thereof, and (5) highly effective pest control chemicals against pine wood nematodes containing hydroxystilbenes or salts thereof which are prepared by synthesizing methoxystilbenes from benzyl phosphonates and methoxybenzaldehydes by a Wittig-Horner reaction, performing demethylation to obtain the hydroxystilbenes, and preparing the salts thereof by conventional methods if necessary.
