A cDNA encoding pheromone $Delta$9 acyl-CoA desaturase, Slit KPSE was isolated from sex pheromone gland of the tobacco cutworm, Spodoptera litura which uses a diene unsaturated fatty acid (UFA) derivative, Z9E11-14 : 2 as a major pheromone component. The fulllength open reading frame coding region of Slit KPSE was inserted in a yeast shuttle vector, YEpOLEX, and two kinds of yeast (Saccharomyces cerevisiae) mutant strains were transformed with the recombinant vector. In the desaturase-deficient ole1 strain, Slit KPSE expressed a complementary enzyme producing two kinds of diene UFAs, more 9-16 : 1 and less 9-18 : 1 at a ratio of 1 : 0.74 exhibiting a typical functional characteristics as one of the pheromone $Delta$9 acyl- CoA desaturase lineage group, KPSE, but no $Delta$9 14C monoene was detectable because of too small amount of 14C saturated fatty acid precursor to be reliably used by Slit KPSE in the transformed cells. However, the another transformed yeast strain elo1 which is deficient of elongase 1, an enzyme converting 14C to 16 C hydrocarbon substrate, was supplemented with some myristic acid (14 : 0) in the medium, and produced a significant amount of 9-14 : 1 in due to a much enhanced level of the 14C substrate suggesting that Slit KPSE may be responsible for making the $Delta$9 double bond on the diene pheromone component.