Long chain alkenes occur in a variety of organisms including insects, plants, and microorganisms [1].  The microbial biosynthetic pathway is pictured below.   The alkenes are proposed to be derived from fatty acids by what is termed a "head-to-head condensation" [2].  However, the enzymes and the exact mechanism of the pathway are unknown.

[1] Kolattukudy, PE (1976) Chemistry and Biochemistry of Natural Waxes, Elsevier, Amsterdam.

[2] Albro, P.W., Meehan, T.D., Dittmer, J.C., 1970, Biochemistry 9, 1893-1898.