Biosynthesis of hydrocarbons in insects: Decarboxylation of long chain acids ton‐alkanes inPeriplaneta

The biosynthetic pathway ofn‐alkanes was investigated in the cockroachesPeriplaneta americana andPeriplaneta fuliginosa. Both sodium [1‐14C] acetate and randomly tritiated long chain fatty acids were incorporated into the cuticular hydrocarbons of both species. The relative incorporation of acetate into each component of the hydrocarbon fraction was about the same as the relative amount of each component in the fraction. In contrast, [R‐3H] hexacosanoic acid was preferentially incorporated inton‐pentacosane inP. americana and [R‐3H] tetracosanoic acid inton‐tricosane inP. fuliginosa. Long chain ketones and secondary alcohols, likely intermediates in the proposed condensation‐reduction pathway forn‐alkane biosynthesis, were not incorporated into hydrocarbon. Results from experiments with dual labeled lauric aicd were also not consistent with the condensation‐reduction pathway. The demonstration of the direct decarboxylation of long chain fatty acids ton‐alkanes one carbon unit shorter and the lack of incorporation of proposed intermediates of a condensation‐reduction pathway constitute the strongest evidence to date that insects utilize an elongation‐decarboxylation pathway forn‐alkane biosynthesis.