Desaturase enzymes introduce a double bond at a specific carbon in a fatty acid chain, with the desaturase usually named after the position in the carbon chain where the double bond is inserted. For example, a delta-9 desaturase inserts a double bond at the 9th carbon of palmitic or stearic acid, creating a monounsaturated fatty acid. The repertoire of fatty acid desaturase enzymes that an organism possesses varies greatly. While insects have relatively few desaturases, there has been a unique proliferation and diversification of delta-9 desaturases. This is thought to to be integral for the production of gender and species-specific sex pheromones. (Adapted from FBrf0221274.)