Insect hydrocarbon classes: Implications for chemotaxonomy

The following hydrocarbon classes have been identified in insect cuticular lipids: A, $\text{n-}\text{alkanes}$; B, olefins, comprising B1, alkenes, B2, alkadienes and B3, alkatrienes; and C, methylalkanes, comprising monomethyl-, dimethyl-, trimethyl- and tetramethylakanes. Biosynthetic pathways have been described for most of the main classes and hydrocarbon composition may be considered a product of an insect's genotype and thus available for taxonomic use. Olefins and methylalkanes usually occur as isomeric mixtures and hydrocarbon composition can be complex. This provides the chemotaxonomist with many potential characters. Preliminary investigations show that hydrocarbon composition not only separates species but also reflects links between species and between higher taxa. A hydrocarbon chemotaxonomy which also takes into account the elongation-decarboxylation pathways used by insects to synthesise their hydrocarbons could provide information on the evolution of hydrocarbon biosynthesis in the insects.