Differentiating between morphologically similar congeneric cerambycid beetle species by comparing cuticular hydrocarbon profiles

The cuticular wax layer of insects comprises a blend of compounds ranging from ∼20 to 40 carbons, which can be straight-chain or branched, saturated, or unsaturated hydrocarbons, along with lesser amounts of long-chain alcohols, aldehydes, ketones, and fatty acids. The species specificity of the chemical profiles of wax layers suggests they may be exploited as chemotaxonomic characters, and they have proven useful for differentiating between morphologically similar species of many insect taxa. We tested the hypothesis that cuticular hydrocarbon (CHC) profiles offer a convenient method of discriminating between morphologically similar species of cerambycid beetles, in particular, the congeners Graphisurus despectus (LeConte in Agassiz 1850) and G. fasciatus (Degeer 1775) (subfamily Lamiinae: tribe Acanthocinini) that are native to the eastern United States. Adults of the 2 species were collected from field sites in east-central Illinois, their cuticular lipids were extracted, and the CHC compositions were characterized by coupled gas chromatography-mass spectrometry. Analysis of the CHC profiles revealed distinct patterns consistent with the designation of the congeners as distinct species, and particular diagnostic hydrocarbons were identified for each species. Sanger sequencing of the mitochondrial cytochrome oxidase I gene supported the hypothesis that the CHC profiles were reliable characters for differentiating the 2 species. These findings demonstrate that analysis of CHC profiles of cerambycid beetles may provide a convenient, rapid, and inexpensive method for reliably distinguishing morphologically similar species, and can guide identification of diagnostic taxonomic characters.