User:Daniel Mietchen/Talks/MPI-ICE 2012/Workshop/Cuticular hydrocarbons

Malayatelura ponerophila silverfish rub their body against Leptogenys distinguenda worker ants to acquire cuticular hydrocarbons to escape detection.

Cuticular hydrocarbons are hydrocarbons that form part of the Arthropod cuticle. These lipids may act as barriers against pathogens or to prevent water-loss from the cuticle and are also used for chemical communication among insects. Cuticular hydrocarbons can differ between sexes and can be used as pheromones for mate recognition, as in the case of nonacosane in Anopheles stephensi. They can also change in composition in different life stages or castes of a same species and are used for nest-mate recognition in social insects. In some species of closely related Drosophila fruit flies these compounds server as a species-specific sex signal and can also give information on the reproductive state (pre or post mating) of individuals .

Cuticular hydrocarbons can differ between closely related species and be used by taxonomists for species recognition. One case is the southern monarch butterfly (Danaus erippus), which until recently was considered a subspecies of the northern monarch butterfly (Danaus plexippus), but was shown to not only have pre- and post-zygotic reproductive isolation from its sister species, but also quantitative differences in its cuticular hydrocarbon profile.

Chemical mimicry and chemical camouflage

Some parasitic arthropods are known to mimic the cuticular hydrocarbon profile of their host to avoid recognition and attack by the host species. The ant mimic spider, Cosmophasis bitaeniata, absorbs the cuticular hydrocarbons of its host ant species by feeding on the ant larvae . Another example is the use of host cuticular hydrocarbons by the parasitic cuckoo wasp, (Chrysis viridula), which mimics its host, the European beewolf (Philantus triangulum) in order to gain access to the beewolf’s nest and larval food supplies. A recent study showed that although beewolves could visually recognize a cuckoo wasp outside the nest and behave aggressively towards it, they did not recognize chemical traces of the cuckoo wasp inside the dark nest. Extracts of the cuticular hydrocarbon profile of cuckoo wasps showed similar composition to the profile of the beewolf host.

Cuticular hydrocarbons have also been shown to be used by insects as a chemical camouflage to escape from predators, such as ants, as is the case of larvae of the Ithomiini butterfly Mechanitis polymnia which show a similar profile as their host plant, Solanum tabacifolium. This similarity in profile was shown to protect larvae from predation by carpenter ants. Predation increased, however, when larvae were transferred to a different species of host plant and were thus no longer camouflaged. In another case, the honeydew-producing treehopper, Guayaquila xiphias, was shown to have the same CHC profile as its host plant Schefflera vinosa, which protects it from being attacked by the ants that normally feed on the honeydew and protect the treehoppers from other attackers. When moved to a different, non-host plant, the treehoppers were recognized as prey and readily attacked by the tending ants.

Applications in forensic studies

Cuticular hydrocarbons have also been shown to be useful for forensic entomology. Individuals of 3 different Calliphoridae flies were shown to have different cuticular hydrocarbon profiles according to their developmental stage (larvae, pupae and adult) which could distinguish age differences of one day between stages and could aid in forensics .