Cuticular hydrocarbon sensillum for nestmate recognition in ants

Ants carry colony-specific blends of cuticular hydrocarbons (CHCs) on their exoskeleton as nestmate-discriminative pheromones and use them for social communication. To discriminate between such colony-specific blends of CHCs, Japanese carpenter ant workers, Camponotus japonicus, have a particular type of sensillum that responds to non-nestmate CHC mixtures but not to a nestmate’s mixture. Once a worker ant detects non-nestmate blends of CHCs, its behavior changes drastically to aggression. Olfactory sensing of water-insoluble compounds like CHCs is mediated by lipophilic ligand carrier proteins. In the receptor lymph of insect chemosensilla those proteins have been discovered and categorized into the pheromone- and the general odorant-binding protein families, or the chemosensory protein family. These molecules are key in bridging chemical ecology and chemosensory physiology in insects, and are believed to be indispensable for the perireceptor event of not only olfactory but also gustatory systems concerned with feeding or mating. Their structure-function relationships have so far been studied in moths, fruit flies and other insects. CjapCSP, the chemosensory protein found in C. japonicus CHC sensilla, is thought to introduce CHCs into the receptor lymph at the same mixing ratio at which they originally occur and to pass them on to the olfactory receptor neurons, which selectively respond to non-nestmate CHCs.