Chemical signals inducing attraction and alarm in European Reticulitermes termites (Isoptera, Rhinotermitidae)

Chemical signals causing attraction and alarm in four European subterranean termite species of the genus Reticulitermes (R. santonensis, R. lucifugus, R. grassei, R. banyulensis) were investigated. Natural extracts and isolated compounds from workers and soldiers were offered as odor source in a petri dish to groups of termites, and their behavioral reaction was registered. Pentane extracts of whole workers were attractive, and in three of the species induced a slight alarm reaction. The extracts contained 3-octanone, 3-octanol, and six fatty acids (C14-C18), presumably originating from the cuticle. Species-specific differences were quantitative. When tested individually or as synthetic mixture the worker compounds were significantly less effective than the natural extract. Only the ketone, the alcohol, and one of the fatty acids had any effect, functioning predominantly as attractants. Reticulitermes soldiers possess a frontal gland, which is employed for chemical defense of the colony, and contains species-specific mixtures of terpenes: monoterpenes, sesquiterpenes, diterpene alcohols, and a sesterterpene. All compounds of the frontal gland secretions proved to be highly attractive to the respective species, acting significantly stronger than worker compounds. The minor volatile compounds, the mono- and sesquiterpenes, function as alarm pheromone in Reticulitermes: they were the most attractive components, and also the ones inducing an intense alarm reaction in both workers and soldiers.