Secretion-grooming in aquatic beetles (Hydradephaga): A chemical protection against contamination of the hydrofuge respiratory region

Summary All Hydradephaga investigated so far crawl onto land when exposed to an increase in water temperature and light intensity and spread the secretion from their pygidial glands over the body surface (secretion-grooming). The secretions have antimicrobial properties and are mainly applied to hydrofuge body regions important for aquatic respiration. Experimental prevention of secretion-grooming leads to the loss of the respiratory air bubble and a significant increase in mortality. These findings support the view that the secretion-grooming of adephagous aquatic beetles, like in some aquatic Heteroptera, inhibits the growth of microor-ganisms, thus preventing the contamination and wetting of the cuticular respiratory structures. Thus it keeps functional the air-retaining hydrophobous body regions essential for aquatic respiration. A model is presented on how secretion-grooming may have evolved in the Hydradephaga. Other possible functions of the pygidial gland secretions are discussed.