Metabolomic profiling upon external digestion in larvae of diving beetles: Cybister Curtis, 1827, Dytiscus Linnaeus, 1758, and Hydaticus Leach, 1817 (Coleoptera: Dytiscidae)

Abstract The SDS–PAGE analysis of prey animals (fly larvae) during external digestion by aquatic predators, the larvae of selected species in dytiscid genera, showed a major component of protein with a molecular weight of ca. 20 kDa. In addition, the analysis of third instar larvae of Cybister brevis Aubé, 1838, by nanoLC–ESI–Q-TOF/MS/MS revealed that the digested body fluid includes a polypeptide with a sequence of 97 amino acids corresponding to hemocyanin N (51% matched by Mascot and BLAST searches) and hemocyanin M (12% matched) derived from flies. We also found evidence indicating that beetle larvae repeatedly release digestive enzymes at least twice while consuming the fly bodies. These results suggest that the digested polypeptides were derived from ubiquitous high molecular substances such as arylphorin subunit C223 precursor included in the body fluid of the fly (Calliphora vicina Robineau-Desvoidy, 1830) that were produced during external digestion by diving beetle larvae.