Chitin digestion in a eusocial insect: the digestive role of larvae in hornet colonies

Chitin is the primary component of the arthropod exoskeleton and one of the most abundant polysaccharides occurring in nature. Many animals possess chitinases, the enzymes able to digest chitin. However, the role of ingested chitin in animal nutrition is unclear and often contested, as in vivo evidence of chitin metabolization is lacking. Here, we used real-time respiratory stable isotope analysis, a non-invasive methodology, to test in vivo chitin digestion and metabolism by an insectivorous social insect, the Oriental hornet (Vespa orientalis). Adult and larva hornets were fed for three days with 13C-labeled chitin, and the delta 13CO2 in their respiration was measured individually. We found labeled carbon in the respiration of larvae but not in that of adult hornets, demonstrating that only the larvae can metabolize ingested chitin. Vespid larvae have been suggested to function as a digestive caste, since the ability of adults to digest protein is limited. We now confirm this role also for chitin, another complex biopolymer. To the best of our knowledge, this is the first report of in vivo digestion of chitin in insects.