Chemical transformation of Quercus wood by Cetonia larvae (Coleoptera: Cetoniidae): An improvement of carbon and nitrogen available in saproxylic environments

Chemical changes to Quercus wood caused by the larvae of the saproxylic beetle Cetonia aurataeformis have been evaluated using elemental analysis, thermal analysis, infrared spectroscopy and nuclear magnetic resonance. Faeces of C. aurataeformis from Quercus rotundifolia tree hollows and faeces of larval C. aurataeformis reared under laboratory conditions were collected and analysed. The results suggest that larval C. aurataeformis are able to decompose the polysaccharides in Q. rotundifolia wood, producing a residue with higher concentration of N and P, and organic structures with different stability than those found in wood. The higher N and P concentrations and the reduction of the particle size would facilitate the activity of decomposing microorganisms on C. aurataeformis faeces. The comparison of the faeces from tree hollows with those from the larvae reared in the laboratory revealed that both N and P concentrations and the stability of organic structures in the region of lignin increased with the amount of time that faeces were in Q. rotundifolia hollows, while the stability of the organic structures in the polysaccharides region decreased. The lower stability of organic compounds in faeces gives rise to an increase of soluble organic matter with higher N concentration than that solubilised from the wood the beetles feed on. Moreover, faeces collected in Q. rotundifolia hollows showed the highest values of humification and aromaticity, determined by the spectroscopic indices of soluble organic matter, highlighting the action of this cetonid in the carbon and nitrogen cycle in saproxylic environments.