Finding A Fresh Carcass: Bacterially-Derived Volatiles And Burying Beetle Search Success

Abstract

When burying beetles first emerge as adults, they search for well-rotted carcasses with fly maggots on which to feed. After attaining reproductive competence, they switch their search and respond to a small, fresh carcass to prepare for their brood. Because the cues used to locate a feeding versus a breeding resource both originate from carrion, the beetles must respond to subtle changes in volatiles during decomposition. We investigated cues used to locate a fresh carcass in the field by (1) a general subtractive method, applying an antibacterial or antifungal to reduce volatiles, and (2) a specific additive method, placing chemicals near a fresh carcass. Five sulfur-containing compounds were studied: dimethyl sulfide (DMS), dimethyl disulfide (DMDS), dimethyl trisulfide (DMTS), methyl thiolacetate (MeSAc) and methyl thiocyanate (MeSCN). For the sulfides, we predicted that DMS would be the most attractive and DMTS the least attractive because of differences in the timing of peak production. We made no a priori predictions for MeSAc and MeSCN. Antibacterial treatment of a carcass aged for 48 h resulted in a 59% decrease in beetles discovering the resource. The addition of MsSAc had no effect on discovery of a fresh carcass, while DMS and DMDS had a limited ability to attract breeding beetles. The chemical that was least well known, MeSCN, had a remarkable effect, increasing beetle numbers by 200-800% on a fresh carcass and almost guaranteeing discovery. DMTS, which is known to attract a variety of carrion insects, was the only compound to significantly reduce beetle presence at a fresh carcass. A laboratory experiment demonstrated that DMTS does not directly inhibit breeding, suggesting that DMTS deters breeding beetles while they fly.