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 compound to reduce microbially derived volatiles, and (2) a specific additive method, placing chemical supplements near a fresh carcass. Five sulfur-containing compounds, known to result from bacterial metabolism of sulfur-containing amino acids, were studied: dimethyl sulfide (DMS), dimethyl disulfide (DMDS), dimethyl trisulfide (DMTS), methyl thiolacetate (MeSAc, also known as S-methyl thioacetate), and methyl thiocyanate (MeSCN). When a carcass aged for 48 h was treated with an antibacterial compound to reduce volatiles, there was a 59% decrease in beetles discovering the resource. The addition of the chemical supplement MeSAc 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, increased beetle numbers by 200–800% on a fresh carcass and almost guaranteed 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.