Does the presence of Ethanol and Flunitrazepam (Rohypnol®) influence the attractiveness of scavenger insects to carcasses? A pilot study in an Atlantic Forest fragment

Flunitrazepam and ethanol are frequently involved in crimes, although studies investigating the effects of pretreatment with both substances on the attractiveness of vertebrate carcasses to necrophagous insects are scarce. In this study, we aimed to investigate the effect of ethanol, flunitrazepam and its combined action on the composition and structure of assemblies of visiting dipterans, as well as on the succession pattern of cadaverous fauna that can assist on forensic investigations. For that, 32 female Wistar rats were equally divided into groups: water (control), ethanol (21 days, only source of fluids), flunitrazepam (single dose, oral route, 2 mg/Kg) and ethanol (21 days, only source of fluids) plus flunitrazepam (single dose, 2 mg/Kg). Animals carcasses were placed in 32 traps set within a protected area and the visiting insects were monitored and collected for five consecutive days. A total of 3,165 necrophagous dipteran from the families Calliphoridae (61.7%), Fanniidae (10.5%), Sarcophagidae (10.4%), Anthomyiidae (4.0%), Muscidae (2.2%), Phoridae (0.9%) were collected. The highest rate of insect’s attraction was observed in the ethanol plus flunitrazepam combined treatment (44.3% of specimens), compared with the ethanol (20.8%) and flunitrazepam (15.0%) treatments, and control groups (19.7%). The composition and structure of the assemblies are more similar in carcasses with ethanol. Besides, the presence of ethanol and combined treatment altered the pattern of insect’s succession. These results indicate that the combined use of both rape-related substances increases the attractiveness of carcasses for insects, which could be a crucial entomological signal found in criminal investigations.