Recovery of male DNA acquired from carrion-feeding insects in a simulated sexual assault scenario

When bodies of sexual assault victims are discovered in advanced stages of decomposition, the recovery of direct DNA evidence is often compromised, posing a challenge in criminal investigations. This study aimed to determine insect colonization and succession patterns on pig carcasses inoculated with semen and to assess the feasibility of recovering Y-chromosomal short tandem repeat (Y-STR) DNA from fly larvae, fly pupae, and beetles. Three female pigs were used as models to simulate sexual homicide scenarios, and an indoor control experiment using chicken livers mixed with 3 mL of semen was also conducted. Larvae and pupae were collected throughout the decomposition process, with crop/gut contents dissected for DNA extraction using the phenol-chloroform method. DNA concentrations were quantified by qPCR, and Y-STR profiling was attempted using the Yfiler™ Plus kit. In the field experiment, colonization by species from the families Calliphoridae, Sarcophagidae, Muscidae, Silphidae, Dermestidae, and Cleridae followed typical succession patterns, although arrival times varied between carcasses, with higher activity observed on semen-inoculated pigs. Larvae from the indoor experiment yielded quantifiable male DNA and produced complete Y-STR profiles at early time points (24-48 h), with partial profiles thereafter (72-96 h). In contrast, larvae from the field experiment contained only 1-3 pg. of male DNA, insufficient for profiling. These findings demonstrate that insect crop contents can preserve male DNA and occasionally yield usable Y-STR data; however, DNA quantities are often too low for successful profiling. Future studies should therefore incorporate additional genetic markers alongside conventional Y-STRs to enable profiling from degraded DNA.