Using Stable Nitrogen Isotope Ratios from Human Skeletal Muscle Tissue for Postmortem Interval (PMI) Estimation (Part 2)

ABSTRACT: Fly larvae were analyzed for stable nitrogen isotope analysis (δ15N) to test if values can be used to predict season of death/decomposition as a first step in developing a robust quantitative method for postmortem interval (PMI) estimation. This is the first study to analyze δ15N values from blow flies (BF) (Ditera, Calliphoridae: Lucilia coeruleiviridis, Calliphora vicina, Calliphora vomitoria, Chrysoma rufifaces) and black soldier flies (BSF) (Diptera, Stratiomyidae: Hermetia illucens) to estimate seasonal PMI in eastern Tennessee. This study is part of a larger project seeking to expand stable isotope methods utilized in forensic anthropology to move beyond questions of geolocation and diet. When BF and BSF δ15N values are used to predict season of placement at the University of Tennessee Anthropology Research Facility, the BF δ15N values only have an overall accuracy rate of 38.4%, while the BSF δ15N values perform better with an overall accuracy rate of 72.6%. Based on the seasonal distribution of BSF δ15N values, it is our recommendation that only δ15N values from BSF be used as a general indicator of winter versus summer placement when values are above 30‰ versus below 18‰, respectively. Analysis of δ15N values in fly larvae is promising as a quantitative PMI estimation method, but further research is needed.