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

Abstract

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.