A blow fly (Diptera: Calliphoridae) pre-colonization interval dataset for improving forensic entomology estimations

Forensic entomology currently represents a precise and accurate approach for estimating the minimum postmortem interval (PMI_MIN) in medicolegal death investigations. However, this field would greatly benefit from baseline data regarding the early stages of body exposure before insects arrive (the pre-colonization interval or pre-CI) to further refine PMI_MIN estimations. The goal of this project was to generate a human-specific pre-CI baseline dataset covering a range of ambient temperatures. Donated human remains (N = 62) were placed at the University of Tennessee Anthropology Research Facility across all seasons over a 3-year period and allowed to be colonized naturally by local blow flies. Initial oviposition events were recorded, and insect eggs from a subset of donors were reared for species identification. Ten donors were randomly selected to constitute the first validation cohort, using the remaining 52 donors as the training dataset. A second validation cohort consisted of 13 additional donors with unknown pre-CI data. The most important pre-CI predictors were statistically grouped, and a 95% confidence interval was determined. Minimum temperature was found to be a statistically significant predictor of the pre-CI (p = 0.000, R² = 0.608), and the pre-CI dataset produced accurate estimations for samples collected above a minimum daily temperature of 22°C. The addition of the pre-CI to larval age estimations significantly improved estimation accuracy (χ = 106.19, df = 4, p < 0.001). The generation of an error rate for this time interval aligns with the recommendations for strengthening forensic science set forth by the National Research Council.