ABSTRACT
Postmortem interval estimations can be complicated by the inter-individual variation present in human decomposition. Forensic entomologists may especially face challenges interpreting arthropod evidence in scenarios that are not "by the book", or that vary in unexpected ways. Therefore, it is important to report instances where blow fly colonization does not align with expected soft tissue decomposition as blow fly larvae are often used to produce a time of colonization (TOC) estimation to infer a minimum PMI. We followed the decomposition and blow fly activity of three human donors at the Anthropology Research Facility (University of Tennessee). Delayed oviposition occurred on one donor 115 d post-placement, whereas two donors experienced blow fly re-colonization after cessation of the consumption phase, one 22 d and one more than 200 d after blow fly larvae were last observed. A null hypothesis model tested whether the entomological TOC and anthropological total body score (TBS) estimations encompassed the time of placement (TOP) for each donor. While the null hypothesis was rejected for all TOC estimations, it could not be rejected for the TBS estimations. We discuss how the non-linear nature of human decomposition can pose challenges to interpreting blow fly evidence and suggest that forensic entomology practitioners should recognize these limitations in both research endeavors and applied casework.
ABSTRACT
To have large numbers of replicates in forensic entomology research, it is often necessary to freeze carcasses and thaw them before use in experiments. Research on the effects of freezing on decomposition is minimal in the literature and the effect that it has on insect (e.g., blow fly, beetle) activity is virtually unknown. The objective of this study was to compare the differences in insect activity occurring on refrigerated only versus frozen-thawed pig carcasses, and to characterize the associated dipteran fauna. Seven pigs, frozen for 2 mo and then thawed before the experiment, were compared with seven pigs killed and stored in a walk in refrigerator approximately 12 h before the start of the experiment. No significant differences in time to the appearance of adult flies, eggs, larvae, or the initiation and conclusion of larval migration were observed between refrigerated only and frozen-thawed pig carcasses. Beetles from the family Staphylinidae also did not show a significant difference in arrival times. Phormia regina (Meigen), Lucilia coeruleiviridis (Macquart), Cochliomyia macellaria (F.), Pollenia rudis (F.), and Hydrotaea leucostoma (F.) comprised the dipteran taxa present on the carcasses. Results suggest that freezing pigs before exposure in the field does not significantly alter blow fly life events or the appearance of staphylinid beetles.
