Assessment of Decomposition Studies Indicates Need for Standardized and Repeatable Research Methods in Forensic Entomology

Abstract

The National Research Council (NRC) released a report in 2009 discussing the “science” used in forensics. Specifically, the report outlined concerns regarding the state of the forensic sciences and what was needed to raise the level of rigor and reliability of these fields in a court of law. In response to this NRC document, the present paper examined several parameters used in decomposition studies that have implications for forensic entomology. Specifically, this analysis was conducted to determine the degree of repeatability in methods across studies as related to general conclusions drawn in court, entomology and forensic investigations. Forensic entomologists primarily analyze insect evidence recovered from decomposing remains to estimate a portion of the Period of Insect Activity (PIA), which encompasses the time of colonization, to infer a minimum Postmortem Interval (PMI). One method utilized by entomologists relies on succession data from published studies to generate estimates of the minimum PMI of a decedent. For this article, approximately 75 publications on arthropod succession on vertebrate carrion were reviewed for 13 criteria that are known to play instrumental roles in governing this process: 1) animal model, 2) time of actual death, 3) euthanasia method, 4) storage method, 5) storage time, 6) time of removal from storage to placement in the field, 7) time of day remains placed in the field, 8) catalog of arthropods associated with the remains over time 9) time of initial insect contact, 10) time of initial colonization (i.e., arthropod offspring located on the remains), 11) study site, 12) number of replicate carcasses and 13) months and season of study. These criteria were selected as they can directly impact arthropod colonization and succession patterns on vertebrate carrion and are easily recorded. Data indicated that such information is highly fragmented, and that key criteria necessary to repeat studies (a core principle of the scientific method) are often lacking in the published literature. As an example, among the studies included in this analysis, we could not find significant associations between arthropod taxa richness and carcass model or carcass size. In the case of carcass size, island biogeography theory predicts that larger areas/resources will hold higher diversity. We suspect that the high degree of reporting variability in taxonomic resolution and taxa-specific study focus precluded such relationships that have been reported for other disciplines of biology. Consequently, we suggest that, to date, because of these issues there has not been a comprehensive analysis (e.g., meta-analysis) to provide general inference of arthropod succession patterns on carrion to predict a minimum PMI. In order to begin standardizing such studies, we suggest that future research endeavors examining arthropod succession on carrion record detailed data for all of the suggested criteria. Doing so can result in data amassed over time for use in comprehensive and strong meta-analyses. Such results could allow for greater appreciation of variation associated with arthropod succession on carrion.