Neal H. Haskell

Using Accumulated Degree-Days to Estimate the Postmortem Interval from Decomposed Human Remains

Forensic anthropologists often rely on the state of decomposition to estimate the postmortem interval (PMI) in a human remains case. The state of decomposition can provide much information about the PMI, especially when decomposition is treated as a semi-continuous variable and used in conjunction with accumulated-degree-days (ADD). This preliminary study demonstrates a supplemental method of determining the PMI based on scoring decomposition using a point-based system and taking into account temperatures in which the remains were exposed. This project was designed to examine the ways that forensic anthropologists could improve their PMI estimates based on decomposition by using a more quantitative approach. A total of 68 human remains cases with a known date of death were scored for decomposition and a regression equation was calculated to predict ADD from decomposition score. ADD accounts for approximately 80% of the variation in decomposition. This study indicates that decomposition is best modeled as dependent on accumulated temperature, not just time.

Comparative Performance and Complementarity of Four Sampling Methods and Arthropod Preference Tests from Human and Porcine Remains at the Forensic Anthropology Center in Knoxville, Tennessee

Abstract Comparative performance and complementarity tests of four arthropod sampling methods (aerial netting, hand collection, pitfall traps, and sticky traps), used by forensic entomologists in death investigations, training workshops, and research trials, were conducted from simultaneously placed human and porcine subjects inside the Forensic Anthropology Center at the University of Tennessee, Knoxville, TN. A secondary aim investigated the widely held claim that pig carcasses are reliable surrogates for human corpses. Over a 35-d period in summer 1989, >72,000 invertebrates from three subjects (one human, two pigs) were sampled of which 93% were members of the forensically important (FI) fauna. Performance tests revealed that hand collections, when performed by an experienced forensic entomologist, consistently yielded the largest fraction of FI arthropods from the total invertebrate catch, followed by aerial netting, sticky traps, and pitfall traps, regardless of subject. Pitfall traps and hand collections were broadly effective at sampling both fly and beetle populations, whereas aerial netting and sticky traps mostly targeted flies. The best two-method combination, based on the highest combined catches of FI taxa, were hand collections and pitfall traps, regardless of subject. Between-subject comparisons revealed negligible preference by FI arthropods for human over pig remains. Insofar as our limited comparisons allow with only three study subjects, these results validated the concept of transferability of “best practices” from one subject to another and confirmed the claim that pig carcasses (of 23–27-kg starting mass) can substitute for human corpses in research and training programs, at least for summer-exposed and unconcealed remains in the first 5 wk postmortem.

Carcass Enrichment Does Not Alter Decay Rates or Arthropod Community Structure: A Test of the Arthropod Saturation Hypothesis at the Anthropology Research Facility in Knoxville, Tennessee

Abstract In a test of an arthropod saturation hypothesis, we asked if the 30-yr history of carcass enrichment at the Anthropology Research Facility, Knoxville TN, has altered carcass decay rates or community structure of sarcosaprophagous arthropods, compared with three local nonenriched sites. Over a 12-d period in 1998, using pitfall traps and sweep nets, we sampled a total of 81,000 invertebrates from freshly euthanized pigs (Sus scrofa L.) placed in these sites. From this number, we sorted 69,286 forensically important (sarcosaprophagous) arthropods. The community structure of these organisms, as measured by species and individuals accumulation curves, rarefaction, and nonparametric correlation, was comparable in all four sites in taxonomic similarity, colonization rates, aerial species richness, and ranked abundances of forensically important taxa on a per carcass basis. Measures of carcass decay rate, remaining carcass weight (%) and periodic weight loss, also were similar. In most cases, carcass surface temperatures and maggot mass temperatures were also statistically indistinguishable. Probability-based results and posthoc power analyses of these variables led us to conclude that the sarcosaprophagous arthropod community of the Anthropology Research Facility is representative of surrounding sites.

Evaluating the utility of hexapod species for calculating a confidence interval about a succession based postmortem interval estimate

Carrion insect succession patterns have long been used to estimate the postmortem interval (PMI) during a death investigation. However, no published carrion succession study included sufficient replication to calculate a confidence interval about a PMI estimate based on occurrence data. We exposed 53 pig carcasses (16±2.5 kg), near the likely minimum needed for such statistical analysis, at a site in north-central Indiana, USA, over three consecutive summer seasons. Insects and Collembola were sampled daily from each carcass for a total of 14 days, by this time each was skeletonized. The criteria for judging a life stage of a given species to be potentially useful for succession-based PMI estimation were (1) nonreoccurrence (observed during a single period of presence on a corpse), and (2) found in a sufficiently large proportion of carcasses to support a PMI confidence interval. For this data set that proportion threshold is 45/53. Of the 266 species collected and identified, none was nonreoccuring in that each showed at least a gap of one day on a single carcass. If the definition of nonreoccurrence is relaxed to include such a single one-day gap the larval forms of Necrophilaamericana, Fanniascalaris, Cochliomyia macellaria, Phormiaregina, and Luciliaillustris satisfied these two criteria. Adults of Creophilus maxillosus, Necrobiaruficollis, and Necrodessurinamensis were common and showed only a few, single-day gaps in occurrence. C.maxillosus, P.regina, and L.illustris displayed exceptional forensic utility in that they were observed on every carcass. Although these observations were made at a single site during one season of the year, the species we found to be useful have large geographic ranges. We suggest that future carrion insect succession research focus only on a limited set of species with high potential forensic utility so as to reduce sample effort per carcass and thereby enable increased experimental replication.

Does carcass enrichment alter community structure of predaceous and parasitic arthropods? A second test of the arthropod saturation hypothesis at the Anthropology Research Facility in Knoxville, Tennessee.

In a second test of an arthropod saturation hypothesis, we analyzed if the on-campus Anthropology Research Facility (ARF) at the University of Tennessee, Knoxville, with its 20+ yr history of carcass enrichment, is comparable to non-enriched sites in community structure of predatory and parasitic arthropods that prey upon the sarcosaprophagous fauna. Over a 12-day period in June 1998, using pitfall traps and sweep nets, 10,065 predaceous, parasitic, and hematophagous (blood-feeding) arthropods were collected from freshly euthanized pigs (Sus scrofa L.) placed at ARF and at three surrounding sites various distances away (S2-S4). The community structure of these organisms was comparable in most paired-site tests with respect to species composition, colonization rates, and evenness of pitfall-trap abundances on a per carcass basis. Site differences were found in rarefaction tests of both sweep-net and pitfall-trap taxa and in tests of taxonomic evenness and ranked abundances of sweep-net samples. Despite these differences, no evidence was found that the predatory/parasitic fauna at ARF was impoverished with fewer but larger populations as a result of carcass enrichment. Comparison of the sarcosaprophagous and predatory/parasitic faunas revealed a tighter (and more predictable) linkage between carrion feeders (sarcosaprovores) and their carrion than between carrion feeders and their natural enemies (predators and parasitoids), leading us to conclude that ARF is more representative of surrounding sites with respect to the sarcosaprovore component than to the predatory/parasitic component within the larger carrion-arthropod community.

Chrysomya rufifacies (Macquart) (Diptera: Calliphoridae) established in the vicinity of Knoxville, Tennessee, USA.

The hairy maggot blow fly, Chrsomya rufifacies (Macquart) (Diptera: Calliphoridae) was collected in large numbers as both adults and immatures in the Knoxville, Tennessee, area during 1998 and is likely established there. The distribution of this species in the Old World, isothermal data, and its collection from mid-Michigan during 1998 suggest that it will eventually occupy most of the U.S. The forensic importance of C. rufifacies makes it probable that it will factor into an increasing number of medicolegal cases, but the expanding distribution of this species decreases its utility as a geographic indicator when postmortem movement of decedents is suspected.

Commonly Used Intercarcass Distances Appear to Be Sufficient to Ensure Independence of Carrion Insect Succession Pattern

Abstract Forensic entomology field researchers have typically placed experimental carcasses ≤50 m apart. Direct observations indicate that this intercarcass distance sufficiently prevents cross contamination by crawling larvae, but seems insufficient to prevent highly mobile adult insects from detecting or visiting more than one carcass. It would be valuable if minimum intercarcass distance ensured independence of replicates, because this is an assumption of common statistical analyses. For 32 domestic pig carcasses exposed during two consecutive summers (range of intercarcass distance 30 to >300 m), possible relationships between: 1) average distance to another carcass and aspects of the succession patterns of forensically important species and 2) intercarcass distance and community similarity indices were estimated with regression analyses. In addition, minimum intercarcass distance was investigated through semivariogram analyses of aspects of the succession interval as well as community similarity indices. Pairwise similarity of time to first occurrence was the only variable that displayed a consistent, in this case negative, relationship to intercarcass distance, although not statistically significant for any single analysis. Semivariogram analysis suggested that under the conditions used for our experiment commonly used intercarcass distances are satisfactory to ensure independence of carcasses.