Pigs vs people: the use of pigs as analogues for humans in forensic entomology and taphonomy research.

Most studies of decomposition in forensic entomology and taphonomy have used non-human cadavers. Following the recommendation of using domestic pig cadavers as analogues for humans in forensic entomology in the 1980s, pigs became the most frequently used model cadavers in forensic sciences. They have shaped our understanding of how large vertebrate cadavers decompose in, for example, various environments, seasons and after various ante- or postmortem cadaver modifications. They have also been used to demonstrate the feasibility of several new or well-established forensic techniques. The advent of outdoor human taphonomy facilities enabled experimental comparisons of decomposition between pig and human cadavers. Recent comparisons challenged the pig-as-analogue claim in entomology and taphonomy research. In this review, we discuss in a broad methodological context the advantages and disadvantages of pig and human cadavers for forensic research and rebut the critique of pigs as analogues for humans. We conclude that experiments using human cadaver analogues (i.e. pig carcasses) are easier to replicate and more practical for controlling confounding factors than studies based solely on humans and, therefore, are likely to remain our primary epistemic source of forensic knowledge for the immediate future. We supplement these considerations with new guidelines for model cadaver choice in forensic science research.

Sampling flies or sampling flaws? Experimental design and inference strength in forensic entomology.

Forensic entomology is an inferential science because postmortem interval estimates are based on the extrapolation of results obtained in field or laboratory settings. Although enormous gains in scientific understanding and methodological practice have been made in forensic entomology over the last few decades, a majority of the field studies we reviewed do not meet the standards for inference, which are 1) adequate replication, 2) independence of experimental units, and 3) experimental conditions that capture a representative range of natural variability. Using a mock case-study approach, we identify design flaws in field and lab experiments and suggest methodological solutions for increasing inference strength that can inform future casework. Suggestions for improving data reporting in future field studies are also proposed.

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.

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.

Designing Standardized and Optimized Surveys to Assess Invertebrate Biodiversity in Tropical Irrigated Rice Using Structured Inventory and Species Richness Models.

Insect pest management depends on simple, rapid, and reliable sampling methods that should also be standardized and optimized. We tested structured inventory, community characterization, and sampling optimization approaches on the invertebrate fauna of Philippine irrigated rice, undisrupted by pesticides, using seven field methods and species richness models. Canopy and floodwater invertebrates were intensively and repetitively sampled from 600 quadrats (∼0.1-m(2) planar area) over dry and wet cropping seasons in one field at the International Rice Research Institute in the Philippines. In the canopy, pooled counts from D-Vac and plant dissections (PD) on the same rice hills ("absolute methodology") were compared with three other methods (i.e., FARMCOP, Blower-Vac, sweep-net), while, in the floodwater, the area collector ("absolute methodology") was compared with three other methods (i.e., FARMCOP, Blower-Vac, strainer-net). Overall, 25 and 50% of the observed richness of canopy and floodwater taxa, respectively, were caught by all four methods. Estimated inventory completeness for the canopy and floodwater averaged 82 and 98%, respectively, after all methods were pooled. To maximize observed richness, optimization results for the canopy recommended allocating the highest sampling effort to D-Vac and PD, followed by the Blower-Vac, whereas the area collector should be assigned the highest sampling effort in the floodwater, followed by the strainer-net or Blower-Vac. Our results suggest that structured inventory and species richness models are useful tools for setting optimization criteria and stopping rules for sampling crop-invertebrate assemblages based on inventory completeness and for enabling more informative biodiversity comparisons.

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.

REWRITING ECOLOGICAL SUCCESSION HISTORY: DID CARRION ECOLOGISTS GET THERE FIRST?

Ecological succession is arguably the most enduring contribution of plant ecologists and its origins have never been contested. However, we show that French entomologist Pierre Mégnin, while collaborating with medical examiners in the late 1800s, advanced the first formal definition and testable mechanism of ecological succession. This discovery gave birth to the twin disciplines of carrion ecology and forensic entomology. As a novel case of multiple independent discovery, we chronicle how the disciplines of plant and carrion ecology (including forensic entomology) accumulated strikingly similar parallel histories and contributions. In the 1900s, the two groups diverged in methodology and purpose, with carrion ecologists and forensic entomologists focusing mostly on case reports and observational studies instead of hypothesis testing. Momentum is currently growing, however, to develop the ecological framework of forensic entomology and advance carrion ecology theory. Researchers are recognizing the potential of carcasses as subjects for testing not only succession mechanisms (without assuming space-for-time substitution), but also aggregation and coexistence models, diversity-ecosystem function relationships, and the dynamics of pulsed resources. By comparing the contributions of plant and carrion ecologists, we hope to stimulate future crossover research that leads to a general theory of ecological succession.

Effects of Bacillus thuringiensis on non-target herbivore and natural enemy assemblages in tropical irrigated rice.

Endotoxins from Bacillus thuringiensis (Bt) produced in transgenic pest-resistant Bt crops are generally not toxic to predatory and parasitic arthropods. However, elimination of Bt-susceptible prey and hosts in Bt crops could reduce predator and parasitoid abundance and thereby disrupt biological control of other herbivorous pests. Here we report results of a field study evaluating the effects of Bt sprays on non-target terrestrial herbivore and natural enemy assemblages from three rice (Oryza sativa L.) fields on Luzon Island, Philippines. Because of restrictions on field-testing of transgenic rice, Bt sprays were used to remove foliage-feeding lepidopteran larvae that would be targeted by Bt rice. Data from a 546-taxa Philippines-wide food web, matched abundance plots, species accumulation curves, time-series analysis, and ecostatistical tests for species richness and ranked abundance were used to compare different subsets of non-target herbivores, predators, and parasitoids in Bt sprayed and water-sprayed (control) plots. For whole communities of terrestrial predators and parasitoids, Bt sprays altered parasitoid richness in 3 of 3 sites and predator richness in 1 of 3 sites, as measured by rarefaction (in half of these cases, richness was greater in Bt plots), while Spearman tests on ranked abundances showed that correlations, although significantly positive between all treatment pairs, were stronger for predators than for parasitoids, suggesting that parasitoid complexes may have been more sensitive than predators to the effects of Bt sprays. Species accumulation curves and time-series analyses of population trends revealed no evidence that Bt sprays altered the overall buildup of predator or parasitoid communities or population trajectories of non-target herbivores (planthoppers and leafhoppers) nor was evidence found for bottom-up effects in total abundances of non-target species identified in the food web from the addition of spores in the Bt spray formulation. When the same methods were applied to natural enemies (predators and parasitoids) of foliage-feeding lepidopteran and non-lepidopteran (homopteran, hemipteran and dipteran) herbivores, significant differences between treatments were detected in 7 of 12 cases. However, no treatment differences were found in mean abundances of these natural enemies, either in time-series plots or in total (seasonal) abundance. Analysis of guild-level trajectories revealed population behavior and treatment differences that could not be predicted in whole-community studies of predators and parasitoids. A more conclusive test of the impact of Bt rice will require field experiments with transgenic plants, conducted in a range of Asian environments, and over multiple cropping seasons.