When entomological evidence crawls away: Phormia regina en masse larval dispersal

Forensic investigation of carcass decomposition and dipteran fly composition over the summer and winter: a comparative analysis of indoor versus outdoor at a multi-story building

This study aimed to explore the rate of decomposition of rabbit carcasses and the succession pattern of the associated dipteran flies outdoor, indoor, and on the roof of a 4-story building during the summer and winter. A total of 6,069 flies were recorded, with 30.91% reported as 2 waves outdoor and on the roof in the summer and 69.09% as 4 waves outdoor in the winter. The roof showed the most flies in the summer but the least in the winter, whereas the outdoor showed the most in the winter but the least in the summer. The ground and first floors showed the most indoor flies, while the second and third floors showed the least in both seasons. Indoor carcasses decomposed slower than those outdoor, and those on the second and third floors decomposed slower than those on the ground and first floors. Ten fly species from 8 families were identified in the winter, compared to 6 from 5 families in the summer. The most abundant species was Musca domestica Linnaeus (Muscidae) on the roof in the summer, while it was Chrysomya albiceps (Wiedemannn) (Calliphoridae) outdoor in the winter. The rare species (singletons) were Musca sp. (Muscidae) and Megaselia scalaris (Loew) (Phoridae) on the first floor in both seasons, Scaptomyza pallida (Zetterstedt) (Drosophilidae) on the ground floor in the summer, and Atherigona orientalis Schiner (Muscidae) outdoor in the winter. These data highlight the variance in carcass decomposition and fly composition across outdoor, indoor, and the roof of human dwellings, which could be of forensic importance.

A preliminary investigation of rabbit carcass decomposition and attracted ants (Hymenoptera: Formicidae) on the seaward coastal beach of Al-Jubail City, Saudi Arabia

The current study was carried out in the seaward coastal beach environment of Al-Jubail City, Saudi Arabia, to analyze the rabbit carcass decomposition process, the succession pattern of associated ants, and their potential utility in forensic investigation. Experiments were conducted over a 4-season course (from autumn 2018 to summer 2019). A total of 9 species belonging to the 2 subfamilies, Myrmicinae and Formicinae, were recorded. The myrmicine species were Crematogaster aegyptiaca Mayr, 1862; Messor ebeninus Santschi, 1927; Messor foreli Santschi, 1923; and Monomorium abeillei Andre, 1881. The formicine species were Camponotus xerxes Forel, 1904; Cataglyphis albicans (Roger, 1859); Cataglyphis hologerseniCollingwood & Agosti, 1996; Cataglyphis viaticoides (André, 1881); and Nylanderia jaegerskioeldi (Mayr, 1904). M. abeillei was the only species recorded in all 4 seasons, while M. abeillei and C. albicans were the dominant species in summer and C. aegyptiaca and C. albicans in spring. Diversity was lowest in the autumn, with only 4 species recorded. The COI gene sequences of 5 species have been successfully deposited in the GenBank database for the first time. In total, 4 carcass decomposition stages were observed, with the longest duration in winter (13 days), the shortest in summer (11 days), and in between for both autumn and spring. Most ant species were present during both decay and dry stages, while M. abeillei, C. aegyptiaca, M. ebeninus, and C. albicans were observed in all decomposition stages. These data may indicate that ants on this coastal beach showed seasonal and geographical succession patterns that could be taken into consideration in forensic investigations.

Decomposition and insect succession of pig cadavers in tents versus outdoors - A preliminary study

The pattern of insect succession and the species composition on cadavers can be influenced by several parameters, one of which is concealment. It has been previously shown for cadavers inside containers (e.g. suitcases or vehicles) or various indoor situations, that concealment can lead to a delayed arrival, altered species composition and decreased number of taxa present at the cadaver. As no data is yet available for the specific environment of tents on these processes, we placed five pig cadavers inside closed two-person tents during the summer of 2021 in a mixed forest in Germany. Five control cadavers were freely accessible for insects. To minimize disturbances, tents were only opened every fifth day over a period of 25 days for estimating the temperature profiles, insect diversity and quantification of the cadavers' decomposition using the total body score (TBS). The temperature inside the tents was only slightly elevated compared to the ambient temperature during the study. Although the tents prevented direct access of adult flies and beetles, the cadavers were colonized because the flies oviposited on the zippers and fly screens of the inner tents. However, the resulting infestation of the cadavers by fly larvae was reduced and delayed, compared to the exposed cadavers. The dominant fly species on both the tent and exposed cadavers was the blow fly Lucilia caesar. Open cadavers showed the expected decomposition patterns with large larval masses. 25 days after placement, only bones and hair remained from the exposed pigs (TBS = 32), while most of the tissue of the cadavers inside the tents was still present (TBS = 22.5) and post feeding larvae were not able to leave the tents. Regarding the attraction of beetles to both treatments, open cadavers were predominately colonized by the silphid Oiceoptoma thoracicum, while the silphid Necrodes littoralis was the most dominant species in the pitfall traps surrounding the tents. Considering the prolonged pre-appearance interval of fly larvae colonizing the cadavers inside tents, the entomological evidence of forensic cases dealing with concealed bodies should be handled with caution, since the post mortem interval might be significantly underestimated.

When the red-lined carrion beetle disrupts successional dynamics on large vertebrate carcasses

In a field study of insect colonization on domestic pig carcasses, the typical colonization sequence took a different turn midway through decomposition when Necrodes surinamensis (Fabricius) (Coleoptera: Silphidae) dramatically increased in abundance on some carcasses. This provided an opportunity to test the prediction that N. surinamensis would aggregate at clumped carcasses but not as much at dispersed carcasses, thus leaving enough resources in less heavily colonized habitat patches to support weaker competitors, as predicted by the aggregation model of coexistence. Larger aggregations of this silphine beetle resulted in the collapse of blow fly (Diptera: Calliphoridae) maggot populations due to intraguild predation, and a decline or exclusion of late-successional insect species. This phenomenon has been reported in a European Necrodes species but it is the first time it is documented with N. surinamensis, a widespread species in North America. Substantial increases in adult and larval populations of N. surinamensis were first documented on clumped carcasses and were not as pronounced on dispersed carcasses. The specifics of N. surinamensis aggregations are discussed with reference to ecological and forensic implications, including the fact that feeding by N. surinamensis larvae makes the remains appear to have been altered by scavengers and decomposing for longer than they have.

Fall Decay Deceleration in Northern Latitudes: Merely a Matter of Cold?

The decomposition of cadavers and large vertebrate carcasses is the result of complex processes primarily influenced by ambient temperatures. Thus, low temperatures can alter decomposition by curtailing tissue autolysis and bacterial decomposition, and by limiting insect activity contributing to necromass removal. In this study, we tested whether carcass decomposition rate is modulated not only directly by temperature and insect occurrence, but also indirectly by the mediation of interactions among insects by ambient temperature. To test this, a comparative analysis of the decomposition of domestic pig carcasses in summer and fall was conducted in Atlantic Canada. The results indicated that carcass decomposition standardized to account for seasonal differences was significantly decelerated in the fall as opposed to the summer during the later decomposition stages and was sometimes incomplete. Moreover, the arrival, presence, and departure of insects from carcasses during ecological succession differed between summer and fall. Necrodes surinamensis (Fabricius) (Coleoptera: Silphidae) and Creophilus maxillosus (Linnaeus) (Coleoptera: Staphylinidae) maintained higher abundances late during succession in the fall than in the summer and their abundance was related to a decline in decomposition rates, probably because these species feed on dipteran larvae promoting necromass removal. These results demonstrate the variability in response to environmental parameters of insects of forensic importance and support the idea that slowed decomposition in the fall may be exacerbated by changes in interspecific interactions among insects. Furthermore, these results suggest that successional studies of insects carried out in the summer have little forensic utility for cadavers found in cold weather conditions.

Not by the Book: Observations of Delayed Oviposition and Re-Colonization of Human Remains by Blow Flies

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.

Death in the paddy field: Carcass decomposition and associated arthropods in subunits of a rice field landscape

Although rice production landscapes are often the scene of homicides, vertebrate decomposition and associated arthropods have never been described from rice paddies. Tropical rice landscapes are typically composed of irrigated/non-irrigated rice fields, fallow land (i.e., uncultivated fields), and low earthen levees (bunds) used as access pathways. The specific microclimatic and environmental conditions associated with each subunit of rice field landscapes are likely to impact carcass decomposition as well as the arthropod species associated with carrion. Here, we tested the hypothesis that the combined effects of constraints on arthropod colonization and survival, scarcity of necromass, limited habitat architecture, and recurrent disturbance limit the ability of carrion-related arthropods to colonize corpses and large carcasses in tropical rice-fields. Our results from monitoring pig carcasses in Philippine rice fields indicated that vertebrate decomposition in irrigated fields was slower and incomplete when compared to non-irrigated fields and bunds. Carcasses were colonized by a small complex of carrion-related arthropods that differed in composition and relative species abundance between dry bunds and relatively humid rice paddies. Fire ants (Solenopsis germinata) were observed frequently on carcasses exposed on bunds, rarely in non-irrigated fields, and almost never in irrigated fields. The presence of fire ants was associated with reduced blow fly (Chrysomya megacephala) abundance. Taken together, this indicates that the arthropod fauna associated with carcasses in tropical rice fields is relatively simple in contrast to the generally high arthropod diversity reported for other ecosystems at tropical latitudes. The limited richness of the community also means that an understanding of the development of one abundant calliphorid blow fly, C. megacephala, may be sufficient to investigate deaths and homicides under conditions similar to the ones described in this study.

Is Forensic Entomology Lost in Space?

Simple Summary

Although they affect most parameters that influence insect presence and development, spatial and scale effects are not normally considered in forensic entomology. Here, we documented the spatial dynamics of an important forensic taxon, the Calliphoridae, in the Greater Moncton area of New Brunswick, Canada. Results indicated that regional aggregation patterns of Calliphoridae differed among species and that the spatial relationship between species varied between aggregation and spatial anticorrelation. Overall, this study suggests that the dynamics of forensic insects in space differ in many ways among species, highlighting the importance for forensic entomology to consider spatial effects.

Abstract

Spatial and scale effects have barely been considered in forensic entomology, despite their pervasive influence on most of the parameters affecting the development of insect larval stages and the progression of insect succession on cadavers. Here, we used smoothing/interpolation techniques and semivariograms to document the spatial dynamics of sarcosaprophageous Calliphoridae, an important forensic taxon, in the Greater Moncton area in New Brunswick, Canada. Results indicated that the spatial dynamics of Calliphoridae differed between species, some species showing strong patterns of regional aggregation while others did not. Multivariate spatial correlations indicated that interspecific relationships in space varied widely, ranging from local and large-scale aggregation to spatial anticorrelation between species. Overall, this study suggested that even within a restricted timescale, the spatial dynamics of Calliphoridae can operate at many scales, manifest in different patterns, and be attributed to multiple different causes. We stress that forensic entomology has much to benefit from the use of spatial analysis because many important forensic questions, both at the fundamental and practical levels, require a spatial solution.

Small Bait Traps May Not Accurately Reflect the Composition of Necrophagous Diptera Associated to Remains

Small bait traps are beginning to emerge in forensic entomology as a new approach to sample early-colonizing necrophagous Diptera species while reducing the investment in time and energy in obtaining information. To test the hypothesis conveyed by the literature that these traps can be a substitute for whole carcasses, we simultaneously documented the Diptera assemblages visiting and colonizing domestic pig carcasses and small traps baited with pork liver. Results indicated that Diptera species occurrence and assemblage composition in the small bait traps and on the carcasses differed, while they were similar when comparing only the pig carcasses. These results are in agreement with the literature that examined insect colonization of other decaying substrates. Although small bait traps can be useful tools to document the communities of necrophagous Diptera in a given area, we stress that caution must be exercised when extending the data obtained by these traps to courtroom proceedings.

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.

Post-feeding activity of Lucilia sericata (Diptera: Calliphoridae) on common domestic indoor surfaces and its effect on development

Developmental data of forensically important blowflies used by entomologists to estimate minimum post mortem interval (mPMI) are established under controlled laboratory conditions for various temperature ranges throughout the stages of egg, 1st-3rd instar, puparia, and adult fly emergence. However, environmental conditions may influence the patterns of development and behaviour of blowflies, potentially impacting on these established development rates. Previous studies investigating indoor colonisation have focused on the delay to oviposition, with behaviour during the post-feeding phase in this setting often overlooked. The environment in which third instar larvae disperse when searching for a pupariation site may vary drastically at both outdoor and indoor scenarios, influencing the activity and distance travelled during this phase and possibly affecting developmental rates. This study investigated the effect of eight common domestic indoor surfaces on dispersal time, distance travelled, and behaviour of post-feeding Lucilia sericata as well as any resulting variation in development. It was found that pupariation and puparia length within a pupariation medium of sawdust (often used in laboratory settings) produced comparable results with that of carpeted environments (those deemed to be 'enclosed'). Non-carpeted environments (those which were 'exposed') produced a delay to pupariation likely due to increased activity and energy expenditure in searching for pupariation sites which enabled burial. In addition, the observed speed of travel during dispersal was seen via time lapse photography to be greater within 'exposed' conditions. Larvae which dispersed upon burnt laminate flooring were observed to travel faster than in all other conditions and showed the only significant variation (P=0.04) in the day of emergence in comparison to the control condition of sawdust. This study has demonstrated that wandering phase activity is affected by the environmental surface which has potential implications for estimating both the distance travelled by dispersing larvae in indoor conditions and with further research, may be a consideration in mPMI calculations.

First record of Phormia regina (Meigen, 1826) (Diptera: Calliphoridae) from mummies at the Sant'Antonio Abate Cathedral of Castelsardo, Sardinia, Italy

The studies of insects from archaeological contexts can provide an important supplement of information to reconstruct past events, climate and environments. Furthermore, the list of the species present in an area in the past allows the reconstruction of the entomofauna on that area at that time, that can be different from the nowadays condition, providing information about biodiversity changes. In this work, the results of a funerary archaeoentomological study on samples collected from mummified corpses discovered during the restoration of the crypt of the Sant’Antonio Abate Cathedral of Castelsardo (Sardinia, Italy) are reported. The majority of the sampled specimens were Diptera puparia, whereas only few Lepidoptera cocoons and some Coleoptera fragments were isolated. Among Diptera, Calliphoridae puparia were identified as Phormia regina (Meigen, 1826) and Calliphora vicina, (Robineau-Desvoidy, 1830) both species typical of the first colonization waves of exposed bodies. Three puparia fragments were also identified as belonging to a Sarcophaga Meigen, 1826, species (Sarcophagidae). Several Muscidae puparia of the species Hydrotaea capensis (Weidmermann, 1818), a late colonizer of bodies, and typical of buried bodies were also collected. The few moth (Lepidoptera) cocoons were identified as belonging to the family Tineidae. This family comprises species feeding on dry tissues and hair typical of the later phases of the human decomposition. Among Coleoptera a single specimen in the family Histeridae, Saprinus semistriatus (Scriba, 1790) and a single elytra, potentially of a species in the family Tenebrionidae, were also collected. Overall, the samples collected indicated an initial colonization of the bodies in an exposed context, mainly in a warm season. This research allows the finding of elements indicating the presence, at least in the past, of P. regina in Sardinia. This species at the moment seems extinct from Sardinia while it is quite common in the continent.

Delayed reception of live blowfly (Calliphora vicina and Chrysomya rufifacies) larval samples: implications for minimum postmortem interval estimates

Forensic entomology evidence collected by police and mortuary staff may be delayed in getting to the entomologist. Live samples may continue developing and alter minimum postmortem interval (PMI_min) estimates. This study investigated development of simulated evidential samples of Calliphora vicina Robineau-Desvoidy and Chrysomya rufifacies (Macquart) (Diptera: Calliphoridae) maggots. Maggots of each species were studied in three developmental classes: “small” (late second/early third instar), “mid” (mid third instar) and “large” (late third instar). Seven replicates of 11 maggots in each class were assigned without food to four treatments: (1) 24 h at 20 °C; (2) 24 h at 4 °C; (3) 48 h at 20 °C and (4) 48 h at 4 °C. There was a significant difference in absolute length change across treatments, reflecting size for C. vicina, and interaction between size, time and temperature for Ch. rufifacies. Calliphora vicina maggots showed minimal mortality, and most second instar larvae moulted by the experiment's end. Chrysomya rufifacies showed heavy mortality and minimal moulting from the second to third instar. Only “large” Ch. rufifacies maggots kept at room temperature for 48 h pupariated. Since these results confirm that development can continue in live unfed maggot samples after their collection, it is not advisable to delay their preservation.

Use of necrophagous insects as evidence of cadaver relocation: myth or reality?

The use of insects as indicators of post-mortem displacement is discussed in many texts, courses and TV shows, and several studies addressing this issue have been published. Although the concept is widely cited, it is poorly understood, and only a few forensic cases have successfully applied such a method. The use of necrophagous insects as evidence of cadaver relocation actually involves a wide range of biological aspects. Distribution, microhabitat, phenology, behavioral ecology, and molecular analysis are among the research areas associated with this topic. This article provides the first review of the current knowledge and addresses the potential and limitations of different methods to evaluate their applicability. This work reveals numerous weaknesses and erroneous beliefs as well as many possibilities and research opportunities.

Predictable weathering of puparial hydrocarbons of necrophagous flies for determining the postmortem interval: a field experiment using Chrysomya rufifacies

Preadult development of necrophagous flies is commonly recognized as an accurate method for estimating the minimum postmortem interval (PMImin). However, once the PMImin exceeds the duration of preadult development, the method is less accurate. Recently, fly puparial hydrocarbons were found to significantly change with weathering time in the field, indicating their potential use for PMImin estimates. However, additional studies are required to demonstrate how the weathering varies among species. In this study, the puparia of Chrysomya rufifacies were placed in the field to experience natural weathering to characterize hydrocarbon composition change over time. We found that weathering of the puparial hydrocarbons was regular and highly predictable in the field. For most of the hydrocarbons, the abundance decreased significantly and could be modeled using a modified exponent function. In addition, the weathering rate was significantly correlated with the hydrocarbon classes. The weathering rate of 2-methyl alkanes was significantly lower than that of alkenes and internal methyl alkanes, and alkenes were higher than the other two classes. For mono-methyl alkanes, the rate was significantly and positively associated with carbon chain length and branch position. These results indicate that puparial hydrocarbon weathering is highly predictable and can be used for estimating long-term PMImin.

Facilitation may not be an adequate mechanism of community succession on carrion

The facilitation model of ecological succession was advanced by plant ecologists in the late 1970s and was then introduced to carrion ecology in the late 1980s, without empirical evidence of its applicability. Ecologists in both disciplines proposed removing early colonists, in this case fly eggs and larvae, from the substrate to determine whether other species could still colonize, which to our knowledge has never been attempted. Here, we tested the facilitation model in a carrion system by removing fly eggs and larvae from carcasses that were exposed in agricultural fields and assigned to one of the following treatment levels of removal intensity: 0, <5, 50, and 100%. Subsequent patterns of colonisation did not provide support for the applicability of the facilitation model in carrion systems. Although results showed, in part, that the removal of fly eggs and larvae decreased the decomposition rate of carcasses, the removal did not prevent colonization by secondary colonizers. Finally, we discuss future studies and make recommendations as to how the facilitation model could be improved, firstly by being more specific about the scale where facilitation is believed to be occurring, secondly by clearly stating what environmental modification is believed to be involved, and thirdly by disentangling facilitation from priority effects.

Developmental Variation of Indian Thermophilic Variety of Scuttle Fly Megaselia (Megaselia) scalaris (Loew, 1866) (Diptera: Phoridae) on Different Substrates

The scuttle flies (Diptera: Phoridae) are important in forensic dipterology, because of their necrophagous habit. They are amongst the first wave of insects visiting human corpses in mechanically barricaded environments; hence their immature stages are generally used for estimation of PMI. The effect of different substrates commonly used for developmental studies was studied to analyze the variation of growth of the thermophilic variety of Megaselia (M.) scalaris prevalent in India on GDM, EDM, and SMS (n = 3). One approach of PMI estimation depends on larvae collected from the crime scene and comparing them with reference data derived from larval rearing to establish PMI. Results showed that there was a significant variation in avg. length (F(2,111) = 15.79873, p = 0.000000917), width (F(2,111) = 14.60528, p = 0.00000234), and biomass (F(2,111) = 37.01727, p = 0.000000000000482) of the immature stages in the three media and the larvae grow maximally in the SMS medium. The results of the present study thus provide baseline data on the growth and developmental pattern of the Megaselia (M.) scalaris, which can be utilized in conjunction with specific geoclimatic reference data, for forensic entomological studies and also for using the phorid as a biocontrol agent of pestiferous insects.

Inter-year repeatability study of volatile organic compounds from surface decomposition of human analogues

Decomposition odour and volatile organic compounds (VOCs) have gained considerable attention recently due to their use by insects and scent detection canines to locate remains. However, a comprehensive and accurate profile of decomposition odour is yet to be confirmed. This is, in part, due to the geographical diversity in the studies conducted and the variation in the methodology and compounds being reported. To date, no repeatability studies of decomposition odour have been conducted in the same environment. In order to address this current gap in the scientific literature, this study conducted three replicate trials in order to evaluate the inter-year repeatability of the decomposition VOC profile in a southern Canadian environment. Surface decomposition trials were conducted during the spring and summer months and the VOCs were analysed by thermal desorption-gas chromatography-mass spectrometry (TD-GC-MS). This study was able to demonstrate that decomposition VOCs are produced consistently during their characteristic stages and that this relationship is maintained under varying environmental factors which influence the rate of decomposition. This consistent production of decomposition VOCs can lead to a better understanding of the mechanisms of soft tissue decomposition and their sources of variation, and it could potentially lead to improved applications of these compounds for the detection of decomposed remains.

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.

Microbial community functional change during vertebrate carrion decomposition

Microorganisms play a critical role in the decomposition of organic matter, which contributes to energy and nutrient transformation in every ecosystem. Yet, little is known about the functional activity of epinecrotic microbial communities associated with carrion. The objective of this study was to provide a description of the carrion associated microbial community functional activity using differential carbon source use throughout decomposition over seasons, between years and when microbial communities were isolated from eukaryotic colonizers (e.g., necrophagous insects). Additionally, microbial communities were identified at the phyletic level using high throughput sequencing during a single study. We hypothesized that carrion microbial community functional profiles would change over the duration of decomposition, and that this change would depend on season, year and presence of necrophagous insect colonization. Biolog EcoPlates™ were used to measure the variation in epinecrotic microbial community function by the differential use of 29 carbon sources throughout vertebrate carrion decomposition. Pyrosequencing was used to describe the bacterial community composition in one experiment to identify key phyla associated with community functional changes. Overall, microbial functional activity increased throughout decomposition in spring, summer and winter while it decreased in autumn. Additionally, microbial functional activity was higher in 2011 when necrophagous arthropod colonizer effects were tested. There were inconsistent trends in the microbial function of communities isolated from remains colonized by necrophagous insects between 2010 and 2011, suggesting a greater need for a mechanistic understanding of the process. These data indicate that functional analyses can be implemented in carrion studies and will be important in understanding the influence of microbial communities on an essential ecosystem process, carrion decomposition.

The potential use of bacterial community succession in forensics as described by high throughput metagenomic sequencing

Decomposition studies of vertebrate remains primarily focus on data that can be seen with the naked eye, such as arthropod or vertebrate scavenger activity, with little regard for what might be occurring with the microorganism community. Here, we discuss the necrobiome, or community of organisms associated with the decomposition of remains, specifically, the "epinecrotic" bacterial community succession throughout decomposition of vertebrate carrion. Pyrosequencing was used to (1) detect and identify bacterial community abundance patterns that described discrete time points of the decomposition process and (2) identify bacterial taxa important for estimating physiological time, a time-temperature metric that is often commensurate with minimum post-mortem interval estimates, via thermal summation models. There were significant bacterial community structure differences in taxon richness and relative abundance patterns through the decomposition process at both phylum and family taxonomic classification levels. We found a significant negative linear relationship for overall phylum and family taxon richness as decomposition progressed. Additionally, we developed a statistical model using high throughput sequencing data of epinecrotic bacterial communities on vertebrate remains that explained 94.4 % of the time since placement of remains in the field, which was within 2-3 h of death. These bacteria taxa are potentially useful for estimating the minimum post-mortem interval. Lastly, we provide a new framework and standard operating procedure of how this novel approach of using high throughput metagenomic sequencing has remarkable potential as a new forensic tool. Documenting and identifying differences in bacterial communities is key to advancing knowledge of the carrion necrobiome and its applicability in forensic science.

Identification of forensically important Sarcophaga species (Diptera: Sarcophagidae) using the mitochondrial COI gene

The identification of species of the forensically important genus Sarcophaga is very difficult and requires strong taxonomic expertise. In this study, we sequenced the mitochondrial cytochrome c oxidase subunit I (COI) gene of 126 specimens of 56 W European Sarcophaga species and added GenBank data to our database to yield a total dataset of 270 COI sequences from 99 Sarcophaga species to evaluate the COI gene as a molecular diagnostic tool for species identification in this genus. Using two simple criteria (Best Match, BM and Best Close Match, BCM), we showed that the identification success using a mini-barcode region of 127 bp was very low (80.7-82.5 %) and the use of this region is not recommended as a species identifier. In contrast, identification success was very high using the standard barcode region (658 bp) or using the entire COI region (1,535 bp) (98.2-99.3 %). Yet, there was a low interspecific sequence divergence (<2 %) in six species groups so that for 16 out of the 99 species (nine of which are of forensic importance), the use of COI barcodes as species identifier should be done with care. For these species, additional markers will be necessary to achieve a 100 % identification success. We further illustrate how such reference databases can improve local reference databases for forensic entomologists.

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.