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Forensic entomology
(2017)
For many members of the forensic community, insects still have an exotic status. This may be one reason why forensic entomology, the analysis of insect evidence for forensic and legal purposes, has not yet achieved the significance it deserves in forensic sciences. The present special issue may help to change that. ...
Recent reports have shown a dramatic loss in insect species and biomass. Since forensic entomology relies on the presence of insects, the question is whether this decline effects the discipline. The present review confirms that numerous studies document insect population declines or even extinction, despite the fact that the rates of decline and the methods used to demonstrate it are still much debated. However, with regard to a decline in necrophagous insects, there is little or only anecdotal data available. A hypothetical decrease in species diversity and population density in necrophagous insects could lead to a delayed colonization of dead bodies and a modified succession pattern due to the disappearance or new occurrence of species or their altered seasonality. Climate change as one of the drivers of insect decline will probably also have an impact on necrophagous insects and forensic entomology, leading to reduced flight and oviposition activity, modified growth rates and, therefore, an over- or underestimation of a minimum postmortem interval. Global warming with increased temperature and extreme weather requires a better understanding about necrophagous insect responses to environmental variations. Here, transgeneration effects in particular should be analysed in greater depth as this will help to understand rapid adaptation and plasticity in insects of forensic importance.
The estimation of the minimum time since death is one of the main applications of forensic entomology. This can be done by calculating the age of the immature stage of necrophagous flies developing on the corpse, which is confined to approximately 2–4 weeks, depending on temperature and species of the first colonizing wave of flies. Adding the age of the adult flies developed on the dead body could extend this time frame up to several weeks when the body is in a building or closed premise. However, the techniques for accurately estimating the age of adult flies are still in their beginning stages or not sufficiently validated. Here we review the current state of the art of analysing the aging of flies by evaluating the ovarian development, the amount of pteridine in the eyes, the degree of wing damage, the modification of their cuticular hydrocarbon patterns, and the increasing number of growth layers in the cuticula. New approaches, including the use of age specific molecular profiles based on the levels of gene and protein expression and the application of near infrared spectroscopy, are introduced, and the forensic relevance of these methods is discussed.
Determination of a minimal postmortem interval via age estimation of necrophagous diptera has been restricted to the juvenile stages and the time until emergence of the adult fly, i.e. up until 2–6 weeks depending on species and temperature. Age estimation of adult flies could extend this period by adding the age of the fly to the time needed for complete development. In this context pteridines are promising metabolites, as they accumulate in the eyes of flies with increasing age. We studied adults of the blow fly Lucilia sericata at constant temperatures of 16 °C and 25 °C up to an age of 25 days and estimated their pteridine levels by fluorescence spectroscopy. Age was given in accumulated degree days (ADD) across temperatures. Additionally, a mock case was set up to test the applicability of the method. Pteridine increases logarithmically with increasing ADD, but after 70–80 ADD the increase slows down and the curve approaches a maximum. Sex had a significant impact (p < 4.09 × 10−6) on pteridine fluorescence level, while body-size and head-width did not. The mock case demonstrated that a slight overestimation of the real age (in ADD) only occurred in two out of 30 samples. Age determination of L. sericata on the basis of pteridine levels seems to be limited to an age of about 70 ADD, but depending on the ambient temperature this could cover an extra amount of time of about 5–7 days after completion of the metamorphosis.
Highlights
• Forensic experts should be questioned about their education and experience.
• Reliability of methods used to estimate the PMI should be evident when exposed in court.
• Judges should question if the right method was used in the right manner.
• The PMI is an estimate and cannot be interpreted as the actual time of death.
Abstract
When a capital crime is committed the post-mortem interval (PMI) is of particular importance in investigating a suspect’s alibi in court. A forensic expert can use different methods to estimate the PMI. This research focuses on who is considered an expert in court and whether the methods used to estimate the PMI are reliable. In this study, the methods used to estimate the PMI and the experts consulted, available in Dutch jurisprudence, in the period 2010–2019 were investigated. Ninety-four judicial cases were included and multiple experts and methods of estimating the PMI were found. As part of this study, the methods that were used to estimate the PMI in court were subjected to the Daubert criteria. Of these methods, only the Henssge nomogram and entomological methods met the Daubert criteria. However, the methods are only useful when applied by the right forensic expert and in the right manner. Unfortunately, this was not always the case.
Estimating the age of the developmental stages of the blow fly Calliphora vicina (Diptera: Calliphoridae) is of forensic relevance for the determination of the minimum post-mortem interval (PMImin). Fly eggs and larvae can be aged using anatomical and morphological characters and their modification during development. However, such methods can only hardly be applied for aging fly pupae. Previous study described age estimation of C. vicina pupae using gene expression, but just when reared at constant temperatures, but fluctuating temperatures represent a more realistic scenario at a crime scene. Therefore, age-dependent gene expression of C. vicina pupae were compared at 3 fluctuating and 3 constant temperatures, the latter representing the mean values of the fluctuating profiles. The chosen marker genes showed uniform expression patterns during metamorphosis of C. vicina pupae bred at different temperature conditions (constant or fluctuating) but the same mean temperature (e.g. constant 10 °C vs. fluctuating 5–15 °C). We present an R-based statistical tool, which enables estimation of the age of the examined pupa based on the analysed gene expression data.
Simple Summary: Forensic entomologists are most often tasked with determining when arthropods colonized living or deceased vertebrates. In most cases, this estimation involves humans; however, pets, livestock, and other domesticated animals can also be illegally killed or victims of neglect. Globally, there is no standard format for the case report, and much of the content is based on the personal preferences of the analyst or standards set within a country. The article below proposes a general overview of sections to be considered when drafting a case report.
Abstract: Forensic practitioners analyzing entomological evidence are faced with numerous challenges when presenting their findings to law practitioners, particularly in terms of terminology used to describe insect age, what this means for colonization time of remains, and the limitations to estimates made. Due to varying legal requirements in different countries, there is no standard format for the entomological case report prepared, nor any guidelines as to the sections that are required, optional or unnecessary in a case report. The authors herein propose sections that should be considered when drafting an entomological case report. The criteria under which entomological evidence is analyzed are discussed, as well as the limitations for each criterion. The concept of a global, standardized entomological case report is impossible to achieve due to national legislative differences, but the authors here propose a basic template which can be adapted and changed according to the needs of the practitioner. Furthermore, while the discussion is fairly detailed, capturing all differences between nations could not be accomplished, and those initiating casework for the first time are encouraged to engage other practicing forensic entomologists or professional associations within their own nation or region, to ensure a complete report is generated that meets lab or national requirements, prior to generating a finalized report.
The bluebottle blow fly Calliphora vicina is a common species distributed throughout Europe that can play an important role as forensic evidence in crime investigations. Developmental rates of C. vicina from distinct populations from Germany and England were compared under different temperature regimes to explore the use of growth data from different geographical regions for local case work. Wing morphometrics and molecular analysis between these populations were also studied as indicators for biological differences. One colony each of German and English C. vicina were cultured at the Institute of Legal Medicine in Frankfurt, Germany. Three different temperature regimes were applied, two constant (16°C & 25°C) and one variable (17–26°C, room temperature = RT). At seven time points (600, 850, 1200, 1450, 1800, 2050, and 2400 accumulated degree hours), larval lengths were measured; additionally, the durations of the post feeding stage and intrapuparial metamorphosis were recorded. For the morphometric and molecular study, 184 females and 133 males from each C. vicina population (Germany n = 3, England n = 4) were sampled. Right wings were measured based on 19 landmarks and analyzed using canonical variates analysis and discriminant function analysis. DNA was isolated from three legs per specimen (n = 61) using 5% chelex. A 784 bp long fragment of the mitochondrial cytochrome b gene was sequenced; sequences were aligned and phylogenetically analyzed. Similar larval growth rates of C. vicina were found from different geographic populations at different temperatures during the major part of development. Nevertheless, because minor differences were found a wider range of temperatures and sampling more time points should be analyzed to obtain more information relevant for forensic case work. Wing shape variation showed a difference between the German and English populations (P<0.0001). However, separation between the seven German and English populations at the smaller geographic scale remained ambiguous. Molecular phylogenetic analysis by maximum likelihood method could not unambiguously separate the different geographic populations at a national (Germany vs England) or local level.
The aim of the current study was to analyze two major pitfalls in forensic entomological casework: delayed evidence sampling and the effect of low-temperature storage of the body. For this purpose, temperature profiles of heavily infested corpses during cooling and cases in which insect evidence was collected both at the scene and during autopsy were evaluated with regard to species composition and development stages found. The results show that the temperature in the body bags remained at higher average temperatures up to 10 °C relative to the mortuary cooler, therefore, sufficient for larval development, with significant differences in temperature between larval aggregations on one and the same body. In addition, we found large differences both in species number, species composition, and the developmental stages found at the scene and during the autopsy. These data and observations underscore the importance of sampling evidence at the scene and recording temperatures throughout the cooling period of a body.
1. Locating an optimal oviposition site can be a challenging task for female insects, especially when dealing with a patchy, unpredictable and ephemeral food source such as carrion. Understanding the biotic and abiotic parameters that influence the oviposition behaviour of necrophagous flies is not just of great biological importance but also essential for their application in legal investigations.
2. In this study, we monitored the oviposition activity of necrophagous flies (Calliphoridae, Sarcophagidae) using mouse carcasses in an urban (city) and a rural (mixed forest) habitat in Frankfurt/Germany over a 2-year period.
3. Over 240 sampling days, 220,963 larvae of 4 blow fly species and 1 flesh fly were sampled. The most abundant species was the blow fly Lucilia ampullacea, followed by its family members Calliphora vicina and Lucilia caesar, the flesh fly Sarcophaga caerulescens and Lucilia sericata. Up to seven environmental parameters were statistically significant predictors for a colonisation of the carcasses, leading to unique patterns of seasonal and daily oviposition activity for all five species.
4. Overall, the analysis showed that the seasonal adaption (the phenology of each species), the habitat (rural vs. urban) as well as temperature are the most important factors influencing the oviposition behaviour and activity of necrophagous blow flies and flesh flies.