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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.
Blow flies are the first insect group to colonize on a dead body and thus correct species identification is a crucial step in forensic investigations for estimating the minimum postmortem interval, as developmental times are species-specific. Due to the difficulty of traditional morphology-based identification such as the morphological similarity of closely related species and uncovered taxonomic keys for all developmental stages, DNA-based identification has been increasing in interest, especially in high biodiversity areas such as Thailand. In this study, the effectiveness of long mitochondrial cytochrome c oxidase subunit I and II (COI and COII) sequences (1247 and 635 bp, respectively) in identifying 16 species of forensically relevant blow flies in Thailand (Chrysomya bezziana, Chrysomya chani, Chrysomya megacephala, Chrysomya nigripes, Chrysomya pinguis, Chrysomya rufifacies, Chrysomya thanomthini, Chrysomya villeneuvi, Lucilia cuprina, Lucilia papuensis, Lucilia porphyrina, Lucilia sinensis, Hemipyrellia ligurriens, Hemipyrellia pulchra, Hypopygiopsis infumata, and Hypopygiopsis tumrasvini) was assessed using distance-based (Kimura two-parameter distances based on Best Match, Best Close Match, and All Species Barcodes criteria) and tree-based (grouping taxa by sequence similarity in the neighbor-joining tree) methods. Analyses of the obtained sequence data demonstrated that COI and COII genes were effective markers for accurate species identification of the Thai blow flies. This study has not only demonstrated the genetic diversity of Thai blow flies, but also provided a reliable DNA reference database for further use in forensic entomology within the country and other regions where these species exist.
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.
Knowledge on the postmortem interval (PMI) of wild boar (Sus scrofa) carcasses is crucial in the event of an outbreak of African swine fever in a wild boar population. Therefore, a thorough understanding of the decomposition process of this species in different microhabitats is necessary. We describe the decomposition process of carcasses exposed in cages. Trial 1 compared a wild boar and a domestic pig (Sus scrofa domesticus) under similar conditions; Trial 2 was performed with three wild boar piglets in the sunlight, shade, or in a wallow, and Trial 3 with two adult wild boar in the sun or shade. The wild boar decomposed more slowly than the domestic pig, which shows that standards derived from forensic studies on domestic pigs are not directly applicable to wild boar. The carcasses exposed to the sun decomposed faster than those in the shade did, and the decomposition of the carcass in the wallow took longest. To assess the state of decomposition, we adapted an existing total body scoring system originally developed for humans. Based on our studies, we propose a checklist tailored to wild boar carcasses found in the field that includes the most important information for a reliable PMI estimation.
Determining the age of juvenile blow flies is one of the key tasks of forensic entomology when providing evidence for the minimum post mortem interval. While the age determination of blow fly larvae is well established using morphological parameters, the current study focuses on molecular methods for estimating the age of blow flies during the metamorphosis in the pupal stage, which lasts about half the total juvenile development. It has already been demonstrated in several studies that the intraspecific variance in expression of so far used genes in blow flies is often too high to assign a certain expression level to a distinct age, leading to an inaccurate prediction. To overcome this problem, we previously identified new markers, which show a very sharp age dependent expression course during pupal development of the forensically-important blow fly Calliphora vicina Robineau–Desvoidy 1830 (Diptera: Calliphoridae) by analyzing massive parallel sequencing (MPS) generated transcriptome data. We initially designed and validated two quantitative polymerase chain reaction (qPCR) assays for each of 15 defined pupal ages representing a daily progress during the total pupal development if grown at 17 °C. We also investigated whether the performance of these assays is affected by the ambient temperature, when rearing pupae of C. vicina at three different constant temperatures—namely 17 °C, 20 °C and 25 °C. A temperature dependency of the performance could not be observed, except for one marker. Hence, for each of the defined development landmarks, we can present gene expression profiles of one to two markers defining the mentioned progress in development.