A general approach for postmortem interval based on uniformly distributed and interconnected qualitative indicators

When insect development meets insect succession: Advantages of combining different methods and insect taxa in estimating the post-mortem interval

Insects are frequently used to estimate post-mortem interval (PMI). Experts usually base their estimates on a single insect taxon and use a single estimation method, even if multiple taxa are present on a cadaver or multiple methods can be applied. In this article we present a case report where multiple insect evidence and methods were used in a homicide case to estimate PMI. Since the true PMI was known, we were able to assess the estimation errors of each method as applied to particular insect evidence. The final grand PMI was derived from a developmental estimate based on third instar larvae of Lucilia illustris/L. caesar species group and a successional estimate based on adult Thanatophilus rugosus beetles. By averaging these estimates we got the grand PMI of almost perfect accuracy (1 % relative error, PMI range: 4.39 ± 0.77 days), which is of course an exceptional situation for entomological methods of estimating PMI. Furthermore, this was the first case report in which the presence and absence of subsequent life stages of carrion insects coupled with the estimation of their pre-appearance interval were used to estimate the PMI range. The results regarding the minimum PMI were fully consistent with the results obtained using the classical developmental method. This finding indicates that in some cases the presence/absence method can be used interchangeably with the developmental method. Finally, we discussed the prospects and limitations of combining insect evidence and methods of their analysis in estimating PMI.

A review of the estimation of postmortem interval using forensic entomology

The postmortem interval (PMI) is a crucial factor in death investigations. For PMIs exceeding 24 h the forensic pathologist must turn to other specialties that focus on decompositional ecology of animals, including humans. Primary among these specialties is forensic entomology. Here, we review the importance of forensic entomology in estimating the PMI, and we examine the factors that influence these estimates. Among key concerns are environmental factors, especially temperature, and aspects of insect biology. Additionally, we examine current methods used for calculating PMI based on insects and their development.

Research trends on forensic entomology for five decades worldwide

Forensic entomology, the study of insects and arthropods in criminal investigations, is crucial for estimating postmortem intervals, determining changes in corpse positioning, and identifying causes of death. This study analyzes global research trends in forensic entomology using data from the Scopus database spanning 1970 to 2024, with data visualized through VOSviewer. A total of 2,261 articles were identified, with an average productivity of 42 papers per year. The leading countries in forensic entomology research are the United States (n = 444), Brazil (n = 266), China (n = 198), the United Kingdom (n = 194), and Germany (n = 156). Current hot topics in the field include pupae, feeding behavior, beetles, and genetics. These findings underscore the ongoing interest and advancements in forensic entomology, highlighting its significance and diverse applications in criminal investigations.

Dynamics of insects, microorganisms and muscle mRNA on pig carcasses and their significances in estimating PMI

The accurate estimate of the postmortem interval (PMI) is of vital significance in the investigation of homicide cases. In this study, three pig carcasses were placed in the field to study the pattern of insect succession, the change of microorganisms and the degradation of muscle tissue RNA during the decomposition process. The results showed that insects could quickly colonize the carcasses and still exist on them until the end of the experiment (41 days). Their development and succession patterns are useful indicators for PMI estimation. The diversity of rectal microorganisms decreased with the decomposition time. In different decomposition periods, significant differences in the rectal and soil microbial composition and relative abundance were found, which could be used to estimate the PMI with an accuracy of 3-4 days. The RNA of muscle tissue was found to have a time-dependent relationship with the PMI. Ppia and Gapdh showed a linear upward trend within 10 h after the death, followed by a gradual downward trend from 10 to 240 h. The expression of β-actin gene showed a gradual downward trend during 0-240 h. This is the first study in China to analyze the changes of insects, muscle RNA and microorganisms on pig carcasses in the same natural environment, which provide basic data for the PMI estimation.

Post-Mortem Interval Estimation Based on Insect Evidence: Current Challenges

During death investigations insects are used mostly to estimate the post-mortem interval (PMI). These estimates are only as good as they are close to the true PMI. Therefore, the major challenge for forensic entomology is to reduce the estimation inaccuracy. Here, I review literature in this field to identify research areas that may contribute to the increase in the accuracy of PMI estimation. I conclude that research on the development and succession of carrion insects, thermogenesis in aggregations of their larvae and error rates of the PMI estimation protocols should be prioritized. Challenges of educational and promotional nature are discussed as well, particularly in relation to the collection of insect evidence.

Eye-background contrast as a quantitative marker for pupal age in a forensically important carrion beetle Necrodes littoralis L. (Silphidae)

Insect pupae sampled at a death scene may be used to estimate the post-mortem interval. The pupal age is however difficult to estimate, as there are no good quantitative markers for the age of a pupa. We present a novel method for pupal age estimation based on the quantification of contrast in intensity between the eyes of a pupa and the middle grey photography card as a standard background. The intensity is measured on a standardized scale from 0 (perfect black) to 255 (perfect white) using computer graphical software and pictures of the eye and the background taken with a stereomicroscope. Eye-background contrast is calculated by subtracting the average intensity of the eye from the average intensity of the background. The method was developed and validated using pupae of Necrodes littoralis (Linnaeus, 1758) (Coleoptera: Silphidae), one of the most abundant beetle species on human cadavers in Central Europe. To develop the model, pupae were reared in 17, 20 and 23 °C, with a total of 120 specimens. The method was validated by three raters, using in total 182 pupae reared in 15, 17, 20, 23 and 25 °C. We found a gradual increase in eye-background contrast with pupal age. Changes followed generalized logistic function, with almost perfect fit of the model. Using our method pupal age was estimated with the average error of 8.1 accumulated degree-days (ADD). The largest error was 27.8 ADD and 95% of age estimates had errors smaller than 20 ADD. While using the method, different raters attained similar accuracy. In conclusion, we have demonstrated that eye-background contrast is a good quantitative marker for the age of N. littoralis pupae. Contrast measurements gave accurate estimates for pupal age. Our method is thus proven to be a candidate for a reliable approach to age insect pupae in forensic entomology.

Rapid molecular identification of necrophagous diptera by means of variable-length intron sequences in the wingless gene

The arrival of arthropods at a corpse exhibits specific temporal patterns, and Diptera play a key role in the initial stages of the decomposition process. Thus, the correct species assignment of the insect larvae found on a decomposing body is an important step in forensic investigations. Here, we describe a molecular procedure to define the species at larval age found on a corpse more quickly and easily than current systems. Our method involves a unique PCR amplification of a DNA segment within the evolutionarily conserved wingless gene, involved in embryo development. The amplified DNA segment contains the fourth intron of wingless, which we found to be variable in length, from about 800 to 3000 bp, among species of necrophagous Diptera. The identification of the amplified segment size in species from Lucilia, Calliphora and Sarcophaga genera, allowed us to determine the species at larval age collected in the early stages of a decomposing body, with a simple PCR amplification and subsequent electrophoresis. This procedure may help in forensic investigations to estimate the minimum Post Mortem Interval (PMI-min) of a body colonized by these larvae, avoiding the use of time-consuming and/or more expensive procedures.