Estimation of physiological age at emergence based on traits of the forensically useful adult carrion beetle Necrodes littoralis L. (Silphidae)

Calibrating insect age at eclosion by size in a gregarious carrion beetle Thanatophilus sinuatus (Staphylinidae: Silphinae)

Recent discoveries have shown that the physiological age at eclosion of forensically useful beetles differs between males and females and between beetles of various sizes. Accordingly, it was postulated that the size and sex of the beetles at eclosion may be used to calibrate their age, which may improve the accuracy of age (and post-mortem interval) estimates in forensic entomology. In this study, we derived thermal summation models for the eclosion for the Central European population of carrion beetles Thanatophilus sinuatus (Fabricius, 1775), (Staphylinidae: Silphinae), and tested the usefulness of sex and size for the calibration of beetle age at eclosion. Although in previous developmental studies, the beetles were reared individually, we reared them in larval aggregations, since in natural conditions T. sinuatus beetles are gregarious. Weak (r2 between 5% and 13%) negative correlations were observed between the size and age of T. sinuatus males or females at eclosion, demonstrating that calibration of age by beetle size and sex may bring only minimal benefits regarding the accuracy of age estimation in this species. However, it may still be worthwhile in the case of extremely large or small beetles. Moreover, the total development times recorded in this study were much shorter than in the previous T. sinuatus study, at 14°C by about 15 days and at 26°C by about 2 days. These differences emphasise the importance of gregariousness for the development of carrion beetles, and at the same time highlight the need for the ecologically-relevant protocols of development studies in forensic entomology.

Temperature models of development for Necrodes littoralis L. (Coleoptera: Silphidae), a carrion beetle of forensic importance in the Palearctic region

Analysis of insects can provide evidence in death cases, for example, by answering the question about the time of death. Apart from flies, beetles are the second most useful insect group in forensic entomology. To elucidate the time of death based on insect evidence, developmental models of a given species are necessary. In this study, we developed such models for Necrodes littoralis, a necrophagous beetle, which is common in the Palearctic region and has great potential in forensic entomology. We monitored the development at 10 constant temperatures (14–30 °C). Larvae were reared in aggregations. Thermal summation models, isomorphen and isomegalen diagrams and growth curves were derived using the data. Depending on the temperature, development lasted between about 23 and 89 days. Mortality was high at the extremes of the temperature range. The thermal summation constant for the total development was 434.7 ± 28.86 accumulated degree-days above a developmental threshold of 9.04 ± 0.55 °C. This is the first comprehensive dataset on the development of N. littoralis. Implications for its use in forensic casework are discussed.

Diptera (Dryomyzidae, Fanniidae, Muscidae, Piophilidae) Associated With Pig Carcasses in a Forest Habitat of Poland: Sex-Related Patterns of Visitation and Effectiveness of Sampling Methods

Our knowledge on many necrophilous dipterans was limited for a long time mainly due to taxonomic issues. Therefore, findings on the sex-related associations with pig carcasses in Dryomyzidae, Fanniidae, Muscidae, and Piophilidae are presented. Moreover, the effectiveness of pitfall traps and sweep nets in fly sampling were compared, since the correct method of collecting insects is critical for the development and application of entomological tools for forensic purposes. The trapped numbers of all species differed significantly in respect to both sexes. The sex ratios were strongly female-biased in most species of Muscidae and in Fanniidae. More females were also collected in Piophilidae, but the proportion of males was higher when compared to muscids. Within Dryomyzidae, the sex ratio differed according to species. Only Dryomyza flaveola (Fabricius, 1794) (Diptera: Dryomyzidae) and Muscina pascuorum (Meigen, 1826) (Diptera: Muscidae) had male-biased sex ratios. Differences in residency patterns between sexes in Stearibia nigriceps (Meigen, 1826) (Diptera: Piophilidae), Liopiophila varipes (Meigen, 1830) (Diptera: Piophilidae), and D. flaveola were statistically insignificant. All studied species were recorded for each sampling method. The effect of the sampling method on the number of individuals was statistically significant for all dipterans but Piophilidae. Pitfall traps outcompeted the aerial sweep net in representing Dryomyzidae and Muscidae, whereas both methods were almost equally effective in the collection of Piophilidae. A varied effectiveness of sampling methods was observed in Fanniidae. The sampling method significantly affected the determination of the appearance time of flies on carcasses, but the effect of species and sampling method was insignificant. Implications for forensic entomology are discussed.

Insect rearing protocols in forensic entomology: Benefits from collective rearing of larvae in a carrion beetle Necrodes littoralis L. (Silphidae)

Forensic entomologists frequently use a developmental method to estimate a post-mortem interval (PMI). Such estimates are based usually on the blow fly larvae or puparia. Data on their development is obtained by rearing them in colonies. In the case of beetles, which can be also useful for PMI estimation, development data is frequently collected by rearing them individually. However, some carrion beetles are gregarious, for instance, Necrodes littoralis (Linnaeus, 1758) (Silphidae). We compared mortality, rate of development and body size of emerged adult beetles reared individually and in aggregations. Mortality was much higher for beetles reared individually, particularly at low temperatures. The rearing protocol affected the time of immature development and the size of adult insects. Individually reared specimens developed much longer at 16°C, whereas at 20°C and 26°C development times of individually reared beetles were slightly shorter. Significant differences in the body size were observed only at 16°C; beetles that developed in aggregations were larger at this temperature. These findings demonstrate that aggregating is particularly beneficial for larvae of N. littoralis at low temperatures, where it largely reduces mortality and facilitates growth. Moreover, these results indicate that in forensic entomology the protocol of individual rearing is unsuitable for gregarious beetles, as it produces reference developmental data of low quality.

An examination of the intrapuparial development of Chrysomya albiceps (Wiedemann, 1819) (Calliphoridae: Diptera) at three different temperatures

The determination of intrapuparial development periods and development times of insects with holometabolous metamorphosis is necessary both in terms of developmental biology and for minimum Post-mortem interval (PMImin) calculations in forensic entomology. In this study, Chrysomya albiceps (Wiedemann, 1819), which is a cosmopolitan species and one of the most rapidly attracted to carrion, was studied. The focus was the intrapuparial development periods of this species at varying temperatures (20, 25, and 30 °C), knowledge which is used in forensic entomology for the estimation of Post-mortem interval (PMI) and is a type of black box. At the specified temperatures, pupae were collected and puparia were dissected hourly; thus, developmental periods were determined, and minimum and maximum starting times of these periods were calculated. With this research, a total of 20 periods, nine of which are new, were determined. The hourly determination of intrapuparial development periods at three different temperatures is the first in the world for this species.

Developmental models of the carrion beetle Thanatophilus rugosus (Linnaeus, 1758) (Coleoptera: Silphidae)

Coleoptera are currently considered a fundamental tool to help solve criminal investigations, allowing forensic entomologists to estimate post-mortem intervals and obtain other ecology-related information. Thanatophilus rugosus (Linnaeus, 1758) is an important necrophagous beetle distributed through most of the Palaearctic region, where it is readily found on human bodies and animal carcasses. In this study, the new thermal summation models for all the developmental stages of Thanatophilus rugosus are provided. Beetles were reared at six different constant and ecologically relevant temperatures (12, 14, 16, 18, 20, and 22 °C), and their developmental times were measured. Thermal summation constants were calculated for each developmental stage (egg, three larval instars, post-feeding stage, and pupa).

Developmental Models of the Forensically Important Carrion Beetle, Thanatophilus sinuatus (Coleoptera: Silphidae)

Carrion beetles of genus Thanatophilus (Leach, 1815) are an important group of necrophagous insects, with great potential for forensic entomology in temperate zones of Africa, America, Asia, and Europe. Developmental models for majority of Thanatophilus species remain unknown. In this study, we will provide new thermal summation models for all the developmental stages of Thanatophilus sinuatus (Fabricius, 1775), one of the most abundant and widespread species of the genus. The beetles were bred at seven different constant temperatures, and developmental time was measured for each developmental stage (egg, three larval instars, postfeeding stage, and pupa). Temperature-sex influence was tested, and thermal summation constants were calculated to be used for postmortem interval estimation during criminal investigations.

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.

New Species of Soldier Fly-Sargus bipunctatus (Scopoli, 1763) (Diptera: Stratiomyidae), Recorded from a Human Corpse in Europe-A Case Report

Simple Summary

In the current study, we present the first record of twin-spot centurion fly larvae, Sargus bipunctatus (Scopoli, 1763), feeding on a human corpse. The morphology of collected imagines and larvae of S. bipunctatus was documented, and a standard COI barcode sequence was obtained. Morphology- and DNA-based methods were used to distinguish the larvae of S. bipunctatus and its relative, Hermetia illucens (Linnaeus, 1758). The potential of S. bipunctatus for practical applications in forensic entomology is currently difficult to assess.

Abstract

The only European Stratiomyidae species known for feeding on human corpses was the black soldier fly Hermetia illucens (Linnaeus, 1758). Analysis of fauna found on a human corpse, discovered in central Poland, revealed the presence of feeding larvae of another species from this family: the twin-spot centurion fly Sargus bipunctatus (Scopoli, 1763). The investigated corpse was in a stage of advanced decomposition. The larvae were mainly observed in the adipocere formed on the back and lower limbs of the corpse, and in the mixture of litter and lumps of adipocere located under the corpse. Adult specimens and larvae were identified based on morphological characters, and final identification was confirmed using DNA barcoding. Implementing a combination of morphological and molecular methods provided a reliable way for distinguishing the larvae of S. bipunctatus and H. illucens. The potential of S. bipunctatus for practical applications in forensic entomology is currently difficult to assess. Wide and reliable use of S. bipunctatus in the practice of forensic entomology requires further studies of the bionomy of this fly.

Forensic Entomology in China and Its Challenges

Simple Summary

Forensic entomologists utilize sarcosaprophagous insect species to estimate the postmortem interval to aid death investigations. In this paper, we present the recent chronology of forensic entomology in China and illustrate how identification, development, and succession data are obtained and applied at the scale of such a large country. To overcome the difficulties and challenges forensic entomology faces in China, a number of countermeasures are provided.

Abstract

While the earliest record of forensic entomology originated in China, related research did not start in China until the 1990s. In this paper, we review the recent research progress on the species identification, temperature-dependent development, faunal succession, and entomological toxicology of sarcosaprophagous insects as well as common applications of forensic entomology in China. Furthermore, the difficulties and challenges forensic entomologists face in China are analyzed and possible countermeasures are presented.

Heat production in a feeding matrix formed on carrion by communally breeding beetles

Insects regulate their body temperature mostly behaviourally, by changing posture or microhabitat. Usually they use heat that is already present in the environment. Sometimes, however, they may manipulate the environment to affect, focus or benefit from thermogenesis. Carrion beetles create a feeding matrix by applying to cadaver surface anal or oral exudates. We tested the hypothesis that the matrix, which is formed on carrion by communally breeding beetle Necrodes littoralis L. (Silphidae), produces heat that enhances insect fitness. Using thermal imaging we demonstrate that heat produced in the matrix formed on meat by adult or larval beetles is larger than in meat decomposing without insects. Larval beetles regularly warmed up in the matrix. Moreover, by comparing matrix temperature and larval fitness in colonies with and without preparation of meat by adult beetles, we provide evidence that formation of the matrix by adult beetles has deferred thermal effects for larval microhabitat. We found an increase in heat production of the matrix and a decrease in development time and mortality of larvae after adult beetles applied their exudates on meat in the pre-larval phase. Our findings indicate that spreading of exudates over carrion by Necrodes larvae, apart from other likely functions (e.g. digesting carrion or promoting growth of beneficial microbes), facilitates thermoregulation. In case of adult beetles, this behaviour brings distinct thermal benefits for their offspring and therefore may be viewed as a new form of indirect parental care with an important thermal component.