Development of Necrobia rufipes (De Geer, 1775) (Coleoptera: Cleridae) under constant temperatures and its implication in forensic entomology

Research Status of Sarcosaprophagous Beetles as Forensic Indicators

In forensic entomology, research focused on sarcosaprophagous flies, but the sarcosaprophagous beetles, as important "forensic indicator species" of late-stage PMI in cadaver decomposition, received less attention. To increase attention on, and use and understanding of, sarcosaprophagous beetles in forensic entomology, this paper presents a bibliometric analysis of the available relevant literature. The occurrence frequency of beetle families and species from succession studies, actual cases, and experiments were calculated and illustrated using graphs. As a result, a total of 14 families and 1077 species associated with carcasses were collected, with Staphylinidae being the most frequently recorded among the families, and Necrobia rufipes (Fabricius, 1781) (Coleoptera: Cleridae) being the most frequently recorded species. In addition, a brief introduction of the cadaver-related beetles of each family is given, and research on the species identification of the immature stages, age estimation of the immature stages, and estimation of the arrival time of sarcosaprophagous beetles are discussed and prospected. This work will aid in the increased use of sarcosaprophagous beetles in forensic science practice in the future.

Carrion insects living within the bones of large mammals: insect conservation and forensic entomology implications

Succession patterns of carrion insects on large mammal's carrion has been widely studied, notably to estimate the post-mortem interval in forensic investigations as accurately as possible. However, little attention has been paid to the carrion insects living inside these bones once a carcass is skeletonized. One very recent study documented flies emerging from pig carcasses, and only scarce authors reported the presence of other carrion insects taking advantage of the bone marrow. We, thus, aimed to (1) estimate the frequency of inner-bone space colonization by carrion insects, with particular attention to bone-skipper flies; (2) identify the insects living inside the carrion bones; and (3) determine whether or not carrion insects found within the bones can successfully exit the bones and complete their development. We extensively sampled 185 large mammals' bones collected from twelve vulture feeding stations and four isolated carcasses in southwest France and northern Spain. Sampled bones were opened, and the insects found inside were identified. For two bones, foramen, i.e., the holes providing a natural entrance and exit to the bone's inner cavity, was monitored with a camera to assess the insect's putative exit. We describe the entomofauna, i.e., the set of insect species, living within the bones, and illustrate insects' ability to exit the bones for their subsequent development and maturity. These results are discussed in the framework of carrion insect conservation and forensic entomology perspectives.

Development of Forensically Important Sarcophaga peregrina (Diptera: Sarcophagidae) and Intra-Puparial Age Estimation Utilizing Multiple Methods at Constant and Fluctuating Temperatures

Sarcophaga peregrina (Robineau-Desvoidy, 1830) has the potential to estimate the minimum postmortem interval (PMI_min). Development data and intra-puparial age estimation are significant for PMI_min estimation. Previous research has focused on constant temperatures, although fluctuating temperatures are a more real scenario at a crime scene. The current study examined the growth patterns of S. peregrina under constant (25.75 °C) and fluctuating temperatures (18-36 °C; 22-30 °C). Furthermore, differentially expressed genes, attenuated total reflectance Fourier-transform infrared spectroscopy, and cuticular hydrocarbons of S. peregrina during the intra-puparial period were used to estimate age. The results indicated that S. peregrina at fluctuating temperatures took longer to develop and had a lower pupariation rate, eclosion rate, and pupal weight than the group at constant temperatures did. Moreover, we found that six DEG expression profiles and ATR-FTIR technology, CHCs detection methods, and chemometrics can potentially estimate the intra-puparial age of S. peregrina at both constant and fluctuating temperatures. The findings of the study support the use of S. peregrina for PMI_min estimation and encourage the use of entomological evidence in forensic practice.

Reporting beetles in a mummified human corpse in Malaysia: Necrobia rufipes (Fabricius, 1781) (Coleoptera: Cleridae) and Dermestes maculatus De Geer, 1774 (Coleoptera: Dermestidae)

This case study reports on two unrecorded Coleopteran species found together on a human corpse in Malaysia. The mummified human remains were discovered in a house in Selangor, Malaysia. The pathologist confirmed that the death was due to a traumatic chest injury. Maggots, beetles, and fly pupal casings were found mainly on the front part of the body. Empty puparia of Diptera were collected during the autopsy and identified later as the muscid Synthesiomyia nudiseta (van der Wulp, 1883) (Diptera: Muscidae). Also, the insect evidence received included larvae and pupae of Megaselia sp. (Diptera: Phoridae). According to the insect development data, the minimum postmortem period was estimated by the time to reach the pupal developmental stage (in days). The entomological evidence included the first record of Dermestes maculatus De Geer, 1774 (Coleoptera: Dermestidae) and Necrobia rufipes (Fabricius, 1781) (Coleoptera: Cleridae), which have not previously been recorded on human remains in Malaysia.

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.

Development of Necrobia ruficollis (Fabricius) (Coleoptera: Cleridae) under Different Constant Temperatures

Simple Summary

Sarcosaprophagous beetles are significant pests, but they are also key indicator insects for postmortem interval estimation. In this paper, the development of Necrobia ruficollis (Fabricius, 1775) at five constant temperatures between 22 °C and 34 °C was investigated. The developmental threshold temperature and thermal summation constant were estimated, the relationship between the larval body length with development time, and the widths of the head capsules and the distance between the urogomphi at different instars were studied. The results provide important basic developmental data for using N. ruficollis to estimate the minimum postmortem interval.

Abstract

Necrobia ruficollis (Fabricius, 1775) (Coleoptera: Cleridae) is an important cosmopolitan storage pest, and also frequently appears on highly decomposed and skeletonized corpses. It is a forensically important species expected to indicate a longer postmortem interval (PMI). Therefore, we investigated the development of N. ruficollis at five constant temperatures between 22 °C and 34 °C. Under temperatures of 22, 25, 28, 31, and 34 °C, the mean (±SD) developmental durations from eggs to adults were 93.00 ± 1.63, 70.67 ± 0.94, 65.33 ± 3.40, 47.33 ± 0.94, and 56.66 ± 8.73 days, respectively. According to the developmental time and accumulated degree hours results, an isomorphen diagram and thermal summation model were generated. The calculated values of developmental threshold temperature and accumulated temperature constant were estimated by a linear model to be 14.51 ± 0.52 °C and 684.12 ± 33.85 degree days, respectively. Lower developmental thresholds, intrinsic optimum temperature, and upper lethal developmental threshold temperature were estimated by a nonlinear model to be 14.61, 25.90, and 34.94 °C. Morphological indexes of larvae were obtained by in vivo measurements. A growth curve and an equation of the relationship between development time and body length were simulated. In addition, the widths of the head capsules and the distance between the urogomphi of larvae at different instars were determined by cluster analysis. Classifiers were created and validated by linear discriminant analysis. These results provide important basic developmental data for using N. ruficollis to estimate the minimum postmortem interval (minimum PMI). However, this study was only conducted under constant temperature, and the applicability of these data to variable temperature conditions needs to be further confirmed.

Effects of Diet and Temperature on the Life History of the Redlegged Ham Beetle (Coleoptera: Cleridae)

We investigated the effects of various foods and different rearing temperatures on the survival and development of the redlegged ham beetle Necrobia rufipes (De Geer) (Coleoptera: Cleridae), a serious pest of dry-cured hams. The diets tested were dried pet food, finely shredded copra, shredded cheese, dry-cured ham, ground fish meal, and mature larvae of Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae). As indicated by the growth index and k-values, N. rufipes populations grew fastest on the pet food and slowest on the copra. On the other hand, N. rufipes fed both ham and T. castaneum larvae produced significantly heavier larvae. The adult beetles lived significantly longer on cheese compared to other foods. Studies conducted to determine the developmental rates of N. rufipes fed pet food at temperatures of 22, 25, 28, and 31°C showed that the total developmental time and longevity of N. rufipes significantly varied at different temperatures tested. The shortest developmental time (93.32 d) was observed at 28°C. Oviposition rate was highest for females reared at 25°C while lowest at 22°C. Based on the development, reproduction, and thermal requirements, the most suitable temperature for N. rufipes was between 28 and 31°C. The results also revealed that larval cannibalism prevailed among adult beetles.

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.

Molecular identification and diversity of adult arthropod carrion community collected from pig and sheep carcasses within the same locality during different stages of decomposition in the KwaZulu-Natal province of South Africa

The current study aimed at molecular identification and comparing the diversity of arthropods communities between pig and sheep carcasses during the cold and warm season in KwaZulu-Natal province of South Africa. Adult arthropods found on and around the carcasses were collected using either fly traps or forceps. Molecular analyses confirmed the identification of twelve arthropod species collected from both sheep and pig carcasses during the cold season. Results showed that 11 of 12 arthropod species were common in both sheep and pig carcasses, with exception to Onthophagus vacca (Coleoptera: Scarabaeidae) (Linnaeus, 1767) and Atherigona soccata (Diptera: Muscidae) (Rondani, 1871) species which were unique to sheep and pig carcasses respectively. However, during the warm season, the sheep carcass attracted more arthropod (n = 13) species as compared to the pig carcass. The difference in the obtained arthropod was due to the presence of O. vacca which was also unique to the sheep carcass during this season. Furthermore, there was an addition of a beetle species Hycleus lunatus (Coleoptera: Meloidae) (Pallas, 1782), which was collected from both sheep and pig carcasses but unique to the warm season. The pig carcass attracted more dipteran flies during both warm (n = 1,519) and cold season (n = 779) as compared to sheep carcass during the warm (n = 511) and cold season (n = 229). In contrast, coleopterans were more abundant on the sheep carcass during the warm season (n = 391) and cold season (n = 135) as compared to the pig carcass in both warm season (n = 261) and cold season (n = 114). In overall, more flies and beetles were collected on both sheep and pig carcasses during the warm season, and this further highlight that temperature influenced the observed difference in the abundance of collected arthropod between seasons.

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.

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.

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

The main entomological method for post-mortem interval involves estimation of age for immature insects found on a cadaver. Forensic entomologists frequently use the thermal summation value for the total immature development (K), which is a measure of physiological time needed to complete development of a species (age at emergence). K is highly variable within the species. Its true value for an adult insect may be estimated based on insect traits such as size and sex at maturity. Here, we have tested, if size and sex of adult beetles of Necrodes littoralis may be useful for the estimation of the true K. Necrodes littoralis is a Palearctic carrion beetle that frequently colonizes human cadavers in forest and agricultural environments. General and sex-specific thermal summation models for the emergence and models for the relationship between size of adult beetles and their age at emergence were developed for N. littoralis. The models were subsequently tested in the validation study. The general K for N. littoralis was about 469 (+/-25 SE) accumulated degree-days above the developmental threshold of about 8.5 (+/-0.45 SE) °C. Thermal summation parameters of the sex-specific models revealed minor differences compared to the general model. A true K was negatively related to the beetle size. Methods for the estimation of K represented its true value with different accuracy. The highest accuracy was obtained when K was estimated using beetle weight as a predictor variable and the sex-specific models for the relationship between K and size, although sex contributed slightly to this improvement. Using this method the estimated K represented the true K with the error of 6.3%, while the error for K from the general thermal summation model was about 9.7%. In conclusion, the findings demonstrate that physiological age at emergence of N. littoralis may be accurately predicted based on the adult beetle size. Necrodes littoralis is a second beetle species in which the age at maturity was more accurately represented by size-based estimates of K than K from the general thermal summation model. Therefore, we encourage testing the relationship between K and size in all insect species that are used in forensic entomology; particularly blow flies and flesh flies.