Diel Activity and Effect of Carcass Decomposition on the Attractiveness to the Forensically Important Species Oxelytrum Discicolle (Coleoptera: Silphidae)†

Oxelytrum discicolle is a carrion beetle commonly found in the Neotropical region, mainly associated with cadavers and carcasses. Information on behavior related to the likelihood of cadaver colonization is scarce. We performed two field experiments in peri‐urban forest in Brazil in order to strengthen our knowledge on O. discicolle behavior. In the first experiment, we assessed the preference for piglet carcasses at different stages of decomposition offered simultaneously in two seasons, dry and rainy, while in the second experiment we investigated the diel activity of adults. A total of 493 adults were collected in the experiments. A significantly higher abundance was detected in the rainy season. There was a marked preference for carcasses at advanced stages. Adults exhibited a typical nocturnal behavior, the number trapped at night was 17 times greater than those collected during the day. Oxelytrum discicolle is nocturnal species that prefers carcasses in advanced stage of decomposition.     

Recommended Practices for Macerating Human Thyroid Cartilage

Visible abnormalities on the thyroid cartilage may be indicative of perimortem trauma including fractures or sharp force trauma. During autopsy, the thyroid cartilage must be freed of surrounding soft tissue before these abnormalities can be clearly observed. Several processing methods were first experimentally tested on pig ears to narrow down which might work best to process human thyroid cartilage. Several methods in the categories of hot water maceration, chemical/enzyme maceration, and dermestid beetles were then tested on a sample of 37 human thyroid cartilages. An adapted 22-point scoring system was used to score the efficacy of each processing method. Chemical maceration using bleach was found to be the best method for removing surrounding tissue from thyroid cartilage, with Arm & Hammer^TM powdered laundry detergent as a close second. These methods are inexpensive, quick, and easy to implement, making them a simple addition to busy medical examiner’s offices or forensic anthropology laboratories.     

Effect of Investigator Disturbance in Experimental Forensic Entomology: Carcass Biomass Loss and Temperature

Abstract: Often carrion decomposition studies are conducted using a single carcass or a few carcasses sampled repeatedly through time to reveal trends in succession community composition. Measurements of biomass and other abiotic parameters (e.g., temperature) are often collected on the same carcasses but are rarely a focal point of the studies. This study investigated the effects that repeated sampling during experiments have on the decomposition of carrion, measured as both gross biomass (carcass plus fauna) and net biomass (carcass only), on carcasses disturbed on every visit (with weighing only or also with the collection of fauna) and on carcasses disturbed only once. Each trial lasted at least 21 days, with samples taken in triplicate. Rat carcasses used in this study were placed in the field on the same day and either weighed on every visit or ignored until a given day. Internal and ambient air temperatures were recorded on each carcass at the time of sampling and on undisturbed carcasses using temperature loggers. The presence of succession fauna did not result in significant biomass loss on most days; however, there were individual days early in decomposition (days 3 through 6) when the succession fauna comprised a large portion of the gross biomass. With the exception of biomass loss by the emigration of maggots on days 4 and 5, neither repeated weighing of the carcasses nor repeated weighing and faunal sampling of the carcasses statistically affected the rate of biomass loss. Internal temperatures of carcasses sampled repeatedly were frequently 2–5°C lower than those that had not been disturbed, and ambient temperatures differed significantly depending on the location of measurement device. Results indicate that methods used historically for biomass loss determination in experimental forensic entomology studies are adequate, but further refinements to experimental methodology are desirable.     

The Effect of Temperature and Laboratory Rearing Conditions on the Development of Dermestes maculatus (Coleoptera: Dermestidae)

Experiments were conducted to study the life cycle of Dermestes maculatus and to establish the total developmental time and the developmental time of immature stages, in relation with six different temperatures. We also analyzed the variations in size, morphology, and other indicators of temporal variation during life cycle of D. maculatus, in relation with temperature. One hundred larvae were selected per experiment, reared individually. The remaining larvae were reared to evaluate and establish temporal variations among the instars (length, cephalic width, and dry weight). In all trials, survivorship was greater than 50% and seven larval instars were found. Data of the average developmental time of immature stages and of the total cycle, at different temperatures, are provided. This is of relevance when estimating particularly, a minimum PMI. No relation between morphometric parameters and temperature was found, suggesting that other random factors may have been involved. Thus, this indicates that the method of isomegalen diagrams could not be used for calculating PMI.     

嗜尸性甲虫在尸体上的演替及其法医学应用前景

作为法医昆虫学的主要研究对象之一,嗜尸性甲虫在腐败晚期干化和白骨化尸体的死亡时间推断中具有双翅目昆虫所无法取代的重要意义,并对尸体的腐败、破坏、分解和姿势改变发挥着不容忽视的作用。本文阐述了嗜尸性甲虫在尸体上的演替,分析了嗜尸性甲虫演替的影响因素,介绍了嗜尸性甲虫在法医学中的应用和前景。虽然目前对嗜尸性甲虫的研究还很少,但嗜尸性甲虫在法医鉴定中的作用将在今后受到越来越多法医工作者的重视。     

Electrophysiological and Behavioral Responses of Thanatophilus sinuatus Fabricius (Coleoptera: Silphidae) to Selected Cadaveric Volatile Organic Compounds

Soon after death, carcasses release volatile chemicals that attract carrion insects including Silphidae. Nevertheless, it is not known which chemical cues are involved in the attractiveness of the carcass. So far, little information is available on the chemical ecology of carrion beetles, particularly concerning the subfamily of Silphinae. The biological role of selected cadaveric volatile organic compounds including dimethyldisulfide (DMDS), butan‐1‐ol, n‐butanoic acid, indole, phenol, p‐cresol, putrescine, and cadaverine on the silphine species, Thanatophilus sinuatus Fabricius, was investigated using both electrophysiological and behavioral techniques. Among the tested cadaveric compounds, butan‐1‐ol and DMDS elicited the strongest electroantennography (EAG) from both T. sinuatus male and female antennae. In a two‐arm olfactometer, males and females were significantly attracted to DMDS for both tested doses, whereas only males were attracted to p‐cresol at 100 ng. Putrescine was repellent to males at the dose of 1 μg.     

Sex‐ and Size‐Related Patterns of Carrion Visitation in Necrodes littoralis (Coleoptera: Silphidae) and Creophilus maxillosus (Coleoptera: Staphylinidae)

The estimation of postmortem interval (PMI) based on successional patterns of adult insects is largely limited, due to the lack of potential PMI markers. Sex and size of adult insects could be easily used for such estimation. In this study, sex‐ and size‐related patterns of carrion attendance by adult insects were analyzed in Necrodes littoralis (Coleoptera: Silphidae) and Creophilus maxillosus (Coleoptera: Staphylinidae). For both species, abundance of males and females changed similarly during decomposition. A slightly female‐biased sex ratio was recorded in N. littoralis. Females of N. littoralis started visiting carcasses, on average, one day earlier than males. There was a rise in size of males of N. littoralis at the end of decomposition, whereas for females of both species and males of C. maxillosus, no size‐related patterns of carrion visitation were found. Current results demonstrate that size and sex of adult carrion beetles are poor indicators of PMI.