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.     

Investigation of nocturnal oviposition by necrophilous flies in central Texas

The need to accurately estimate the postmortem interval (PMI) has prompted research into factors affecting fly oviposition (i.e., oviposition and/or larviposition) on a corpse. Research efforts have focused on whether or not diurnally active flies oviposit during nighttime hours. This study reports that nocturnal oviposition (defined as occurring between 2100-0600 h CDST (Central Daylight Savings Time)) did not occur on freshly killed white rats or mice, on beef (fresh or aged up to 48 h), on freshly thawed pigs, nor, usually, on thawed pigs that were aged for up to 48 h. Limited oviposition did occur between 2100 and 2120 h on one bloated pig at a lighted rural site. Necrophilous flies were present and active at lighted and dark sites (urban and rural) before and immediately after sunset, but fly activity on the bait ceased within 50 min postsunset and did not resume until after 0600 h. These observations support other studies reporting that diurnally active flies do not oviposit during the nighttime.     

Spread and habitat selection of Chrysomya albiceps (Wiedemann) (Diptera Calliphoridae) in Northern Italy: forensic implications

Abstract: Habitat selection exploited by Chrysomya albiceps during its initial spread in Northern Italy was analyzed in relation to landscape structure. The results of two short studies and a case report are here discussed. C. albiceps was not found on experimental pig carcasses in the urban area of Pavia. It was missing in the woody mountains surrounding Lecco, but it was found in the same area, at a lower altitude, within the typical “urban sprawl” landscape. It was then recorded in a natural reserve, among a rich carrion‐fly population. Indications coming from habitat selection suggest that C. albiceps has not yet saturated its potential ecological niche in newly colonized areas of Northern Italy. Factors like temperature, altitude, and interspecific competition can act as limiting factors, affecting habitat selection and distribution in newly colonized areas; the influence of those factors has to be taken into account for forensic purposes.     

Internal Morphological Analysis for Age Estimation of Blow Fly Pupae (Diptera: Calliphoridae) in Postmortem Interval Estimation*

Abstract: Larvae and pupae of blow fly species are frequently used in postmortem interval estimation, their age indicating minimum time since death. Most studies have considered age estimation of larvae, neglecting study of pupae. Relative development of external pupal features is useful, but there are also internal changes during metamorphosis that may be indicators of age, utilizing histological techniques. This study aimed to optimize preservation and histological analysis of blow fly pupae, specifically Calliphora vicina Robineau‐Desvoidy and Lucilia sericata (Meigen), and to examine internal features with potential for age estimation. Effect of hot‐water‐killing and different preservatives were examined. It was determined that blow fly pupae should be pierced through the three tagma, hot‐water‐killed, and preserved in 80% ethanol as the optimal preservation for subsequent analyses. Hematoxylin and eosin stained pupal sections revealed differences in brain and thoracic muscle development throughout the pupal stage with potential for age estimation.     

Collembola of the grave: a cold case history involving arthropods 28 years after death

This report describes a cold case in which a cadaver of a 28-year-old female was exhumed in February 2005 from a cemetery in Battle Creek, Michigan. She had sustained a gunshot wound to the head and was found dead in her home on November 15, 1977. The body of the victim was subsequently embalmed and then buried at a depth of 1.8 m in an unsealed casket that was placed inside an unsealed cement vault. The exhumation yielded thousands of live specimens of a single species of the order Collembola or spring tails, Sinella (Coecobrya) tenebricosa (Entomobryidae). This species is considered to be a "tramp" species, cosmopolitan in the United States and Canada. Due to the ideal environmental conditions at the site, the population of this species underwent growth and development inside the casket for a number of years. Collected with the Collembola were large numbers of Acarina (mites) of the Family Glycyphagidae, and fly puparia, Conicera tibialis Schmitz (Order: Diptera, Family: Phoridae), also known as coffin flies. These invertebrates are sometimes mentioned by forensic investigators as occurring on corpses in graves, but aspects of their life history are rarely described. The species of Collembola that was found surviving and reproducing on this corpse in a casket exhumed after 28 years was the oldest reported grave site occurrence for any collembolan species based on a survey of the literature back to 1898.     

Experimental and casework validation of ambient temperature corrections in forensic entomology

This paper expands on Archer (J Forensic Sci 49, 2004, 553), examining additional factors affecting ambient temperature correction of weather station data in forensic entomology. Sixteen hypothetical body discovery sites (BDSs) in Victoria and New South Wales (Australia), both in autumn and in summer, were compared to test whether the accuracy of correlation was affected by (i) length of correlation period; (ii) distance between BDS and weather station; and (iii) periodicity of ambient temperature measurements. The accuracy of correlations in data sets from real Victorian and NSW forensic entomology cases was also examined. Correlations increased weather data accuracy in all experiments, but significant differences in accuracy were found only between periodicity treatments. We found that a >5°C difference between average values of body in situ and correlation period weather station data was predictive of correlations that decreased the accuracy of ambient temperatures estimated using correlation. Practitioners should inspect their weather data sets for such differences.     

Insect Successional Pattern of a Corpse in Cooler Months of Subtropical Southeastern Texas

Abstract:  Here, we characterize the cool weather insect fauna found associated with partially skeletonized and desiccated human remains recovered from an abandoned house in an urban area of subtropical, coastal Galveston County, Texas, and use the information to conclude an approximate postmortem interval of 7–10 months. The predominant factors that allow for a confident assessment of the postmortem interval include climatological data, entomological data, and anthropological data. The documented insect fauna represents a unique assemblage present in a particular environment (an urban abandoned house in coastal Texas) at a particular time of year (winter) and includes expected forensically significant insects such as calliphorid flies, muscid flies, and dermestid beetles but also includes less commonly encountered insects such as an unusually dense population of live case-making clothes moths.