The Forensic Entomology Case Report-A Global Perspective.

Forensic practitioners analyzing entomological evidence are faced with numerous challenges when presenting their findings to law practitioners, particularly in terms of terminology used to describe insect age, what this means for colonization time of remains, and the limitations to estimates made. Due to varying legal requirements in different countries, there is no standard format for the entomological case report prepared, nor any guidelines as to the sections that are required, optional or unnecessary in a case report. The authors herein propose sections that should be considered when drafting an entomological case report. The criteria under which entomological evidence is analyzed are discussed, as well as the limitations for each criterion. The concept of a global, standardized entomological case report is impossible to achieve due to national legislative differences, but the authors here propose a basic template which can be adapted and changed according to the needs of the practitioner. Furthermore, while the discussion is fairly detailed, capturing all differences between nations could not be accomplished, and those initiating casework for the first time are encouraged to engage other practicing forensic entomologists or professional associations within their own nation or region, to ensure a complete report is generated that meets lab or national requirements, prior to generating a finalized report.

Volatile organic compounds in variably aged carrion impacted by the presence of the primary colonizer, Cochliomyia macellaria (Diptera: Calliphoridae).

The attraction and colonization of vertebrate remains by carrion-associated arthropods are processes largely governed by olfaction. As remains decompose, they emit a bouquet of volatile organic compounds (VOCs), which in part originate from endogenous and exogenous microbes surrounding the carcass or from the carcass itself. The composition and concentration of VOCs are influenced by the presence and abundance of microbial species and arthropods. Blowfly species, such as Cochliomyia macellaria, play a critical role in nutrient recycling and the decomposition process of carrion. Gas chromatography-mass spectroscopy analysis was used to identify and classify volatile emissions from insect-colonized (with C. macellaria) and uncolonized rat carcasses, as well as a standard Gainesville diet, over a 10-day period. There were significant differences in composition and abundance of compounds present in each treatment, with significant effects of time, and different compound composition between treatments. Notable indicator compounds included, but were not limited to, indole, dimethyl disulfide, and dimethyl trisulfide. A high compound richness, and a low compound diversity, was detected over the 10-day period. The indicator compounds detected across all treatments were found to be of microbial origin, highlighting the importance of microbes in decomposition processes and arthropod attraction to carrion. This study also discusses the significant impact of necrophagous arthropods to the VOC profile of carrion. The results of this study provide insight into the changes in decomposition VOCs over time, with an explanation of compounds in high concentration known to be attractive to carrion-colonizing arthropods.

Influence of Substrate Age and Interspecific Colonization on Oviposition Behavior of a Generalist Feeder, Black Soldier Fly (Diptera: Stratiomyidae), on Carrion.

Variation in resource utilization plays a significant role in determining the success or failure of a species. Generalist species across numerous taxa have exhibited success in feeding strategies for a variety of reasons. This study investigated the colonization and oviposition habits of a generalist carrion-feeder, Hermetia illucens L. (Diptera: Stratiomyidae), to varying conditions of carrion decay and colonization. Oviposition treatments consisted of combinations of variably aged decaying rats, both uncolonized and colonized with a heterospecific carrion-feeder. The black soldier fly exhibited a greater preference for oviposition on aged carrion, regardless of carcass colonization status. However, when presented with the option to colonize a plant-based diet, there was a significantly greater (40.4%) oviposition response to this diet. Results of this study highlight the ability of the black soldier fly to colonize fresh or aged carrion with or without a primary colonizer present, further supporting the recognition of this species as a generalist. These data demonstrate potential inaccuracies in the utility of H. illucens as time of colonization indicator species for legal investigations, and, in some regard, can be considered an exploitative niche-specialist (i.e., relying on plant-carrion interface for immature development) when found in association with carrion.

Influence of Substrate Age on Oviposition Behavior of a Specialist Carrion Colonizer, Cochliomyia macellaria (Diptera: Calliphoridae).

The location and consumption of carrion by arthropods is a process that can be potentially distinguished temporally based on the makeup of the associated community. In fact, succession on carrion is a continuum of different generalist and specialist arthropods entering and leaving the system. Blow flies commonly associated with vertebrate remains are considered specialists due to their reliance on carrion as a source of food for offspring and protein for females. However, this specialization may come at a price; increased competition for resources and greater risk of local extinction. The present study examined the effects of the presence or absence of intraspecific colonization, carcass age, and exposure time on the colonization and oviposition responses of the specialist, primary colonizer, the secondary screw worm, Cochliomyia macellaria (Fabricius) (Diptera: Calliphoridae). Carcass age, exposure time, and colonization status significantly influenced the ovipositional response of C. macellaria. This species exhibited an oviposition preference for aged carcasses, with a tendency for higher oviposition after 8-h exposure time, but no preference between previously colonized or uncolonized carcasses. Mean egg hatch rate was also shown to be influenced by the aforementioned factors, with mean hatch rates varying between 81.26 and 90.97% across various treatments. These results provide insight into mechanisms driving succession on carrion, as well as highlight the variation observed in successional studies for the targeted species. Investigators relying on arthropod succession to indicate a time of colonization should proceed with caution in relying solely on the assumption primary colonizers only arrive and colonize fresh carrion.

Heat accumulation and development rate of massed maggots of the sheep blowfly, Lucilia cuprina (Diptera: Calliphoridae).

Blowfly larvae aggregate on exposed carcasses and corpses and pass through three instars before wandering from the carcass and pupating. The developmental landmarks in this process can be used by forensic entomologists to estimate the time since the insects colonised the carcass, which sets a minimum post mortem interval. Large aggregations of feeding larvae generate a microclimate with temperatures up to 15°C above ambient conditions, which may accelerate larval development and affect forensic estimates of post-mortem intervals. This study investigated the effects of heat accumulated by maggot masses of Lucilia cuprina at aggregations of 20, 50 and 100 larvae, each at incubation temperatures of 18°C, 24°C and 30°C, using body length and life stage as developmental indicators. Aggregation temperatures reached up to 18.7°C above ambient temperature, with significant effects of both size and temperature of the aggregation on the development time of its larvae. Survivorship was highest for all life stages at 24°C, which is near the developmental optimum of L. cuprina. The results of this study provide a broadly applicable method of quantifying heat accumulation by aggregations of a wide range of species of forensic importance, and the results obtained from such studies will demonstrate that ambient temperature cannot be considered the only source of heat that blowfly larvae experience when they develop on a carcass. Neglect of temperatures within larval aggregations will result in an overestimation of post-mortem intervals and thus have far-reaching medicolegal consequences.

Effect of temperature on development of the blowfly, Lucilia cuprina (Wiedemann) (Diptera: Calliphoridae).

The blowfly Lucilia cuprina is a primary colonizer of decaying vertebrate carrion, and its development provides a temperature-dependent clock that may be used to estimate the post-mortem interval of corpses and carcasses in medicolegal forensic investigations. This study uses the development of L. cuprina raised on a substrate of chicken liver at six constant temperatures from 18 to 33 °C to calibrate a thermal accumulation model of development for forensic applications. Development was optimal near 24 °C; above this temperature, survival of post-feeding life stages was increasingly compromised, while below it, development was increasingly retarded. The lower developmental threshold (~12 °C) and thermal summation constants of L. cuprina are distinct from those reported for Lucilia sericata, verifying that it is essential to identify African Lucilia specimens accurately when using them to estimate post-mortem intervals.