Muscina prolapsa (Harris 1780): Ein bislang unterschätztes Werkzeug der forensischen Entomologie

It is all about the insects: a retrospective on 20 years of forensic entomology highlights the importance of insects in legal investigations

This study highlights the importance of insect evidence by evaluating 949 insect-associated cases, including 139 entomological reports, from 2001 to 2019 at the Institute of Legal Medicine Frankfurt/Germany. With a high number of cases in the summer months and a low number in the colder season, 78.5% of the bodies were found indoors, regardless of year or month. In more than 80% of the cases, where PMI information was available (n = 704), the presumed PMI ranged from 1 to 21 days, a period during which entomological evidence can provide a day-specific estimate of PMI_min. In cases where insects have been identified to species level (n = 279), most bodies were infested by one or two species with a maximum of 10 different species. Overall, a total of 55 insect species were found. Information on biology, activity and distribution of the most abundant taxa is given and applied for 5 case histories estimating different PMI_mins of up to over 6 months. Despite proved importance and scientific development of forensic entomology, insects are still rarely considered as a tool in forensic case work. The main reasons are a lack of awareness and (too) late involvement of a forensic entomologist. Our work shows that forensic entomology is an independent discipline that requires specialist expertise.

Decomposition process for buried rat (Rattus norvegicus, Berkenhout 1769) carcasses in Riyadh city, Saudi Arabia: A preliminary study

The present report outlines the initial observations from an ongoing study examining the decomposition rate of buried rat (Rattus norvegicus, Berkenhout 1769) carcasses in Riyadh city, Saudi Arabia. Eight rat carcasses were buried in separate holes at depths of 20 and 40 cm (four holes per depth) to allow natural decomposition and examined at 10-day intervals up to 40 days. During the study period, environmental factors such as humidity, soil temperature, and air temperature were monitored at each depth on a daily basis. At the end of each burial period, one carcass from each depth was exhumed and the degree of decay and presence of insect activity were examined. The results showed that burial depth and temperature were major factors affecting the decomposition rate, whereas no insect activity was observed. The findings of this study can be used to more accurately estimate the time since burial of carcasses.

Thermal requirements of immature stages of Chrysomya albiceps (Diptera: Calliphoridae) as a common forensically important fly

Entomological material may be used to estimate the time since death occurred (postmortem interval, PMI) in forensically obscure cases. The method that is commonly used to calculate minimum post-mortem interval (mPMI, i.e., the least amount of time since one can be confident death occurred) is based on the relationship between insect development and ambient temerature. Isomegalen and isomorphen diagrams are among methods allowing to calculate the age of necorphagous insects, yet thermal summation models provide the most precise and acurate estimations. The digrams are prepared based on the length or the developmental stages of the larvae as a function of time and mean ambient temperature. A knowledge of thermal requirements, in particular lower temperature threshold (D_z) at which development of a species terminates, is of essential importance to calculate ADD (Accumulated Degree Days). In this study different temperature regimes were used to construct the isomorphen diagram, examinate changes in larval body length at different ambient temperatures and to estimate the thermal requirements for developemnt of Chrysomya albiceps, the most common dipteran species reported on human and animal cadavers in Iran. Six development events including hatching, 1st ecdysis, 2nd ecdysis, wandering, pupariation and eclosion were studied under eleven constant temperature regims (17-37 ⁰C). The development rate of Ch. albiceps increased as temperature increased. The larval length peaked at the end of third stage and then decreased at wandering stage. The maximum larval length occurred at 72 h post oviposition at either 31, 33, or 35 °C. At 17 °C, larvae did not hatch from eggs and at 37 °C wandering larvae did not proceed to pupariation, and thus larval development were analysed at the nine left over temperatures. The development stages required at least (D_z ± SE) 13.04 ± 0.37, 14.29 ± 0.45, 15.69 ± 0.56, 15.18 ± 0.56, 14.94 ± 0.48, and 11.23 ± 0.41 °C to reach one of the successive developmentl events, respectively. The estimated thermal summation constant (k) for those the six events were 10.43 ± 0.27, 19.31 ± 0.32, 27.87 ± 1.3, 55.94 ± 1.82, 66.69 ± 3.5, and 143.52 ± 5.61 ADD accordingly.

Thermal requirements for the development of immature stages of Fannia canicularis (Linnaeus) (Diptera: Fanniidae)

Entomological material may be used to estimate the time since death occurred (minimum post-mortem interval, mPMI) in forensically obscure cases. The method commonly used to calculate mPMI is the application of a thermal summation model. Little is known about the thermal requirements of Fanniidae. To fill this gap, the influence of temperature on the development time of Fannia canicularis (Linnaeus), a cosmopolitan species with the potential to be used in forensic entomology, was studied. An experiment was performed under nine ambient temperatures. The thermal summation constants (k) and developmental zeros (T_min) of this species were calculated for six developmental events: hatching, first ecdysis, second ecdysis, wandering, pupariation, and eclosion. Data were primarily analysed with two linear models, and then, since the relationship between temperature and development rate is curvilinear close to the lower and higher developmental thresholds, the relationship was also modelled using three nonlinear models. A fourth nonlinear model was also used to estimate the intrinsic optimum temperature of F. canicularis, at which the population size is maximal and the mortality is the lowest. At 33 °C, larvae did not hatch from eggs, and thus changes in larval body length were analysed at the eight remaining temperatures. Fannia canicularis development from egg to eclosion required a mean ± SE of 481.73 ± 9.89 degree-days above a lower threshold temperature of 4.64 ± 0.19 °C. At the lowest experimental temperature tested, 10 °C, F. canicularis successfully completed all developmental events, although ca. 30% of wandering larvae proceeded to the inactive stage instead of pupariation. Results obtained from nonlinear models were not satisfactory and did not allow us to consider them as reliable from a biological point of view.

Characterizing forensically important insect and microbial community colonization patterns in buried remains

During violent criminal actions in which the perpetrator disposes of the victim's remains by burial, the analysis of insects and bacterial colonization patterns could be necessary for postmortem interval (PMI) estimation. Our research aimed to assess the decomposition process of buried rat carcasses from shallow graves (40 cm), the diversity and dynamics of insects and bacteria throughout the decomposition stages, and the environmental parameters' influence on these variations. The results provide further insight on decomposition in soil and contribute to a broader understanding of the factors involved in decomposition by qualitatively and quantitatively analysing the decomposer community (bacteria and insects). Additionally, two bacterial taxa, Enterococcus faecalis and Clostridium paraputrificum that were investigated for the first time as PMI indicators using quantitative polymerase chain reaction (qPCR) showed differential abundance over time, promising data for PMI estimation. The current study on the decomposition of buried rat carcasses in a natural environment will strengthen the current knowledge on decomposed remains from shallow graves and represents an effort to quantify insect and bacterial taxa as PMI estimators.

Muscidae (Diptera) of forensic importance-an identification key to third instar larvae of the western Palaearctic region and a catalogue of the muscid carrion community

The Muscidae is one of the main dipteran families recognized as important for medico-legal purposes. Although an association of adult flies with decomposing human and animal bodies is documented for about 200 taxa worldwide, cadavers and carrion represents a breeding habitat for considerably fewer species. Species that do colonize dead human bodies can do so under diverse environmental conditions and, under certain circumstances, Muscidae may be the only colonizers of a body. Because of difficulties in identification, many studies have identified immature and/or adult muscids only to the genus or family level. This lack of detailed species-level identifications hinders detailed investigation of their medico-legal usefulness in carrion succession-oriented experiments. Identification to species level of third instars of Muscidae of forensic importance and the utility of larval morphological characters for taxonomic purposes were subjected to an in-depth revision. A combination of characters allowing for the discrimination of third instar muscids from other forensically important dipterans is proposed. An identification key for third instar larvae, which covers the full set of cadaver-colonising species of Muscidae from the western Palaearctic (Europe, North Africa, Middle East), is provided. This key will facilitate more detailed and species-specific knowledge of the occurrence of Muscidae in forensic entomology experiments and real cases. The carrion-visiting Muscidae worldwide are catalogued, and those species breeding in animal carrion and dead human bodies are briefly discussed with regard to their forensic importance.

The colonisation of remains by the muscid flies Muscina stabulans (Fallén) and Muscina prolapsa (Harris) (Diptera: Muscidae)

In the field, the muscid flies Muscina stabulans (Fallén) and Muscina prolapsa (Harris) only colonised buried baits in June, July and August. The two-species co-occurred on baits buried at 5cm but only M. prolapsa colonised baits buried at 10cm. Other species of insect were seldom recovered from buried baits regardless of the presence or absence of Muscina larvae. In the laboratory, both M. stabulans and M. prolapsa preferentially colonised liver baits on the soil surface compared to those buried at 5cm. Baits buried in dry soil were not colonised by either species whilst waterlogged soil severely reduced colonisation but did not prevent it entirely. Dry liver presented on the soil surface was colonised and supported growth to adulthood but if there was no surrounding medium in which the larvae could burrow then they died within 24h. M. stabulans showed a consistent preference for ovipositing on decaying liver rather than fresh liver, even when it had decayed for 41 days. The results for M. prolapsa were more variable but it was also capable of developing on both fresh and very decayed remains. Blood-soaked soil and dead slugs and snails stimulated egg-laying by both species and supported larval growth to adulthood. Mushrooms, melon, and bananas also stimulated egg-laying although to a much lesser extent and very few larvae survived to adulthood. Horse faeces stimulated extensive egg-laying but the larvae invariably died during the first or second instar and none survived to pupariation. This information could be useful when determining the forensic significance of Muscina larvae recovered from dead bodies.