Effect of body mass and clothing on carrion entomofauna.

Carcass mass largely affects pattern and rate of carrion decomposition. Supposedly, it is similarly important for carrion entomofauna; however, most of its likely effects have not been tested experimentally. Here, simultaneous effects of carcass mass and clothing are analyzed. A factorial block experiment with four levels of carcass mass (small carcasses 5-15 kg, medium carcasses 15.1-30 kg, medium/large carcasses 35-50 kg, large carcasses 55-70 kg) and two levels of carcass clothing (clothed and unclothed) was made in a grassland habitat of Western Poland. Pig carcasses (N = 24) were grouped into spring, early summer, and late summer blocks. Insects were sampled manually and with pitfall traps. Results demonstrate that insect assemblages are more complex, abundant, and long-lasting on larger carcasses, whereas clothing is of minor importance in this respect. Only large or medium/large carcasses were colonized by all guilds of carrion insects, while small or medium carcasses revealed high underrepresentation of late-colonizing insects (e.g., Cleridae or Nitidulidae). This finding indicates that carcasses weighing about 23 kg-a standard in forensic decomposition studies-give an incomplete picture of carrion entomofauna. Residencies of all forensically relevant insects were distinctly prolonged on larger carcasses, indicating that cadaver mass is a factor of great importance in this respect. The pre-appearance interval of most taxa was found to be unrelated to mass or clothing of a carcass. Moreover, current results suggest that rate of larval development is higher on smaller carcasses. In conclusion, this study demonstrates that carcass mass is a factor of crucial importance for carrion entomofauna, whereas the importance of clothing is small.

Effect of body mass and clothing on decomposition of pig carcasses.

Carcass mass and carcass clothing are factors of potential high forensic importance. In casework, corpses differ in mass and kind or extent of clothing; hence, a question arises whether methods for post-mortem interval estimation should take these differences into account. Unfortunately, effects of carcass mass and clothing on specific processes in decomposition and related entomological phenomena are unclear. In this article, simultaneous effects of these factors are analysed. The experiment followed a complete factorial block design with four levels of carcass mass (small carcasses 5-15 kg, medium carcasses 15.1-30 kg, medium/large carcasses 35-50 kg, large carcasses 55-70 kg) and two levels of carcass clothing (clothed and unclothed). Pig carcasses (N = 24) were grouped into three blocks, which were separated in time. Generally, carcass mass revealed significant and frequently large effects in almost all analyses, whereas carcass clothing had only minor influence on some phenomena related to the advanced decay. Carcass mass differently affected particular gross processes in decomposition. Putrefaction was more efficient in larger carcasses, which manifested itself through earlier onset and longer duration of bloating. On the other hand, active decay was less efficient in these carcasses, with relatively low average rate, resulting in slower mass loss and later onset of advanced decay. The average rate of active decay showed a significant, logarithmic increase with an increase in carcass mass, but only in these carcasses on which active decay was driven solely by larval blowflies. If a blowfly-driven active decay was followed by active decay driven by larval Necrodes littoralis (Coleoptera: Silphidae), which was regularly found in medium/large and large carcasses, the average rate showed only a slight and insignificant increase with an increase in carcass mass. These results indicate that lower efficiency of active decay in larger carcasses is a consequence of a multi-guild and competition-related pattern of this process. Pattern of mass loss in large and medium/large carcasses was not sigmoidal, but rather exponential. The overall rate of decomposition was strongly, but not linearly, related to carcass mass. In a range of low mass decomposition rate increased with an increase in mass, then at about 30 kg, there was a distinct decrease in rate, and again at about 50 kg, the rate slightly increased. Until about 100 accumulated degree-days larger carcasses gained higher total body scores than smaller carcasses. Afterwards, the pattern was reversed; moreover, differences between classes of carcasses enlarged with the progress of decomposition. In conclusion, current results demonstrate that cadaver mass is a factor of key importance for decomposition, and as such, it should be taken into account by decomposition-related methods for post-mortem interval estimation.

Temperature-dependent appearance of forensically useful flies on carcasses.

Flies are frequently used for postmortem interval (PMI) estimations. These estimates are usually based on the age of larval or pupal specimens. However, the age defines only the minimum PMI. In order to move forensic entomology further, a method useful for the estimation of an interval preceding insect appearance on a corpse called the pre-appearance interval (PAI) is needed. Recently, it was demonstrated that the PAI of several carrion beetles is closely related to the temperature prevailing throughout this interval. Hence, it was postulated to estimate PAI from temperature. In order to check premises for using this approach with flies, a test of the relationship between adult or oviposition PAI and temperature was made for nine species of European flies. Data on PAI originated from pig carcasses decomposing under various temperatures. Adult PAI of Hydrotaea dentipes, Hydrotaea ignava, Hydrotaea similis, Phormia regina, and Stearibia nigriceps and oviposition PAI of S. nigriceps were exponentially related to temperature. Only S. nigriceps revealed a close relationship, demonstrating solid premises for PAI estimation from temperature alone. Adult and oviposition PAI of Calliphora vomitoria and adult PAI of Hydrotaea pilipes were not related to temperature. Adult and oviposition PAI of Lucilia sericata and Lucilia caesar responded similarly, with an abrupt and large increase in a narrow range of low temperatures and no response in a broad range of high temperatures. Probably, different mechanisms form the basis for the response of PAI to temperature in flies colonizing carcasses shortly after death and flies colonizing carcasses later in the decomposition process.

Insects colonising carcasses in open and forest habitats of Central Europe: search for indicators of corpse relocation.

Several traces may reveal the post-mortem relocation of a corpse. Insects are particularly useful for that purpose. The use of insects for inferring the transfer of a corpse rests on a premise that particular species colonise corpses in different habitats. However, only some insects reveal a strong preference for a given type of habitat. In order to find those insects which colonise corpses exclusively in open habitats, as opposed to forest habitats, a pig carrion study was made in rural open and rural forest habitats of Central Europe. Lucilia sericata (Diptera: Calliphoridae), Dermestes frischi, Dermestes laniarius (Coleoptera: Dermestidae), Omosita colon, some species of Nitidula (Coleoptera: Nitidulidae) and Necrobia rufipes (Coleoptera: Cleridae) were found to breed exclusively in open habitats. Only Oiceoptoma thoracicum (Coleoptera: Silphidae) avoided definitely breeding in open habitats. Sarcophaga caerulescens (Diptera: Sarcophagidae) regularly bred in open habitats but rarely bred in forests. Accordingly, L. sericata, D. frischi, O. colon, species of Nitidula and supposedly N. rufipes may be classified as indicators of corpse relocation from rural open to rural forest habitats of Central Europe. Only O. thoracicum may be classified as an indicator of the relocation in an opposite direction.

A simple computer-assisted quantification of contrast in a fingerprint.

A simple method for quantification of contrast in a fingerprint is proposed. Contrast is defined as the average difference in intensity of pixels between valleys and ridges in a fingerprint. It is quantified from a scanner-acquired image of the fingerprint using a histogram function of Adobe Photoshop. The method was validated with black inked prints and marks developed with aluminum powder. Moreover, we tested resistance of the method to rater-dependent errors and dependence of the measurements on the resolution of an image and the model of the scanner. For both groups of fingerprints, the method gave coherent and easily interpretable quantitative values for contrast. There were no significant differences between measurements performed by different raters and by the same rater in a test-retest procedure. However, the method was found to be instrument dependent, as measurements were significantly affected by image resolution and the model of the scanner.

Temperature-dependent appearance of forensically useful beetles on carcasses.

Estimating the pre-appearance interval (PAI) of carrion insects from temperature is a new and promising improvement of entomological methods for post-mortem interval estimation. In order to use this approach in casework, a taxon should demonstrate a close relationship between PAI and temperature. In this article we test this relationship in selected species of beetles, namely Thanatophilus sinuatus Fabr., T. rugosus L., Necrodes littoralis L. (Silphidae), Necrobia rufipes De Geer, N. violacea L. (Cleridae), Dermestes frischii Kug. (Dermestidae), Creophilus maxillosus L., Philonthus politus L., Ontholestes murinus L. (Staphylinidae), Saprinus semistriatus Scriba, S. planiusculus Motch. and Margarinotus brunneus Fabr. (Histeridae). Data were collected from 30 pig carcasses decomposing under different temperature conditions in open and forest habitats of Western Poland. Beetles were sampled with pitfall traps and with manual and soil sampling. The on-site temperature of the ground level was recorded. The relationship was tested separately in adult and larval stages. All species, except for D. frischii, revealed significant relationship between PAI and temperature. In all cases PAI was found to decrease exponentially with an increase in temperature. Moreover, above some temperature it was nearly constant. The relationship was strong in the case of adult and larval N. littoralis, adult N. rufipes, adult and larval C. maxillosus, adult P. politus, S. semistriatus and S. planiusculus. The relationship of moderate strength was found for adult and larval T. sinuatus, adult N. violacea and adult M. brunneus. In the case of adult T. rugosus and O. murinus the relationship was weak. Current results demonstrate that there are solid premises for estimating PAI from temperature in T. sinuatus, N. littoralis, N. rufipes, N. violacea, C. maxillosus, P. politus, S. semistriatus, S. planiusculus and M. brunneus. Implications for forensic entomology are discussed.