The identification of Diptera of the grave and their succession patterns during winter and summer in central South Africa, with reference to forensic applications

[摘要] English: Forensic entomology is a specialist branch of forensic sciences in whichinformation about insects is used to draw certain conclusions when investigatingmedico-legal cases involving both humans and wildlife. The primary applicationof insects collected from a crime scene is to determine the Post-Mortem Interval(PMI). One of the principal cornerstones in the effective application of forensicentomology is the correct identification of species found at a crime scene. Theestimation of PMI using succession and developmental data is dependent uponthe specific species that were present on a cadaver. The aim of this study wasto identify the members of the Diptera that are capable of colonising buriedcarrion within a Free State grassland area, as well as to compare below grounddipteran data with above ground dipteran succession patterns.The field experiments, conducted in order to determine what species of Dipteraare capable of reaching buried carrion during winter and summer months, aswell as to determine the succession patterns of Diptera on buried remains, wereconducted on the west fields of the University of the Free State campus, incentral South Africa. The area is characterised by dry mild winters and warmersummers, with occasional rainfall periods. A total of seven pigs (Sus scrofaLinnaeus 1758) were used during each season, which consisted of one aboveground control carcass and six separate below ground carcasses buried at 60cm. Below ground carcasses were left for predetermined periods of time andwere excavated on separate occasions over each 120 day trial period tomonitor dipteran occurrence, colonisation and dipteran interactions.Members of Diptera were found to colonise carcasses at 60 cm during bothwinter and summer trials. Higher dipteran species diversity was noted on theburied winter carcasses in comparison to the buried summer carcasses. Fourspecies of Diptera, Megaselia scalaris (Loew 1866) (Phoridae), Conicera tibialisSchmitz 1925 (Phoridae), Muscina stabulans (Fallén 1817) (Muscidae) andLeptocera Olivier 1813 sp. (Sphaeroceridae) were seen to occur on wintercarcasses, with first colonisation taking place from day 21 of the winter trial.Three species of the Diptera, M. scalaris, Leptocera sp., and SarcophagaMeigen 1826, were seen to colonise buried summer carcasses, with first colonisation taking place from day 21 of the summer trial. Dipteran faunalcomposition on buried carcasses was noted to be different to that of Diptera onabove ground carcasses during both the winter and the summer trials.Statistical analysis showed that there was a significant difference betweenabove ground and below ground dipteran faunal similarity.Preservation experiments on immature Diptera of the grave for identificationpurposes showed that the standard preservation mediums used for insects offorensic importance, such as ethanol solution and formaldehyde solution, arenot effective. Preservation of adult samples was successful in 70% ethanolsolution. Breeding trials under laboratory conditions proved effective in breedinglarval instars found on buried carcasses through to adulthood for identification.Due to the difficulty in preservation of immature individuals of Diptera of thegrave, and the ease of breeding larvae of these dipteran species, identificationswere done on adult specimens. Adult Diptera were described based ontaxonomic criteria, including wing venation, setal hairs and the hypopygium ofmale phorid specimens, and a simplified identification key was successfullycompiled using morphology of the adult Diptera of the grave.

[发布机构] University of the Free State