Description of the life stages of forensically important Coleoptera in the central Free State

Abstract

The identification and the development of beetles of forensic importance remain understudied when compared to the number of studies conducted on development and identification of the life stages of flies of forensic importance in central Free State. This hinders our understanding of what beetle species are associated with decomposing carcasses and how we can use their immature stages and their development to determine Post Mortem Interval. It is important to make correct species identification when calculating PMI because development data of one species cannot be used for the forensic significance of another species, even in closely related species. In recent successional studies that have been conducted in central Free State, beetles of forensic importance have been identified to family or genus level. Carcasses used in this experiment were domestic pig (Sus scrofa domesticus) with a total of three pigs between the weights range of 32.5-49kg, Cape baboon (Papio ursinus) with a total of two baboons weighing 18 and 19kg and one sheep (Ovis aries) weighing 44kg. The carcasses were placed on the Western side of the campus of the University of the Free State. The carcasses were allowed to decompose and insects were collected twice a day during the decomposition period. The aim of this project was to describe morphological characteristics, used to develop keys with which to differentiate between beetle species (adults and immatures) associated with decaying carcasses in central Free State. A total of eighteen beetle species representing eight families of forensic importance (Silphidae, Staphylinidae, Histeridae, Dermestidae, Cleridae, Trogidae, Scarabaeidae, and Nitidulidae) were collected from the carcasses. Some beetle species were reared under laboratory conditions with the intention of obtaining immatures life stages that were not found in the field. The rearing temperature was set to 28 ± 2ºC and a photoperiod of 12L:12D was maintained in the insectarium. A 3 to 4cm soil layer was laid down in some breeding containers and moist cotton wool was used to maintain the soil moisture levels. In some breeding containers, only sawdust and styrofoam were used as pupation refugia. Of eighteen species collected, only two species completed their development under laboratory conditions. Some of the beetles that were collected are already described in literature, and these beetles were redescribed using both external and internal (internal male genitalia) morphological characteristics. Some of the species were only identified to genus level and, in future, the morphological characteristics and micrographs provided in this study will help with identification for both successional and developmental studies.