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Browsing Genetics by Author "Brink, S. L."
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Item Open Access DNA profiling from the crop content of sarcophagidae spp. larvae(University of the Free State, 2017-01) Barnard, Adri Marlene; Wessels, L.; Ehlers, K.; Brink, S. L.English: Morphological analysis of insect evidence plays a significant role in crime scene investigation. With the influence of DNA analysis in forensic cases, which now also plays a key role in forensic entomology, more emphasis has been placed on a dual preservation goal when collecting insect evidence. Previous studies indicated that it might be possible to identify the last meal of sarcophagid maggots using gut content combined with DNA profiling. For gut content analysis it is imperative to be familiar with the internal morphology as well as maggot gastric emptying. However, insufficient information is available on the morphology of Sarcophaga cruentata maggot alimentary canals as well as the rate of maggot gastric emptying. Also, considering the use of insects for both PMI and DNA analysis, the current preservation methods are not necessarily suitable for maggot preservation for DNA analysis of the crop content. Various preservation methods were examined for optimal preservation of both morphology and gut content. In order to understand gastric emptying, the internal gut structures and movement of food through the gut was examined. Fully fed maggots were removed from the food source and hot water killed at 3 hour intervals for up to 30 hours to investigate gastric emptying. Crop content DNA analyses were performed to attempt identification and DNA profiling of the maggots’ last meal. Due to the inhibiting effect of formalin on DNA analysis and the extensive dehydration of prolonged ethanol storage, -80°C was investigated for sample preservation which generally provided good results. Inconsistent results were obtained using the various preservation and DNA analysis combinations tested. Sarcophagidae gut morphology analysis indicated gross anatomical similarity to Chrysomya megacephala. External tracking of food movement proved difficult. After digestive tract dissection it was found that the mid- and hindgut coiled around each other. Due to the coiled structure of the gut, the exact location of the food bolus could therefore not be determined without dissection. The expected gastric emptying was not consistently observed with pronounced variability in results. Nevertheless, it was observed that the maggot crops were completely empty by 30 hours post removal from food source. DNA profiling of the crop content supported previous findings, although only partial STR profiles were obtained. It is unlikely that full profiles will be obtained when analyzing gut content due to the degraded nature of the food source, as well as the effect of digestive enzymes present in the maggot saliva regurgitated onto the food source. Various recommendations can be made based on the results. At crime scenes maggots should be killed in warm water (± 60°C for 30 seconds), dried on paper towel and stored in 80% ethanol while transported to the laboratory. Samples should be removed from the ethanol within 24 hours after collection, dried and stored individually in microcentrifuge tubes at -80°C (or similar low temperatures) until analysis is performed. During analysis samples should be handled on ice, ensuring the integrity of the sample, as it was found that samples defrosted rapidly after removal from the -80°C storage. It is further recommended to use commercially available kits when analyzing maggot gut samples due to the additional clean-up steps present in the kits. These clean-up steps aid in limiting the addition of fats and lipids from the maggot internal structures that could inhibit downstream DNA analysis of samples. Overall this study reinforced the possibility of using maggot crop content for providing STR profiles of the victim and/or perpetrator. Although only partial STR profiles were obtained, it indicated that, with further investigation and optimization, this is an interesting avenue for future research with many unexplored avenues for aiding in crime scene investigation.