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The study and application of underwater decomposition from an entomological perspective for the purpose of post-mortem interval estimation

Student thesis: Doctoral Thesis

Introduction
While decomposition and insect succession on land are well understood, much less is known about these processes in aquatic environments. The aim of this thesis is to present a series of studies designed to investigate these processes in the South of England, beginning with a questionnaire and semi-structured interviews with various practitioners to assess the need for this type of research to take place. This is followed by a series of field studies recording and comparing decomposition and insect & invertebrate colonisation across different aquatic environments.
Overall these studies provide new knowledge about insect succession in freshwater in the South of England, and some steps have been made towards making ocean-based research more accessible for small laboratories. Additionally, research suggests that the main requirements of Senior Investigating Officers (SIOs) is for forensic entomology data to be presented in a way that is easily understandable and usable in casework (unpublished data, Chapter 4), and these studies represent the first steps towards being able to provide data that meets these requirements.

Forensic Entomology and Underwater Death Investigation: A Review of its Utilisation and Potential
To assess the need for an investigation into aquatic decomposition, a questionnaire was designed to establish the current scope and utilisation of forensic entomology in aquatic death scene investigations, and was distributed to forensic practitioners and other professionals involved in underwater death investigations. Following this, a focus group was conducted with Senior Investigating Officers and was designed to explore experiences of professionals with more managerial experience. The outcomes suggest that there is considerable scope for use of entomology at aquatic death investigations, but that it is not being used to its full potential. Practitioners welcomed future research and agreed that there is a need for better awareness of entomology, but emphasised the need for better engagement between the forensic scientist and investigator.
Influence of Two Enclosed Water Types on Entomological Species Colonisation in Portsmouth, UK
A pilot study was undertaken to collect some preliminary data and begin to develop a methodology for the in-depth studies. Here, two rabbit Oryctolagus cuniculus Linnaeus (Lagomorpha: Leporidae) carcasses were decomposed in lidded plastic boxes in an urban garden environment. One box was filled with water and sediment obtained from a local stream and the other was filled with sea water and sand collected from the Solent (Portsmouth, Hampshire, UK). Entomological samples were collected from both carcasses until they were both fully disarticulated (151 days) and the decompositional changes were also monitored. A catalogue of insect specimens is provided. Some initial guidance for collection of entomological specimens from remains found in small enclosed aquatic environments is also proposed.
A Preliminary Investigation of Faunal Colonisation of Remains in Open Water
Here, three different approaches for investigating decomposition and insect succession in an ocean environment were tested with a view to providing a methodology appropriate for use by small labs without access to expensive and highly specialised equipment. Method 1 used a modified crayfish pot to enclose a piglet carcass and incorporated a GoPro™ camera to monitor decomposition and marine fauna feeding behaviour using timelapse photography. Method 2 made use of a whelk pot to house the carcass and improve the rate of trapping feeding fauna. Finally, method 3 took a combined approach using a lobster pot to both house the piglet carcass and trap feeding fauna, as well as using timelapse photography to monitor decomposition and feeding behaviour. Method 3 was found to yield the largest amount of usable data of the three methods tested, primarily showing an abundance of shore crabs.
A Checklist of Arthropods Associated with Piglet Carcasses Decomposing in a Freshwater Pond Environment in Southeast England
In this experiment, four piglet Sus scrofa domesticus Linnaeus (Artiodactyla: Suidae) carcasses were allowed to decompose naturally in a man-made freshwater pond located in a woodland area near Wickham, Hampshire, UK. Throughout the decomposition period, insect specimens were collected and the changes in decomposition state were recorded until the carcasses were fully skeletonised. As with the pilot study, a catalogue of colonising insect species is provided.
Effects of Environmental Temperature on Oviposition Behaviour in Three Blow Flies Species of Forensic Importance
Various factors are known to affect blow fly behaviour with respect to oviposition of which temperature is the most significant factor. These variables apply equally in aquatic environments, however much less is known about the processes of decomposition and invertebrate colonisation in these environments. Here, the oviposition behaviour of three species of forensically important blow fly (Calliphora vicina, Calliphora vomitoria and Lucilia sericata,) was studied under controlled laboratory conditions over a range of temperatures (10 to 40°C). Lower temperature thresholds for oviposition of 16°C and 17.5°C were established for C. vomitoria and L. sericata respectively, whilst C. vicina continued to lay eggs at 10°C. C. vomitoria and L. sericata both continued to lay eggs at 40°C, whilst the highest temperature at which oviposition occurred in C. vicina was 35°C. While this study was not conducted in an aquatic environment, it nonetheless provides important background information for understanding insect colonisation of remains in water, where temperatures may be lower than on land.

Original languageEnglish
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Award dateSep 2019

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