A Preliminary Investigation of Insect Colonisation and Succession on Remains in New Zealand Terry L
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Available online at www.sciencedirect.com Forensic Science International 176 (2008) 217–223 www.elsevier.com/locate/forsciint A preliminary investigation of insect colonisation and succession on remains in New Zealand Terry L. Eberhardt a,*, Douglas A. Elliot b a The University of Auckland, Department of Chemistry, Forensic Science Programme, Building 301, Level 5, 23 Symonds St., Auckland, New Zealand b Institute of Environmental Science and Research Limited (ESR), A Crown Research Institute and The University of Auckland, Forensic Science Programme, New Zealand Received 22 May 2006; received in revised form 25 July 2006; accepted 20 September 2007 Available online 21 February 2008 Abstract A preliminary, systematic field study on the process of decomposition and associated insects was conducted, for the first time, in New Zealand. Using pig carcasses as an animal model for human decomposition, insect colonisation and succession was monitored in three different habitats in the Auckland region where remains are likely to be found. A significant difference in the rates of decomposition was found among the three different habitats of an open field, coastal sand dune area and native bush during the autumn/winter season. The primary colonisers of all carcasses were Calliphora stygia Fabricius (Calliphoridae), Chrysomya rufifacies Macquart (Calliphoridae) and Hydrotaea rostrata Robineau-Desvoidy (Muscidae). Two species were identified as possible representatives of the habitats in which they were found; Fannia sp. (Fanniidae) in the open field habitat and Calliphora hilli Patton (Calliphoridae) in the native bush habitat. Also identified was Sylvicola sp. (Anisopodidae) as a possible indicator of damp habitats as well as a likely indicator of a longer postmortem interval. This preliminary investigation presents a broad outline of the insects associated with remains and the order in which they appear in the Auckland region. # 2007 Elsevier Ireland Ltd. All rights reserved. Keywords: Forensic entomology; Insect succession; Decomposition; Postmortem interval 1. Introduction were most likely laid can be estimated. This interval of time provides the minimum time elapsed since flies first had access Forensic entomology is the application of the study of insect to the body and is based on the premise that the time required biology to criminal matters. The utilisation of insects in for larval development is predictable for each species of fly. forensic entomology is primarily associated with death The second method is based on the biological principle of investigations. However, it is not restricted to such events succession, where the colonisation of remains, as an ephemeral and may be used to determine the location of an incident [1,2], habitat, occurs in a reasonably predictable sequence. Succes- the presence and time of infliction of wounds [3], the length of a sional stages are represented by the variety of insect species period of neglect in the elderly or children [4], and the detection present at a particular time. This diversity is then compared to of drugs and poisons [5,6]. known successional patterns for that geographic area or habitat. In determining a postmortem interval, which is defined as The time required for the diversity of species to become as the time elapsed between death and discovery, insects provide established as they were at the time of discovery represents the evidence by two main methods. The first method is based on the estimated postmortem interval. age of fly larvae, as flies are the primary colonisers of a corpse. Many different variables may have an effect on the amount By determining the age of the larvae found with a corpse and of time that has elapsed since death. Ambient factors such as then using retrospective calculation, the time when the eggs temperature, local weather conditions and the surrounding habitat can have an influence on the length of the postmortem interval. Other influential factors include the season, body * Corresponding author. Tel.: +64 9 815 3670; fax: +64 9 849 6046. deposition (e.g. burial, exposed or indoors), and overall E-mail address: [email protected] (T.L. Eberhardt). geographical location. These variables can each have a 0379-0738/$ – see front matter # 2007 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.forsciint.2007.09.010 218 T.L. Eberhardt, D.A. Elliot / Forensic Science International 176 (2008) 217–223 different effect and may combine in different ways at a which the dorsal aorta was cut to ensure death by internal exsanguination. particular crime scene. If the variables are not considered, they After death, the carcasses were sealed within plastic bags and transported to the study sites. may have a deleterious effect on the accuracy of a postmortem Three pig carcasses were placed 50 m apart in each habitat; two of which interval estimate. served as the research carcasses and one of which served as a control from Previous related work conducted between 1981 and 1983 in which no samples were collected. The control carcass was used to determine New Zealand involved the collection of insects associated with what, if any, disturbance was caused by the continual visitation and collection of human remains received for autopsy in Auckland [7]. The insects. Each carcass was dressed in a cotton T-shirt and underwear (modelling a common homicide scenario where the victim is clothed), then placed within a research presented here however, is the first systematic field chicken wire cage. The cage had a hinged lid and front panel to allow for access experiment to be conducted in New Zealand and aims to to the carcass and was constructed using PVC piping (2.5 cm) as the frame, enhance the information currently used to make an estimate of welded wire mesh (1 cm) as the base and 2.5 cm chicken wire as the sides and the postmortem interval based on insect evidence. Conducted top of the cage. This cage design ensured that the carcass would be in full during the autumn/winter season, the aims of this study were: contact with the ground and allowed for full environmental exposure while preventing scavenging from animals in the area. No sign of animal or human firstly, to observe and record insect species involved in the disturbance was noted during the study. primary colonisation of remains and their general rate of Weather stations, consisting of a maximum/minimum thermometer and a development in a natural setting; secondly, to observe and rain gauge were erected at each of the habitat sites. Weather data were collected record the order in which different insects appear and utilise the during each site visit for the duration of the study. However, the comparison of remains (succession) and; thirdly, to compare the process as it weather between the three habitats was restricted to consideration of the first 3 weeks, as site visits after this time decreased in frequency. Comparison of the occurs in three different habitats. To accomplish these aims, this values collected in the later part of this study would be inappropriate as the field experiment used pig carcasses as an animal model to values were cumulative and would therefore not accurately reflect the daily simulate human decomposition in three different habitats in the temperatures and rainfall experienced in the habitat. Auckland region. The study sites were visited 6 days a week for the first 3 weeks and every New Zealand is comprised of two main islands and several other day for the following 2 weeks. Site visits then tapered off until the last day of observation, 128 days after death. During each visit, the state of the carcass, smaller islands. The city of Auckland is located on the North weather conditions and insect activity were observed and recorded. A photo- 0 0 Island at 36851 S latitude and 174845 E longitude. The graphic record was also maintained for the duration of the study. Auckland region experiences a mild temperate climate where Representative samples of insects were collected from on, in and under the the average daily autumn temperature (March, April and May) carcasses and by sweep net above the carcasses to ensure as many different is 16 8C, with an average daily maximum temperature of 20 8C species as possible were collected. Samples of eggs and fly larvae were divided in two where half were killed at the site by immersion in near-boiling water and and an average daily minimum temperature of 12 8C. The half were taken to the laboratory for rearing. The rearing of larvae was for average daily winter temperature (June, July and August) is confirmatory identification purposes. 11 8C, with an average daily maximum of 15 8C and an average daily minimum of 7.5 8C. There is no snow and frost is uncommon. 3. Results Five general stages of decomposition, modified from 2. Materials and methods descriptions provided by Goff [9], were identified. These Three different habitat sites were chosen based on the most common stages are subjective rather than discrete changes and are areas where a body is likely to be found in the Auckland region. The first generally accepted as artificial boundaries placed on a continual habitat was an open field consisting of mixed grasses, where intermittent process for the purposes of description [12–14]. The stages grazing by sheep and cattle is the predominant land activity. This site were named fresh, bloated, active decay, post-decay, and provided maximum environmental exposure. The second habitat chosen was a coastal sand dune area. The study sites in this habitat were located skeletal. For the purposes of this study, the fresh stage was approximately 1 km from the ocean and were partially shaded by low considered to be from the moment of death to the onset of shrubs (young manuka trees, Leptospermum sp.). The third habitat chosen bloating.