Effect of Burning on Minimum Post-Mortem Interval (Minpmi) Estimation from an Entomological Perspective

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AEFS 1.1 (2017) 17–31 Archaeological and Environmental Forensic Science ISSN (print) 2052-3378 https://doi.org.10.1558/aefs.32472 Archaeological and Environmental Forensic Science ISSN (online) 2052-3386

Effect of Burning on Minimum Post-Mortem Interval (minPMI) Estimation from an Entomological Perspective

Amoret P. Whitaker

University of Winchester and Natural History Museum, London

[email protected]; [email protected]

Forensic entomologists are often employed to estimate the minimum post-mortem interval of bodies in cases of untimely or unexplained death. Although some cases have involved burnt remains, few studies have been carried out to assess whether entomology can still be utilised. Only one major study has been carried out which determined that even after a major house fire, blow fly larvae can still be identified and used to estimate a minimum post-mortem interval. Most studies have investigated whether burning affects the attraction of blow flies to burnt bodies, and their subsequent oviposition. Results vary, but suggest that blow flies may be more likely to oviposit on bodies which have undergone considerable burning, where the splitting of the skin has resulted in the exposure of suitable oviposition sites, whereas bodies only mildly burnt may be too dry for oviposition. In addition, although most studies have utilised some type of accelerant to facilitate the burning, this has not been taken into account with regards to blow fly attraction or larval development. This review paper gives an overview of the current literature relating to burnt bodies and the use of entomology to estimate a minimum post-mortem interval in such cases.

Forensic entomology is the study of insects within a legal context, and can be divided broadly into three main areas of interest—stored product pests, urban entomology, and, the area in which the term is most frequently applied, medico-legal cases (Hall et al. 2012). In the latter area, a forensic entomologist may be employed to assist a legal investigation in cases of myaisis (the infestation of live animals or humans by insects) or in cases of unexplained or untimely death, most often to estimate the minimum post-mortem interval (minPMI) (Hart et al., 2008). Although it is one role of forensic pathologists to estimate time since death, the methods they employ, including the post-death conditions of livor mortis, algor mortis and rigor mortis, are only really applicable during the first 48–72 hours after Keywords: Blow fly oviposition, forensic entomology, minimum post-mortem interval, Crow-Glassman Scale, fire, burnt bodies

© Equinox Publishing Ltd. 2017, Office 415, The Workstation, 15 Paternoster Row, Sheffield, S1 2BX 18 Amoret P. Whitaker death (Campobasso et al. 2001) and even then there is considerable variation (Bourel et al. 2003). Beyond that time, the pathologist uses their medical knowledge and experience to estimate time since death. In some cases, the body may have died or decomposed under particular conditions which may affect the normal decomposition process. These conditions may include anaerobic environments, where the body has been hidden or otherwise enclosed, and thus decomposed in an oxygen-starved environment. Factors such as clothing, and the type of materials involved, may also affect decomposition processes (Goff 1992). Burial (Payne et al. 1968) and underwater (Payne and King 1972) environments will also alter the usual decomposition process, and fire will alter the body by causing dehydration and reduced protein content (Campobasso et al. 2001). In order to estimate the minimum post-mortem interval, the forensic entomologist estimates the age of the insects colonising the body. In the majority of cases, the first insects to do this are the blow flies (Diptera: Calliphoridae). Both males and females detect a body by the odour it omits during the early stages of decomposition (Cam- pobasso et al. 2001), but females are attracted in much larger numbers. The males feed on the body and take advantage of the mating opportunities, and the female also feeds on the body and lays her eggs (oviposits) on it. The eggs hatch out into 1st instar larvae, which feed on the body’s soft tissues, and moult into two further stages, 2nd and 3rd instar. Once they have completed their feeding stage of development, the larvae generally disperse away from the body to find a suitable pupariation site, although some species such as Protophormia terraenovae pupariate on the body itself (Busvine 1980). The age of the insects is calculated using a method based on pre-determined rates of development, which differ between even closely related species. Insects are poikilothermic, with their rate of development depending on the external temperature, thus the colder it is the slower they develop, and the hotter it is the faster they develop (Ames and Turner, 2003). Therefore forensic entomologists can estimate an insect’s age (i.e. the time they were laid as eggs [sometimes as larvae] on the body) using a method of ADD (accumulated degree days) or ADH (accumulated degree hours), which is calculated by time x days or time x hours, respectively. Thus, if you know the number of ADD/ADH required for a species to reach a certain stage of development, and you can estimate the temperature at which it was developing, you can estimate the time taken for the insect to reach that stage. However, it is important to emphasise that it is the minimum post-mortem interval that is being estimated, i.e. the time since egg-laying, rather than actual time since death. Although blow flies have an extraordinary sense of smell, and may locate a body within minutes of death, the time taken for the female blow fly to locate and lay her eggs on the body, sometimes referred to as the pre-oviposition period (POP), is uncertain. Under some circumstances egg-laying may be considerably delayed, such as if the body is wrapped, buried, enclosed, submerged in water, indoors, or somehow less accessible to the blow fly (Goff 1992; Mann et al. 1990). One condition which may affect the pathologist’s estimation of time since death is that of a burnt body, caused by fire and resulting in physical changes to the body. In

CGS Level Description Level # 1 Constitutes burn injuries characteristic of typical smoke death. The body may exhibit blistering of the epidermis and singeing of the head and facial hair. Recovery of the body is similar to that for other victims not involving burn injury. The body is recognizable for identification at this level. Level # 2 Defines a body that may be recognizable but most often exhibiting varying degrees of charring. Further destruction of the body is limited to the absence of elements of the hands and/or feet, and possibly, the genitalia and ears. Addi- tional searching near the body is warranted for recovery of disarticulated elements. Identification is made, most often, by the collaboration of medical examiner and forensic odontologist. Level # 3 Shows further destruction of the body, with major portions of the arms and/or legs missing. The head is present at this level although identity is non-recognis- able. The search area for associated disarticulated remains should be widened. A forensic anthropologist should be included to facilitate successful search and recovery procedures at the death scene. Identification is co-ordinated by a medical examiner who may require the aid of a forensic odontologist. If needed, a forensic anthropologist may be called on to determine gender, age, race, etc. from the skeleton. Level # 4 Corresponds to a degree of extensive burn destruction whereby the skull has fragmented and is absent from the body. Some portions of the arms and/or legs may still remain articulated to the charred body. Search and recovery should be aided by a forensic anthropologist using systematic bioarchaeological methods including screening procedures to locate small body fragments and dental elements. Identification is coordinated by a medical examiner using forensic anthropologist and odontologist consultants, as needed. Level # 5 Represents the final level of the proposed scale. At this level, the body has been cremated and little or no tissue is present. The remains are highly fragmentary, scattered and incomplete. A forensic anthropologist should be an on-site consultant for identification and recovery of the cremains. Personal identification is most difficult at this level and a forensic anthropologist may be best trained to interpret cremains for identifying physical attributes of the deceased. Recovery of dental elements will require the expertise of a forensic odontologist. As with all fire deaths, a medical examiner is, mostly likely, the designate to coordinate consultant activities. Table 1. Crow-Glassman Scale (CGS) for describing the extent of burn injury to human remains (Glassman and Crow 1996). a retrospective study carried out in France (Fanton et al. 2006) on the causes of fires involved in the deaths of 40 people, it was found that 52% of the fires were accidental, 16% were caused as part of a suicidal act, and 31% were a criminal act. In the latter case, the most likely reason was in order to cover up a homicide by attempting to destroy evidence. As a result of the recovery of ~80 bodies at the Branch Davidian compound at Mount Carmel in Waco, Texas, in 1993, and the subsequent investigation, it was recognised that although there existed an accepted and recognized scale of burn injuries for living subjects, based on the “degree” of burns, i.e. percentage, depth and extent of damage (Glassman and Crow 1996), there was at that time no such universal scale to describe

© Equinox Publishing Ltd. 2017 20 Amoret P. Whitaker the extent of burn damage to deceased bodies. Glassman and Crow (1996) therefore produced the Crow-Glassman Scale (CGS) which is divided into five levels, with each succeeding level describing increasing destruction of the body, outlined in Table 1. The main purpose of the implementation of the CGS was to standardise the description of burnt deceased remains in order to aid communication between different personnel and specialists involved in the investigation and identification of burnt remains. One might assume that any insect evidence would be either absent or destroyed in the event of fire. Although a forensic entomologist may still be able to contribute valuable information even in the absence of insects, an investigator is less likely to employ a forensic entomologist unless there is considerable and obvious evidence of insect activity. However, linking the different CGS levels to the effect of burning on insect activity could help inform investigators as to whether a forensic entomologist could usefully be employed in an investigation involving fire and burnt remains, specifically in order to estimate minimum time since death. There are, however, at least two different scenarios which must be considered with respect to insect evidence —did the fire take place before or after colonization by insects? A fire may occur during or soon after death, which will have the following effect on the body: 1. Change in odour, therefore potential changes in the attraction of the body to blow flies 2. Change in physical structure, therefore potential changes in the egg-laying behaviour of adult blow flies and subsequent development of the larvae Conversely, a fire may occur sometime after death, either set deliberately in an attempt to destroy evidence, or it may be accidental. If a fire occurs some time after death, the body may have already been colonised by insects, and therefore it is possible that any entomological evidence present may also be destroyed. Anderson (2005) carried out a large scale study to determine whether existing insect evidence would be destroyed in a house fire. Three pig carcasses were placed in different areas of a house (the bedroom, the living room, and in the bathtub in the bath- room). Although the house was largely sealed, and therefore inaccessible to blow flies, two holes were made in a mesh screen over one window to ensure that blow flies were able to get access to the bodies, which they did after five days. The carcasses were left to decompose and once some of the colonising insects had begun to emerge as adult flies, fires were started in the house. Each pig carcass was set alight individu- ally, then extinguished 4–5 minutes after the fire was visible from the outside of the house, a time deemed a reasonable emergency response time, before being investigated for remaining insect evidence. Finally, a pig carcass (the control) that had been colonised by insects outside the house was placed in the basement, together with its insect inhabitants, and the entire house was set alight and left to burn to the ground. Anderson (2005) found that in all four carcasses, some insect evidence remained suf- ficiently intact to identify to species. This included larvae which were still identifi- able to species and life stage by their cephalopharyngeal skeleton (mouthparts), even though some were dead, presumably due to the heat of the fire, and others were heat-

© Equinox Publishing Ltd. 2017 Effect of Burning on Minimum Post-Mortem Interval 21 damaged. Those insects which were found to be still alive after the fire had been protected from direct contact with the heat of the fire by blankets or mattresses, and it was still possible to rear these through to adults, as would routinely be done during any forensic investigation. Deceased remains may be wrapped in blankets in order to conceal, transport and dispose of a body, and these wrappings have been found to pro- tect pre-colonized insect evidence during periods of flame burning that would result in CGS Level #2 burns (Pacheco and VanLaerhoven, submitted). Thus in a case such as this, where a fire was started after insect colonisation, it would still be possible to estimate a minPMI using insect evidence, despite the house in which the bodies were located having been almost entirely destroyed by fire. Anderson (2005) also suggested that any remaining entomological debris should be collected as soon as possible after a fire, as much of it became saturated from the water used to extinguish the fires, which would result in rapid decomposition of the insect evidence. She also noted that decomposition odours were still detectable after the initial fires, so that adult blow flies were attracted to the burnt cadavers. Anderson’s (2005) study closely resembles a forensic case carried out in early Feb- ruary some years ago, by the author of this paper, on behalf of the Natural History Museum, London. A fire crew were alerted to a fire in a corrugated metal outbuilding, and extinguished the fire within approximately fifteen minutes of two people being seen running from the scene who, it was assumed, had started the fire. Once the fire was extinguished, and the embers raked over, a body was found to be inside the building. The cadaver was dressed, somewhat decomposed, with CGS Level #2 burns, and insect evidence was visible on and around the body. The insect evidence was collected both at the scene and at the post-mortem, and the oldest evidence was identified as empty puparial cases of two bluebottle blow flies, Calliphora vicina and C. vomitoria. There were also live 3rd instar larvae of Hydrotaea (Ophyra) capensis, a member of the house fly family, which usually colonise bodies some time after death. Small numbers of some additional insect species, of less forensic value, were also identified. Further analysis using estimated temperatures at the scene suggested that the latest date that the Calliphora spp. had been laid as eggs on the body was five months previ- ously, at the beginning of October the previous year. It was clear from the age of the insects colonising the body that death had occurred well before the fire was set, and the fire itself did not completely destroy the insect evidence, enabling estimation of a minPMI. It is unlikely that the people who set the fire did so to deliberately try and destroy evidence, indeed it was deemed likely that they were not aware that there was a body in the outbuilding at all, and at the inquest, an open verdict was given regarding the death of the person whose body was found. Blow flies detect their food source and oviposition site by odour, therefore any changes in that food source may affect whether, or to what extent, blow flies are attracted to it, and therefore when, or indeed if, the females first lay their eggs on the body. A number of studies have been conducted to determine whether burning of a body delays oviposition or alters the developmental rates of larvae feeding on it. A clear distinction should be made between burning as a result of funerary cremation, and that which might occur as part of criminal activity, usually in an attempt to

© Equinox Publishing Ltd. 2017 22 Amoret P. Whitaker destroy forensic evidence. In funerary cremation, the body is burnt for an extended period of time, from 760–982°C for 1–2 hours, resulting in complete calcination, removing all water and organic material (Warren, 2008). In contrast, although a fire set by a criminal may burn at a high temperature, the fire may be extinguished within a relatively short period of time and, unlike a funerary cremation, a body present in a criminal act of fire-setting is therefore unlikely to be entirely destroyed. The first documented case in which an entomologist was employed to estimate minPMI in a case involving a burnt body was published by Nuorteva et al. (1967), in which they describe the body of a badly burned man discovered in an old concrete pill-box in Finland on 25th August 1965. The man had last been seen alive 8–9 days before, on 16th August 1965, and a post-mortem investigation concluded that he had died from heart failure, leading to the accidental spread of the fire to petrol cans contained within the pill-box. Analysis of the entomological evidence suggested that egg-laying of Calliphora vicina, the bluebottle blow fly, occurred 7–8 days prior to discovery of the body. Despite the abundance of Lucilia spp., greenbottle blow flies, at that time of year in Finland, none were found to have colonised the body, and this was attributed to the body being located out of direct sunlight. The delay of one day before colonisation of the body may also be due to the enclosed nature of the concrete structure (typically with only small openings in the side), reducing accessibility of the body to blow flies, rather than the burnt nature of the body. The location of cadavers, and attraction or accessibility to blow flies, must always be taken into account, even in cases concerning a burnt body. In an unpublished study carried out by Meek, there was a delay of one week prior to oviposition by blow flies on a pig carcass contained within the boot (trunk) of a car that was set on fire (Catts and Goff 1992), though whether it was lack of accessibility to the carcass due to its containment, rather than the burnt condition of the body, is unclear. Studies of unburnt pig carcasses placed in the front seat of cars immediately after death demonstrated a delay of 16–18 hours for blow flies to enter the vehicles, with oviposition observed 24–28 hours following death (Voss et al. 2008). Introna et al. (1998) describe two cases from Italy in which entomological evidence was recovered from partially burnt bodies, enabling minPMI’s to be estimated. In the first case, the body was recovered from a burnt car, and the description given of the burn damage to the body suggests CGS Level #2 – #3. The internal organs had been exposed by the burning, where a large larval mass was observed. The minPMI estimated from the entomological evidence was concurrent with the last sighting of the deceased when they were alive, around four days prior to discovery of the body. Introna et al. (1998) suggested, however, that there may be a delay in oviposition of blow flies on charred bodies recovered from burnt cars, whilst the fire extinguishes itself and the body has cooled down to a suitable temperature for oviposition. In a second, very similar case, two charred bodies, again described as having CGS Level #2 – #3 burns, were found in a burnt out car. Again, the minPMI estimate of 36–48 hours corresponded to that of the last sighting of the two people whilst alive, although in this case the bodies were disposed of, and the car set alight, at night-time. Therefore the delay in oviposition could be attributed both to the requirement for the heat to

© Equinox Publishing Ltd. 2017 Effect of Burning on Minimum Post-Mortem Interval 23 reduce, and for the reduced activity of blow flies at night-time, resulting in oviposition taking place the following morning. Even small differences in location may alter the length of time it takes for blow flies to oviposit on a body. Caserio et al. (2014) carried out a study using six whole chickens, with three unburnt controls and three test carcasses burnt on an outdoor grill to CGS Level #1. Although there were some differences in decomposition rate between different carcasses, all were colonised by insects, regardless of whether they were controls or burnt. The paper does not state whether there was any significant difference in oviposition time between the control and the burnt carcasses, but one important observation was made, that in one of the burnt carcasses the skin of the abdomen ruptured, exposing a greater area of raw flesh suitable for oviposition, although the authors do not state whether oviposition did occur in those areas. This is similar to the effect of an open wound, caused by a knife or gunshot, which may lead to localised oviposition and hence an aggregation of larvae (or larval mass) in the wound area. In this study an additional factor was introduced, however, as the experimental carcasses were placed in one of three areas—direct sunlight, partially shaded and completely shaded—which may have a significant difference on ambient temperature and therefore oviposition behaviour and subsequent development of blow flies (Catts 1992). Avila and Goff (1998) carried out two experiments on pig cadavers, each experiment with one burnt pig, burnt to CGS Level #2 burns, and one control pig. Although the replication was very limited, the burnt pigs were found to be more attractive to blow flies, with the majority of eggs laid on them either one or four days prior to on the control pigs. Blow flies were even observed alighting on unburnt parts of the burnt carcass, whilst other parts of the body were still actively burning. However, there was no difference in colonising species, insect succession, or larval development rates between the control and burnt bodies. As in the experiment conducted by Caserio et al. (2014), the burning of the cadavers caused cracks in the skin, which created alterna- tive oviposition sites to the natural body orifices in which blow flies usually oviposit. Using rabbits, Mahat et al. (2016) investigated the effect of CGS Level #1, #2 and #3 burns on blow fly oviposition and development over four replicate studies, each with a control carcass and one of each of the three CGS burn levels. They found no difference in oviposition times between the control carcasses and those burnt to CGS Levels #1 and #2, but a one day delay in oviposition on the CGS Level #3 carcasses. They suggested this may be due to the greater charring of the body tissues in the more burnt carcasses, resulting in reduced decomposition odours. Similarly, in an unpublished Masters research study, McCarthy (2016) used pigs heads as the experimental carcasses in two separate experiments, with one unburnt control, and three burnt to CGS Levels #1, #2 and #3, requiring burning of five, 10 and 15 minutes respectively. It was noted that burning the pigs’ heads for a longer period of time would have caused severe physical disintegration. The study was carried out in winter, when temperatures ranged from 1.9°C–14.0°C (mean = 8.7°C) and 1.5°C– 12.2°C (mean = 7.1°C), so fly activity would be expected to be reduced compared to summer time. In the first experiment, egg masses were observed to be laid on the

© Equinox Publishing Ltd. 2017 24 Amoret P. Whitaker control and CGS Level #1 pig’s head on Day 6 and on CGS Levels #2 and #3 on Day 7. In the second experiment, egg masses were observed to be laid on the control and CGS Levels #1 and #2 on Day 7 and on CGS Level #3 on Day 9. So there was no delay in oviposition on pigs’ heads burnt to a lesser extent, but a delay of 1–2 days on those burnt for a longer period. It was noted that egg-laying was observed predominantly on the cut surface of the necks, where there was exposed muscle tissue, reflecting the assumption that a cut/exposed surface is a suitable area for oviposition. McCa- rthy (2016) also endeavoured to compare development rates of larvae between the different CGS Level carcasses. Small numbers of larvae were sampled from each pig’s head, and it was found that although fewer larvae were observed on the CGS Level #3 pig’s head, those larvae were found to be 10–20% larger than those that had developed on CGS Levels #1 and #2. She also reported that Calliphora vomitoria favoured the control and CGS Level #1 pigs’ heads, whereas C. vicina favoured CGS Level #2 and #3 pigs’ heads. For unknown reasons, the larvae which had developed on CGS Level #3 did not survive to adulthood, but all other flies reared from the control carcasses, and those burnt to CGS Levels #1 and #2 were of a comparable size. A large-scale experiment carried out by Gruenthal et al. (2012) using 24 pig carcasses as controls and 24 pig carcasses burnt to CGS Level #1 on the head, neck and limbs, and CGS Level #2 on the torso, did not, unfortunately, report much on the arthropod activity during the course of the experiment, although they did note that dung flies (Scathophaga stercoraria) visited both burnt and control carcasses, congre- gating mainly in the most burnt areas of the experimental carcasses. Although no larvae of this species were collected, larvae of Calliphora vicina and C. vomitoria were collected from both sets of cadavers. Their results showed that although there was no overall difference in rate of decomposition of the burnt and unburnt carcasses, there were differences depending on the degree of burning. The head/neck and limbs of the burnt carcasses decomposed slower than those of the unburnt carcasses, while the torsos of the burnt carcasses decomposed faster than the torsos of the unburnt carcasses. The implication is that CGS Level #1 burning results in dehydration of the skin, therefore perhaps rendering it an unsuitable site for blow fly oviposition, whereas the CGS Level #2 burning results in splitting of the skin, allowing the exposure of unburnt internal body tissue and seepage of body fluids, resulting in a substrate that may be more attractive to egg-laying blow flies. Vanin et al. (2013) also suggested that there may be altered insect succession on burnt pigs, because of the physical changes caused by charring, e.g. splitting of the skin, resulting in differential decomposition, leading to the emission of a variety of odours, resulting in different species of insect being attracted at the early stages of decomposition, rather than a succession of insects as decomposition progressed, as is usually the case. In their study using pigs burned to CGS Level #2 – #3, they reported that although Calliphorid flies (blow flies) arrived on both burnt and unburnt carcasses at the same time, other Diptera (fly) and Coleoptera (beetle) species arrived earlier on the burnt carcasses. As blow flies are usually the first insects to find and colonise a body, and therefore are the most accurate with regards to estimating minimum post-mortem interval, this alteration in succession should not alter the

© Equinox Publishing Ltd. 2017 Effect of Burning on Minimum Post-Mortem Interval 25 accuracy of estimating PMI by aging the blow flies colonising the body. However, if one were to try to use succession of different insect species to give a PMI estimation, there would clearly be problems if they are not colonising the carcasses in the expected order and at the expected stages of decomposition. Similarly, in experiments carried out using rabbit carcasses, Mashaly (2016) determined that burnt carcasses attracted more adult flies, specifically Lucilia sericata and Musca domestica, than unburnt ones during the fresh stage, however they also concluded that burning had no effect on rate of decomposition of the carcass, but that it did have an effect on insect succession, with greater numbers of beetles also being attracted to the burnt bodies than to the unburnt ones. However, in this study only adult insects were collected, therefore there is no indication of whether the increased number of flies on the burnt cadavers resulted in a greater number of egg masses, and thus increased larval load. They suggested, however, that the burning of bodies had no effect on estimation of post-mortem interval compared to the control bodies. Kolver (2009) carried out experiments with pig carcasses in South Africa, burning the carcasses to different levels ranging from CGS Level #2 – #3. Using a total of 53 pigs, the study was carried out over three years and four seasons, enabling compari- sons to be made between seasons as well as between burnt and unburnt carcasses. In warmer seasons, oviposition of blowflies (Chrysomya chloropyga, C. marginalis and C. albiceps) occurred one day earlier on the burnt carcasses, but in colder seasons, oviposition occurred three to five days earlier, with one exception, when oviposition occurred five days later on the burnt carcass during a cold period. Thus in the majority of carcasses, the burning of pigs did not deter oviposition and in fact, any estimate of minPMI would have been more accurate on the burnt carcasses than on the unburnt carcasses. In a second case carried out by the NHM, London, (Martin Hall, personal communication), very similar to that described by Nuorteva et al. (1967), a body was found in an old underground concrete bunker in which it was clear that a fire had taken place. The body was in the characteristic “pugilistic” pose, the muscles of the body having contracted as a result of the heat of the fire, and had CGS Level #2 burns. On removal of the body, the paler skin on the back of the body, which had been protected from direct contact with the fire, was visible. Large numbers of blow fly larvae at different developmental stages were feeding on the body, and there were also adult flies in the bunker and recently laid eggs on the body. The insect evidence was identified as belonging to two species, Calliphora vicina and C. vomitoria, the oldest species being four days old. The temperature in the bunker was buffered from large diurnal fluc- tuations and was estimated to have been a fairly constant 14°C. Although there was no physical deterrent to adult flies entering the bunker, they may have taken longer to locate the body than if it had been lying on the ground outside, due to the reduced odour dispersion. There was no evidence of burned insects and the fire was estimated to have been set the day before the first egg-laying took place. Thus, a slight delay in egg-laying occurred, more likely due to the hidden location of the body than to the fact that the body had been burnt. The fact that the body was partially burnt had not deterred the flies from egg-laying.

© Equinox Publishing Ltd. 2017 26 Amoret P. Whitaker This case emphasises an important aspect of burning which needs to be taken into account, that a body, even if deliberately set alight, is unlikely to be uniformly burnt throughout. If the body is lying on a substrate, especially a hard substrate such as concrete or stone tiles, the side of the body in contact with the substrate is unlikely to have received burns as severe as exposed areas of the body, if at all. As suggested by Gruenthal et al. (2012), any unburned regions of the body will be dependent upon the resting position of the body and combustibility of the substrate on which it is lying. Bodies from house or room fires often show only minor damage on the side lying against the floor, where the flames have no direct contact with the body (Bohnert, 1998). As in the case of the body in the metal outbuilding, this also means that any larvae developing under the body, which is often the case, will also be protected from the immediate effect of the flames. Oliveira-Costa et al. (2013) burned a single carcass using gasoline, and suggested that due to the resulting dried skin and odour of the accelerant, the burnt carcass was made less attractive to blow flies than the control, unburnt carcass. Although they did not specify a CGS Level, the photograph suggests CGS Level #1, with no obvious splitting open of the abdomen. They observed that the initial stages of decomposition were much shorter in the burnt carcass than in the unburnt carcass—1 and 3 days respectively in the fresh stage, 2 and 5 days respectively in the bloat stage, 4 and 17 days respectively in the decay stage, 12 and 38 days respectively in the post decay stage. In the final, skeletal/dry, stage the trend was reversed, with 55 and 15 days respectively, although at what point this stage comes to an end is unclear. In terms of species attraction, greater numbers of blow flies were attracted to the control pig in the first two stages of decomposition, with no flies at all attracted to the burnt carcass in the fresh stage of decay. As this stage only lasted one day in the burnt carcass, during which time no eggs were observed to be laid, this amounts to just one day delay in oviposition, most likely due to the dried skin. This concurs with Wardle (1921) who suggested that in order to be suitable for blow fly oviposition, the surface of a potential food source should be moist and that the protein content should not be coagulated by heat. In testing a number of meat products, he found that fresh organs and meat were attractive to blow flies, but even lightly cooked meat became unsuitable for oviposition, due to desiccation. Heo et al. (2008) used petrol to burn a single pig carcass, which was compared to an unburnt, control carcass. No indication is given regarding the CGS level of burning, the length of time for which it was burnt, or the resulting physical appearance. How- ever, the burnt pig did go into the bloat stage, so the burning was not severe enough to cause the abdomen to split open, suggesting a CGS Level #1 burning. Oviposition began on the control pig within one hour of being placed out, but no flies were seen visiting the burnt carcass until the following day, when eggs were laid in the body orifices of the burnt pig. This pig was also heavily infested with red ants, which may have affected the ability of blow flies to lay eggs on it, and may also have resulted in the greater number of flies visiting the control pig. The authors also suggest that it may have taken a while for the temperature of the freshly burnt pig to reduce to a level that made it suitable for egg-laying. In some of the studies described (e.g.

© Equinox Publishing Ltd. 2017 Effect of Burning on Minimum Post-Mortem Interval 27 Caserio et al. 2014; Gruenthal et al. 2012; McCarthy 2016; Pacheco 2015), the burnt carcasses are allowed to cool, before transporting them to the study site, therefore no indication is given of whether the heat of the carcasses, immediately after burning, might delay oviposition. McIntosh et al. (2016) used pig carcasses to compare insect succession on five unburnt carcasses and five carcasses burnt to CGS Level #2 in Western Australia. They noted that the decomposition of the burnt carcasses was accelerated compared to the unburnt carcasses, with the splitting of burnt skin resulting in no obvious bloat stage. The assemblage of insect species associated with carcasses were comparable between both burnt and unburnt pigs, although the arrival and departure times were different, and depended upon species of insect. Of five named species of blow fly, they reported that one species colonised both treatments on the same day, three species of blow fly colonised the burnt carcasses 24 hours earlier than the unburnt carcasses, and one species of blow fly colonised the burnt carcasses 48 hours earlier than the unburnt carcasses. So it appears that there may be differences in attraction to burnt carcasses between different species of blow fly, and we cannot assume that different species will behave in the same way in respect to burnt remains. Only one reported study so far has been carried out under laboratory rather than field conditions, enabling factors such as ambient temperature and fly species to be controlled. Pacheco (2015) tested two factors—competition between two fly species, Phormia regina and Lucilia sericata, and the effect of skin split by burning on choice of oviposition sites. Results suggested that both species preferentially chose areas of the skin which had split over natural orifices as a suitable oviposition site. Foetal piglets were burned to CGS Levels #1, #2 and #3, with Level #0 classed as a control, and there were five replicates of each, with 20 piglets used in total. Although it is not stated how long the burning was carried out for, this study estimated the amount of biomass loss after burning, but prior to blow fly colonisation. Bodies burnt to CGS Level #2 lost twice the biomass as Level #1, and CGS Level #3 lost four times the biomass of CGS Level #2 and eight times the biomass of Level #1. Cracking of the skin occurred in only some of the Level #1 piglets, but consistently on all of the Level #2 and #3 piglets, with approximately twice as many cracks on the Level #3 piglets as on the Level #2 piglets. Both fly species predominantly oviposited in the cracks in CGS Level #3 piglets, with some oviposition in the cracks in CGS Level #2 piglets by L. sericata. Therefore the lower the CGS Level, the fewer the cracks and therefore the more likely flies were to oviposit in the usual locations, such as the head. Although developmental rates were not compared between CGS Level burns, it was found that the survivorship of colonising insects increased with an increase in CGS burn level, perhaps due to fewer eggs being laid and therefore less competition for food resource, despite the loss of biomass due to burning. Pacheco (2015) suggested that although burning a carcass can lead to more oviposition sites due to the appearance of cracks, burning can also destroy other potential oviposition sites. Locations on the head, such as the ears, which are the usual preferred oviposition sites for blow flies, become badly burnt as the CGS level increases and can therefore result in oviposition being no longer possible at those sites, resulting in a preference for blow flies to ovi-

© Equinox Publishing Ltd. 2017 28 Amoret P. Whitaker posit in cracks caused by burning instead. There is another related aspect which also needs to be considered when using forensic entomology to investigate burnt bodies. In the course of criminal activity, fires may be lit in a hurry, using whatever fuel is immediately available. Previous studies in the specialised field of entomotoxicology have determined that some substances may have an effect on the development rate of insects, either slowing it down or speeding it up (Introna et al. 2001). Generally the substances tested have been pre- scription drugs, simulating the scenario of an accidental overdose or suicide. How- ever, the use of accelerants to start a fire may also have an effect either on the attraction of adult blow flies to remains and/or on the developmental rate of the larvae feeding on those remains. Some of the studies cited used accelerants to start the fires —petrol (Kolver, 2009), gasoline (Anderson 2005; Avila and Goff 1998; Pai et al. 2007), charcoal and lighter fluid (Caserio et al. 2014)—although none of them investigated any possible effect that the accelerants may have had on the insects’ development. In the study by Mahat et al. (2016) the different levels of CGS burn were achieved by increasing the amount of fuel used and the period of time the carcasses were allowed to burn. Specifically, the amount of fuel used was 0.5L for CGS Level #1, 0.75L for Level #2, and 1.5L for Level #3, and there is a possibility that an increased amount of accelerant results in a decreased attraction to blowflies. One of the most important challenges for the future is to combine experimental data and practical case work (Amendt et al. 2004). Only one study to date has carried out a “mock” crime scene using a burnt pig carcass, which can be directly compared with a case involving a burnt human cadaver. Pai et al. (2007) placed a pig carcass, burnt to CGS Level #2 in woodland in July, thereafter sampling insects from the body, which they determined to be Chrysomya megacephala and C. rufifaces. Adult blow flies were observed visiting the pig cadaver within five minutes of exposure, and within 17 hours there were eggs and 1st instar larvae present, though no indication was given of how soon after deposition of the body oviposition took place. In measuring the larvae and recording ambient temperatures they were able to estimate rate of development of the larvae. Six weeks later, the partially burnt body of a young woman was found, just six kilometres from where the pig had been located. There were 2nd and 3rd instar C. megachephala larvae collected from body, and using the developmental data generated by the samples collected from the pig, the authors estimated the minimum PMI of the woman to be 50 hours. A man was apprehended and admitted the murder, stating that he had disposed of the body 46 hours prior to its discovery, with no indication that the body had been stored elsewhere prior to disposal. So the minimum post-mortem estimate given, based on the data generated by the pig experiment, was just four hours out. This clearly shows the benefit of car- rying out controlled experiments in order to recreate real crimes scenarios. In many of these experimental studies, burnt carcasses appear to be more attractive to blow flies, which oviposit on them earlier than on control, unburnt carcasses. So it seems clear that the burning of carcasses does not inhibit blowfly colonisation, and therefore forensic entomology can still be utilised to estimate a minimum post- mortem interval. However, all these studies use CGS Levels #1, #2 and #3. In prelimi-

© Equinox Publishing Ltd. 2017 Effect of Burning on Minimum Post-Mortem Interval 29 nary tests, Pacheco (2015) found that foetal piglets burned to CGS Levels #4 and #5 did not attract any fly oviposition at all. This should, perhaps, be investigated more thoroughly. Many of these studies also describe the stages and rate of decomposition of the carcasses themselves. Whilst this may have a bearing on insect succession, the important factor in estimating a minPMI is when blow flies oviposited on a body. The use of the Crow-Glassman Scale in assessing the degree of burning is important with regards to forensic entomology, because it appears that it is the degree of burning that determines the rate of blow fly oviposition, rather than the state of decomposition of the body. Cases of burnt bodies are challenging to forensic pathologists, as there are no useful elements for the estimation of time since death, such as rigor mortis, algor mortis and livor mortis (Introna et al. 1998). It is clear from the research outlined above that burning is not a deterrent to insects colonising a body, and that an accurate minPMI may still be estimated using forensic entomology. However, further studies need to be carried out to determine the effect of different levels of burning on cadavers and their subsequent attraction to insects. In some cases only some parts of body may be burnt, leaving unburnt areas which are attractive to insects. In other cases, enough burning may occur for the body to rupture, revealing raw flesh, similar to the wound left by a weapon, which would give a suitable oviposition site. Therefore reduced burning does not necessarily result in greater attraction to insects. In addition, other factors must still be taken into account, such as location of the body and its accessibility to blow flies, season and temperature, blow fly species preferences, as well as any accelerants that may have been used in the fire. Further studies also need to be carried out to determine whether developmental rates of different species are affected by feeding on burnt remains, as this is critical if trying to estimate a minimum post-mortem interval. Regardless of these limitations, it seems clear that forensic entomology can be effectively used to determine minPMI in cases of burnt cadavers. References Amendt, J., C. P. Campobasso, E. Gaudry, C. Reiter, H. N. LeBlanc and M. J. R. Hall. 2007. “Best practice in forensic entomology—standards and guidelines.” International Journal of Legal Medicine 121: 90–104. https://doi.org/10.1007/s00414-006-0086-x Amendt, J., R. Krettek and R. Zehner. 2004. “Forensic entomology.” Naturwissenschaften 91: 51–65. https://doi.org/10.1007/s00114-003-0493-5 Ames, C. and B. Turner. 2003. “Low temperature episodes in the development of blowflies: Implications for postmortem interval estimation.” Medical and Veterinary Entomology 17(2): 178. Anderson, G. S. 2005. “Effects of Arson on Forensic Entomology Evidence. Canadian Society of Forensic Sci- ence Journal 38(2): 49–67. https://doi.org/10.1046/j.1365-2915.2003.00421.x Avila, F. W. and M. L. Goff. 1998. “Arthropod succession patterns onto burnt carrion in two con- trasting habitats in the Hawaiian Islands.” Journal of Forensic Sciences 43(3): 581–586. https://doi. org/10.1520/jfs16184j Bhadra, P., A. Hart and M. J. R. Hall. 2014. “Factors affecting accessibility of bodies disposed in suit- cases to blowflies.” Forensic Science International 239: 62–72. https://doi.org/10.1016/j. forsciint.2014.03.020

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