Decomposition and insect succession on cadavers inside a vehicle environment

ORIGINAL PAPER

Decomposition and insect succession on cadavers inside a vehicleenvironment

Sasha C. Voss Shari L. Forbes Ian R. Dadour

Accepted: 23 April 2007 / Published online: 15 August 2007 Humana Press Inc. 2007

Abstract This study presents differences in rate ofdecomposition and insect succession between exposedcarcasses on the soil surface and those enclosed within avehicle following carbon monoxide (CO) poisoning. Nine45-kg pigs were used as models for human decomposition.Six animals were sacriced by CO gas, half of which wereplaced within the drivers side of separate enclosed vehi-cles and half were placed under scavenger-proof cages onthe soil surface. A further three animals were sacriced bycaptive headbolt and placed under scavenger proof cageson the soil surface. The pattern of insect succession andrate of decomposition were similar between surface car-casses within trials regardless of the mode of death. Pro-gression through the physical stages of decomposition was34 days faster in the enclosed vehicle due to highertemperatures there compared to external ambient temper-atures. Patterns of insect succession also differed betweenthe vehicle and surface treatments. Carcass attendance byrepresentatives of the Calliphoridae was delayed within thevehicle environment by 1618 h, while oviposition was notobserved until 2428 h following death. In contrast,attendance by Calliphoridae at surface carcasses occurredwithin 1 h of death, and oviposition occurred within 68 hof death. Typical patterns of insect succession on the car-casses were also altered. Carcass attendance by represen-tatives of the Coleoptera occurred during the bloat stage of

decomposition at surface carcasses but was delayed untilthe onset of wet decomposition (as dened by carcassdeation and breakage of the skin) within the vehicleenvironment. This study provides baseline data outliningthe decomposition patterns of a carcass enclosed within avehicle following CO poisoning in Western Australia.Understanding how variations in decomposition situationsimpact on the rate of decomposition and patterns of insectsuccession is essential to obtaining an accurate estimate ofminimum post-mortem interval (PMI).

Keywords Carbon monoxide poisoningDecomposition Forensic entomology InsectSuicide Vehicle

Introduction

Decomposing remains provide a temporary, changinghabitat which can support a large microorganism andarthropod community [1]. Invasion of a body by insectsand other arthropods occurs soon after death and generallyfollows a predictable sequence [2, 3]. While geographicallyspecic, the pattern of arthropod succession on a cadaverhas been well documented by forensic researchers globally[47]. Where the pattern of arthropod succession on a ca-daver is known, analysis of the arthropod fauna can be usedto estimate the post-mortem interval (PMI). This aspect ofthe science, forensic entomology, is regularly used by po-lice services in forensic investigations worldwide in caseswhere the time of death is unknown [8].

When using arthropods to estimate PMI, it is importantto consider the factors which may affect the rates andpatterns of insect invasion on the body. The inuence ofenvironmental conditions, including temperature, humidity

S. C. Voss (&) I. R. DadourCentre for Forensic Science, School of Anatomy and HumanBiology, University of Western Australia, Mail Bag M420,35 Stirling Highway, Crawley, WA 6009, Australiae-mail: [email protected]

S. L. ForbesFaculty of Science, University of Ontario Institute ofTechnology, Oshawa, ONT, Canada

Forensic Sci Med Pathol (2008) 4:2232DOI 10.1007/s12024-007-0028-z

and rainfall, has been previously investigated [9]. Cir-cumstances surrounding the death scenario may also affectthe initial time of appearance of insects on a body [10].Drugs and toxins present in decomposing tissue have beenshown to affect oviposition of adult ies and the rate ofdevelopment of y larvae [11, 12]. The burning andhanging of carcasses have also been studied to determinetheir effect on decomposition and, subsequently, arthropodsuccession [1, 3]. Wrapping a body in several layers ofblankets can also cause a delay of up to several days inblowy invasion of a corpse by reducing access to thebody [9, 10].

One scenario which has not previously been well doc-umented is the decomposition of a cadaver in a closedvehicle environment where y access is restricted. A studyin Louisiana attempted to estimate the time delay preced-ing blow y strike on a body placed inside a vehicle trunkcompartment [10]. Although preliminary results suggesteda delay of 3 days, conclusive results have not yet beenpublished. Furthermore, decomposition in a trunk com-partment is not comparable to decomposition within thevehicle interior, yet investigators are often faced with suchcases in relation to suspected suicides. Intentional inhala-tion of carbon monoxide (CO) gas from the exhaust of avehicle accounts for a large number of suicidal deathswithin Australia each year [13, 14]. In most instances, thevictim is found within the vehicle with a hose leading fromthe exhaust pipe through the back window to the interior ofthe sealed vehicle [13, 15].

Carbon monoxide is a colourless, odourless gas which ishighly poisonous and can be fatal in large concentrations.Death by CO poisoning is commonly the result of delib-erate exposure to the gas within a conned space, such as avehicle [1618]. Death occurs as a result of oxygendeprivation at a cellular level whereby the binding of CO toblood haemoglobin in place of oxygen reduces the oxygen-carrying capacity of the blood [17, 19, 20]. Even lowconcentrations of inhaled CO (1500 ppm) over a prolongedperiod can result in a lethal concentration of carboxyhae-moglobin in the blood [19, 20]. Death can occur in lessthan 20 min from initial exposure [17, 21, 22].

Many suicides conducted in vehicles occur in isolatedareas, and the vehicle is parked in wooded areas for thepurposes of concealment [21]. Such sites can be heavilyshaded, with only minimal exposure to the sun. Detectionof the vehicle may take weeks or months, during whichtime decomposition of the body will commence. Withinsuch a situation, aspects of insect succession on decom-posing remains may be altered as a result of the initial highconcentration of CO present within the vehicle and theability of each species to gain access to the vehicle interior.

The objective of this study was to determine the patternof entomological succession on a decomposing carcass

placed inside a closed vehicle environment following itssacrice by CO poisoning. The results are compared todecomposition and insect succession within an open, sur-face environment. The signicance of the research is di-rectly related to the requirement by police, coronial andjustice systems for an accurate estimation of PMI, partic-ularly in regards to suicide investigations.

Materials and method

The decomposition trials were conducted in a wildlife re-serve situated 23 km south of Perth, Western Australia(3210S, 11550E). The study area consisted of 253 ha ofcoastal bushland on Bassendean sands with a Mediterra-nean climate and average yearly rainfall of approximately900 mm [23, 24]. The surrounding vegetation was low,open woodland, and each site was in a wooded, partiallyshaded area.

The study utilised non-human corpses to mimic ysuccession in a simulated suicide environment. Ethicalrestrictions in Australia prevent the use of human bodiesin decomposition trials, and current debate among expertssuggests that decomposing pigs (Sus scrofa) are the nextmost reliable model [9, 10]. Nine 45-kg pigs were used asmodels for human decomposition. Three animals wereused per trial, and each trial was replicated three times.Within trials, two animals were euthanised in a chambercontaining 99% pure CO, and the third was sacriced bycaptive headbolt, as commonly utilised in abattoirsthroughout Australia. The headbolt wound was immedi-ately closed using a silicon sealant so that the wound didnot present a focus for insect activity. Following death,the pigs were immediately clothed in cotton shirts andshorts.

Within 10 min death, one of the dressed, CO-sacricedpigs was placed in the front seat on the drivers side of anenclosed vehicle. Prior to this, all vents to the vehicle weresealed. Following placement of the pig carcass within thevehicle, exhaust fumes were pumped into the interior forapproximately 8 h. Exhaust fumes were produced bymeans of an additional vehicle with the engine idling on afull tank of unleaded petrol. The duration was based onpreliminary tests of the running vehicle used and theresulting time taken for it to eventually stall when theengine was idling (unpublished data, IR Dadour). Thedoors and vents to the vehicle remained sealed for 5 daysfollowing death to allow for the undisturbed succession ofarthropod fauna. The date of death was designated as Day0, and on Day 5 the doors were opened for sampling andthe vents unblocked. The vehicles obtained for use in thisstudy were all sedans with a similar interior layout (FordFairlane, Holden Gemini and Nissan Bluebird).

Forensic Sci Med Pathol (2008) 4:2232 23

The decomposition process and insect activity were re-corded using an infrared video camera (Sanyo VC9212B/WCCD) bolted to the inside roof of the vehicle. This wasconnected to a time lapse VCR (Sanyo TLS1600P) andprogrammed with a recording speed of two frames persecond. Daily observations through the windows of thevehicle also provided additional information. The temper-ature inside the vehicle was measured and recorded usingTinytag Plus temperature data loggers (Hastings DataLoggers, Port Macquarie, NSW, Australia). An abdominalprobe inserted into the abdomen of the pig post-mortemrecorded changes in internal temperature of the cadaver viaa connection to a Tinytag Plus data logger. All data loggerswere programmed to record the minimum and maximumtemperature at 30-min intervals. Unfortunately, upon re-trieval of the data loggers at the completion of the study wediscovered that two of them had been damaged during thestudy. Temperature data for the inside of the vehicle in trial2 (autumn 2001) and the internal carcass temperature of theheadbolt-sacriced surface pig in trial 3 (autumn 2004)were lost.

The remaining two pigs, one sacriced by CO and theother by captive headbolt, were placed directly on the soilsurface approximately 10 m from the vehicle and eachother, in a wooded, partially shaded site. Abdominal probeswith accompanying Tinytag Plus data loggers were in-serted post-mortem into the abdomen to record internalbody temperatures. Each pig was surrounded by a metalcage covered with 2.5-cm mesh to protect it from largeanimal scavenging. The cage sides were extended 30 cminto the ground to prevent scavengers burrowing beneaththe cage. Ambient temperature, humidity and soil tem-peratures outside of the vehicle were recorded using aDatataker DT50 data logger (Hinco Instruments, CanningVale, WA, Australia). The two surface carcasses acted ascontrols. Control animals allowed a comparison ofdecomposition and entomological succession in a closedvehicle environment with the same processes in anopen outdoor environment during identical seasonal con-ditions. Two controls were used to determine whetherdifferences in decomposition occurred based on the style ofeuthanasia.

Using identical methodology, this set-up was repeatedthree times using a total of nine animals in summer 2001,autumn 2001 and autumn 2004. Replicates were not runconcurrently due to the logistics associated with obtaininga suitable vehicle for the decomposition of large animalcarcasses.

Sampling occurred on a daily basis, with recordingsmade of the progression of decomposition, species com-position and insect attendance at each carcass. For surfacecarcasses, sampling was conducted from Day zero. Ini-tially, for vehicle carcasses, video recordings of the vehicle

interior and visual assessment through the transparent glassof the vehicle windows were used to identify the stage ofdecomposition, species composition and insect attendanceat each carcass. Following the rst 5 days, the door to thevehicle was opened for a 5-min period each day to allowfor the collection of observed samples. Representativesamples of taxa were collected from all carcasses to allowaccurate identication. Previous studies have shown thatsampling does not signicantly alter the decompositionprocess [1]. Larval samples were reared through to matu-rity in the laboratory for ease of species identication.Emphasis was placed on the collection and identication ofkey indicator species for estimating PMI rather than acatalogue of all arthropod species present. Carcasses weremonitored throughout decomposition until they hadreached the skeletal stage.

Values are given as the mean standard error; thesignicance level was 0.05. Analyses of variance (ANO-VA) with Student-Newman-Keuls multiple-comparisontest were calculated after Zar [25]. ANOVA was used toidentify differences between species occurrence anddiversity between trials.

Results

Decomposition progression

Five observable stages of decomposition were recognisedfor both surface-exposed and vehicle-enclosed carcasses:fresh, bloat, wet decomposition, dry decomposition andskeletal [2628]. In this study, the rate of progressionthrough these stages differed between the surface andvehicle carcasses, dependant on temperature and thedecomposition environment. No differences were evidentin the progression of decomposition between the surfacecarcasses within each trial, regardless of the mode of death(Table1).

Fresh

This stage commences from the instant of death until theonset of bloat. In this study, the duration of this stage wasthe same for both surface and vehicle carcasses (Day 01).As expected, the temperature inside the vehicle was con-sistently higher than the outside ambient temperature. In allreplicates, there was an initial gradual decline in internalbody temperature as the carcasses began to equilibrate withthe ambient temperature (algor mortis). However, this wasless marked in the vehicle replicates than in the surfacereplicates due to the expected higher internal temperaturesof the vehicle (Fig.1). Discolouration of the skin (livormortis) resulted from the gravitational settling of the blood

24 Forensic Sci Med Pathol (2008) 4:2232

and was particularly evident in the lower legs of the carcasswithin the vehicle replicates.

Bloat

This stage is dened by the gradual ination of the carcassresulting from the production of gases by anaerobic bacteriain the body and ends when the carcass eventually deates.The duration of this stage differed between trials and be-tween surface and vehicle carcasses within trials (Table1).Bloat duration was consistent between vehicle carcasses ineach trial (3 days). Surface carcasses remained in bloat for alonger period (4, 7 and 4 days, respectively) than vehiclecarcasses. The differences in the duration of bloat in surfacecarcasses between trials are partially accounted for byaverage ambient temperature differences between trials(25.0 0.61, 17.0 0.52 and 20.1 0.71C, respectively).

Wet decomposition

This stage commences when the skin of the carcass hasbroken as a result of gas build-up and larval feeding. Theremaining skin surface appears marbled due to putrefac-tion, and extensive uid leakage is evident. No discernablepatterns were evident in terms of the duration of wetdecomposition between vehicle and surface carcasses.However, the duration of the wet decomposition stage wasconsiderably shorter in trial 3 for both vehicle and surfacecarcasses than in trials 1 and 2 (Table1). Differences in the

duration of wet decomposition between trials correspondclosely to variations in the internal carcass temperaturesthroughout the wet decomposition stage (Fig.1). Forexample, throughout this stage the internal carcass tem-perature of the vehicle pig in trial 3 (41.5 2.74C) washigher than that observed in trial 1 and 2 (35.7 0.82 and27.7 0.69C, respectively).

The length of the wet decomposition stage observed ineach trial was more closely related to the internal carcasstemperature than ambient temperature (Table1; Fig. 1).For example, throughout the wet decomposition stage, theinternal temperatures of the surface carcasses were higherin trial 2 (Surface(CO) = 28.7 0.45C; Surface(Headbolt)=27.1 0.46C) than in trial 1 (Surface(CO) = 25.6 0.31C; Surface(Headbolt)= 24.4 0.91C), and the dura-tion of wet decomposition in trial 2 was shorter by 2 daysdespite the comparatively higher ambient temperaturerecorded throughout trial 1. Extensive larval aggregationsof both beetles and ies were observed in association withthis stage, potentially contributing to the observed carcasstemperature differences (see faunal succession section).

Dry decomposition

This stage is characterised by a reduction in esh and uidand by an abundance of the dry constituents of the carcass,predominantly skin, cartilage and bone. Differences in thetime taken to progress from dry decomposition to the skel-etal stage were evident between vehicle and surface pigs and

Table 1 Comparison of the progression of decomposition stages observed under three decomposition environments in three separate seasons:carcass enclosed in a vehicle simulating death by carbon monoxide (CO) poisoning, carcass exposed on the soil surface following CO poisoningand a carcass exposed on the soil surface following captive headbolt

Stage of decomposition Duration of decomposition stage (days since death)Vehicle (CO) Surface (CO) Surface (headbolt)

Trial 1: Summer 2001 Fresh 1 (01) 1 (01) 1 (01)Bloat 3 (24) 4 (25) 4 (25)Wet decomposition 10 (514) 11 (616) 11 (616)Dry decomposition 19 (1533) 20 (1736) 20 (1736)Skeletal >Day 34 >Day 37 >Day 37

Trial 2: Autumn 2001 Fresh 1 (01) 1 (01) 1 (01)Bloat 3 (24) 7 (28) 7 (28)Wet decomposition 11 (515) 9 (917) 9 (917)Dry decomposition 21 (1636) 23 (1840) 23 (1840)Skeletal >Day 37 >Day 41 >Day 41

Trial 3: Autumn 2004 Fresh 1 (01) 1 (01) 1 (01)Bloat 3 (24) 4 (25) 4 (25)Wet decomposition 6 (510) 6 (611) 6 (611)Dry decomposition 16 (1126) 19 (1230) 19 (1230)Skeletal >Day 27 >Day 31 >Day 31


between the three trials. Within trials, the duration of drydecomposition was consistently shorter for the vehicle car-casses than for the surface carcasses (Table1). A higherambient temperature inside the vehicle was evidentthroughout the dry decomposition stage (Fig.1). The dura-tion of dry decomposition for surface carcasses was longestin trial 2 (23 days), while the progression through the drydecomposition stage in the surface carcasses of trial 1 and 3were considerably faster (20 and 19 days, respectively).

Skeletal

This late stage is identiable by the absence of soft tissue:only bones, cartilage and hair remain. Overall, vehiclecarcasses reached the skeletal stage faster by between 3and 4 days than their corresponding surface carcasses.Decomposition progressed more quickly in trial 3 for bothvehicle and surface carcasses, particularly the wetdecomposition stage where larval activity and abundancedrives the rate of decomposition (Table1).

Faunal succession

Of the predominant taxa observed in association with bothsurface and vehicle carcasses throughout the duration ofthe three trials, we identied a total of 22 arthropod taxa,representing 13 families and three orders (Table2). Rep-resentatives of the order Diptera were the rst colonisers ofall nine carcasses, closely followed by representatives ofthe order Coleoptera as decomposition progressed. Thepattern of insect succession was essentially the same be-tween the surface carcasses, regardless of the mode ofdeath, and the pattern of insect succession associated withthe stages of decomposition was similar between trials.Differences in the timing of insect colonisation were evi-dent between the vehicle and surface replicates within trialsfor all three trials (Figs.24).

Based on video recordings of the vehicle interior, adulties were observed inside the vehicle 1618 h after death.This is in sharp contrast to the surface carcasses where ieswere observed within the rst hour after death. Videoobservations and collection of larvae from the carcassesindicated a distinct lag in the timing of oviposition betweenvehicle and surface carcasses. Eggs and rst instar larvae of

Fig. 1 Temperature recordings of ambient temperature, temperatureinside the vehicle and internal temperatures of carcasses enclosed in avehicle following death by carbon monoxide poisoning [Car (CO)];exposed on the soil surface following CO poisoning [Surface (CO)]and exposed on the soil surface following sacrice by captiveheadbolt [Surface (Headbolt)]. From top to bottom: trial 1 (summer2001), trial 2 (autumn 2001) and trial 3 (autumn 2004), respectively

Table 2 Taxa collected and identied from decomposition studies atHarry Waring Marsupial Reserve, south-west of Perth, WesternAustralia

Order Family Genus and species

Diptera Calliphoridae Lucilia sericataCalliphora albifrontalis

Calliphora dubia

Chrysomya rufifacies

Chrysomya varipes

Chrysomya megacephala

Muscidae Hydrotaea rostrataMusca domestica

Musca vetustissima

Stomoxys calcitrans

Sarcophagidae Not identied beyond familyPiophilidae Not identied beyond family

Coleoptera Dermestidae Dermestes aterDermestes maculatus

Histeridae Saprinus sp.Staphylinidae Creophilus erythrocephalusScarabaeidae Onthophagus taurusCleridae Necrobius rufipesTrogiddae Omorgus tateiTenebrionidae Helea castor

Hymenoptera Chalcididae Not identied beyond familyFormicidae Iridomyrmex sp.


the blowy species, Chrysomya megacephala and Calli-phora dubia (laviposition), were observed on the surfacecarcasses as early as the afternoon of Day 0 while secondinstar larvae were evident on Day 1. In comparison, eggswere not observed on the vehicle carcasses until the latemorning of Day 1.

During bloat, larvae ofCalliphora albifrontalis, C. dubia,Chrysomya varipes C. rufifacies and C. megacephala wereobserved on both vehicle and surface carcasses. Sarcoph-agids, the largest ies, were not observed on the vehiclecarcasses during either the fresh or bloat stages of decom-position but were repeatedly evident at surface carcasses in

Fig. 2 Dominant insect taxaassociated with the stages ofdecomposition of three pigcarcasses sacriced and placedat Harry Waring MarsupialReserve, south-west of Perth,Western Australia in summer2001.CO Pig sacriced by COpoisoning,HB pig sacriced bylethal headbolt,Car pig placedin an enclosed vehicle,Surfacepig placed on the soil surface.Filled diamonds indicate thepresence of adults,opendiamonds indicate the presenceof larvae with or without adults


these early stages (Figs.24). These early colonisers wereeventually replaced by the y speciesHydrotaea rostrata inthe latter stages of decomposition. The generation of heat bylarval masses throughout both the bloat and wet decompo-sition stages was evident in internal carcass temperaturemeasurements, where carcass temperatures were consistently

above ambient temperatures throughout these stages [10,29]. As decomposition progressed, internal carcass tem-peratures gradually declined before equilibrating withambient temperature (Fig.1).

Fly emergence commenced during the wet decomposi-tion stage in all carcasses and continued through to the

Fig. 3 Dominant insect taxaassociated with the stages ofdecomposition of three pigcarcasses sacriced and placedat Harry Waring MarsupialReserve, south-west of Perth,Western Australia in autumn2001.CO Pig sacriced by COpoisoning,HB pig sacriced bylethal headbolt,Car pig placedin an enclosed vehicle,Surfacepig placed on the soil surface.Filled diamonds indicate thepresence of adults,opendiamonds indicate the presenceof larvae with or without adults


latter stages of the dry decomposition phase, with theexception of the black carrion yHydrotaea rostrata. Pu-pae of H. rostrata were still evident during the earlyskeletal stage.

Greater diversity was observed in association with thesurface carcasses throughout the fresh and bloat stages of

decomposition. In contrast, the number of species observedon the vehicle carcasses lagged behind that found on thesurface carcasses. Species diversity peaked on the vehiclecarcasses during the wet decomposition stage, and thenmatched the species diversity of the surface carcassesduring the latter stages of decomposition. This timing lag

Fig. 4 Dominant insect taxaassociated with the stages ofdecomposition of three pigcarcasses sacriced and placedat Harry Waring MarsupialReserve, south-west of Perth,Western Australia in autumn2004.CO Pig sacriced by COpoisoning,HB pig sacriced bylethal headbolt,Car pig placedin an enclosed vehicle,Surfacepig placed on the soil surface.Filled diamonds indicate thepresence of adults,opendiamonds indicate the presenceof larvae with or without adults


was primarily represented by the Coleoptera (Figs.24).Necrophagous and predatory beetles in the families Cleri-dae, Dermastidae, Histerdae and Staphylinidae commonlyarrived on the surface carcasses during the bloat stage ofdecomposition but were not observed on the vehicle car-casses until the wet decomposition stage. One exceptionoccurred in 2004 where two beetle species,Necrobiusrufipes and Dermestes maculatus, were observed on thevehicle carcass on the nal day of bloat.

Seasonally, the ongoing occurrence of species andoverall species diversity observed in association with thecarcasses in trial 1 were slightly lower than those of trials 2and 3 (F2,6 = 6.53, P < 0.05). Trials 2 and 3 were con-ducted during the autumn while trial 1 was conducted inthe summer. Average temperature differences between thethree trial periods (trial 1 = 25.1 0.61C; trial2 = 21.0 0.71C; trial 3 = 17.0 0.52C) and seasonalvariation in species abundance may be linked to the ob-served differences.

Discussion

Insect succession within Australia has been described inprevious reports [3032]. While some differences occurredas a result of zoogeographic and climatic differences be-tween studies, the species pattern of insect succession andprogression of decomposition observed for the surfacecarcasses of this study were similar to those noted in pre-vious investigations [31, 33]. However, the results of thisstudy indicate signicant differences in the rate ofdecomposition and pattern of insect succession between acarcass enclosed in a vehicle following CO poisoning and asurface carcass in contact with the soil.

The overall progression of decomposition through theidentied physical stages was 34 days faster within thevehicle environment than in a surface decomposition situ-ation. The duration of both the bloat and dry decompositionstage was shorter within the vehicle compared to the sur-face situation. This can be partially attributed to the con-sistently higher temperatures experienced within theenclosed vehicle compared to the external ambient tem-perature outside the vehicle. At higher temperatures,microbial and insect activity increases, a factor relevant toboth the bloat stage and the gradual removal of skin andtissue by beetle activity during the dry decomposition stage[34, 35]. However, no difference was observed in theduration of the wet decomposition stage between thevehicle and surface carcasses. Throughout this stage, larvalactivity is at a peak and, correspondingly, the internalcarcass temperature was at its highest. This suggests thatheat generation by larval aggregations was comparablebetween surface and vehicle carcasses regardless of

ambient temperature differences and that internal carcasstemperature was a major contributing factor driving thisstage.

A basic assumption in estimates of PMI is that the initialinvasion of remains by arthropods occurs soon after death.Our ndings for surface carcasses were consistent withearlier decomposition research where Calliphoridae activ-ity was noted within the rst hour of exposure at surfacecarcasses [3, 35]. However, this was not the case for thevehicle decomposition environment. Calliphorid ies werein evidence within the vehicle 1618 h after death, andeggs were not observed until the late morning of Day 1(2428 h after death). The presence of ies and theoccurrence of oviposition within the vehicle demonstratethat ies were able to gain access to the vehicle despite theclosed windows and doors. Access was most likelyachieved through the air vents of the vehicle, and the timespent obtaining access to the vehicle interior would likelyhave contributed to the observed delay in y attendanceand oviposition. While the presence of CO and its slowdissipation over time within the vehicle may well havecompounded the observed delay, a similar study ofdecomposition within an enclosed vehicle following sac-rice by a headbolt (not CO) is consistent with thesendings in relation to carcass attendance (unpublished data,IR Dadour). Further, death by CO poisoning did not alterthe observed pattern of insect succession or rate ofdecomposition in surface carcasses. Surface decompositionfollowing sacrice by headbolt or CO poisoning wassimilar within trials.

The results of this study identify the need to incorporatea 24- to 28-h delay for oviposition by Calliphoridae whenestimating PMI for situations in which the body is dis-covered within an enclosed vehicle. Attendance by adultbeetles was also different between surface and vehiclecarcasses with the attendance of representatives of the or-der Coleoptera delayed until the wet decomposition stagewithin a vehicle environment. In contrast, beetles wereobserved during the bloat stage of surface carcasses, al-though larvae were not observed until the wet stage ofdecomposition. A delay needs to be considered whenestimating PMI based on larval age and patterns of insectsuccession for enclosed vehicle situations.

The accuracy of a PMI estimation depends on availableknowledge of insect biology and behaviour in relation tothe use of decomposing remains as a food resource.Knowledge pertaining to surface decomposition cannotreliably be applied to alternative situations often encoun-tered in homicide/suicide cases. Previous studies have re-ported that the circumstances of decomposition, such ashanging and wrapping of the body, can impact on thepattern of insect succession and the progression ofdecomposition [3, 9]. Our ndings with regard to death


within an enclosed vehicle have also highlighted theuniqueness of each situation. Understanding how suchsituations impact on decomposition and insect successionis necessary to obtain an accurate estimate of PMI. Thisstudy provides baseline data outlining the decompositionpatterns of a carcass enclosed within a vehicle followingCO poisoning for the accurate estimate of PMI in WesternAustralia. While the data presented here can be used toimprove the accuracy of PMI estimates in vehicle-relateddeath situations, further work is needed to accurately pre-dict internal vehicle temperature when presented with thediversity of vehicle models and their respective thermalproperties.

Educational message

1. The pattern of insect succession and rate of decom-position was similar between surface carcassesregardless of the mode of death (CO poisoning vs.captive headbolt).

2. Patterns of insect succession differed between vehicleand surface carcasses.

3. Decomposition was 34 days faster for carcasseswithin an enclosed vehicle compared to surfacedecomposition.

4. Carcass attendance by representatives of the Calli-phoridae was delayed for vehicle carcasses by 1618 h.

5. Fly oviposition occurred within 68 h following deathfor surface carcasses but was not observed until 2428 h following death for vehicle carcasses.

Acknowledgements We would like to thank Andy Szito, Depart-ment of Entomology, Agriculture Western Australia, for speciesdetermination, Natalie Campman, Jeremy Lindsey and Dr. MichelleHarvey for their assistance with sampling and rearing of entomo-logical samples. For helpful comments on earlier versions of thismanuscript, we thank Dr. Alexander Larcombe, Clinical Sciences,Telethon Institute for Child Health Research, Western Australia.Thanks are also extended to the Western Australian Police PropertyTracing Section who provided the vehicles used in this study. Specialthanks to Bob Cooper (University of Western Australia) for grantingaccess to the study site and ongoing eld support. This research wasconducted with the approval of the University of Western AustraliaAnimal Experimentation Ethics Committee (Ethics no. RA/3/100/022).

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Decomposition and insect succession on cadavers inside a vehicle environmentAbstractIntroductionMaterials and methodResultsDecomposition progressionFreshBloatWet decompositionDry decompositionSkeletal

Faunal succession

DiscussionEducational messageAcknowledgementsReferences

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Decomposition and insect succession on cadavers inside a vehicle environment

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