Upload
others
View
2
Download
0
Embed Size (px)
Citation preview
INSECT SUCCESSION PATTERNS
ON DECOMPOSING SWINE
CARCASSES IN TASMANIA:
A SUMMER STUDY
Tracy FONG
A thesis submitted in fulfillment of the requirements for the degree of
Master of Forensic Science (Professional Practice)
in
The School of Veterinary and Life Sciences
Murdoch University
Dr. Paola A. Magni
July, 2017
ii
Declaration
I declare that this manuscript does not contain any material submitted previously for the
award of any other degree or diploma at any university or other tertiary institution.
Furthermore, to the best of my knowledge, it does not contain any material previously
published or written by another individual, except where due references has been made in the
text. Finally, I declare that all reported experimentations performed in this research were
carried out by myself, except that any contribution by others, with whom I have worked is
explicitly acknowledged.
Signed: Tracy FONG
Dated: July 25, 2017
iii
Acknowledgements
The author would like to express their sincere gratitude to the following people for their
support throughout the completion of the Masters degree:
Dr Paola Magni: No words can express how thankful I am for all your help, support and
guidance throughout this process. Thank you for always being there for me when I had
concerns and problems, always having my back whenever I needed and having the patience
to teach me insect identification. I am forever grateful for everything you have done to make
this project such a success and giving me this opportunity to work along-side you; it has been
such an amazing journey.
C. K. & S. Farguhar: Thank you for supplying the pigs’ central to this research, without the
pigs this research would not have been a success.
The Active Agricultural Paddock and Department of Primary Industries, Parks, Water and
Environment Facility: Thank you for allowing the use of your site as decomposition sites for
the research.
David North and Melle Zwerver , Tasmania Police: A very big thank you to the both of you
for all your hard work and patience with this research. Your time and effort is greatly
appreciated.
iv
Table of Contents
Title Page .................................................................................................................................. i
Declaration ............................................................................................................................... ii
Acknowlegements ....................................................................................................................iii
Part One
Literature Review .................................................................................................................. 1
Part Two
Manuscript ............................................................................................................................. 33
v
1
- Part One -
Literature Review
INSECT SUCCESSION PATTERN
ON DECOMPOSING SWINE
CARCASSES IN TASMANIA: A
SUMMER STUDY
2
TABLE OF CONTENTS
List of figures ....................................................................................................................... 3
List of tables ........................................................................................................................ 4
Abstract ............................................................................................................................... 5
1. Introduction .................................................................................................................... 7
2. Discussion ........................................................................................................................ 9
2.1 Decomposition .................................................................................................. 10
2.1.1 Stages of decomposition: fresh ............................................................. 10
2.1.2 Stages of decomposition: bloat ............................................................. 11
2.1.3 Stages of decomposition: decay ............................................................ 12
2.1.4 Stages of decomposition: dry/remains ................................................... 12
2.1.5 Stages of decomposition: skeletonisation ............................................. 12
2.2 Decomposition mediated by insects ................................................................ 13
2.3 Entomology decomposition studies ................................................................. 14
2.3.1 Environment conditions ........................................................................ 15
2.3.1.1 Indoor environment ................................................................. 15
2.3.1.2 Outdoor environment .............................................................. 16
2.4 Entomology decomposition studies in Australia ........................................... 18
3. Experimental design elements ..................................................................................... 20
3.1 Australian environmental conditions ............................................................. 21
3.1.1 Tasmania geographical location .......................................................... 22
3.1.2 Temperature conditions in Tasmania ................................................... 23
3.2 Best practice in forensic entomology decomposition studies ........................ 25
3.2.1 Collection at study site .......................................................................... 26
3.2.2. Rearing in laboratory .......................................................................... 26
4. Experimental aims and hypothesis ............................................................................. 26
5. Conclusion ..................................................................................................................... 28
6. References ...................................................................................................................... 29
3
LIST OF FIGURES
Figure 1: Map view of Australia ................................................................................... 21
Figure 2: Map view of Launceston and Devonport cities within Tasmania ................. 22
4
LIST OF TABLES
Table 1: Monthly temperatures recorded for Tasmania .............................................. 23
5
ABSTRACT
Forensic entomology is the study of insects and arthropods associated with legal
investigations. Forensic entomology methods have been used worldwide to deal with
several different criminal matters, but in particular to assist in determining a more accurate
time since death of humans and animals. Soon after the death event, the odour of the body
attracts various insect species to the carcass. These organisms will reach the dead body in a
predictable sequential arrival pattern which allows the identification of the insects
associated to the stage of decomposition to become invaluable information during legal
investigations.
Insect succession patterns have been studied largely around the world by using the
predictable sequential arrival pattern of different insect species that become attracted to the
decomposing carcass at various stages of the decay. The species composition in different
parts of the world can be distinctive to that region or overlap across a vast area. Many
factors can affect the rate of decomposition of the carcass and therefore affecting the
pattern of insect succession.
Currently, in some countries there are insufficient studies detailing the seasonal variation
of insect succession patterns on decomposing remains. To date, there have been no
published studies detailing insect succession patterns on decomposing remains in the
Tasmania. This data is essential as it can become invaluable during legal investigations, as
it can be used in conjunction with existing methods to assist in determining the time since
death.
The present research represents the first insect succession pattern research to be undertaken
in Tasmania investigating the insect succession patterns on decomposing swine carcasses
in two contrasting location sites in Tasmania, agricultural and suburban, during one
6
summer season. This research aimed to provide a preliminary database, detailing
forensically important insects on decomposing carcasses within the Tasmania geographical
region during the warm season. The degree of consistency in insect succession and insect
succession waves were investigated over a 39-day study during one summer season.
7
1. INTRODUCTION
Forensic entomology is the study of insects and arthropods associated with legal
investigations (Voss, Spafford, & Dadour, 2009). Forensic entomology is a method used
worldwide to assist in determining a more accurate time since death or post mortem
interval (PMI) (Voss et al., 2009). This method can also be used in situations where
additional useful information is uncovered in cases such as homicide, suicide or
unexplained death.
Human remains is a highly nutritious source which can attract a variety of organisms
including insects and other arthropods1 when the body begins to decompose (Schotsmans,
Forbes, & Márquez-Grant, 2017). Therefore, human decomposition involves a very
complex biological process where the body undergoes several different stages. The
decomposition process is largely dependent on factors such as environment conditions,
geographical location, deposition conditions such as surface, burial or submersion, climatic
conditions such as temperature, season, habitat, accessibility and time of day, various
activity of bacterial, insect and vertebrates, as well as the properties each individual carcass
exhibits (Hyde, Haarmann, Petrosino, Lynne, & Bucheli, 2015; Roberts, Spencer, &
Dabbs, 2017; Voss, Cook, & Dadour, 2011).
Since the end of the 1800s it has been experimentally proven that the arrival of insects is
not random, different necrophagous organisms are interested in feeding only at certain
stages of decomposition (Megnin, 1894). Groups of insects interested in subsequent stages
of the body decomposition are known as “successional waves of decomposition” (K.G.V.
Smith, 1986). Insect succession involves the process of invasion by insects to the carcass
soon after death thus resulting in mass amounts of fly eggs and larvae present on the
1 For easiness of the reader, from this point onwards the text will simply refer to “insects” when considering
insects and other arthropods.
8
carcass. This process continues by further attracting subsequent insect species that feed and
reproduce off the carcass (Gill, 2005; Voss, Forbes, & Dadour, 2008).
In several studies after Megnin’s one in France (Megnin, 1894), insect succession patterns
have been be studied all around the world by using the predictable sequential arrival
pattern of different insect species that become attracted to the decomposing carcass at
various stages of the decay (Morris, Dadour, 2005). The obtained data have become
invaluable during legal investigations worldwide, as they can be used in conjunction with
existing methods to assist in determining the time since death (or minimum Post-Mortem
Interval, minPMI) as well as the post-mortem movement of the body (Jens Amendt et al.,
2007; Goff, 1993).
Correct identification of insects as well as the known pattern of insect succession is vital
for each specific geographical region. This is because after approximately 24 to 48 hours
after death, insect invasion is the most accurate type of measure to determine minPMI
(Goff, 1991). However, many factors such as the geographic location, deposition
conditions and climatic conditions can affect the rate of decomposition and thus the pattern
of insect succession (Roberts et al., 2017; Voss et al., 2011). The position of the carcass,
size and type can also influence the time of arrival and duration of stay of the insects (Gill,
2005; Voss et al., 2009).
Research studies within the area of forensic science can typically be conducted by two
different types of scenarios; experimental research or case-work research. Experimental
research is a more controlled type of research approach where one variable is usually
manipulated and analysed accordingly. In comparison to a case-work type of research
scenario where it involves predominately of case-work which deals with real professional
cases rather than research itself.
9
Currently, there is insufficient studies detailing the level of variation (seasonal) regarding
insect succession patterns on decomposing remains. In Australia, insect succession data
that have been published are based mainly in New South Wales Victoria and Western
Australia. To date, there have been no published studies detailing insect succession
patterns on decomposing remains in Tasmania. Thus, a gap focusing on insect succession
data in the Tasmania region (as well as any other geographical regions) have yet to be
studied and published. This data is essential as it can be used during legal investigations to
assist in determining minPMI within forensic science.
This research aimed to provide a database, detailing forensically important insects on
decomposing carcasses within the Tasmania geographical region during the summer
season. Commonalities and dissimilarities were investigated with replications at two
contrasting habitats, agricultural and suburban. The degree of consistency in insect
succession and insect succession waves were investigated over a 39-day study during one
summer season.
2. DISCUSSION
This section is aimed to address the literature available in relation to insect succession on
decomposing carcasses, both experimental and case-work. This includes what has
previously been studied based on numerous factors which can affect both insect succession
and the decomposing carcass. These factors include, but are not limited to temperature,
season, time of day and accessibility of the carcass, the carcasses size and type, vertebrate
scavengers as well as the biology and geographic distribution of the necrophagous insects
which can influence both the time of arrival and duration of stay (Gill, 2005).
10
2.1 Decomposition
Decomposition is the process of tissue breakdown from dead organisms. Decomposition
commences immediately after time of death where the body temperature of the deceased
decreases to the temperature of its surroundings (K. G. V Smith, 1986; Voss et al., 2008).
This decomposition process is dependent on many factors such as environment conditions,
geographical location, deposition conditions such as surface, burial or submersion, climatic
conditions climate conditions such as temperature, season, habitat, accessibility and time of
day, various activity of bacterial, insect and vertebrates, as well as the properties each
individual carcass exhibits (Hyde et al., 2015; Roberts et al., 2017; Voss et al., 2011).
In a terrestrial environment, the deceased body generally undergoes five stages of
decomposition: fresh, bloat, active decay, advanced decay, dry remains and skeletisation.
2.1.1 Stages of decomposition: fresh
The initial stage of decomposition is the fresh stage where visible changes become
apparent. This stage consists of three additional stages within itself; algor mortis, rigor
mortis and livor mortis. Algor mortis is the first stage within the fresh stage of
decomposition. At this stage the internal body temperature of the carcass decreases to the
temperature of its surroundings immediately after time of death has occurred (K. G. V
Smith, 1986; Voss et al., 2008). Shortly after, rigor mortis takes place. Rigor mortis is
caused by the breakdown of glycogen and the build-up of lactic acid which causes
stiffening of muscles fibres (K. G. V Smith, 1986). Rigor mortis is dependent on several
intrinsic and extrinsic factors and can occur anywhere between two to six hours after time
of death and can last for up to 24 to 84 hours (Hayman & Oxenham, 2016).
11
Livor mortis is the other process of the fresh stage. It is evident from blood pooling in
certain areas of the body which becomes evident approximately two hours after death and
become fixed at approximately four to six hours, however in some situations livor mortis
can appear as soon as 15 minutes after death (Hayman & Oxenham, 2016). This process of
blood pooling can assist in estimating minPMI since the colour of the blood pool can
provide a rough estimation of the time frame. Initially, the blood pool will appear red in
colour but will change to purple as time progresses; however, colder temperatures will
delay this process (Hayman & Oxenham, 2016). This method of estimating minPMI is an
unreliable method as it is often subjective to human observation errors.
Insect invasion commences at the fresh stage of decomposition where they deposit either
eggs, larvae or maggots into any openings on the carcass body. The eggs are then laid and
hatched inside the carcass where internal feeding activity occurs (Lee Goff, 2009).
2.1.2 Stages of decomposition: bloat
The second stage of decomposition is the bloat stage and is defined by the gradual visible
inflation of the carcass and ends when the carcass eventually deflates. This is as a result
from the production of gases by anaerobic bacteria in the body (Voss et al., 2008). This
process results in a drastic increase of the internal body temperature of the carcass as it
involves a combination of both putrefaction and metabolic activities of maggots (Lee Goff,
2009). At this stage, the carcass becomes a target habitat for numerous insects to feed off
and reproduce on.
12
2.1.3 Stages of decomposition: decay
After the bloat stage, the decay stage begins and is defined by the deflation of the bloat
stage. At this stage, the outer layer of the skin on the carcass becomes broken due to gas
build-up, activity of maggot feeding and bacterial putrefaction (Lee Goff, 2009). Insect
succession on the carcass is during the decay stage is more evident as they are able to feed
off the carcass both internally and externally (Lee Goff, 2009).
2.1.4 Stages of decomposition: dry/remains
The dry/remains stage is defined by a reduction in flesh and fluid with the presence of dry
skin, mainly made up of skin, cartilage and bone on the carcass caused by insect
succession removing the flesh (Lee Goff, 2009; Voss et al., 2008).
2.1.5 Stages of decomposition: skeletonisation
Skeletonisation is the final stage of the decomposition process. This stage is defined by the
absence of soft tissue whereby only bones, cartilage and hair remains (Voss et al., 2008).
Typically, succession is no longer evident at this stage, however during the early portions
of skeletonisation, soil-dwelling taxa may come and feed of the carcass which can be a
valuable source of information (Lee Goff, 2009). The skeletonisation stage has no definite
end, but is subjective to the variety of soil fauna present at different points in time thus
indicating the time frame on how long the carcass has been at the point (Lee Goff, 2009).
13
2.2 Decomposition mediated by insects
The study of the decomposition of the organic matters (corpse and carcasses) has been well
researched, however studies relating to insect succession patterns on decomposing
carcasses have not been as heavily focused on worldwide. The species composition in
different parts of the world can be distinctive to that region or overlap across a vast area
(Gill, 2005). Carrion insects are largely influenced by season whereby a carcass exposed
during warmer months will have a richer and different fauna from a carcass exposed during
colder months where less faunal succession is present (K. G. V Smith, 1986).
There are many factors that affect insect succession which have been studied such as
climate conditions, seasons and geographic locations; however, many other factors and
geographic regions has been less frequently studied (Forbes, Perrault, Stefanuto, Nizio, &
Focant, 2014). Majority of studies relating to decomposition are usually performed in
warmer climate conditions due to the elevated temperature thus allowing rapid visible
changes (Forbes et al., 2014). Alongside the effect of seasons, temperature and humidity
also varies accordingly dependant on the geographic location. This therefore affects insect
succession patterns and thus provides a different database for minPMI determination in
specific regions.
Therefore, there is a gap that needs further studies in relation to insect succession on
decomposing carcasses within Australia in different geographical regions under various
types of conditions.
14
2.3 Entomology decomposition studies
The use of human remains is prohibited for the use of research for many reasons
constituting largely of ethical and religious reasons (K. G. V Smith, 1986). As a result,
animal carcasses, in particular swine carcasses, are more commonly used, especially within
forensic entomology studies. This choice of substituting swine carcasses as a predominant
animal of choice for studies relating to decomposition is because decomposing pigs have
similar body compositions are thus the next most reliable model to the human body; they
can also be readily available with uniform mass and size as to prevent bias within the
research (Dadour, Cook, Fissioli, & Bailey, 2001; Gill, 2005).
Majority of insect succession patterns studies have been based in certain countries,
including but not limited to Brazil2, China
3, Egypt
4, Canada
5, Europe
6, Hawaii
7, India
8,
Malaysia9, New Zealand
10, South Africa
11 and United States of America
12. The study of
insect succession within Australia has also been studied, however only a small number
have been studied which are limited only to certain regions such as Western Australia
(Dadour et al., 2001; O'Brien, Forbes, Meyer, & Dadour, 2007; Voss et al., 2011; Voss et
al., 2008; Voss et al., 2009), New South Wales (Forbes et al., 2014; Gherlenda, Esveld,
2 Studies on blowflies (Diptera, Calliphoridae) on swine carcasses were researched in a caatinga area north-
eastern Brazil 3 Studies on insect succession associated with human and animal remains were researched in Shenzhen,
China 4 Studies on identification of forensically important insects on exposed remains during a summer season were
researched in north-eastern Egypt 5 Studies on decomposition and insect succession were researched in Whitehorse, Yukon territory in Canada
6 Studies on insect succession and carrion decomposition on various forest habitats were studied in central
Europe 7 Studies on the comparison of insect species on decomposing remains inside dwellings and outdoors were
researched on the island of Oahu, Hawaii 8 Studies on insect succession on decaying rabbit carcasses were researched in Punjab, India
9 Studies on insect succession and decomposition rates associated with partially buried swine carcasses were
researched in a palm plantation in Malaysia 10
Studies on insect colonisation and succession on remains were researched in New Zealand 11
Studies on the influence of clothing and wrapping on carcass decomposition and insect succession during
winter seasons were researched in central South Africa 12
Studies on Diptera, Calliphoridae flies on swine carcasses were researched in rural-north of central Florida
15
Hall, Duursma, & Riegler, 2016; Johnson, Mikac, & Wallman, 2013) and Victoria (M. S.
Archer & Elgar, 2003).
2.3.1 Environment conditions
The type of environment whereby the carcass is situated can affect the decomposition
process. The deposition conditions such as surface, burial or submersion, climatic season
such as temperature, rainfall and seasons, activity of bacteria, insects and vertebrates, as
well as many other factors will affect the decomposition process. Direct sunlight will
increase the temperature that the carcass endures, thus speeding up the decomposition
process which in turn affects insect succession (Gill, 2005). However a shaded area could
limit the direct climatic conditions and therefore cause the carcass to decay at a faster rate,
despite the lower temperatures (Gill, 2005).
2.3.1.1 Indoor environment
Certain insects found on decomposing carcasses will only be found in an indoor type
environment situation unless all the windows were open and the body was exposed to
bright sunlight (K. G. V Smith, 1986).
Goff conducted a research in Hawaii comparing the different types of insect succession on
decomposing remains located both in an indoor and outdoor environment situation. The
research showed remains situated indoors had a dominant Diptera larvae type association
while remains situated outdoors had a dominant Coleoptera species type present (Goff,
1991).
16
Ramos-Pastrana et al. conducted a research in an urban area of Colombia analysing the
insects associated to indoor body decay of a white pig within a controlled indoor
environment for a period of 54 days. The research showed the Calliphoridae family was
the most dominant insect family followed by Muscidae and Sarcophagidae (Ramos-
Pastrana, Velasquez-Valencia, & Wolff, 2014).
2.3.1.2 Outdoor environment and confined environment
In an outdoor type of environment situation, the insects (especially maggots) found on the
body will be a good indicator of whether the body has been laying in direct, a shaded area
or even both (K. G. V Smith, 1986). In a confined environment situation however,
different rates of decomposition can occur in comparison to both the indoor and outdoor
environment. Voss et al. conducted a research inside a vehicle following carbon monoxide
poisoning in Western Australia. Varying rates of decomposition and insect succession were
analysed between carcasses that were exposed on the soil surface with and without
scavenger proof cages as well as inflicted injured carcasses with those carcasses that were
poisoned with carbon monoxide that were placed inside an enclosed vehicle. The research
showed the rate of decomposition and pattern of insect succession was similar between the
surface carcasses, regardless of the mode of death. However, the rate of decomposition of
the carcasses enclosed in the vehicle was 3 – 4 days faster due to the higher temperatures
within the vehicle in comparison to the external ambient temperature. The pattern of insect
succession also differed with the enclosed vehicle carcasses with insects of the Coleoptera
appearing during the bloat stage of decomposition at the surface carcasses but did not
appear until the onset of the wet decomposition stage within the vehicle environment
carcasses (Voss et al., 2008).
17
Anton et al. conducted a research on two different substrates during four different periods
in central Europe analysing the insect succession patterns on decomposing swine carcasses.
The research showed that insect succession is dependent on seasonality and weather
conditions as the carcass maintained a bloated appearance even after 133 day in the winter
season but reached the dry stage of decomposition within only eight days in the summer
season. Although the decomposition process time varied greatly, the insect succession
types also varied accordingly to the seasons (Anton, Niederegger, & Beutel, 2011).
Benbow et al. however conducted another research to observe the difference between
insect succession patterns in relation to seasonal differences during all four seasons in
Ohio, America. This research showed the richness amount of insects was generally lower
during early decomposition stages and increased through the intermediate stages with the
decay stage being the most rich. The research also showed the insect composition during
the succession varied among each of the four seasons with insects in the Calliphoridae
species type being more dominant during summer and autumn seasons, while insects in the
Coleoptera species type were more dominant during winter seasons thus indicating there is
a difference in insect succession types during the different seasons (Benbow, Lewis,
Tomberlin, & Pechal, 2013).
Another research was conducted in New Zealand for the first-time by Eberhardt and Elliot
monitoring the insect succession and colonisation in three different outdoor habitats at the
same time. The rate of decomposition was found to be different between the three habitats
but the dominant insect species that were found on the carcasses similar; these species
include Calliphora stygia (Diptera: Calliphoridae), Chrysomya rufifacies (Diptera:
Calliphoridae) and Hydrotaea rostratain (Diptera: Muscidae) (Eberhardt & Elliot, 2008).
Bygarski and LeBlanc conducted a research comparing and identifying the different types
of insect succession that feed off swine carcasses in northern Canada. This research
18
showed the dominant insect species that were found on the carcasses were Protophormia
terraneovae (Diptera: Sarcophagidae) and Thanatophilus lapponicus (Coleoptera:
Silphidae) and concluded that the geographic region has a significant effect on the type of
insect that feeds off the decomposing carcass thus affecting the decomposition rate
(Bygarski & LeBlanc, 2013).
Alves et al. conducted another research analysing blowfly species associated with the
stages of decomposing swine carcasses in dry and rainy seasons in the northeast of Brazil.
This research concluded that the abundance of different insect species during the dry
seasons and rainy season were not the same. During the dry seasons, the dominant insect
species wre Cochliomoyia macellaria (Diptera: Calliphoridae) and Chrysomya albiceps
(Diptera: Calliphoridae) while in the rainy seasons, Chloroprocta idioidea (Diptera:
Calliphoridae) was the dominant insect type (Alves, Santos, Farias, & Creao-Duarte,
2014).
2.4 Entomology decomposition studies in Australia
In Australia, the first forensic entomology succession research was conducted in
Queensland using carcasses from various mammalian species; however, the first
systematically forensic succession research published was conducted in Victoria using
still-born swine carcasses in a dry forest geographic location (M. Archer & Wallman,
2017). This research supported the fact that temperatures and rainfall significantly affects
the decomposition rate.
Archer and Elgar conducted a research analysing the insect succession data on swine
carcasses during different seasons throughout two years in Victoria. This research showed
two Chrysomya species (flies) were restricted to months with higher temperature
19
conditions in comparison to Omorgus and Saprinus species (beetles) which were more
dominant in cooler temperature conditions. This indicates that different insect types feed
off decomposing carcasses dependent on the climatic seasons (M. S. Archer & Elgar,
2003).
McIntosh, Dadour and Voss conducted a research comparing insect succession associated
in relation to burnt and unburnt decomposing swine carcasses in Western Australia during
the autumn season. This research showed burnt carcasses had a faster decomposition rate
in comparison to the unburnt carcasses; however, insect species that came to feed off the
carcass remained consistent between the two scenarios but the richness between the two
scenarios were significantly different. The differences noted between the two scenarios
were the arrival time of late colonisers as well as the development of colonising insects
thus indicating that burnt carcasses affect both the decomposition rate and insect
succession (McIntosh, Dadour, & Voss, 2017).
Voss, Cook and Dadour also conducted another research comparing the effect of insect
succession patterns on clothed and unclothed decomposing carcasses in Western Australian
during the autumn season. It was observed that as the ambient temperatures increased it
corresponded to faster decomposition rates; the insect succession pattern also maintained
consistent with a slight variation. Australophyra rostrata was observed to appear in two
distinct waves of succession on the clothed carcasses while only one wave appeared on the
unclothed carcasses; Lucilia sericata was also observed to appear one day earlier on the
clothed carcasses. Another variation observed was that larval feeding lasted longer and
larvae mass were more widely distributed throughout the carcass on the clothed carcasses
(Voss et al., 2011).
20
Voss also investigated insect succession patterns based on annual seasonal variations of
decomposing remains at two contrasting locations; bushland and agricultural in Western
Australia. It was concluded that the insect succession patterns of the two habitat locations
were strongly correlated and that the differences were greatly due to species absences at
the agricultural site. However it was also observed that the insect types significantly varied
over different seasons year by year (Voss et al., 2009). O’Brien et al. conducted another
research to identify major scavengers on decomposing carcasses in southwest of Western
Australia. One of the major differences observed between the seasons was the richness in
insect composition during summer; this suggests the insect activity are influenced based on
seasonality. Another differenced observed in the research is the feeding patterns; during
the summer season insects feed during the cooler hours of the morning and evening while
in the winter season insects feed during the warmer hours of the day (O'Brien et al., 2007).
There has been a research in Tasmania regarding blowfly succession from possum carcass
(Lang, Allen, & Horton, 2006); however, to date, insect succession patterns decomposing
carcass has not yet been studied.
3. Experimental design elements
In light of the research presented, it is evident that the geographic region, season,
temperature and many other factors will have a large effect on the rate of decomposition
and thus the insect succession patterns. It is therefore essential to research the insect
succession patterns on decomposing carcasses in respect to these factors thus eventually
create a database detailing the seasonal insect succession patterns on decomposing
carcasses in relation to specific factors.
21
The research is an experimental type of research which utilised swine carcasses to mimic
human carcasses to investigate the insect succession patterns on decomposing carcasses.
As mentioned previously, geographic region and habitat is a large factor that affects the
decomposition rate and insect succession patterns, therefore this research will look at the
difference in insect succession patterns on decomposing swine carcasses placed in two
different outdoor geographical habitats in Tasmania, Australia.
To date, there is no published data on insect succession pattern on decomposing carcasses
in the Tasmania region.
3.1 Australian environmental conditions
Australia is the sixth largest country in the world covering an area of approximately 12
million square kilometres, of this approximately 91% of Australia is covered in native
vegetation. Due it Australia’s large size, a variety of climate conditions is experienced with
two main seasonal patterns; these patterns are broken down into summer/autumn and
winter/spring which affects the environmental conditions into a wet and dry pattern
("About Australia,").
During summers seasons in Australia, the temperature in the southern cities including New
South Wales, Canberra, Victoria, Tasmania, Adelaide and Perth range on average between
16C to 26C whilst during winter seasons, the temperature ranges on average between
6C to 12C ("About Australia,").
22
3.1.1 Tasmania geographic location
Tasmania is Australia’s smallest state (see Fig. 1). It is south of Bass Trait and is an island
extension located 240 km south-east off the corner of the Australian mainland with an area
of 90,758 square kilometres ("Tasmania facts," 2017) . Launceston is the second largest
city in Tasmania which lays north of Tasmania while Devonport is a city which lays north-
west of Tasmania (see Fig. 2).
Tasmania’s natural vegetation patterns consists mainly of forest clearance and tree thinning
(New Zealand, 1994)
Figure 1: Map view of Australia. Tasmania is an island located 240 km South-East off
the corner of the Australian mainland (source: https://www.google.com.au/maps) .
23
Figure 2: Map view of Launceston and Devonport cities within Tasmania. Launceston
lays north of Tasmania while Devonport is a city which lays north-west of Tasmania
(Devonport is marked by the red marker) (source: https://www.google.com.au/maps).
3.1.2 Temperature conditions in Tasmania
Throughout the year, Tasmania has four distinct seasons. The warmest months are during
December to March with an average maximum between 17C and 23C ("Discover
Tasmania," 2017). The hottest months for Devonport fall between the months of December
and February, where the average maximum temperature exceeds 25C and the average
minimum temperature falls below 2C (see Table 1) (Bureau of Meteorology, 2017).
24
Table 1: Monthly temperatures recorded for Tasmania (Launceston Airport Station)
during 2016 displayed as average monthly maximum and minimum temperature and
maximum temperature recorded within the month (all in degree Celsius).
Month Average minimum
temperature
Average maximum
temperature
Maximum
recorded
temperature
January 12.7 25.8 32.5
February 12.1 24.9 31.3
March 10.2 22.2 28.8
April 7.4 19.3 24.1
May 5.7 14.4 17.9
June 4.0 12.4 16.8
July 3.6 11.9 14.9
August 2.3 12.6 15.8
September 5.3 15.7 20.8
October 4.8 15.9 20.4
November 7.4 19.0 25.6
December 9.2 22.5 32.2
This research was conducted at two study sites, an agricultural site which was located
within an agricultural active paddock situated approximately 8 km north-east of
Devonport, Tasmania (411026.6S, 1461723.6E). The site was used for potato
cultivation at the time of the research; the area used for the research was in the south-east
corner of the paddock which was not used for farming and was located at the end of a
gravel farm road with private and restricted access. The second study site was located at a
25
suburban site within a scientific facility (Department of Primary Industries, Parks, Water
and Environment Facility) situated approximately 5 km south of Launceston, Tasmania
(412809.8S, 1470828.6E). The site is used as a scientific facility; the area used for the
research was approximately 0.13 km south of the facility which was surrounded by a grass
paddock with buildings, roads and trees nearby. The two study sites were situated
approximately 100 km apart.
3.2 Best practice in forensic entomology decomposition studies
In forensic entomology, the collection and preservation of insects, arthropods and maggots,
larvae and egg should follow the best practice. The following equipment is essential (K. G.
V Smith, 1986):
Gloves and protective clothing
Forceps for picking up specimens off the carcass individually
Small trowel for picking up larger specimens or quantity of the carcass
Small artist’s paint brush for picking up tiny specimens that might be damaged by
forceps
When collecting specimens that are already dead, regardless of which stage the specimens
are at, storing them in 70% to 95% ethanol is ideal. This enables preservation of the
specimens a more accurate identification type due to a more defined morphological and
molecular structure (J. Amendt, C. P. Campobasso, et al., 2007).
26
3.3.1 Collection at study site
Any insects hovering around and are settled on the decomposing carcasses were captured
using suitable entomological protocols and transferred to a plastic container with a tight
screw-top lid. These collected insects were then killed and preserved in 70% ethanol to
preserve the internal structures. Following each sample that was collected was then
immediately documented with the site details, date and location where the insects was
collected in respect to the body. Additional supplementary information may also be noted.
Any eggs, maggots and larvae found feeding off the carcasses were collected with either
clean forceps or a small trowel and placed into 70% ethanol. A small sample of each type
and size was then collected and kept alive for rearing at the laboratory.
3.3.2 Rearing in laboratory
Rearing of live insects collected from the scene allows entomologists to more accurately
identify species. This is particularly important when morphological differences are not
distinct and thus a definite determination of a species cannot be determined.
Larvae should be reared in moist conditions in containers opened to the air as closed
containers will encourage mould (K. G. V Smith, 1986).
4. Experimental aims and hypothesis
The objective of this research is to determine the insect succession pattern on decomposing
swine carcasses in two different areas in Tasmania approximately 100 kilometres apart.
This was completed by collection of the different various insects that came to feed of the
27
carcasses and identification these insect species will be conducted. This information can
then further be analysed and determination of the insect arrival pattern are to be recorded
over the entire duration of the research. Since the succession of insects are influenced
greatly by the physical position and conditions of the carcass, two swine carcasses were
placed in two locations, Launceston and Devonport over one summer season during
December 2014 to January 2015. Subsequently, the aims and hypothesis to be tested:
Aims:
1. Compose a database of forensically important insects found on the swine carcasses
used in this experiment.
2. Determine the insect succession pattern on decomposing carcasses placed in the
two locations, Launceston and Lillico.
3. Find commonalities or dissimilarities between the insect successional waves in in
the two locations, Launceston and Lillico.
Experimental Hypothesis:
H0: Insect succession have a similar type of pattern associated with decomposing swine
carcasses placed in two different geographic habitats in Tasmania during the
summer weathered season.
H1: Insect succession do not have a similar type of pattern associated with decomposing
swine carcasses placed in two different geographic habitats in Tasmania during the
summer weathered season.
A gap in previous research relates to insect succession patterns in Tasmania, Australia
conducted within the same geographic area but in different habitat types. Research around
insect succession patterns is usually conducted at a single location located within a single
geographic location. However, various habitats have different insect succession influences
28
with very few studies comparing insect succession patterns within the same geographic
area but different habitat types (Voss et al., 2009).
The locations where the Launceston decomposition site was in a suburban location with
grass paddocks. Surrounding the grass paddock were buildings, roads and trees. The
location where Devonport decomposition site was in an active agricultural paddock being
used for potato cultivation with a small number of medium sized trees surrounding the site.
5. Conclusion
Decomposing carcass remains exposed in an outdoor environment situation are dependent
on the decomposition process but are also subjective to scavenging fauna (O'Brien et al.,
2007). The scavenging fauna is dependent on the geographic region, season and weather
conditions that affect the decomposition rate and thus the pattern of insect succession
whether the carcass is located indoors or outdoors. Weather conditions play an important
factor in insect succession patterns as cold and/rain weather climate conditions inhibit fly
activity (K. G. V Smith, 1986).
In conclusion, insect succession on a decomposing carcass is dependent on a large number
of factors which have not yet all been researched. At present, there is no available data for
insect succession patterns based in Tasmania, Australia detailing the effect of swine
decomposition and insect succession. Therefore, this data needs to be researched to allow a
more accurate minPMI determination in this area.
Further research needed in the area of research of decomposition and insect succession in
cooler climate as insect succession may vary according to temperatures in different
29
geographic regions. This can therefore again ensure a more accurate minPMI estimation
and thus identification of the victim’s remains (Forbes et al., 2014).
6. References
Abd El-bar, M. M., & Sawaby, R. F. (2011). A preliminary investigation of insect
colonization and succession on remains of rabbits treated with an organophosphate
insecticide in El-Qalyubiya Governorate of Egypt. Forensic Sci Int, 208(1-3), e26-
30. doi:10.1016/j.forsciint.2010.10.007
About Australia. Out natural environment. Retrieved from
http://www.australia.gov.au/about-australia/our-country/our-natural-environment
Alves, A. C., Santos, W. E., Farias, R. C., & Creao-Duarte, A. J. (2014). Blowflies
(Diptera, Calliphoridae) Associated with Pig Carcasses in a Caatinga Area,
Northeastern Brazil. Neotrop Entomol, 43(2), 122-126. doi:10.1007/s13744-013-
0195-4
Amendt, J., Campobasso, C. P., Gaudry, E., Reiter, C., LeBlanc, H. N., & Hall, M. J.
(2007). Best practice in forensic entomology - Standards and guidelines. Int J Legal
Med, 121(2), 90-104. doi:10.1007/s00414-006-0086-x
Amendt, J., Campobasso, C. P., Gaudry, E., Reiter, C., LeBlanc, H. N., & Hall, M. J.
(2007). Best practice in forensic entomology--standards and guidelines. Int J Legal
Med, 121(2), 90-104. doi:10.1007/s00414-006-0086-x
Amendt, J., Campobasso, C. P., Gaudry, E., Reiter, C., LeBlanc, H. N., & J. R. Hall, M.
(2007). Best practice in forensic entomology—standards and guidelines.
International Journal of Legal Medicine, 121(2), 90-104. doi:10.1007/s00414-006-
0086-x
Anton, E., Niederegger, S., & Beutel, R. G. (2011). Beetles and flies collected on pig
carrion in an experimental setting in Thuringia and their forensic implications. Med
Vet Entomol, 25(4), 353-364. doi:10.1111/j.1365-2915.2011.00975.x
Archer, M., & Wallman, J. (2017). The development of forensic entomology in Australia
and New Zealand: an overview of casework practice, quality control and standards.
Australian Journal of Forensic Sciences, 49(2), 125-133.
doi:10.1080/00450618.2015.1137972
Archer, M. S., & Elgar, M. A. (2003). Yearly activity patterns in southern Victoria
(Australia) of seasonally active carrion insects. Forensic Sci Int, 132(3), 173-176.
Benbow, M. E., Lewis, A. J., Tomberlin, J. K., & Pechal, J. L. (2013). Seasonal
necrophagous insect community assembly during vertebrate carrion decomposition.
J Med Entomol, 50(2), 440-450.
Bygarski, K., & LeBlanc, H. N. (2013). Decomposition and arthropod succession in
Whitehorse, Yukon Territory, Canada. J Forensic Sci, 58(2), 413-418.
doi:10.1111/1556-4029.12032
Byrd, J. H., & Castner, J. L. (2010). Forensic Entomology – The utility of arthropods in
legal investigation (2 ed.): CRC Press, Boca Raton, FL, USA.
Byrd, J. H., & Tomberlin, J. K. (2010). Laboratory rearing of forensic insects. In J. H.
Byrd & J. L. Castner (Eds.), Forensic entomology—the utility of arthropods in
legal investigation (pp. 177-200). Boca Raton, FL: CRC Press.
30
Campobasso, C. P., Di Vella, G., & Introna, F. (2001). Factors affecting decomposition
and Diptera colonization. Forensic Sci Int, 120(1-2), 18-27.
Dadour, I. R., Cook, D. F., Fissioli, J. N., & Bailey, W. J. (2001). Forensic entomology:
application, education and research in Western Australia. Forensic Sci Int, 120(1-
2), 48-52.
Discover Tasmania. (2017). Retrieved from
http://www.discovertasmania.com.au/about/climate-and-weather
Eberhardt, T. L., & Elliot, D. A. (2008). A preliminary investigation of insect colonisation
and succession on remains in New Zealand. Forensic Sci Int, 176(2-3), 217-223.
doi:10.1016/j.forsciint.2007.09.010
Forbes, S. L., Perrault, K. A., Stefanuto, P. H., Nizio, K. D., & Focant, J. F. (2014).
Comparison of the decomposition VOC profile during winter and summer in a
moist, mid-latitude (Cfb) climate. PLoS One, 9(11), e113681.
doi:10.1371/journal.pone.0113681
Gherlenda, A. N., Esveld, J. L., Hall, A. A., Duursma, R. A., & Riegler, M. (2016). Boom
and bust: rapid feedback responses between insect outbreak dynamics and canopy
leaf area impacted by rainfall and CO2. Glob Chang Biol, 22(11), 3632-3641.
doi:10.1111/gcb.13334
Gill, G. J. (2005). Decomposition and arthropod succession on above ground pig carrion
in rural Manitoba (TR-06-2005). Retrieved from Manitoba:
Goff, M. L. (1991). Comparison of insect species associated with decomposing remains
recovered inside dwellings and outdoors on the island of Oahu, Hawaii. J Forensic
Sci, 36(3), 748-753.
Goff, M. L. (1993). Estimation of Postmortem Interval Using Arthropod Development and
Successional Patterns. Forensic Sci Rev, 5(2), 81-94.
Hayman, J., & Oxenham, M. (2016). Human Body Decomposition. San Diego, UNITED
STATES: Elsevier Science.
Hyde, E. R., Haarmann, D. P., Petrosino, J. F., Lynne, A. M., & Bucheli, S. R. (2015).
Initial insights into bacterial succession during human decomposition. Int J Legal
Med, 129(3), 661-671. doi:10.1007/s00414-014-1128-4
Johnson, A. P., Mikac, K. M., & Wallman, J. F. (2013). Thermogenesis in decomposing
carcasses. Forensic Sci Int, 231(1-3), 271-277. doi:10.1016/j.forsciint.2013.05.031
Lang, M. D., Allen, G. R., & Horton, B. J. (2006). Blowfly succession from possum
(Trichosurus vulpecula) carrion in a sheep-farming zone. Med Vet Entomol, 20(4),
445-452. doi:10.1111/j.1365-2915.2006.00654.x
Lee Goff, M. (2009). Early post-mortem changes and stages of decomposition in exposed
cadavers. Exp Appl Acarol, 49(1-2), 21-36. doi:10.1007/s10493-009-9284-9
McIntosh, C. S., Dadour, I. R., & Voss, S. C. (2017). A comparison of carcass
decomposition and associated insect succession onto burnt and unburnt pig
carcasses. Int J Legal Med, 131(3), 835-845. doi:10.1007/s00414-016-1464-7
Megnin, J. P. (1894). La faune de cadavres. Application de l’entomologie a la medicine
legale. . G. Masson, Paris Encyclopedie Scientifique des Aide-Memoire.
Meteorology, B. o. (2017). Climate statistics for Australian locations. Retrieved from
http://www.bom.gov.au/jsp/ncc/cdio/cvg/av?p_stn_num=091126&p_prim_element
_index=0&p_comp_element_index=0&redraw=null&p_display_type=statistics_su
mmary&normals_years=1971-2000&tablesizebutt=normal
New Zealand, D. o. S. a. L. I. (1994). The Macquarie World Atlas (Revised edition ed.).
Australia, New South Wales: Macquarie Library in association with Australian
Surveying & Land Information Group.
31
O'Brien, R. C., Forbes, S. L., Meyer, J., & Dadour, I. R. (2007). A preliminary
investigation into the scavenging activity on pig carcasses in Western Australia.
Forensic Sci Med Pathol, 3(3), 194-199. doi:10.1007/s12024-007-0016-3
Ramos-Pastrana, Y., Velasquez-Valencia, A., & Wolff, M. (2014). Preliminary study of
insects associated to indoor body decay in Colombia. Revista Brasileira de
Entomologia, 58, 326-332.
Roberts, L. G., Spencer, J. R., & Dabbs, G. R. (2017). The Effect of Body Mass on
Outdoor Adult Human Decomposition. J Forensic Sci. doi:10.1111/1556-
4029.13398
Schotsmans, E. M., Forbes, S. L., & Márquez-Grant, N. (2017). Taphonomy of Human
Remains. Somerset, UNKNOWN: John Wiley & Sons, Incorporated.
Smith, K. G. V. (1986). A Manual of Forensic Entomolgy. New York: British Museum,
Department of Entomolgy.
Smith, K. G. V. (1986). A Manual of Forensic Entomology. London: Trustees of the
British Museum, Natural History and Cornell University Press.
Tasmania facts. (2017). Retrieved from http://www.about-australia.com/tasmania-facts/
Voss, S. C., Cook, D. F., & Dadour, I. R. (2011). Decomposition and insect succession of
clothed and unclothed carcasses in Western Australia. Forensic Sci Int, 211(1-3),
67-75. doi:10.1016/j.forsciint.2011.04.018
Voss, S. C., Forbes, S. L., & Dadour, I. R. (2008). Decomposition and insect succession on
cadavers inside a vehicle environment. Forensic Sci Med Pathol, 4(1), 22-32.
doi:10.1007/s12024-007-0028-z
Voss, S. C., Spafford, H., & Dadour, I. R. (2009). Annual and seasonal patterns of insect
succession on decomposing remains at two locations in Western Australia.
Forensic Sci Int, 193(1-3), 26-36. doi:10.1016/j.forsciint.2009.08.014
32
33
- Part Two -
Manuscript
INSECT SUCCESSION PATTERN
ON DECOMPOSING SWINE
CARCASSES IN TASMANIA: A
SUMMER STUDY
34
Insect succession pattern on decomposing swine
carcasses in Tasmania: a summer study.
Tracy Fong1, Paola Magni
1, David North
2, Melle Zwerver
3, Ian Dadour
4
1 Murdoch University, School of Veterinary and Life Sciences, Perth, WA
2 Tasmania Police Forensic Services, Hobart
3 Tasmania Police, Devonport Police Station
4 University of Boston, School of Medicine, Boston, Massachusetts
Abstract
Insect succession patterns have been studied largely around the world by using the
predictable sequential arrival pattern of different insect species that become attracted to the
decomposing carcass at various stages of the decay. Currently, in some countries there are
insufficient studies detailing the seasonal variation of insect succession patterns on
decomposing remains. To date, there have been no published studies detailing insect
succession patterns on decomposing remains in the Tasmania. This data is essential as it
can become invaluable during legal investigations, as it can be used in conjunction with
existing methods to assist in determining the time since death.
The present research represents the first insect succession pattern study to be
undertaken in Tasmania investigating the insect succession patterns on decomposing swine
carcasses (Sus scrofa domesticus Erxleben). For the purpose of this research, 3 swine
carcasses have been placed in two contrasting location sites in Tasmania, agricultural and
suburban, during the summer season. This study aimed to provide a preliminary database,
detailing forensically important insects on decomposing carcasses within the Tasmania
35
geographical region during the hot season. The degree of consistency in insect succession
and insect succession waves were investigated over a 39-day study during one summer
season. Evident in this study, decomposition rates are varied according to different habitat
types as well as marginal variations of insect succession assemblage.
Keywords: decomposition, Tasmania, insect succession, forensic entomology.
Introduction
Forensic entomology is the study of insects and other arthropods associated with
legal investigations (Voss et al., 2009). Forensic entomology is a method used worldwide
to assist in determining a more accurate time since death or minimum post mortem interval,
minPMI (Voss et al., 2009). Insects13
can also be used in situations where additional
information such as presence of drugs, possible movements of the corpse and presence of
lesions are uncovered in cases of suspicious death (Byrd & Castner, 2010).
Human remains is a highly nutritious source which can attract a variety of
organisms when the body begins to decompose (Schotsmans et al., 2017). Human
decomposition involves a very complex biological process where the body undergoes
several different stages. The decomposition process is largely dependent on factors such as
environment conditions, geographical location, deposition conditions such as surface,
burial or submersion, climatic conditions such as temperature, season, habitat, accessibility
and time of day, various activity of bacterial, insect and vertebrates, as well as the
13 For easiness of the reader, from this point onwards the text will simply refer to “insects”
when considering insects and other arthropods
36
properties each individual carcass exhibits (Hyde et al., 2015; Roberts et al., 2017; Voss et
al., 2011).
It has been experimentally proven that the arrival of organisms, such as insects and
necrophagous, is not random but however these insects are more interested in only feeding
at certain stages of decomposition (Megnin, 1894). Insect succession involves the process
of invasion by insects to the carcass soon after death thus resulting in mass amounts of fly
eggs and larvae present on the carcass. This process continues by further attracting
subsequent insect species that feed and reproduce off the carcass creating a successional
wave of decomposition (Gill, 2005; K. G. V Smith, 1986; Voss et al., 2008).
Insect succession patterns have been studied largely around the world by using the
predictable sequential arrival patterns of different insect species that become attracted to
the decomposing carcass at various stages of the decay (Morris, Dadour, 2005). The
obtained data have become invaluable during legal investigations worldwide, as they can
be used in conjunction with existing methods to assist in determining the time since death,
minPMI as well as the post-mortem movement of the body (Jens Amendt et al., 2007;
Goff, 1993).
Correct identification of insects as well as the known insect succession patterns is
essential for every specific geographical region. This is because after approximately 24 -
48 hours after death, insect invasion is the most accurate type of measure to determine
minPMI (Goff, 1991). However, many factors, as mentioned previously, can affect the rate
of decomposition and thus affect the insect succession pattern (Roberts et al., 2017; Voss et
al., 2011). The position of the carcass, size and type can also have an influence in the time
of arrival and duration of stay of the insects (Gill, 2005; Voss et al., 2009).
Currently, there is insufficient studies detailing the level of variation (seasonal)
regarding insect succession patterns on decomposing remains. In Australia, insect
37
succession data that have been published are based mainly in New South Wales (Forbes et
al., 2014; Gherlenda et al., 2016; Johnson et al., 2013), Victoria (M. S. Archer & Elgar,
2003) and Western Australia (Dadour et al., 2001; O'Brien et al., 2007; Voss et al., 2011;
Voss et al., 2008; Voss et al., 2009). To date, there have been no published studies
detailing insect succession patterns on decomposing remains in Tasmania. Thus, a gap
focusing on insect succession data in the Tasmania region (as well as any other
geographical regions) have yet to be studied and published. This data is essential as it can
be used during legal investigations to assist in determining minPMI within forensic
science.
This study aimed to provide a database, detailing forensically important insects on
decomposing carcasses within the Tasmania geographical region during the summer
season. Commonalities and dissimilarities were investigated with replications at two
contrasting habitats, agricultural and suburban. The degree of consistency in insect
succession and insect succession waves were investigated over a 39-day study during one
summer season.
2. Materials and methods
2.1 Study site
A 39-day survey of animal decomposition was conducted at two study sites from
the 12th
of December 2014 to the 19th
of January 2015. The first site (agricultural) was
located within an agricultural active paddock situated approximately 8 km north-east of
Devonport, Tasmania (411026.6S, 1461723.6E). The site was used for potato
cultivation at the time of the research; the area used for the research was in the south-east
corner of the paddock which was not used for farming and was located at the end of a
38
gravel farm road with private and restricted access. The second study site (suburban) was
located within a scientific facility (Department of Primary Industries, Parks, Water and
Environment Facility) situated approximately 5 km south of Launceston, Tasmania
(412809.8S, 1470828.6E). The site is used as a scientific facility; the area used for the
research was approximately 0.13 km south of the facility which was surrounded by a grass
paddock with buildings, roads and trees nearby. The two study sites were situated
approximately 100 km apart.
2.2 Animal model
In Australia, the use of human remains is legally prohibited for the use of field-
based research constituting largely of ethical and religious reasons (K. G. V Smith, 1986).
As a result, animal models, such as dogs, rats, swines and guinea pigs are the only option
available for research relating to insect succession data and information based on
geographic location and seasonality of minPMI . The preferred animal model, swines (Sus
scrofa domesticus Erxleben), are most commonly used because they have similar body
compositions and are thus the next most reliable model to the human body; they can also
be readily available with uniform mass and size as to prevent bias within the research
(Dadour et al., 2001; Gill, 2005). For this study, swine carcasses were used as
decomposition models. Carcasses14
(weight 400 – 500 g) were obtained from C. K. & S.
Farguhar, a piggery in Bridgenorth, Tasmania. On the same day after the carcasses were
shot in the head and plugged with silicon, the carcasses were transported and placed into
the study sites.
14
For easiness of the reader, from this point onwards the text will simply refer to
“carcasses” when considering swine carcasses and decomposing pig.
39
2.3 Sampling procedure and subsequent analyses
On the first day when the swine caresses were shot in the head (day 1), six
carcasses were transported and individually placed within scavenger proof cages
throughout each of the two study sites (three carcasses per site). The cage design prevented
animal scavenging but still allowed insect access. Also present at the second site,
suburban, was green coverings that were used to obscure any potential views of passing
motorists and/or pedestrians. Sampling of the insect fauna were conducted every day up
until day 35 of the research. The sampling days encompassed periods of significant
decomposition stages. Representative samples of insect fauna were collected, including
eggs, larvae, pupae and adults. Samples of insect fauna were also collected within a 2-
meter radius of the carcass.
Collected samples were labelled in relation to carcass number, replicate number,
collection site and sampling times, these samples were placed into screw-top containers.
Half of larvae samples were killed in hot water and preserved in 70% ethanol, as per best
practice in forensic entomology (J. Amendt, C.P. Campobasso, et al., 2007); the remaining
samples were reared to adulthood to aid in identification (Byrd & Tomberlin, 2010).
The collected samples were taken to Perth, Western Australia for the taxonomical
identification by an entomologist. The samples were separated and organised according to
collection site, carcass number and date of collection. Each sample was observed under a
steromicroscope (Leica® MZ8) and identified in terms of life instar and
family/genus/species when possible.
2.3 Environmental data collection (temperature and rainfall)
Daily records of ambient temperature were obtained from weather stations around
the state representative of the second study site, suburban (Launceston) using a data
40
logger. Further records of ambient temperatures and rainfall levels were obtained from the
Bureau of Meteorology website (Meteorology, 2017).
2.4 Assessment of the stage of decomposition
In addition to insect sampling, all carcass replicates were observed daily for the
first week and subsequently every two to four days for identification of decomposition
stages. Photographs of the carcasses were taken each observation day. Decomposition is
the process of tissue breakdown from dead organisms which commences immediately after
time of death (K. G. V Smith, 1986; Voss et al., 2008). There are five different stages of
decomposition: fresh, bloat, decay, dry/remains and skeletonisation (Figure 2) (Lee Goff,
2009; Voss et al., 2008). For this study, carcasses were considered in fresh stage from the
moment of death to the onset of bloat. Bloat commenced when inflation of the carcass
occurred and concluded upon deflation of the carcass. The decay stage was considered to
when the carcass deflation concludes and the outer layer of the skin on the carcass
becomes broken leaving only dry constituents remaining (Lee Goff, 2009). The
dry/remains stage was considered at this point and prolongs until only skin, cartilage and
bone is left on the carcass (Lee Goff, 2009; Voss et al., 2008). Carcasses were considered
in skeletonised stage when the absence of soft tissue was noted on bones, cartilage and hair
remains (Voss et al., 2008).
3. Results
3.1 Decomposition process and environmental data
The progression and duration of each decomposition stage were not entirely
comparable between the two sites within the 39-days (Table 1). While the fresh stage of
decomposition showed the same duration, the following stages needed more time to be
41
completed in the agricultural site compared with the suburban site. The reason for this
may be found in the fact that the environmental temperatures at the agricultural site were
typically lower than the suburban site. The agricultural site showed an average minimum
temperature of 11.2C and maximum temperature of 23.6C, in comparison to the
suburban site where the ambient temperatures were at an average minimum temperature of
13.2C and maximum temperature of 22.5C (Figure 1). The duration of the decay stages
differed largely between the two decomposition sites lasting either 21 (agricultural) or 10
(suburban) days with all carcass replicated reaching the dry/remains stage by day 25. The
onset of decay was relatively rapid with the carcasses remaining relatively fresh until day
3. The duration of the decay stage was comparatively longer, lasting 7-11 days at the
agricultural site and 3-6 days at the suburban site (Figure 2).
3.2 Insect succession
Throughout this study, 11 insect taxa, representing 9 families were identified in
association with the carcass decomposition (Table 1). Representatives of the order Diptera
were the primary initial colonisers of all carcasses. Two genus of fly were present on the
carcass throughout the decomposition at both the agricultural and suburban sites. Early
colonisers arriving during the fresh stage of decomposition included Calliphora sp.
(Diptera: Calliphoridae), and Calliphora albifrontalis Malloch (Diptera: Calliphoridae).
Secondary colonisers, Lucilia sp. (Diptera: Calliphoridae) reached the carcasses during the
bloat stage, but only at the suburban site. Additional colonisers arriving later during
decomposition (10 days in) include the flies of the family Muscidae (Figure 3).
Carcasses at the suburban site was observed to contain eggs and larvae of
Calliphora sp., which were present up until the skeletonisation stage of decomposition
whereby the muscids and various beetles (Coleoptera) took over. In contrast, the carcasses
42
present at the agricultural site again contained eggs and larvae of Calliphora sp. but only
up until the dry/remains stage; the presence of pupae then became present until the
skeletonistion stage of decomposition. Muscids were present during the early stages of
decay and remained present until the skeletonisation stages; beetles were also present at
various random stages during the decomposition process.
Table 1: Summer succession of insects on carcasses at two study sites, agricultural and
suburban, over 39-days in Tasmania, Australia. Data summarised by decomposition stages.
Life stages are identified by E (eggs), L (larvae), P (pupae), PF (larva in post feeding
instar) and A (adults). X = specimen collection.
Order Family Species
E L E L A L P PF A L P PF A L P PF A
Diptera Calliphoridae C. albifrontalis X X X X
Calliphora sp. X X X X X X
Lucilia sp. X X
Muscidae X X
Coleoptera Dermestidae X X
Cleridae X
Histeridae X
Order Family Species
E L E L A L P PF A L P PF A L P PF A
Diptera Calliphoridae C. albifrontalis X X X X X X X X X
Calliphora sp. X X X X X X
Muscidae X X X X X X X X
Coleoptera Forficulidae X
Staphylinidae X X X X
Dermestidae X X X X X
Cleridae X X X
Silphidae X X X X
Carabidae X
Histeridae X X
Suburban
1 - 3.
Fresh
4 - 9.
Bloat
Days
10 - 24.
Decay
25 - 31.
Dry/Remains
32 - 39.
Skeletonisation
Agricultural Days
1 -2. 3 - 7. 8 - 10. 11 12 - 39.
Fresh Bloat Decay Dry/Remains Skeletonisation
43
Figure 1: Average ambient temperature at two study sites, agricultural and suburban, over
39-day in Tasmania, Australia. Temperatures are represented in degrees Celsius and
rainfall in millimetres according to each site.
05
10
15
20
25
30
35
40
45
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39
Tem
per
atu
re (°C
)
Days of Research
Average ambient temperature and rainfall during
research period in Tasmania
Temperature (Agricultural Site) Temperature (Suburban Site)
Rainfall (Agricultural Site) Rainfall (Suburban Site)R
ain
fall (
mm
)
44
Figure 2: Decomposition process at various stages at the two study sites, agricultural and
suburban
Agricultural site Suburban site
Day 2
Day 6
Day 27
Day 9
Day 6
Day 2
Day 9
Day 35
Day 11
Day 29
45
Figure 3: Comparative view of the two location sites, agricultural and suburban,
analysing the succession of order Diptera of each carcass during the 39-day summer study
in Tasmania, Australia. Data summarised by the presence of specific species. Carcasses are
identified by location (A = agricultural site; S = suburban site) and repetitions (3 carcasses
each site), e.g. A1 = swine carcass n°1 at agricultural site, S1 = swine carcass n°2 at
suburban site.
4. Discussion
This study considered the seasonal insect succession patterns on decomposing
swine carcasses at two contrasting location sites in Tasmania. In the short term, insect
assemblages differed over the 39-day decomposition process during the summer. As no
previous studies have yet been published within the Tasmania geographic region, no
comparative analyses were able to be conducted to determine whether this insect
assemblage differences observed are consistent with Tasmania.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 17 19 21 22 23 25 27 29 32 35
A1
A2
A3
S1
S2
S3
A1
A2
A3
S1
S2
S3
A1
A2
A3
S1
S2
S3
A1
A2
A3
S1
S2
S3
Calliphora sp.
Calliphora albifrontalis
Lucilia sp.
Diptera
Muscidae
Calliphoridae
Order Family Species Days
46
According to previous research within Australia relating to the insect succession
patterns on decomposing carcasses, insect succession patterns change based on seasonal
variations, however, temperature variations were not accounted for in some studies (M. S.
Archer & Elgar, 2003; Voss et al., 2009). It has also been identified that differences
between geographic region will affect insect succession patterns. In this study, ambient
temperature variations were only obtained from one location site which cannot be used at
the alternative site for comparative purposes, however, temperature data was able to be
obtained off the Bureau of Meteorology website and thus observed commonalities and
dissimilarities can be explained to an extent.
Within the two location sites, the duration of decomposition stages significantly
differed, however the pattern of insect succession had commonalities between them. Since
the ambient temperature at the agricultural site were typically lower in comparison to the
suburban site, the slower rate of decay at the agricultural site (Table 1) can be explained
by the temporal variation (Figure 1) thus slowing down the insect succession pattern rate.
After analysis of the comparative data observing Diptera insect assemblages (Figure 3), it
is visible that majority of the species from the Calliphoridae family tend to appear early on
in the decomposition process stages and remains around for the remainder of the study
duration. In comparison to species from the Muscidae family where they tend to appear at
a much later stage into the decomposition process and remains present for the remainder of
the study duration. This pattern of insect succession is also consistent amongst previous
studies within Australia, even where the study has have been carried out for a duration of 2
years (McIntosh et al., 2017; Voss et al., 2008; Voss et al., 2009). These studies also show
within the order Diptera, the Calliphoridae family appears in the early stages of
decomposition followed by the presence of the Muscidae family at a later stage, however,
these studies contain a much larger array of insect assemblages and species.
47
The validity of applying collected reference data from one habitat for analyses of
another habitat within the same geographic region is uncertain whether the insect
assemblage is different and yet to be studied. Insect succession research is usually
conducted at one single location thus representing only one habitat type (Abd El-bar &
Sawaby, 2011; Alves et al., 2014). Variation between habitats are known to alter
decomposition rates and thus influence insect succession patterns (Campobasso, Di Vella,
& Introna, 2001). As evident in this study, decomposition rates are varied according to
different habitat types as well as marginal variations of insect succession assemblage,
however, for the most part, the insect succession patterns were reasonably consistent
(Table 1, Figure 3). Marginal variations in insect succession patterns are usually related to
the species’ habitat preferences (Voss et al., 2009). At the suburban site, the presence of
Lucilia sp. was not detected in the agricultural site. This finds explanation in the fact that
Lucilia species have a preference for higher temperatures compared to Calliphora species
(K.G.V. Smith, 1986). The variations of beetles present from the order Coleopteran were
compared in this study as a part of the insect succession patterns because the beetles are
more of an opportunistic insect that comes and feeds off remains at no specific time frame
but rather just for the purpose of available food source.
This result suggests there is a reasonable scope to establish baseline insect
succession reference data ranging from a single study site to a numerous decomposition
sites as well as habitat types within a given geographic region. As such, ongoing research
in the area of insect succession patterns is still highly required in order to establish an
extensive baseline reference data for all seasons and habitat types within every geographic
region. For example, insect succession pattern have not yet been investigated in other
various parts of Australia, such as South Australia and Northern Territory.
48
5. Conclusion
This is the first insect succession pattern study to be undertaken in Tasmania
investigating the seasonal insect succession patterns on decomposing swine carcasses at
two contrasting location sites in Tasmania. As no previous studies have yet been published,
no comparative analyses were able to be conducted to determine whether this insect
assemblage observed are consistent.
Within the two location sites, agricultural and suburban, the duration of
decomposition stages significantly differed since the ambient temperature at the
agricultural site were typically lower in comparison to the suburban site. After observation
of the insects belonging to the order Diptera, insect assemblages showed majority of the
species from the Calliphoridae family tend to appear early on in the decomposition process
and remains around for the remainder of the study duration. In comparison to species from
the Muscidae family where they tend to appear at a much later stage into the
decomposition process and remains present for the remainder of the study duration. This
pattern of insect succession is also consistent amongst other previous studies within
Australia, however, these studies contain a much larger array of insect assemblage as they
were carried out for a duration of 2 years in different habitat types and geographical
regions.
At present, few studies of insect succession patterns contain more than one season
time frame, thus limiting their application within forensic cases, therefore ongoing research
is still highly required in order to establish an extensive baseline reference data for all
seasons and habitat types within every geographic region. For example, insect succession
pattern have not yet been investigated in other various parts of Australia, such as South
Australia and Northern Territory. Further studies is also required in Tasmania during
49
varying seasons, habitat types as well as various different circumstantial situations, such as
clothed/unclothed, buried/exposed, concealed/exposed carcasses.
Acknowledgements
The author would like to thank C. K. & S. Farguhar for their support in supplying the pigs
central to the study conducted, the active agricultural paddock and Department of Primary
Industries, Parks, Water and Environment Facility for allowing the use of their site as
decomposition sites for the study.
References
Abd El-bar, M. M., & Sawaby, R. F. (2011). A preliminary investigation of insect
colonization and succession on remains of rabbits treated with an organophosphate
insecticide in El-Qalyubiya Governorate of Egypt. Forensic Sci Int, 208(1-3), e26-
30. doi:10.1016/j.forsciint.2010.10.007
Alves, A. C., Santos, W. E., Farias, R. C., & Creao-Duarte, A. J. (2014). Blowflies
(Diptera, Calliphoridae) Associated with Pig Carcasses in a Caatinga Area,
Northeastern Brazil. Neotrop Entomol, 43(2), 122-126. doi:10.1007/s13744-013-
0195-4
Amendt, J., Campobasso, C. P., Gaudry, E., Reiter, C., LeBlanc, H. N., & Hall, M. J.
(2007). Best practice in forensic entomology - Standards and guidelines. Int J Legal
Med, 121(2), 90-104. doi:10.1007/s00414-006-0086-x
Amendt, J., Campobasso, C. P., Gaudry, E., Reiter, C., LeBlanc, H. N., & J. R. Hall, M.
(2007). Best practice in forensic entomology—standards and guidelines.
International Journal of Legal Medicine, 121(2), 90-104. doi:10.1007/s00414-006-
0086-x
Archer, M. S., & Elgar, M. A. (2003). Yearly activity patterns in southern Victoria
(Australia) of seasonally active carrion insects. Forensic Sci Int, 132(3), 173-176.
Byrd, J. H., & Castner, J. L. (2010). Forensic Entomology – The utility of arthropods in
legal investigation (2 ed.): CRC Press, Boca Raton, FL, USA.
Byrd, J. H., & Tomberlin, J. K. (2010). Laboratory rearing of forensic insects. In J. H.
Byrd & J. L. Castner (Eds.), Forensic entomology—the utility of arthropods in
legal investigation (pp. 177-200). Boca Raton, FL: CRC Press.
Campobasso, C. P., Di Vella, G., & Introna, F. (2001). Factors affecting decomposition
and Diptera colonization. Forensic Sci Int, 120(1-2), 18-27.
Dadour, I. R., Cook, D. F., Fissioli, J. N., & Bailey, W. J. (2001). Forensic entomology:
application, education and research in Western Australia. Forensic Sci Int, 120(1-
2), 48-52.
50
Forbes, S. L., Perrault, K. A., Stefanuto, P. H., Nizio, K. D., & Focant, J. F. (2014).
Comparison of the decomposition VOC profile during winter and summer in a
moist, mid-latitude (Cfb) climate. PLoS One, 9(11), e113681.
doi:10.1371/journal.pone.0113681
Gherlenda, A. N., Esveld, J. L., Hall, A. A., Duursma, R. A., & Riegler, M. (2016). Boom
and bust: rapid feedback responses between insect outbreak dynamics and canopy
leaf area impacted by rainfall and CO2. Glob Chang Biol, 22(11), 3632-3641.
doi:10.1111/gcb.13334
Gill, G. J. (2005). Decomposition and arthropod succession on above ground pig carrion
in rural Manitoba (TR-06-2005). Retrieved from Manitoba:
Goff, M. L. (1991). Comparison of insect species associated with decomposing remains
recovered inside dwellings and outdoors on the island of Oahu, Hawaii. J Forensic
Sci, 36(3), 748-753.
Goff, M. L. (1993). Estimation of Postmortem Interval Using Arthropod Development and
Successional Patterns. Forensic Sci Rev, 5(2), 81-94.
Hyde, E. R., Haarmann, D. P., Petrosino, J. F., Lynne, A. M., & Bucheli, S. R. (2015).
Initial insights into bacterial succession during human decomposition. Int J Legal
Med, 129(3), 661-671. doi:10.1007/s00414-014-1128-4
Johnson, A. P., Mikac, K. M., & Wallman, J. F. (2013). Thermogenesis in decomposing
carcasses. Forensic Sci Int, 231(1-3), 271-277. doi:10.1016/j.forsciint.2013.05.031
Lee Goff, M. (2009). Early post-mortem changes and stages of decomposition in exposed
cadavers. Exp Appl Acarol, 49(1-2), 21-36. doi:10.1007/s10493-009-9284-9
McIntosh, C. S., Dadour, I. R., & Voss, S. C. (2017). A comparison of carcass
decomposition and associated insect succession onto burnt and unburnt pig
carcasses. Int J Legal Med, 131(3), 835-845. doi:10.1007/s00414-016-1464-7
Megnin, J. P. (1894). La faune de cadavres. Application de l’entomologie a la medicine
legale. . G. Masson, Paris Encyclopedie Scientifique des Aide-Memoire.
Meteorology, B. o. (2017). Climate statistics for Australian locations. Retrieved from http://www.bom.gov.au/jsp/ncc/cdio/cvg/av?p_stn_num=091126&p_prim_element_index=
0&p_comp_element_index=0&redraw=null&p_display_type=statistics_summary&normal
s_years=1971-2000&tablesizebutt=normal O'Brien, R. C., Forbes, S. L., Meyer, J., & Dadour, I. R. (2007). A preliminary
investigation into the scavenging activity on pig carcasses in Western Australia.
Forensic Sci Med Pathol, 3(3), 194-199. doi:10.1007/s12024-007-0016-3
Roberts, L. G., Spencer, J. R., & Dabbs, G. R. (2017). The Effect of Body Mass on
Outdoor Adult Human Decomposition. J Forensic Sci. doi:10.1111/1556-
4029.13398
Schotsmans, E. M., Forbes, S. L., & Márquez-Grant, N. (2017). Taphonomy of Human
Remains. Somerset, UNKNOWN: John Wiley & Sons, Incorporated.
Smith, K. G. V. (1986). A Manual of Forensic Entomolgy. New York: British Museum,
Department of Entomolgy.
Smith, K. G. V. (1986). A Manual of Forensic Entomology. London: Trustees of the
British Museum, Natural History and Cornell University Press.
Voss, S. C., Cook, D. F., & Dadour, I. R. (2011). Decomposition and insect succession of
clothed and unclothed carcasses in Western Australia. Forensic Sci Int, 211(1-3),
67-75. doi:10.1016/j.forsciint.2011.04.018
Voss, S. C., Forbes, S. L., & Dadour, I. R. (2008). Decomposition and insect succession on
cadavers inside a vehicle environment. Forensic Sci Med Pathol, 4(1), 22-32.
doi:10.1007/s12024-007-0028-z
51
Voss, S. C., Spafford, H., & Dadour, I. R. (2009). Annual and seasonal patterns of insect
succession on decomposing remains at two locations in Western Australia.
Forensic Sci Int, 193(1-3), 26-36. doi:10.1016/j.forsciint.2009.08.014