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.

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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).

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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.

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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).

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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.

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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).

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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).

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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).

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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.

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