This thesis wants to develop an understanding of the effects of Gammalin-20 on forensically relevant insect species found on poisoned rabbit carrion, and their changes in abundance, rate of development, and succession order.
In a study conducted at the University of Ibadan, the entomotoxicological appraisal of carrion insects found on rabbits poisoned with Gammalin-20 was carried out. Two rabbits were used as surrogate human models, with one euthanized with Gammalin-20 and the other serving as a control. The flies and larvae found on the carcasses were collected and stored in alcohol. It was found that Calliphoridae were the most dominant carrion insects, while Sarcophagidae were less dominant. The control group had a greater diversity and species composition of carrion insects compared to the Gammalin-20 poisoned rabbits. Growth indicators like length and weight of the larvae were also comparatively higher in the control group. Temperature and humidity measurements were also conducted. The effects of the poison on the developmental and succession patterns of the insects were also examined.
TABLE OF CONTENTS
Dedication
Acknowledgement
List of figures
List of tables
Abstract
CHAPTER ONE INTRODUCTION
1.1 Forensic Entomology
1.2. Gamalin-20
1.3. Justification for the study
1.4. AIMS AND OBJECTIVES OF THE STUDY
CHAPTER TWO LITERATURE REVIEW
2.1. Forensic entomotoxicology
2.2. Subdivisions of forensic entomology
2.2.1. Medico-legal forensic entomology
2.2.2. Stored-product forensic entomology
2.2.3. Urban forensic entomology
2.3 Decomposition
2.4. SUCCESSION OF INSECTS
2.5. Factors Influencing Carrion Insects Development
2.5.1. Temperature and Humidity
2.5.2. Light
2.5.3. Drugs
2.5.4. Habitat
2.6. Arthropods Associated With Carcass
2.6.1. Sarcophagidac
2.6.2. Calliphoridae
2.6.3. Dermestidae
2.6.4. Silphidae
2.6.5. Cleridae
2.6.6. Staphylinidae
2.6.7. Muscidae
2.6.8. Taxonomy of carrion insects
2.6.9. Brief Review of Identification Keys
2.7. Forensic Entomotoxicology
2.7.1. Application of Forensic Entomotoxicology
2.7.2. Review of Previous Studies
2.7.3. Gammalin
CHAPTER THREE MATERIALS AND METHODS
3.1. STUDY SITE
3.2. Sample collection and processing
3.2.1. Sampling for insects
3.2.2. Sampling for maggots
3.2.3. Sampling for pupa
3.2.4. Measurement of environmental variables
3.3. Sample analyses
CHAPTER FOUR RESULTS AND DISCUSSIONS
4.1. Abundance and species composition of carrion insects on Rabbit carcass
4.3. Effect of Gamalin 20 on the length and weight of larva.
4.4. Variations in environmental variables at the study site.
CHAPTER FIVE DISCUSSION
5.1. Abundance and species composition of carrion insects on rabbit carcass
5.2. Carrion insect succession on rabbit carcass
5.3. Effect of Gamalin on the length and weight of larva
5.4. Variations in environmental variables at the study site
5.5. Conclusion and Recommendation
References
LIST OF FIGURES.
Fig.1 Mean Body Length of The Larvae ofChrysomya albicepsCollected From Pig Carcass
Fig.2.Mean Body Weight of The Larvae OfChrysomya albicepsCollected From Pig Carcass
Fig 3. Summary of mean relative humidity recorded in the field experiment
Fig.4. Summary of ambient and carcass temperature recorded at the field experiment
Fig.5. Fresh stage of decomposition
Fig.6. Bloat stage of decomposition
Fig.7. Active stage of decomposition
Fig.8. Advance stage of decomposition
Fig. 9. Dry stage of decomposition
LIST OF TABLES
Table 1. Abundance of forensically important insects collected from rabbit (RT1) treated with 20ml gamaline-20
Table 2. Abundance of forensically important insects collected from rabbit (RT2) treated without poison (control)
Table 3. Occurrence matrix of carrion insect stages in RT2 (control)
Table 4. Occurance matrix of carrion insect stages in RT1
ABSTRACT
Forensic entomotoxicological appraisal of carrion insects found on rabbits poisoned with Gammalin-20 was carried out at the back of the stadium on the campus of the University of Ibadan. Two rabbits,Oryctolagus cuniculusL., weighing between 4 and 4.5kg were used as surrogate human models. One (RT1) was euthanized with 20ml of Gammalin-20 while the other one sacrificed by cervical dislocation served as the control experiment. Adult flies were collected from the carrions using a sweep net and stored in 70% alcohol. The larvae were collected into a bowl by using a spatula, demobilized with hot water and later placed in sample bottles containing 70% alcohol. Pupae were also collected using forceps, demobilized with hot water and later transferred into sample bottles containing 70% alcohol. Ambient and carcass temperature was measured using infrared thermometer while relative humidity was recorded using a digital hygrometer. Calliphoridae and Muscidae were the initial pioneers of the decomposing carcass and were seen during the fresh stage, while Sarcophagidae arrived shortly after the fresh stage of decomposition. It was found that Calliphoridae was the most dominant carrion insect while Sarcophagidae was the least dominant among the pioneer and Dermestidae were the late pioneer. The control group had more abundance and species composition of carrion insects than the Gamalin-20 poisoned rabbits. The length and weight of the larvae as indices of growth were also observed to be comparatively higher in the control than the 20ml poisoned rabbit with gamalin-20. The highest mean temperature value for the decomposing 20ml treated rabbits was 32.55°C while its lowest mean value was 23.2°C. The highest carcass temperature was recorded on the sixth day during active decomposition in the control and 20ml Gamaline-20 treated rabbits. The highest mean relative humidity value was 98.5 % while the least recorded was 67% due to the rainy season. The succession pattern of the flies, their abundance, rate of development, effects of the poison on the developmental pattern were all determined.. It was observed from this study that Gammalin-20 delayed insect colonization and slowed down the rate of larvae development. This decomposition role has however, proven that insects found on the decomposing carrion if properly studied with environmental variables can be used to estimate the time that elapsed since death or post mortem interval that can be extrapolated to human cases of homicide.
CHAPTER ONE INTRODUCTION
1.1 Forensic Entomology
Forensic entomology is a branch of forensic science which deal with the study of insects associated with the corpse of humans or wildlife for the estimation of time of death or postmortem interval (PMI) (Catts and Goff, 1992). Postmortem interval (PMI) is the space of time between the time death occurs and the time the corpse is discovered (Catts and Haskell, 1990). It is the scientific study of the invasion of the pattern of succession of arthropods with the developmental stages of different species found on decomposing cardavars during legal investigations (Verma and Paul 2016). It is the study ofThis study is employed in criminal investigation studying the insect and arthropods usually dipterans associated with decomposing corpse and carrion of vertebrates (Amendt,et al, 2014). It deals with the application and studies of insects and other arthropods in crime investigation. It helps to provide useful and vital information in homicide cases, cause and manner of death, as it helps in the identification of both the criminals and the victim at the scene of death (Sukontasonet al, 2007). This aspect of science in now widely recorgnized and practice in the courts in developed countries of the world because of the vital information it provides in the identifying criminals and victims while excluding suspects (Catts, 1990 ).
As forensic entomology evolved over the last hundred years, a new field, forensic entomotoxicology has emerged. This investigates for the presence or absence of toxins or drugs in various arthropods (Intronaet al.,2001). Development of forensic entomotoxicology has been a great advancement in the detection and identification of drugs or toxins in bodies which have been significantly composed or burned where fluids and tissue may be at a premium (Gosselinetal.,2011).
From 1980, entomologists started to detect drugs in insects, hoping it would be useful in carrying out forensic investigations (Beyeret al, 1980, Intronaet al, 2001). Entomotoxicology has a major interest in determining drug abuse just before death, especially in skeletonized remains where there are no tissue or fluids left. Toxicological analyses can also in highly decomposed remains, be facilitated using insects as less interferences in the analytical run due to matrix decomposition (Nolteet al, 1992, Kintzet al, 1990).
Deaths that occur as a result of organochlorine pesticides poisoning are usually detected by analysis of body fluids and tissues for the presence of the toxic agent. Particular difficulties were encountered when these procedures were performed on remains in an advanced stage of decomposition. In 1989, Gunatilake and Goff were able to detect poisoning by organophosphate in a putrefying body by analyzing arthropod larvae.
The knowledge of local insect assemblages and their growth rate including population dynamics is important in the area of forensic entomotoxicology. This has helped to determine how much time has passed since the death of an individual and also the cause of the death. Successional patterns of the invasion of carrion insects may provide information on the indication of time that has elapsed since death over longer time intervals (Amendt,et al, 2007). Forensic entomotoxicological evaluation is important because a large number of arthropods are carrion insects.
In forensic investigations, the detection of drugs or other harmful toxic chemicals is vital. If the investigation involves a badly decomposed, skeletonized, or missing corpse, however, obtaining this information can be challenging, and may necessitate the use of a specialised discipline of forensic toxicology known as entomotoxicology.
1.2. Gamalin-20
Gamalin 20 is an organochlorine pesticide widely used in veterinary and human medicine for treating ectoparsites and pediculosis (Teklit and Tesfakires, S.,2016). It also has application as a broad spectrum in the eradication of phytophagous and soil inhibiting insects, ectoparasites of animals, public health pest, used on crops to control their pest and stored product pests and seed treatment. It is used for killing of the fish as a fishing technology in the fishing industry. Lindane is the active ingredient contain in Gamalin 20. Lindane has application in the treatment of seeds. It is used also in creams and shampoos for the control of lice and mites in humans. Gamalin-20 is also commonly used as a suicidal agent as it is affordable and readily available. Gamalin-20 has been banned in many countries of the world due to concern on neurotoxicity and iti adverse effects on the environment but has been approved by the Food and Drug Administration (FDA) as a second-line therapy treatment ofPediculosis capitis(head lice),Pediculosis pubis(pubic lice), or scabies in patients more than two years of age.
1.3. Justification for the study
Despite various studies of forensic entomotoxicology which have been carried out, no study has been done on the evaluation of cause of death by analyzing the carrion insects found on lindane-poisoned rabbits in South West Nigeria. This becomes necessary with the recent upsurge in the use of lindane in agriculture and in our water bodies with different pesticides, including lindane. Justifying the need for this study include:
i. No such study has been done using lindane in Nigeria and in Southwestern part before using rabbit.
ii. Lindane is a commonly used suicide and homicide agent in Nigeria.
iii. Carrion insect is poorly doccumented in Nigeria, hence the need for more study
1.4. AIMS AND OBJECTIVES OF THE STUDY
i. To assess the effect of Lindane pesticide on the developmental stages of insect larvae found on the rabbit carrion.
ii. To assess the abundance and species diversity of carrion insects found on the rabbit carrion.
iii. To study the succession pattern of the carrion insects found on the decomposing animal.
iv. To assess ambient humidity and carcass temperature at the carrion site.
CHAPTER TWO LITERATURE REVIEW
2.1. Forensic entomotoxicology
Forensic entomology is the study of forensic insects that colonize and feed on the flesh of dead bodies of humans and animals for purposes of law and helping legal entities to solve criminal cases. It is the use of insects as evidence in courts of law. Profering solution to forensic cases complicated with the issues of identity of the victims and time elapsed since crime occured has become a lengthy and difficult task for crime scene scientists. Forensic entomotoxicology is also the study of the application of insects and other arthropods in crime investigation (Catts and Goff, 1992).
It is also the study of insects associated with corpse in an effort to determine the time elaspsed since death (Bhatet al,2011). Forensic entomotoxicology is also the study of how insects feed on decomposing human remains to generate vital information that can aid in medico-legal investigation (Cruz and Albert, 2006). Commonly answered questions using forensic entomotoxicology include, time since death, location of death, origin of victim, environmental condition to which a body has been exposed, location of traumatic wound sites, and identification of toxicological deaths.
Forensic entomoology as a scientific discipline interprets the information relating to cause death using insect specimens as a vital witness in legal cases in order to provide information not available by using the usual methods of classic pathology (Singhet al, 2008).
2.2. Subdivisions of forensic entomology
There are three subdivisions of forensic entomology:
2.2.1. Medico-legal forensic entomology
In medico-legal context, forensic entomology focuses on evidences gathered through the studies of arthropods at scenes of suicide, murder, physical abuse, contraband trafficking and rape. In the investigation of murder cases, it deals with the type of insects eggs found, the location on the decomposing body and the order in which they appear (Albert, ,2006). This is very vital in providing important information for determining postmortem interval (PMI) and the location of death under investigation. The arthropod feature that is most important in medico legal forensic entomology is the importance as carrion feeders, feeding on corpse of both humans and other animals. Thus, they give valuable answers to important questions in any criminal investigation, such as whether death occurred at the recovery scene or the body was moved to another point following death (Albert, 2006). This is possible because many insects exhibit endemism, or possess a well defined phenology (active only at a certain season, or time of day), their presence in combination with other evidence can establish potential links to times and locations where other events may have occurred.
2.2.2. Stored-product forensic entomology
Stored-product forensic entomology is the study of insects that infest stored foodstuffs in the home. It is mostly used in litigation over insect infestation or contamination of commercially distributed foods. It involves the detection, prevention and eradication of the pests. Stored produce insect-pest are commonly found in food (stored) and the forensic entomologist uses this study as an expert witness during both criminal and civil proceedings involving food contamination (Hall and Brandt, 2012).
2.2.3. Urban forensic entomology
Urban forensic entomology majorly concerns pests infestations in buildings gardens or that may be the basis of litigation between private parties and service providers such as landlords or exterminators.
The urban aspect also deals with the insects that affect man and his environment. This area has both civil and criminal components as urban pests may feed on the living and the dead. The damage caused by their feeding activity can produce marks and wounds on tissues that may be misinterpreted as resulting from human abuse. Urban pests are of great economic importance, and the forensic entomologist may become involved in civil proceedings resulting in monetary damages (Smith, 1986).
These studies may also indicate the appropriateness of certain pesticide treatments and may also be used in stored products cases where it can help to determine chain of custody, when all points of possible infestation are examined in order to establish the party at fault (Bledsoe, 2008)
2.3 Decomposition
Decomposition, macroscopically and microscopically is the process of degradation of a corpse into its basic respective constituents through the activities of microorganisms, arthropods and scavengers. Decomposition is a natural process that occurs for every organism that has died. Initially, the degradation processes may not be visible to the naked eye as the process starts at the cellular level, and gradually the changes will progress to macroscopic level and form the post mortem changes. Decomposition of an exposed cadaver is a continuous process, beginning at the moment of death and ending when the body is reduced to a dried skeleton (Goff, 2009).
Signs of death
Strong indications that a warm-blooded organism is no longer alive include:
(i). Respiratory arrest (no breathing)
(ii). Cardiac arrest (no pulse)
(iii). Brain death (no neuronal activity)
(iv). Pallor mortis, paleness which happens in the 15-120 minutes after death
(v). Livor mortis, a settling of the blood in the lower (dependent) portion of the body
(vi). Algor mortis, the reduction in body temperature following death. This is generally a steady decline until matching ambient temperature
(vii). Rigor mortis, the limbs of the corpse become stiff and difficult to move or manipulate
(ix) Decomposition, the reduction into simpler forms of matter, accompanied by a strong, unpleasant odour.
During the decomposition process, different groups of sarcophagous arthropods, especially insects are attracted to the decomposing body. Some are attracted to the remains which they utilize as a medium for oviposition or feeding, while others are attracted by the aggregation of other arthropods that they prey on (used as a food source) (Payne 1965). This process continues even beyond the dry remains stage as the bones still undergoes decomposition although at a much slower rate. In the end, the whole decomposition process allows the recycling of energy flow and nutrient into the surrounding ecosystem which is a very vital process of the ecosystem (Hamzahet al2014).
Various processes will eventually lead to complete decomposition of animal remains, including the activities of bacteria, disarticulation by carnivores, weathering, and insect colonization. Decomposing carrion supports a wide diversity of several organisms, many of which are insects. Decomposing carcass can also support a large, dynamic insect community. Apart from the ecological interest, carrion decomposition and succession studies have proven important in forensic entomology (Kyerematen, 2012). It is known that insects are usually the first organisms to arrive on a body after death, and they colonize in a predictable sequence. The body progresses through a recognized sequence of decomposition stages, from fresh to skeletal, over time (Peters, 2003). Each of these stages of decomposition is attractive to a different group of sarcophagous arthropods, primarily insects (Anderson and van Laerhoven, 1996).
After death, the human body and its constituent undergoes decomposition process: 64% water, 20% proteins, 10% lipids, 1% carbohydrates and 5% minerals are broken down into simpler compounds, until they reach their building block ingredients, i.e. Carbon (C), Hydogen (H), Oxygen (O), Nitrogen (N), Phosphorus (P) and Sulphur (S). These events are studied during what we call the chemical decomposition of corpses (post mortem decomposition). The post mortem decomposition follows two main phases, the first one is autolysis which consists of the enzymatic self-digestion of the cells and paves the way for the second phase, i.e. putrefaction (Zhou and Byard, 2011, Goff, 2009).
Autolysis is a cellular self-destruction process caused by hydrolytic enzymes that were originally contained within cells (Enwere 2008, Shirleyet al., 2011). Autolysis normally begins at cells, which are metabolically active or contain large amount of water, lysosomies and hydrolytic eurymes Organs that are involved in high adenosine triphosphate (ATP) production and membrane transportation such as liver and brain are also muore susceptible to autolysis reaction as compared to other organs (Gennard 2007, Swannet al.,2010). At this level, the degradation can only be observed at histological level. Putrefaction on the other hand is degradation of tissue by microorganism activity, such as bacteria, fungi and protozoa, which originate from normal biota in human body especially in gastrointestinal tract
Post mortem changes occur in early and late phase. Early post mortem changes include algor mortis, rigor mortis and livor mortis while the late post mortem changes involve breakdown of soft tissue leading to noticeable macroscopic changes (Swift, 2006, Lee, 2009). For corpses that remain in fresh stage, PMI is mostly estimated through examination of algor mortis, livor mortis and rigor mortis.
Once the corpse enters putrefaction stage, post mortem changes and stage of decomposition provide merely a rough range of PMI due to influence of too many variables (Shattuck, 2009, Myburgh, 2010). Stages of decomposition are mostly determined by post mortem changes observation or faunal succession pattern analysis (Hauet al.,2014). There are various stages in describing the extent of decomposition, minor variations often present depending on the point of view of researchers and geographical differences.
As death proceeds, there are a series of early changes to the body that result in a definite change in the physical nature and/or appearance of the body prior to the onset of gross, recognizable decompositional changes. These changes have traditionally been used in estimations of the PMI and may be a source of confusion if not recognized.
One of the early changes observable is livor mortis, also referred to as lividity, post-mortem hypostasis, vibices and suggilations. These observable early changes are physical process. While the individual is alive, the heart is actively functioning and circulating blood through the body system. Once death set in, blood circulation stops and the blood begin to settle, by gravity, to the lowest portions of the body. This results in a discoloration of those lower, dependent parts of the body. Although beginning immediately. the first signs of livor mortis are typically observed after a period of approximately 1 h following death with full development being observed 2-4 hours following death (Nashelksy and McFelley, 2003). At this time, the blood is still in liquid form and pressing on the skin will result in the blood being squeezed out of the area (blanching), only to return once pressure is removed. This situation continues until 9-12 hours following death, at which time the pattern will not change and the livor mortis is said to be fixed. Rigor mortis is a chemical change resulting in a stiffening of the body muscles following death due to changes in the myofibrils of the muscle tissues. Following death, the body immediately becomes limp and is easily flexed. As aldenocine triphosphat (ATP) is converted to aldenocine diphosphate (ADP) and lactic acid is produced lowering the cellular pH, locking chemical bridges are formed between actin and myosin resulting in formation of rigor typically, the onset of rigor is first observed 2-6 h following death and develops over the first 12hours. The onset begins with the muscles of the face and then spreads to all of the muscles of the body over a period of the next 4-6 h (Gill-King, 1996), Rigor typically lasts from 24 to 84 h, after which the muscles begin to once again relax. The onset and duration of rigor mortis is governed by two primary factors temperature and the metabolic state of the body. Lower ambient temperatures tend to accelerate the onset of rigor and prolong its duration, whereas the opposite is found in warmer temperatures. If the individual has been involved in vigorous activity immediately prior to death, the onset of rigor is more rapid, Body mass and rates of cooling following death also influence the onset and duration of rigor mortis. As rigor disappears from the body, the pattern is similar to that seen during the onset, with the muscles of the face relaxing first.
Once death has occurred, the body ceases to regulate its internal temperature and the internal temperature begins to approximate the ambient temperature. In most instances this involves a cooling of the body until ambient temperature is reached, most often in a period of 18-20 h (Fisher, 2007). This stage is known as "Algor mortis".
There are normally five stages of decomposition, which are fresh, bloated, active decay, advanced decay and skeletal stage but sometimes bloated stage and active decay are incorporated into one as early decay stage. Observations used to describe the decomposition. process are generally applicable everywhere because all corpses decompose with similar pattern of decomposition.
The Fresh Stage begins at the moment of death and continues until bloating of the body becomes evident.. Autolysis cellular destruction occurs in this stage and leads to early post mortem changes (Hamzahet al.,2014). There are few distinctive, gross decompositional changes associated with the body during this stage although greenish discoloration of the abdomen, liver, skin cracking may be observed. The insect invasion of the body generally begins with the natural body openings of the head, anus and genitals, and wounds present on the body (Goff, 2009).
Bloating is the distension or swelling of body parts due to accumulation of decompositional products (mainly gas) produced by microorganism in anaerobic putrefaction at any anatomically possible spaces in body, organs and soft tissues. Bloating normally starts at abdomen then slowly expands to other body parts, which include genital and face with eye and tongue protrusion (Hamzahet al.,2014).
The principal component of decomposition, putrefaction, begins during the Bloated Stage.
The anaerobic bacteria present in the gut and other parts of the body begin to digest the tissues. Their metabolic processes result in the production of gasses that first cause a slight inflation of the abdomen. When this is noted, the Bloated Stage is considered to begin. As this progress, the body may assume a fully inflated, balloon-like appearance (Goff; 2009). The start and termination points for the stages of decomposition are largely subjective, but there is a definite physical event marking the start of the decay stage. This is when the combined activities of the maggot feeding and bacterial putrefaction result in the breaking of the outer layer of the skin and the escape of the gasses from the abdomen. At this point, the body deflates and the Decay Stage is considered to begin. During this stage, strong odour of decomposition are present. The predominant feature of this stage is the presence of large feeding masses of Diptera larvae.
Dry remains of skeletal stage is reached when there is a very high degree of bone exposure but extreme breakdown of the bone material has not started. Only a small quantity of dried skin, tendon, and cartilage will be visible at this stage. On the surface of the bone, there may be some moisture or grease from the surroundings, and the stench of decomposition usually fades away.
2.4. SUCCESSION OF INSECTS
In forensics, succession refers to the orderly and predictable arrival of faunal specimens at a cadaver. The type and composition of fauna found on a corpse indicate the stage of decomposition (Megnin, 1894, Reed, 1958; Payne 1965), as well as the environmental conditions and length of exposure. As a result, understanding successional patterns can aid in the estimation of the postmortem interval (PMI). Temperature, relative humidity, rainfall, exposure to sunshine, and whether or not the body is covered or inside a structure are all elements that influences succession patterns. Succession studies can provide information on species variety, the number of individuals in each species, the life phases present, and the number of individuals in each life stage.
At the family level, the chronology of arthropod colonization on cadavers is rather consistent between locations (Early and Goff, 1986). As a result, successional patterns at the genus and species levels are only predicted within the boundaries of the cadaver's discovery location (Bass, 1983 and Anderson, 2001). To estimate the PMI based on successional pattems, the composition of taxa discovered on a corpse at the moment of discovery (corpse fauna) is compared to the makeup of the arthropod assemblage at a specific time determined from an animal model (baseline fauna) (Schoenly er al 1996). Decomposition rates and successional patterns are influenced by the size and kind of carcass (Watson and Carlton, 2003).
Carrion insect colonization has been shown to follow a predictable pattern (Tabor and Brewster, 2004). As forensically significant insects are either drawn to specific decomposition products or are predators on these necrophagous insects, the specific period of colonization of certain insects on carrion can be determined (Smith, 1986). For a given geographical region and a set of variables, the sequence of insect succession on carrion is known. Intervals based on succession patterns, on the other hand, necessitate knowledge about the insect fauna in the geographic region where the corpse is discovered, as species vary greatly (Anderson and VanLaerhoven, 1996). The invertebrate assemblage on carrion is also influenced by the ambient temperature, season, and microclimate of the postmortem environment (Catts and Haskell; 1990).
As carrion decay advances, the insects establish a series of invading species that are eventually exterminated. Smith (1986) identified four types of insects that can be found on rotting carrion:
i) Necrophagous species that feed on dead animals (carrion).
ii) Predators and parasites that prey on necrophagous species: this group also includes schizophagous species that feeds on the body initially and then turn predaceous afterwards.
iii) Omnivorous that feed on carrion as well as other arthropods such as ants, wasps, and some beetles;
iv) Springtails and spiders, for example among other species, use the body as an extension of their surroundings. For the purposes of forensic entomological studies, the first two groupings are gound to be forensically important. They are mostly Diptera (flies) and Coleoptera (beetles) order. The succession pattern in which the arthropods colonise the carrion is determined by the carrion's state of decomposition (Amendt and Krettek R, 2004). True flies, also known as Diptera, are the most commonly used insects in forensic examinations. Calliphoridae (blow flies), Sarcophagidae (flesh flies), and Muscidae (house flies) are the most common species in this order. Sarcophagidae (flesh flies) and Calliphoridae (blow flies) usually arrive minutes after death. Muscidae (house flies) delays until the body reaches the bloat stage of decomposition before colonising (Joseph, Vargheese et al,2011).
2.5. Factors Influencing Carrion Insects Development
Several factors affect the composition and development of carrion insects. These factors include, insect succession, pace of decomposition, biogeoclimatic zone, temperature, humidity, type of organism, carcass developmental stage, and carcass physical state are all elements that influence the makeup of carrion communities (Mannet al. 1990), (Anderson 2010; Hanski 1987).
The factors impacting insect activity associated with decomposing human remains have been established. The actual insect colonization, development, and associated succession were coupled with factors impacting the insect(s) directly as well as environmental conditions such as temperature, light, access to the remains, and precipitation also influence the behaviour of forensically-important insects (Byrd and Casmer; 2010). Other determinants, such as microbial colonization and physiology associated with the remains or with the insects, are now recognized as important influences on the behaviour of forensically-relevant arthropods. Understanding insect population dynamics can be very challenging due to the large number of biotic and abiotic factors that must be taken into account. Of these factors, weather is generally considered to be one of the most important. For example, temperature, rainfall, relative humidity and other weather-related factors can strongly affect the survival, development, fecundity and behaviour of individual insects. Each developmental stage takes a known amount of time, depending on the temperature and availability of food. Temperature is especially essential since insects are 'cold-blooded,' which means that when the temperature rises, their metabolic rate increases and their development time lowers, andvice versa(Sayle, 1928).
2.5.1. Temperature and Humidity
The life cycle of insects is heavily influenced by temperature and understanding of the developmental responses of insects to temperature is vital (Régnière, 2012, Powel, 2). It has an impact on the rate of development or the number of generations produced (Juetal., 2011). Temperature has a significant impact on the lives of all organisms. The number of generations that pass in a year is directly proportional to the ambient temperature. Every insect has a specific temperature or temperature range within which normal living activities continues effectively without interruption. This is referred to as the optimum or ideal temperature. At this temperature, every organism performs optimally. Temperature affects the rate of chemical reactions within cells and tissues. Temperature affects metabolic processes, which increases until it reaches the optimum level before it either stabilizes or decreasing at the highest temperature. Insect undergoes series of changes as a result of unstable temperature and it enters diapause (resting stage) at extreme temperature. Hibernation is the term for a resting stage of organisms caused by a drop in temperature. Organisms enter into aestivation when the resting stage is caused by a high temperature (Sayle, 1928), At this point, the temperature is not favorable. This is a survival mechanism for most living things. Every insect species has its own ideal temperature and moisture range for maximum development as well as a preferred feeding habit. The optimum temperatures for most insect species ranges between 25 and 32°C. At temperatures below 14°C and above 42°C, the rate of development is reduced and most storage pests will die at temperatures below 5°C and above 45°C.
The optimum relative humidity for most species is around 70%, with the minimum ranging from 25-40% and the maximum 80-100%. Only a few species can thrive in extremely dry environments (Howe 1965). Blow flies are known to be moisture-sensitive. Blow fly larvae have been observed to flee a carcass when moisture levels are too high, halting larval growth (Payne, 1965). Larval silphids and staphylinids have the opposite reaction to moisture levels than blow fly larvae and can endure greater moisture levels. Many of these insects, on the other hand, will not be able to complete their development if the carcass is completely dried (Payne, 1965; Payne and King, 1970). Temperatures in carrion can be considerably increased by a combination of microbial metabolism and aggregations of fly larvae. The microbial activity and maggot masses within the carcass create conditions that are considerably different from the surrounding environment. Payne (1965) discovered that the temperature difference between the corpse and the air was roughly 16°C, whereas Turner and Howard (1992) found carcass temperatures to be 19-27°C above ambient temperature. Since the inside temperature of a carcass can be significantly greater than ambient temperature, carrion temperature has a significant impact on carrion insect development (Intronaet al., 1989; Cianci and Sheldon, 1990, Goff, 1990; Greenberg, 1991; Catts, 1992).
2.5.2. Light
One of the most essential ecological elements controlling many areas of insect life is radiant energy (light). Light has a significant impact on several important aspects of insect biology, including feeding, growth, development, diapause, survival, and ethology.
2.5.3. Drugs
Some medication effects on these flies are dependent on the drug concentration, whereas others are merely dependent on its presence. Drugs can have a range of effects on the developmental rate of flies. In cases where forensic entomology is employed, substances such as Cocaine, Heroin, Morphine, Methamphetamine, Methylene Dioxymethamphetamine, Triazolam, Oxazepam, Chloripriamine, Barbiturates, Malathion, Nonmptyline and Amitryptiline, and Paracetamol are regularly encountered.
Various studies have demonstrated that the administration of various medications and toxins prior to death has an effect on maggot development rate, resulting in an erroneous PMI estimate based on insect development. Drugs ingested by the deceased person can accumulate in the larvae of flies that feed on carrion. Toxicological compounds are difficult to evaluate in bodies that are in advanced stages of decomposition or have been skeletonized. The larvae feeding on this body can be macerated and analysed using thin-layer chromatography, gas chromatography, and/or mass spectrometry in these cases. Toxins can affect the larvae's developmental phases. The presence of cocaine and heroin in the carcass can hasten larval growth. Insect colonisation can be slowed by poisons in the carrion, such as malthione (Chen et al 2004).
2.5.4. Habitat
Carrion species composition can be influenced by different habitat and, as a result, insect succession can be influenced by different settings. Tessmer and Meck (1996) discovered several differences in the species composition of calliphords on carrion placed in woodland versus pastureland habitats. When monitoring mouse carrion in sunny and shaded settings, Isicheet al(Isicheet al, 1992) discovered a variation in calliphorid species abundance and diversity. Only two species were detected in the shady area, while four species were found in the sunlit area.C. vicinawas found in both habitats in carrion, but the abundance of this specie was more in the shady area. Differences in insect succession were also noted in different parts of a rainforest ecosystem, with unique shifts in species composition (Early and Goff, 1986; Tullis and Goff, 1987).
Carrion insects feed on the remains of decomposing carcasses, hence, food availability plays a major role in maggot development.
The presence of insect larvae on the carcass can be used to estimate PMI for up to one month (Amendtet al;2004). The first step is to correctly identify the species.
The maturation and growth rate of different species differs. The age of the larvae must be determined in order to estimate the PMI. This can be done by measuring the length or dry weight of the oldest larvae and comparing it to reference data. The pace of development of the larvae is influenced by the temperature of the environment (ambient temperature). Each stages of growth has its own set of temperature requirements, therefore each species has its own set of accumulated degree days or cumulative degree hours to reach completion. After obtaining the larvae's thermal history, it can be compared to temperatures at the death scene to determine PMI. The first-generation adult flies can also be used to estimate the age. The shriveled wings and thin abdomen help to identify them (Tullis and Goff, 1987). An insect colonization succession model can be used to estimate the PMI when the insects colonizing the carrion in a certain location are known (Schoenly and Reid, 1987).
All of the elements that determine insect colonization and succession on carrion are significant and distinct to different locales, and they might even vary from case to case. When establishing the time of death of a corpse, data from one region and assumptions based on previous occurrences should be used with caution. To develop precise insect species lists and arrival timeframes for use in forensic investigations, studies in various geographical locations and under various conditions are required. Furthermore, research into the effects of seasonality, temperature, and habitat on carrion insect colonization in various places is critical, which is why this study is necessary.
2.6. Arthropods Associated With Carcass
Although many insects are found on or around the body, not all of them are relevant in establishing the post mortem interval (PMI). Some of the insects captured are just opportunistic and have no bearing on PMI assessment. According to Goff (1993), there are four main arthropod-corpse relationships that are widely accepted:
Many insects occur on or near the corpse, but not all of them are useful in determining the PMI. Some insects that are collected are simply opportunistic and do not play a role in PMI estimation. Goff (1993) outlines four basic arthropod-corpse 11 relationships that have generally been accepted:
1.Necrophagous species: Necrophagous species are insects or arthropods that colonize and feed directly on remains of decomposing body which they did not kill (Goff, M.L. 1993). A variety of necrophagous insect species are found on or around a corpse and depending on their preference for a given stage of decomposition, a certain chronological pattern of colonization is supposed to take place (Byrd & Castner 2010). Species from the orders Diptera (such as, Calliphoridae, Sarcophagidae, Muscidae, Stratiomyidae) and Coleoptera (such as, Dermestidae, Silphidae, Cleridae) have been linked with criminal investigations that extrapolate their use in estimating the post-mortem interval (or period of insect activity, as suggested by Tomberlinet al. 2011). Arthropods species present at remains vary by geographical locations. Some common species of Caliphoridae (blowflie) includes,Phormia regina, Protophormia terraenovae Caliphora vicina and Lucilia sericata(Smith, 1986).
Collecting and studying the forensically important insects found feeding on or around a body remain, a forensic entomologist is able to estimate the postmortem interval (the time elaspsed since death occurred). Dipterans (true flies) are mostly used in forensic investigations. Calliphoridae (blowflies), Musidae (house flies) and Sarcophagidae (flesh flies) are the predominant species in this Order. Calliphoridae and Sarcophagidae usually arrive within minutes following death. Musidae on the other hand delay colonization until the body reaches the bloat stages of decomposition (Josepet al., 2011).
Moment after death, cells start dying and self-digestion of the cells by enzymatic action start digesting the internal cells through the process of autolysis (Journal of forensicdental science,2011). The changes that occur immediately after death continue to occur over a prolonged period of time at different rates for different organs. Bacteria present in the gastrointestinal tract begin destroying the soft tissues producing fluids and gases. Insects are attracted to the volatile molecules called apeneumones escaping from the decomposing body. Forensic researchers are able to identify these volatile chemicals released at different stages of decomposition of the body. (Journalof forensic dental sciences,2011). The molecules released during each stage can modify the insect behavior. Craiget al., (1950) reported that putrative sulfur-based compounds were responsible for initially attracting the flies to the decomposing carcass but egg laying or oviposition of the flies are induced by ammonium-rich compounds present on the carrion (Craiget al, 1950).
These are the taxa that feed directly on the corpse. Dipteran species, particularly those in the Calliphoridae and Sarcophagidae families, and coleopterans in the Silphidae and Dermestidae families, are among these taxa. During the first two weeks of decomposition, necrophagous species are the most important group for PMI estimation (Goff, 1993).
2. Predators and parasites of necrophagous species: Several beetle families (Silphidae, Staphylinidae, and Histeridae) and fly families are predators and parasites of necrophagous species (Calliphondae and Stratiomyidae).
3. Omnivorous species: Taxa that feeds on both the corpse and the arthropods connected with the corpse. Wasps, ants, and some beetles are all members of this family.
4. Adventive species include opportunistic species such as Collembola, Acari, centipedes, and spiders that use the corpse as an extension of their normal environment (Goff, 1993).
2.6.1. Sarcophagidac
Sarcophagids are commonly known as flesh flies. Many are scavengers that eat rotting animal tissue, while others are parasites of other invertebrates and a few parasitize vertebrates, making them principal myiasis producers (Borror et al. 1989; Aspoas, 1994). Depending on the time of year and geographic location, carrion can attract a variety of sarcophagid species. Sarcophagids are the primary colonists of carrion in temperate and tropical environments. In comparison to the calliphorids, members of this family are regarded a secondary invader of carrion in cooler climates (Payne 1965; Early and Goff 1986; Tantawiet al. 1996).
2.6.2. Calliphoridae
Blow flies, green and bluebottle flies, and screwworm flies are all members of the Calliphoridae family of flies. Many members of the Calliphorinae subfamily are necrophagous. When there is no any carrion available, these insects feeds on dungs and other decomposing waste (Hall, 1948; Gillott, 1995). This family's life cycle includes an egg, three larval instars, a prepupa, a pupa, and an adult stage. The first two larval instars, as well as the early third instar, actively feed on carrion, while the later third instar stage wanders. Competition, carrion size, temperature, and humidity are the key elements that determine blow fly establishment and larval development on carrion (Denno and Cothran, 1976; Intronaet al. 1991). Calliphords frequently take advantage of food resources first, allowing them to outcompete other fly species. Female calliphorids' high fecundity and quick larval growth promote fierce competition for food and space, especially on little carrion (Payne, 1965; Denno & Cothran, 1976; Levotet al, 1979; Hutton and Wasti, 1980).
2.6.3. Dermestidae
During the dry remnants stage of decomposition, dermestids are usually prevalent (Payne and King 1970; Smith 1986). Tantawi et al. (1996), on the other hand, discovered these beetles feeding on carrion after the maggots had stopped feeding during the advanced decomposition stage. Dermestids were abundant in the summer, scarce in the fall and winter, and non-existent in the spring, according to the researchers.
2.6.4. Silphidae
Silpids are ubiquitous on carrion throughout the decomposition process, and they usually stay until the carcass is totally dried (Payne, 1965). Maggots are a frequent food source for larvae and adults, although little is known about silphid feeding behaviour. Some biologists have never seen silphids eat carrion and have concluded that they are voracious predators (Smith, 1986). Silphids have been found eating both camion and larvae, implying that they are only partially predatory (Payne and King, 1970).
2.6.5. Cleridae
In both adult and larval stages, most clerids are predatory. Many can be found feeding on insect larvae on tree trunks, logs, flowers, and leaves (Borroret al.1989). Members of the Necrobia spp. family are scavengers, which differs from the family's general feeding habits. Adult Necrobia spp. have been seen on carrion during the decay stage, but they usually appear on the carcass with the dermestids and nitidulids in the drier stages (Payne & King 1970; Tantawiet al, 1996). Their feeding role on carrion, like that of the other carrion beetles, is largely unknown. Tantawietal. 1996) found no signs of predatory behaviour in clerids found on rabbit carcasses. Payne and King (1970) observed Necrobia spp. feeding solely on carrion, implying that these beetles are true carrion feeders.
2.6.6. Staphylinidae
Staphylinids are the most prevalent carrion predators and prey on a variety of insects, but they appear to feed a lot on maggots (Smith, 1986; Tantawiet al,1996). Payne and King (1970) detected over fifty species on pig carrion, the earliest of which arrived in the early stages of bloat and stayed until all insect activity stopped. Many species of larval Alcocharinae are ectoparasites of calliphorid pupae, and both larval and adult staphylinids are predators (Payne and King, 1970). They also said that these beetles were active at all hours of the day and night, feeding on a variety of insects, but that fly larvae seemed to be their favourite.
2.6.7. Muscidae
Muscids are common flies found in a wide range of habitats, and some are closely related with humans. Except in the most arid settings, muscids are small to medium-sized dipterans that can be found in a variety of terrestrial and aquatic habitats (P. Skidmore, 1985). This family includes species that reproduce and feed on trash, dung, and carrion (Smith, 1985), Muscids are more typically linked with carrion during the decay and post-decay periods, when the internal organs are exposed, according to their feeding preference. This family's forensic significance has not been thoroughly documented. Many researchers keep track of their existence and/or abundance, but they find it too unstable to be utilise as a predictor of the time of death.
2.6.8. Taxonomy of carrion insects
Reed (1958) classified arthropods into groups based on the stages of decomposition in which they were most commonly found. The families Silphidae, Histeridae, Staphylinidae, Muscidae, Calliphoridae, and Sarcophagidae were found in the Fresh stage of decomposition; those in the Bloated stage included the families Silphidae, Histeridae, Staphylinidae, Muscidae, Calliphoridae, and Sarcophagidae; those in the Decay stage included The distribution of insect taxonomic groups by stage was shown to vary seasonally and across land types.
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- Quote paper
- Emmanuel Tyokumbur (Author), 2023, Lindane Effects on Carrion Insects. A Forensic Entomotoxicological Appraisal Using Euthanized Rabbits, Munich, GRIN Verlag, https://www.hausarbeiten.de/document/1364231
