A study was carried out on the forensic entomological evaluation of carrion insects of pigs poisoned with paraquat between July and September 2018, on the main campus of the University of Ibadan. Paraquat is a commonly used suicide agent because it is easily available and very cheap. Pigs for the study were obtained from Akinyele meat market in Ibadan, Oyo state. The pigs were then weighed and euthanized with 60ml and 80ml of paraquat while the third pig without poison served as the control. Adult carrion insects were collected from the carrions using a sweep net and they are then immobilized using by spraying them with insecticide. The larva were collected into a bowl by using a spoon. The larvae were then immobilized with hot water and are later placed in appropriate sample bottles. Pupae were collected using a forces.
TABLE OF CONTENT
Abstract
Table of Contents
List of Tables
List of Figures
CHAPTER ONE INTRODUCTION
1.1 Entomotoxicology
1.2 Carrion insects
1.3 Paraquat
1.4 Aims and Objectives of the Study
CHAPTER TWO LITERATURE REVIEW
2. 0 Introduction
2.1 Medico-legal forensic entomology
2.2 Stored product entomology
2.3 Urban forensic entomology
2.4 Decomposition
2.5 Insect Succession
2.6 Factors affecting fly development
2.7 Types of Carrion Insect and Arthropods
2.8 Paraquat
2.9 Review of Previous Literatures
CHAPTER THREE MATERIALS AND METHOD
3.1 Study Site
3.2.1 Sample collection and processing
3.2.2 Preparation of Pigs for Set-up
3.2.3 Mounting the pigs
3.2.4 Sampling of carrion insect stages
3.3 Measurement of larval body length and weight
3.4 Measurement of carcass temperature and humidity
CHAPTER FOUR RESULTS
4.1 Abundance and species composition of carrion insects on pig carcass
4.2 Carrion insect succession on pig carcass
4.3 Effects of paraquat on the length and weight of the control, 60ml and 80ml larva
4. 4 Variations in environmental variables at the field site
CHAPTER FIVE DISCUSSION
5.1 Abundance and species composition of carrion insects on pig carcass
5.2 Carrion insect succession on pig carcass
5.3 Effects of paraquat on the length and weight of larvae
5.4 Variations in environmental variables at the field site
5.5. Conclusion
REFERENCES
ABSTRACT
A study was carried out on the forensic entomological evaluation of carrion insects of pigs poisoned with paraquat between July and September 2018, on the main campus of the University of Ibadan. Pigs for the study were obtained from Akinyele meat market in Ibadan, Oyo state. The pigs were then weighed and euthanized with 60ml and 80ml of paraquat while the third pig without poison served as the control. Adult carrion insects were collected from the carrions using a sweep net and they are then immobilized using by spraying them with insecticide. The larva were collected into a bowl by using a spoon. The larvaes were then immobilized with hot water and are later placed in appropriate sample bottles. Pupae were collected using a forces. At the end of the experiment, we found that Muscidae was the most dominant carrion insect in all the groups of the decomposing pigs. Sacrophagidae was the least dominant in the 60ml and 80ml paraquat poisoned pigs. The control group had more diversity and specie composition of carrion insects than the paraquat poisoned pigs. The length and weight of the larvas were also observed and both parameters were found to be appreciably more in the control group than in the 60ml poisoned paraquat group. The parameters were also considerably more in the 60ml paraquat group compared to the 80ml paraquat group.
Keywords: Forensics, Forensic entomology, Toxicology, Paraquat, Insect carrion, Decomposition, Crime
LIST OF TABLES PAGE
Table. 1 Abundance of forensically important insects collected from pig carrion treated with 60ml paraquat
Table 2: Abundance of forensically important insects collected from pig carrion treated with 80ml of Paraquat.
Table 3: Abundance of forensically important insects collected from pig carrion from control group (0ml Paraquat)
Table 4: Occurrence matrix of carrion insect stage in 60ml of paraquat treated pigs
Table 5: Occurrence matrix of carrion insect stages in 80ml at paraquat treated pigs
Table 6: Occurrence matrix of carrion insect stages in control group
LIST OF FIGURES PAGE
Fig. 1 Histogram showing the mean body length of the larva of Musca domestica collected from pig carcass
Fig. 2 Histogram showing the mean body weight of the larva of Musca domestica collected from pig carcass
Fig. 3 Comparison of Control and 60ml paraquat- poisoned pig carcass temperature recorded in the field experiment
Fig. 4 Comparison of Control and 80ml paraquat -poisoned pig carcass temperature recorded in the field experiment
Fig. 5 Comparison of Control and 60ml paraquat poisoned pig carcass relative humidity recorded in the field experiment
Fig. 6 Comparison of Control and 80ml paraquat- poisoned pig carcass relative humidity recorded in the field experiment
Fig. 7 Fresh decomposition stage
Fig. 8 Bloat decomposition stage
Fig.9. Active decomposition stage
Fig. 10. Advanced decomposition stage
Fig.11. Dry decomposition stage
Forensics entomotoxicological evaluation of carrion insects of pigs poisoned with paraquat
CHAPTER ONE INTRODUCTION
1.1 Entomotoxicology
Entomotoxicology is derived from "entomo" which literally means insects and "toxicology" which means the study of toxins, therefore Entomotoxicology can simply be defined as the study of toxins or poisons in insects (Amendt et al, 2004). There has been increase in drug related deaths in many parts of the world both in developing countries like Nigeria and developed countries like USA(Catts and Goff, 1992). Sometimes these corpses remain undiscovered for many days or weeks after death. Most times, the corpses are in the skeletonized stage of decomposition or most other stages of decomposition in which there won't be enough tissue on the corpse that can allow for post mortem evaluation (Goff, 1993). But scientist and law enforcement agencies must find one way or another to investigate the cause of the death and the type of poison so that they can know if the death is as a result of homicide, suicide, or if the death occurred as a result of drug overdose(Catts and Goff 1992).
Forensic entomotoxicology is the method of combating crimes using the knowledge from the study of toxins or poisons in insects (Catts and Goff, 1992). It can also be defined as the application of the study of poisons present in insects in unravelling possible crimes. In recent times, it has been proven that it is possible to detect various toxins and controlled substances by analysis of insects, larvae skins or puparial skin present near the corpse. (Crosby et al, 1986). Forensics entomotoxicology is also important in contraband trafficking (Crosby et al, 1986). In many part of the world, the sale of cocaine and some other narcotics have been generally banned. If a forensic Entomotoxicological study is conducted on a body and the trace of cocaine or other narcotics is found on the insect, it is then obvious that the decedent must have been taking such narcotics while he or she was alive. Forensic entomotoxicology is also very useful in civil cases involving the infestation of urban buildings and gardens or the contamination of a wide range of commercial products (Catt's & Goff, 1992)
Forensic entomotoxicology is most commonly used to estimate Post Morten Interval (PMI) in cases involving homicide (Wallman, 2003: Dadour and Morris, 2009). The initial signs of soft tissue decay occurs within the first 72-96hours after death. After the initial stages of decomposition are complete, the accurate determination of PMI is not possible but insects found on the deceased can enable entomologist to provide an estimation ranging from one day up to more than 2 months (Schoenly et al., 1992). Important forensics Entomotoxicological insects are called "carrion insects".
1.2 Carrion insects
Carrion insects are insects that are associated with decomposimg or deteriorating remains (Nuorteva, 1977). Carrion insects are very important in the ecosystem as they help in the breakdown of dead and decomposing organisms and they also return nutrients mostly in the form of nitrates to the soil. The breakdown of dead and decomposing organisms by carrion insects does not only replenish nutrients to the soil, it also makes the environment free from pollution which may lead to the fast spread of diseases especially when the body are washed into water bodies and the water is consumed by different animals(Kreitlow , 2010). Carrion insects may be the fastest means and most important means of decomposition in some areas especially areas where the large mammals and bird scavenger such as coyotes, dogs, wolves, foxes, crows and vultures are not found.
Not all the carrion insects found on a decomposing body feeds directly on the body. Some may feed on the insects that are associated with feeding on the carrion while others may use the carcass as extension of their environment. (Janaway et al, 2009)
Forensic entomologists classify the carrion arthropod species into different ecological categories in order to establish the arthropods’ role at the remains and their applicability for determining the PMI. The ecological categories include:
1 Necrophagousspecies, thatfeed only on thecarrion,
2. Predatory speciesthat feed on other arthropodspresentatthecarrion and parasiticspecies, which parasitisethelarvaeand/or pupaepresentatthe remains,
3. Omnivorousspecies, thatfeed on both thecarrion and theother arthropod colonisers, and
4. Incidentals, wheretheremainsareused asan extension of their environment.
Immature and mature stages of a species can belong to different categories based on their feeding preferences (Catts and Goff, 1992; Amendt et al, 2004).
1.3 Paraquat
Paraquat is a poisonous substance that is broadly utilized as a herbicide (plant executioner), principally for weed and grass control. (Revkin, 1983).
In the United States, paraquat is accessible fundamentally as a fluid in different qualities. The US Environmental Protection Agency arranges paraquat as "limited utilize." This implies it can be utilized just by individuals who are authorized implements (Buzik et al 1997). Paraquat has also been linked to the development of Parkinson's disease (Kamel, 2013)
Since paraquat is exceptionally harmful, the frame that is promoted in the United States has a blue color to shield it from being mistaken for refreshments, for example, espresso, a sharp scent to fill in as a notice, and an additional operator to cause retching on the off chance that somebody drinks it. Paraquat from outside the United States might not have these shields included (DJ Wohlfahrt, 1982).
1.4 Aims and Objectives of the Study
i. To assess the abundance and specie composition of carrion insect found on the pig carcass poisoned with paraquat
ii. To assess the succession patterns of the carrion insects during the decomposition stages.
iii. To assess the effect of paraquat on the length and weight of the insects larva found on the treated and untreated pigs
iv. To assess the effects of temperature and humidity on the abundance and diversity of the carrion insects on the pig carcass.
CHAPTER TWO LITERATURE REVIEW
2.0 Introduction
Forensic entomology is a field of forensic science which includes utilization of the investigation of insects and different arthropods in criminal examination and lawful cases (Verma and Paul, 2016). The standards of forensic entomology have been utilized to determine wrongdoing for a great many years however they turned into a piece of Western science just in the nineteenth century. It is primarily associated with death investigations; however, it may also be used to detect drugs and poisons, determine the location of an incident, and find the presence and time of the infliction of wounds.
There are three main fields in forensic entomology, and they are
Stored product forensic entomology
Medico-legal forensic entomology
Urban forensic entomology
2.1 Medico-legal forensic entomology
This sub-field of forensic entomology gathers evidence through the study of insects and other arthropods at a crime scene such as murder and suicide. It most often involves the study of insect eggs and maggots, in what order they appear and where on the body they are found. Because insects occur only in particular places and are active only at a particular season, their presence can reveal a lot about location and time of the crime (Catts and Goff, 1992). Medicolegal forensic entomology covers evidence gathered through arthropod studies at the scenes of murder, suicide, rape, physical abuse and contraband trafficking (Catts and Goff, 1992).
2.2 Stored product entomology
It investigates cases of insect infestation or contamination of commercial foods with an aim to find evidence relevant for litigation (Catts and Goff, 1992).
2.3 Urban forensic entomology
This aspect of forensic entomology typically focuses on pests infestations that are related to litigation such as legal disputes between exterminators and landlords. Besides studying insects and other arthropods, urban forensic entomology typically also involves toxicological studies, for example the appropriateness of pesticide application (Catts and Goff 1992).
2.4 Decomposition
Decomposition is the process by which organic substances are broken down into simpler inorganic matter. The process is a part of the nutrient cycle and is essential for recycling the finite matter that occupies physical space in the biosphere (Keh, 1982) . Bodies of living organisms begin to decompose shortly after death. Animals, such as worms, also help decompose the organic materials. Organisms that do this are known as decomposers . Piglets are mostly used when conducting animal decomposition experiment especially when the experiment is related to humans or when the major aim of the experiment is to draw inference which can relate to what obtains in humans. Pigs are used because a pig resembles a human body in its fat distribution, cover of hair and ability to attract insects (Smith, 1986).
2.4.1 Stages of decomposition
2.4.1. a. Stage 1: The living pig
A live pig is not outwardly decomposing, but its intestine contains a diversity of bacteria, protozoans and nematodes. Some of these micro-organisms are ready for a new life, should the pig die and lose its ability to keep them under control (Smith, 1986).
2.4.1.b.Stage 2: Fresh decay stage
Although the body shortly after death appears fresh from the outside, the bacteria that before death were feeding on the contents of the intestine begin to digest the intestine itself. They eventually break out of the intestine and start digesting the surrounding internal organs. The body's own digestive enzymes (normally in the intestine) also spread through the body, contributing to its decomposition. On an even smaller scale, enzymes inside individual cells are released when the cell dies. These enzymes break down the cell and its connections with other cells (Tantawi et al., 1996)
From the moment of death flies are attracted to bodies. Without the normal defences of a living animal, blowflies and house flies are able to lay eggs around wounds and natural body openings (mouth, nose, eyes, anus, genitalia). These eggs hatch and move into the body, often within 24 hours. The life cycle of a fly from egg to maggot to fly takes from two to three weeks. It can take considerably longer at low temperatures (Smith, 1986).
2.4.1.c. Stage 3: Bloat Putrefaction
Bacteria break down tissues and cells, releasing fluids into body cavities. They often respire in the absence of oxygen (anaerobically) and produce various gases including hydrogen sulphide, methane, cadaverine and putrescine as by-products. People might find these gases foul smelling, but they are very attractive to a variety of insects (Catts and Goff, 1992).
The buildup of gas resulting from the intense activity of the multiplying bacteria, creates pressure within the body. This pressure inflates the body and forces fluids out of cells and blood vessels and into the body cavity (Catts and Goff, 1992).
The young maggots move throughout the body, spreading bacteria, secreting digestive enzymes and tearing tissues with their mouth hooks. They move as a maggot mass benefiting from communal heat and shared digestive secretions (Catts and Goff, 1992).
The rate of decay increases, and the smells and body fluids that begin to eminate from the body attract more blowflies, flesh flies, beetles and mites. The later-arriving flies and beetles are predators, feeding on maggots as well as the decaying flesh. They are joined by parasitoid wasps that lay their eggs inside maggots and later, inside pupae
2.4.1.d Stage 4: Active decomposition
The bloated body eventually collapses, leaving a flattened body whose flesh has a creamy consistency. The exposed parts of the body are black in colour and there is a very strong smell of decay (Smith, 1986).
A large volume of body fluids drain from the body at this stage and seep into the surrounding soil. Other insects and mites feed on this material (Smith, 1986). The insects consume the bulk of the flesh and the body temperature increases with their activity. Bacterial decay is still very important, and bacteria will eventually consume the body if insects are excluded (Smith, 1986).
By this stage, several generations of maggots are present on the body and some have become fully grown. They migrate from the body and bury themselves in the soil where they become pupae. Predatory maggots are much more abundant at this stage, and the pioneer flies cease to be attracted to the corpse. Predatory beetles lay their eggs in the corpse and their larvae then hatch out and feed on the decaying flesh. Parasitoid wasps are much more common, laying their eggs inside maggots and pupae (Smith, 1986).
2.4.1 e. Stage 5: Advanced decomposition
State of decay
All the remaining flesh is removed over this period and the body dries out. It has a cheesy smell, caused by butyric acid, and this smell attracts a new suite of corpse organisms. The surface of the body that is in contact with the ground becomes covered with mould as the body ferments (Catts and Goff, 1992)
The reduction in soft food makes the body less palatable to the mouth-hooks of maggots, and more suitable for the chewing mouthparts of beetles. Beetles feed on the skin and ligaments. Many of these beetles are larvae. They hatch from eggs, laid by adults, which fed on the body in earlier stages of decay (Smith, 1986). The cheese fly consumes any remaining moist flesh at this stage, even though it is uncommon earlier in decay. Predators and parasitoids are still present at this stage including numerous wasps and beetle larvae (Smith, 1986).
2.4. Stage 6: Dry decay
The body is now dry and decays very slowly. Eventually all the hair disappears leaving the bones only (Bourel et al., 1999)
Animals which can feed on hair include tineid moths, and micro-organisms like bacteria. Mites, in turn, feed on these micro-organisms (Bourel et al., 1999).
They remain on the body as long as traces of hair remain, which depends on the amount of hair that covers the particular species. Humans and pigs have relatively little hair and this stage is short for these species (Bourel et al., 1999).
2.5 Insect Succession
Insect Succession on Carrion Insects associated with carrion may be classified according to their ecological role. Necrophages feed and breed on the carrion itself (Payne, 1965). These species typically occur in succession and respond to decompositional changes of the carcass. These species are often the most important in providing useful forensic information. The Calliphoridae are the most prominent necrophages. Sarcophagids, muscids and piophilids may also be necrophagous. Silphids, clerids and dermestids also feed and breed within the carrion ( Payne, 1965; Keh, 1985; Smith, 1986; Catts and Goff, 1992;). There are also parasites and predators of the necrophagous species. These species are less well understood in terms of their usefulness in forensics, but are nonetheless considered the second most important group that occurs on carrion (Payne, 1965; Smith, 1986; Catts and Goff, 1992 ). Staphylinids and histerids are important predators of carrion fly larvae and are therefore important in terms of the ecological dynamics of carrion (Tantawi et al. 1996). Adventives or incidental species are found in and around the carrion, but only use it as an extension of their own environment. Grasshoppers, crickets, springtails, mites, pillbugs and centipedes fit into this category. It should also be noted that many spiders, centipedes and ants are found in and around carrion and may become incidental predators (Seastedt et al. 1981; Keh, 1985; Catts and Goff, 1992; Smith, 1986; Lord 1990 ). Even though the latter two categories are not considered forensically important, there are over 60 insect families that play an important role in carrion ecology (Smith, 1986).
Insect colonization of carrion can be described as a rapid invasion of the carcass by adult calliphorids, sarcophagids and muscids, resulting in the presence of huge numbers of dipteran eggs and larvae (Smith, 1986). This provides an abundant food supply for predacious beetles such as silphids and staphylinids. Insect diversity reaches a maximum during the fresh, bloat and decay stages of decomposition. As the carcass decays, there is a distinct decrease in species richness. As the food resource becomes depleted, insects disperse from the carcass and different species that prefer the later stages of decay for food and development arrive. Piophilids, clerids and nitidulids are typically associated with the carcass during the advanced decay stage and dermestids are typically associated with the dry remains stage. This change in species composition on carrion over time is called insect succession. This general pattern has been observed by many scientists and is typical of both temperate and tropical areas (Tantawi et al, 1996).
Diptera and Coleoptera comprise about 60% of the total necrophagous fauna found on carrion (Payne, 1965; Greenberg, 1991). Of the estimated 23 fly and 19 beetle families commonly associated with carrion, there are only about 10 families considered to be worth studying in depth in terms of their forensic value (Greenberg, 1991 ). Among the Diptera, the main families are the Calliphoridae, Sarcophagidae, Muscidae and Piophilidae. Calliphorid larvae, and to a lesser degree, sarcophagids and muscids, are the primary flies responsible for the majority of carrion decomposition during the earlier stages of decomposition (Aspoas, 1994; De Jong, 1994; Tantawi et al, 1996). In the Coleoptera, the main families are the Silphidae, Staphylinidae, Cleridae and Dermestidae and to a lesser degree, geotrupids and trogids (Payne and King, 1970). Many of the beetle species associated with carrion are predators of maggots and only a few are true carrion feeders (Smith, 1986). However, accounts of the feeding roles of many carrion beetles and other invertebrates are lacking and more research is needed to understand their function during the later stages of decomposition (Kulshrestha and Satpathy, 2001).
2.6 Factors affecting fly development
Factors affecting fly development may include geography, seasonal influence, temperature/ humidity, habitat variation etc.
2.6.1 Habitat Influences
Different habitats can influence carrion species composition and in turn affect insect succession. Tessmer and Meek (Tessmer and Meek, 1996 ) noted several differences in species composition of calliphorids on carrion placed in woodland versus pastureland habitats. They found that a greater abundance of blow flies was associated with the pasture habitat. Isiche et al. (Isiche et al, 1992) found a difference in the calliphorid species abundance and diversity when observing mouse carrion in sunny and shaded habitats. Four species were found in the sunny area and only two of these species were observed in the shaded area. Carrion in both habitats contained C. vicina, but this species was more abundant in the shaded area. There were also differences in insect succession in different areas of a rainforest habitat where distinct changes in species composition were observed (Early and Goff, 1986; Tullis and Goff, 1987).
Research on insect succession has been somewhat restricted to terrestrial habitats, and as a result, few studies in aquatic habitats have been performed (Johnson and Ringler, 1979; Haskell et al. 1989; Singh and Greenberg, 1994; Vance et al. 1995; Hobischak and Anderson, 1999; Hobischak and Anderson, 2002). The successional changes within different habitat types are forensically important. Research is necessary for different habitat types to have data for estimates based on similar conditions, so more confidence can be placed in the inferences made for time of death (Bourel et al.1999).
In many forensic cases, bodies have been buried or disposed of in houses, buildings and in the trunks of cars. This has lead to some questions about the effects of the availability or accessibility of carrion on insect succession. Goff (1991) compared case studies involving remains found outdoors versus indoors and reported significant differences in insect colonization. He suggested that certain fly taxa were restricted to indoor situations and that this information could be used for cases where the body is colonized indoors and then later moved outdoors. It was noted that many of the beetle species were poorly represented in the indoor situations.
2.6.2 Seasonal factors
Carrion insects are impacted by season, with specific peaks in activity, abundance and species richness (Smith, 1986; Tantawi et al. 1996; Anderson 2000). Calliphorids and sarcophagids exhibit definite seasonal preferences in terms of activity and abundance (Baumgarnter and Greenberg, 1985; Introna et al. 1991; Aspoas, 1993; Tantawi et al. 1996; Bourel et al. 1999). A corpse exposed in the spring and summer will have a different fauna from one exposed in the late fall or winter, when insect activity has decreased or ceased (Smith, 1986).
In Egypt, Chrysomya vicina was abundant in the winter, L. sericata bred successfully in fall, winter and spring and Chrysomya albiceps (Wiedemann) was abundant in summer, spring and fall (Tantawi et al, 1996). Phaenicia cuprina (Wiedemann) was numerous throughout the warm months in the southern United States with peak abundance occurring in the summer ( Hall, 1948; Goddard, 1988). Cynomya cadaverina was not abundant during the winter and P. sericata numbers peaked in the late spring and early summer (Goddard, 1988).
In tropical areas, seasonal influences are related to rainfall and seasons are more appropriately referred to as wet and dry. Differences in species abundance, activity and species richness are also evident in these regions. Baumgartner and Greenberg (1985) found differences in the abundance in species of blow flies during these two seasons in Peru. Abundance of blow flies was greatest in the wet season and least in the dry season. The differences in abundance for this area were also related to altitude and proximity to human habitation. Seasonal effects that occur within the same area can influence insect abundance. Bourel et al, (Bourel et al, 1999) found a considerable difference in blow fly colonization of rabbit carrion from one year to the next. In 1996, C. vicina and C. vomitoria were the first species present to colonize the spring-exposed carcasses. However, these species did not arrive until day three and did not lay eggs until day five. In the following year, the activity of these species differed in terms of oviposition. The carrion was exposed during the same time period and C. vicina and C. vomitoria were seen actively laying eggs on the first day of exposure (Bourel et al, 1999). Since there are differences in these generalizations, studies of insect activity and abundance should be conducted throughout a given year and over many years.
The seasonal differences in abundance and activity of blow flies are evident and can be useful in estimating time of death. This is especially useful for corpses found years after death, since blow fly pupal cases and cast beetle skins can be dated to estimate the season of death (Strong and Adams, 1990). However, the breakdown and fragmentation of pupal cases and beetle exuviae can be caused from disturbance, sun exposure, moisture, and soil acidity (Teskey & Turnbull, 1979; Nuorteva, 1987; Anderson, 2000). This technique may not be applicable for all regions that experience extreme weather conditions such as cold winters. Generalizations about seasonality must therefore be applied carefully in forensic situations since many factors can alter this type of evidence (Catts, 1992).
2.6.3 Temperature and Humidity
Temperature and humidity heavily influence insect activity and rates of oviposition and development (Smith, 1986; Gillot, 1995; Anderson and Cervenka, 2001). This influences the overall rate of decomposition since insect activity is either accelerated or inhibited depending on temperature. Payne (1965) found that the reduction of carrion was slower on cool, cloudy days. The opposite was recorded on warmer days since high temperatures intensified insect activity, resulting in a rapid depletion of the carcass. Therefore, slower decomposition rates and decreased insect activity alter the timing of insect arrival to the carcass, which in turn affects the rate of decay.
Blow flies are typically sensitive to moisture levels, thus when moisture is too high, blow fly larvae will leave a carcass and have been noted to cease larval development (Payne, 1965). Larval silphids and staphylinids have an opposite response to moisture levels and are able to withstand higher moisture levels than blow fly larvae. However, many of these insects will not complete development if the carcass conditions are too dry (Payne, 1965; Payne and King, 1970). A combination of microbial metabolism and aggregations of fly larvae can greatly increase temperatures in carrion. These maggot masses and microbial activity create conditions within the carcass that are very different from the surrounding environment. Payne (1965) found that the temperatures of the carcass and air differed by about 16 °C. Turner and Howard (1992) recorded carcass temperatures of 19-27 °C above ambient. Carrion temperature has a profound effect on carrion insect development, since the internal temperature of a carcass can be considerably higher than ambient temperature (Hanski, 1976; Introna et al, 1989; Cianci and Sheldon, 1990; Goodbrod and Goff, 1990; Greenberg, 1991; Catts, 1992 ).
Research on the time spans for species development at different temperatures is key for estimating time of death (Smith, 1986; Catts and Goff, 1992; Byrd and Butler, 1996; Anderson, 2000; Byrd and Allen 2001). Generally, each stage of blow fly development will progress at a slower rate at low temperatures. Davies and Ratcliffe (1994) compared the egg and larval development of C. alpina (Zettermann) and C. vicina at low temperatures. It was found that C. vicina could survive and develop slowly at very low temperatures. They determined that C. vicina is important in a forensic context, since postmortem intervals are based on the oldest specimens. Presence of these slow-growing larvae on a body could be misinterpreted since the larvae developing from these eggs will grow faster and appear to be older than the slow growing larvae, therefore altering the estimate of time of death (Davies and Ratcliffe, 1994). The microclimate created by maggot masses can also create error in estimating time of death, since the ambient temperature is typically used to estimate the larval growth stage (Turner and Howard, 1992).
Ideally, insects should be collected directly from the body at the death scene but in many questionable death situations, collection of entomological evidence is left until after the body has been moved and chilled at the morgue (Johl and Anderson, 1996). Research on how refrigeration affects necrophagous fly activity and effects of low temperatures on blow fly development have been necessary to determine whether or not larvae continue to feed and develop on the body during refrigeration (Davies and Ratcliffe, 1994; Grisbaum et al, 1995; Johl and Anderson, 1996; Anderson, 2000). This is problematic since the refrigeration temperatures for body storage may vary and larvae could continue to grow and develop at different rates, therefore influencing the time of death estimate. Calliphora vicina larvae were shown to develop, albeit slowly, at temperatures below 4 °C and the lag in development seemed to be equal to the length of temperature exposure, with some exceptions (Johl and Anderson, 1996). Any lag in development is important to recognize, especially if trying to implicate a murder suspect to a victim. In order to make better forensic inferences, studies on the effects of temperature on the different stages of larval development must be referenced prior to estimating time since death. (Anderson, 2000)
2.6.4. Carrion Insects Development
Carrion insect development is also influenced by the biology of the necrophagous insects. Appetite and reproductive state of adult blow flies can influence whether they are ready to use carrion as a food source or medium for oviposition (Dethier and Bodenstein, 1958). Carrion may be available and in ideal condition before the blow flies have finished developing their eggs, therefore causing a delay in arrival or oviposition. Bourel et al. (1999) found C. vicina and C. vomitoria arriving at rabbit carcasses three days after exposure and reported that these flies did not lay eggs until day five. They did not provide any explanation for the delay in arrival or oviposition, but these results differed from the findings of other researchers who reported calliphorid species arriving at the carcass within minutes of death and eggs laid within an hour of death (Anderson and VanLaerhoven, 1996).
Blow flies are usually diurnal in activity and rarely lay eggs at night (Greenberg, 1985). Typical daily activity of adult blow flies peaks in the early afternoon and little activity occurs in the early morning and late afternoon (Baumgartner and Greenberg, 1985). This is a very important detail in forensics cases. From this information, it is assumed that a corpse found at night or in early morning infested with calliphorid eggs or early instar larvae, may have died the previous day or earlier. Greenberg (1990) published evidence contrary to this generalization. He observed nocturnal oviposition of P. sericata, P. regina and C. vicina. He concluded that oviposition is temperature dependent and is not directly influenced by time of day. This is an important observation since the assumption that blow flies rarely oviposit at night can change a postmortem interval by as much as 12 hours (Catts, 1992).
Alterations in blow fly colonization can result from competition between and within fly species. Hutton and Wasti (1980) found that larval competition between P. sericata and P. regina resulted in a 60% reduction in survival rate for P. regina. They established that P. sericata was more competitive than P. regina, despite abundant food and space. Some fly species have different food requirements that can influence their ability to succeed under certain conditions. Chrysomya megacephala (Fabricius), for example, requires less food than other species to develop (Levot et al. 1979). This is an important adaptation for carrion flies since many different calliphorid species may arrive at the same carcass at the same time. Competition between different fly families is also apparent on carrion. Denno and Cothran (1976) recorded calliphorids as the primary invaders of rabbit carrion in California and observed small populations of sarcophagids at the carcasses. They established that when the oviposition of calliphorids was artificially reduced, the numbers of the sarcophagids increased significantly. There are other factors that can cause a decrease in the arrival time to carrion.
Effects of adventive species and vertebrate scavenging, impact the succession of insects on carrion. Fire ants, Solenopsis geminata (Fabricius), can have a major impact on necrophagous insects (Early and Goff 1986; Wells and Greenberg, 1994). It was found that the colonization of carrion, and in turn the rate of decomposition, was retarded when fire ants were in significant numbers. Vertebrate scavengers can intensify oviposition by creating large wounds by feeding and tearing flesh from a carcass. This creates a larger and ideal surface area for fly oviposition since more soft and bloody tissue is exposed. Common vertebrate scavengers are bears, coyotes, wolves, foxes and skunks (Nation and Williams, 1989; Dillon, 1997; Anderson, 2000). Scavengers can also have the opposite effect and eliminate insect colonization on a carcass. Wolves, for example, can completely devour the carcass tissue and organs, leaving nothing for carrion insects to feed on or breed in (Anderson, 2000).
All of the factors that influence the colonization and succession of insects on carrion are important and unique to different regions and can even differ from case to case. Data from one region and assumptions based on past cases should, therefore, be used with caution when determining time of death of a victim. Studies in different geographical areas and under varied conditions are necessary to generate accurate insect species lists and arrival times for use in forensic cases. Furthermore, research on the effects of seasonality, temperature and habitat on carrion insect colonization within different regions is important, hence the need for this study.
Geography
Picard and Wells (2010) concluded that this pattern of local relatedness is likely to occur within the larvae collected from the corpse. This is of importance to forensic entomologists; as such differences in geographic population genetic structure may be used to determine if a body has been moved during the post-mortem period.
Regional and geographic differences will result in different colonisation and succession patterns. Anderson (2010) noted that even over short distances, variations in microclimate can significantly affect the colonisation rates of carrion-associated insects. Similarly, Michaud et al. (2010) found that habitat preferences of carrion insects can change depending on the geographical region in question. Some insect species associated with carrion are specific to either a rural or urban environment (Anderson, 2010; Brundage et al., 2011; Kavazos and Wallman, 2012). If an insect is located exclusively in a specific habitat or location, it may be used to determine whether the body has been moved (e.g. from an urban to a rural area) (Hwang and Turner, 2005). For example, Brundage et al. (2011) found that whilst Compsomyiops callipes (Bigot), Calliphora latifrons Hough, 1899, and Lucilia mexicana Macquart, 1843 (species native to the study area in California) were largely abundant in rural areas, they were rarely recorded in an urban environment where introduced Lucilia spp. thrived. The application of molecular techniques such as mitochondrial DNA barcoding, sequence, and phylogenetic analysis presented by Harvey et al. (2003a; 2003b; 2008) could therefore assist in identifying differences within species and between species with regard to their geographic location. It is clear from the foregoing discussion that a great deal of care is needed in accurately determining PMI and that, generally, data generated in one biogeoclimatic zone or geographic region should not be used to determine the PMI estimate in a different region (Anderson, 2010). Furthermore, the picture can be obliterated by potential movements and expansion of taxa to additional geographical areas (particularly in relation to changing climate or anthropogenic effects, such as location of waste management facilities). As a result, caution is required when reaching forensic conclusions based on results from different geographical areas (Grassberger and Frank, 2004). Gallagher et al. (2010) have also shown that there are considerable regional variations with respect to maggot developmental times. Lucilia sericata maggots from three geographically distinct populations displayed variation in developmental times when exposed to different temperature treatments. Gallagher et al. (2010) deduced that differences in the developmental times may result from adaptation to a number of local environmental constraints, including temperature. As a result, regionally specific developmental tables for species may be required when using maggot development to estimate the PMI.
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- Quote paper
- Emmanuel Tyokumbur (Author), 2020, Paraquat Effects on Carrion Insects. A Forensics Entomotoxicological Assessment Using Euthanized Pigs, Munich, GRIN Verlag, https://www.hausarbeiten.de/document/1360162
