LECTURE 3: FORENSIC ENTOMOLOGY Flashcards
1
Q
What is a crime scene
A
- The place where an offence has been committed and forensic evidence may be gathered – any evidence, even insects
2
Q
Entomology
A
- Scientific study of the insects, a branch of zoology
- Scientific study: molecular genetics, behaviour, biomechanics, biochemistry, systematics, physiology, developmental biology, ecology, morphology, palaeontology, mathematics, anthropology, robotics, agriculture, nutrition, forensic science, and more……
- Insects: mostly arthropods with 6 legs, but also others such as arachnids and myriapods
- From Greek ἔντοµος, entomon = insect; and -λογία, - logia = study
3
Q
Forensic entomology
A
- The use of insects and other arthropods in legal investigations
- Legal investigations: not just murders
- From latin “forense” and “forum” = pertaining to legal trials
4
Q
Why insects?
A
- Insects are present in every environment
- Insects eat basically everything and in the various stages of life insects have different diets
- Insects share life environment and food with humans
- Insects are interested in humans and their products for food/shelter Why insects…?
- Insects are heterothermic = body temperature varies with environmental temperature, therefore their life cycle can be longer (in cold environment) or shorter (in warm environment)
- Avoid insects? Good luck!
- Food source + optimal temperatures = GROWTH & REPRODUCTION
- Insects share life environment and food with humans + Insects are interested in humans and their products
5
Q
Life cycles are the key of arthropods’ success because immature and adults:
A
- Live in different environments (and in different time)
- Eat different food
- No competition = more success
- Mosquito example – presence of them can lead to idea/conclusion of the body having contact with fresh water at some point
6
Q
Holometaboly
A
complete metamorphosis (butterfly/mosquito starts in water)
7
Q
Hemimetaboly
A
incomplete metamorphosis (cricket)
8
Q
Ametaboly
A
no metamorphosis
9
Q
Insects are
A
heterothermic
10
Q
heterothermic
A
time needed to complete the life cycle is a matter of temperature at which they grow
11
Q
four types of entomology
A
- Urban entomology – bed bugs for example, legal action
- Negligence
- Insects damages
- Agricultural pests
- Hygiene - Stored products entomology – close to biosecurity
- Food contamination
- Contamination of other items - Forensic veterinary entomology
- Investigation about time of death. poisoning, negligence and abuse against animals - Medico-legal entomology
- Investigation about time of death, poisoning, presence of drugs, negligence and abuse against humans
12
Q
The stages of decomposition:
A
- Fresh
- Begins almost immediately; enzymatic breakdown of cells and tissue (autolysis) begins
- Visible signs limited - Bloated
- Metabolic activity of bacteria produces gases, causing the carcass to inflate and swell
- Pressure forces fluids from natural orifices, producing strong odours - Active decay
- Liquefaction and disintegration of tissues observed
- Odours persist - Advanced decay
- Decomposition rate decreases due to loss of mass
- Eventually, dry remains are all that remain
13
Q
Why is knowledge of decomp important
A
Insects are interested in different stages of decay – different meat more or less rotten -insight into what stage is present
14
Q
Odour causing chemicals in decay process
A
Cadaverine
Putrescine
Skatole
Indole
15
Q
Francesco Redi (1626-1697)
A
- Italian physician, naturalist, biologist and poet.
- He is referred to as the “founder of experimental biology”
- He was the first person to challenge the theory of spontaneous generation by demonstrating that maggots come from eggs of flies (1668).
16
Q
Mégnin stated that corpses are exposed to “successional waves” =
A
predictable insects species groups that are interested in subsequent phases of the decomposition process.
- The identification of the successional waves may help to estimate the time since death.
- generally 8 waves of insect, not always 8 though- depends on if protected or not
17
Q
Successional waves are in dependence of:
A
- Environmental temperatures
- Place where the corpse spend the PMI period
18
Q
Insects of forensic interest
A
- Necrophagous Flies (Diptera)
- Necrophagous Beetles (Coleoptera)
- Blowflies mainly/ and maggots… be open to all
19
Q
Blow fly life cycle
A
- Blow flies lay eggs which are long cylinders, sperm enters egg after the egg is layed – so thermal stress such as too cold could mean sperm dies and therefore egg dies.
- Structures on lines on egg called raphe can be used for species of identification
- Fly will choose wet easy access places to lay eggs such as nose, ear, mouth, genitalia and needs to be wet to avoid dehydration of larvae, especially when hot which is why also usually hiddenish
- Goes from maggot to cocoon (pupae) to fly
- Because they need to shrink to pupae form, we need to look at stomach content so decide if it is younger or older – and skin with get darker and darker
- posterior spiracle of maggot can be used for species identification
- Pupae get darker and darker too – red – darker – to like a dark purple I would say – then quite dark, even brown – then fly is born
20
Q
INVESTIGATION ABOUT “TIME”
A
- Time since death (PMI)
- Colonization prior to death
- Time of mistreatment
- Postmortem submersion interval (PMSI)
21
Q
P.M.I.
A
Post Mortem Interval (time since death)
o Time between the death event and the discovery of the corpse
- 3 days window…and many limitations especially with animals!
22
Q
ALGOR MORTIS “death heat”
A
- Post Mortem cooling of the body((about 1°C/h)
- Multiple variable on algor mortis are:
− Body dimensions
− Posture
− Clothing
− Ambient Temperature − Air movement - Tends to level off the environmental temperature
23
Q
RIGOR MORTIS “death stiffness”
A
- Stiffness of muscles due to lactic acid
- Starts around 2-4 hours after death
- Reaches maximum stiffness 8-12 hours after death
- Begins to fade 18-24 hours after death
- Disappears 24-30 hours after death
24
Q
LIVOR MORTIS “death color”
A
- Settling of blood in body due to gravity
- Develops 2-4 hours after death occurs
- Non-fixed (blanchable) 8-12 hours after death
- Fixed (non-blanchable) >8-12 hours after death
25
Olfaction system
plays an important role in guiding the behavior of insect species.
26
Antennal sensilla
detect the odours.
27
Ecology
is the study of the interrelationships between organisms and their environment
28
Factors that influence ecosystems
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Abiotic – Not living factors
Temperature
Air (O2, CO2, N2)
Water/ humidity
Soil, pH, light
Wind
Salinity
Inorganic nutrients (N,P)
Toxicological substances
Covering
Access
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Biotic – Living factors
Competition for food
Competition for space
Competition for reproduction
Predation
Symbiosis (mutualism, parasitism)
Disease agents
```
29
Carrion insects: How to avoid/minimise competition and predation?
1. Successional waves*
o Pioneers organisms colonise first and modify the environment
o The new environment and the activity of the first organisms summon other organisms interested in the new environments (more suitable for them) and in the organisms already present (e.g. parasite and predators)
2. Different ecological roles in the food chain
o Archaeoentomology
3. Post-feeding wandering
30
Accumulated Degree Days (ADD) or Accumulated Degree Hours (ADH)
is the summation of temperature (°C) above the lower developmental threshold (LDT) multiplied by time (days or hours)
- ADD = Time X (Temp – LDT)
31
When it comes to lay eggs, female blowflies choose places:
1. Not too hard to penetrate
2. With high level of humidity
3. With easy access to the internal (orifices EENT & lesions – modify shape, make it disappear, indicate there was a lesion) part of the body
32
Myasis
Parasitic infestation of the body of a live mammal by fly larvae (maggots) that grow inside the host while feeding on its tissue. Although flies are most commonly attracted to open wounds and urine- or feces-soaked fur, some species can create an infestation event on unbroken skin as vector agents for their parasitic larvae.
33
TOXICOLOGICAL INVESTIGATION
- Presence of drugs in the insects
| - Effects of drugs on insect survival and growth rate
34
Entomotoxicology
o Food chain – “you are what you eat” Application of toxicological methods and analytical procedures on necrophagous insects feeding on decomposing tissues Insect CHITIN is similar to hair/nail KERATIN
