Transcript Forensic Entomology

Forensic Entomology
MAGGOTS AND TIME OF DEATH ESTIMATION
Entomology is the
Study of Insects
Images from:
www.afpmb.org/military_entomology/usar
myento/files/ArmyEntomology.ppt
Insect Biology
 Insects are the most diverse and abundant forms of life
on earth.
 There are over a million described species- more than
2/3 of all known organisms
 There is more total biomass of insects than of humans.
of humans.
 Insects undergo either incomplete or complete
metamorphosis (Egg to larva to pupa to insect)
 Larva have a soft tubular body and look like worms. Fly
species larvae are “maggots”
What is Forensic Entomology?
 Forensic Entomology is the use of the insects and other
arthropods that feed on decaying remains to aid legal
investigations.
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Medicolegal (criminal)
Urban (criminal and civil)
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“legal proceedings involving insects and related animals that affect
manmade structures and other aspects of the human environment”
Stored product pests (civil)
Medicolegal Forensic Entomology
 Often focuses on violent crimes
 Determination of the time (postmortem interval or PMI) or site of
human death based on identification of arthropods collected from
or near corpses.
 Cases involving possible sudden death
 Traffic accidents with no immediately obvious cause
 Possible criminal misuse of insects
Postmortem interval (PMI)
 Forensic Entomology is used to determine time since
death (the time between death and corpse discovery)
 This is called postmortem interval or PMI).
 Other uses include
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movement of the corpse
manner and cause of death
association of suspects with the death scene
detection of toxins, drugs, or even the DNA of the victim through
analysis of insect larvae.
Forensic Entomology is Applied Biology
 If it weren’t for decomposition of all living things, our
world would fill up with dead bodies.
 When an animal dies, female insects will be attracted
to the body. They enter exposed orifices or wounds and
lay eggs or larvae.
 A forensic entomologist:
identifies the immature insects
 determines the size and development of the insects
 calculates the growth of the insects and passage through
stages of the life cycle in laboratory
 compares the growth against weather conditions to estimate
time of oviposition
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Succession of Insects on the Corpse
 Estimates of postmortem intervals based on insects present on
the remains are based on:
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The time required for a given species to reach a particular stage of
development.
Comparisons of all insect species present on the remains at the time of
examination.
 Ecological succession occurs as an unexploited habitat (like a
corpse) is invaded by a series of different organisms.
 The first invasion is by insect species which will alter the habitat
in some form by their activities. These changes make the
habitat attractive to a second wave of organisms which, in turn,
alter the habitat for use by yet another organisms.
Ecology of Decomposition
 Necrophages - the first species feeding on corpse tissue.
Includes rue flies (Diptera) and beetles (Coleoptera).
 Omnivores - species such as ants, wasps, and some beetles that
feed on both the corpse and associated maggots. Large
populations of ominvores may slow the rate of corpse’s
decomposition by reducing populations of necrophagous species.
 Parasites and Predators - beetles, true flies and wasps that
parasitize immature flies.
 Incidentals – pill bugs, spiders, mites, centipedes that use the
corpse as an extension of their normal habitat
Image: http://www.nlm.nih.gov/visibleproofs
Decay Rates Are Variable
 Studies of decay rates of 150 human corpses at in the
Anthropological Facility in Tennessee (The Body Farm)
 Most important environment factors in corpse decay:
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Temperature
Access by insects
Depth of burial
 Other Factors
• Chemical-- embalming agent, insecticides, lime, etc.
• Animals disrupting the corpse
Time of Death can be broadly estimated
up to about 36 hours
Temperature
Stiffness
Time of death
Warm
Not stiff
Dead less
than three hours
Warm
Stiff
Dead between 3
to 8 hours
Cold
Stiff
Dead between 8
to 36 hours
Cold
Not stiff
Dead in more
than 36 hours
Differentiate between PMI and Time of
Death
 These may not always equate.
 Post mortem interval is restricted to the time that the
corpse or body has been exposed to an environment
which would allow insect activity to begin.
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Closed windows
Body in box or bag
Cold temperatures
Deeper burial
Insect species arrive at a corpse in waves
like clockwork
 Calculate the heat/thermal energy (accumulated
degree hour) required for each stage of the Green
Bottle Fly’s life cycle.
 Possibly the greatest potential source of error in using
arthropod successional patterns lies in the collection of
speciments.
 Must only be done correctly to accurately sample the
insects.
Image: http://www.nlm.nih.gov/visibleproofs
Calculating PMI from
Accumulated Degree Hours (ADH)
From
Egg
To
Temp Hours
1st Instar 70° F
ADH
Cumulative ADH
23
23 x 70=
1610 ADH
1610
1st Instar 2nd Instar
70 °
F
27
27 x 70=
1890 ADH
1610+
1890
2nd Instar 3rd Instar
70 °
F
22
22 x 70=
1540 ADH
1610+1890+
1540
3rd Instar
Pupa
70 °
F
130
130 x 70= 1610+1890+
9100 ADH 1540+9100
Pupa
Adult Fly
70 °
F
143
143 x 70= 1610+1890+
10010 ADH 1540+9100
+10010
Calculating ADH from Climate Data
Using the Data
 3928 ADH in these three days (952+1488+1488).
 How many ADH of 70º are there in these 3 days?
 3928/70=56.11 hours
 72 hours at 70º would have the insects passing to the 3rd
instar. But 72 hours at colder temperatures and insects
will only be at 2nd instar stage.
Five Stages of Decomposition Fueled by Insect
Activity.
 Fresh
 Bloat
 Decay
 Post-decay
 Dry (skeletal)
Fresh
 Begins at death
 Flies begin to arrive
 Temperature falls to
that of the ambient
temperature.
 Autolysis, the
degradation of
complex protein and
carbohydrate
molecules, occurs.
Bloat
• Swells due to
gases produced
by bacteria
• Temperature
rise of the
corpse
• Flies still
present
Decay
 Gases subside,
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decomposition fluids seep
from body.
Bacteria and maggots
break through the skin.
Large maggot masses and
extreme amounts of fluid.
Unpleasant odor
Larvae beginning to
pupate.
Corpse reduced to about
20% of it’s original mass.
Post-Decay
 Carcass reduced to
hair, skin, and bones.
 Fly population reduced
and replaced by other
arthropods.
 Hide beetles are
dominant in dry
environments.
 Mite and predatory
beetle populations
increase.
Dry (Skeletal)
 Does not always occur especially if corpse is in a wet
region. Maggots will stay longer and hide beetles will not
appear.
 In wet environments the hide beetles are replaced with
nabid and reduviid insects.
 The corpse is reduced to at least ten percent of the
original mass.
 In the last stage (Skeletal Stage), only bone and hair
remain.
Accumulated Degree Hours
 ADH may be calculated using temperature and hours.
 This works because there is direct correlation between
temperature and maggot development.
 These calculations were somewhat approximate but
relatively accurate.
Review Questions 1-9
 What is Forensic Entomology?
 Explain 5 applications/uses of insects in forensic science.
 Describe the stages of death: Algor Mortis; Livor Mortis;
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Rigor Mortis.
Describe the stages of decompositions.
What are the most important environmental factors in
corpse decay?
Identify the name and origin of chemical released during
each stage of decomposition.
Why is it important to know what chemicals are produced
as the body proceeds through decomposition?
What are the 2 insect orders most commonly found on a
decaying corpse.
Describe the life cycle of the Insects found on a decaying
corpse. How does this life cycle help explain time of death.
Review Questions 10-15
 What is postmortem interval (PMI)?
 Time of death can be estimated up to about 36 hours
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using temperature and stiffness. Explain how
temperature and stiffness is used to estimate time of
death
Explain the difference between (PMI) and time of
death.
What is Accumulated Degree Days (ADD) and
Accumulated Degree Hour (ADH).
How is the (PMI) used to calculate (ADH or ADD)?
Provide an example?
Explain the proper techniques, equipment and
procedures required for collecting insects for use in
forensic investigations.