Forensic Entomology

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Forensic Entomology

• Maggots and Time of Death Estimation

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Entomology is the Study of Insects Images from
www.afpmb.org/military_entomology/usarmyento/files
/ArmyEntomology.ppt
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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

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What is Forensic Entomology?

• Forensic Entomology is the use of the insects and
  other arthropods that feed on decaying remains to
  aid legal investigations. 
• Medicolegal (criminal)
• Urban (criminal and civil)
• legal proceedings involving insects and related
  animals that affect manmade structures and other
  aspects of the human environment
• Stored product pests (civil) 

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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

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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
• 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.

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Forensic Entomology is Applied Biology

• If it werent 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
• 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.

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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 corpses
  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

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Image http//www.nlm.nih.gov/visibleproofs
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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
• Temperature
• Access by insects
• Depth of burial
• Other Factors
• Chemical-- embalming agent, insecticides, lime,
  etc.
• Animals disrupting the corpse

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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
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• Temperature Stiffness Time of Death

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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.
• Closed windows
• Body in box or bag
• Cold temperatures
• Deeper burial

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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 Flys 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.

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Image http//www.nlm.nih.gov/visibleproofs
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Calculating PMI from Accumulated Degree Hours
(ADH)
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Calculating ADH from Climate Data
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Using the Data

• 3928 ADH in these three days (95214881488).
• How many ADH of 70º are there in these 3 days?
• 3928/7056.11 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.

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Five Stages of Decomposition Fueled by Insect
Activity.

• Fresh
• Bloat
• Decay
• Post-decay
• Dry (skeletal)

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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.

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Bloat

• Swells due to gases produced by bacteria
• Temperature rise of the corpse
• Flies still present

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Decay

• Gases subside, 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 its original mass.

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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.

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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.

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Methods

• This project took place at the Huntington
  landfill beginning on September 5, 2003.
• Two different areas were chosen to deposit two
  pigs.
• Pig 1 was laid in a sunlit area.
• Pig 2 was laid in a shaded woodland area about
  100 feet away at an elevation of approximately 20
  feet.

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Methods

• Both pigs were placed in cages constructed of
  wood and one inch chicken wire that were staked
  to the ground to protect from predatory animals.
• Prior to starting the project, great care was
  taken to prevent insect activity from taking
  place. After they died, the pigs were
  individually tied in two black garbage bags,
  placed in feed sacks, and secured.

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Methods

• The pigs were kept at -80C in the laboratory.
• They were placed in plastic bins in order to thaw
  for 48 hours prior to placement at the landfill.
• Closed environment was maintained until they were
  deposited at the site.

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Methods

• Pigs with a genetic line of a minimum of fifty
  percent Yorkshire.
• They were 8-10 weeks old and weighed
  approximately 40-50 pounds.
• Both died on July 11, 2003 approximately 12 hours
  apart. One died a natural death and the other
  was culled from the litter.
• Both of the carcasses were in very similar
  condition there were no breaks, tears or cuts in
  the skin.

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Methods

• Daily observations were made at both sites
  throughout the day at 7am, 1pm, 7pm, and 1am.
• Air, ground, and maggot mass temperatures were
  taken at each visit and observations were
  recorded.
• At 7am and 7pm they also collected maggot samples
  for analysis and photographed the scene.
• Observations were noted and samples taken for a
  period of nine days.

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Methods

• Using insect tweezers, the investigators
  collected a number of maggots and dropped the
  samples immediately into boiling water, to kill
  the bacteria in the maggots and also to
  straighten their bodies for easier analysis.
• The maggot samples were taken from different
  areas of the body in which there were large
  numbers present.

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Methods

• The maggots were then placed into a labeled jar
  and preserved with 70 EtOH.
• They also collected interesting arthropods for
  analysis.
• All of the samples were labeled and stored for
  later analysis in the laboratory.

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Phormia regina
Spiracles are incomplete Third-instar larvae
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Phaenicia species
Spiracles are complete Third-instar larvae
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Results Fresh Stage

• Flies began to arrive within minutes of pig
  placement however, laying of eggs was delayed
  12-18 hours.
• There was already some green discoloration on Pig
  2 at the beginning of the fresh stage, possibly
  due to the fact that it was dead about 8 hrs
  before Pig 1.
• 72 hrs later, the first signs of bloating
  occurred, ending the Fresh Stage.

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Results Bloat stage

• At about 72 hours, noticeable bloating began to
  occur in Pig 1.
• However, Pig 2 did not show visible signs of
  bloating until about 92 hours.
• The gap between the two pigs might have been even
  greater if they had both died at exactly the same
  time.

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Results Decay Stage

• Decay stage started around 102 hours.
• At this point, the maggots had broken the skin
  and the pigs had begun to deflate.
• Decompositional fluids began to seep from the
  carcass.
• There was a green froth around the pig and also a
  dark fluid ring around the body of Pig 1.
• Maggot activity increased tremendously, and
  maggot mass temperature reached its high during
  this stage.

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Results Post-decay Stage

• When the experiment was terminated due to the
  fact that maggot activity had ceased, the pigs
  had reached the Post-Decay Stage.
• They were mostly skin, bones, and hair, but there
  was some tissue remaining.

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Temperature is a Factor Pig 1

• The graph shows an elevation for maggot mass
  temperatures over ambient
• The fluctuation in ambient temperature induced
  elevated maggot activity which is consistent with
  other similar experiments.

Sunlit Pig
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Temperature is a Factor Pig 2

• The ambient temperature for Pig 2 was more
  constant because it was in a shaded area.
• The temperatures for Pig 1 fluctuated more than
  those of Pig 2.

Shaded Pig
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Phormia Average Maggot Length vs. Time

• Shows a gradual increase then decrease for the
  Phormia regina
• The maggots feed and grow to a certain point when
  they begin to leave the carcass to find a safe
  place to pupate.

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Phaenicia Average Maggot Length vs. Time

• Two peaks for the Phaenicia
• Infers two generations for Pig 1.

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Two Different Maggot Generations

• These are distinguishable by the length and
  obvious size difference.
• This is why we believe there are two peaks in our
  graph data for the Sunlit Pig.
• The photograph was taken at a time consistent
  with the influx at 132 hours.

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Discussion

• Two different species of maggots were collected
  over the nine day period.
• These two species were analyzed at their third
  instar stages they were able to determine the
  difference by comparing their spiracles.
• The third instar was the only stage that they
  analyzed species determination was more evident
  at this stage of development.
• They also reared a sample of maggots from each
  pig for later species analysis.

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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.

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ADH and Pig Results

• ADH for Pig 1 was calculated as 4885.2 after nine
  days.
• ADH for Pig 2 was calculated as 4488.6 after nine
  days.
• These can be used to determine PMI for carcasses
  found in this area in similar conditions.

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The End