Forensic Entomology

• What is Entomology?

  Forensic Entomology is where this study can help give insight into legal investigations through the examinations and analysis of insect material.
• Entomology: Origins

  -Association between decomposing bodies and insects a well-known topic since antiquity

  Modern Forensic Entomology:

  -The Scientific method

  -Against Spontaneous generation:

  Francesco Redi in 16th  century (maggots from eggs)

  -Development of technology (e.g. microscope) at end of 16th century
• Disciplines

  Forensic Entomology: Knowledge of insects to legal

  cases, in both civil and criminal law

  Funerary archaeoentomology: Knowledge of insects  to studies of archaeological human remains
• Divided into 3 main areas:

  URBAN ENTOMOLOGY (human environment):

  •Pest infestations in buildings, gardens

  •Basis of legal dispute between private parties & service providers

  •Most appropriate pesticide treatments

  STORED-PRODUCT ENTOMOLOGY:

  •Infestation or contamination of commercially distributed foods

  •Prevention, detection & eradication of contamination

  MEDICO-LEGAL OR MEDICO-CRIMINAL ENTOMOLOGY
• What do they do?

  -analysis of the pattern of corpse colonization by successive “waves” of Arthropods (Insects)

  -determination of the life stage of insects, usually flies, collected in, on, or near the body.

  1.Collect samples.

  2.Collect environmental data (ADD).

  3.Process/rear samples.

  4.Identification species.

  5.Draw conclusions based information collected
• Why do we need to know?

  -Estimating mPMI in death investigations

  -Body transfer or previous  concealment

  -Confirm ‘cadaver presence’

  -DNA

  -Detect drugs or poisons (Extomotoxicology)
• Biological classification -> Taxonomy

  Kingdom

    Phylum

    Class

    Order

    Family

    Tribe

    Genus

    Species
• Classification / Taxonomy: INSECTS

  Kingdom - Animalia

  Phylum – Arthropoda (insects, arachnids, myriapods, and   crustaceans)

  Class – Insecta

  Sub-class Pterygota Apterygota

  Exopterygota Endopterygota Archaeognatha      Zygentoma
• Exopterygota

  Mayflies

  Grasshoppers

  Dragon/Damsel flies

  Cockroaches

  True bugs - bedbug

  Mantids
• Endopterygota

  Lepidoptera

  Ants

  Wasps

  Bees

  Diptera

  Coleoptera
• How to differentiate: Dichotomous keys

  •A dichotomous key is a series of questions or statements that lead to an identification of a object/species/place etc.

  •Statements tend to be in pairs (couplets) and are labelled a and b. Each pair is labelled successively so the reader goes down the list. No one item can fall into both categories and they must be accurate.

  •There should be one less numbered step than the total number of objects to be identified.
• Insects and decomposition

  -Decomposition influenced by the insects, which visit and colonise the body

  -Decomposition process: removal and alteration of body’s soft tissue and e.g. bone, hair - *Over 72 hours , less medical information available with which to correlate the PMI

  -Forensic entomology for PMI uses Taxonomy, ecology, morphology, physiology

  -Postmortem artifacts by insects – AM injuries
• PMI- Cadaver succession

  • Insects visit corpses either to eat or to lay eggs.
  • Different insects like different environments and thus arrive at different stages of decomposition.
  • Insects can vastly speed up the rate of putrefaction.
  • Insects visit corpses in a particular successive series. They are predictable and thus can be used to estimate PMI
• PMI- Cadaver succession

  •We know about succession from observations and studies carried out on other animal carcasses e.g. pigs

  •Succession can be affected by a number of things – weather, climate, ground condition, time of day.

  •Distance is not a big issue they will go a long way ~7km for a corpse.

  
• What are the types of invertebrates feeding on a corpse?

  • Necrophages: first species feeding on corpse, blowflies, hide beetles, clown beetles
  • Omnivores: ants, wasps, some beetles that feed on corpse and maggots
  • Predators or necrophagous: rove beetles, ground beetles, wasps
  • Incidentals: hoverflies, spiders, mites
• PMI- Cadaver succession-insects attract to the body

  • Fresh:

  •Calliphoridae, Muscidae

  • Bloated:

  •Calliphoridae, Sarcophagidae, Phoridae, Histeridae, Silphidae

  • Decay:

  •Staphylinidae, Histeridae, Silphidae, Piophilidae

  • Dry:

  •Dermestidae, Trogidae
• Life cycles

  •Insects undergo either incomplete or complete metamorphosis (complete from Egg to larva to pupa to insect)

  •Larva have a soft tubular body and look like worms.  Fly species larvae are called “maggots”

  
• Blow fly – life cycle

  Larva Stages 1 - Within 23 hours

  Larva 2 - After 2 ½ days

  Larva Stage 3 - After 4-5 days

  Pupa- After 18-24 days

  Adult- After 21-24 days

  Soon after Death—blowfly eggs can be found in the moist, warm areas of a corpse < 8 hrs
• Identifying species: Summary

  -Identification of species is fundamental because development,  phenology, distribution and ecology are specific to single species  or groups of species

  •Population specific

  •Species specific

  •Temperature specific
• Identifying species: Summary

  -Social interaction and food availability → biology and behaviour of species

  -Insects show strong seasonality (active only on specific periods)

  -Insects also have an environmental preference

  Insect development has a temperature range – optimum

  This follows a linear trend with a positive correlation between temperature and developmental rate
• Identifying species: Summary

  -Intrinsic condition of a body (i.e. size, cause of death presence of wounds) also affect colonization

  -Accessibility of a body produces first selection on the colonising  species

  -E.g. Exposed bodies are commonly colonised by Calliphoridae (blowflies) whereas they don’t tend to colonise buried bodies

  
• PMI and Entomology

  What needs to be known?

  • Species
  • Stage of development for the specific species
  • Standards for development timings

  (assumption that eggs were laid soon after death)

  • Temperature history
• Life cycle – Developmental stages and Temperature

  • Data exists for the development at different temperature

  , however this only gives an indication unless you know they were at that specific temperature the whole time.

  
• Life cycle – Temperature fluctuations

  • Insects are ‘cold blooded -> As the temperature increases, the eggs hatch at a faster rate.
  • There is an optimum temperature (Development Threshold Temperature, DTT); outside this threshold development stops.
  • lower temp slows and halts development, and very high temp denatures and kills.

  
• Definitions of key terms

  • temperature threshold below which growth and development will not take place the base temperature or Effective Temperature (EF)*
  • Insects use a proportion of the environmental energy (thermal units) to grow and develop -> These

  thermal units are called DEGREE DAYS (DD)

  • DD can be added together to reflect periods of development. In this case, they are called ACCUMULATED DEGREE DAYS (ADD)
  • If the period is shorter and the length of time being discussed is in hours, then the thermal values will be as accumulated degree hours (ADH).
• • the temperature threshold below which growth and development will not take place the basal temperature or ET:

  - Calculated for specific species in laboratories

  
• Calculate DEGREE DAYS (DD)

  • Insects use a proportion of the environmental energy (thermal units) to grow and develop. These thermal units are called DEGREE DAYS (DD)
  • Degree days work on the assumption that temperature and time are linked.

  1 ˚ C for 1 hour = 1 degree hour

  1 ˚ C for 1 day = 1 degree day

  5 ˚ C for 3 hours = 3 ˚ C for 5 hours = 15-degree hours
• Accumulated Degree data

  • Between the upper and lower thresholds, the rate of growth of the insect is linear in relation to temperature increase.
  • Physiological energy budget is represented as a rectangle of time in relation to temperature.

  
• Thermal history to know T° at crime scene

  •Data collected from weather stations.

  •Data collected at scene (at time of body recovery and after)

  •Temperature of the corpse

  Caution:

  -sun effect

  -discrepancies between site and weather station

  -thermal properties of e.g. clothing

  -thermal properties of the cadaver/pre-mortem condition

  -maggot mass
• Influences

  Maggot mass

  • As few as 25 larvae have discernible effects on temperature

  • Temperatures as high as 20˚C higher than ambient are possible

  • Temperature not uniform; higher in centre

  • larvae may rotate within the mass

  • Can undermine process of PMI estimation

  • May be impossible to discern maggot mass occurrence –and its effect on the microclimate- after larval stage is complete

  • Other insects attracted by the maggot mass
• Other Influences

  • Drugs – Entomotoxicology
  • Data from the insects can be used to test for drugs.
• Factors affecting decomposition speed &  composition of cadaver feeding fauna

  Preferred areas are natural (eyes, nose, mouth…) or unnatural (wounds): MANNER/CAUSE OF DEATH