Forensic Entomology

Forensic entomology

“any aspect of the study of arthropod counterparts that interact with legal matters” (Hall, 1990)

What is the main type of estimate that forensic entomology can provide?

Post Mortem Interval (PMI)

Other than PMI, entomology can provide evidence about what?

• peri-mortem trauma

• child and elderly abuse

• movement of body (indoors vs. outdoors)

• extraneous drugs and toxins

• insect and victim DNA

Two key tasks at the scene regarding temperature and PMI estimation

1.) comprehensively recording scene temperature regimes

2.) comprehensively document other contextual and environmental factors that could affect insect development

Insects are exothermic (poikilotherms), which means what?

• cannot control temperature internally

• metabolic rates determined by ambient temperature

• rate of development will depend on temperature regime

• specific insect ecology and physiology

What entomology clues can be used to make a child and elderly abuse case?

• maggots/eggs in diapers and clothing indicating neglect

• time span without a diaper/clothing change can be estimated in the same manner as PMI

What entomological evidence can be used to support peri-mortem trauma?

Flies colonize exposed mucosa post-mortem (natural orifices), but the presence of maggot masses in other areas signal broken skin (i.e., trauma)

What is an example of how entomological evidence can be used to support the movement of a body after death?

Ex. body buried at an outdoor scene, but only colonized by indoor fly species (Musca domestica)

• indoors vs outdoor species

• rural vs urban species

• habitat distribution

Entomology and extraneous drugs and toxins?

• drugs detectable in maggots and cuticle of puparia even after millennia

• also detectable in development pattern of larvae

DNA of insect and victim?

• larval DNA matching population of specific location

• victim DNA identified from puparia

Subphylum: Chelicerata (MAP)

• Class Merostomata (horseshoe crabs, eurypterids)

• Class Arachnida (spiders, ticks, mites, scorpions)

• Class Pycnogonida (sea spiders)

Subphylum: Crustacea (5)

• Class Remipedia

• Class Cephalocarida

• Class Branchiopoda (fairy shrimp, water fleas, etc.)

• Class Maxillopoda (ostracods, copepods, barnacles)

• Class Malacostraca (isopods, amphipods, krill, crabs, shrimp, etc.)

Subphylum: Uniramia (ICD)

• Class Insecta (head+thorax+abdomen)

• Class Chilopoda (centipedes) (head+trunk)

• Class Diplopoda (millipedes) (head+trunk)

In Forensic Anth, our goal is not identifying insects, but to ______ insects

collect (using the outdoor scene data collection form, which has a section on entomological data)

Phylum Arthropoda

crustaceans, insects, spiders, and relatives

PMI Estimation: Main method based on physiological temperature

Combination of temperature data and insect physiology and development

T/F All insects/arthropods are equally useful for physiological temperature PMI

False; it depends on the reproductive/life cycle of the insect

What are the three types of insect life cycles?

1.) Ametabolous

2.) Hemimetabolous

3.) Holometabolous

Ametabolous

undifferentiated nymph, no maggot

Hemimetabolous

differentiated nymph, but no maggot

Holometabolous

maggots and puparia

Which insect life cycle is best for PMI estimation?

Holometabolous

Class Insecta: Subclass Apterygota examples

bristletails, snowflies, springtails, diplura, and anoplura: wingless insects!

(Insecta) Ametabolous development

little or no metamorphosis; the nymphs are small versions of the adults

→ Age estimates must be based on size: more variability and less precise

T/F Identifying insects is our goal

False; this is too difficult!

For Apterygota (wingless), age estimates must be based on size, but this leads to more _____ and less _____

variability; precision

Ptergyota

winged insects

What are the two divisions of Pterygota?

1.) Exopterygota

2.) Endopterygota

Exopterygota

wings form externally

(ex. earwigs, mayflies, true bugs, lice, dragonflies, grasshoppers, crickets, roaches, termites, praying mantises)

Exopterygota have _____ life cycles, which means they undergo ____ developmental stages

Hemimetabolous; 3

What are the 3 developmental stages of the hemimetabolous life cycle? (Exopterygota)

1.) Egg

2.) Nymph

3.) Adult

→ harder to estimate age because more variability in stage transition timing

Endopterigota

wings form internally

(beetles, two-winged flies, bees, wasps, and ants, butterflies and moths, scorpion flies, lacewings, fleas, stylopids, caddis flies)

What are the 4 Holometabolous developmental stages? (Endopterygota)

1.) Egg

2.) Larva

3.) Pupa

4.) Adult

The entomologist can calculate the age of an holometabolous larva in 2 main ways:

1.) Dissecting the pupa to check the stage of development of the different tissues

• during pupation, the larval tissues are basically “digested” and reorganized in almost completely new adult tissues

• the sequence of development of new tissues is very precise, and the times of development are very constant

• microscopic examination required

2.) Growing the insects at a constant temperature and then checking how long it took them to reach the next developmental stage

In any case, growth depends directly on _______, so this information is the main tool of the forensic entomologist to calculate PMI

temperature

Invertebrate animals, including insects and nematodes, require a certain amount of heat to develop from one point in their life cycles (instar) to another; this measure of accumulated heat is known as ________________ _____

physiological time

T/F The amount of heat required to complete a given organism’s development does not vary

True; the combination of temperature (between thresholds) and time will always be the same

Physiological time is often expressed and approximated in units called ___________

degree-days

Degree-days

the accumulated product of time and temperature between the developmental thresholds for each day

Minimum or lower developmental threshold

is the temperature below which insect development is negligible

Maximum or upper developmental threshold

is the temperature at which insect growth stops

PMI - from degree of development

time elapsed since egg deposition and corpse discovery

• larvae of the same age hatch and molt in synchrony

• to translate the developmental stage of the insect into real time elapsed we only need to calculate the number of degree-days elapsed during a certain amount of “regular” days (or hours)

Calculating degree-days

• the degree-days accumulated during a given day will be represented by the shadowed area

• there are different methods to estimate that area, the simplest one is by calculating DD (Base x) = ([HT-LT]/2) -x

• things are actually not that easy, and there are many more accurate methods, but basically they are just different ways of estimating the area between the thresholds

Another source of error is that, in reality, growth rate does not increase regularly with temperature, but it rather what?

decreases above an optimal temperature

T/F Specific models must be estimated for different species and populations

True

Do insects evolve fast?

Yes

• in forensic entomology, the local guy is the king of the hill

• cheap but high end

• optimal research niche

Calculating PMI from degree of development steps:

1.) Rear maggots/puparia at lab, at constant temperature, until adult eclosion

2.) Degree days elapsed at the scene (DDs) before recovery: Total DD required for development (DDt) minus DD elapsed at lab (DDL)

3.) Go back in time adding the degree days for that species accumulated the day before recovery, the previous day, etc., until they add to DDs

Longer-term estimates for PMI

• there is a natural succession of insects on a corpse, and a time and place that is best suited for each type of insect to feed on the corpse

• for example, one species may be best suited to feed on a freshly killed corpse and another species may be best suited to feed on corpse that has been dead for two weeks

• this succession of insects on the corpse also allows for us to estimate how long the individual has been dead, and also can serve to assess cadaver transportation

The dead body acts as an empty ecosystem to colonize, similar to a forest after a fire, but what is the first group of insects to arrive on the scene?

Calliphoridae

Calliphoridae

(ex. blowflies)

• usually metallic

• arista plumose at least 2/3 length

• 2-3 notopleural bristles

• they do not have mandibles, so they “lick” their food

• their larvae do not have mandibles, and after eclosion they feed on the body’s flesh

• they have to focus on natural or artificial orifices on the body, making them good indicators of wounds

A way of recording succession was introduced in 1992 by Schoenly et. al, called the _________ _____

Occurence Matrix

• a species, or stage (instar), is noted as being present or absent at a given time following death (PMI value)

• Species collected from the victim are compared to the occurrence matrix and the PMI values for which one would find that assemblage are identified

Factors that affect PMI

• individual species characteristics

• environment and context

• weather and season

• maggot mass

• body alterations

• clothing and accessibility to body

• drugs and other toxins

• insect colonization preceding death, etc.

• evidence documentation, recovery, and preservation

What to look for at the scene?

1.) General habitat

• dictates the insects that could be found on the body

2.) Local weather regime

3.) Body

4.) Vegetation

5.) Soil

6.) Placement of the body in context

• note exact placement of the body (map; which parts are in contact with the substrate; where it would be sunlight and shade during normal daylight cycles)

• note unusual manmade, scavenger-caused or naturally occurring alterations (trauma, mutilation, burning, covering, burial, movement, dismemberment)

7.) Insect activity

• note insect activity within 3-6m of the body

  • observe flying, resting or crawling insects, adults and larvae or pupae, within this proximity to the body

• note the immature stages of adult insects

  • eggs, larvae, pupae, empty pupal cases, cast larval skins, fecal material, exit holes, or feeding marks on the remains

8.) Temperatures

• essential to reduce the range of error of the PMI estimates

• remember that Fahrenheit and Celsius degrees are different

Recording temperatures

• Ambient temperature

  • Take readings at 0.3 to 1.3 m heights near the body

• Ground temperature

  • Laser, or place thermometer on the ground above surface ground cover

• Body surface temperatures

  • Laser, or place thermometer on skin surface

• Under-body surface temperature

  • Slide the thermometer between the body and ground surface or laser immediately after removing the body

HOBO pendants

• collects temperature and light intensity readings continuously, at time periods selected by the user (ex. every 30s or every 10 min, etc.)

• temperature data downloaded into a computer

• can also be left at scene spots for several days, in order to estimate precise temperature/light exposure regimes (waterproof and very durable)

• economical ($40-50 range)

Maggot mass temperature

• surface temperature with laser thermometer

• insert “meat” thermometer into center of maggot mass (do not stab body!)

Soil temperatures

• take immediately after body removal at a ground point, which was under the body before removal

• take also temperatures 1-2 m away from the body

  • under ground cover (grass, leaves, etc.)

  • at 4cm soil depth

  • at 20cm soil depth

Insect collection of adults!

• the first insects to collect are the adult flies and beetles from the body or from body surroundings

• adult flies can be trapped with an insect net

• adult beetles can be collected with forceps or gloved fingers

• adult insects can flee the scene very rapidly once disturbed

Insect collection of eggs and larvae!

• 50-60 should be collected form maggot mass

  • if more than one mass, note location of mass on label

• collect a wide range of sizes, but especially the larger ones

• separate by size ranges and photograph with scale

How to collect live larvae:

• place in a styrofoam cup with a tight fitting lid (poke small holes in the lid)

• place a food substrate and source of humidity, such as a moist paper towel, beef or pork liver in the container

• if to be stored for more than a couple hours, and to mail them, add a soil substrate (vermiculite) under the liver (make sure it is loose soil!)

• avoid extremely high or low temperatures

• mail overnight; can add a temperature/light recorder → HOBO

Why is a soil substrate important for live larval collection?

• when about to pupate, larvae become very active, searching for soil to bury themselves

• if not available, they can expend all their energy and die

• active larvae in this stage, or at high temperatures also use more oxygen

Are temperatures closer to the lower (colder) or higher (hot) threshold more harmful?

Hotter; cold just slows them down

½ cup of loose vermiculite or potting soil:

• allow larvae to bury themselves into the soil if they enter pupation stage

• provide moisture

• ½ cup or more helps the cups to stay vertical and more stable during transport (win-win)

Why must the cup stay vertical at all times?

you do not want to bury and suffocate the non-pupating larvae

Why add a small amount of small liver chunks to the cup?

• feed larvae and additional moisture

• not necessary for puparia

• RISK

  • large chunks of liver could suffocate larvae

  • liver will liquify fast at high temperatures, and due to larval activity, potentially drowning larvae

  • soil absorption helps prevent drowning, if you didn’t add too much

  • check liver and change out with fresh one every 2-3 hours at hot scenes, as well as immediately upon arrival at the lab and before mailing it

Use as many cups as necessary!

• should not be overcrowded

• separate containers for separate maggot masses or locations

Why add perforated lid and scotch tape to secure cup tightly?

• larvae are Houdini-level escapists

• perforations not larger than pin-size

What should be on your cup label?

• geographical location (city, county, state)

• date and hour of collection

• case number

• location on the body from which the specimen was removed

• name of the collector

Transporting/mailing larvae cup:

• drinks cooler (better for scene and transport)

• mailing styrofoam box kit

• 1.) place freshened or newly prepared cups

  • secure them to stay vertical and stationary with packing filling material or cup holders

  • make sure not blocking lid holes and leaving enough room/air for the insects to breathe

• 2.) add single, medium-sized dry ice pack

  • the goal is preventing the larvae from getting too hot, not freezing them

• 3.) Place isolating material between cups and ice-pack

  • if ice pack touches the cup, it can cause local freezing

  • thick styrofoam sheet, empty cardboard box or similar

• 4.) activate and place HOBO reader

  • constant temperature tracking every few seconds

  • light sensor registers whether box is open (chain of custody)

• 5.) Drive to entomologist or box and overnight mail immediately

Dead larvae and adults

• adult insects and larvae can be placed in 70% ethyl alcohol (rubbing alcohol)

  • any higher than 80% makes specimens brittle for dissection and microscopic examination

  • less than a 65-70% concentration can cause the specimens to rot

  • adults can also be placed alive in plastic or glass vials and refrigerated (a cooler with ice will work); but you will have to put them in alcohol to mail them