Forensics- Entomology
Explain the 2 methods to determine PMI
1. Using maggots age and developmental stage -used within a month of death, 3 larval stages -analyses the oldest insect on corpse (not full grown, latest from pupae) 2. Using successional waves of insects -used after a month of death to a year or more -body changes due to decomposition, different stages attract different species
What are the 2 main anatomy features of an insect?
Cuticle layer- exoskeleton, resistant to degradation Spiracle- breathing holes, easy to identify an adult, larvae have patterns of spiracles
Explain the Blow Fly Life cycle (if temp at 70F)
Egg(23hrs)->1st instar larva (27hrs)->2nd instar larva (22hrs)-> 3rd instar larva (130hrs)-> Pupa (143hrs)-> adult fly
What are the 7 Classifications?
Kingdom, Phylum, Class, Order, Family, Genus, Species
Explain succession
The order fo different species arrived at the corpse, either too feed off of another species or lay eggs
What is Entomology and when is it used?
Using insect evidence to solve crimes, mainly 'when' but can also answer Where, where and who
List some limitations of Entomology
Weather effect, misidentification, predatory species (wasps/ants) can carry off eggs
What are the 5 stages of corpse decay
1.Fresh- during TOD, body cold to ambient air/soil temp, blow fly eggs hatch (12-18hrs) 2.Bloated- Intestinal bacteria putrefies the body, internal temp=53C, house flies arrive, more predatory species, pH of soil (alkaline) 3.Decay Active- maggots break through skin, body deflates as gas escapes, increase of necrophages (feed on body), and predatory beetles (feed on larva), temp falls, only 20% corpse remains (skin, cartilage, bone) 4.Post Decay- Dry-Larva gone, hide beetles most numerous, predatory (rove and hipster) beetles,# of mites increased (feed of algae and fungi) Wet- 3rd instar larva (blow fly and flesh fly) no hide or hipster beetles, moth flies exploit 5.Skeletal- 10% of corpse left (bones and hair)
Case Studies- Black Bear Cubs
100km north of Winnipeg, in July 3 dead black bear cubs found near a garbage dump Shot in the neck, disembowled, gall bladders removed (can be used for medicine) Result: killed for profit Blow fly eggs and adult blow flies, were the only insects remaining on body's Egg development helped determine TOD DNA linked poacher to cubs, both sentenced to 3 months jail, Judge though Entomologist evidence was most compelling
Explain how to collect evidence such as eggs, maggots, soil and pupae
Eggs- paint brush or forceps, half preserved in 75%ethanol, 50%isopropanol, other half kept damp and given food (sent to a lab and grown) Maggots- temp of maggot mass determined, size noted, half preserved (same solution),other half kept alive Soil-Berlese funnel Pupae- labeled (dark or tan), collect newly emerged flies
Why is the cuticle so important?
Hard insect exoskeleton, its extremely resistant to decay
When could Entomology be used in cases involving Drugs?
If a poison is involved, or if the victim was using drugs
Case study- Bugs clear convicted murder
Steven Truscott, 14, 1958, accused of murdering a childhood friend, Lynn Sentenced to die in Canada but decided he was too young, served 10years, released on parole Truscott was last person to see Lynn alive, body found 2 days later raped andmurdered Pathologist placed TOD at 7:15-7:45pm based on stomach food contents (unreliable) Years later(2007), entomologists looked at reports and pictures to conclude TOD was much later when Steven had an alibi Maggots were too small to backup previous statement (after entomologist procedure had developed) 48 years after original conviction, Truscott was freed, court reversed conviction but could not state him as innocent because not enough witnesses from original crime scene
