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Unformatted text preview: Forensic Entomology Establishing a Time of Death
Dr. Wayne Rowley Department of Entomology Iowa State University Forensic Entomology has a focus on violent death. Medicolegal Entomology has been suggested by some as an alternative to Forensic Entomology Deals with insects and related arthropods that interact with legal matters. When did Death Occur? PMI (Postmortem Interval) Forensic Entomology is about establishing the time period that a body has been exposed to insect (arthropod) activity. Establishing a PMI is based on knowing that colonization of a corpse follows a predictable succession of arthropod species As decomposition progresses Different species are present Different developmental stages
are present Knowing the rate at which various stages develop allows us to estimate the manner of death if the body was moved from one
site to another the length of the postmortem interval Forensic Entomologist must have a knowledge of: Medical Entomology Insect Taxonomy Insect Classification Fruit Fly life cycle studies used as models for determining how developmental stages of an insect relate to time. The ability to accurately identify arthropods (species and their developmental stages) is fundamental to forensic entomology. Two groups of insects are important in the decay process
Flies Beetles There are a number of Blow Fly species that colonize a corpse. The most common species in Iowa is the Black Blow Fly, Phormia Regina Accurate identification establishes the foundation on which all subsequent inferences are based. Blow Flies similar to this one are metallic colored: Black-Bottle Fly Black Blow Fly Bronze-Bottle Fly Green-Bottle Fly Life Cycle of a typical fly eggs larvae puparia adults Minutes after death volatile chemicals are emitted that attract flies that lay eggs in clusters or masses. Independent fly eggs are small several flies can lay thousands of eggs in
a short time Time from laying to hatching is : Species Specific temperature dependant Flies lay eggs in natural and artificial openings on the body. Most Fly larvae go through 4 developmental stages 1st stage 2nd stage 3rd stage prepupal stage Maggots (fly larvae) on a corpse can reach tremendous numbers Fly larvae develop in semi-liquid tissue and are the first insects on a corpse Maggots cause a dramatic consumption of the corpse tissue Fully developed larvae (prepupae)
Leave corpse Burrow into soil pupate Adult flies emerge form pupal case mature larvae (prepupae) leave body to pupate Accumulations of adult flies near the corpse are a clue to PMI Beetles arrive after the corpse has dried out to some extent Dermestid Rove Beetle http://www.happydranch.com/rove.html Clerid Beetle Scarab Beetle http://www.junglewalk.com/info/Beetle-information.asp Silphids Things to Remember
Development time is: species dependant temperature dependant colonization involves indigenous species Time Frame for Colonization Volatile Chemicals Eggs Laid Eggs Hatch 1st Instar Larvae 2nd Instar Larvae 3rd Instar Larvae (2 Phases) active feeding stage wandering stage Pupae Eggs are laid in natural and artificial openings in the body
Egg 1st Instar Larvae 2nd Instar Larvae 3rd Instar Larvae (feeding) 3rd Instar Larvae (wandering) Pupae Development
(hours) 15-25 22-26 11-22 20-96 80-112 6-14 From Kamal (1958) Total time required for development (egg to adult) for most of Kamal's flies was 10-27 days. Habitats vary considerably From Catts & Haskell, 1960 ...
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This note was uploaded on 03/27/2008 for the course CHEM 540 taught by Professor Thiel during the Spring '08 term at Iowa State.
- Spring '08