Forensic Entomology Larvae Using the developmental stages of insects to determine TOD Pupae Eggs Adult Adult
Forensic Entomology The study of insects in relation to a criminal investigation. Insects arrive at a decomposing body in a particular order and then complete their life cycle based on the surrounding temperature. By collecting and studying the types of insects found on a body, a forensic entomologist can predict the time of death. “When one biological clock stops, others begin.” --Neal Haskell, reknown forensic entomologist
Stages of Decomposition • Initial Decay-Although body shortly after death appears fresh from outside-bacteria in body’s intestine before death begin to digest intestine itself. • Autolysis-bacteria exit intestine and digest internal organs. The body's own digestive enzymes spread throughout body • Enzymes inside cells-released when cell dies-break down cell and connections with other cells • Flies are immediately attracted to dead bodies Without normal defense of living animal- blowflies and house flies lay eggs around wounds and body openings • Eggs hatch and move into body within 24 hours. Life cycle of a fly from egg to maggot to fly-2-3e weeks
Stages of Decomposition 2. Putrefaction-4-10 days after death • Putrefaction-destruction of soft tissues by of micro-organisms-results in catabolism of tissue into gases and liquids • First visible sign-formation of sulfhaemoglobin in settled blood. • Releasing fluids into body cavities-anaerobic respiration - produce hydrogen sulphide, methane, cadaverine, putrescine, butyric and propionic fatty acids • Distention of gut-Gas build up from multiplying bacteria-internal pressure-inflates body and forces fluids from cells and blood vessels into body cavity • Rate of decay increases-blowflies, flesh flies, beetles and mites • Late-arriving insects-predators-feed on maggots and flesh -Maggot masses
Stages of Decomposition 3. Black Putrefaction-11-20 days after death • Bloated body collapses-creamy flesh-exposed parts are black in color and very strong smell of decay. • Body fluids drain from body and seep into soil • Insects consume most of the flesh and body temperature increases with activity. • Bacterial decay important-bacteria consume body if insects are excluded • Several generations of maggots-migrate from body and bury in soil to pupate • Predatory maggots are much more abundant • Pioneer flies cease to be attracted to corpse. • Predatory beetles lay their eggs in the corpse and their larvae then hatch out and feed on flesh
Butyric Fermentation • 20-50 days after death • Dessication of corpse-remaining flesh is removed and butyric acid released • The surface of body in contact with ground becomes covered with mold as body ferments. • Beetle larva and adults feed on skin and ligaments. • Predators and parasitic wasps and beetles
Dry Decay • 50-365 days after death • Body is dry and decays slowly-Eventually leaving only skeleton • Diagenesis-process that changes skeleton’s proportions of organic (collagen) and inorganic components (hydroxyapatite, calcium, magnesium)
PMI--Postmortem Interval PMI-amount of time b/w TOD and body’s discovery Estimation of PMI- set minimal and maximal PMI Minimal PMI -determined by estimating age of developing immature insects collected when corpse is discovered Maximum PMI-determined from species of insects present and weather conditions needed for the activity of these species
Temperature Ambient heat plays a role during egg and early larval development but after that its effect decreases rapidly. Maggot masses generate their own heat. Taking temperature of the maggot mass can find it as high as 125 degrees F.
Forensic Entomology Larvae Using developmental stages of insects to determine TOD Pupae Eggs Adult Adult
Forensic Entomology • The study of insects in relation to a criminal investigation • Insects arrive at decomposing body in a sequence and complete their life cycle based on surrounding temperature • Forensic entomologist can predict the time of death
Metamorphosis Complete metamorphosis (holometabolous) -development from egg to larva to pupa to adult The white crust in the picture are the fly eggs.
Larva Larva hatch from the eggs and increase in size by growth steps called instars. Larva migrate from corpse and develop into an inactive pupal stage During this time, the adult insect develops internally. Two larval instars.
The Blowfly • Acts as both necrophages and as predator • One of the most common species on dead bodies • Often arrive within 10 minutes • Feed on blood and lays eggs in body cavities • If food source is exhausted- will prey on other species in same genus (Chrysomya)
Maggots (fly larvae) are remarkable eating machines • Posterior spiracles • Spiracles are used for breathing-posterior spiracles-means that maggots can breath & feed 24 hrs a day
First instar Third Instar Second instar
Types of Insect Collections Collection are done in three ways: • Aerial • Hand • Live Sampling
Aerial Collection • Use a net in figure 8 motion over cadaver • Collect flies and put them in ethyl acetate • After a few seconds-put flies into 75% ethyl alcohol-label date, time, case #, location, sample type and collector.
Live Sampling“Maggot Motels” • Collect 10 to 15 live maggots of varying sizes into a rearing chamber • Allow to develop into pupae and then into adults.
Hand Collection • Collect maggots with forceps • Put in boiling water to stretch them out and fix them • Put maggots into ethanol with a label containing date, time, case #, location and collector