3Forensic EntomologyUsing the developmental stages of insects to determine TODLarvaePupaeEggsAdultAdult
4Forensic EntomologyThe 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
6Determining the Time of Death (TOD) Using Forensic Entomology
7Stages 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 bodyEnzymes inside cells-released when cell dies-break down cell and connections with other cellsFlies are immediately attracted to dead bodies Without normal defense of living animal- blowflies and house flies lay eggs around wounds and body openingsEggs hatch and move into body within 24 hours. Life cycle of a fly from egg to maggot to fly-2-3e weeks
8Stages of Decomposition 2. Putrefaction-4-10 days after deathPutrefaction-destruction of soft tissues by of micro-organisms-results in catabolism of tissue into gases and liquidsFirst 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 acidsDistention of gut-Gas build up from multiplying bacteria-internal pressure-inflates body and forces fluids from cells and blood vessels into body cavityRate of decay increases-blowflies, flesh flies, beetles and mitesLate-arriving insects-predators-feed on maggots and flesh -Maggot masses
13Stages of Decomposition 3. Black Putrefaction days after deathBloated body collapses-creamy flesh-exposed parts are black in color and very strong smell of decay.Body fluids drain from body and seep into soilInsects consume most of the flesh and body temperature increases with activity.Bacterial decay important-bacteria consume body if insects are excludedSeveral generations of maggots-migrate from body and bury in soil to pupatePredatory maggots are much more abundantPioneer 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
19Butyric Fermentation 20-50 days after death Dessication of corpse-remaining flesh is removed and butyric acid releasedThe 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
22Dry Decay 50-365 days after death Body is dry and decays slowly-Eventually leaving only skeletonDiagenesis-process that changes skeleton’s proportions of organic (collagen) and inorganic components (hydroxyapatite, calcium, magnesium)
26PMI--Postmortem Interval PMI-amount of time b/w TOD and body’s discoveryEstimation of PMI- set minimal and maximal PMIMinimal PMI -determined by estimating age of developing immature insects collected when corpse is discoveredMaximum PMI-determined from species of insects present and weather conditions needed for the activity of these species
27TemperatureAmbient 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.
28Forensic EntomologyUsing developmental stages of insects to determine TODLarvaePupaeEggsAdultAdult
29Forensic EntomologyThe study of insects in relation to a criminal investigationInsects arrive at decomposing body in a sequence and complete their life cycle based on surrounding temperatureForensic entomologist can predict the time of death
31MetamorphosisComplete metamorphosis (holometabolous) -development from egg to larva to pupa to adultThe white crust in the picture are the fly eggs.
32LarvaLarva hatch from the eggs and increase in size by growth steps called instars.Larva migrate from corpse and develop into an inactive pupal stageDuring this time, the adult insect develops internally.Two larval instars.
33The Blowfly Acts as both necrophages and as predator One of the most common species on dead bodiesOften arrive within 10 minutesFeed on blood and lays eggs in body cavitiesIf food source is exhausted- will prey on other species in same genus (Chrysomya)
43Types of Insect Collections Collection are done in three ways:AerialHandLive Sampling
44Aerial Collection Use a net in figure 8 motion over cadaver Collect flies and put them in ethyl acetateAfter a few seconds-put flies into 75% ethyl alcohol-label date, time, case #, location, sample type and collector.
45Live Sampling “Maggot Motels” Collect 10 to 15 live maggots of varying sizes into a rearing chamberAllow to develop into pupae and then into adults.
46Hand Collection Collect maggots with forceps Put in boiling water to stretch them out and fix themPut maggots into ethanol with a label containing date, time, case #, location and collector