3Insect BiologyInsects are the most diverse and abundant forms of life on earth.There are over a million described species- more than 2/3 of all known organismsThere is more total biomass of insects than of humans. of humans.Insects undergo either incomplete or complete metamorphosis (Egg to larva to pupa to insect)Larva have a soft tubular body and look like worms. Fly species larvae are “maggots”
4What is Forensic Entomology? Forensic Entomology is the use of the insects and other arthropods that feed on decaying remains to aid legal investigations. Medicolegal (criminal)Urban (criminal and civil)“legal proceedings involving insects and related animals that affect manmade structures and other aspects of the human environment”Stored product pests (civil)
5Medicolegal Forensic Entomology Often focuses on violent crimesDetermination of the time (postmortem interval or PMI) or site of human death based on identification of arthropods collected from or near corpses.Cases involving possible sudden deathTraffic accidents with no immediately obvious causePossible criminal misuse of insects
6Postmortem interval (PMI) Forensic Entomology is used to determine time since death (the time between death and corpse discovery)This is called postmortem interval or PMI).Other uses includemovement of the corpsemanner and cause of deathassociation of suspects with the death scenedetection of toxins, drugs, or even the DNA of the victim through analysis of insect larvae.
7Forensic Entomology is Applied Biology If it weren’t for decomposition of all living things, our world would fill up with dead bodies.When an animal dies, female insects will be attracted to the body. They enter exposed orifices or wounds and lay eggs or larvae.A forensic entomologist:identifies the immature insectsdetermines the size and development of the insectscalculates the growth of the insects and passage through stages of the life cycle in laboratorycompares the growth against weather conditions to estimate time of oviposition
8Succession of Insects on the Corpse Estimates of postmortem intervals based on insects present on the remains are based on:The time required for a given species to reach a particular stage of development.Comparisons of all insect species present on the remains at the time of examination.Ecological succession occurs as an unexploited habitat (like a corpse) is invaded by a series of different organisms.The first invasion is by insect species which will alter the habitat in some form by their activities. These changes make the habitat attractive to a second wave of organisms which, in turn, alter the habitat for use by yet another organisms.
9Ecology of Decomposition Necrophages - the first species feeding on corpse tissue. Includes rue flies (Diptera) and beetles (Coleoptera).Omnivores - species such as ants, wasps, and some beetles that feed on both the corpse and associated maggots. Large populations of ominvores may slow the rate of corpse’s decomposition by reducing populations of necrophagous species.Parasites and Predators - beetles, true flies and wasps that parasitize immature flies.Incidentals – pill bugs, spiders, mites, centipedes that use the corpse as an extension of their normal habitat
11Decay Rates Are Variable Studies of decay rates of 150 human corpses at in the Anthropological Facility in Tennessee (The Body Farm)Most important environment factors in corpse decay:TemperatureAccess by insectsDepth of burialOther FactorsChemical-- embalming agent, insecticides, lime, etc.Animals disrupting the corpse
12Time of Death can be broadly estimated up to about 36 hours Temperature Stiffness Time of deathWarm Not stiff Dead lessthan three hoursWarm Stiff Dead between 3to 8 hoursCold Stiff Dead between 8to 36 hoursCold Not stiff Dead in morethan 36 hours
13Differentiate between PMI and Time of Death These may not always equate.Post mortem interval is restricted to the time that the corpse or body has been exposed to an environment which would allow insect activity to begin.Closed windowsBody in box or bagCold temperaturesDeeper burial
14Insect species arrive at a corpse in waves like clockwork Calculate the heat/thermal energy (accumulated degree hour) required for each stage of the Green Bottle Fly’s life cycle.Possibly the greatest potential source of error in using arthropod successional patterns lies in the collection of speciments.Must only be done correctly to accurately sample the insects.
18Using the Data 3928 ADH in these three days (952+1488+1488). How many ADH of 70º are there in these 3 days?3928/70=56.11 hours72 hours at 70º would have the insects passing to the 3rd instar. But 72 hours at colder temperatures and insects will only be at 2nd instar stage.
19Five Stages of Decomposition Fueled by Insect Activity. FreshBloatDecayPost-decayDry (skeletal)
20Fresh Begins at death Flies begin to arrive Temperature falls to that of the ambient temperature.Autolysis, the degradation of complex protein and carbohydrate molecules, occurs.Gasses produced by the metabolic activities of the anaerobic bacteria first cause a slight inflation of the abdomen. The carcass may later assume a fully inflated, balloon-like appearance. Adult and larval blowflies in large numbers attracted to fluids seeping from body, normal soil dwelling fauna depart soil because of seepage of fluids; some muscid flies and ants which can feed on larvae and retard maggot activity.
21Bloat Swells due to gases produced by bacteria Temperature rise of the corpseFlies still present
22Decay Gases subside, decomposition fluids seep from body. Bacteria and maggots break through the skin.Large maggot masses and extreme amounts of fluid.Unpleasant odorLarvae beginning to pupate.Corpse reduced to about 20% of it’s original mass.Decay Stage - Black Putrefaction (Days 5-11) -- Decay stage begins when the abdominal wall is broken, allowing gasses to escape and carcass deflates. This process is facilitated by feeding activities of larval flies present on the exposed remains. Adult flies start to leave body, mainly larval mass. Carcass begins to assume a blackened, wet appearance, and most of the flesh will be removed by the maggots. Toward end of this period, carcass will begin to dry and beetles feed on drier tissue. Flies start to pupate. Predatory beetles such as rove beetles and histerids come to feed on other insects.
23Post-Decay Carcass reduced to hair, skin, and bones. Fly population reduced and replaced by other arthropods.Hide beetles are dominant in dry environments.Mite and predatory beetle populations increase.Postdecay Stage - Butyric fermentation (Days 10-25) -- In dry habitats, remains consisted of dry skin, cartilage and bones. Site for dermestid beetles, histerids, fly pupae, immature and adult rove beetles. In wet habitats, a large quantity of wet, viscous material, termed byproducts of decomposition, was found in the soil under the remains. Site for immature and adult moth flies, sphaerocerid and muscid flies, rove beetles.
24Dry (Skeletal)Does not always occur especially if corpse is in a wet region. Maggots will stay longer and hide beetles will not appear.In wet environments the hide beetles are replaced with nabid and reduviid insects.The corpse is reduced to at least ten percent of the original mass.In the last stage (Skeletal Stage), only bone and hair remain.Dry Stage (Days 25 +) -- This stage is reached when mainly bones and hair remain. Odor is primarily that of normal soil and litter. Some dermestid beetles, histerids, fly pupae, immature and adult rove beetles, normal soil fauna (mites) start to return. Can last several months to even years.
25Accumulated Degree Hours ADH may be calculated using temperature and hours.This works because there is direct correlation between temperature and maggot development.These calculations were somewhat approximate but relatively accurate.
27Review Questions 1-9 What is Forensic Entomology? Explain 5 applications/uses of insects in forensic science.Describe the stages of death: Algor Mortis; Livor Mortis; Rigor Mortis.Describe the stages of decompositions.What are the most important environmental factors in corpse decay?Identify the name and origin of chemical released during each stage of decomposition.Why is it important to know what chemicals are produced as the body proceeds through decomposition?What are the 2 insect orders most commonly found on a decaying corpse.Describe the life cycle of the Insects found on a decaying corpse. How does this life cycle help explain time of death.
28Review Questions 10-15 What is postmortem interval (PMI)? Time of death can be estimated up to about 36 hours using temperature and stiffness. Explain how temperature and stiffness is used to estimate time of deathExplain the difference between (PMI) and time of death.What is Accumulated Degree Days (ADD) and Accumulated Degree Hour (ADH).How is the (PMI) used to calculate (ADH or ADD)? Provide an example?Explain the proper techniques, equipment and procedures required for collecting insects for use in forensic investigations.