Forensic Science Chapter 5: Entomology PDF

# Forensic Science Chapter 5: Entomology ## Forensic Entomology - Study of insects is called entomology and forensic entomology is the interpretation of insect evidence in civil or criminal investigations. - Insect has 3 body segments: Head, Thorax, Abdomen and a hard exoskeleton. - Analysis inclu...

# Forensic Science Chapter 5: Entomology ## Forensic Entomology - Study of insects is called entomology and forensic entomology is the interpretation of insect evidence in civil or criminal investigations. - Insect has 3 body segments: Head, Thorax, Abdomen and a hard exoskeleton. - Analysis includes how insect's presence and development is impacted by environmental factors such as location, temperature, humidity, amount of rainfall, and sunlight. - Insects can reveal lots of information including: - Postmortem Interval: Time between body was discovered and death - Time of year - Identification of a geographic range - Wound location - etc. - **Myiasis:** Parasitic infestation of blowfly and screwworm fly larvae in living people. ## History of Forensic Entomology - Bergeret D'Arbois observed **insect succession** (predictable and sequential pattern that different species of insects colonize and inhabit a decomposing organism). - Dr. David G Hall's book **Blowflies of North America** laid the groundwork for future forensic entomologists. - **Daubert Standard:** Rule used in courts to evaluate the admissibility and reliability of expert witness testimony. ## Science of Forensic Entomology: Insects and Decomposition - Most important factors for most organisms to survive: - Suitable temperatures - Correct amount of moisture - Suitable food source, etc. ## Decomposition - Decomposing body undergoes a series of predictable chemical and physical changes. - Allows habitat for organisms such as bacteria, fungi, blowflies, etc. - **Ex:** Adult blowfly lay their eggs on a recently deceased body and feed on the body fluids. - The larvae feed on the softer flesh. ## Regular Changes in a Decomposing Body - **Fresh:** Warm, newly dead body (0-3 days) - **Bloated:** Corpse emits odors of decaying flesh, lots of fluids is released and beetles begin to arrive (3-6 days). - **Putrification/Putrefaction:** Smell of rotting flesh in bloating stage. - **Active Decay:** Body emitting gases of decay with strong odors, darkened tissues - many insects present (6-11 days). - **Black Putrification:** When body turns black and skin liquifies, happens in active decay stage. - **Advanced Decay:** Organism starts to dry out, most flesh is gone (11-25 days). - **Dry or Skeletal Decay:** Mostly bones remain (25+ days). ## Blowflies (Bottle Flies): First In Succession - As bacteria start to decompose tissue, two gases called putrescine and cadaverine (odors) are released to alert blowflies to a location to lay eggs. - Adult flies use their proboscis to suck up protein rich fluids. - The female flies lay their eggs in clusters (about 50) usually in mouth, nose, ear, vagina, or anus, or injury. - Look like clustered white rice grains. - The moist tissue will provide the maggots of the fly food and moisture. ## Blowflies Undergo Complete Metamorphosis (Egg-Larva-Pupa-Adult) - **Rate of development varies on temperature; the warmer the faster the development.** - After depositing eggs, they release pheromones that attract other blowflies. - Eggs develop into larva which has 3 stages called instars (1st in about 1.8 days, 2nd in 2.5 days, 3rd in 4.5 days). - With each instar, the size increases. - Then prepupa (6-12 days) and then pupa (18-24 days) and then after 21-24 days, adult fly. ## Morphology of Blowflies: - Front/Anterior end of white larva is slender and tapered with 2 dark hooks that enable the larva to dig the flesh. - The Rear/Posterior end is more rounded and has 2 circular areas called spiracles - each spiracle has spiracle slits used for breathing. - 1st instar has 1, 2nd instar has 2, and so on. - This allows them to eat and breathe at the same time. ## Nutrition and Digestion in Larvae - The crop (food storing organ) in larvae is where tissue is temp stored and in the second instar, you can see the dark region of crop on the uppermost end of maggot. - During 3rd instar it dips away as the body fat hides it. - After 3rd instar, the crop no longer stores food. ## Larva to Adult - The outer covering is shed and a new cuticle is produced. - The larva moves away in search of a dry, dark area to pupate, and the thick cuticle hardens into a pupal case and changes from golden brown to dark brown color. - The Ptilinum (fluid filled structure in head of blowfly) inflates and breaks pupal case. ## Houseflies, Flesh Flies, and Coffin Flies - Houseflies are smaller and has a gray thorax with 4 dark longitudinal stripes. - Food sources for adults are sugar, sweat, blood, urine, and feces. - Can also be indicators of abuse due to the attraction of urine and feces. - Flesh flies are medium sized and have black/gray longitudinal stripes on thorax and checkerboard pattern on abdomen. - They deposit larvae onto flesh. - Coffin flies are about the size of fruit flies and are usually seen in a wrapped victim because they can fit through. ## Beetles and Other Insects of Decomposition - Have 2 sets of wings - 1st set is a shell like covering that protects body and 2nd set is used for flying. - Also have metamorphosis. - Grubs (beetle larvae) have 3 pairs of legs unlike fly larvae. - The Carrion Beetles arrive after flies to eat the fly larvae and then mate on the body. - The Beetles remove some of the flesh and bury it with their eggs for food supply when eggs develop into larvae. ## For Food Supply - Diff Preferences: - They follow a predictable path of insect succession on a decomposing body. - Clown beetle feeds on fly eggs and fly/beetle larvae. - Hide beetle feeds on dry remains of corpse. - Ants, Bees, Wasps, and Spiders can also feed on body, eggs, or larvae of the flies/beetles - delay the development for blowfly larvae and affect PMI. ## Characteristics of Forensic Entomology - Insects and Insect Larvae and Insect Succession can help forensic scientists estimate PMI. - At crime scenes, insects are preserved immediately to provide entomologist with examples of insect and life stages when body was discovered. - Second Collection of live insects is sent to forensic entomologist for identification. - Entomologist breeds and raises the insect to conditions similar to crime scene. - Time required for completion similar to crime scene is used to estimate PMI and documented. ## Insects and PMI Estimates - Blowflies are considered the timekeeper for PMI. - If blowfly eggs are present, and no larvae is present, PMI is usually less than 24 hrs. - If most of insects are in the third instar, calculations are made to determine how long it took using average daily temperature. - Sometimes bodies/skeletal remains are found months or years after the death. - Some insects are only active in summer or during spring or fall. - Scientists consider life cycle of each type of insect, their favored habitat, and food sources to estimate PMI. ## Factors Affecting Development - Forensic Entomologists must take consideration with environmental factors such as temperature, humidity, amount of rainfall. - **Oviposition:** Egg Laying - Doesn't happen at night, in rain, or if any other conditions aren't suitable. - Feeding maggot masses can have a temperature 5-20 degrees higher than surrounding temperature, which can speed up development. ## Other Questions Are: - Was it clothed, wrapped, frozen - leading to delays? - Was it buried? - Was it exposed to sun, shade, or wind? (affect when eggs are laid) ## Accumulated Degree Hours - In Estimating PMI, Scientists must consider the lower limit threshold (temperature below which growth, development, and egg laying cease). - Usually 50 degrees Fahrenheit/10 degrees Celsius. - Time Spent at a particular insect stage is expressed in **Degree Hours (DH).** - Found by multiplying the time by the temperature (in Celsius). - Sum of all DH required to adulthood is **Accumulated Degree Hours or ADH.** ## To Estimate PMI Using ADH: - Add Max and Min temp for 24 hour period and divide by 2 to get average temperature. - Subtract lower limit threshold (10 degrees Celsius or 50 degrees Fahrenheit) to get adjusted temperature. - Use (Adjusted temperature) in degrees Celsius x time in 24 hrs. - **Ex:** If body was found at 3PM, then the time is 15 hours. - **ADD:** Accumulated Degree Days. - Total amount of thermal energy received over a period of days. ## Processing a Crime Scene for Insect Evidence ## Insect Collection Procedures 1. **Death Scene Observations:** - Location of Crime Scene (general habitat and weather conditions) - Location of body in reference to vegetation (indoors/outdoors, sun or shade, wet or dry) - Body Condition (any wounds or injuries and state of decomposition) - Insect Observations 2. **Collection of Meteorological Data:** - Thermometers should not be exposed to light. - Ambient temperature should be taken at chest level, and maggot mass temperature should be taken at the center of the mass. - Max and Min daily temperatures from an accurate source. - Rainfall amounts for a period of one to two weeks before victim disappearance to 3 to 5 days after body was discovered. 3. **Collections:** - Collect adult insect first and place in killing jar - labeled and labeling should have geographic location, date and hour of location, where it was found, and name of collector. - **Larvae and Eggs:** - Search first for eggs after adult insects. - Search for largest and probably oldest larvae to ensure accurate PMI. - Collect about 50 maggots per mass including the most developed larvae and place them in killing jars with 75-80% ethyl alcohol. - **Pupal Cases: ** - Search pupal cases in dry areas such as victim hair, clothing, rugs, clothing pockets, and several feet away from body. - Empty pupal cases should be collected and intact ones should not be preserved. - Collect insects from surrounding soil. ## Analysis of Insect Evidence 1. Determine if insect evidence is consistent with insects normally found at the crime scene. - If insects are atypical, this indicates body was moved. 2. Provides evidence that victim was restrained based on house fly attraction to urine and feces. 3. Provides evidence of origin or route of drug trafficking. 4. Mainly provide evidence of PMI. ## Insect Identification - Today, **Polymerase Chain Reaction (PCR)** is used to amplify (copy) small amounts of insect DNA which then can be analyzed using faster and more reliable DNA methods. - DNA of crime scene larvae is compared to known insect species, which helps us find crime scene locations, if body moved after death, if body was buried, submerged, or exposed, or time of year. ## Victim Identification Based on Insect Evidence - **DNA analysis of the larva's crop can provide DNA evidence of victim.** - By macerating (softening the contents) the crop's contents, the ingested tissues and DNA can be analyzed using PCR, and DNA from victim bone can also be used for comparison. ## Determine Victim's Exposure to Drugs, Alcohol, or Toxins - Larval crop content analysis can reveal if victim was under influence of alcohol, drugs, or poisons using thin layer chromatography/gas chromatography and mass spectrometry. ## Quizlet Terms - **Necrophages:** Bugs that directly eat the corpse. - Flies and Beetles. - **Diptera:** Latin name for fly. - **Predator Bugs:** Burying Beetles, Rove Beetles and Hister Beetles. - **Coleoptera:** Latin Name for Beetle. ## How Eyeball Determine Time of Death: - **Eyes Open:** - Cornea dies within minutes. - Cloudiness less than 2 hrs. - **Eye collapses more than 24 hrs for both eyes.** - **Eyes Closed:** - Cornea dies within 2 hrs. - Cloudiness occurs within 12-24 hrs. - Closing Eyes slows PMI down. ## 4 Factors that can affect PMI: - **Weather** - Whether or not body was covered. - If other species kept bugs from coming. - Any poisons or drugs were in body to affect larvae. - **Temperatures:** - Body is warm + Not stiff = Not dead more than 3 hrs. - Body is warm + Stiff = Dead between 3 to 8 hours. - Body is cold + Stiff = Dead between 8 to 36 hours. - Body is cold + Not stiff = Dead more than 36 hours. ## 3 Main Branches of Forensic Entomology: - Medicological, Urban, Stored.