Blowfly Introduction The blow fly lays its eggs on dead animals to provide food for its carnivorous larvae as they hatch. This means that in nature, the life cycle of the blow fly is part of the decomposition process of dead bodies. The study of this phenomenon by entomologists has lead to our ability to estimate the time since death by examining which stage of growth blow fly is in when found on the cadaver. The forensic entomologist conducts examinations at crime scenes and examines the insect evidence found there to bring evidence to court cases involving human cadavers. To make a determination, the scientist makes visual observations, collects insect evidence, determines the stages of development, and calculates the time of initial deposit of the blow fly eggs on the cadaver. In the laboratory the scientist rears collected specimens to confirm the species and more accurately establish the stage of growth. They then compile their findings and make a “best guess estimate” as to how long the cadaver has been dead. www.nlm.nih.gov/visibleproofs Blow Fly Life Cycle Credit: Cleveland Museum of Natural History www.nlm.nih.gov/visibleproofs Entomology Worksheet Student Name: Date: 1. What kind of information is provided on the Blow Fly Life Cycle handout? 2. Calculate the heat/thermal energy (accumulated degree hour) required for each stage of the Green Bottle Fly’s life cycle. Table 1: ADH of the Green Bottle Fly From Egg To First instar Temperature 70° F 70° F 70° F 70° F 70° F ADH (accumulated degree hour) 70 X 23 = 1610 ADH Hours 23 27 22 130 143 3. Using the above Table 1 as the reference, calculate and fill in the blank areas. a. How many hours does it take for a green bottle fly egg to become an adult fly? hours Convert these hours to days and hours b. For a maggot at the beginning of the second instar stage, how may hours does it take to reach the third instar if the ambient temperature is at 77° F? hours c. If you are rearing a Green Bottle Fly pupa, at what temperature do you need to keep the pupa to have the adult fly merge in about 7 days? F d. Determine whether each of the following is a constant or a variable in the experiment: Table 2: Constants and Variables Constant Variable Life cycle stages Temperature Time between the life cycle stages ADH 4. Describe in your own words how insect life cycles can be used in estimating the time of death. www.nlm.nih.gov/visibleproofs Climatological Data, Sylvia Hunt case, 1986 Credit: Courtesy of William L. Krinsky, M.D., Ph.D. www.nlm.nih.gov/visibleproofs Climatological Data, Sylvia Hunt case, 1986 Credit: Courtesy of William L. Krinsky, M.D., Ph.D. www.nlm.nih.gov/visibleproofs Entomology Case Worksheet Name: Date 1. What task was Dr. Krinsky asked to help with in the 1986 murder case? 2. What types of evidence and information did Dr. Krinsky gather? 3. What kind of observations did Dr. Krinsky make about the collected insect evidence? 4. How did Dr. Krinsky process the blow fly puparia collected from the carpet on September 22, 1986? Why? 5. What are some factors (variables) that affect the insect life cycle? 6. Describe in your own words how insect life cycle is applied in estimating the time of death. www.nlm.nih.gov/visibleproofs Student Worksheet: Climatological Data & ADH Calculation Name Date Review the “Preliminary Local Climatological Data” from WSO Bridgeport CT and review the following questions: 1. Review the data sheet and list three top categories of information that may affect entomological factors? 2. Review the wind and precipitation data. Would these two factors affect entomological behaviors highly, moderately, or not much? Explain your analysis. 3. Complete the following table based on the climatological data sheet and the fact that Dr. Krinsky started to rare some collected specimen at 5 PM on September 22*: Table 1: ADH calculation for period between September 7-22, 1986 Date (September) 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 Average Temperature 56° F 62° F 62° F 65° F 58° F Hours 17* 24 24 24 Daily ambient thermal energy 952 1488 1488 1560 ADH (accumulated degree hour) 952 2440 3928 www.nlm.nih.gov/visibleproofs 4. Dr. Krinsky used various entomological references in calculating the ADH to count back to the earliest possible time of ovipostion by adult black blow fly. One of the references used states that at a constant 80° F, it takes between 10-12 days from the oviposition to emergence of the adult fly. a. Calculate the ADH at constant 80° F and fill in row A in Table 2 below. b. Calculate the thermal heat provided at Dr. Krinsky’s laboratory for the 25 flies emerged at 4 PM on September 27. Fill in row B in Table 2. c. Subtract B from A and record them on row C. d. Use the values from row C and Table 1 above to identify corresponding dates in row D. Table 2: Calculations 10 days Row A Life cycle duration ADH value at 80° F B ADH from Laboratory' C subtract B from A (remaining ADH value) approximate date of the oviposition based on Table 1 D 11 days 12 days 5. When do you estimate the earliest possible date when the first adult blow flies deposited eggs on the victim’s body? www.nlm.nih.gov/visibleproofs
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