Forensic Science Unit 12 Notes

Entomotoxicologists who study blowflies and other flies have found that cocaine causes a(n) _____ in _____ size whereas methamphetamine causes a(n) _____ in _____ size.

increase, larva, decrease, pupa

Use the table above to organize the selected insects in the order their populations would first peak at a corpse from first to last.

1. Blowflies 2. Carrion beetles 3. Rove beetles 4. Dermestid beetles

Put the lifecycle stages of insect metamorphosis in order:

1. Egg 2. Larva 3. Pupa 4. Adult fly

For a maggot at the beginning of the third instar stage, how many hours does it take to reach the Pupa stage if the ambient temperature is at 77 ℉?

118 hours

How many days does it take to get from egg to adult fly at 70 degrees F?

14

After calculating how many hours it takes for a green bottle fly egg to become an adult fly, convert the hours to days and hours.

14 days, 9 hours

How much faster did the third instar reach pupa by increasing the temperature by 7 degrees?

14 hours

How long does it take to get from a hatching larva to cocooned pupa at 70 degrees F?

179 hours

Which of the following cannot be determined from insect analysis?

All of these can be determined from insect analysis.

Which of the following is not a complicating factor that affects the rate of development of larvae on a body?

Cause of death

The age of the youngest insects on the body determines the minimum PMI.

False

The insects of greatest value to forensic entomology are dermestid beetles (family Dermestidae), because they are usually the first insects to colonize a body after death, often within hours.

False

The life cycles of insects are predictable in that they happen in the same steps and in the same time frame without regard to temperature.

False

A dog was found dead by strangulation Monday morning at 8:00 a.m. behind a warehouse. The owner was contacted. He said the dog was at home and fine until it escaped Saturday afternoon around 4:00 p.m. when his wife opened the door. Investigators collected adult flies, first instar larvae, and second instar larvae, but no pupae. Would you consider the owner a suspect in the dog's strangulation death? Why or why not? Provide evidence with your explanation.

From the time the dog reportedly escaped to the time the dog was found was approximately 40 hours. If the first flies that arrived laid eggs immediately, there would only be adult flies, eggs, and first instars on the body. First instars take about 23 hours to develop, but it would take another 27 hours for second instars to form. That's a total of 50 hours. The dog has only been "missing" for 40 hours. Something is fishy.

Which stage can be broken down into first, second, and third instar stages?

Larva

A body is found, and investigators collect first instar larvae, eggs, and adult flies but no other stages in larval development or pupae. How long do you estimate that the body has been dead?

One day to a day and a half

A body is found in a field, and insect evidence is collected including adult flies, first, second, and third instar larvae, and pupae. However, none of the pupae have been ruptured. All are intact and carrying developing flies. How long has the body been in the field?

Over a week but less than two weeks

ADH is based on_____.

Time and temperature

Constant

Time between life cycle stages at 70 degrees F Life cycle stages

How many hours does it take for a green bottle fly egg to become an adult fly?

345

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 five days?

83 degrees F

Variable

ADH Temperature

One morning, a body was found off a running path by a jogger. The body was in active decay, but there were only adult insects flying around and no visible maggots. Why is this scenario unlikely and how can it be explained?

Active decay begins after two to three days, and insect egg laying is only within a few hours. The body was likely stored in a sealed container for a few days and dumped that morning.

The Anthropological Research Facility is located at _____.

University of Tennessee

Describe in your own words how insect life cycles can be used in estimating the time of death.

When a crime scene involves a dead body, it is sometimes accompanied by insect evidence including flies and beetles and their larvae, eggs, and pupae. Because these insects have a relatively defined life cycle depending on the weather, it is possible to calculate the postmortem interval by looking at the various stages of colonization of insects on or within the body. This is a fairly accurate method because insects tend to colonize the corpse from minutes to mere hours after death.

A Forensic Entomologist is called to a crime scene where a body is found with maggots covering it. The Entomologist takes samples of many of the maggots found and then turns to the Forensic Investigator and says "I can say with certainty that the time of death is about 4:00pm 4 days ago." 1) Why is he incorrect? 2) What would have been a more appropriate response? 3) What analysis should be performed in order to determine an estimated postmortem interval?

You should recognize that there are many factors that affect the decomposition of a corpse and it is impossible to know the exact time with certainty. However, a close approximation can be made with a little more investigation. First the maggots would need to be taken back to the lab to determine which type of fly laid the eggs. It would also be necessary to determine the temperature of the body and the ambient temperature over the past several days. Different types of flies will help to narrow down the estimated time of death. Insects, eggs, larvae, and pupae can be found on the body but also in the folds of clothing or in the soil or carpet beneath the body. Insects initially colonize orifices like the mouth and eyes as well as any wounds on the body. 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.