ADI & Entomology Worksheet for forensic science students, focusing on estimating time of death using insect development stages and temperature data.

Let’s go step by step through each question on the worksheet. We’ll use the data from the table to answer everything.

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Question 1: Calculate how many hours are elapsed between egg laying and hatching for each stage. Fill in the table.

We’re given “Egg Laying” times (in days) and “Hatch” times (in days). To find hours, we multiply the difference in days by 24 (since 1 day = 24 hours).

- Stage 1: Egg laying = 0 days, Hatch = 3 days → 3 - 0 = 3 days → 3 × 24 = 72 hours
- Stage 2: Egg laying = 0 days, Hatch = 5 days → 5 - 0 = 5 days → 5 × 24 = 120 hours
- Stage 3: Egg laying = 0 days, Hatch = 6 days → 6 - 0 = 6 days → 6 × 24 = 144 hours
- Stage 4: Egg laying = 0 days, Hatch = 7 days → 7 - 0 = 7 days → 7 × 24 = 168 hours

Wait — looking at the table again, it says:

> Stage | Egg Laying | Temp. Range | Hours
> 1st | 0 days | 70°F | 72
> 2nd | 0 days | 80°F | 96
> 3rd | 0 days | 85°F | 120
> 4th | 0 days | 90°F | 144

Actually, the “Hours” column is already filled in! So maybe the task is just to verify or understand that these numbers come from multiplying days by 24? But since they’re already there, perhaps this part is done.

But let’s check Question 2 next — it refers to using the table to calculate hours until third instar.

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Question 2: Using Table 1 in the reference, calculate until it hits the third instar. _______ hours. Convert these hours to days. _______ days.

“Third instar” means Stage 3. From the table, Stage 3 takes 120 hours to hatch.

So:

→ Hours until third instar = 120 hours

Convert to days: 120 ÷ 24 = 5 days

✔ Answer: 120 hours, 5 days

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Question 3: If a maggot is beginning its second instar stage, how many more hours does it take to reach the third instar?

Second instar = Stage 2 → hatches at 96 hours
Third instar = Stage 3 → hatches at 120 hours

Difference: 120 - 96 = 24 hours

✔ Answer: 24 hours

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Question 4: Determine which factor would be most likely to affect the decomposition process.

Options: Environmental Conditions, Time Between Life Cycle Stages, Constant, Variable

Decomposition is affected by things like temperature, moisture, insects, etc. — all environmental factors.

Also, in forensic entomology, environmental conditions (like temp) directly affect how fast maggots grow.

So best answer: Environmental Conditions

✔ Answer: Environmental Conditions

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Question 5: Describe in your own words how life cycles can be used to estimate time of death.

When someone dies, flies lay eggs on the body. Those eggs turn into maggots, then pupae, then adult flies — each stage takes a certain amount of time depending on temperature.

By seeing what stage the maggots are in, and knowing how long each stage takes at that temperature, scientists can work backward to figure out when the eggs were laid — which is close to the time of death.

Example: If you see 3rd instar maggots, and you know they take 5 days to get there at 85°F, then the person probably died about 5 days ago.

✔ Answer: Life cycles help estimate time of death because each stage (egg → larva → pupa → adult) takes a predictable amount of time based on temperature. By identifying the current stage of insects on the body, experts can count backward to estimate when the insect first arrived — which is usually soon after death.

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Question 6: You need to consider that each species has a thermal summation threshold... Use the formula below to find the PMI (Post Mortem Interval)

Formula:
PMI = (Accumulated Degree Hours needed for development) ÷ (Average daily temperature – Threshold)

Given:
- Accumulated Degree Hours (ADH) needed = 500
- Average daily temperature = 80°F
- Threshold = 50°F

So:

PMI = 500 ÷ (80 - 50) = 500 ÷ 30 ≈ 16.67 days

But wait — ADH is usually in *hours*, so if 500 is in degree-hours, then PMI should be in *hours*? Let me check the context.

Looking back: “Use the formula below to find the PMI (Time of Death)”

And the formula uses “Accumulated Degree Hours”, so result will be in hours.

So:

PMI = 500 ÷ (80 - 50) = 500 ÷ 30 = 16.67 hours

That seems too short for a real case — but maybe it’s simplified.

Alternatively, sometimes ADH is given per day? No — standard is degree-hours.

Wait — in the table earlier, stages took 72, 96, 120, 144 hours — so yes, hours.

So 500 degree-hours ÷ 30 degrees = 16.67 hours.

But let’s double-check the math:

80 - 50 = 30
500 ÷ 30 = 16.666... → round to 16.7 hours

✔ Answer: Approximately 16.7 hours

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Question 7: Finally, we can do the ACCUMULATED DEGREE HOURS (ADH) calculation!

Table:

| Stage | Hours | Avg Temp (°F) | Min Temp (°F) | Degrees Over Min | ADH |
|-------------|-------|---------------|---------------|------------------|-----|
| Egg | 23 | 70 | 50 | 20 | ? |
| 1st Instar | 27 | 70 | 50 | 20 | ? |
| 2nd Instar | 22 | 70 | 50 | 20 | ? |
| 3rd Instar | 130 | 70 | 50 | 20 | ? |
| Prepupa | 118 | 70 | 50 | 20 | ? |
| Pupa | 264 | 70 | 50 | 20 | ? |

ADH for each stage = Hours × (Avg Temp - Min Temp)

Since min temp is always 50, and avg temp is always 70, then degrees over min = 20 for all.

So:

- Egg: 23 × 20 = 460
- 1st Instar: 27 × 20 = 540
- 2nd Instar: 22 × 20 = 440
- 3rd Instar: 130 × 20 = 2600
- Prepupa: 118 × 20 = 2360
- Pupa: 264 × 20 = 5280

Total ADH = sum of all = 460 + 540 + 440 + 2600 + 2360 + 5280

Let’s add step by step:

460 + 540 = 1000
1000 + 440 = 1440
1440 + 2600 = 4040
4040 + 2360 = 6400
6400 + 5280 = 11,680

✔ Total ADH = 11,680

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Question 8: So how was this technique developed? Give an example...

This method was developed by observing how insects develop on dead bodies under controlled temperatures. Scientists recorded how long each stage took at different temps, then created formulas to reverse-calculate time of death.

Example: In one famous case, a body was found with blowfly larvae. Experts knew that at 75°F, those larvae take 5 days to reach that stage. Since the average temp was 75°F, they estimated the person died 5 days before discovery.

Another example: If a body is found with pupae, and pupation takes 10 days at 80°F, but the weather was cooler (say 70°F), they adjust using degree-days to get accurate timing.

✔ Answer: This technique was developed by studying insect growth rates at different temperatures. For example, if a body is found with third-instar maggots, and scientists know that at 80°F it takes 5 days to reach that stage, they can estimate the person died about 5 days ago — adjusting for actual temperature using degree-hour calculations.

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Now, compiling final answers clearly:

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Final Answer:

2. 120 hours; 5 days
3. 24 hours
4. Environmental Conditions
5. Life cycles help estimate time of death because each stage (egg → larva → pupa → adult) takes a predictable amount of time based on temperature. By identifying the current stage of insects on the body, experts can count backward to estimate when the insect first arrived — which is usually soon after death.
6. 16.7 hours
7. ADH values: Egg=460, 1st=540, 2nd=440, 3rd=2600, Prepupa=2360, Pupa=5280; Total ADH = 11,680
8. This technique was developed by studying insect growth rates at different temperatures. For example, if a body is found with third-instar maggots, and scientists know that at 80°F it takes 5 days to reach that stage, they can estimate the person died about 5 days ago — adjusting for actual temperature using degree-hour calculations.