Question

Describe one design flaw type (not an error source,) its effect on the reliance of the data, and how you would redesign the experiment to deal with this flaw.

Experimental design

In this experiment, we will study the effects of the quantity of food provided to

tobacco hornworm larvae on their ingestion, assimilation, and excretion. We will have

two treatments (food with and without added fiber), and each student will maintain one

larva feeding upon one of the two diets.

You may want to collaborate with another student in your group in the

maintenance of your caterpillars; however, you are entirely welcome to do all

measurements on your own caterpillar. Should you choose to share the responsibility

of caterpillar maintenance and data collection, be sure you and your lab partner know

how to contact each other in case something will prevent one of you from performing

these actions in a timely fashion. Neglecting caterpillars will mean the pooled class

data are compromised; in addition, without regular cleaning, the food provided easily

molds and the mold overtakes and kills the caterpillars.

Procedure: setup (Day 0)

1. Each student does one setup, which each consists of:

• One disposable plastic container with lid

• One tobacco hornworm larvae

• Hornworm diet of the appropriate type (plain (control) or fiber added)

• Small plastic weigh boat (tared weight on bottom)

• Filter paper (or paper towels)

2. Moisten a small square of paper (3cm x 3cm) (it should not be dripping, just

moist) and place it in the bottom corner of the plastic container.

3. Punch small holes in the lid of your container to allow some air exchange. Do not

make these holes too big; we want to keep the moisture and the larvae in!!

4. Mass out 2.5 g of caterpillar food. Place this bolus on a small plastic weigh boat.

Place the boat in a corner of the container over the paper. Record this as

the initial mass of food provided.

5. Mass your larva and add it to the container. Record this mass in the data table.

6. Mark the container with your name (include your partner’s name if you’re sharing

responsibilities), instructor’s name and the diet type (plain, fiber added) on

a piece of tape.

7. Conditions during the study: tobacco hornworm larvae will grow and pupate

quickly with light at about 27°C. We’re keeping them at room temperature

(~ 22°C) which will slow their development; limiting light will slow them

further. Unless the larvae grow so fast they’re pupating during the

Bioenergetics of caterpillars 3

experiment, we will leave them in the light. (*** tell your instructor if you

have any larvae that pupate ***)

8. Place the containers on the counter in the lab with the rest of the class’

containers. Check at least every day to be sure the food has not been

used up. Follow the instructions below for what to do over the duration of

the experiment.

Procedure: maintenance for the duration of the experiment

1. Check your larvae regularly; if possible, checking every day will ensure the filter

paper does not dry out entirely and the larvae do not run out of food.

2. On the designated days (see table below), do the following:

• remove all the fecal pellets. Look for any that appear grey with black

pieces. This represents molted skin which has been ingested and

egested. Remove this and save for later. Mass the fecal pellets

together; record this mass

• Mass the egested molt and add it to the mass of the worm going forward

from this point.

• mass any uneaten food, record this value, and discard the old food

• rinse out the container and dry it if it is dirty or if any mold has developed

• replace the filter paper with new, moistened filter paper

• on the designated feeding days, mass out more food (the amount will

probably have to be adjusted as they grow and eat more; give them

what you think they will eat in a day, until your next visit) and provide

this to the larvae. Be sure to record the mass of the food added.

• mass your larva and record the value in the data table below

Procedure: break down experiment (see table below for date)

1. Collect the fecal pellets, mass them, and record the value.

2. Mass your larva and record this mass. Put this datum into the table below.

3. Mass any remaining (unconsumed) food and record this value.

4. Clean up: put the larva into the container provided for this purpose. Throw away

any remaining uneaten food. Wash out each container and set it out to dry.

Clean up any remaining materials from the lab, if any.

Answer 1