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Procedures
First, select an area to set up the specimens for daily observations.
The students should be able to access the specimens, handle them,
look at them under the microscopes or hand lenses, and perform
other experiments and procedures. One possibility is to have
an area where the specimens are stored when not being studied, and tables where the groups
can take them to do their activities with. Choose one of the following
for the activites. You may print them out:
- What
is an insect? Although the larva does not have the properties
of an insect, it is the adult stage that is used to classify
the animal.
- Pass out the Hypothesis/Conclusion sheet to each student. Discuss
with them the different stages in the insect's life. Draw the
cycle on the board. Questions for discussion:
- What do you think each stage uses for food? Consider how
they travel and shape of mandibles or feeding structure
- How does this effect humans?
- Would you consider the Corn Earworm a friend or fiend?
In the Hypothesis section of the sheet, write down your
thoughts on this question.
- Pass out the Duty Schedule and Specimen Development Charts to
each group. Go through the types of information they will have
to record on the Chart. Allow time for each group to fill in
the duty schedule.
- Use a thin paintbrush to pick up the newly hatched larvae and put
into cups with the diet. Try to put one per cup to avoid the
larvae from eating each other. The diet will be enough for
the duration of the larval
 stage.
The cup will fill with frass (excrement) by
the end of the stage. Each student group may want to have 10
to 20 cups. Label the cups with the date and number for documentation
purposes.
Use a new Specimen Development Chart for each cup.
- Explain that each day, the specimens will have to be monitored
and checked. The data must be recorded on the duty schedule.
The final data, for example length of the larva right before
pupating, should be recorded on the Chart. This will have the
maximum development
information on each specimen for the entire cycle.
The larva will go through five moltings (instars) before
pupating. Prior to pupating, they will shrink a little and
be more passive.
These two caterpillars are in the fourth instar stage of 19
days. Note the color variation.
- Rinse them off in
2% bleach, then rinse off in water again. You can sex the pupae
by holding them under a dissecting microscope or strong handlens
and looking for the markings as shown below.
- Place them in the jars
and hang strips of paper towel from the top to create a place
for the moths to go instead of being on the bottom where
they
could damage each other after emerging. For safety and logistical
purposes, 2-liter soda bottles work well. They are plastic
and
will not break. They have dimples as a base and the students
can put one pupa in each. They can also write the pupa number
and sex on the outside of the bottle so that they can keep
track of each pupa.
- Have the moth diet ready as shown below.
The solution is 1 part sugar, 9 parts water. Place
it in the jars or bottles with the pupae for the moths to
feed on after emerging. They will sip the liquid from the
wick using
their proboscis (a scanning electron microscope picture of
a butterfly proboscis).
** CAUTION When dealing with the moths,
be careful not to inhale the scales. This could cause problems
over a prolonged period. This can be avoided by keeping
the bottles covered, washing hands after handling the moths.**
If it is necessary to sex
the moths, hold them and gently squeeze the abdomen. The
females will have a brownish
small part pop out. The females are generally less active
and
have shorter, fatter abdomens than the males. They also
tend to be
darker.
The ideal temerature for the entire process is 80 to 85 degress.
At normal room temperautre, the process will take just a
couple more days.
- Questions for discussion:
- Is the Corn Earworm a friend or fiend? Consider emergence
rates and discuss how fast these insects can multiply.
- What are the benefits of this insect's presence?
- What are the drawbacks?
- How can we make useful use of this insect? Keep in mind that
we cannot have the moth without the larva.
To view pictures of students recording data, please click here
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