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Activities: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10
Activity Three
An Insect Life Cycle
Objectives
Students will observe the development
of a common insect (Drosophila melanogaster) through all of its
life stages and compare it to the life cycle of beetles (Galerucella
sp.) and other common insects.Mealworms (Tenebrio sp.) may
be substituted because their life cycle is more similar to that of
Galerucella sp.)
Methods
Students will trap adult fruit flies
and describe the development from egg to adult, comparing it to that
of beetles. In doing so, they will learn standard methods for handling
fruit flies and develop a colony for later study of population growth.
Students may also raise mealworms (Tenebrio sp., available from
many pet shops and easily grown in bran meal) to compare the life cycle
with that of Galerucella sp. Allow approximately 20 minutes,
two days per week for four weeks.
Background
In order to understand interactions between
Purple Loosestrife and Galerucella sp. It is necessary for students
to become acquainted with its life cycle and development. Fruit flies
and mealworms provide model populations that have a shorter life cycle
and are much easier to obtain and maintain. In the process it will also
be easier for students to understand the concept of exponential growth
and limiting factors.
Materials
Two or three baby food jars or wide mouthed
glass vials per group, small piece of ripe banana, cotton batting and
cheesecloth for stoppers, hand lense or stereo microscope.
Procedure
Have students label the vials or jars
with their name and date and place a 1" section of a ripe banana
in the bottom. Insert a small strip of index card or heavy paper into
the banana for adults to rest on and pupae to be attached. Place outside
in a shaded location for 1-2 days, or until adult fruit flies are seen
inside the vials. Stopper with a cotton ball wrapped in cheesecloth
and place the vial in a warm shaded location of the classroom. Approximately
every other day, allow students time to observe the development of eggs
and larvae using a hand lense or stereo microscope.
These may be removed for study with a cotton swab
or wooden splint. Students should make careful drawings of all stages
seen together with written descriptions of changes and behavior. When
adults appear, some may be transferred into another vial and inactivated
for study by placing the vial in an ice bath until chilled to inactivity.
As time progresses present pictures of the life cycles of other insects,
including beetles and Galerucella sp. Proper terminology should
be taught at this time.
Extensions
Depending on the season, it may be possible
to observe some of the stages of development of Galerucella sp.
on Purple loosestrife plants or of other insects on other host plants.
A record of the population size of the fruit flies may also be kept.
It will be necessary to transfer colonies to new medium if the old medium
becomes moldy. If photographic or video equipment is available, students
may document the stages of development with still or video pictures
and present the results to the class.In addition to or at the same time
as the above investigation, students may set up and observe a colony
of the common mealworm (Tenebrio sp.). These may be obtained
from most pet shops and easily maintained in plastic or glass containers
of bran cereal. These are much larger than Drosophila sp. and
may be handled with forceps and viewed with a magnifying glass or stereo
microscope.
Evaluation
The following factors may be taken into account in evaluation of student
progress:
- Lab book with drawings and observations is evaluated
as project goes on.
- Grade will be based on accuracy of drawings,
number and quality of written observations.
- Students should be observed as the project proceeds
and graded on the basis of technique, involvement, cooperation and
interaction with group members.
- Students may be quizzed on the details and terminology
of insect development as information is presented.
- Groups may be graded on the quality of a presentation
such as a poster, multimedia presentation, or video.
Activities: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10
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