Overview & Lesson Sequence

Focus on Standards & Assessment

Materials Needed, Preparation & Planning, Management Strategies

Background Info

Intro Activity
Why Study Populations?

Meet the Aphids

Research Project
Aphid Population Growth

Data Analysis I

Data Analysis II

Optional Activity
The Power of Exponential Growth

References

Glossary

Suppliers

Resource Sheets

Great Gravidity Home

CISEO Home

Meet the Aphids

Materials Needed Per group:

• 3-4 eyelash brushes
• 1 Petri dish habitat (see Petri Dish Habitat instructions) or 1 bottle cap or jar lid for each student or student group
• distilled water, 1 gallon
• eye dropper
• host plant leaves, 1 for each dish
• scissors
• live adult aphids
• dissecting microscope or TriLens
• overhead transparency or photocopies of
• External and Internal Anatomy of
• Aphids diagrams

Class Time Required: approximately 45 minutes

In order to better understand population growth factors that students will be exploring in later activities, they need a background on aphid anatomy, behavior, and reproduction. Aphids are used because they grow and reproduce quickly. In this activity students will observe adult aphids and collect information on aphid biology. They will become familiar with techniques and materials used in subsequent activities.

Check Students' Prior Knowledge of Insects

Using the following prompts, conduct a discussion with students to find out what they already know about insects.

What are some outstanding characteristics of insects? (six legs, exoskeleton, antennae, compound eyes, metamorphosis, highly diverse group of organisms)

Where do insects live? (almost everywhere, even in snow)

What do insects eat? (plants and animals, living or dead; many are parasites, living in the bodies of other animals, including insects.)

How do insects affect crops? (chew plants, suck plant juices, carry plant pathogens)

How do they affect us? (biting pests, disease transmission, compete with us for food and fiber)

How are insects like other animals? (Like all living things they grow, reproduce, adapt and respond to their environment.)

If students have little or no prior knowledge of insects, you may want to conduct a lesson that provides this information. One idea would be for students to research various topics in reference books and on the Internet and share the information with the rest of the class. Specific topics could include insect reproduction, parthenogenesis, metamorphosis, and specific information about aphids including production of honeydew.

Observe live aphids
Distribute a bottle cap, a jar lid or a Petri dish habitat to each student to serve as an observation dish. A Petri dish habitat works better for longer observation periods because it provides a more favorable environment for both the aphid and the leaf. Have each student transfer one leaf and one adult aphid to their dish. Have all students individually observe aphids using hand lenses and/or dissecting microscopes, before returning aphids to the colony. Students should use journals to make drawings, notes, and write questions as they observe the insects.

Share Observations
Ask students to share their observations. Encourage them to give evidence for their answers. Be sure to have the overheads of the External and Internal Anatomy of Aphids on display and refer to them. Facilitate the discussion by asking the following:

What part of an aphid's anatomy indicates how it eats? Describe. (piercing and sucking mouth parts)

Where on the plant might aphids live? (underside of leaves, on the tender new growth)

How do they get from one place to another? (walk; some stages have wings and can fly from one plant to another)

Do aphids reproduce sexually, asexually or both? (both) Why would an organism be capable of both? (survival adaptation; asexual reproduction allows for rapid colonization of a plant; sexual reproduction ensures genetic diversity)

How might parthenogenesis affect their population growth rate? (Under favorable conditions, growth can be exponential"J" curve)

What type of metamorphosis do aphids have? (incompleteyoung insects are called "nymphs" and gradually get larger until they become adults; incomplete metamorphosis starts with an egg stage.)

What other biological or ecological factors might affect aphid population growth? (condition of hostplant, presence of predators or parasites, etc...)

Predict what would happen to the aphid population if

environmental conditions were highly favorable? (Population would grow rapidly.) What form of reproduction would the aphids use? (Mostly asexual reproduction) What form of reproduction would they use if conditions were not favorable? (Sexual reproduction to produce winged morphs that can fly to a hostplant in a better environment, or to produce eggs that survive the winter.)

Assessment
Over the course of this activity use the Observation Check sheet to record students' attainment of the learning objectives listed at the beginning of the lesson. Review students' journal entries to determine what level of conceptual understandings they are developing. Students should be able to make a generalized statement about advantages and disadvantages of sexual and asexual reproduction. They should also be able to begin describing the impact of various environmental factors (variables) on the rate of population growth.