PURPOSE:  To investigate the structure of a goldenrod plant and insect food web.

MATERIALS: 10 round goldenrod galls, paper towels, hand pruner or paring knife with glove, dissection needle, tweezers, hand lens, Key to Common Goldenrod Gall Insects.

INTRODUCTION:  When you look closely at goldenrod plants in fall or winter, you will see that some plants have enlarged areas on the stem called galls.  The enlarged area develops after an adult gall fly injects an egg into the growing tip of the stem.  The egg hatches into a larva, and may undergo metamorphosis in the gall to become a pupa.  The gall may also contain the larva or pupa of the giant wasp, obtuse wasp, or sometimes the mordellid beetle.  Some gall insects eat goldenrod gall tissue, and some eat other insects in the galls.

In this activity, you will identify and count gall insects.  You will use class data to draw a food web that shows how energy from the sun is transferred to the insects.

PROCEDURE:

A. Unfold and stack several paper towels to make a firm cutting surface.  With pruner partially cut through gall's equator, rotate gall about a quarter turn and cut again. The gall can usually be opened at this point without cutting the animal inside. If using a knife and gloves carefully insert the knife blade into the gall along its equator.  Twist the knife until the gall pops open.

B.  Use the key to identify the common name of each insect.  Record your data on your insect data sheet.

C.  Share your data with others in your class.  Record the class data on your insect data sheet.

D.  Use class data to list the different kinds of insects in the galls from least abundant to most abundant on your insect data sheet.

CONCLUSIONS:

1. The first link in a food chain or web is a producer.  A producer manufactures its own food by photosynthesis.  What is the producer organism in the goldenrod plant and insect food web?

2. The second link in a food chain or web is a primary consumer or herbivore.  A primary consumer is an organism that feeds upon producers.  The primary consumer is usually the most abundant animal species.  Use class data to decide what insect species is probably the primary consumer in the goldenrod food web.

3. Secondary consumers or carnivores are the highest links in a food chain or web.  Secondary consumers are usually less abundant than the primary consumers.  Use class data to decide what insect species are probably secondary consumers in the goldenrod food web.

DISCUSSION:

4. Use your answers to questions 1-3 to draw a possible goldenrod food web on your insect data sheet.

5. Some of the galls you observed may have been opened by a predator that eats insects in winter.  What kind of animal could this predator be?  Add this animal to your goldenrod food web diagram.

6. Your teacher will show you the actual goldenrod food web based on many population observations over many years.  How does the food web you constructed compare to actual food web?  If the food webs are different, give one possible reason why the class data on insect abundance might be different from the actual abundance of the insects.

7. What is the source of energy for the goldenrod plant?

8. What is the source of energy for the insects in the food web?

Name_________________________

GOLDENROD INSECT DATA SHEET

YOUR DATA:  In the spaces below, make a sketch of one of each kind of organism you find and identify.  Include its color and size (in millimeters).  Use tally marks ( //// ) to record the number of each kind you find.

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Gall fly               Obtuse wasp                 Giant wasp
larva or pupa          larva or pupa               larva or pupa







Color:                  Color:                     Color:
Size:                   Size:                      Size:
Number:                 Number:                    Number:

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Unknown #1              Unknown #2                 Empty

   






Color:                  Color:
Size:                   Size:
Number:                 Number:                    Number:

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CLASS DATA:  Record the total number of each kind of insect.

INSECT ABUNDANCE CHART:  Use class data to rank the insects from most abundant to least abundant.

Least Abundant:______________________________

               ______________________________

               ______________________________

               ______________________________

Most Abundant: ______________________________

POSSIBLE GOLDENROD FOOD WEB:  Do this step only after you answer questions 1-3.

KEY TO COMMON GOLDENROD GALL INSECTS

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1a. Long, narrow gall. . . . . Gall moth (Gnorimoschema gallaesolidaqinis);
                                              or one of its wasp predators

1b. Round gall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

2a. White or tan larva that moves when gently touched. . . . . . . . . . 3

2b. Brown pupa that does not move when touched . . . . . . . . . . . . . 4

3a. Large white larva (about 8mm long, 4mm wide) in a chamber with tunel .
                                            Gall fly (Eurosta solidaginis)

3b. Small white or tan larva (about 5mm long, 2mm wide) in chamber with  
                                NO tunnel."Giant" wasp (Eurytoma gigantea)

4a. Large brown pupa (about 8mm long, 4mm wide) in chamber with tunnel . .
                                            Gall fly (Eurosta solidaginis)

4b. Smaller brown pupa (about 7 mm long, 2 mm wide) in chamber with NO 
                        tunnel . . .  Obtuse wasp (Eurytoma obtusiventris)

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