This activity is a discovery opportunity that may be used alone or as an introduction to "More About Goldenrod Galls", "Goldenrod Food Web Dynamics", or "A Study of Goldenrod Galls". In these follow-up activities, gall insects are classified, counted, and arranged into a food web, and discussion questions are quantitative.
TOPICS: Insects, classification, ecology
LEVEL: Middle and high school
TIME: 30-45 minutes. The discovery aspect of this activity can be completed in 15 minutes.
ADVANCE PREPARATION: Collect galls yourself, with the class, or have students collect galls as a homework assignment. Bring in 2 intact plants, one with and one without galls on stem, to introduce activity and use with question 4. You may wish, from January - April, to collect galls 3-4 weeks in advance and store in a jar at room temperature to allow adult insects to emerge. (This does not work in the autumn.)
MATERIALS:
If "More About Goldenrod Galls" is done, use 10 galls. DO NOT USE RAZOR BLADES for this activity. They break too easily. We suggest hand pruners. Those with a double edge cut into galls allowing students to safely break the gall open without cutting the animal inside. Cheaper alternatives include sturdy pocket knives or one-piece scalpels, which nonetheless can cause accidents unless used with gloves. See SAFETY NOTE below. DO NOT GIVE THE INSECT KEY TO STUDENTS until they have completed step B
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PREDICTIONS:
Encourage creative, logical, and critical thinking. Reasonable guesses for gall formation include small animal inside (worm or insect), plant response to injury (scarring), or infection by microorganisms
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SAFETY NOTE:
If knives are used. Galls are round and hard, and may cause the knife to slip aside suddenly. Practice opening the galls yourself, and then demonstrate proper techniques to students. We strongly encourage the use of hand pruners
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PROCEDURE:
If class will do an additional goldenrod gall activity, you may wish to omit Step C and defer questions 3 and 4 to save time.
QUESTIONS 3 and 4 require higher-order thinking skills. We recommend that you discuss these question with your class before having students write out their answers
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2.
A small animal (insect larva or pupa); common names will vary
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3.
Some insects die after galls are formed. Predators open some galls and eat the insects
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4.
Some goldenrod individuals are highly resistant to the ball gallmaker while others are very susceptible. Thus one can find almost the same pattern of attack within a field year after year even though the overall density will shift. Also, insect pests do not usually infest every available plant. The number of insects and the distribution of plants varies from year to year. These insects usually infest only one species of goldenrod (Solidago altissima), not all goldenrod species
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DO NOT GIVE THIS KEY TO STUDENTS UNTIL THEY HAVE COMPLETED STEP B.
A more complete key can be found in the "Goldenrod Food Web Dynamics" activity.
STEP 3b. The species name gigantea means "giant". However, the "giant" wasp larvae is actually the smaller of the two common wasp predators.
NOTE: A small mordellid beetle larva is sometimes found in the wall of a goldenrod gall. If it bores into gall chamber, it may eat the gall fly or wasp larva along with the goldenrod plant, leaving a pile of gray sawdust in an empty chamber.