To enhance student motivation, do "What's Inside Goldenrod Galls" prior to this activity.

TOPICS:  Insects, classification, ecology

LEVEL:  High school and advanced placement

TIME:  15 min for prediction discussion; 45 min for field work which may be done as homework; 45 min for lab work.

ADVANCE PREPARATION:  Collect 2 intact goldenrod plants, one with and one without a gall, and several galls to open for the class.  Show them to your class while discussing predictions.  You may wish to collect galls 3-4 weeks in advance and store in a jar at room temperature to allow adult insects to emerge. (This only works from January - April, not in the fall.) .

MATERIALS: DO NOT USE RAZOR BLADES for this activity.  They break too easily.  We suggest double-edged hand pruners. These cut into galls allowing students to safely break the gall open without cutting the animal inside, or a finger. Cheaper alternatives include sturdy pocket knives or one-piece scalpels used with a glove  See SAFETY NOTE below .

PREDICTIONS: In class discussion, encourage creative, logical, and critical thinking.  We recommend that you introduce the following ideas if they are not suggested by students:  Insect biomass (and usually numbers) must be less than that of the plants.  Some plants are not parasitized and most plants have only one gall.  The final number of predators must be less than the original number of parasites, since each predator must eat a parasite to live and some parasites are not eaten .

STEPS A to E may be done as a homework assignment .

STEP C: You may wish to discuss how to accomplish step C with your class prior to data collection.  One way is to collect all the goldenrod stems in the circle in the plastic bag, empty the bag in a clear area outside the circle, and then count and record the stems with and without galls .

SAFETY NOTE: If a knife is 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 recommend the use of hand pruners.

QUESTIONS 7-11 require higher-order thinking

skills.  We recommend that you discuss these questions with your class before having students write out their answers .

2. Goldenrod plant .

3. Gall fly larvae are herbivores and are usually the most abundant insect in galls .

4. Obtuse wasp and giant wasp larvae are predators that consume gall fly larvae.  Obtuse wasps are usually more abundant than giant wasps.  Mordellid beetles, if found, eat the goldenrod plant tissue and may also consume gall fly or wasp larvae as well .

5. Answers will vary; accept all that do not contradict the data.  Many webs might fit the limited data available to the class.  (See answer to question 8) .

6-7. Answers will vary; accept all that do not contradict the data .

8. Solid lines are typical class results.  Dotted lines are shown in the event that mordellid beetles are found

Chance (random variation) can make small population samples appear different from actual population sizes.  (As an example, if you choose one human family at random, the sex ratio of boys to girls may be very different from the l:l ratio of the general population).  Also, each predator (gall wasp) represents one eaten prey insect (gall fly).  Increasing the fly abundance data to include the larvae eaten by wasp predators may explain some differences.  For example, if a student counted 4 gall fly larvae and 6 wasps, the original number of gall fly larvae in the population was 10. .

9. Reasonable answers include:  If parasitism rate is high, then weakened plants may die or have reduced reproductive rates.  If parasitism rate is low, plant population reproductive rate is probably unaffected.  Available evidence suggests that insect parasites have little effect on plant growth, but may reduce seed production and vegetative propagation of most plants. .

10. Reasonable answers include:  If predation rate is high, then local insect population may decline.  The effect would depend on the ability of insects from other areas to reinvade the region.  If vertebrate predation rate is low, insect population size will depend on goldenrod population size and other external factors, like weather .

11. Actual winter predators may be birds (woodpeckers, chickadees, nuthatches) or small mamals (mice, squirrels).  Methods include direct observation, videotaping methods, deductions from scratch or teeth marks, trapping methods, stomach content analyses of suspected species, and so on.

This key is designed to identify the last occupant of the gall, even if the insect is missing.  Note that mordellid beetles are ordinarily rare.

STEP 4b.  The species name gigantea means "giant".  However, the "giant" wasp larvae is actually the smaller of the two common wasp predators.