Parasites and Goldenrod Galls Teacher Instructions

Goldenrod is parasitized by a range of insects. Many of these insects (such as the goldenrod gall fly) lay an egg in the stem of the plant. The plant responds to the invasion by walling off the affected area, creating a ‘gall’. The insect larvae is protected by this gall, and feeds and over winters in the goldenrod stem. In spring, if the larvae has avoided predation by birds (primarily chickadee), it emerges. Many students presume that the gall contains seeds or normal plant material.

Materials:  POE sheet for each student (or pair)  goldenrod stems for each student or group of students-(one stem with a gall and one stem without galls)  sharp scissors and/or scalpel to open the gall, tweezers and clean dissecting trays  hand lenses and dissecting microscopes for each group  identification sheets for the galls from The Solidago Ruosta Gall Homepage (http://wwwfacstaff.bucknell.edu/abrahmsn/solidago/main.html). This site contains a very useful identification key- teachers who are unfamiliar with the insects can find informative pictures and descriptions. This site is also quite useful for identifying the insect contents of the galls. Ideally students could explore this page using a computer (or computers) in the classroom while they completed the dissection.

Procedure

1. With your students – or on your own- collect goldenrod stems from fields or open areas. Collect goldenrod stems with galls and without galls. Ideally it would be nice to have one stem that has a gall and one stem without a gall for each student.

If you are not familiar with goldenrod or galls- please vist The Goldenrod Gall Fly and Goldenrod site (http://www.ed.fnal.gov/entry_exhibits/insect/goldenrod.html). This site has some nice pictures of goldenrod and galls.

2. Show students the two forms of goldenrod- one stem with the gall and one stem without.

3. Have students create a focus question on their POE sheet (e.g Which is the ‘normal’ plant; what is inside the gall)

4. Ask students to predict what they think will be the outcome to their generated question. Record their predictions on their POE sheet. Have them try to come up with explanations that support their predictions and record these on their POE sheet. Encourage students to guess! Remind them that this is what scientists do when they begin their research.

5. Have students dissect the goldenrod using scissors or scalpels. If scalpels are used, use caution- the galls can be very hard and dry.

6. Have students use hand lenses and dissecting microscopes to examine the galls.

7. Encourage them to record their explanations in the box on the POE sheet.

8. Following this activity, students should generate some new questions that focus on the predictable or unpredictable results of this activity. These questions can be used to guide lesson planning.