SPOTTED KNAPWEED GALL FLY LAB
(PC): Feel free to copy (control-c) and paste (control-v) all or any part of this document into your favorite word processor and modify it as you see fit. Also, modify it to fit what ever grade level and comfort level you have.
spotted knapweed flower Urophora affinis female. V.Farquhar. U. affinis galls. R.Richard
Left: spotted knapweed flower and seed heads. T. Breitenfeldt
Center: Urophora affinis female. V. Farquhar.
 Right: U. affinis galls. R. Richard
The center and right photo's will be replaced by photo's taken by WHS students as the "99-'00 school year progresses.  Many thank you's to V. Farquhar and R. Richard for the temporary use of these photo's!

Gallery of WMS 7th Graders Working On Gall Fly Lab  -slow download.
Student Data
Cage Set Up/Larva Pictures
Pictures of: Larvae, Galls, seed heads, and seeds.
Introduction:
   Spotted knapweed (Centaurea maculosa) is a category 1 noxious weed in Montana.  It is a native of Europe and Asia and was accidentally brought to North America by humans.  However, the natural creatures (Insects, bacteria, fungi, nematodes, etc.) that help control it in Eurasia were not brought along with it.  This allows spotted knapweed to out compete our native North American plants in their native habitat because our native plants are constantly being fed upon by the many native natural creatures that have evolved with them over time.  Where as, spotted knapweed in North America has no creatures controlling it (except us humans) and is therefore, a noxious weed.
    To help solve this spotted knapweed problem, people have gone to Europe and searched for biological control agents that eat spotted knapweed.  These creatures are then rigorously tested to make sure that they are host specific (eat ONLY spotted knapweed).  They are then brought back to North America, studied some more, and finally released into the field in hopes that they will help control this noxious weed.
    Part of Integrated Pest Management (IPM) is using as many biological control agents as possible along with all the other management strategies, to help bring the infestation level of this weed under control.
    In this lab you will be using two insects imported from Europe whose larvae form galls in the seed heads of spotted knapweed and reduce seed production of the plant.  These small flies are Urophora affinis and Urophora quadrifasciata (Diptera: Tephritidae).  In short, the flies lay their eggs in the seed heads of spotted knapweed in the summer and the larvae soon hatch and eat some of the seeds in that seed head.  This causes the plant to form a callous like swelling around the larvae called a gall (thus the name spotted knapweed seed head gall fly).  These larvae stay in the seed heads all fall and winter.  In late winter or early spring they pupate while still in the seed head and emerge as adults in late spring or early summer, to do it all again.

Goals:
-The students will be able to explain what a noxious weed is and why it is a  weed.
-The students will be able to explain what a biological control agent is and how  it is part of IPM.
-The students will be able to explain or draw the life cycle of spotted knapweed.
-The students will be able to explain or draw the life cycle of a spotted knapweed gall fly. -The students will dissect an infected knapweed seed head and, observe and draw a gall and a larvae.
- The students will combine data on the numbers of galls/seed head, find a class average, and use these data and this statistic to predict the number of expected gall flies that should emerge from 100 seed heads kept in an insect cage in the lab.
-The students will take data on the number of knapweed gall flies that actually emerge from 100 seed heads in the cage and make hypothesis as to why the number differed from that expected.
Materials:
-An infestation of spotted knapweed (Centaurea maculosa) that is infested with one or both of the spotted knapweed gall flies, that you can go to in the winter.  In Montana, the gall flies occur almost every where knapweed occurs.
-Hand lenses and/or stereoscopes.
-Hand dissection equipment: forceps (tweezers), teasing needles, scissors.
-An insect cage.  We use 1 m square cages purchased from Bioquip.
-Insect aspirators (bug suckers), also from Bioquip.
-Insect pins, also from Bioquip or almost any other biological/scientific supply house.
-Text books with sections on insects and flowering plants (including the life cycles), or insect and plant field guides.
Procedure For Teacher:
-Introduce the idea of noxious weeds- show a slide show, use the Internet, bring in a speaker, or grow a weed in your classroom from seed or rootstock.
-Right before or soon after Christmas, go to your spotted knapweed site and randomly collect enough seed heads that each student will have 5 and you have the 100 you need for the cage.  Be sure and use gloves as the dead plants are sharp.  Also,  transport them in a manner that you do not spread  the seeds!  Note: do not collect them too early in the fall as the larvae need an extended period of cold (however, you can store them in the refrigerator for a period of time but  not in the freezer!) before they will emerge.  Also, do not wait and collect them too late in late winter as they will start to pupate and the students can not see the larvae.
-Set up hand dissection and observation equipment.
-Hand out lab (copied from below and modified as you see fit) and discuss.
-Have each student dissect one practice seed head, count the galls, and observe and draw the galls and larvae.
-Have students go to lab stations, dissect 5 seed heads, count the galls in each, and record this on their labs and the board.  They will use these data to figure the average number of galls/seed head.
-Place 100 (or more) seed heads in an insect cage.  Place the cage in a warm lighted area not in direct sunlight.  Lightly mist seed heads with water weekly.
-Have the students use the class average to predict the number of gall flies they expect to emerge from the seed heads in the cage.  For instance, if the class average was 4.32 galls/seed head, they should expect 432 flies to emerge from the 100 seed heads in the cage.
    (class average x #seed heads = expected # of flies).
-Have the class observe the cage each day.  After several weeks, flies will start to emerge.  The students should aspirate (remove from cage with a bug sucker) and count the flies each day.  They should record the number emerged each day and keep a total number of flies emerged.  Flies will emerge for about a month.  Note: it will be too early to release the flies into the environment (there are plenty of flies!!) so preserve  them in a freezer or in alcohol.  The students can observe and/or mount them as you see fit.
-When the flies are through emerging, have the students use their data to complete their lab write up.
(PC): Feel free to copy (control-c) and paste (control-v) all or any part of this document into your favorite word processor and modify it as you see fit.
SPOTTED KNAPWEED GALL FLY LAB-STUDENT
Due Date____________               Name________________
Introduction:
    Spotted knapweed (Centaurea maculosa) is a category 1 noxious weed in Montana.  It is a native of Europe and Asia and was accidentally brought to North America by humans.  However, the natural creatures (Insects, bacteria, fungi, nematodes, etc.) that help control it in Eurasia were not brought along with it.  This allows spotted knapweed to out-compete our native North American plants in their native habitat because our native plants are constantly being fed upon by the many native natural creatures that have evolved with them over time.  Where as, spotted knapweed in North America has no creatures controlling it (except us humans) and is therefore, a noxious weed.
    To help solve this spotted knapweed problem, people have gone to Europe and searched for biological control agents that eat spotted knapweed.  These creatures are then rigorously tested to make sure that they are host specific (eat ONLY spotted knapweed).  They are then brought back to North America, studied some more, and finally released into the field in hopes that they will help control this noxious weed.
    Part of Integrated Pest Management (IPM) is using as many different biological control agents as possible along with all the other management strategies (such as spraying herbicides, tilling, and hand pulling), to help bring the infestation level of this weed under control.
    In this lab you will be using two insects imported from Europe whose larvae form galls in the seed heads of spotted knapweed and reduce seed production of the plant.  These small flies are Urophora affinis and Urophora quadrifasciata (Diptera: Tephritidae).  In short, the flies lay their eggs in the seed heads of spotted knapweed in the summer and the larvae soon hatch and eat some of the seeds in that seed head.  This causes the plant to form a callous like swelling around the larvae called a gall (thus the name spotted knapweed seed head gall fly).  These larvae stay in the seed heads all fall and winter.  In late winter or early spring they pupate while still in the seed head and emerge as adults in late spring or early summer, to do it all again.
Procedure:
1. Observe the teacher demonstration about how to dissect a seed head and count the galls.
2. Practice a seed head dissection on the practice seed head.  Data: Using a hand lens or a stereo microscope, draw a gall.  Break a gall carefully open and draw a larvae.
3. Carefully dissect 5 seed heads and count the galls in each.  Data: Record these 5 pieces of data and list them on the board.
4. Data: Record all the data for the whole class.
5. Statistic: Find the average number of galls/seed head.  (sum of class galls divided by the total number of seed heads)
6. As a class, place 100 (or more) seed heads in an insect cage.   Place the cage in a warm
lighted area not in direct sunlight.  Lightly mist seed heads with water weekly.
7. Predict: using the formula (class average x #seed heads = expected # of flies) make a hypothesis predicting the number of flies that should emerge from the seed heads in the cage.
 

________ = expected # of flies. (show your work).

8. Observe the cage each day.  After several weeks, flies will start to emerge.  Aspirate (remove from cage with a bug sucker) and count the flies each day.  Data: record the number emerged each day and keep a total number of flies emerged.  Flies will emerge for about a month.  Note: it will be too early to release the flies into the environment (there are plenty of flies!!) so preserve them in a freezer or in alcohol.
9. After the flies seem to stop emerging, wait about two more weeks to be sure all are out.
10. Mount (or display) a gall fly as your teacher directs.

Results: Describe WHAT HAPPENED while you were completing the lab.
 

Discussion Questions:
1. Draw and label the life cycle of spotted knapweed Centaurea maculosa (a flowering plant).  Include: flower, fruit, seed, seedling, stem, leaf, root, pollen, stamen, pistil, and ovule.  Remember, a cycle makes a complete circle.
 

2. a. What is a noxious weed?  b. Why is spotted knapweed a weed?  c. What characteristics of a plant might make it become a weed?

3. a. Draw and label the life cycle of a spotted knapweed gall fly (complete metamorphosis).  Include: egg, larvae, pupa, adult.  b. Attach (or redraw) your drawings of a larvae and a gall.

4. a. What is Integrated Pest Management (IPM)?  b. What is a biological weed control agent?  c. Using information your teacher provides for you and/or the Internet, list and briefly describe 3 other ways besides biological control that people use to control spotted knapweed.

5. The spotted knapweed gall flies lower seed production of spotted knapweed (10%-40%) and also, cause the plant to use some of its stored food reserve to form galls in its seed heads.  a. Will they be able to control this weed?  b. Why?

6. a. Did more or less flies emerge from the caged seed heads than expected?  b. List 3 hypothesis as to why the number differed from your expected number.

7. Give your opinion of this lab.  a. What parts would you leave the same?  Why?  b. What parts would you change?  Why?
 

mtwow.org HOME