These activities allow students to investigate behavioral responses of the large Milkweed bug, Oncopeltus fasciatus, and the mealworm, Tenebrio molitor or Tenebrio obscurus, to external stimuli of light, color, and temperature. During the activities, students formulate hypotheses to research questions presented. They also observe insects for a period of time, record observations, analyze the data, and draw conclusions. Important outcomes include experience with critical and analytical thinking and appreciation for the process of science as well as the biology of living things. The activities described herein are appropriate for upper elementary grades, middle school, and high school biology classes.
Keywords: behavior, biology laboratory activities, insects, mealworm, Milkweed bug
Insect studies are an excellent opportunity to provide firsthand observation to your students with little hassle. The large Milkweed bug (see Figure 1) is nearly perfect for classroom rearing for several reasons: it can be maintained with minimal care; all of its life stages are visible and development is fairly rapid; the sexes are easily distinguished; and it is harmless and colorful. Mealworms (not true worms but larval beetles) are easy insects to rear as well (see Figure 2). All that is required is a container and food, although they will benefit from having water supplied by a wet paper towel or cloth. Both the larvae and the adults are tough and not easily injured, and they do not bite-aspects that enhance their usefulness in the classroom. Furthermore, because they are relatively slow moving and the adults do not fly, escapes are seldom a problem.
The activities described below allow students to investigate behavioral responses of the large Milkweed bug, Oncopeltusfasciatus, and the mealworms, Tenebrio molitor and Tenebrio obscurus, to a variety of external stimuli. The stimuli are analogous to those typically encountered by insects in their natural settings. The responses are immediate and easily observable in typical biology classroom settings. Students develop their observation skills and ask questions about what they have observed as they search for patterns and generalizations, develop hypotheses, and assess the quality of the data collected. The overall outcome is that students gain an appreciation for the process of science by doing science. The activities described herein are appropriate for upper elementary grades, middle school, and high school life science courses and address the National Science Standards that focus on science as inquiry, life science, and measurement.
FIGURE 1. Milkweed bugs on common milkweed plant. Both adult (far left) and immatures (right) are present. The immatures can be identified by their shorter (immature) wing structures.
FIGURE 2. The photograph shows the three developmental stages of the beetle, Tenebrio molitor. The larval stage (left), pupal stage (center), and adult stage (right). The larval stage of this insect is commonly referred to as the yellow mealworm.
As mentioned earlier, mealworms are the larvae of certain black beetles. The yellow mealworm, T. molitor, is the species usually available from commercial sources. The larvae are honey-brown in color and the adults are shiny black. As its name implies, the dark mealworm, T. obscurus, is a darker yellow-brown color and the adult is a dull black color. Initial stocks are readily obtained from biological supply houses, pet stores, and fish bait dealers. They can also be found around stored grain facilities and feed stores or anywhere there is spilled grain. The large Milkweed bugs can also be purchased from biological supply houses (see Appendix A) or collected from milkweeds.
Additional information about how to rear insects such as large Milkweed bugs and mealworms can be found from a variety of sources (see Appendix A). Because meal worms are not “true worms,” an activity to determine why mealworms are not worms, but insects, is an appropriate exercise to conduct prior to beginning the laboratory activities describe here.
All animals respond to their environment with either instinctive or learned behavior. Even forms that lack a well-defined brain or nervous system have distinctive behavior patterns. In many simple animals, there is an instinctive or fixed pattern of behavior, which is referred to as taxis. Taxis is either a direct movement in response to some stimulus in the environment or a series of trial and error movements that ultimately lead the animal into appropriate conditions or favorable environments.
Two factors that influence animal behavior are physiology and external stimuli. An example of animal behavior that is closely tied to its physiology is prdation. When a predator seeks prey, its nervous system and digestive system are involved. The lack of food in the digestive system is part of the information the nervous system processes and interprets as hunger, which stimulates food- seeking behavior. External stimuli can also direct certain animal behaviors as exemplified by the wood lice (see Figure 3), also known as “roly-poly bugs” or “pill bugs.” Roly-poly bugs live best in moist conditions and tend to congregate in moist places. When their environment begins to dry, roly-poly bugs start moving until they encounter another moist area. These simple movements keep roly-poly bugs in favorable environments, ensuring their survival.
Within their own genetic capabilities and physiological demands, animals do what they can to successfully cope with their particular environments for as long as possible. In so doing, they move from place to place, seek food, avoid predators, and reproduce.
Each activity described below, presents a research question. Students should develop a hypothesis in the form of a statement that attempts to answer the research question. At this point, it is helpful to explain the experimental design of the activities and address any questions students may have regarding collecting and analyzing the data. After the data has been collected and analyzed, ask students to draw conclusions from the results and formulate a statement of whether or not the data supports their hypothesis. In addition, after the completion of each exercise, direct them to speculate on the significance of their findings. This involves an interpretation of the data with respect to what is currently known and how it relates to the biology of insects. Their interpretations can be presented through a group discussion or in a formal paper or lab report. It is also appropriate for students to develop a presentation of their results, especially if they pursue any of the extensions of the activity described below. These presentations can be accomplished with the use of computer software such as MS Power Point (Microsoft Corporation) or construction of a poster or other graphic displays.
FIGURE 3. “Roly-poly bugs,” sometimes referred to as “pill bugs,” are shown here. These gentle arthropods are of the order Isopoda. They live under stones and in damp places.
ACTIVITY 1: INSECT RESPONSETO LIGHT AND COLOR
The purpose of this exercise is to observe insect responses to light and color. Students will determine if the insects under investigation have a preference for light or dark conditions and if they have a color preference.
Materials needed per group of 2 or 3 students:
1. Insects, 20 to 30 milkweed bugs and/or 20 to 30 mealworms per group.
2. A large (9 in. 13 in.) cake pan (aluminum or glass) or a plastic tub.
3. Two “lids,” pieces of Plexiglass or window glass, each large enough to cover the pan.
4. Cardboard to cover half of the cake pan.
5. Lamp, a goose neck desk lamp equipped with a 40 watt light bulb.
6. Colored light bulbs: white, red, yellow, green, and blue; 40 watt if available. Cellophane: clear, red, yellow, blue or green may be used as a substitute if you use white or clear light bulbs. Metal lampshades may be covered with the colored cellophane to produce different color exposures. Different colored construction paper placed underneath a clear glass pan will work as well.
Part A: Response to Bright or Dark Light Conditions
Research Question: Do the insects show a preference to certain light conditions?
1. Check the fit of the Plexiglass or glass “lid” to the pan. If the fit does not appear to be escape-proof, smear a layer of petroleum jelly (approximately 1.0 to 1.5 cm width) around the inside rim of the pan. (Note that decisions about who does steps 1- 3 in Part A and B will be up to your judgement, depending on the grade level and whether glass or plexiglass is used.)
2. Position the lamp, with a white colored light bulb, to illuminate the cake pan evenly from above. Record the light bulb wattage and temperature of room in the data table shown in Figure 4.
3. Place 20 to 30 insects of the same kind in the center of the pan and cover with the lid. Then immediately cover half of the lid with cardboard.
4. Observe and count the number of insects in the dim or low light area (under the cardboard) and the bright light area (uncovered) at five-minute intervals. Record the results in Figure 4.
Generally the Milkweed bugs will congregate in the lighted area while mealworms prefer the dim lighted or dark areas. Students should try to expl\ain what they have observed with respect to the biology of the insects. For example, mealworms are regarded as a stored grain pest. They are typically found in and around grain elevators where light conditions are dim or there is no light at all. Large Milkweed bugs, on the other hand, are typically found on milkweed plants during daylight hours.
Variations of the Activity
Students may ask further questions that require a greater understanding of insect biology. Listed below are some questions that generally come up after working with these insects. Students can develop hypotheses to the following research questions, and then design and conduct experiments to test their hypotheses.
1. Do adult insects respond differently than immatures with respect to light conditions?
2. Do male and female adults respond differently with respect to light conditions?
3. Do male and female immatures respond differently with respect to light conditions? (Not recommended for mealworms because their sex is very difficult to determine when they are larvae; the sex of adults are much easier to distinguish.)
4. Do young immatures respond differently than older immatures with respect to light conditions?
Because these activities require a greater understanding of insect biology, it may be necessary to allow more time for students to acquire additional background information specific to Milkweed bugs and mealworms (see Appendix A). Students may elect to develop a presentation of their results or a poster for display in the classroom.
Part B: Response to Different Colors of Light
Research Question: Do the insects show a preference for color?
FIGURE 4. Data table for Activity 1A and B: Response to Light and Color. The dim light area is under the cardboard that covers half of the arena, the bright lighted or colored lighted area is the uncovered portion of the arena. Students observe insects under different light conditions and record the number of insects at each time interval. Students should be instructed to record the room temperature and the light bulb wattage.
1. Repeat steps 1-3 of the previous experiment using different colored light bulbs.
2. Another way to set up this experiment is to cut pieces of colored cellophane (red, yellow, blue, and green) and cover the pan lid with the different colors. Lay a colored piece of cellophane on the clear lid. Carefully place the second piece of Plexiglass/glass over the cellophane thus creating a “cellophane sandwich.”
3. Center the lamp with a white or clear light bulb over the pan. Record the light bulb wattage in Figure 4.
4. Place 20 to 30 insects of the same kind in the center of the pan and immediately cover with the “cellophane sandwich” lid, being careful to center it over the pan and under the lamp. Cover half of the pan with cardboard as previously described.
5. Observe and record the number of insects in the two areas at 5- min intervals as previously described. Record the results in Figure 4.
Some of the mealworms will avoid the bright light and therefore the bright colors as well. Some of the large Milkweed bugs will congregate under the bright colors. It is not unusual to see no pattern at all with this set up. From my experience with this activity, the number of insects under any one particular color was never large enough to be significant.
Variations of the Activity
The variations described above can be applied to this activity as well. In addition, students may intuitively want to test combinations of colors (including clear or no color) rather than using the dim light or dark condition with one color. Moreover, student may want to vary the wattage of the light bulb and test if this has any effect on behavior.
FIGURE 5. Diagram of a bug trough set-up for the temperature gradient experiment. The ends of the bug trough and the top can be enclosed with plastic wrap. Holes in the top allow thermometers to be inserted, which will permit students to measure and to record a temperature gradient. (Diagram by Barb Ball)
ACTIVITY 2: INSECT RESPONSETO TEMPERATURE
The purpose of this exercise is to observe insect responses to varying temperatures (warm/hot or cold) and determine if there is a preference.
Materials needed per group of 2 or 3 students:
1.Bug trough (see Figure 5; refer to Appendix B for instructions on how to build a bug trough).
2. Plastic wrap to cover the bug trough.
3. hot plate or electric heating pad.
4. Water and ice.
5. Two large beakers (600 ml or larger). One will be used for ice water and the other for hot water as shown in Figure 5.
6. Five Celsius thermometers.
Safety Precautions: Care should be taken when using electric heating pads or hot plates. Instruct the students to keep the setting low to avoid injuring the insects or themselves and to prevent damage to the bug trough. Plastic products could melt from high temperatures attained from hot plates. Therefore, large beakers containing hot water are recommended. Never leave the bug trough unattended. Remove thermometers from the bug trough and place them in a secure location when not in use.
Research Question: Do the insects show a temperature preference?
1. Place one end of the bug trough on a large beaker of water heated with a hot plate or electric heating pad under it. Adjust the setting to achieve the desired temperature. Because of the variability of hot plates or heating pads, it is recommended that the instructor determine what settings work best prior to letting the students work with the equipment. Place the opposite end of the bug trough on a large beaker of ice water. (Again, who performs steps 1-3 is based on your discretion.)
2. Cover with plastic wrap and allow a temperature gradient to become established (about 10 minutes). Thermometers can be inserted through the plastic wrap to confirm and record a temperature gradient. The temperatures indicated in the table in Figure 6 are approximate and serve as a guide for establishing a range of temperatures that can be expected as a result of the bug trough set- up. Once the temperatures are recorded, thermometers should be removed from the bug trough and placed in a secure location when not in use.
3. Release 20 to 30 insects of the same kind in the center of the bug trough (cut an opening in plastic wrap).
4. Observe and count the number of insects in the cold, cool, warm, and hot areas at five-minute intervals. Record the results in Figure 6.
FIGURE 6. Data table for Activity 2: Insect Response to Temperature. Students measure and record the temperature (0C) at each described section of the bug trough (Figure 2), then place 20 to 30 insects in the middle of the bug trough and observe where the insects migrate in response to the different temperatures. At each time interval, the number of insects is recorded in the data table. The temperatures indicated are approximate and may vary from set-up to set-up.
Typically, most insects will avoid cold temperatures. During the beginning of this activity, the insects may appear to move indiscriminately about the bug trough. As time passes, they will congregate to the warmer end of the bug trough.
Variations of the Activity
Design and conduct experiments to determine if:
* Adults and immatures respond differently
* Male and female adults respond differently
* Young and old immatures respond differently
* Young and old adults respond differently
As stated before, these activities require a greater understanding of insect biology and may require additional background information specific to the insects used for these activities.
The instructor can pool the class data to create a larger sampling. Students can then perform elementary statistics (mean, standard deviation, standard error) on the class data and compare the class results to their own. This enables students to assess the significance of the quality and variability in the data collection process. They will also learn the value of controls and experimental design through comparison with the results of other groups. In addition, by comparing the results of both insect types, students will be able to develop a greater appreciation for the diversity of insects and their biology.
Instruct the students to write a formal laboratory report. The laboratory report format should include a title, an introduction section describing the background information and a logical hypothesis based on the research question, a materials and methods section, results section (including data tables and graphs of the data), and conclusions/discussion section. In addition, the use of computers and appropriate software provides a means for incorporating technology into the activity. Student can use word processing software to generate the written portion of their report and spreadsheet software to generate data tables, analysis of the data, and graphs. As mentioned before, students can develop and give presentations of their investigation to the class using MS PowerPoint software.
Because each investigation is initiated with a research question, it is reasonable to expect students to be able to develop a hypothesis that indicates their understanding of basic biological principles related to the insects under investigation. Furthermore, students can be expected to describe the experimental design and methodology as it pertains to the collection and analysis of data, and provide a clear explanation of the results. Consideration should be given to the students’ ability to critically evaluate the experimental results, accept or reject the hypothesis, support their conclusions with examples taken from the data collected, and generate inferences to explain their findings. From my experience, students discovered quite a few connections between behavior and biology including the following:
* Insects tend to avoid cold places because they are cold blooded and cannot move around as easily incold environments.
* If the temperature is cold enough to freeze the water in their bodies, the ice crystals that form will damage their cells and cause death.
* If the environment is too warm, they also risk losing too much water, and death would result as well. An example is given in the Background section with respect to the roly-poly bugs’ behavior to seek moist places.
Students are encouraged to make connections based on information they gather from doing research, and the teacher should be skilled enough to guide students in their research. The most obvious connection is the relationship between where a particular insect is found in the environment and its ability to survive there. From my experience, students realize that different insects can survive in different environments because of adaptation (natural selection).
Insect studies offer a broad range of instructional opportunities as well as provide students with positive learning experiences. The insects studied in this activity can be observed firsthand with few restrictions compared to vertebrate animals. Furthermore, insects are inexpensive, easy to rear, and take up little space. These insects as well as others provide teachers with excellent models to illustrate many biological processes that occur in all living organisms as well as basic principles such as ecology and behavior.
I wish to thank Barb Ball, Department of Biological Sciences Graphics Laboratory, Northern Illinois University, for her technical assistance with the graphics. Also, special thanks to Mr. James Kalisch, Department of Entomology, University of Nebraska-Lincoln for his gifts of insect photographs.
JON S. MILLER is an assistant professor of biology and directs the secondary Teacher Certification Program for biology and general science at Northern Illinois University, DeKalb, Illinois, USA. His research interests focus on signal transduction in insect cellular immunity. In addition to his duties with teacher certification, Dr. Miller works with in-service biology teachers for professional development and consultants with school district science departments for K-12 science curriculum reform.
Appendix A: Resources for Obtaining and Rearing Large Milkweed Bugs and Mealworms
* Carolina Biological: http://www.carolina.com
* Keeping and raising mealworms: http://www.icomm.ca/dragon/ mealworm.htm
* Mealworm information: httpV/insected.arizona.edu/mealinfo.htm
* Milkweed bug rearing: http://insected.arizona.edu/milkrear.htm
* Milkweed bug information: http://www.geocities.com/ brisbane_bugs/MilkweedBug.htm
Insect Biology Resources:
* Borror, D., C. Triplehorn, and F. Norman. 1989. An introduction to the study of insects (6th ed). New York: Saunders College Publishing/Harcourt Brace College Publishers.
* DaIy, H., J. Doyen, and A. Percell III. 1998. Introduction to insect biology and diversity. New York: Oxford University Press.
* Romoser, W., J. Stoffolano, and W. Brown. 1994. The science of entomology. Dubuque, IA: William C. Brown Publishers.
Appendix B: Building a Bug Trough
A bug trough (Figure 5) is a narrow trough in which one can test insect responses to stimuli such as light, odors, humidity, or temperature. It can be built of cardboard, wood, foam-core board, plastic, or metal. It should be one to four inches wide and long enough to establish a gradient of at least 75 cm. One to 1.5 meter lengths work well. Wood, foam-core board, and cardboard troughs are not very good for testing response to temperature gradients, as these materials are poor heat conductors. A metal or plastic trough works best for conduction. The trough can be fashioned from sheet metal, but it is much simpler to use a piece of gutter material (metal or vinyl) that can be purchased from a local home improvement store. Use a gutter with a flat bottom and, preferably, one with two straight sides. Vinyl gutters are smooth and slippery, making it difficult for the insects to move about. You can cover the bottom of the trough with masking tape to give the insects traction for walking or crawling.
The trough should be covered to prevent insects from “going over the wall” and to prevent air currents from disturbing the temperature or odor gradient being tested. Clear plastic wrap works well for this purpose and allows for easy observation.
Copyright HELDREF PUBLICATIONS Summer 2004