Objectives

1. To formulate a hypothesis and design an experiment to test your hypothesis.
2. Communicate hypothesis and experimental design to your peers.

BEAN BEETLE EXPERIMENT

Goal: To formulate a hypothesis and design an experiment to test your hypothesis.

Today, each lab group will choose one of the following observations and questions to pursue further. Next week, you will perform an experiment designed by you to test the question that you have chosen to investigate. Prior to beginning the experiment, each group will give a 5 minute presentation on their question, hypothesis and the experiment that was designed by the group.

OBSERVATIONS AND QUESTIONS ABOUT BEAN BEETLES

Males are driven to find females and mate with them. Typically, males find females and begin mating in 15 minutes in small containers. Male beetles have been observed attempting to mate with other male beetles.

1. What senses do males use to find their mates?
2. Does mating decrease or increase a beetle's lifespan?
3. Does the presence of females reduce or increase the attempts of male-to-male mating attempts?
4. Does the presence of extra male beetles increase or decrease the time it takes to successfully mate with a female beetle?

It is claimed that adult bean beetles do not need to eat or drink.

5. Would beetle lifespan increase in the presence of food?
6. Do beetles survive longer in the presence of light or in the presence of dark?

Females prefer to lay eggs on their natal bean (the bean from which they emerge).

7. Are female beetles picky about the size of natal bean?
8. Are female beetles picky about whether an egg has already been laid on a natal bean?
9. Will females lay eggs on beans without a seed coat?
10. What makes the natal bean attractive to the female - its color or shape?

Supplies Available

• Virgin Male and Female Beetles
• Non-virgin Male and Female Beetles
• Mung Beans (natal bean) with seed coat, Mung bean without seed coat, Mung Beans with eggs
• Others Bean Types (Adzuki beans, Black-eye peas, Chick-peas, Black Beans)
• Water, Yeast, Fruit Fly media
• Petri Dishes, Scissors, Microscopes, Electronic Balances
• Beetle "storage" areas include: (a) cool area (b) warm area (c) dark area (d) light area

EXPERIMENTAL DESIGN

You need to answer each of these questions in your experiment design paper. This paper is due at the beginning of lab. Each group will give a five minute presentation on their question and the experiment they will perform to answer that question.

1. State your question (or reword the question).
2. State your purpose.
3. State your hypothesis.
4. List your variables.
1. What is your independent variable?
2. What is your dependent variable(s)?
3. What is your controlled variable (s)?
5. Design your experiment.
1. What materials or organisms will you need? How many?
2. Write out a step by step procedure.
• Consult your "Available Supply List"
• Remember to include a control group
• Remember to include replicates in your experimental design
• Statistics might be useful (e.g. t-test, ANOVA)

This experiment was written by A. D'Costa and M. Schlueter.  

Copyright © by Allison D'Costa and Mark Schlueter, 2014. All rights reserved. The content of this site may be freely used for non-profit educational purposes, with proper acknowledgement of the source. All other uses are prohibited without prior written permission from the copyright holders.

1st lab period.

1) Introduce the bean beetle to students.

A brief (10-15 minutes) lecture introduces students to the bean beetle. Photographs are used to train the students to recognize this species and identify the sexes (Blumer & Beck, 2011). The bean beetle's life cycle (egg -larva -pupa -adult) is discussed. Next, students are given Petri dishes containing beetles growing on mung beans and are trained how to observe and handle the beetles.

2) Engage the students in experimental design and data analysis using a previously set-up experiment.

Following the introduction, a brainstorming session is facilitated. The whole class participates in the design of a controlled experiment to answer the question "If given a choice of various bean types, do beetles prefer to lay their eggs on the bean type from which they hatched (natal bean)?" (Beck & Blumer).

The entire class works together to formulate a hypothesis and design an experiment to test it. The class defines the control group, experimental group, independent variable, dependent variable, and controlled variables and decides the number of replicates that are appropriate. The instructor then provides the class with the results of the previously set-up experiment. Students tally the data and make conclusions on whether the data support or reject the hypothesis that was developed. The lab is concluded with a discussion of the strengths and weaknesses of the experiment.

Experimental setup: The instructor sets up the experiment as follows, a week before the laboratory. This will provide "real data" for students to tally while in the lab. To set up, place three virgin male beetles and three virgin female beetles hatched from mung beans (natal bean) into Petri dishes containing an equal number of mung, adzuki, and black-eyed peas (10 beans each) for about 1 week. A week later the plates are ready for the students to tally the number of eggs on each bean type to determine whether the beetles had a preference for their natal bean or not.

3. Student groups choose a question and design their own experiment with appropriate sample sizes and controls.

Students are divided into groups of four and are told that they will perform their own group experiment during the next lab period. They are provided a list of bean beetle observations and questions, as well as a list of materials that will be available for their use (see Student handouts).

2nd lab period.

4) Students present experimental design to peers and perform the experiment in class.

As each group presents, the instructor and peers make recommendations. The students set up their experiment and, in the next few weeks, gather data and make conclusions on whether their data support or reject their hypothesis. Students are asked to reflect on how they could improve their experiment. Each student writes a laboratory report.

Preparation:

Fresh cultures of bean beetles can be obtained from Carolina Biological Supply. Stocks are made by growing the beetles to sufficient numbers in mason jars containing whole mung beans (or other bean type) covered with mesh. After 4-6 weeks at room temperature (or 3-4 weeks at 30°C), new beetles will emerge in large numbers, and they are ready to divide further. Stocks in mason jars should be replenished with fresh beans every 4-6 months. Because bean beetles are potential agricultural pests, the old cultures should be placed in a freezer for 4 days and then thrown in the trash.

To obtain virgin females and males, add fresh mung beans to a Petri dish along with several males and females. Allow females to lay eggs for several days. Beans with a single egg must be isolated (for example, each placed in a well of a 12-well plate), so that when the adult hatches, it remains a virgin.

Data collection:

An example of a typical student experiment: (see example student outline & data in Downloads)

Observation (from student handout): It is claimed that adult bean beetles do not need to eat or drink.

Question: Would adding suitable food or water increase the life span of the adult bean beetle?

Hypothesis: If food or water was provided, adult bean beetles would live longer.

Control group: 2 males and 2 females in empty Petri dish, no beans/ food/ water

Experimental group A: 2 males and 2 females placed in Petri dish containing fruit fly media

Experimental group B: 2 males and 2 females placed in Petri dish containing some yeast

Experimental group C: 2 males and 2 females placed in Petri dish containing whole mung beans

Experimental group D: 2 males and 2 females placed in Petri dish containing natal beans

Experimental group E: 2 males and 2 females placed in Petri dish containing naked beans (seed coat removed)

Independent variable: The food item or water given to the beetle

Dependent variable: Lifespan of the beetle measured in days

Controlled variables: Equal number of newly emerged males and females, all placed at the same temperature in a lab drawer.

Experimental Design:

There will be 6 groups (1 control and 5 experimental A, B, C, D, E). Each group will have 3 replicates, or 3 Petri dishes. Petri dishes will be stored in a lab drawer at room temperature. Each group will be checked every day around the same time and the number of dead beetles will be recorded. The experiment ends when all the beetles are dead.

Data analysis:

Students were introduced to t-test. Some data required ANOVA which was conducted by the instructor (see Student data).

References:

Beck, C.W. & L.S. Blumer. Natal Bean Discrimination by Bean Beetles. http://www.beanbeetles.org/new_website/wp-content/protocols/natal_preference/

Blumer, L.S. & Beck, C.W. (2011). Bean beetles: a model organism for inquiry-based undergraduate laboratories. www.beanbeetles.org.

D'Costa, A.R. & Schlueter, M.A. (2013). Scaffolded instruction improves student understanding of the scientific method & experimental design. American Biology Teacher, 75, 18-28.

Schlueter M.A. & D'Costa, A.R. (2013). Guided Inquiry Lab using Bean Beetles for Teaching the Scientific Method and Experimental Design. American Biology Teacher, 75, 214-218.

This experiment was written by A. D'Costa and M. Schlueter.  

Copyright © by Allison D'Costa and Mark Schlueter, 2014. All rights reserved. The content of this site may be freely used for non-profit educational purposes, with proper acknowledgement of the source. All other uses are prohibited without prior written permission from the copyright holders.

Sample Student Product

THE EFFECT OF FOOD ON ADULT BEAN BEETLE (CALLOSOBRUCHUS MACULATUS) SURVIVAL: DOES FEEDING INCREASE THE LIFESPAN?

1) Introduction to beetles, & why they are easy to study

Bean Beetles (Callosobruchus maculatus) are common agricultural pests found in the tropics and subtropics of both Africa and Asia. Bean beetle larvae feed and develop exclusively inside the seed of legumes (Fabaceae).

They have a rapid life cycle that includes a 10-14 day adult stage. It is currently believed that adult bean beetles do not feed after the larva stage, focusing only on reproduction as an adult. The main purpose of this study was to determine whether food would increase the lifespan of adult bean beetles.

2) Your question

THE EFFECT OF FOOD ON ADULT BEAN BEETLE (CALLOSOBRUCHUS MACULATES) SURVIVAL: DOES FEEDING INCREASE THE LIFESPAN?

3) Details of expt: how you collected virgins, set up, etc.

First, we allowed males and females to mate in a large petri dish full of mung beans. The females laid eggs on the beans. Beans that held the purest white egg(s) were collected and placed individually in 24-well plates, where the bean beetle larvae will grow and hatch from their natal bean as either a virgin male or virgin female. The day that each bean beetle hatched was recorded, and then the main procedure began for that bean beetle. Each bean beetle was randomly designated to one of the 6 experimental food groups as one of the 5 replicates. All of the bean beetles were contained in petri dishes under their specific conditions. Once a bean beetle was added to the experiment, his or her lifespan was observed, recorded, and analyzed.

The experiment was set up with six different food groups, which were labeled as the following: 1) No food (Control group), 2) Fruit fly media, 3) Yeast, 4) Sugar water, 5) Natal bean, and 6) Naked beans. Each group consisted of five Petri dishes, of which contained five replicates of 1 male, 2 males, 1 female, 2 females, and 1 male with 1 female, respectively. (The experimental procedure is expanded and written out in more detail below.)

Project Plan "Experimental Set-up" (Full Detail)

Food Group 1 - Nothing (control group)

Dish 1 - 1 male (5 replicates 1A, 1B, 1C, 1D, 1E)

Dish 2 - 2 males (5 replicates 2A, 2B, 2C, 2D, 2E)

Dish 3 - 1 female (5 replicates 3A, 3B, 3C, 3D, 3E)

Dish 4 - 2 females (5 replicates 4A, 4B, 4C, 4D, 4E)

Dish 5 - 1 male and 1 female (5 replicates 5A, 5B, 5C, 5D, 5E)

Food Group 2 - Fruit Fly Media (soak with water)

Dish 6 - 1 male (5 replicates 6A, 6B, 6C, 6D, 6E)

Dish 7 - 2 males (5 replicates 7A, 7B, 7C, 7D, 7E)

Dish 8 - 1 female (5 replicates 8A, 8B, 8C, 8D, 8E)

Dish 9 - 2 females (5 replicates 9A, 9B, 9C, 9D, 9E)

Dish 10 - 1 male and 1 female (5 replicates 10A, 10B, 10C, 10D, 10E)

Food Group 3 - Yeast (soak with water)

Dish 11 - 1 male (5 replicates 11A, 11B, 11C, 11D, 11E)

Dish 12 - 2 males (5 replicates 12A, 12B, 12C, 12D, 12E)

Dish 13 - 1 female (5 replicates 13A, 13B, 13C, 13D, 13E)

Dish 14 - 2 females (5 replicates 14A, 14B, 14C, 14D, 14E)

Dish 15 - 1 male and 1 female (5 replicates 15A, 15B, 15C, 15D, 15E)

Food Group 4 - Whole Beans

Dish 16 - 1 male (5 replicates 16A, 16B, 16C, 16D, 16E)

Dish 17 - 2 males (5 replicates 17A, 17B, 17C, 17D, 17E)

Dish 18 - 1 female (5 replicates 18A, 18B, 18C, 18D, 18E)

Dish 19 - 2 females (5 replicates 19A, 19B, 19C, 19D, 19E)

Dish 20 - 1 male and 1 female (5 replicates 20A, 20B, 20C, 20D, 20E)

Food Group 5 - Natal Bean

Dish 21 - 1 male (5 replicates 21A, 21B, 21C, 21D, 21E)

Dish 22 - 2 males (5 replicates 22A, 22B, 22C, 22D, 22E)

Dish 23 - 1 female (5 replicates 23A, 23B, 23C, 23D, 23E)

Dish 24 - 2 females (5 replicates 24A, 24B, 24C, 24D, 24E)

Dish 25 - 1 male and 1 female (5 replicates 25A, 25B, 25C, 25D, 25E)

Food Group 6 - Naked Beans (seed coat removed)

Dish 26 - 1 male (5 replicates 26A, 26B, 26C, 26D, 26E)

Dish 27 - 2 males (5 replicates 27A, 27B, 27C, 27D, 27E)

Dish 28 - 1 female (5 replicates 28A, 28B, 28C, 28D, 28E)

Dish 29 - 2 females (5 replicates 29A, 29B, 29C, 29D, 29E)

Dish 30 - 1 male and 1 female (5 replicates 30A, 30B, 30C, 30D, 30E)

4) Raw data: Please see Excel sheet

5) Results

Student Handout [pdf] [docx]

Instructor's Notes [pdf] [docx]

Sample Student Product [pdf] [docx]