| Imagine living your entire life in a plastic container of dried beans, from conception to a peaceful death at a ripe old age. Sure, microbes do it all the time, but I didn’t think any animal could. I learned differently when I met the bean beetle (Callosobruchus maculatas) at a mini-workshop at the ABLE 2006 meeting.
Chris Beck (Emory University), Larry Blumer, and Lea Brooks (both of Morehouse College) teamed up to bring this wonderful workshop to Purdue. With funding from the National Science Foundation, they have been working to develop the bean beetle as a model organism for research in undergraduate biology classes. They even have a website (http://www.beanbeetles.org) where you can find lots of information about this useful animal, including sample lab activities and many other resources.
As I learned in the workshop, bean beetles spend their lives on beans. The adults don’t eat or drink. After mating, the females lay eggs on the surfaces of beans. The eggs hatch into larvae that burrow into the beans. That’s where they complete their development, eating bean innards as they go. Within a few weeks, the adults emerge to lay their own eggs. Our workshop instructors told us that the beetles do especially well on organic adzuki beans, mung beans, and black-eyed peas.
In the workshop, we did a behavior experiment designed to test the hypothesis that a female bean beetle would rather hang out on her “natal” bean variety (the type she hatched from) than on another type of bean. Each of us set a female beetle free in a covered, three-sector choice chamber constructed from a plastic Petri dish divided into thirds with borders made of silicone caulk. We recorded the amount of time she spent in each sector. (In case you’re keeping score, my beetle didn’t seem to care where she was, which I understand is a typical result for this experiment).
As party favors, Larry, Chris and Lea gave away cultures of bean beetles on mung beans. I used mine to start my own little farm at home, which has since grown to 15 containers – five for each of three types of beans. By the way, if you think it’s easy to find organically grown adzuki beans in Norman, Oklahoma, you’ve obviously never been here!
With some helpful advice from Chris, I used my new arthropod friends in my nonmajors biology class in August. Instead of the “black box” activity that we usually do for our first lab, I made choice chambers and had the students do the same experiment we did in the ABLE workshop, complete with data sheets to observe the beetle behavior. This activity led easily into a discussion of the elements of an experiment. We then left the beetles in their choice chambers for a week to let them lay eggs on the beans of their choice. In the following lab period, the students used hand lenses and counted the eggs in each sector to test the hypothesis that the beetles prefer laying eggs on their natal beans.
We then asked the students to come up with the next question they would like to answer if they could. We had hoped they would ask questions like “Does it matter if the beans are organic or not?” or “Do multiple larvae hatch from a bean on which a female lays multiple eggs?” Instead, most of their questions were direct derivatives of the choice chamber experiment, such as whether the beans would prefer larger, smaller, softer, harder, darker, or lighter beans. Next time, we will instruct students not to come up with “egg-laying preference” questions; I hope that will force them to branch out a little more.
We will definitely use the bean beetles again next spring. Even if we don’t use them for other labs later in the semester, I loved that the students were working with real live organisms on their very first day in lab, and they seemed to enjoy following up with their beetles during the next week. Several asked whether they would be allowed to monitor their beetles throughout the semester. The fact that the beetles are so easy to raise is also a big plus.
If you haven’t tried making friends with bean beetles already, I urge you to give it a try. Thanks to the ABLE 2006 mini-workshop, I’m a fan, and so are my T.A.s and students. Not bad for a tiny arthropod that lives out its life in a container of beans!
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