Principal Ecological Question Addressed

Are phytophagous insects, specifically bean beetles (Callosobruchus maculatus), able to adapt rapidly to a change in larval host species?

What Happens

In an initial lab period, students work individually and then in small groups to design an experiment to determine whether bean beetles have adapted to a new larval host. Second, groups present their proposed experimental designs to the class and are guided by the instructor to a consensus experiment. Third, each student sets up one replicate of each treatment of a reciprocal transplant experiment. A minimum of 48 hours later, students isolate beans with single eggs. Approximately 4 weeks later, students collect data on life history traits of emerging adult beetles. The resulting data are analyzed to determine if bean beetles have adapted to the new host.

Experiment Objectives

1. Design an experiment to evaluate whether bean beetles (Callosobruchus maculatus) rapidly adapt to a change in larval host.
2. Conduct a consensus experiment to evaluate rapid adaptation in bean beetles.
3. Analyze and interpret the resulting data to determine whether adaptation to a new larval host has occurred.

Equipment/Logistics Required

The experiment requires having dense cultures of bean beetles from which females can be isolated. Beetles should be from cultures reared on a natal host (typically mung beans) and from cultures switched to a new host several generations prior to the experiment. If new cultures are initiated approximately 2 months before the lab period, there will be sufficient time for two generations of beetles, which will result in dense cultures. When possible, we supply one culture of each type (natal and new host) to each group of students working in pairs; however, each culture should have sufficient beetles for use by multiple student groups. As bean beetles are a tropical species, they develop most rapidly in warmer temperatures. The time estimates for the experiments are based on rearing beetles in incubators at 30˚C. Beetles can be reared at room temperature. However, this will extend larval development by 1-2 weeks.

Currently, cultures of bean beetles reared on different host types may be obtained from the authors. In the future, they may be available from commercial suppliers.

Below is a list of materials for a class of 24 students.

• 24 magnifiers 2.5x, 4” diameter self-standing with folding base (Fisher #14-648-19 or VWR #62379-535, approximately $50.00 US per unit) or dissection microscopes
• 24 bean beetle cultures with newly emerged adults (12 cultures for each host type)
• 12 plastic 150mm Petri dishes for picking adults females from cultures
• 96 plastic 35mm Petri dishes for oviposition by isolated beetles
• Many 35mm Petri dishes for holding individual beans OR flat-bottom tissue culture plates (6 or 12 well)
• 0.1mg analytical balance for weighing beetles
• 30 Vernier calipers for measuring beetle characteristics
• Dried beans (preferably organic) of the species used for culturing the beetles. Typical hosts that beetles colonize include mung beans, adzuki beans, and blackeye peas.

Summary of What is Due

During the first lab period, students will produce an experimental design to examine rapid adaptation to a new host in bean beetles. After collecting and analyzing the data, eachstudent will write a scientific paper based on the pooled results of the class.

Keyword Descriptors

Ecological Topic Keywords:

Adaptation, evolution, individual ecology, life history, host specificity

Science Methodological Skills Developed:

data analysis, evaluating alternative hypotheses, experimental design, factorial experiment, hypothesis generation and testing, quantitative data analysis, scientific writing, statistics, graphing

Pedagogical Methods Keywords:

Cooperative learning, guided inquiry