34 Natal Bean Discrimination by Bean Beetles
Adapted from C. Beck and L. Blumer by Staci Forgey, TCC Biology Faculty
Objective
Design and perform a set of experiments to evaluate whether female bean beetles (Callosobruchus maculatus) discriminate between suitable species of beans.
Introduction
Bean beetles, Callosobruchus maculatus, are herbivorous pest insects that are found in Africa and Asia. Females lay their eggs on the surface of beans. Eggs are laid singly and hatch into larvae (maggots) several days later. The larva then burrows into the bean and will form a pupa 21–30 days after the egg is deposited. They mature 24–36 hours after emergence from the pupa and do not need to feed.
Adults typically live for 1–2 weeks. Mating and oviposition occur during this time period. Females will choose the best substrate (bean) to lay their offspring on, since the larvae cannot move. By choosing a substrate for oviposition, the female chooses the food resource available to her offspring (Brown and Downhower 1988). This is a critical choice for the female, as it influences the growth, survival, and future reproductive success of her offspring (Mitchell, 1975, Wasserman and Futuyma, 1981). Females can lay eggs on a wide range of bean species, but very few bean species will result in normal development and the successful emergence of adults. Some species of beans are toxic to larvae (Janzen 1977).
Materials
In class, you will be provided with live cultures of bean beetles containing adults that have been raised on mung beans (Vigna radiata).
Female beetles are easily identified in the live cultures because they have two dark stripes on the posterior of the abdomen, whereas the posterior abdomen of males is uniformly light in color.
You will also have access to petri dishes and several types of beans.
Experimental Design
Since the oviposition choices of females influence the survival and future success of their offspring, females may be very sensitive to the species and condition of the beans on which they are depositing eggs.
Each group should design a set of experiments to address whether female bean beetles discriminate between suitable species of beans. We will revisit the experiment next week and collect our data set. We will choose one experiment to perform as a class.
As a group, list several ways we might examine female bean choice for oviposition. We will pick one experiment from the class to perform. Write your ideas below.
**Stop here. We will go over ideas for our experiment as a class and choose one to perform**
Outline the agreed-upon experiment using the criteria below.
- Formulate a hypothesis for this week’s experiment. Be specific!
- We will revisit the experiment in a week to collect data on the number of eggs laid. Formulate a hypothesis for this experiment.
- Identify the independent variable(s).
- Identify the dependent variable(s).
- What variables will you keep standard?
- What is your control?
- Design data collection tables for bot