Female bean beetle response to approaching males in bean beetles (Callosobruchus maculatus)
Student handout
Objectives
 Brainstorm characteristics (female, male, and environmental) that may influence how female
bean beetles respond to approaching males.
 Design and perform an experiment that determines how one of these characteristics may affect
how females respond to approaching males.
Introduction
Polyandry is a common mating system in which females mate with more than one male during the
breeding season. Types of animals exhibiting polyandry are incredibly diverse and include some birds
(e.g., red-winged blackbirds), insects (e.g., honeybees), mammals (e.g., chimpanzees) and fish. Benefits
associated with polyandry include receiving good genes from a mate and increased assurance that eggs
will be fertilized (Alcock 2010). Females may also receive gifts (e.g., food) when they mate with males
(Alcock 2010). Costs associated with polyandry include time and energy spent searching for additional
mates, risk of losing parenting help from a male that detects female cheating, and health risks (e.g., STDs
and injury during mating; Alcock 2010). Given the costs that may accompany multiple matings,
examining female choice associated with mating is important in understanding polyandrous mating
systems.
Female bean beetles (Callosobruchus maculatus) are polyandrous (Arnqvist et al. 2005) and are injured
when the spines on the male’s intromittent organ penetrate the female genital tract (Crudgington and
Siva-Joth 2000). Female bean beetles have limited ways to deter approaching males. Essentially, they can
kick or move away (Savalli and Fox 1999). Female bean beetles exhibit premating activity that includes a
fixed standing posture accompanied by contraction and relaxation of the abdomen (Rup 1986). Rup
(1986) stated that female bean beetles always terminate the mount by dragging and kicking the male,
indicating that female choice plays a role in mating.
Which male a female “chooses” may be driven by characteristics of the male, characteristics of the female
herself, or characteristics of the environment. The main question to be addressed in this experiment is:
What characteristics influence female responses to male courtship attempts?
Materials
 Bean beetles raised on mung beans and bean beetles raised on black eyed peas
 Petri dishes (35 mm and 90 mm)
 Unused mung beans and black eyed peas
 Rulers
 Markers
 Dissecting scopes
 Forceps or small paintbrushes
 Stopwatches
 Other assorted items that your experiment requires
Experimental Design
The research question is: What characteristics influence female responses to male courtship attempts?
Your specific hypothesis and prediction will be determined by your group, as this is an open-inquiry lab.
Week 1: You may use online resources to assist you in the following activity.
K. Buckholz and S. Larimer. www.beanbeetles.org
Brainstorm characteristics of males that might influence a female’s choice to mate with them.
Brainstorm characteristics of females that might influence their choice to mate with males.
Brainstorm characteristics of the environment that might influence a female bean beetle’s choice to mate
with males.
Week 2: Complete the following in lab.
As a group, choose one characteristic from one list above on which to focus for your experiment:
____________
Research question:
Research hypothesis:
Research prediction:
Null hypothesis:
Prediction associated with null hypothesis:
Describe your methods:

list the variables you will manipulate in your experiment
K. Buckholz and S. Larimer. www.beanbeetles.org

list the variables that you will keep constant in your experiment

describe the data you will collect (to determine if your prediction supports your hypothesis)
and how frequently you will collect data

list each possible outcome for your experiment

describe your experimental set-up (pictures may help), focusing on how variables will be
manipulated, characteristics of beetles you’ll use, and how many replicates you’ll have of
each condition

state the statistical test that you will use to analyze your data and justify use of this test.
K. Buckholz and S. Larimer. www.beanbeetles.org
** You will write a report of your study. Details are provided in a separate document.
Literature Cited
Alcock J. 2010 Animal Behavior. 9th ed. Sunderland, MA: Sinauer Associates.
Arnqvist G, Nilsson T, Katvala M. 2005. Mating rate and fitness in female bean weevils. Behav Ecol
16:123-127.
Crudgington HS and Siva-Jothy MT. 2000. Genital damage, kicking and early death – the battle of the
sexes takes a sinister turn in the bean weevil. Nature 407:855-856.
Rup RJ. 1986. Mating and its attendant behavior in Callosobruchus maculatus (F.) (Coleoptera:
Bruchidae). J Stored Prod Res 222:77-79.
Savalli UM, Fox CW. 1999. The effect of male mating history on paternal investment, fecundity and
female remating in the seed beetle Callosobruchus maculatus. Funct Ecol 13:169-177.
K. Buckholz and S. Larimer. www.beanbeetles.org