THE EFFECT OF LIGHT ON MONARCH LARVAE

GROWTH

EDU 246

Michele Koomen

October 31, 2008

Libby Beytien-Carlson (lbetien@gustavus.edu)

Heather Jopp (hjopp@gustavus.edu)

Ashley Neaton (aneaton@gustavus.edu)

Erin Truebenbach (etrueben@gustavus.edu)

“On my honor, I pledge that I have not given, received, or tolerated others’ use of

unauthorized aid in completing this work.”

Abstract:

1

In the beginning of our experiment, we had three experimental groups of nine larvae,

separated by the amount of light exposure. These categories were constant light (under a desk

lamp of 60 watts for twelve hours a day), natural light (average dorm room), and constant

darkness (inside closet). The purpose of our experiment was to see if there is any relationship

between the amount of light exposure and larvae growth. Looking at our results, we found that

the larvae under the desk lamp grew faster compared to the other two groups. One obstacle

involved in our experiment was the quality of the food supply. The milkweed may have been

contaminated or spoiled due to the changing of the season, and therefore unappetizing for the

larvae. Another problem that may have influenced our results is the health of the larvae.

Because our experiment only contained nine larvae in each group, a small percentage (three) of

our larvae were lost due to fatalities in the first couple weeks. We learned that conducting an

experiment with larger sample sizes is more reliable and accurate than smaller samples. We also

found that larvae growth is affected by the amount of light they are exposed to.

Introduction:

On the first day of Elementary Science, we were all excited to learn that we would

receive a monarch larva for our very own. Excited to see how our new friends would grow and

develop, we kept detailed observations in our science journals until they reached the monarch

stage. This experience is now behind us, but it provided us with the inspiration to conduct our

present experiment. After brainstorming through ideas, we were interested by how the larvae

would develop under different lighting conditions. So we came up with our research question:

“How does the amount of light in the environment affect the growth of the monarch larvae?”

We also came across a similar study from some Elementary Science students from last year.

Holly Bohlen, Kristin Carr, Mary Ellen Korby, and Alisha Rheaume did a study titled,

“Monarchs: Light vs. Dark Conditions Affect on Rate of Growth.” After looking through their

experiment, we came up with some ideas on how to improve the study. We used a bigger sample

size, we learned what data to record, we looked at their limitations and tried to reduce those best

2

we could, and we took a look at their results, which lead us to our three hypotheses. HA1: The

higher amount of light exposure will lead to a higher growth outcome. HA2: The lower amount

of light exposure will lead to a higher growth rate. HO: All the larvae will grow at about the

same rate, no matter how much light exposure. Our variables would then be the amount of light

(independent), and the growth of the larvae (dependent).

Design and methodology:

Before we began our experiment, we gathered some required materials. We used nine

liter containers, a scale (in grams), a ruler (with centimeters), a constant supply of common

milkweed, and of course the monarch larvae. At the beginning of our experiment, we received

27 total larvae, all similar in size. We separated these into three different experimental groups

based on different light exposures. We then put three larvae in each container. Three containers

were kept under a desk lamp with a 60 watt bulb for twelve hours a day. Another three

containers were under normal lighting conditions and represented our control group. The last

three containers were kept in a dark closet, with almost no light exposure. We fed all the larvae

the same amount of common milkweed to insure that the growth would not be altered by varied

food sources. In order to record our data, every Tuesday and Thursday we met after class and

weighed (in grams) and measured (in centimeters) each larva and found the average for each

container. We observed our larvae sample for three weeks beginning on September 24, 2009,

and ending October 13, 2009. By the end of this time period, we recorded our data even though

some larvae had reached the chrysalis stage, while others had not.

Results:

Average Weight Results (grams)

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Average Length Results (centimeters)

WEIGHT (grams)

UNDER LAMP (60 Watt bulb)

NORMAL LIGHTING CONDITIONS

Mean Median Mode9-24-09 .024 .023 .0239-29-09 .034 .035 .03410-1-09 .061 .098 .08

10-6-09 (1fatality)

.49 .43 .45

10-8-09 .665 .68 .6810-13-09 (2 chrysalis, 3 j-

form).665 .665 .665

Sept 24 Sept 29 Oct 1 Oct 6 Oct 8 Oct 13

CLOSET .023 .046 .17 .307 .539 .812 (3 in j-form/chrysalis)

ROOM .024 .034 .061 .49 .665 .665 (5 in j-form/chrysalis)

LAMP .024 .063 .23 .64 .849 1.102 (5 in j-form/chrysalis)

Sept 24 Sept 29 Oct 1 Oct 6 Oct 8 Oct 13

CLOSET .59 1.19 1.56 2.45 3.243 3.675 (3 in j-form/chrysalis)

ROOM .73 1.04 1.78 2.85 3.467 3.85 (5 in j-form/chrysalis)

LAMP .61 1.29 2.18 3.11 3.83 4 (5 j-form/chrysalis)

Mean Median Mode9-24-09 .024 .023 .0239-29-09 .063 .067 .06510-1-09 .23 .27 .2710-6-09 .64 .56 .510-8-09 .849 .68 .62

10-13-09 (5 chrysalis, 1death)

1.102 1.102 1.102

4

CLOSET

Mean Median Mode9-24-09 .023 .023 .0239-29-09 .046 .043 .04510-1-09 .17 .1 .110-6-09 .307 .27 .3310-8-09 .539 .506 .51

10-13-09 (1 chrysalis, 2j-form)

.812 .812 .812

LENGTH (centimeters)

UNDER LAMP (60 Watt bulb)

NORMAL LIGHTING CONDITIONS

Mean Median Mode9-24-09 .73 .77 .749-29-09 1.04 1 110-1-09 1.78 1.77 1.77

10-6-09 (1 fatality) 2.85 2.75 2.810-8-09 3.467 3.6 3.6

10-13-09 (2 chrysalis, 3j-form)

3.85 3.85 3.85

CLOSET

Mean Median Mode9-24-09 .59 .57 .579-29-09 1.19 1.2 1.2

Mean Median Mode9-24-09 .61 .64 .679-29-09 1.29 1.33 1.3310-1-09 2.18 2.1 2.1410-6-09 3.11 3.43 3.510-8-09 3.83 4.2 4.2

10-13-09 (5 chrysalis, 1death)

4 4 4

5

10-1-09 2.18 2.1 2.1410-6-09 3.11 3.43 3.210-8-09 3.83 4.2 4.2

10-13-09 (1 chrysalis, 2j-form)

4 4 4

Interpretation and Discussion:

We are comparing our results to our null hypothesis, which states that all the larvae will

grow at about the same rate, no matter how much light exposure. Prior to the experiment we

were not sure how the results would end up. However, when the end of the experiment came, we

found that the larvae grew best under the 60 watt light bulb, and the ones in the closet were the

slowest to develop. Looking at our data, one can see this result by the numbers recorded each

week. The larvae under the lamp grew at a more rapid rate than the other groups and had more

larvae in the chrysalis and/or j-form shape by the end of the experiment. The results we found

were also consistent with another similar study performed by previous students. Both studies

found that light affected the growth rate positively. So, our study adds to the evidence that light

does have an effect on larvae growth.

Implications:

Throughout the experiment, we experienced many limitations. Through these limitations

we came up with many ideas to make our experiment even better if we were to perform the

experiment again. The first thing that we would change in our experiment would be the size of

the population. We thought that having a sample size of 45-50 larvae would give more accurate

results. In addition, with a bigger sample size, fatalities wouldn’t affect the data as much as a

smaller sample size. In the future, we would like to improve the environments of the larvae as

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well. We would do so either by giving the larvae a bigger area to live in, such as a pickle jar or

other larger container. The other thing we considered was having each larva in his or her own

individual container. By making the housing either bigger or having the larvae in their own

containers, we believe it would help them better grow and develop. Another change for future

projects, if possible, would be to have a personal scale to weight the larvae in the closet. This

would help with the consistency of the experiment by keeping them in a constantly dark

environment. One last change we would make for our experiment was the amount of food. If

we had stored a supply of adequate, healthy milkweed, the larvae would have been better off,

and had a consistent supply of milkweed.

Limitations:

Throughout this experiment, we encountered many limiting factors that affected our

results. The first limitation we experienced was receiving the larvae at different ages. This was

a limitation because we were not able to obtain a consistent and accurate sample. This could

have skewed our results, because the larvae under the light could have been older than the rest of

the sample; therefore, they could have grown quicker and would have reached the chrysalis stage

quicker. A second limitation that we experienced was having the larvae in consistent darkness.

An occurrence of this was when we had to measure and mass the larvae. The constant changing

of light from consistent darkness to natural sunlight to artificial lighting in the classroom could

have caused skewed results. Another factor that may have played a role was the amount of

larvae in each container. Having each larva in his or her own container may have displayed a

different result. Being in a container with other larvae could have affected how the larvae

interacted with one another. Evidence of this was when our larvae were seen head butting and

fighting each other. Because of this friction between the larvae, more fatalities may have

resulted rather than if the larvae were in separate containers. Another limitation we experienced

in our study was the amount of food and the condition of the food. The food played a crucial

role in the development and growth of the larvae. Our food source consisted of common

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milkweed, but due to weather conditions, the supply was inadequate and scarce. At one point of

our experiment, we found our milkweed to become brown and moldy, causing the larvae to stop

eating and growing. The food source may have been a contributing factor to the mortalities. A

further limitation that we experienced was the problem of death in our experiment. Throughout

the experiment, we lost three larvae, leading to inaccurate data. Also relating to death, one

container may have been contaminated with disease. In one container in the closet, a larva

exploded after reaching the chrysalis stage. This may have caused the rest of the population to

become diseased, therefore influencing the growth and development of the other larvae in that

container. Another obstacle we experienced was when we measured the length of the larvae. It

was hard to get an accurate measurement of their length due to activity of the larvae.

Connecting with Nature:

As we conducted our experiment, we found that it connected to the Nature of Science

article in many ways. One of the ways that nature connected to our experiment was the concept

that the world is understandable, in the areas that nature can affect the growth and development

of a species. We also learned about the process of conducting an experiment. We looked at

every aspect of an experiment. We posed our own question, created three hypotheses, conducted

the experiment, collected the data, and finally analyzed the results that were needed to answer

our question. We found results to be solid evidence to what has been previously conducted.

This shows that scientific knowledge is durable, but can be modified throughout the years.

Modifications can occur through the changes in technology, the amount of knowledge available,

the way the experiment is conducted, and the types of resources available. Our experimental

topic is a topic that can be looked at in more detail, and can be studied for further

experimentation.

Conclusion:

8

At the beginning of our experiment, we were unsure what outcomes would occur.

However, as the experiment unwound, we found that light actually did affect how the monarch

larvae grew. We found that the larvae in the most lighting grew at the fastest rates. We are

unsure of why this resulted the way it did. One possible explanation could be that the constant

light exposure triggered their minds to think that it was always day time, and therefore caused

them to eat more. As a group, we experienced numerous limitations, but also grew from these

limitations. Our next experiment would include many new and improved methods of rearing the

monarchs. Overall, we learned how a variable, such as light, can affect the growth of monarch

larvae.

References

American Association for the Advancement of Science.  (1989).  Project 2061: science for all

Americans. Washington, DC: Author.

Bohlen, H., Carr, K., Korby, M.E., Rheaume, A. (2008). Monarchs: Light vs. Dark Conditions Affect on Rate of Growth.

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Appedixes:

9/24/2009 9/29/2009 10/1/2009Weight Avg

(g)Length Avg

(cm)Weight Avg

(g)Length Avg

(cm)Weight Avg

(g)Length Avg

(cm)CLOSET

# 1 0.023 0.57 0.054 1.16 0.2 1.67#2 0.022 0.7 0.043 1.2 0.1 1.33#8 0.024 0.51 0.041 1.2 0.1 1.67

Totalavg 0.023 0.59 0.046 1.19 0.17 1.56

ROOM#3 0.027 0.77 0.035 1 0.07 1.47#5 0.023 0.6 0.033 1 0.098 1.77#9 0.022 0.83 0.037 1.13 0.16 2.1

Totalavg 0.024 0.73 0.034 1.04 0.061 1.78

LAMP

10

#4 0.028 0.7 0.054 1.33 0.287 2.1#6 0.023 0.5 0.067 1.33 0.27 2.6#7 0.022 0.64 0.069 1.2 0.134 1.83

Totalavg 0.024 0.61 0.063 1.29 0.23 2.18

10/6/2009 10/8/2009 10/13/2009WeightAvg (g)

Length Avg(cm)

WeightAvg (g)

Length Avg(cm)

Weight Avg(g)

Lenth Avg(cm)

CLOSET# 1 0.27 2.3 0.459 3.1 1.036 3.6#2 0.45 2.94 0.506 3.4 0.5875 3.75#8 0.2 2.1 0.651 3.23 2 in j-form, 1 in chrysalis

Totalavg 0.307 2.45 0.539 3.243 0.812 3.675

ROOM

#3.41 (1

fatality)2.75 (1fatality) 0.68 3.7 1 chrysalis, 1 j-form

#5 0.63 3.13 0.74 3.62 j-form &

.865 4.3

#9 0.43 2.67 0.574 3.11 chrysalis &

.465 3.4Totalavg 0.49 2.85 0.665 3.467 0.665 3.85

LAMP#4 1.1 3.67 1.287 4.2 3 chrysalis#6 0.56 3.43 0.68 4.2 2 chrysalis, 1 death#7 0.27 2.23 0.58 3.1 1.102 4

Totalavg

0.64 3.11 0.849 3.83 1.102 4

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avg