Monster Monarchs?
Brad Blue, Charissa Pederson, Rachel Wagner
Monticello, MN
Abstract |
Introduction | Methods |
Results | Discussion |
Acknowledgements | Literature Cited
Abstract
Will adding nutrients to a monarch's diet affect its growth and development? To
find the answer to our question, we had a control group and three different treatments
for milkweed which was fed to monarch larvae. Each day we would weigh and measure
each larva. From these treatments we found that the nutrients had a negative affect
on the larval growth and development, specifically their survival rate. None of
the larvae with fat added to their diets even made it to the pupa stage. A few of
the larvae in the protein treatment did pupate but none of them survived until the
end of our study. The sugar supplement had the least effect on the survival of the
monarchs, with 67% surviving until release compared with 93% of the control group.
Although the added nutrients dramatically increased the mortality rate of the monarchs,
they did not appear to affect the size or the developmental stages of the surviving
monarchs (with the exception of the group in the fat treatment – these died quickly).
Introduction
Monster monarchs? Can you imagine it? We did and, instead of imagining, we tried
to raise enormous monarchs. We decided to supplement the monarchs’ diet to determine
if the supplements would create the monster monarchs that we were seeking. Our research
question was "Will adding nutrientsa monarch's diet affect its growth and development?"
The nutrients we used were dissolved sugar (sugar), dissolved vegetarian protein
drink (protein), and spray on vegetable oil (fat). These three treatments were applied
to the principal diet of the monarch, i.e., milkweed. The control was water-rinsed
milkweed.
After coming up with this question we formed several hypotheses.
- Ha1: Fat (vegetable oil) will affect the monarchs’
growth and development.
- Ha2: Sugar (dissolved) will affect the monarchs’ growth
and development.
- Ha3: Protein (vegetable protein supplement) will affect
the monarchs’ growth and development.
- Ha4: Several of the nutrients will affect the monarchs’
survival rate.
- Ho: Adding nutrients will have no effect on the monarchs’
growth and development.
Methods
Each group member (Brad, Charissa, and Rachel) started out with 40 monarch eggs,
10 eggs in each of the three treatments and 10 eggs in the control group. We kept
each treatment in a separate tub which was replenished daily with fresh milkweed.
Every day we weighed the larvae on a metric scale and measured them with a metric
ruler. We also recorded the instar of each larva.
For each of the treatments, we placed a damp paper towel on the bottom of each tub
to maintain cleanliness. For the control group, we bathed the milkweed leaves in
tap water. For the sugar group, we mixed 3 sugar packets in 1/2 cup of water and
bathed fresh leaves in it. For the fat group, we sprayed a thin layer of vegetable
oil on both sides of the leaves. For the protein group, we dissolved 4 tsp. of protein
supplement in 1/2 cup of water. Then we bathed the leaves in the supplement and
placed them in the tubs. We fed each mixture to the correct larvae through pupation.
When they were adults, we fed them honey water and nectar from fresh flowers. The
butterflies were housed in net cages outside.
We conducted T-Tests on the final weight of the larvae prior to pupation and on
the final weight of the adult monarchs before being released. One week after the
last monarch emerged from its chrysalis we released our monarchs into the wild.
We used Chi-Square tests to determine the difference in mortality rates between
the treatments.
Results
Immediately, it became apparent that the fat supplement group was in trouble. The
larvae became discolored, did not gain weight or develop; they looked sickly and
by day four over 80% were dead. None of them survived through the fifth day. We
speculated that their problems might be related not only to their diet but also
to the physical presence of the oil on their bodies. Their tentacles and feet got
pasted to their bodies; they looked greasy and had difficulty moving.
We also had a high death rate within the protein treatment group. 33% of the larvae
pupated and only 4 (13% ) of the pupae emerged from chrysalis. None of them were
alive one week later.
Of the treatment groups, the ones whose diet was supplemented with sugar did the
best, with 67% still alive at the end of our experiment compared with 93% of our
control group (Figure 1).
Figure 1. Percent of larvae surviving in one control and three treatment groups.
Based on these data, we see that the treatment groups’ survival rate averaged 33%
while the control group’s was 93%. Using Chi-Squared analysis of mortality rates,
we can reject our null hypothesis with a confidence of 99.9%. Our findings definitely
support hypotheses Ha4; the supplements did have an effect on the Monarch’s
survival rate, a very negative effect. However, we see a slightly different picture
by looking at the growth rate of the survivors (those that did not die). The growth
rate of the Sugar and Protein treatments did not vary significantly from that of
the control group (Figure 2).
Figure 2. Average mass of larvae in one control and three treatment groups.
Using T-tests to find the differences between the final weights of larvae before
pupation we find:
- Control vs. Sugar: calculated t = 0.984 and t-critical = 1.34 (90%)
- Control vs. Protein: calculated t = 1.45 and t-critical = 1.63 (90%)
- We could not analyze the Fat treatment because they were all dead.
In terms of growth, we cannot reject our null hypothesis, because there is not a
significant statistical difference between the final weights of these groups. Likewise,
concerning the final weights and wing spans of the adult monarchs, we found no significant
differences, in fact the size of the sugar treatment survivors was slightly larger
(although not statistically significant) (Table 1).
Table 1. Average mass and wingspans for individuals surviving to adult stage.
|
Treatment |
Surviving |
Mass (g) |
Wingspan (cm) |
|
Control |
28 |
0.49 |
9.7 |
|
Sugar |
20 |
0.52 |
10.1 |
|
Protein |
0 |
-- |
-- |
|
Fat |
0 |
-- |
-- |
Discussion
We have not found the magical supplement that would grow "Monster Monarchs".
In fact, all of our treatments had a negative impact on the health of our monarchs.
Our experiment did, however, raise many interesting questions that could direct
future study.
We encountered difficulty in defining and measuring the terms in our hypothesis.
For instance, in determining growth and development, we came up with seemingly contradictory
results. On the one hand we intuitively know that a high mortality rate is not compatible
with healthy growth and development. However, one of the indicators we chose to
measure growth and development was the mass of the larvae and later the wing span
of the adult monarchs. These measures showed no significant difference between treatment
groups at any point in the development of the monarch (with the exception of the
"fat" treatment). At first glance, this would seem to indicate that if
the treatment didn’t kill them it wouldn’t negatively affect their health. But upon
examination we see that 10 larvae from the protein treatment entered the pupal stage,
at approximately the same weight as the control group (our assumption being at the
same level of health), but only four out of the protein treatment emerged (40%)
compared to 100% of the control group. Obviously, the supplements affected the monarchs’
health in ways in which a scale and a ruler were not able to measure. It would be
interesting to extend the duration of the experiment to see if the treatment group
reproduces at the same rate as the control group and to see if there are any residual
effects on subsequent generations.
Acknowledgements
Many and warm thanks to Dr. Karen Oberhauser, (University of Minnesota, Ecology)
the creator and inspiration behind this and many other monarch projects, Lee Schmitt
and Dawn Cameron (Science Museum of Minnesota) for their collaboration and orchestration,
and the National Science Foundation for the fiduciary commitment. Thank you to Carol
and Thomas Minoque for use of their property and our families for their support
of our science education.
Literature Cited
Hoth, Jürgen, Leticia Merino, Karen Oberhauser, Irene Pisanty, Steven Price, and
Tara Wilkinson, eds. 1999. 1997 North American Conference on the Monarch Butterfly.
Commission for Environmental Corporation: Montreal, QC.
Monarch Lab Web site: http://www.monarchlab.umn.edu
Oberhauser, Karen and Goehring, Liz. 1999. Monarchs in the Classroom. An Inquiry-Based
Curriculum for Middle School. Revised edition, Monarchs in the Classroom:
University of Minnesota.