Brad Blue, Charissa Pederson, Rachel Wagner

Monticello, MN

Abstract  |  Introduction  |  Methods   |  Results  |  Discussion  |  Acknowledgements  |  Literature Cited  |  Research Projects

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.

H_a1: Fat (vegetable oil) will affect the monarchs’ growth and development.

H_a2: Sugar (dissolved) will affect the monarchs’ growth and development.

H_a3: Protein (vegetable protein supplement) will affect the monarchs’ growth and development.

H_a4: Several of the nutrients will affect the monarchs’ survival rate.

H_o: 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 H_a4; 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.

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.