Each year we pose some questions and challenges for students. We know some teachers have used these ideas for classroom discussions and a few students have used Monarchs as the basis for Science Fair or independent study projects, but we haven't received much feedback. I guess you are all shy, but there is no need to be. Let's share our experiences and learn from each other! We can't make much progress unless we all communicate. If you have a report on a Monarch project, and wish to share it with others, please send it to us and we will make it available online.
The following challenges are in the form of questions about Monarch mysteries. Each mystery can be answered in two ways: you can provide an answer or hypothesis and/or you can show how you could test a hypothesis, in other words write a short research proposal. The answers to these questions about Monarchs are unknown, but by making careful observations and/or designing appropriate experiments, students can obtain answers to these and many other questions that will contribute to our knowledge of Monarch biology.
There are some pretty neat questions to investigate and they are not as hard as they look. Give them a try and send us your report.
What is the preferred sugar concentration of nectars used by Monarchs?
If given a choice of colors associated with feeding dishes, will Monarchs show a preference for a particular color?
How much leaf tissue (in weight) does a Monarch larva consume through all of its larval stages?
Since male Monarchs are larger and heavier than females, do male larvae eat more leaf tissue?
What is the ground speed of a migrating Monarch in the absence of wind?
How does wing beat frequency change with wind speed and direction?
How do Monarchs use thermals (rising masses of warm air) to reduce the energetic cost of flight?
Milkweed species vary greatly in leaf toughness and chemistry. Do Monarchs reared on different milkweed species all grow at the same rate and reach the same size?
Each year there are reports of Monarchs that wash up on the shores of large lakes in substantial numbers. Usually these observations are made in late September or early October. Cold fronts and sudden storms are associated with some of these deaths but often the weather is moderate (65-75°F) when this occurs. Why? Think physics and muscle physiology! For those with some skills in physics and math, it shouldn't be too difficult to develop a predictive model that would explain the conditions under which Monarchs drown while attempting to cross lakes.
NECTAR AND FLOWER COLOR
Scientists usually ask questions that are derived from observations and known facts. For example, Monarchs feed on nectar and we know that nectars vary among flower species in the amount of sugar and amino acids they contain. However, flowers also differ in color. In the field you observe that Monarchs visit blue/purple flowers more frequently than white flowers. Why? Could it be the differences in nectar or color, or even something else, that determines the differences in visitation rate? How would you find out? Hint: Think of a series of simple experiments that involve only artificial nectar and color. Your first objective is to determine whether Monarch choose to visit flowers based on color. Once the role of color is established, you can design tests to determine if Monarchs can discriminate between nectars of different qualities.
DO THEY MIGRATE?
Here's a tough one. Do Monarchs reared in the classroom in September join the migration if released outdoors? Propose experiments to determine the conditions that induce diapause and/or migration (they may not be completely linked). Hint: Light duration and temperatures are variables you can manipulate in the classroom but to really know what is going on you need "natural" controls.
There are several species of aphids that feed on milkweeds and lots of things feed on the aphids, except those yellow/orange aphids. Nobody seems to feed on them. Is this true? And, if so, why aren't they attacked by predators? To answer this challenge you will need to make some first hand observations, learn some milkweed chemistry, and propose a number of hypotheses and experiments with typical aphid predators such as ladybugs and lacewings. Of course, you could easily get sidetracked doing some nifty experiments on aphid population growth. They're amazing! Have you ever seen an aphid give birth to baby aphids? It's cool.
LAYING ON THE GREEN
It often happens that two different scientists reach opposite conclusions based on tests or observations of what appear to be the same thing. Recently, in response to questions and observations about Monarch butterflies laying eggs on "anything green" Karen Oberhauser maintained that milkweeds or the "essence of milkweed" must be present for egg laying to occur, and she cited the recent study by Haribal, M. and J. Renwick (1996): Oviposition stimulants for the Monarch butterfly - flavonal glycosides from Asclepias curassavica. Phytochemistry 41:139-144. In this paper, the authors show that one factor that stimulates egg laying is the presence of flavonal glycosides in the leaves. They also showed that females will lay eggs on an opaque material covering a plant; that is, the females laid eggs even though they couldn't see or touch the leaves.
In contrast, in my laboratory, even in the absence of plants, Monarch females laid so many eggs on the green teflon scrubbers we use in our feeders, that we had to stop using them. However, we found that they would seldom lay eggs on the yellow, orange, blue, red or purple scrubbers whether milkweed was present or not. (Richard Esdale also observed egg laying on a yellow plastic sponge soaked in a artificial nectar in the absence of milkweeds).
How can we resolve these apparent differences? The first observation emphasizes the role of scent stimuli and suggests, but does not show, that vision is not important. The second observation implies that vision, and the color green in particular, can be important if combined with other stimuli. What does the green teflon scrubber sitting in the nectar dish have in common with the plants? A little bit of logic and some research will give you the answer.
WHY THE BOTTOM?
Monarch females are choosy egg layers and in the wild they place most of their eggs on the undersides of new leaves on milkweed plants. But why do they choose to lay eggs on the undersides when it would appear to be easier, and to take less time, to lay the eggs on the upper surfaces of the leaves?
This is really pretty easy. Start by asking some questions about the microenvironments found on the upper and lower leaf surfaces. Once you have formulated your hypotheses and logically established why it might be important for females to lay eggs on the undersides of leaves, explain why they don't always do so. In the research proposal, show how you would test your hypotheses.
DO MONARCHS COMPETE WITH OTHER SPECIES?
This is a question for young ecologists. What do we mean by competition? What kinds of competition are there? What do organisms normally compete for? If you can give a general answer to these questions, you can then ask if Monarchs compete with other species.
What do you think? Given what you know about the biology of Monarchs and other organisms that Monarchs are likely to interact with, what are your hypotheses regarding the intensity of competition between Monarchs and other species. Whether you think competition is strong or weak, how would you test your hypothesis?
For students younger than 12 years of age:
We know that Monarchs will feed from dishes containing teflon scrubbers and artificial nectar. The teflon scrubbers are available in a variety of colors and the nectar can be easily prepared. The challenge is to design an experiment using the feeders and nectar to show one or more of the following:
1. Whether Monarchs have a color preference.
2. Whether Monarchs prefer nectar with a specific sugar concentration.
3. Whether Monarchs can "remember" or learn a color, nectar type or dish location