From the farm to the supermarket to your dinner table...

Who are the pollinators that cause fruits to form from flowers? A pollination lesson from the supermarket and library.

By Stephen Buchmann

 

As you visit the supermarket, past colorful row upon row of neatly stacked fruits and vegetables, do you ever wonder how all that fruit gets there for you to easily select and eat. Or, as you crunch into a brilliant Red Delicious apple or green Granny Smith for a lunchtime snack--what were the steps involved to actually produce that fruit on the tree? In this lesson we'll be concerned with the very earliest steps in this process and not later events once the fruit is ripe, harvested and eventually carried in a giant semi-trailer truck to your neighborhood supermarket. Instead, we want to know, and for your class to think about, 'pollination' and the little animals, usually bees,that visited those apple blossoms and other flowering crops.

Classroom Activity:

Your class might choose to go on a field trip to your local supermarket, the produce department, or simply discuss some of your favorite foods which are fruits and vegetables. Another good choice would be to select a popular household or gardening magazine which can supply your class with colorful photographs and ideas for your food selections. Your first assignment is to select two foods which are either fruits or above-ground vegetables (such as tomatoes or zucchini). Do not select grains or nuts for this exercise. Once you have picked two fruits or vegetables you're ready to begin on your mystery pollinator adventure.
I) Did you see any flowers for sale in the supermarket?

If you live in a large city, there may have been a florist shop in the market. Were these flowers there for customers to buy and eat? No, those flowers are meant as gifts, floral bouquets to adorn and beautify a table in your home. Sometimes, however, flowers are sold in the supermarket for people to eat. These would include flowers such as nasturtiums. Do you like Broccoli? Then, you have actually eaten hundreds of tiny flower buds hiding under that yummy melted cheese sauce! Usually, however, when we go to the market to select produce, the flowers are long gone, having been transformed in an awe-inspiring process, the metamorphosis from flower to fruit. This lesson is all about flowers which require visits by bees, birds, bats, butterflies, moths, flies, beetles and other animals--the pollinators-- which carry the pollen from flower to flower producing the fruits and seeds that follow many weeks or months later.

Did you know that about every 4 out of 5 bites of food you eat is the direct result of bees and other animals pollinating those fruits and vegetables? That's right. About 80% of all the food we eat comes from fruits and vegetables that were insect-pollinated. Only 20% of our diet consists of grains and nuts which are wind-pollinated, and therefore do not require animal pollinators. So, remember that fact and thank a pollinator today. Without the birds and the bees, we would have a very boring lunch at school and possibly a nearly empty table at home.
II) Okay, your class has selected two types of food from the produce section. Now what's next? Here's where your school or local public library comes to the rescue. For both types of foods you picked (let's say it was an apple and a zucchini), you need to find out through some library research what those blossoms look like before they turn into the familiar fruits we eat. Of course, you could always visit an apple tree or garden plot and see the flowers firsthand--maybe even observing what kind of pollinators visit them--but many of the foods you selected may not grow in your area or bear flowers in the springtime when you are doing this pollination activity lesson. Your teacher and classmates can all help find a photograph or line drawing of what your two flowers look like. A color photograph would be the best to use for this exercise. Use all types of library reference books to track down what they look like. Encyclopedias are excellents sources, or maybe you'd like to go on a flower scavenger hunt across the Internet and World-Wide Web.

Make up a simple data sheet for the exercise as follows:

Flower   Color(s)   Scent     Size     Shape     Rewards
Name
========================================================
Apple
--------------------------------------------------------
Zucchini
--------------------------------------------------------
You may think of other floral charateristics to take note of, but these are the basic ones you'll need to finish this exercise. Write in the name of your two flowers on the lefthand side of the paper down the rows under the Flower Name heading. Then, across the other columns, put in the features of the flowers you discover from your library research and looking at drawings, paintings or photographs. Also, write down any information your reference books may have on what types of animals visit your flowers and who the real pollinators could be.III) Pollinator 'Syndromes'

Now that you know something about what shape, size, color your flowers are, along with information about their floral scents or whether they offer enticements of nectar or pollen, as floral rewards, to hungry pollinators, we can begin the final step in making the link from flowers on plants to food in your grocery store.

Pollinating animals visit flowers not because they are pretty or smell nice, but because the flowers offer sugary nectar (often twice as sweet as Coca-Cola!) and protein-rich pollen grains and they are hungry. Pollinating honey bees, Blue Orchard Bees, Leafcutter bees or bumblebees constantly search for food for themselves and for their ravenous grub-like larvae back at the nest. The flowes are 'trading' nutritious foods in the hopes that pollinating insects will be attracted, accidentally become dusted with bright yellow pollen and transfer the microscopic pollen grains from flower to flower. The pollen grains contain the sperm cells that must be transferred from the male parts of a flower (the anthers) to the top of the 'pistil' (known as the stigma) which is on the female part of a flower. This transfer of pollen from flower to flower (or even within the same flower) is known as pollination. Once there, the pollen grains send down thin pollen tubes carrying the sex cells needed to unite (fertilize) with the ovules within the swollen ovary at the base of the flower. Once fertilized, these little green ovules rapidly become the seeds within the swollen edible part that we call the fruit, like the white flesh of an apple surround the dark brown seeds within the apple core. Without the bees that carried the pollen grains on their bodies from flower to flower, there would be no apples or many many other fruits and vegetables. Without these little go-betweens, our diet would be limited to things like corn, rice, wheat and nuts which are pollinated by the wind and don't depend upon animals.

From your list of floral attributes (size, shape, color, scent, rewards) you can make a highly educated guess about what types of pollinators visit and pollinate your flowers, without ever having seen the plant in bloom or the pollinators actually visiting them. How? By using a technique we call 'pollinator syndromes' since different kinds of pollinators like certain kinds of flowers and are unable to visit other types.

Be thinking about the following questions and discuss them with your teacher and class:

  1. What size is your flower? (tiny, small, average, very large)
  2. Does the flower open during the daytime or at night? (what kinds of pollinators are active by day or night)
  3. What color(s) is your flower? Do certain pollinators visit flowers of a certain color?
  4. Does your flower have an unusual shape, such a long narrow tube, which for example a fuzzy fat bumblebee couldn't fit into? Does your suspected pollinator have the right equipment to visit the blossom and extract the nectar or collect the pollen?
IV) Confused? Here are some helpful hints about what kinds of flowers pollinating animals like to pair up with in this matching game in nature:
  1. Bees- Both honey bees and native wild bees such as bumblebees are attracted to flowes with bright lively colors (especially blues and yellows). They can't see the color red, so won┬╣t visit blossoms that are red. The flowers may be massed into a group of many smaller flowers, or may have a 'landing platform' for the bees to stand upon while they drink nectar or collect pollen. Such bee flowers often have pleasing fresh scents that humans find attractive. There is abundant nectar and pollen.
  2. Birds- (hummingbirds in this case) Red is the banner that says "Eat Here" to these fast-flying living jewells. The throat of these pink, orange or red blossoms is narrowly constricted so that only their narrow bills can enter to extract the abundant but dilute nectar. The flowers have no scent that we can detect. There is no landing platform on the flowers.
  3. Bats- Unless you live in the American southwest (such as Texas, Arizona, New Mexico or southern California) you aren't likely to have picked a flower pollinated by bats. Most of this happens in the tropical rainforests. Bat blossoms are large and very sturdy. The flowers are always presented at night as in the case of our Century plants (the genus Agave). There is lots of dilute nectar and the flowers are usually not brightly colored. They don't even smell that good. Some people think these flowers smell musty or like fruit. Some bananas are pollinated by bats.
  4. Butterflies- Blossoms built for butterflies have lively colors, especially pinks, blues and yellows. They are often grouped together in small masses. The floral tube is often narrowly restricted to just allow their slender tongues (the proboscis) into the opening. Fat bees keep away! They have very pleasant floral scents and abundant nectar.
  5. Moths- Not many of our crop plants are pollinated by moths, but just in case you selected one, here is some information. These flowers open during the evening or at night when moths are active. They often have very sweet pleasant scents (like night-blooming Jasmine) which we can smell from a long distance away. The flowers are almost always white and have abundant nectar but not much pollen. There may or may not be a landing area.
  6. Flies- "Yuck!" you say? Flies, especially the flower flies in the family Syrphidae are important pollinators. There hairy bodies are great for transporting those little pollen grains around helping to pollinate flowers and set those fruits. Flies may visit many types of blossoms, especially big open masses of them like on goldenrod. They also visit flowers which can smell like rotting meat (Has your mother ever had the experience of having a Stapelia plant from Africa bloom on the kitchen windowsill?). Other flowers trap and hold flies inside (like the Dutchman's Pipe) as pollinators. Did you know that you have flies (midges in this case) to thank for pollinating the cacao blossoms whose seeds are ground up to make the chocolate in your candy bar?
  7. Beetles- There are more kinds of beetles alive today than any other kind of insects. They are usually generalists and often visit many types of flowers for food, especially in the tropics. They are called 'mess and soil' pollinators because they generally wander around on the flower eating and chewing on everything. Very large flowers with numerous parts (such as a Magnolia) are pollinated by beetles. Beetles are not important pollinators of our crop plants like bees are. These blossoms often smell like overripe fruit.
V) Putting It All Together

Make the best guess you can on the kind of animal that you think your flowers would be pollinated by in nature. Have someone from your class put all the information on the chalkboard and tally up the responses. Have your class vote on the best candidate for the pollinator of that apple, zucchini or whatever fruit or vegetable you happened to pick out from your supermarket visit.

Consult your library reference books and see what the experts say about the types of animals that visit your flowers before they turned into the familiar fruits and vegetables you eat every day. How many flowers were pollinated by bees, how many by some other kind of animal. Compare your answers with those of other classes in your school who may have done the same exercise.
VI) Other Pollinator Questions to Think About



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