MAY
2008

 

 

 

By
Tom Turpin
 
Professor of
Entomology
Purdue University

 

 

 

 

 

05-08-08

Bees and Blossoms Play the Pollination Game

Children's poet Aileen Fisher sums up the relationship between bees and flower blossoms in these lines from different poems: "Dandelions make pollen for the bees to take," and "buzzy old bees, dusting pollen from off their knees on apple blossoms." Poet Fisher is describing nature's pollination game.

Pollination is the key to plant reproduction. Most types of plants reproduce through seeds that develop following pollination. Pollination occurs when the pollen from the male part of a flower fertilizers the female part of a flower. The result is a seed that will germinate and produce a new plant.

There are three general ways that pollen is transferred in plants. The first, self-pollination, is when pollen is released and fertilizes the female structure in the same flower or in another flower on the same plant. Corn is such a plant. In corn, pollen falls from the tassel to fertilize the silks on the developing ear.

The two other types of pollination involve pollen being moved from one flower to another. When the pollen is carried by the wind, the plant is known as wind pollinated. Such plants produce a lot of pollen and are the bane of hay fever sufferers.

Many plants enlist the aid of animals to transfer pollen from one plant to another. Insects are the majority of the pollen carriers of the world, but hummingbirds and a species of bat also carry pollen. Bees are the primary insect pollinators. Several other types of insects, including butterflies, moths, a few beetles and a wasp or two also transport pollen.

But animals don't play the pollination game just for the fun of it. They play for pay. And the plants that need living creatures to transport pollen pony up the pay. What is the pay? It's pollen and nectar, both of which are food items for the animals that play the pollination game.

The system works this way. The reproductive parts of plants are called flowers. The flowers are a source of pollen and or nectar for the animals that become pollinators. While the animal is visiting the flower it gets covered with pollen. And this is where the plants in the pollination game play the trump card. For the system to work, the animal pollinator must, while carrying pollen, visit another flower of the same plant species. So each plant limits the amount of nectar or pollen available to force the pollinator to visit another flowers to complete a load. When this happens, pollen is moved from flower to flower, resulting in cross-fertilization.

To enhance the effectiveness of the pollination system, the best insect pollinators are what scientists call flower constant. That means that when these insects are collecting a load of nectar or pollen, they visit the same type of plant on one trip, for instance apple blossoms.  When most people think of insect pollinators, honey bees come to mind. Indeed, honey bee colonies are moved into apple orchards, orange groves and blueberry fields to guarantee pollination and fruit yields. As poet Fisher pointed out, bumble bees are also good pollinators.

Bees of all types are good pollinators because they collect pollen as a food source. However, not all insects called bees are pollinators. Yellow jackets are wasps but are sometimes called bees. Yellow jackets feed on other insects and sweet liquids, like fruit juices, but these insects do not consume pollen.

Some of the best bee pollinators are called leaf cutter bees. These small, sometimes brightly colored, bees live a solitary lifestyle. They are not social insects. Each bee has a nest and collects and stores pollen in cells in the nest as food for bee larvae. Leaf cutters partition the nest with sections of cut leaves. Such solitary bees are responsible for pollination of many flowering plants. These tiny bee pollinators go unnoticed by most people. But we appreciate their work when we take a bite out of a juicy apple that is a result of the insect-and-flower pollination game.

 

Writer: Tom Turpin
Editor: Olivia Maddox