LS: Speaking of Science Column February 23, 2009
First in a two-part series on bees.
One of the surprising but moving experiences of my life was the night I first watched a cell actually divide in two.
We all have learned that cells do this. I had seen television specials, documentaries and teaching films showing cell division. So it was surprising to me that when I actually saw the event myself, I found it profoundly emotional. Maybe that’s just me.
Later I was similarly affected in a class where I had students place corn pollen in a special
solution, and we watched the pollen tubes grow before our very eyes. This growth can occur in just minutes and is easily observed under a microscope. Corn pollen can grow up to 12 inches to reach a plant’s ovary. As I sat at a microscope and watched a mystery of life occur before my eyes, I was surprisingly moved.
Pollen is normally deposited on the stigma of a flowering plant, a structure rising some distance above the ovary (in human terms). The pollen tube grows down to the ovary and bursts, releasing two sperm cells onto the ovary. One sperm cell unites with the ovary to create the embryo. The other sperm cell unites with a special cell to form the endosperm.
The endosperm will become the food supply that nourishes the new embryo and/or humans in many instances. We intercede and eat the endosperm of such plants as wheat, barley, oats, corn, peaches, pears, cherries, apricots, grapes, berries, cucumbers, tomatoes and peppers.
Getting pollen to the stigma is a bit of a trick for plants since they are generally immobile and can’t get together in some central location to socialize. The process is called pollination, and generally it occurs in one of two ways: either by wind or by an intermediary animal.
Bees are the best known of these pollinators, although not the only ones. And while most folks think honey bees are the best pollinators, this isn’t true. In fact, honey bees are not even native to North America. They were first brought by the early pilgrims and quickly spread out to fill the continent. But prior to that there was a rich population of native bees on this continent that pollinated everything necessary very efficiently.
In fact, North America has one of the richest populations of these solitary bees in the world.
There are approximately 4,000 species of native bees in North America. These bees do not form large colonies with honey stores like honey bees do. Instead, each female mates and sets about establishing her own nest. She finds an appropriate site and lays her eggs one at a time, provisioning each egg with pollen and nectar for the year. After laying her last eggs she dies. But the new generation lives invisibly within her nest for the remainder of the year. This generation will hatch out at appropriate times the following year to complete the cycle.
Many of these bees are extremely local, found in only specific regions. Some are tied to the life cycle of a single plant and are found only where that plant thrives. Others are more general and widespread. Many of them nest in the ground. Others nest in hollow stems, or old beetle holes in logs. Many are very small, significantly smaller than honey bees.
They are not even colored in what most of us would think of as typical bee coloration.
Because they spend most of the year inside a nest, are active for only short periods and may not look like ordinary bees, they are invisible to most lay people.
However, “by their fruits ye shall know them.” Native bees out-pollinate honey bees by tremendous amounts. Native bees are the hidden pollinators. Often, when they are not present, crop yield is poor and losses are attributed to weather or disease, when instead it is a lack of pollinators. These little creatures are out of human sight, and out of human mind.
Gary McCallister is professor of Biology at Mesa State College and also owner/operator of Flaming Moth Productions and the Bee bar Bee Ranch, supplier of native bees, native bee nests and native bee information. He has a doctorate in biology.