Bees most efficient pollinators

StoryImage( ‘/Images/Story//Auto-img-11533344548789.jpg’, ‘Photo by Dr. Robert A. Hedeen’, ‘Two bees gather nectar and pollen from a head of flowers.’);

Flowering plants have two types of flowers—perfect and imperfect.

The perfect flower has both male (stamens) and female (pistil) sexual organs, and pollen produced by the stamens may fertilize the ovule in the pistil of the same flower.

On the other hand, imperfect flowers contain only one set of reproductive organs, are termed either staminate or pistillate, and must depend on some outside force to transfer the pollen of one plant to the pistil of another.

Many of our most important plants have imperfect flowers, so help from the outside is necessary for them to reproduce. Wind blowing the pollen from one plant to another sometimes accomplishes this, but insects are, by far, more responsible for the transfer of pollen from a male plant to a receptive female plant. Several groups of insects may act as pollinators, but no group is more efficient in this process than bees.

Bees belong to the insect order Hymenoptera (membranous wings), which includes the ants, bees and wasps. This group is the most advanced of all insects, and has evolved many specialized features. Approximately 20,000 species of bees have been described, and they are found all over earth, except Antarctica.

Bees are, by far, the most efficient pollinators in the natural world, being singularly adapted to do this job. They may focus on gathering either nectar or pollen, depending on their greater need at a given time. Nectar is used as an energy source, and pollen as a source of protein and other essential nutrients.

To suck up the sugary nectar from a flower, bees have an elongated, hollow proboscis that may be unfurled to reach deep into a flower to get at the goodies. Most bees are covered with hairs that give them a fuzzy appearance, and, as they root around in a staminate flower, pollen grains adhere to the hairs. In addition, the body hairs contain an electrostatic charge that facilitates the sticking of pollen grains to the hairs. As they move from flower to flower, pollen is rubbed off their bodies and fertilizes a female flower.

Bees foraging for pollen will periodically take a time-out to groom themselves and, with the aid of their legs, sweep the attached pollen into special receptacles found on the legs and, sometimes, the underside of the abdomen. These pollen receptacles are called pollen baskets and are used to transport the pollen back to the hive or nest, where it is made into bee bread to be used as food.

Pollen baskets are of special interest to me as they were first described about 1910 by the late Dr. D.B. Casteel, longtime chairman of the Department of Zoology at The University of Texas. It was a great privilege for me, as a graduate student, to be Dr. Casteel’s assistant in the entomology and Advanced Invertebrate Zoology courses he taught. I used to have an autographed reprint of the paper he published describing pollen baskets, but it has been lost in the shuffle of many moves over the years.

Honey bees are very efficient pollinators, and many beekeepers have relegated the importance of honey production to their use as pollinators. Hives of bees may be transported long distances to be rented out to owners of orchards and other producers of crops that, to be profitable, require bee fertilization. Of course, any production of an excess supply of honey is a bonus. Honey provides the food for the bees, as they winter-over in the hive. For a colony to avoid starvation, a sufficient amount must be left in the hive until flowers appear again in spring.

Visiting flowers to gather nectar and pollen is a hazardous occupation for bees. Assassin bugs and spiders frequently hide in flowers to catch bees for dinner. Some birds have a special affinity for bees and capture them when they leave a flower. In addition, bees are especially susceptible to some insecticides used in the garden, and may be killed by direct poisoning or the tainting of their food supply.

It is estimated one-third of the world’s food supply depends on insect pollination, most of which is accomplished by bees.

Next time you go into a supermarket and marvel at the display of the many fruits and vegetables displayed, remember the shelves would be practically empty if not for our good friends, the bees.

From the July 19-25, 2006, issue

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