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Diversify With Pollen Bees

This article is reprinted with the author's permission from American Bee Journal , Volume 134, No. 9, September, 1994. It has been modified slightly from the original version.

Dr. Suzanne W.T. Batra
Bee Research Laboratory
U.S. Department of Agriculture
Agricultural Research Service
Beltsville, Maryland

Pollen Bees

Pollen bees! What are these? Who ever heard of them? If you have not heard of pollen bees, that's not surprising, because this inclusive term was coined only in 1992, to describe all the bees other than honey bees that help to pollinate our crops and wild flowers. They have also been called "native bees," "wild bees," and "non-Apis bees." Before Europeans brought honey bees to North America, pollen bees did all of the bee pollination work here. The term "honey bees" includes bees that store liquid honey and make waxen combs that people can harvest. Some of these bees have been domesticated for the sake of their honey and wax production. There are 7 species of true honey bees, all in the genus Apis, including the two domesticated or managed species that are used for crop pollination. There are over a hundred species of tropical stingless honey bees, which are closely related to Apis. Several species are kept in hives by Native Americans for honey and wax production. Honey bee societies are unusual among social insects because honey bee queens cannot survive or start new nests without the aid of a swarm of daughter workers. Such "hyper-social" queens are too specialized to ever succeed on their own, as do pollen bees.

All of the rest of the bees (Apoidea) are called pollen bees, because they are valued only for their services as pollinators. Although they do make honey from nectar, they make only a little of it, and it is mixed up with pollen and other substances, such as glandular secretions and plant oils, to make the bee bread used to feed their brood. Thus, it is not palatable for humans. Their brood cells are usually not made of wax, but instead may be made of dried mud, bits of leaves, plant resins, plant hairs, and glandular secretions, even including polyesters. They may be underground, or in holes in wood or twigs. Most kinds of pollen bees have neither queens nor workers, but live as solitary bees, where all females mate, and then each makes her own simple nest of about ten cells, provisions them all by herself, and lays all the eggs. Thus, she is a single working mother, dying of old age and hard work before her offspring emerge from their cells. A few kinds of pollen bees, such as bumble bees and some sweat bees, are "eusocial," when the mother bee lives long enough to become a queen and have the assistance of her worker daughters. Usually, solitary pollen bees have only one generation annually. Different species are active adults at different times of the year, each flying for 4-6 weeks, their adult activity coinciding with the period of bloom of their preferred host plants. The rest of the year, most live as developing brood and dormant adults in cells. This characteristic makes them easy to manage for crops that have a brief blooming period, since the bees can be put into the crop during their adult stage, and then put into storage for the rest of the year, when they are not needed. Each bee species to be used should be teamed up with the crop that it prefers, and used in a climate similar to that in its native land. Unlike drone honey bees, the long-lived, independent male pollen bees contribute to pollination, because they frequently visit flowers for nectar.

There are over 20,000 species of pollen bees world wide. That's twice the number of species as all the birds (9,040) and five times the number of mammal species (4,000) in the world. Pollen bees have diversified to occupy all habitats, except underwater and in Antarctica. Because they are efficient pollinators, most of the beautiful diversity of floral shape, size, color and fragrance has evolved to attract pollen bees. In North America alone, there are over 3,500 species of pollen bees. They are of varied sizes and colors, from big, black, buzzy carpenter and bumble bees to tiny green sweat bees. They are most diverse and abundant in deserts, prairies and other undisturbed natural habitats. Due to intensive and extensive cultivation, irrigation, monoculture crops, pesticide use, urbanization and even traffic, which makes bee road-kill, natural populations of pollen bees have declined in many areas. Thus, since the 1950's it has become necessary to use honey bees for pollination, and to develop methods to artificially raise or manage pollen bees for use on some crops. Although most pollen bees are solitary bees, with only one female per nest, these females can be very gregarious, preferring to make their nests side-by-side in the same area, much like urban apartment-dwellers. Such gregarious solitary bees are the best to manage, in order to get numerous bees and nests all together in a small space, handy to manipulate for crop pollination.

Perhaps after reading this far, you would like to try raising and using your own pollen bees. There is no problem to keep both pollen bees and honey bees. Because honey bees have such a long foraging range, and visit a wide variety of flowers, they get along well with the pollen bees, which tend to forage near their nests. For example, I keep a total of over a thousand hornfaced bees (Osmia cornifrons), fuzzyfoot bees (Anthophora pilipes), mustached bees (Anthophora abrupta), and alfalfa leafcutter bees (Megachile rotundata) at the bee yard here at Beltsville, where there are also 21 very active honey bee hives, with supers. The pollen bees still multiply, although they may do better elsewhere.

The easiest and least expensive way to start with pollen bees is simply to manage habitat to attract and hold populations. This is much like managing property to attract birds and other wildlife. You may not know what species of pollen bees live naturally in your area, but you may be sure that some sorts will be present, to thrive if nesting materials and flowers are plentiful at the time of their seasonal activity. Most pollen bees are sun-loving creatures, and they prefer to nest in dry places or in exposed, sandy well drained soil, where the morning sun wakes them up early, and the midday sun keeps their nests warm. For wood and stem-nesting bees, piles of dry branches, dry, seasoned, untreated lumber with nail or beetle holes, dry, pithy stems, and dry, hollow reeds and sections of bamboo are attractive. A source of water and mud nearby attracts those bees that make cells of mud. Thus, timber and brush dumps, old, weathered buildings, and untended hedgerows with plenty of dead branches are highly attractive, although your neighbors may not agree. Bees that live underground often prefer south-facing sandy banks, especially in cold climates. They could be encouraged by removing shady vegetation. South-facing, steep cliffs with a dry area under an overhang, dry adobe walls, and shallow caves attract other species. Bumble bees usually nest in abandoned field mouse nests, which are often in undisturbed areas, such as woodlots, hedgerows, old barns, and brush or compost piles.

The mass rearing of pollen bees for use in pollination is more challenging because each species of pollen bee has its own special requirements for nesting. If the nesting materials are not quite right, the pollen bees will not use them, but buzz off elsewhere to seek appropriate nest sites. The domestication of honey bees began centuries ago, but because we are just beginning to domesticate pollen bees, there is much to learn. An easy way to multiply bees that nest in holes in wood is to set out "trap nests" where you know such bees already live. Trap nests are dry pieces of 4 x 4 or 4 x 6 that are drilled with smooth-walled holes of the same diameter and depth as those that the bees are using, set out near the natural nesting area in winter, well before annual activity begins. Some of the bees will move into the trap nests. During dormancy, the trap nests can be moved to another location, for use in crops the following year.

The first species of pollen bee to be brought into management was the hornfaced bee (Osmia cornifrons). A Japanese apple grower, E. Matsuyama, noticed these small brown bees rapidly working his apple blossoms and nesting in nail holes in his wooden house near the orchard, in the 1930's. Soon he made more nail holes in his house, and as the bees multiplied and his apple crop prospered, he switched to cutting sections of hollow reeds for the bees to nest in. Soon, word got out, and his neighboring growers started raising the bees. Scientists studied them and made improvements. Now, hornfaced bees pollinate a third of Japan's apples, and their use is spreading to North American and China. What did Mr. Matsuyama find so good about hornfaced bees? Why not stick with the good old reliable honey bee?

There are many reasons for the rapidly increasing popularity of hornfaced bees and their close relatives for pollinating fruit trees. (Their more recently domesticated relatives are the native North American mason bee or blue orchard bee, Osmia lignaria, and the European bees, Osmia cornuta and Osmia rufa). Some reasons are: (1) these bees are active in the spring, before honey bee colonies reach large sizes; (2) they prefer fruit flowers, thus stay in the crop; (3) they usually contact the flowers' anthers and stigmas on every visit; (4) they fly rapidly, thus working many flowers; (5) the pollen is carried loosely under the abdomen, thus being freely dusted on the stigmas; (6) males also pollinate; (7) their short flight range keeps them in the orchard; (8) growers can easily raise their own bees; (9) they are gentle, with a mild sting; and (10) they can be stored away between pollination seasons. As few as 80 female hornfaced bees are needed per hectare of apples. Similarly, 300 blue orchard bees per hectare are enough. In Europe, only 3 Osmia cornuta per almond tree will provide adequate pollination. This contrasts sharply with the 2 to 6 hives containing thousands of honey bees recommended per hectare of orchard. So why not try pollen bees as a sideline? Bees could be raised and sold to growers, or they could be rented for pollination.

In North America, some beekeepers have diversified into raising small, blackish alfalfa leafcutter bees (Megachile rotundata) for high-value alfalfa seed production. As with hornfaced bees, the raising of alfalfa leafcutter bees was started by a grower, W. D. Clarke, in Canada, in 1943. Scientists improved management techniques, popularity rapidly grew, and now leafcutter bees are used wherever alfalfa seed is produced. These bees have become big business, bringing in over $11 million annually. Leafcutter bees make their cells out of bits of leaves in holes in wooden boards and other materials, which are kept in shedlike shelters in the alfalfa fields, at the rate of about 100,000 bees, costing $500, per hectare. Alfalfa leafcutter bees came to North America on their own, as stowaways from Europe, about 1935. Another excellent alfalfa pollinator is the turquoise-banded alkali bee, native to western North America (Nomia melanderi). It nests gregariously in the ground, as densely as 2,000 nests per square meter. The management of this bee was developed in the 1950 by scientists, especially W. P. Stephen and G. E. Bohart. Growers make "bee beds," which are plots of specially prepared soil, near the alfalfa field, for nesting. Both leafcutter bees and alkali bees are superior to honey bees for alfalfa pollination because they work rapidly, stay in the crop, and "trip" the spring mechanism in the flower that releases the pollen. Think of them while you munch on alfalfa sprouts, along with alfalfa-fed beef and milk. (Read more about the alfalfa leafcutting bee on the Pollination Ecology Web)

The latest success story concerns bumble bees for pollination of tomatoes in greenhouses. Although many people have raised bumble bees over the years, it was not possible to mass-rear colonies year-around until methods were developed by the European scientists, V. Ptacek, P. F. Roseler, and R. de Jonghe in 1985. Because honey bees do not vibrate tomato flowers to release pollen, growers had been hand-pollinating and using mechanical vibrators on hothouse tomato flowers. The bumblebee business took off like a bumble bee! Now, over 300,00 colonies of several species are used to pollinate hothouse tomatoes in many countries. So, enjoy a bumble bee beefsteak tomato, along with your alfalfa sprouts and apples, as the search for new pollinators goes on.


1. Batra, S. W. T. 1984. Scientific American 259:120-127.
2. Free, J. B. 1993, Insect Pollination of Crops. Academic Press, N.Y. 684 pp.
3. Peterson, S. S., C. R. Baird and R.M. Bitner 1992. Bee Science 2:135-142.

Dr. Suzanne Batra
Bee Research Laboratory
Agricultural Research Service, USDA, Bldg. 476
Beltsville, Maryland 20705 U.S.A.

DrBatra.jpg (24589 bytes)

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