A brief review of the classification of insects and their relatives may help the reader to understand the scope and magnitude of those insects referred to by the general term "wild bees."

All known animal organisms have been arbitrarily classified by specialists into phyla, classes, orders, families, genera, and species, with some subdivisions in between. For example, the phylum Arthropoda contains numerous classes including the Insecta, which is divided into numerous orders, one of which is the Hymenoptera, which in turn is divided into superfamilies, one of which is the Apoidea (bees). Wild Bees

The Apoidea of America north of Mexico have been classified in different ways by different specialists, but Stephen et al. (1968) classified them into the seven families listed on this page. Also listed are the more important genera in each family.

There are about 19,000 described species of bees in the world (Linsley 1958). At least 5,000 species of bees are in North America (Bohart 1952*), and, with the exception of one species, Apis mellifera L., the domestic honey bee, all of them are grouped under the general term "wild bees."

Family ¹ Important genera
Short-tongued bees:
Andrenidaea Andrena, Panurginus, Perdita, Pseudopanurginus Colletidae Colletes, Hylaeus Halictidae Agapostemon, Dufournea, Halictus, Nomia Melittidae Hesperapis, Melitta Long-tongued bees: Anthophoridae Anthophora, Melissodes, Nomada, Xylocopa Apidae Apis, Bombus, Euglossa, Melipona, Trigona Megachilidae Anthidium, Lithurgus, Megachile, Osmia

¹ Two relatively obscure families, Fideliidae and Oxaeidae, are omitted.

Only to al limited extent has man learned how to manipulate a few species in a few genera of wild bees. He can construct nesting sites and transport immature leafcutter bees (Megachile pacifica) (see "Leafcutter Bees") and alkali bees (Nomia melanderi) (see "Alkali Bees"). These bees are used in large-scale pollination of legume crops in the Western States.

Numerous species of the genera Melipona and Trigona are induced to nest in prepared domiciles, such as hollowed-out gourds, hollow tree sections, or manufactured hives, from which a few ounces to a few pounds of honey may be harvested. Some of these colonies are also placed near crops needing pollination (see "Stingless Bees and Meliponiculture").

Slight progress has been made in inducing numerous species of bumble bees (Bombus spp.) to nest in specially prepared boxes or nests that can be transported to fields to be pollinated (see "Bumble Bees").

Osmia bees (Osmia spp.) can be induced to nest in bamboo canes, which are then transported to fields to be pollinated (see "Osmia Bees").

Logs of softwood, in which carpenter bees (Xylocopa spp.) can construct nest tunnels, are provided near plantings of passionfruit (Passiflora spp.) to encourage these bees to nest near and pollinate the flowers (see "Carpenter Bees").

Other steps mentioned by Bohart (1971), which may have actually increased the wild bee populations at least in the eastern half of the United States, include:

1. Opening up of forested areas, which created more favorable conditions for bees.
2. Paving highways, which concentrated moisture along roadsides.
3. Introduction of "weeds" upon which the bees forage.
4. Growing numerous crops upon which the bees forage.
5. Bringing desert areas into bloom (with irrigation).

Plantings on which wild bees may forage or reproduce, are also made and protected from fires, floods, overgrazing, or insecticide exposure.

Otherwise, little is known about manipulation of the thousands of other species of wild bees.

Numerous species of wild bees, however, can be found almost anywhere plants grow, for example, the Melissodes bees (Melissodes spp.) in cottonfields (Butler et al. 1960). Wild bees doubtless provide, in the aggregate, millions of dollars to the economy of agriculture. Their value to range, forests, fields, and ornamental flowers is impossible to measure, but it should not be overlooked. The demonstrated value of the few species over which man has learned to exercise some control is sufficient to support the claim that this group of largely overlooked insects is an essential segment of our agriculture as well as our general ecological environment. As such, more intensive study should be made of the various species to determine the practicability of their preservation, culture, and use on various insect-pollinated crops.

Although ants, beetles, butterflies, moths, and many other groups of insects contribute to the pollination of plants, Apoidea are of greatest interest and by far the most important as pollinators, especially in temperate regions.

The families of Apoidea have plumose or branched hairs at least on the top of the thorax, the first joint of the hind tarsi is enlarged, and they provide their young with a diet of nectar and pollen. This is even true of the "cuckoo bees" (several genera in various families), which lay their eggs in the nests of other bees. Male bees have 13 segments in the antennae; the females, 12.

The sting (a modified ovipositor) of the female or the exposed genitalia of the male readily identify the sex of the individual. Apoidea may be solitary, gregarious, or social.

A solitary species is one in which the female prepares and provisions the cell, deposits the egg, and then seals the cell completely unassisted. More than one cell may be constructed, but only one at a time. After the cell is sealed, no further attention is given it, and the adult may die within a few days.

Gregarious bees are solitary individuals that endeavor to nest in close proximity to each other. The alkali bee (Nomia melanderi) belongs to this category. It builds individual nests in the ground--as many as 100 nests per square foot of soil.

Social bees live together in a society and have divided duties. The queen is the sole or primary egg-laying individual. Her active life is relatively prolonged, and she maintains contact with at least some of her adult offspring. Ants, bees, wasps, and termites include species with the most highly developed insect societies.

The time of day that wild bees forage differs with the species involved. Those that feed only at dawn are referred to as matinal bees. Crepuscular bees feed both at dawn and near dusk. A few species are nocturnal in their foraging, but the great majority feed when the sun is shining, because that is when the majority of the flowers are open (Linsley 1960).

The distance that the different species of wild bees may forage must vary enormously. Janzen (1971) reported that an individual Euplusia surinamensis (L.) returned to its nest from a distance of 23 km (14.3 miles). He calculated that another individual flew as much as 24.4 km (15.2 miles) to and from the foraging area. By comparison, the alkali bee (Nomia melanderi) may forage 4 or 5 miles from its nesting site (Stephen 1959); whereas the alfalfa leafcutter bee (Megachile pacifica) usually forages within only a few hundred feet of the nest (Bohart 1962b).

Visitation to plants by wild bees is highly variable. Some species visit many different families of plants, others visit only a few closely related families, and still others visit only a single species or closely related species. In different instances, each type of activity would be advantageous.

ALKALI BEES

The alkali bee (Nomia melanderi Cockerell) has been known for many years to be a highly efficient and effective pollinator of alfalfa, particularly in the area north and west of Utah. It is a highly gregarious solitary bee that nests in large numbers in saline soils with a silt loam or fine sandy loam texture.

The culture and utilization of this bee has been studied and promoted over the last two decades, particularly by Bohart (1952*, 1958, 1967, 1970a 1970b, 1972), Menke (1952a, 1954), Stephen (1965), and Stephen and Evans (1960). Much of the material presented herein was developed by these men.

Life history and habits.--Alkali bees are nearly as large as honey bees. They are black, with iridescent copper-green stripes across the abdomen (fig. 22A). The male bee has much larger antennae than the female. Being gregarious, alkali bees may construct 100,000 or more nests in an area 40 by 50 feet. Nesting sites with an estimated 200,000 nests have been reported (Bohart 1952*). The nest (fig. 22B), a 10 mm (0.4 inch) vertical tunnel, may extend 10 inches below the surface but is usually only 3 to 5 inches deep (Frick et al. 1960). There may be 15 to 20 cells usually arranged in a single comb-shaped cluster. Each cell is an oval cavity, slightly larger than the main tunnel, about one-half inch long, lined first with soil and then with a waterproof transparent liquid applied with the bee's glossa. Each cell is provisioned with a 1.5- to 2-mm oval pollen ball, made up of 8 to 10 bee loads of pollen mixed with nectar. The soil removed from the tunnel is dumped at the tunnel entrance to form a conical mound 2 to 3 inches across.

The adult bees emerge from late June to late July, depending upon the location and season. The males appear a few days ahead of the females. Before emergence, each bee is confined to its natal cell for 3 days as an egg, 8 days as a growing larva, 10 months as a full grown dormant larva, 2 weeks as a pupa, and several days as a hardening, maturing adult (fig. 22C). During the approximate 1 month of her active adult life, the female constructs, provisions, and lays an egg in each of 15 to 20 cells.

Mating occurs during the 3 days the entrance tunnel is under construction, usually during the first day. The males patrol back and forth over the nesting site, and they will mate with any number of females; however, they rarely bother a mated female after she becomes actively engaged in constructing the nest (Stephen 1959).

About the third day after construction starts, the first cell is completed. Pollen is then collected and formed into a pellet in the cell, an egg is laid on the pollen, and the cell is immediately sealed by a spiral ceiling and a soil plug. Then work is begun on the next cell, and no further attention is paid to the last one. Thereafter, the daily routine consists of fashioning another cell off the main tunnel, providing it with a pollen ball, depositing the egg and sealing the cell. About one cell is completed each day (Bohart and Cross 1955). Usually only one nest is prepared and provisioned by a female. There is usually only one generation a year in the intermountain States, but in California two and sometimes three generations appear from May to September.

[gfx] FIGURE 22.- The alkali bee. A, Adult; B, nesting site; C, cells excavated to show immature stages.

Food sources and feeding characteristics.--Alfalfa nectar and pollen constitute the primary source of food for most female alkali bees. They visit a few other plant species, for example, clovers, mint, onions, Russian thistle, salt cedar, and sweetclovers. In alfalfa seed producing areas, however, most of the nests are provisioned with nectar-moistened pollen balls derived from alfalfa.

While foraging, alkali bees do not trip the alfalfa blossoms as rapidly as do the leafcutter bees, but almost every blossom they visit is tripped. Because of the large number of flowers the females visit, they become highly effective. Bohart (1952*) stated that two large nesting sites in Utah, one of which had an estimated 200,000 nesting females, "provided good pollination for the alfalfa-seed fields within a radius of at least 2 miles." The males visit flowers for nectar only and only occasionally trip the flowers.

Alkali bee nesting sites or "beds".--Within recent years, research by Bohart (1958), Bohart and Knowlton (1952), Frick et al. (1960), Fronk ^{5 ,}Stephen (1959, 1960), and Stephen and Evans (1960) has resulted in the development of a dependable method of preparing and stocking nesting sites or bee beds for the alkali bee. Such beds can now be prepared and stocked successfully in areas where this bee had not previously occurred.

There are certain basic requirements of an acceptable bed. It must have a moisture supply capable of rising to the surface. This usually requires a hardpan layer a foot or more below a porous soil that tends to hold the moisture and permits its movement from the source of supply to the surface. Conditions should permit rapid drainage of surface water. The underlayer should range in texture from a silt loam to a sandy loam with no more than 7 percent clay-size particles. The surface should be firm but not have a hard crust. If some salt does not appear on the surface, about 1 pound of salt per square foot of surface should be raked into the first 2 inches. This seals the surface layer and thus slows down evaporation.

The bed should be kept relatively free of weeds. It should not be flooded during the active bee season or excessively disturbed by livestock or vehicles.

When bee beds are constructed by alfalfa seed growers, about 3 feet of soil is removed from the selected site. The flat-bottomed excavation is then lined with 0.006-inch plastic film. The excavation is backfilled with an inch of soil, a 10-inch layer of gravel, and 2 feet of appropriate soil. Salt is usually added to the surface as mentioned above. Water can be supplied through a piece of tile that extends from the gravel bed to several inches above the surface.

The size of the bee bed may be determined by the size of the plastic sheet. Bohart (1952*) indicated that an acre of bee bed might be sufficient for 100 acres of alfalfa, but conditions vary so much that the only safe recommendation seems to be to have as many bees as the forage will support.

After the bed is prepared, alkali bees may find and migrate to it if other beds are within a mile or so. At greater distances, the bees must be brought in. One-cubic-foot blocks of undisturbed soil from established bee beds may be transferred and imbedded at the new site during the winter while the bees are in the resting stage (Stephen 1965). The bees can also be transferred as dormant larvae in individual containers (Bohart 1958). Generally, attempts at transferring adults have not been successful.

Diseases and enemies.--Numerous diseases, pests, and other enemies inflict damage on alkali bees. Bohart (1952*) mentioned insects, including ambush bugs, bee flies, chalcids, clerid beetles, conopid flies, cuckoo bees, meloid beetles, robber flies, tiger beetles, velvet ants, and wasps. Crab spiders are also a problem, but mites, although present, are of little consequence (Cross and Bohart 1969). Vertebrate enemies include birds that feed on the adults and mice and skunks, which usually feed on the larvae. Bacterial and fungal diseases may suddenly strike and seriously diminish the population of a bee bed. Trampling of the nesting sites by livestock, traffic by vehicles, unwise use of pesticides, and flooding during the active bee season can also reduce populations or destroy the site.

Possibilities and limitations.--There is little doubt that where populous alkali bee beds occur the bees of these beds pollinate alfalfa in a highly efficient manner and contribute to the production of bumper seed crops (Menke 1952b). According to Bohart (1970b), a 3,000 ft2 bee bed cost about $600 to build and stock in 1970. Stephen (1965) stated that a well- populated, 1,500 ft2 bed should provide adequate pollination for about 40 acres of seed alfalfa. At the same rate, the 3,000 ft2 bed should take care of 80 acres for several seasons. At current honey bee colony rental rates, alkali bees would be much more economical than honey bees.

Alkali bees also have some strong limitations. Their services are confined to areas of the West where rainfall, particularly during the active season, is unlikely. The beds cannot be transported; therefore, the crop to be pollinated must be planted near the bed. The bed must be planned and constructed many months before its pollination service is expected. Finally, a bee bed may be lost--quickly and easily--to flooding, predators, parasites, diseases, or pesticides and other agricultural practices.

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5 FRONK, W. D. INCREASING ALKALI BEES FOR POLLINATION. Wyo. Agr. Expt. Sta. Mimeo. Cir. 184, 7pp. 1963.

LEAFCUTTER BEES

Life History and Habits.--The alfalfa leafcutter bee (Megachile pacifica Panzer) is a relative newcomer to America, although there are many other leafcutter bees here. Hurd and Michener (1955) listed 124 species in California alone. Bohart (1962b) stated that M. pacifica was found "about 30 years ago " in the vicinity of Washington, D.C., possibly brought over from eastern Europe or western Asia. It spread rapidly across the Northern States to the Pacific coast. Bohart (1972) stated that "it occupies roughly the northern three-fourths of the contiguous United States." In many areas, the alfalfa leafcutter bee became the most important pollinator of alfalfa (fig. 23).

As its name implies, this highly gregarious solitary bee lines its nests with circular sections cut from alfalfa leaves (Stephen 1961), although it will cut sections from petals of large ornamental flowers. The nests are in hollow tubes or tiny holes above ground (fig. 24). The charcoal-gray adult bee is only slightly larger than a housefly.

[gfx] PN-3759 FIGURE 23. - Alfalfa leafcutter bee collecting pollen from alfalfa.
FIGURE 24.- Alfalfa leafcutter bee nests in opened nesting tubes.

The female bee emerges from May to July (depending upon location), mates, and immediately searches out a nesting hole. She prefers a tube or tunnel into which she can barely fit (five thirty-seconds of an inch) but will accept a somewhat larger one if necessary. When one is found, she begins the construction of a cell in it. She builds the first cell at the base of the tube, using freshly cut oblong pieces of leaves. This cell is then filled about half full with a mixture of pollen and nectar. An egg is placed on the food, and the cell is capped with circular pieces of leaf. Another cell is immediately started directly above the first one, and the process is repeated until the tube is nearly filled with cells. After the final cell is sealed with a large number of circular leaf pieces, another tube is begun if pollen and nectar continue to be available.

A female may live 2 months and lay 30 or 40 eggs during her lifetime. About two out of three adults that emerge from the cells will be males. A theoretical increase of about tenfold per generation is possible if ample nesting holes are available and the bees are somewhat protected; however, Bohart (1962b) stated that a fivefold increase from year to year is probably optimistic. There is usually a partial second generation that may overlap the first, which would enlarge the expected increase.

The eggs hatch in 2 or 3 days, and the larvae feed on the food in the cell. Larval development is completed in about 2 weeks, and some individuals continue development and emerge as adults about 23 to 25 days after the egg was laid. Others remain without further development as larvae until the next year when they complete their development and emerge as adults.

The males emerge about 5 days before the females. As soon as the female emerges she mates, and although the males may mate many times, the females mate only once (Hobbs 1967).

Leafcutter bees (as well as alkali bees) can be handled in almost complete safety. The female has a sting but rarely uses it and then it causes only slight pain. This enables an unskilled worker to handle these bees with assurance of safety, even when thousands are flying about.

Food sources and feeding characteristics.--The alfalfa leafcutter bee derives its food and nesting material primarily from alfalfa; however, it will forage on sweetclovers (Melilotus spp.), white clover (Trifolium repens L.), some of the wild mints (Mentha spp.), and a few other species. Goplen (1970) reported that this bee preferred purple alfalfa flowers to yellow flowers to a degree that influenced pod and seed set. The effect of this preference in commercial seed production has not been determined.

The adult does not forage at temperatures below 70 deg F (Hobbs 1967). The female visits flower after flower in rapid succession, tripping almost every flower visited, 11 to 15 per minute. She forages no farther from her nest than necessary, usually within the field where the nest is located, and most often within a few hundred feet of the nest. The male visits flowers for nectar only and seldom trips a flower. Hobbs (1967) stated that alfalfa fields can be thoroughly pollinated in 3 weeks with about 40,000 females per acre. Klostermeyer (1964) indicated that at least 2,000 females per acre were necessary for each 500 pounds of clean alfalfa seed produced. Other figures fall between these extremes.

Rearing and utilization.--The tendency of the alfalfa leafcutter bee to nest in individual tubes in close proximity to hundreds of other nesting females enables man to use this bee to a highly profitable and satisfactory degree in the pollination of alfalfa fields. Growers have been rapidly adopting this bee since 1958 when a Utah grower began making thousands of nesting holes around his outbuildings so the bees could increase their population. Methods of rearing and manipulation have also changed as the widespread value of these bees has become accepted.

Special "bee boards" have been prepared for rearing these bees - 4-inch by 4-inch timbers about 4 feet long with closely spaced holes three- sixteenths of an inch in diameter bored 3.5 inches deep (fig. 25). These bee boards, with about 2,000 holes filled with leafcutter bee nests sold for about $40 (Bohart 1972). The boards became so useful and sought after in alfalfa seed fields of the Pacific Northwest that bee board "rustling" became a problem until growers began branding their boards for easy identification.

Some growers used packets of 7/32-inch soda straws cut into 4.5- inch lengths for their bee boards. The bases were dipped in paraffin, and the pieces were packed into small open-ended cartons.

Hobbs (1964, 1965) stated that straws less than seven thirty-seconds of an inch produced more male bees but that about equal numbers of males and females emerged from larger straws. He was convinced that all tubes should be at least 7/32 - inch in diameter.

Grooved laminated boards composed of wood, particle board, or polystyrene plastic can be clamped together to form nesting holes or tunnels but, most important, they can be taken apart, so that the cells can be examined for dead, diseased, or parasitized ones and the healthy ones removed and concentrated for winter storage or shipment. Bohart (1972) stated that the price for 10,000 healthy cells (1 American gallon) was $100.

Hobbs⁶ reported that polystyrene grooved boards were being manufactured and used in Canada. He stated that they were more readily accepted by the bees and that bees using them worked longer hours than bees in wood boards. The machine-made polystyrene boards, being exactly alike in shape, could be easily assembled or put through the cell stripper, a device for removing the cells from the grooves. A polystyrene board filled with cells weighs 13 pounds as compared to 45 pounds for the cell-filled wood boards. However, the polystyrene material is delicate and must be handled carefully. Also, mice will chew the material to get to the cells. Finally, the cells sometimes mold because moisture given off by the pupa is not absorbed by the plastic. Plastic blocks with tunnels, plastic straws, and corrugated paper are also used to a limited extent.

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6 HOBBS, G. A. FURTHER INFORMATION ON ALFALFA LEAFCUTTER BEEKEEPING. 9pp. canada Agr. Res. Sta., Lethbridge. 1969. (mimeographed.)

Winter storage.--The cells can be left outside during the winter, but mortality for various reasons is high. For best results, they should be stored in a dry, cool place, about 30 deg to 40 deg F., then incubated the following spring to cause emergence as adults when desired. They can be stored in the bee boards just as they are brought from the field or they can be removed from the grooves of laminated boards by the cell stripper. Storage in the bee boards increases the difficulty of controlling diseases, parasites, and predators but storage in loose cells increases the dangers of parasitism if no control measures are taken.

About 3 weeks before alfalfa is due to begin flowering, the cells are placed in trays in a storage room such as that described by Wilson (1968) where the temperature is held at 85 deg F. and the relative humidity, from 50 to 75 percent. There should be one cell for each tunnel to be used at the nesting site. About one-half of the adults will be males and some of the females will perish, but each surviving female should be expected to fill two or three nests. Pans of water with lights (preferably ultraviolet) shining on them should be placed beneath the trays. The parasitic chalcids and dermestids should emerge first, and, being attracted to the lights, they drown in the water (Waters 1966). The males begin to emerge several days before the females. The females should be removed to the field about the 21st day after they are placed in incubation.

[gfx] FIGURE 25.- Alfalfa leafcutter bee nests and shelters. (Note use of brands on nesting boards to discourage theft.) A, Stationary shelter; B, portable shelter; C, stationary shelter with wire screen to protect nests form birds.

Usage and handling of nests and shelters.--Size and shape of shelters vary greatly. Some are no more than 4 by 4 by 4 feet, others are the size of a one-room dwelling. Johansen et al. (1969) suggested the nesting area be 4 by 8 feet in size and the shelters be 140 yards apart, with about 20,000 filled nest tunnels at the start of the season.

Bohart and Knowlton (1967) gave the following specifications for a good shelter; it should-

1. Protect the nesting material against high-angle rays of the sun when the weather is hot.

2. Have an easterly exposure.

3. Afford some shelter from wind and rain.

4. Provide good ventilation.

5. Be large enough to be conspicuous for the bees and have plenty of nesting holes. (Yellow apparently increases conspicuousness, but black, green, and blue are most attractive for nesting.)

6. Be placed 2 1/2 feet or more above ground.

7. Be built so that covers may be added for protection against birds or pesticides.

In addition--

• Shelters should be distributed in the field at the rate of one shelter with 10,000 nesting females for each 5 acres of alfalfa.
• Soil around the sesting site should be bare so that incoming bees may light on it and absorb heat before entering the nest.
• Ants near the nest should be controlled with a nonresidual insecticide, but the bees should be protected from this or other pesticides. Chicken wire should cover the front or openings to exclude bee-eating birds.
• Above all, shelters should be able to withstand wind that is likely to occur when they are in use.
• Shelters should be movable by winch, fork, rollers, or trailer.
• Land beneath the shelters should not be irrigated because the water may cool down the shelter, or the bees may fall into it and drown.
• When the first bees begin to emerge, the tray should be closed and taken to the field. There it should be opened just wide enough for the bees to escape but not enough for mice to enter. The bee boards should be in place in the shelter before the bees are released.
• If 10,000 females are to be released at a shelter and the average bee board has 2,000 holes, there should be about 15 bee boards at each shelter.

Diseases and enemies.--When the alfalfa leafcutter bee began to increase in population, it seemed to have no important diseases, pests, or parasites. Within a decade, however, scores of natural enemies had appeared, some of which were serious. The tiny parasitic wasp (Sapyga pumila Cresson) first mentioned by Torchio (1963) as a potential threat was verified by Torchio (1970) as causing a high percentage (6.9 to 65.3 percent) of the cells to be parasitized. Torchio (1972) recommended trapping for satisfactory control of this wasp. Some degree of control has been devised for the other insect enemies. Birds can be screened away from the nests with chicken wire, and rodent control measures can protect the bees and their nesting materials from mice.

Insecticides sprayed over neighboring property are unlikely to be a problem, but if the alfalfa field is treated they can be serious. Alfalfa leaf material used in the nest can be toxic if treated with persistent insecticides even before the blooms appear or the bees emerge. Confining the bees for protection from pesticides is a poor solution but moving the bee boards at night to a cool dark place for a day or two may be feasible.

Possibilities and limitations.--There are many advantages in the use of alfalfa leafcutter bees. They perform excellently in the pollination of alfalfa. They can be handled safely without fear of the stings by the operator or the neighbors. They multiply rapidly. They forage primarily only in the field to which they are supplied. They can be transported easily and economically in the immature stage, in which most of the year is spent. They do not require constant nurture and manipulation like the honey bee requires. They can be supplied to any field where desired (fig. 26) unlike the alkali bee that is in a permanent nesting site. Their use is so practical and different that they now constitute a new entomological industry (Bohart 1970b), and Bohart (1970a) urged honey beekeepers to become leafcutter beekeepers. The use of leafcutter bees can be combined with honey bee pollination. Williams (1968) listed 15 dealers who were marketing drilled boards in Idaho and Washington, and three who were marketing grooved laminated boards, one each in California, Oregon, and Utah.

There are some limitations to the bee. It is of economic value to few other plants besides alfalfa. Its usage has not been successfully adapted to the arid Southwest. A similar bee (M. concinna Smith) in the Southwest (Butler and Wargo 1963) seems to be less gregarious, although Butler and Ritchie (1965) indicated that it might be reared artificially on bee- collected pollen and sugar sirup. Because of the newness of the leafcutter bee as a commercial pollinator, little is known about its diseases, parasites, and enemies and their long-term effect on it. For its use to be successful, a devoted leafcutter beekeeper would be required to look after its welfare. Where this bee has been successfully used, the alfalfa seed growers have harvested bounteous seed crops, and, unless unforeseen disaster strikes, its use is likely to increase.

PN-37 63 FIGURE 26.--Alfalfa leafcutter bee shelters in alfalfa field.

STINGLESS BEES AND MELIPONICULTURE

Members of the Apidae subfamily Meliponinae or "stingless bees" are social insects. Some species have clusters of as many as 80,000 individuals; other species, less than 100. The two important genera are Melipona and Trigona. They do not occur in the United States but are present and of economic significance in Mexico as well as Central and South America. Trigona spp. also occurs in Africa, Southern Asia, and Australia. They are mentioned here because of their widespread distribution over the tropical and subtropical areas of the world, their value in the pollination of many crops, and their long-time culture for the production of honey and "wax".

These bees have been studied taxonomically by Schwarz (1948) and behaviorally by several men, especially by Nogueira-Neto (1948a, b, 1950, 1951), Nogueira-Neto and Sakagami (1966), Kerr (1946, 1 948, 1951), Sakagami (1966), Sakagami and Oniki (1963), Sakagami and Zucchi (1967), and Zucchi et al. (1967). Meliponiculture was reviewed and discussed from the practical standpoint by Ordetx and Perez (Ch. 5: 45-55 1966). The following discussion is drawn largely from the above references.

The females possess weak or vestigial stingers but are unable to inflict pain with them, hence the term "stingless bees." Some species have mandibles sufficiently strong to inflict a mild bite or to pull hairs, or they may crawl into the ears or nostrils of the intruders. Others emit a caustic liquid from the mouth that, in contact with the skin, causes intense irritation. Most species, however, are not bothersome to man, and he may safely manipulate them with ease, even to having his face within inches of a Trigona nest containing many thousands of individuals.

Stingless bees were kept by man centuries before the arrival of Columbus or the common honey bee (Bennett 1964). Some species produce an acceptably delectable honey, as much as half a gallon per colony per year. Others produce less desirable, thin (35 percent moisture versus half that amount in our domestic honeys), strongly acid honeys. One species (Trigona (Lestrimellita) limao Smith) produces a honey used to induce vomiting (Bennett 1965). The most common species used in miliponiculture is Melipona beechii Bennett.

When the wax is secreted from the glands on the abdomen of stingless bees it is similar in appearance to that of Apis mellifera, but it is then mixed with propolis and the product, called cerumen or Campeche wax, is more or less black. Cerumen is used for waterproofing on farms and in villages, in ink and lithography, and in other restricted ways.

Originally, the colonies were kept in gourds, tree trunks, or similar cavities, but an improved hive has been developed that permits easy manipulation and transportation of these bees (fig. 27). This hive is about a cubic foot in volume--sufficient for the 3,000 to 5,000 bees in an M. beechii cluster. If necessary, additional space can be added for larger clusters. A nest of Trigona clavipes (F.) in a hollow tree, sketched to scale by Sakagami and Zucchi (1967), was 8 by 8 by 50 inches and had a worker bee population that "apparently exceeded several tens of thousands." It contained "at least 20" horizontal brood combs separated from the collection of pollen and honeypots. The size of hive acceptable to a colony of this size was not given.

Life histories and habits.--The size of stingless bees varies from 2 to 14.5 mm. Trigona duckei Friese is the smallest species of stingless bee known; Melipona interrupta Latrielle is the largest. M. beechii is slightly smaller than Apis mellifera. The colors of the different species vary from black to brown, red, orange, yellow, and white.

The nest entrance is frequently reduced to permit only a single bee to enter at a time. The nest may be covered by a membranous wax and propolis network, which envelops and protects the nest and brood. There may be a single or multiple layer of brood--the individual cells vertical in some species, horizontal in others --or the cells may be in a cluster like grapes. Some species use the brood cells only once, then they are destroyed and reconstructed. The honey and pollen are not stored in the brood comb but in irregular cells outside of the broodnest.

The queens of Trigona are reared in queen cells, similar to those of Apis mellifera. Melipona queens develop in cells that externally seem to be no different from those that produce drones and workers, usually one queen to three to six workers. The workers of Melipona fill the cell with food before the egg is deposited. Each colony has a single sovereign queen but tolerates numerous virgins. A 4,000 worker bee population of M. beechii may have 50 virgin queens living harmoniously with the mother queen. Mating occurs in the air.

Advantages of stingless bees as pollinators.

• Stingless bees do not sting, therefore they are not a hazard to man or animals nearby.
• They collect and utilize considerable nectar and pollen throughout most of the year, therefore, numerous flowers must be visited and pollinated.
• They can be manipulated in hives like honey bees.
• The hives are small, easily handled, and relatively inexpensive.
• The colony is unlikely to become hopelessly queenless.
• The byproducts of honey and cerumen are usable.

Disadvantages of stingless bees.

• Stingless bees cannot tolerate cold weather, therefore, they are limited to the tropical and subtropical regions.
• The byproducts are produced only in small quantities, and they are less desirable than those of the honey bee.

[gfx] 27.- Stingless bees. A, nest ina a constructed hive; B, closeup of nest showing bees, brood, and honey storage area.

OTHER IMPORTANT BEES

Bumble bees.--There are dozens of species of bumble bees (Bombus) in the United States. Most of them are excellent pollinators of a wide variety of crops (fig. 28), although in some plant species they cut a hole in the base of the corolla and "rob" the nectar without effecting pollination.

Bumble bees start each spring in a new nest. A mated female, that overwintered in solitary hibernation, finds a suitable nest site in the spring, possibly an abandoned mousenest in a ditchbank or brush pile.

A wax cell is constructed and stocked with a mixture of pollen and nectar, upon which several eggs are laid. Soon the smaller sterile females (workers) emerge, and the nest is enlarged (fig. 29). These workers relieve the queen of all duties except egg laying, and colonial life emerges. During the summer, the colony grows and becomes more complex. Toward fall, males and sexually mature females develop and mate. Soon thereafter, the mated females abandon the nest and go into solitary hibernation, and the males and immature females die off (Medler and Carney 1963).

The size of the nest varies with species of Bombus as well as with forage available. Michener and LaBerge (1954) listed the contents of a large B. medius Cresson nest in Mexico as follows:
1 queen
0 males
800 workers (sexually immature females)
28 eggs 126 immature stage
804 empty cocoons
1,227 cocoons filled with honey
23 pollen pots filled with pollen
27 empty pollen pots

They concluded that the queen had produced 2,183 offspring by June 21, when the nest was examined. Most nests have far less than this number. Holm (1960) recorded from 31 to 930 total cells in colonies of Bombus terrestris (L.), and from 41 to 600 in B. Iapidarius (L.), at the end of the season. However, Westbury (1971) concluded that colonies are normally unlikely to exceed 400 adults with only 20 to 30 workers present at any one time.

Medler (1958) believed that bumble bees would soon be successfully managed, and suggested that "bombiculturists" be trained to culture and manage bumble bees for pollination. Because of the potential importance of these bees as pollinators if they could be managed, many research workers both before and since have studied them.

Bumble bees can be induced to occupy manmade nests or hives, such as the 6-inch cube hive used by Hobbs (1966) and hives, cans, or tile used by Fye and Medler (1954) and others. They can also be induced to live, mate, nest, and hibernate in greenhouses to a degree that they can be useful as pollinators of small plots (Pedersen and Bohart 1950). Holm (1966) reported that 31 species have been colonized. Unfortunately, their culture is considerably hampered by their nest abandonment each fall. This characteristic prohibits the maintenance of colonies, such as is the case with honey bees or Meliponinae; storage of immature stages as with leafcutter bees, or even maintenance of the immature stages in the area, as with the alkali bees.

Bumble bees are further hampered by diseases and parasites; predators such as mice, skunks, badgers and birds, and man-created problems such as pesticides and the destruction of nesting sites. Their usefulness under natural conditions can be increased by the individual grower or the community where their services are desired. They can be "encouraged" in an area by providing nests and nesting areas for them. Their enemies can be controlled and consideration can be given in the use of herbicides and insecticides. Crops can be planted or wild flowers encouraged on which they can forage during periods when food might otherwise be unavailable.

[gfx] FIGURE 28.- Bumble bee collecting nectar from a wildflower (Colutea arborescens L.)
FIGURE 29.- Nest of Bumble bee. A, honey pots; B, pollen cell; C, egg baskets or cocoons; D, young brood in wax cells.

Carpenter bees.--The carpenter bees (Xylocopa spp.) have not been cultured in a true sense although their nesting in certain areas has been encouraged by placement of soft timbers in which they can construct nesting tunnels (see "Passion Fruit"). Because of their large size (almost an inch in length and about half as wide), they resemble large bumble bees but do not have a true pollen basket on the hind leg. They are usually metallic black.

The bees are solitary but numerous ones may be attracted to soft timber in which they can tunnel. This tunnel may be 1 foot long or longer and about one-half inch wide. There may be numerous cells separated by partitions formed by chips of wood cemented together. About 30 to 31 days are required for development from egg to adult.

Because of their lack of gregariousness, these bees are only of limited value where appropriate nesting timbers can be provided. They also have a strong tendency to cut holes in the bases of flowers that have long slender corolla tubes.

Osmia bees.--Bohart (1972) reviewed the information on Osmia pollination. He stated that O. cornifrons (Rad.) has been successfully managed for apple pollination since 1958 in northern and central Honshu, Japan. The bees are captured away from fields or orchards treated with insecticide, taken to the orchard, and released at the time of apple bloom. The bees nest in bamboo and hollow reeds placed by the growers on shaded platforms in or near the apple orchards. These bees usually begin to fly about 2 weeks before apples come into bloom. They fly at temperatures as low as 45 deg F., some 20 deg below that at which honey bees fly.

Levin ( 195 7) induced O. Iignaris Say to nest in specially prepared tubes, 3/8 by 4 by 6 inches, bored in lumber. Levin and Haydak (1957) were able to rear the same species on bee-collected pollen but not as efficiently as on Osmia-collected pollen.

Free and Williams (1970) showed that O. rufa (L.) tended to be gregarious and could be induced to nest in drinking (soda) straws. It showed a preference for Rubus spp. and other specific plants, indicating that it could be used to advantage.

When a crop is transferred from one area to another, there is always the possibility that the native pollinating agent might be left behind. It might be interesting to ponder over the number of instances a new crop has failed in an area merely because the proper pollinating agent did not accompany the crop. The need for the transfer of bumble bees to New Zealand for pollination of the new crop (to that country) (see "Red Clover") is an example. Also, the effect of the accidentally introduced leafcutter bee into the United States on alfalfa seed production can show the importance of bringing in an improved pollinating agent.

The laborious hand pollination of cacao (see "Cacao") may be due in part to the transfer of this plant without including its pollinating agent or agents. The possibility of increased production or quality of hybrid tomatoes might be considerably enhanced if one of the wild bees of Peru that visit tomato flowers could be successfully brought to this country and cultured. Hurd et al. (1971) and Michelbacher (1968) pointed out the possibilities for increased yield and quality of cucurbits in many areas if some of the squash bees were introduced.

Bohart (1962a) considered the possible value and problems associated with introduction of foreign pollinators and stressed the need for knowing the habits of a pollinator before its importation is made. Some dangers that might and should be avoided are introduction of (1) unwanted arthropod diseases, parasites, and predators; (2) insects with undesirable characteristics, such as stinging or biting people or destroying flowers; or (3) insects that molest or dispossess efficient native pollinators.

There seems to be ample opportunity for reward in exploration of other countries for superior pollinators. For example, if hybrid soybeans materialize through use of male sterility, what might be found in the way of an efficient pollinator in the Orient from whence soybeans came?

The accidental release of the African honey bee in Brazil, with its associated problems, illustrates the need for caution at all stages in the importation of a new species.

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