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Management of Wild Bees

By FRANK D. PARKER and PHILIP F. TORCHIO
Research leader and research entomologist, respectively, Science and Education Administration, Pollinating Insect-Biology Management, Systematics-Research, Logan, Utah 84322.

BEEKEEPING IN THE UNITED STATES
AGRICULTURE HANDBOOK NUMBER 335
Revised October 1980
Pages 144 – 160

The term “wild bee” is used commonly for all bees except honey bees in the genus Apis (hence, apiculture or culturing of honey bees). Many persons also refer to feral honey bees as wild bees, so the term is somewhat ambiguous. Bees generally are distinguished from other flying hymenopterous insects by their characteristic plumose body hairs. Bees are of many sizes, shapes, and colors. Some of the smallest bees, Perdita, are less than 3 mm, whereas our largest leafcutter bee is over 80 mm. Almost the entire range of colors is found among the brightly marked bees, including many beautiful metallic species.

Almost anywhere in the United States, one can easily observe many species of bees actively visiting flowers for nectar and pollen or engaged in the processes of constructing nests. There are approximately 5,000 species known to occur in North America, plus an estimated 1,500 species not yet described. Wild bee experts agree there are at least 30,000 species of bees in the world. This number of species is more than all the fish, bird, and reptile species combined.

Most bee species construct either single or complex nests in the ground. Some make earthen, leaf, or resin nests on rocks and plants. Other bees make or utilize crevices in rocks or plant stems, insect borings, and plant galls for their nesting sites.

Most bees live a solitary existence-each female after mating locates and builds her nest without the aid of other bees, and usually at a distance from her sister bees. However, some bees are quite gregarious and nest close to one another, sometimes in dense populations of up to a million nests in a few acres of soil.

Some bees prefer to nest at the same site year after year, but others relocate their nests each season. A small percentage of our wild bees are social or semisocial; that is, there is a division of labor among the bees occupying a single nest. Our total knowledge of the habits of bees in the United States is quite limited; less than 10 percent of their biologies have been observed and recorded.

Value of Wild Bees as Pollinators

One cannot easily place a dollar figure on the value of wild pollinators, simply because total impact on the environment is not known. The potential for utilizing, encouraging, or maintaining populations of wild bees has been barely researched. It has been calculated that the mere weight of wild pollinators outnumbers honey bee populations by hundreds of times. Studies on the impact of each pollinator species on fruit or seed production of our major crops is almost nonexistent.

We know that transfer of pollen from one plant to another or from one plant part to another part of the same plant is essential for the reproduction of most flowering plants; Without pollinators, most of our native flowering plants would decline, disappear, or be replaced by nonflowering weedy species. Yet, reproduction each season of the multitude of wild flowering plants is often taken for granted to aid in maintaining soil moisture and fertility, and to provide food not only for wild life but for our domestic livestock as well. How many billions of dollars are these benefits worth?

It is easy to document the value of crop species visited by bees, but here again the importance of wild bees as crop pollinators has been sorely neglected. It has long been the general consensus that honey bees adequately pollinate crops and there is little need for wild bees. Unfortunately, such statements are premature since adequate research on the economic benefits of wild pollinators has not been done. Conversely, the research completed on the few wild pollinator species thus far studied has returned much compared with its investment costs.

The dependence on one species for crop pollination sometimes creates problems such as now being experienced in our almond industry. In California, there are not enough colonies of honey bees available to effectively pollinate the total almond acreage, and it is steadily increasing. Honey bees must be transported from as far as Minnesota and Canada, which substantially increases pollination costs and results in higher costs to the consumer. It seems wise to make greater efforts to study, conserve, and try to manage as many species of wild bees as possible.

There are several crops that are underpollinated by the honey bees, either because the bees are not physically adapted to pollinate them or the crops are not attractive to honey bees. Some of our most important crops, valued at billions of dollars, are in this category. These crops are alfalfa, soybeans, cotton, vegetable seed, and sunflowers, each of which is adapted to specific types of pollinators.

Recent research on the utilization of several species of wild bees as crop pollinators is just beginning to indicate some of their economic benefits. Currently, there is a viable multimillion dollar industry centered around the manufacture and sale of equipment, propagation, and pollination by contract of one of these wild pollinator species, the alfalfa leafcutter bee.

The alkali bee was the first wild bee to be utilized as a crop pollinator in the United States beginning in the early 1950′s. Since that time, the alfalfa leafcutter bee and the blue orchard bee have been domesticated as crop pollinators.

Leafcutter Bees

There are many species of leafcutter bees that visit blooming alfalfa, but for the most part, our native species have not increased their populations to the point of being manageable. However, several Eurasian species have become established in the United States, and Megachile rotundata has become the principal alfalfa pollinator in several Western States. The alfalfa leafcutter bee, previously called Megachile pacifica, arrived on our east coast during the early 1930′s and has spread to most parts of the United States and northern Canada.

In the 1950′s, alfalfa seed growers noticed large populations of leafcutter bees pollinating their fields and began to increase the bees by providing nest holes in various kinds of wooden objects. By the 1960′s, research at government facilities and western experiment stations had developed practical means of culturing large populations of the bees. Seed growers who managed these bees began to see significant increases in alfalfa seed yields. Leafcutter bees were particularly effective in areas that had no alkali bees. During the 1970′s, intensive management practices have resulted in dependable leafcutter bee populations that ensure adequate pollination of western alfalfa seed fields.

The alfalfa leafcutter bee, about half the size of the honey bee, is black with white-yellowish bands on the abdomen (fig. 1). These bees are particularly fond of sweet clover and will visit it to the exclusion of alfalfa. Other crops visited for pollen are forage legumes, mints, crucifers and many weeds or garden plants. The adults commonly are found flying about near outbuildings, fence posts, cliff banks, or other suitable nesting sites. These leafcutter bees can utilize almost any small holes and will commonly plug small tubing, electrical sockets, and nail holes. Other favorite nesting sites are between the siding on frame homes and between or under the shakes or shingles on buildings. With such numerous nesting sites available, it is easy to understand why these bees became quite common and how large populations can be obtained for agricultural use.

FIGURE 1.-Alfalfa leafcutter bee: Left, Female carrying pollen on the under side of the abdomen; center, cutting a leaf for nest material; oblong pieces are used for the sides of cells, circular pieces for capping the cells; right, egg floating on larval food supply of pollen and nectar at the base of the cell.

Biological Features

Leafcutter bees are advantageous for alfalfa pollination because they:

(1) Usually forage within fields where they nest, making them less susceptible to being killed by pesticides applied to adjacent fields, and likely will not pollinate fields owned by other growers;

(2) Collect pollen from and trip the alfalfa flower readily at the rate of 8 to 10 florets per minute;

(3) Forage about the same time alfalfa blooms;

(4) Are predictable in incubation of adult stages;

(5) Have a long field life-up to 9 weeks-and a high rate of reproduction (maximum of 39 cells);

(6) Are gregarious and nest in manmade objects;

(7) Select older leaves for nesting and are not destructive of shrubs and trees;

(8) Have sturdy leaf cells and cocoons and thus are suited to mechanized management operations.

Populations

There are no consistent numbers of leafcutter bees used to pollinate alfalfa. The rate depends primarily on each seed grower’s management practices. However, it has been calculated that as few as 2,000 females per acre can adequately set up a field. The maximum carrying capacity has been estimated at 14,000 bees per acre. Early management recommendations were that small populations of bees be placed throughout the field for uniform coverage. This practice has changed gradually to the present concept of “mass pollination,” whereby large populations of leafcutter bees (400,000) are placed on small acreages (25 to 50 acres) for a few days and then removed. The primary advantages of this type of management are that adequate pollination can be obtained in a short period, the bees can be used to pollinate additional fields, and fields can be treated regularly for pest insects without harm to the bees.

Nesting Materials and Shelters

Many kinds of nesting media have appeared during the last two decades of leafcutter bee management, and there are many claims of success. Substantial population increases have been obtained in several types of nesting media, but the most commonly used materials are boxes of soda straws, drilled boards (with or without removable backs), grooved boards, plastic wafers, and rolled-cardboard units. There are advantages and disadvantages to each type used. These characteristics are shown in table 1, although grower choice-unproved data from bee production-appears to determine which media are used.

TABLE 1.-Relative desirability of various nesting materials for Megachile rotundata 1

Field shelters have changed from the initial small A-frame capable of holding a few boards to the large, self-contained, incubation-emergence type mounted on a trailer and capable of holding several hundred nesting units (fig. 2). It was assumed that facing the shelters to the east promoted increased bee activity, but research demonstrated that this practice actually increases mortality of young bee larvae. Sunlight penetrates the nesting holes and heats the larvae to as high as 130°F by 10 a.m. It is recommended that no sunlight actually strike the nesting units.

FIGURE 2.-Field shelters for alfalfa leafcutter bees: Left, The loose-cell technique of stocking shelters; right, a mobile field shelter that holds 400,000 nests.

Some additional recommendations for shelters are:

(1) Use the conspicuous, larger sizes to attract and keep bees at the shelters;

(2) Ventilate each shelter to prevent an accumulation of heat at the top or through the sides;

(3) Place chicken wire or grills across the open end of the shelter to provide protection from birds;

(4) Remove debris from emerging bees, nest cleaning, and leaf drop from the floor to prevent an increase in scavenger beetles or moths;

(5) Mount shelters on a trailer with wide tires so movement does not jar the bees.

Storage During the Winter

Most growers store their bees as overwintering larvae in cold rooms set at 36° to 40°F. The leaf cells are removed from the nesting media (loose cells) or are left intact, depending on the kind of management used. Cold treatment prevents a buildup of scavenger beetles, moths, and other nest destroyers that can damage unprotected nests. Although this practice is widely used, caution is needed so bee larvae are not stored too early in the season (before they spin a cocoon and change to the overwintering stage). To prevent injuring bees by early storage, the nesting media should not be placed in cold storage for at least 2 weeks after removal from the field.

Generally, if nests are stored during the summer, larvae destined for the second generation will die, causing considerable problems in the emergence pattern the next season. Also, bee larvae stored at constant low temperatures for long periods have a higher death rate (10 percent) than those left at outside temperatures (in Utah). So growers should determine the abundance of nest destroyers and their potential for destruction before long-term cold storage of larvae.

Incubation

Growers must decide when bees will be needed in the spring to begin incubation of larvae at temperatures averaging 86° to 90°F approximately 20 days before bee emergence. The most critical factor during the incubation process is temperature maintenance. When large lots of bees are incubated, the heat from bee larvae can be high enough to raise the room temperature to the point of actually killing the larvae. Therefore, adequate cooling, as well as heating, is required during the incubation process. The level of humidity is not nearly as important as maintaining the temperature level. Newly emerged bees or those still in cocoons can be held as long as a week at reduced temperatures (55° to 60°), if inclement weather occurs during the release schedule.

Protection From Parasites and Predators

Parasite-predator control during incubation should be exercised, especially in the loose cell method, as a 5-percent infestation could easily increase to 80 to 90 percent without some type of control. Most leafcutter bee parasites can complete two generations during the time required for normal emergence of the bees. Adequate control of pests during incubation has been obtained through the use of sprays, repellents, light, or emergence traps.

The leafcutter bee is attacked by numerous insects, and considerable attention must be given to maintenance of a pest-free population if an increase in bee populations is to be realized. Table 2 lists the common insects associated with leafcutter bee nests in some parts of the United States.

TABLE 2.-Characteristics of nest associates of the alfalfa leafcutter bee

Probably the most important type of parasite-predator control is the maintenance of clean bee stocks by excluding pest populations through changing nesting media yearly or by utilizing emergence traps. Most pest species can be controlled during incubation or emergence through the use of sprays or traps.

Currently, chalk brood, a disease associated with bee larvae, is increasing. In some Western States, the incidence of this disease has increased to as high as 80 percent of the overwintered bee larvae. However, little is known of the causal organism and its taxonomic status. We still do not know whether the organism is the cause or merely a symptom of these bee losses. Until these questions are adequately researched, control measures cannot be devised. However, it has been shown that growers who use clean nesting media have less chalk brood than those who reuse infested nesting media.

Additional Practices

It can be highly advantageous for honey bee keepers to handle leafcutter bees in addition to their honey bee colonies. The cost of maintaining and increasing bees is much less than the potential income from selling bees or their services. New bee boards sell for about $5 each and are $50 to $70 each when covered with bees. Cells removed from bee boards or boxes (loose cells) sell at an average of $100 a gallon (10,000 cells a gal). Many individuals have made a high profit by setting out bee boards on old outbuildings, cliff banks, and other likely nesting sites and collecting the filled boards for resale in the fall. Beekeepers also might consider custom pollination-providing the pollinators and shelters for fields during the flowering season for a percentage of the crop.

Other Leafcutter Bees

Megachile concinna, the Pale Leafcutter Bee

This species is quite similar to the alfalfa leafcutter bee; M. rotundata. Except for minor structural differences, they are hard for the novices to distinguish. In California, these two species often are confused. The pale leafcutter bee is found in the warmer Southern and Southwestern States. It is an African species that was accidentally introduced into North America late in the 19th century. This species has not been managed like M. rotundata, primarily because its nesting requirements have not been adequately researched. It is capable of producing almost a complete second generation, and females have a tendency to nest in places other than the nesting shelter, such as holes in the ground. However, recent field tests indicate that M. concinna is an exceptionally good alfalfa pollinator. In field tests M. concinna made more cells and the plants produced more seed than did M. rotundata in similar tests.

M. apicalis and M. leachella

Both of these Eurasian species are found in the United States, but infrequently. They are potential forage legume pollinators, and populations of both are being studied as candidate alfalfa pollinators.

The Alkali Bee

The alkali bee is brightly colored and nests in the ground in dense colonies. Each female excavates its own tunnel and cells, and there is no division of labor among the progeny. The bee was quite common in many Western States, but populations recently have declined drastically. Its usefulness as a crop pollinator was first noted in the 1940′s, when large populations were observed pollinating alfalfa in Utah. By the 1950′s, some growers in several Western States were improving natural nesting sites and constructing artificial bee beds. In the late 1960′s and 1970′s, the use of alkali bees declined in most areas due to replacement by the alfalfa leafcutter bee. Recently, parasites and diseases of the leafcutter bee have reduced its advantages, and there is increasing interest in using the alkali bee for alfalfa pollination. Certain growers in eastern Washington and the San Joaquin Valley of California have relied consistently on the alkali bee as an alfalfa pollinator, and they are convinced that the alkali bee is the best alfalfa pollinator (fig. 3).

FIGURE 3.-Alkali bees: A, An adult female; B, Part of an underground brood chamber showing eggs and larvae on pollen-nectar food supply; C, An artificial nesting site; water is added to the bed through the drain site. Each nest (about 1,500) is marked by characteristic mound of soil.

Alkali bees collect nectar and pollen from a number of plants. The main crop plants visited are alfalfa, sweetclover, onions, and mints. Weedy plants also are visited, and these include saltcedar (Tamarix), morning glory (Convolvulus), grease-wood (Sarcobatus), Russian thistle (Salsola), Rocky Mountain bee plant (Cleome), and several crucifers.

Alkali bees in California usually emerge in May and in Utah as late as August. Depending on location, these bees may have one or more generations per season. Males usually emerge a day or so before the females and begin patrolling the nesting area in search of newly emerged females, which they pounce upon readily. The males often are so numerous at nesting sites that they tend to discourage females from constructing nests.

On warm days, the females visit fields from about 2 hours after sunrise to 2 hours before sundown. They are capable of tripping alfalfa flowers at an average rate of 12 per minute. Normally, they provision at least one cell per day and in their lifetime provision about 12 cells (maximum 24). This foraging activity results in about 2,000 alfalfa flowers tripped per day per female and at least 25,000 flowers per female lifetime. The alkali bee visits shaded and exposed flowers, thereby increasing its pollination efficiency. The pollen and nectar provisions are stored in clusters of cells made 8 to 16 inches beneath the surface of silty loam soil.

The provisions are formed into a flattened ball with an egg deposited on the upper surface. The egg soon hatches, and successive stages of larval forms consume the provisions before entering an overwintering stage or progressing on to the pupal-adult stages and emerging to begin another generation.

Nesting Sites

Alkali bees are encouraged to nest in either natural or artificial nesting sites located in the ground (fig. 3). Generally, the soil is a silty loam, but the bees will utilize sandy soil or types with more clay particles. The most critical factor in managing alkali bee populations is the maintenance of proper soil moisture. Soil moisture levels can be measured easily by using soil tensiometers. Soil moisture in the beds and on the surface is maintained by adding salts, either calcium chloride (CaCl) or sodium chloride (NaCl), to the water. Natural nesting sites are found in seep areas where there is a constant supply of moisture extending upwards to the ground surface. Natural nesting sites can be maintained by placing a series of blind ditches to grade throughout adjacent areas and providing water for seepage to the sites.

Fencing is used to prevent packing or destruction of the soil surface by both farming operations and livestock. Weeds must be controlled to ensure a bare and attractive surface.

Artificial beds can be made readily by creating a water reservoir beneath the soil surface (fig. 3, right). The recipe for artificial beds calls for the following:

(1) Excavate a hole about 4 feet deep with sloping sides and construct ridges of soil in the bottom of the excavation to divide it into compartments;

(2) Line the bottom and side with thick-gage plastic sheeting and place several inches of soil on the plastic to prevent punctures;

(3) Place several cloth sacks of soil in each compartment;

(4) Add a foot of gravel on top of the soil to hold the water and install vertical pipes and perforated drain pipe in a radial pattern from the base of a stand pipe in the gravel layer;

(5) Stretch a layer of burlap on the gravel layer to prevent soil infiltration;

(6) Fill the remaining hole with soil to the surface level, forming a gentle crown to prevent ponding;

(7) Add water and salts to the stand pipe and reshape the surface as soil compaction takes place;

(8) Add brine solution to the soil surface before nesting.

Stocking of new or replenished nesting sites can be accomplished by two methods. The most common method involves digging cubic-foot blocks of undisturbed soil from a densely populated bee bed and incorporating the blocks into a new or revitalized bed before emergence of the bees in the spring. These soil blocks often contain 200 larvae each and can be purchased from growers, especially in the State of Washington. Another method of seeding an artificial bed is to sweep up newly emerged adults from natural nesting sites and release them after dark at the new site. Holes are prepared in the bed for the bees to crawl into and be protected during the night. Better results are obtained also by transplanting adults to a bed where alkali bees are active. The adults cannot be transferred to a new bed if the new area is within the old flight range (5 to 9 miles).

The area for the bee bed depends on the acreage to be pollinated. Millions of alkali bees can be produced in an area of less than 1 acre. The most ideal situation is for a community-based operation, since these bees can fly great distances and growers who build bee beds generally have no control of where their bees will forage. Alkali bees easily can fly several miles to the fields of another grower, and this long flight range makes them especially susceptible to pesticides applied in densely cultivated farming areas.

The population of alkali bees needed to set seed is highly variable and depends on the condition of the field. Most recommendations are for saturation at the level available forage can support, but it has been calculated that an acceptable level of alkali bee females per acre is between 3,500 to 5,000.

Protecting Bees from Parasites

Alkali bees are attacked by a number of insects and animals. Among the more common are the bombyliid (Heterostylum robllstum), a sarcophagid fly (Euphytomina nomivora), and conopid flies (Zondion obliquefasciatum). Generally, high populations of these flies indicate the bed is not adequately populated with bees, since well-populated sites provide good defense by limiting oviposition by the flies. Some fly control has been obtained by traps or sprays.

A recent nest predator found in some areas is the black blister beetle (Meloe nigra). This beetle is easily controlled, since the flightless females must crawl from the site to deposit their eggs.

Various methods are used to discourage vertebrate predators such as birds and skunks. Federal laws now protect most animals, so growers must seek information at the local level before using control measures.

Heavy rain also can contribute to the destruction of bee cells by creating a favorable environment for soil pathogens to develop and destroy the pollen. No effective control measures have been developed to protect bees from infrequent drenching by summer rains.

Blue Orchard Bee

During the last 25 years, orchard acreages planted to stone and pome species increased dramatically. The major pollinator species for these crops is the honey bee, but-unfortunately-its colony numbers steadily decreased during the same 25-year period. We decided, therefore, to search for alternative pollinator species of these crops. A survey was initiated in 1970 and by 1972 we found a most promising species, Osmia lignaria Say, that was named the blue orchard bee. We have worked since to develop an effective management program for its use in orchards. Research on this species is nearing completion, and growers are rapidly becoming aware of its real potential as an alternate pollinator of orchard crops (fig. 4).

FIGURE 4.-Blue orchard bee: A, Adults and cocoons (pupae); B, collecting pollen from an apple blossom; C, two eggs laid on a pollen ball in the nest, cells are divided by discs of mud.

The blue orchard bee is a native species widely distributed across most of the contiguous United States and southern Canada. It has been collected in diverse habitats from sea level to elevations of 7,000 ft, but it is not found in low deserts or subtropical areas. Two allopatric subspecies are recognized, and these are isolated by the Rocky Mountains.

This robust bee flies early in the spring when few other species are active, and its size (slightly shorter than the honey bee) and color (blue-black) are diagnostic. Like the alfalfa leaf cutter bee, it carries light-colored pollen on the underside of its abdomen. Females have a flat-tipped, brilliant-green prong protruding from the head directly above each mandible.

Biology

This bee nests in existing holes and fills them with a series of cells. Each female collects mud, carries it to her nest, and constructs a thin-walled partition that completely seals the cavity near its terminus. She subsequently collects nectar and pollen on each foraging trip and deposits these materials directly in front of the mud partition until the lower half of the horizontal cavity is filled with a loaf-shaped provision. An egg is deposited on the surface of the provision, and the cell is sealed by a second mud partition in front of the provision. A series of cells is thus constructed until the cavity is filled. Finally, the nest entrance is sealed with a thick plug of mud.

Eggs hatch within a week, and each larva consumes its provision for a month. A characteristic cocoon is spun, after which the larva enters a “rest” period for approximately a month. Pupation occurs in late summer, and the resultant adult remains in the cocoon through the winter. As the temperature rises in the spring, adults chew through cocoons and nest partitions, take flight, mate, and reestablish nesting.

Nesting Materials

Three nesting materials (straws, drilled holes in wood, and drilled holes in stryofoam) have been tested for trapping populations and establishing them in orchards. The blue orchard bee will nest in all three materials, but drilled wood is the most attractive for nests. The preferred hole depth is 5 to 6 inches, and the most attractive size of hole is 9/32-in diameter.

Trapping

In Utah, the best areas for trapping this species are in undisturbed drainages with mixed stands of maple and aspen interrupted by open meadows. Trapping is also good on the periphery of agricultural areas in habitats that include a ready supply of mud, early bloom, and dead trees with beetle holes.

Trap nests, each having 30 to 60 holes, are attached horizontally to old stumps early in the year before nesting activities. The traps are removed 1 month following the initiation of nesting and stored until the following year in shaded, outdoor areas having good ventilation.

Nest Shelters

Experiments completed to date in commercial orchards indicate that the best size for nest shelters is a boxlike structure approximately 32 by 16 by 12 inches (wooden military foot lockers serve as ideal shelters). The shelters are attached to metal fence posts and faced in a southeast direction to catch the morning sun. Each shelter is filled with trap-nest materials. Several shelters should be used for each acre pollinated.

Population

Cage studies on almond demonstrate that fewer than 10 female lignaria bees will adequately pollinate a tree. While this cannot be applied directly to open pollination conditions, the information can be used to indicate the approximate number of blue orchard bees required to pollinate each acre. Since males of this species also visit blooms frequently and are proved pollinators, we estimate that 600 nesting females will adequately pollinate 1 acre of fruit trees.

Commercial Utilization

Field populations of the blue orchard bee have been tested only recently, but results of such studies justify comments on the advantages of this species as an orchard crop pollinator. These are:

(1) Nesting is completed during the short period of orchard bloom when pesticides normally are not applied. As a consequence, growers can easily schedule post-bloom pesticide schedules without affecting their pollinator force.

(2) The blue orchard bee initiates daily flight at temperatures 2° to 5° lower than for the honey bee, and individuals visit orchard bloom consistently throughout the daylight hours. This can be of much significance during “bad” weather years.

(3) Both sexes of O. lignaria visit orchard bloom throughout their adult lives. Therefore, the entire population serves as a pollinator force.

(4) This species increases its nesting efficiency by flying short distances to collect pollen and nectar provisions when bloom is adequate. Proper management, therefore, can be applied to better guarantee full pollinator utilization on individual properties.

(5) The normal adult flight periods of this species are short in comparison to those of other pollinators, and its annual appearance is early in the spring when inclement weather conditions are common. Nevertheless, this species is successful because females rapidly collect pollen over long daily flight periods. These facts, together, indicate the bee can serve as an effective pollinator of massive plants, such as orchard crops, that have short flower life.

(6) The blue orchard bee has its complement of nest associates, but these species have been nearly eradicated in field population tests by applying proper management techniques.

(7) The nests and nesting materials used for this species are relatively light. Therefore, management of large field populations will require fewer pieces of expensive equipment designed to move and transport heavy pollinator units.

(8) Few worker-hours, relatively, are needed for management of the species and this is restricted to a short period annually.

(9) Necessary transport of nesting populations throughout the summer months is eliminated in managing the blue orchard bee because it is an obligatory one-generation species.

(10) Osmia lignaria can successfully nest and pollinate crops in competition with other pollinator species visiting the same crops.

If the acreage of orchard crops continues to expand as it has in the last 25 years, it soon will be impossible to supply enough pollinators for these crops, regardless of the species used. This problem can be resolved, however, by using a multiple-species approach. Further, those presently involved in honey bee pollination could easily adapt their operations to accommodate management of additional species for concomitant use. The management of multiple species already has proved successful for several western honey bee suppliers who have added the alfalfa leafcutter bee to their operations.

Related Species

Sibling species of the blue orchard bee occur in other parts of the world. One of these, Osmia cornifrons, occurs in Japan and is an established pollinator of apple in that country. We cooperated with Japanese scientists recently in working with this species in Utah. While the study population nested well under Utah conditions, its progeny did not overwinter successfully. Another SEA scientist is working with this species in the Washington, D.C., area to determine if climatic conditions on our east coast (similar to Japan’s) will permit successful overwintering of O. cornifrons.

Populations of the European species, Osmia cornuta, have been received from a Spanish collaborator, and we have completed studies of its biology and pollinator potential. Unlike the Japanese species, cornuta overwintered well under Utah conditions, and we are increasing our greenhouse-reared populations for possible field release in the near future.

Other European species are being established in our Utah greenhouses, and their status as potential pollinators has yet to be deciphered.

Other Pollinators

Bumble Bees

Bumble bees are important pollinators of many of our native plants, especially those growing at high elevations. Also, bumble bee species are associated with our crop plants, but no successful attempts have been made to utilize them on a large scale. The number of workers per colony is quite low (50-100), and the profitability of using such small colonies of bumble bees is unknown (fig. 5). Researchers, however, are studying means of increasing colony size and extending the life of colonies to more than a single season.

FIGURE 5.-Bumble bees: Left, Four common species of western bumble bees; right, large nest of Bombus morrisoni.

The generalized life cycle of a colony of bumble bees is as follows: the mated queen overwinters in some type of hybernaculum. In the spring, she becomes active and begins searching for a nesting site to make cells, lay eggs, and begin a colony. After nest establishment and the emergence of the first workers, the queen enlarges the colony with the aid of the numerous workers so that its size increases during the season. By fall, new queens, drones, and workers are being produced. Then the new queens mate, leave the colony for overwintering sites, and the old queen, workers, and drones gradually die.

Bumble bees are quite cyclic in their abundance, and this periodicity has been linked to cycles of rodent populations in whose old nests many of these bees find suitable nesting sites. Several bumble bees are quite common, and can be trapped by placing nesting boxes out in spring or by catching overwintered females before they begin to build their nests in the spring. Many of the captured females will begin to make colonies in these boxes, if pollen and nectar are provided. After the queen begins making cells and the first workers appear, the box can be opened and the bees allowed to forage in the field.

Anthophorids

Several species of Anthrophoridae have the potential of being used as crop pollinators. Although they nest in the ground, artificial nesting sites have been made from blocks of adobe, which are readily accepted by these bees. Excellent nesting and reproductions by some native species such as Anthophora urbana, A. pacifica, and A. bomoides have been obtained in greenhouses, but these species have not yet been field tested. A Polish species, A. parietina, has been successfully tested in hairy vetch in that country.

Other anthophorid bees are potential pollinators of such crops as cotton (Diadasia and Ptilothrix) and sunflowers (Diadasia and Melissodes). These bees possess characteristic habits such as gregarious nesting and restricted floral visitation, which make them potential crop pollinators. No research, however, has been done on utilizing them as such.

There are several genera of bees, such as Peponapis and Xenoglossa, whose sole host plants are species of native and cultivated squash. Some species nest in dense aggregations and might be managed somewhat like our alkali bees. However, no management programs have been developed to utilize these efficient pollinators on a commercial scale.

Introduction of Foreign Pollinators

There have been only two intentional introductions of pollinators from other countries to the United States. The most obvious and successful is the honey bee. Its introduction has been so successful that additional introductions have been largely ignored. The other example is a group of fig wasps without which hybrid figs cannot be produced (except with hormonal sprays).

Several additional species of bees and wasps have become established in the United States, mostly inadvertently via our numerous vehicles of commerce. One, the alfalfa leafcutter bee, has become the most important of these adventive species. Many other species of potential crop pollinators are known to exist in foreign countries and might be valuable supplements to our existing species.

A principal shortcoming of the honey bee as a pollinator of specific crops is its wide host range. This results in a large share of each colony’s population not pollinating the desired crop. Thus, the best means of obtaining specific pollinators would be the introduction of oligotrophic species that have a principal host plant.

There are many examples of foreign species that have definite affinities for certain of our important crop plants. For example, alfalfa in its native home in Eurasia is effectively pollinated by several genera and species of bees that do not occur in the United States (fig. 6). All these species are excellent choices for an introduction program to increase seed yields in areas of poor alfalfa seed production. Promising species of tomato and red clover pollinators are known to exist in Central America and South America, but no populations have been imported for preliminary trials. With the origin of a large number of our cultivated crops being other countries, an expanded program for the introduction and establishment of exotic pollinators should be expanded rapidly.

FIGURE 6.-Eight species of Iranian bees that pollinate alfalfa.

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