Bees and pollination

Honey bees are our most important managed pollinators. Their activity assures sufficient cross-pollination, without which small or misshapen fruits and low yields may result. Although many species of bees can be found in an orchard during bloom, most of these species vary in their abundance from year to year. In addition, regular pesticide applications may limit the number and variety of these pollinators, and some agricultural practices destroy their natural nesting sites. Honey bees can be managed, however, to provide consistent pollinator abundance from year to year. Also, bumble bee colonies are becoming increasingly available for orchard pollination. Although the cost of bumble bee colonies has been prohibitive in the past, the cost of these units has decreased substantially in recent years and some growers are purchasing and using them with good results.

The changing pollination picture
With the introduction of parasitic honey bee mites, the pollination picture is changing rapidly. Abundant feral colonies (wild colonies nesting in trees or other cavities) once provided a measure of pollination security for fruit and vegetable growers; however, this is no longer the case. Feral honey bee colonies are now nearly nonexistent in most areas. Estimates vary, but the Northeast may have lost 80 percent of its feral honey bees.

Despite intense efforts to protect their bees, beekeepers are losing large numbers of colonies to these mites and the diseases they transmit. As a result, fewer beekeepers are providing honey bee colonies for growers. In addition, the quality of honey bee colonies, at times, may be marginal for the purpose of pollination. Never before has the pollination situation been so critical. To ensure maximum crop yields, growers now must give careful attention and consideration to crop pollination.

To ensure adequate quality and numbers of colonies, growers should consider the following:

  • Contact beekeepers early. Since honey bee colonies may be in short supply during some years, it is critical to contact beekeepers as early as possible so they know you are depending on them to supply bees. If you do not have a past relationship with the beekeeper, you should make initial contact with him or her in the fall. Beekeepers assess the survival and strength of their colonies from mid-February to mid-March. Contact your beekeeper during this time to be certain that enough bees are available for spring pollination. In addition, you should make every effort to give beekeepers at least 48 hours' notice to move bees onto the crop.
  • Draw up a pollination contract. To prevent misunderstandings, it is a good idea to draw up a pollination agreement between the grower and the beekeeper. This will ensure that enough pollinators are provided and that beekeepers are protected from pest control practices that may injure bees (see Figure 1-5).
  • Obtain an adequate number of colonies. The number of honey bee colonies you will need will vary depending on the crop, location, attractiveness of the crop, density of the flowers, length of the blooming period, colony strength, and competitive plants in the area. The rule of thumb is to start with one colony per acre and make adjustments from there. Areas well populated with wild solitary bees and wild honey bee colonies will not need as many rented colonies.
  • Obtain bees at the appropriate time. For apples and other tree fruit, move colonies in at 10 to 25 percent bloom. If primary blossoms produce the choice fruit, however, bees should be present at the start of bloom or when king bloom on the south side of trees starts to open. Competing bloom from other flowers in the orchard, such as dandelions, should be eliminated by mowing, cultivation, or the use of herbicides. For melons, cucumbers, squash, strawberries, blueberries, and cranberries, honey bees should be moved onto the crop when the crop is attractive to the bees. This means that there should be many blooming flowers (10 to 20 percent) to attract bees to the crop.
  • Place colonies for maximum effect. Place colonies in groups of four to eight in favorable locations throughout the orchard or field to provide even distribution of the bees. In large orchards or fields, pollination is just as effective if groups of 10 to 20 hives are strategically distributed in sunny, wind-protected spots. Colonies should be protected from the wind and exposed to the sun from early morning until evening. Bales of straw or packing boxes stacked behind colonies offer wind protection. Colony entrances that face east or southeast encourage bee flight. Hives should be placed off the ground, and front entrances should be kept free of grass and weeds. Do not place colonies under trees or in the shade.
    Bee activity is determined by weather and by conditions within the hive. Bees rarely fly when the exterior temperature is below 55°F. Wind speeds above 15 mph seriously slow activity, and activity stops when winds are between 21 and 25 mph. The stronger the colony, the lower the temperature at which bees initiate flight. Cold, rainy weather inhibits foraging. Under marginal weather conditions, foraging is limited to trees close to the hives. An extended period of inclement weather may require greater hive distribution to obtain adequate coverage.
  • Assess colony strength: be sure you are getting strong colonies. It is important that the colonies you rent are healthy and contain a large enough population to do the job. For pollination, package bees (bees purchased through the mail and recently installed) and small hives are inferior to strong, overwintered colonies. The field bee population generally is correlated with the amount of brood in the hive. In packages and weak colonies, most of the hive population must remain in the hive to maintain temperatures of 93 to 95°F and rear brood. Two weak colonies are not equal to one strong colony! Colony strength can be assessed in several ways.
  1. Inspect hives. This method is the most time-consuming, but also the most accurate for assessing the quality of your investment in rented honey bee colonies. Colonies used for springtime pollination should have the following at minimum:
    • a laying queen,
    • one and one-half or two stories (hive bodies or boxes),
    • four to six frames of brood, and
    • enough adult bees to cover six to eight frames.
      These are minimum requirements; stronger colonies with larger populations make superior pollination units and may command a higher price. As these stronger colonies are opened, bees will "boil out" or cover the tops of the frames. When smoked, however, the bees move down onto the frames and may not cover the frame tops. In this case, the frames themselves should be covered with bees. Note that there will be some variability in the quality of the colonies you rent. As a general rule, a group of colonies with 10 percent falling below the minimum standard is acceptable if 10 percent are above the minimum standard. Also, for a variety of reasons, some colonies may become queenless for a time; however, if these colonies meet all the other minimum requirements they still will be effective pollination units.The Pennsylvania Department of Agriculture Apiary Inspection Service runs a hive evaluation program for colonies used in pollination situations. Inspections are performed by request only. Requests may be made by either the grower or the beekeeper and should be arranged through the state apiarist at the PDA Bureau of Plant Industry, 2301 North Cameron Street, Harrisburg, PA 17110; telephone 717-772-5225. Requests for inspections should be made as early as possible to facilitate scheduling. If an evaluation is requested by the grower, the beekeeper will be informed that a request has been made.
      Inspections are performed by the local or state apiarist. Colonies are inspected objectively to determine the colony size (number of supers), the presence of a laying queen, the number of frames of brood and adult bees, and the presence of disease and parasites. At least 10 percent of the colonies in an apiary, or a minimum of five colonies, are selected at random for inspection. Inspected colonies are identified by sticker. If selected colonies are banded or stapled, these are not refastened by the inspector. A copy of the evaluation report is given to both the grower and the beekeeper.
  2. Assess traffic at hive entrance. This method is less time consuming but also less accurate. On a warm (70 to 80°F), calm day between 11 a.m. and 3 p.m., bee traffic at hive entrances should be heavy. During a one-minute observation period, strong colonies should have 50 to 100 or more bees arriving and leaving the hive. Bees also should be seen arriving with pollen pellets on their back legs. In weak colonies, perhaps only 10 to 20 bees will be seen arriving and leaving. Colonies that are being used for summer pollination should have even heavier traffic at the hive entrance.
    Another crude way to assess colony strength is to observe entrances when temperatures are cool (between 55 and 60°F). The stronger the colony, the lower the temperature at which bees will fly. In general, weaker colonies rarely fly when temperatures are below 60°F. Strong colonies will fly when temperatures are between 55 and 60°F. In general, honey bees rarely fly when temperatures are below 55°F.
  3. Assess bee density on the crop. This method allows you to assess the contribution of wild pollinators (honey bees only) in addition to rented bees. If you are using rented colonies, however, this method tells you little about the quality of the bees you have rented. We suggest that if you use this technique and find that the number of bees on the crop is low, you then use options (1) or (2) to assess the strength of the rented bees before renting additional bees.
    For apple trees, make observations in late morning during king bloom; at a glance you should see one to two bees foraging on blooms. Make several assessments at different locations around the orchard. Note: This guideline is appropriate only for honey bees and is not accurate for bumblebees or solitary bees. It is only a rough guideline and may change depending on variety and planting conditions.
  • Carefully consider the use of bee attractants. Research on sugar-based attractant sprays for improving pollination indicates that such materials are generally ineffective. The entire tree is sprayed with the attractant and bees collect the sugar off the leaves, usually without visiting the flowers. Although this brings more bees into the field or orchard, more pollination does not necessarily occur. In addition, the sugar may be detrimental if it serves as a medium for the growth of sooty molds. Other attractants containing bee-derived communication pheromones, such as geraniol, have proven more successful, but further testing is needed before a full recommendation can be made.
    One of the newest and most promising attractants, Fruit Boost®, contains honey bee queen mandibular pheromone. Canadian research has shown that when it is sprayed on flowering crops, queen mandibular pheromone can result in dramatic increases in yields for some crops. This product is sold in both Canada and the United States, and is being marketed mainly for use on pears, highbush blueberries, Gala apples, and in vegetable seed production. U.S. distributors are located in the Pacific Northwest. For more information, contact Phero Tech, Inc., 7572 Progress Way, RR 5, Delta, British Columbia, Canada V4G 1E9; phone: 604-940-9944; fax: 604-940-9433.
  • Other precautions and requirements. Beekeepers should be given at least 48 hours' notice to move bees onto or off the crop. Insecticides applied on or near the crop before or during bloom are a serious threat to bees. Give the beekeeper 48 hours' advance notice of any applications so that the bees can be removed from the field or orchard. Honey bees need water for temperature regulation and brood production. Provide a clean water supply near the hives. Keep orchard wheel ruts and areas around the pesticide sprayer fillpoint drained to eliminate a possible insecticide-laden water source.


Additional information
The publications listed below are available at your county extension office or by contacting the Penn State Department of Entomology at 814-865-1896, or on the MAAREC Web site.

  • Beekeeping Basics
  • Beekeeping Topics: Sources of Bees for Pollination in Pennsylvania, Bees and Insecticides, Pollination Contracts, Basic Biology and Management of the Japanese Hornfaced Bee


Sources of pollination rentals
Growers who need bees should make contracts with the beekeepers as early as possible (mid-February) so that proper preparations can be made. Specialized management is necessary in order to develop strong, efficient colonies, especially for early spring pollination. Therefore, beekeepers need to know how many colonies are needed and the approximate time of delivery as early as possible.

For an up-to-date list of beekeepers with colonies of bees for rent ("Sources of Bees for Pollination in Pennsylvania"), please visit the MAAREC Web site or contact your county extension office or the Penn State Department of Entomology at 814-865-1896.

Alternative pollinators
Growers of bee-pollinated crops, particularly apples, are becoming increasingly interested in the possible use of solitary bees as managed pollinators. Two species in the genus Osmia (mason bees) are currently being used, on a limited basis, for tree fruit pollination: the blue orchard mason bee (Osmia lignaria), our native mason bee, and the hornfaced bee (Osmia cornifrons), a mason bee that has been introduced from Japan.

Unlike honey bees, mason bees are solitary, meaning all females mate, reproduce, and provision their own nests. Although these bees are solitary, they are gregarious and prefer to nest in groups. Under natural conditions, these bees nest in hollow reeds or stems of plants, but they can be easily encouraged to nest in cardboard tubes or wooden nesting blocks drilled with holes of the correct diameter.

In the Mid-Atlantic-region, Osmia are active only for about 6 to 8 weeks from about mid-April through mid-June. Males emerge about 1 week before pear trees bloom in the spring. Females emerge 2 to 3 days after males, or longer, depending upon weather conditions. Mating occurs immediately after females emerge.

Both male and female bees make floral visits. Females collect primarily pollen and carry it on the lower surface of their abdomens (unlike honey bees, which carry pollen on their legs). After their ovaries have developed fully, females begin provisioning cells and laying eggs within the nest "tube." They collect a large mass of pollen first and then nectar, which they regurgitate on the pollen ball. This sticky nectar acts as glue to hold the egg on the pollen ball. After the egg is laid, a mud wall is built and the next cell is provisioned and the next egg is laid. Females can make 1 to 2 cells a day under favorable conditions.

Newly laid eggs take approximately 3 days to hatch. The larvae consume the pollen over a 2 to 3 week period. They later pupate and develop into adults, but will remain within their cells throughout winter and emerge the following spring about 1 week before pear bloom.

Management of Osmia
Once they are initially obtained, Osmia species are relatively easy to manage. They will nest in cardboard tubes or wood blocks that have 5/16-inch diameter openings and are between 4 and 10 inches deep. Under favorable conditions, and with availability of abundant nest sites, populations tend to double or triple from year to year. Females tend to nest in the same area (instead of flying off to seek a new nesting site) when there are 3 to 5 times as many empty as full tubes. Both species of Osmia are susceptible to parasitic wasps if they are left in the field during June and July. It is best to remove the nesting tubes from the field once the adult bees are no longer active and store them in an unheated, parasite-proof shelter.

The Japanese hornfaced bee is less cold-tolerant and must be sheltered when temperatures get below 10°F. They do best in a humid, temperate climate, in USDA Plant-Hardiness Zones 5 through 8. You may place hornfaced bees in a refrigerator for winter storage, but make sure humidity levels stay around 75 percent. Hornfaced bees require a cold period before they can emerge from their cells. It should be noted that experience has shown that Osmia obtained from the western U.S. may not adjust well to conditions in the Mid-Atlantic region.

While the Japanese hornfaced bee does not occur naturally in our area, the blue orchard mason bee (Osmia lignaria) and other solitary bees are common throughout the Mid-Atlantic region. It may be possible to encourage these bees to form aggregations in your orchard simply by providing nesting sites and restricting the use of pesticides during the short period that these bees are active.

To learn more about the management of solitary bees, where to obtain these bees and/or cardboard nesting tubes, please visit the MAAREC Web site or contact your county extension office or the Penn State Department of Entomology at 814-865-1896

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