Agriculture, Pêche et Aquaculture
 
Department of Agriculture, Aquaculture and Fisheries
New Brunswick's Provincial Flower:  The  Violet  (Viola  cucullata) New Brunswick's Provincial Bird:  The  Chickadee  (Parus  atricapillus)
  Native Bees that Pollinate Wild Blueberries




B.6.0

INTRODUCTION

Prior to the large-scale use of honeybee colonies in wild blueberry fields, the crop was pollinated primarily by native bees. Native bees are alternately referred to as "wild bees" and "pollen bees", and there are over 25,000 species of wild bees in the world - 3,500 in North America alone. In contrast to these bees, the european honey bee is the only truly "social bee" in North America. While bumblebees have a social phase (i.e. a colony) during the warmer months, most native bees are solitary. This means that each female lives alone in a nest of her own construction which she provisions with no cooperation from other females. However a few of these species nest in close proximity to one another forming aggregations.

Over 60 species of native bees have been identified in the wild blueberry production regions of Eastern Canada and Maine. Many of these species are better adapted to the crop than the managed pollinators like honeybees and alfalfa leafcutting bees, but in most fields the numbers of native bees are insufficient to pollinate the huge number of flowers which modern management produces. Nonetheless, native pollinators continue to make an important and often substantial pollination contribution to blueberry production.

Many of the pollination attributes of these native bees, such as their ability to forage in marginal weather conditions and sonication (shaking) of flowers to harvest pollen, make them extremely effective pollinators. These include the native leafcutting bees, the digger bees, bumblebees and some of the sweat bees. As a whole, the effectiveness of some of these may be as much as four times that of honey bees.

The goal of this fact sheet is to familiarize wild blueberry growers with the principal native pollinators, and to suggest ways to conserve and enhance their numbers.

BUMBLE BEES

Life cycle. Bumble bees have an annual colony cycle that begins early in the spring when overwintered queens emerge from their hibernation sites in the soil to feed on spring flowers and search for a suitable location (often a former rodent nest) for the new colony. Once the site has been found, the queen collects pollen, forming it into a lump upon which she lays her first brood of 7 or so worker eggs. The eggs hatch soon after, and begin feeding on the pollen lump, and on additional pollen and nectar collected by the queen. Adults emerge from a short pupation about 21 days after the eggs are laid. This first group take over pollen and nectar collection while the queen continues to lay successive waves (broods) of worker eggs. By mid-summer, a colony contains between 20 and 100 workers, depending on the species. It is around this time that the colony begins to produce males and queens. The new queens leave the nest, and after mating dig 5-10 cm into the soil for hibernation. As autumn approaches, the remainder of the colony declines and dies. The hibernating queen emerges the following spring to begin the cycle again.

Rearing bumblebees. Scientists and beekeepers have attempted to rear bumble bees for decades, both by constructing artificial nesting sites in fields, and by rearing the bees indoors in controlled environments. Commercial interests have made significant advances in rearing bumblebees in controlled environments for use in agriculture (particularly greenhouses). While commercially reared bumblebees may one day be used for wild blueberry pollination, the cost of using domesticated bumble bees for wild blueberry pollination is presently prohibitive.

Some of the most successful attempts at encouraging bumble bee nesting in field sites has come from burying wooden boxes containing upholsterer's cotton for nesting material. Access for the bees is achieved by attaching plastic hosepipe between the entrance and the surface of the ground. It seems that only the tunnel actually needs to be buried, and it may not be necessary to fully bury the nest. This may depend on the species of bees which is being attracted.

BUMBLE BEES AT A GLANCE:

picture of a bumblebee

  • actual size: 13-28 mm (1/2 - 1inch)

  • Buzz pollinators

  • Flowers visited per minute: 10-18

  • Distribution in NB: more abundant in the south than the north

  • Some of the other wild plants that are important to blueberry bumble bees: a huge list of plants including willow, most clovers and sweetclovers, rose, alfalfa, fireweed, daisy, iris, lambkill, the milkweeds (Apocynum and Asclepias); chicory, St. John's wort, evening primrose, moosewood (Viburnum), hardhack, goldenrod, buttercup, lilac, dandelion, wild sarsparilla, vetch, butter and eggs (Linaria), raspberries, yarrow, and asters.

  • Preferred habitat features: a wide variety of flowering plants until early fall, abandoned forage fields (including clover) and meadows nearby, woodland debris, abandoned mouse nests, small areas of uncultivated land, proximity to undisturbed areas, such as woodlots, hedgerows, windbreaks, old barns and brush or compost piles.

ANDRENID BEES

Life cycle. Andrenid bees (or "digger bees" or "mining bees" as they are also referred to) are solitary ground nesters. They are important pollinators of wild blueberry both in number and pollination effectiveness. A week or so before wild blueberries bloom, both adult males and females emerge from nests constructed the previous season. After mating, the female excavates a burrow in the soil that consists of an entrance similar to that of an anthill, a vertical shaft and a series of lateral tunnels terminating in brood chambers (see Figure 1). These burrows may be as deep as 45 cm (18 inches). Within the burrow, the female applies a waterproof lining to the walls of the brood chamber, then lays an egg on a mass of pollen and nectar. This mass sustains the larva until the fall, when bees reach the overwintering adult stage. Early in the spring, the bees emerge from the ground to begin the cycle again. Digger bees often nest within wild blueberry fields, choosing sites that have sandy well drained soils and some protective cover by vegetation. The choice of suitable sites often means that several nests are dug relatively close to each other.

Although Andrenid bees are able to forage on a wide variety of plants, they tend to remain loyal to blueberry once they have begun to forage on it.

examples of burrows built by andrenid bees and other similar bees
Figure 1: Examples of burrows built by andrenid bees and other similar bees

ANDRENID BEES AT A GLANCE:

andrenid bee

  • Actual size: 7-14 mm (¼ - ½ inch)

  • Buzz pollinators

  • Flowers visited per minute: 5-10

  • Distribution in NB: abundant in all regions

  • Some of the other wild plants that are important to blueberry andrenids: shadbush, currants, raspberry and blackberry, maple, strawberry, willow, labrador tea, huckleberry, bunchberry, chokecherry, Rhodora, dandelion, lambkill, rose, sumac, clovers and sweet clovers, hardhack, apple.

  • Preferred habitat features: These bees prefer pliable soil with a thin organic layer on south-facing banks amidst a plant stand of sparse to intermediate density. These bees would definitely benefit from the presence of other plants which flower before and after the wild blueberry.

HALICTID BEES

Life cycle. Halictid bees are often called sweat bees because some species are attracted to human perspiration during hot weather. These small bees share a life cycle similar to that of andrenid bees. The female halictid excavates nests in the soil, with burrows consisting of a horizontal shaft and a series of brood chambers. There are several variations on the nest architecture. The lining of the halictid brood cells have a shiny, varnish-like finish. While the halictids are considered a minor pollinator in most wild blueberry situations, their abundance in north-eastern New Brunswick suggests that there may be advantage in encouraging their preservation and enhancement.

HALICTID BEES AT A GLANCE:

halictid bee

  • Actual size: 3.5-15 mm ( 1/8 - ½ inch)

  • Buzz pollinators

  • Flowers visited per minute: 4-8

  • Distribution in NB: abundant in north-eastern New Brunswick

  • Some of the other wild plants that are important to blueberry halictids: there are records of these bees on most of the flowering species one can find in the wild blueberry growing regions, with shadbush, strawberry, moosewood (Viburnum), rhodora and raspberry being among the most important.

  • Preferred habitat features: These bees prefer pliable soil with a thin organic layer on south-facing banks amidst a plant stand of sparse to intermediate density. These bees would definitely benefit from the presence of other plants which flower before and after the wild blueberry.

OSMIA BEES


A nest for Osimias

an Osimia bee

Life cycle. Though Osmia bees (or mason bees as they are commonly called) are not common bees in many NB wild blueberry fields, they are efficient pollinators of the crop and studies in Maine wild blueberry fields suggest that their numbers can be increased by trap nesting. Some Osmia bees are used as commercial pollinators in Japan, Europe and the US. In Eastern Canada, these bees fly for about 7 or 8 weeks each spring. Females make nests in pre-existing burrows such as those made by bark beetles in dead trees. A nectar-pollen mass is placed toward the end of the tunnel and an egg is deposited on this mass. This cell is then sealed with a thin partition of chewed leaf material, and the female constructs 7 or 8 such cells. The last of these is sealed with a plug. The process is similar though not identical to that of the alfalfa leafcutting bee illustrated on page 2 of fact sheet B.7.0. After hatching, the larva feed for approximately 3 weeks, at which time they spin a cocoon. The larvae pupate 2 to 3 weeks later, reaching their adult overwintering stage by late summer. They emerge the next spring to mate and begin the life cycle again.

The Osmia bees take well to man-made nesting sites. These have been made in a variety of forms, but pine or fir wood blocks do seem to be the preferred source. These can be cut in a variety of forms (see photo), with a tunnel depth of approximately six inches (15 cm) and a hole size of approximately 5/16 inches (0.8 cm). These should be drilled with a sharp bit to ensure a smooth surface. To prevent mold or fungus build-up, cellophane-coated paper tubes should be inserted inside of the tunnels. The blocks should be mounted at eye-level along field edges on trees or buildings, with a southeast orientation so as to capture morning light. The blocks can be brought inside in October and stored at 2-4?C (35-40?F) to improve winter survival More details on nest block construction and supplies can be obtained from the Provincial Blueberry Specialist or your regional DAFANB horticulturalists.

The Osmia bees appear to enjoy the presence of other plants as well as the wild blueberry. These include willow, shadbush, strawberries, cinquefoil, raspberry, clovers, violet, and many of the spring-flowering plants found in the understory of hardwood forests.

GENERAL CONSIDERATIONS FOR ENHANCING POLLINATION BY WILD BEES

A few methods for maintaining and enhancing wild pollinators have been suggested here. These have included: the maintenance of warm, sandy sites for andrenid and halictid bees as well as maintenance and construction of nesting sites for bumble bees and Osmia bees. A few more general considerations for the maintenance of native pollinators are:

  • the encouragement of a diversity of flowering plants around wild blueberry fields;

  • the maintenance of a diversity of field and forest types (meadows, woodland of various ages, forage and other flowering crops) around wild blueberry fields;

  • planting of flowers (esp clovers) for bees;

  • establishment or maintenance of windbreaks to encourage pollinator survival and activity;

  • maintenance of water and mud for sustenance and nest building;

  • the maintenance of smaller fields, so that bees do not experience feast or famine from one year to another;

  • a vigilant use of pesticides, especially during the pollination period.

References:
Batra, Suzanne. 1994. Diversify with Pollen Bees. American Bee Journal 134(9): 591-593. Free, J.B. 1993. Insect Pollination of Crops. Academic Press, NY. 684 pp.

Javorek, S.; K. MacKenzie, and D. Rogers. 1995. Bee Pollinators of Apple and Lowbush Blueberry in Nova Scotia. NSDAM. 12pp.

Osgood, E.A.1972. Soil characteristics of nesting sites of solitary bees associated with the lowbush blueberry in Maine. Technical Bulletin 59, Univ. of Maine, Orono. 8pp.

Stubbs, C.S.; H.A. Jacobson; E.A. Osgood and F.A. Drummond. 1992. Alternative Forage Plants for Native (Wild) Bees Associated with Lowbush Blueberry , Vaccinium spp., in Maine. Technical Bulletin 148. Univ. of Maine, Orono. 54 pp.

Stubbs, C.S.; F.A. Drummond and S.L. Allard. 1997. Bee Conservation and Increasing Osmia spp. in Maine Wild Blueberry Fields. Northeastern Naturalist. Vol.4

Prepared by: John Argall, P.Ag., Provincial Blueberry Specialist, New Brunswick Department of Agriculture and Rural Development; Kenna Mackenzie, Berry Entomologist, Agriculture & Agri-food Canada, Kentville Research Station; Steve Javorek, Biologist, Diversified Pollination Services; Gaetan Chiasson, P.Ag., Horticulture Specialist, New Brunswick Department of Agriculture and Rural Development; Bernard Savoie, P.Ag., Horticulture Technician, New Brunswick Department of Agriculture and Rural Development.

Spring 1998


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