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:
