Commercial Bumble Bee Pollination of Lowbush Blueberry

The commercial bumble bee, Bombus impatiens, has been used in Maine lowbush blueberry since the late 1990s. Studies conducted in 1995-1998 and published in 2001 showed that B. impatiens was a good pollinator of lowbush blueberry. Stocking density was estimated at 3/4-1 quad (set of four, 250-bee colonies) per acre. Subsequent research reported here has shown that on an individual bee basis, B. impatiens is 2.5 times more efficient per floral visit in placing pollen on the stigma. Foraging behavior suggests that bumble bees may be more consistent at producing outcrossing among clones than honey bees, although individual honey bees are more likely to be floral constant than bumble bees. By 2004, some blueberry growers questioned the efficacy of commercial bumble bees. To address these concerns, a three-year validation experiment was conducted from 2005-2007. Seven to nine isolated individual small blueberry fields (2-25 acres) were selected each year to compare bumble bees with honey bees or no commercial pollinators (n = 3 to 5 fields per treatment) It was verified that 2.5 quads/ha was a suitable stocking density and did not differ in pollination level from 7.5-10 honey bee hives per ha. A central place foraging behavior could not be demonstrated with bumble bees in these smaller fields. It was established that as the foraging force of bumble bees increased, which varied between hives and fields, better fruit set resulted.