Mitigation of pollen limitation in the lowbush blueberry agroecosystem: effect of augmenting natural pollinators

Growers of small fruit crops often supplement the natural pollinator community by introducing pollinators into commercial orchards and fields, but there are relatively few studies that test the extent to which such interventions increase fruit yield. To test whether plants are limited by pollen availability, inflorescences in 78 commercial lowbush blueberry fields during three years were hand-pollinated either with supplemental outcross pollen, or marked and left as controls (open-pollination). Maximum fruit set with supplemental pollination was in the range 50–65%, whereas with open-pollination, it was slightly, but significantly lower, in the range of 47–57%, suggesting that pollen limitation can affect fruit set. In a two-year experiment, we augmented native pollinators with introduced honey bees, bumble bees, and leaf cutter bees and all combinations in 48 fields. Stigmatic pollen loads were influenced by the total numbers of managed bees in a field in 2010 but not 2011. The presenc...