Efficiency of airborne pollen released by honeybee foraging on pollination in oilseed rape: a wind insect-assisted pollination

Oilseed rape (Brassica napus L.) is an entomophilous crop. Its pollen is covered with sticky pollenkitt and not readily released from the anthers. We investigated the role of foraging honeybees in making this pollen airborne. To assess this, six cages were laid over male-fertile (MF) and male-sterile (MS) plants; at flowering, three cages received a honeybee colony while the others served as controls. On average, approximately 25% more pollen grains were deposited on sticky slides (covered with gauze) in cages with honeybees, compared to control cages. The fruit and seed set per not-empty pod of 5 MS plants bagged under gauze to avoid bee visits were 7 times and 3.4 times higher, respectively, in the cages with honeybees than in control cages without honeybees. These results demonstrate the role of bees in releasing airborne pollen, as well as the effectiveness of this insect-assisted wind pollination: at close range, honeybees participate to pollination without touching the female flowers.